We investigate large-amplitude baryon acoustic oscillations (BAO's) in off-diagonal entries of cosmological power-spectrum covariance matrices. These covariance-matrix BAO's describe the increased attenuation of power-spectrum BAO's caused by upward fluctuations in large-scale power. We derive an analytic approximation to covariance-matrix entries in the BAO regime, and check the analytical predictions using N-body simulations. These BAO's look much stronger than the BAO's in the power spectrum, but seem detectable only at about a one-sigma level in gigaparsec-scale galaxy surveys. In estimating cosmological parameters using matter or galaxy power spectra, including the covariance-matrix BAO's can have a several-percent effect on error-bar widths for some parameters directly related to the BAO's, such as the baryon fraction. Also, we find that including the numerous galaxies in small haloes in a survey can reduce error bars in these cosmological parameters more than the simple reduction in shot noise might suggest.
The current Swift sample of gamma-ray bursts (GRBs) with measured redshifts allows to test the assumption that GRBs trace the star formation in the Universe. Some authors have claimed that the rate of GRBs increases with cosmic redshift faster than the star formation rate, whose cause is not known yet. In this paper, I investigate the possibility for interpreting the observed discrepancy between the GRB rate history and the star formation rate history by the cosmic metallicity evolution, motivated by the observation that the cosmic metallicity evolves strongly with redshift and GRBs prefer to occur in low metallicity galaxies. Adopting a simple model for the relation between the GRB production and the cosmic metallicity history as proposed by Langer & Norman, and a star formation rate determined by Hopkins & Beacom from current observations, I show that the observed redshift distribution of the Swift GRBs can be reproduced with a fairly good accuracy. Although the results are limited by the small size of the GRB sample and the poorly understood selection biases in detection and localization of GRBs and in redshift determination, the results suggest that GRBs trace both the star formation and the metallicity evolution. If the star formation history can be accurately measured with other approaches, which is presumably achievable in the near future, it will be possible to determine the cosmic metallicity evolution with the study on the redshift distribution of GRBs.
We assess the relative merits of weak lensing surveys, using overlapping imaging data from the ground-based Subaru telescope and the Hubble Space Telescope (HST). Our tests complement similar studies undertaken with simulated data. From observations of 230,000 matched objects in the 2 square degree COSMOS field, we identify the limit at which faint galaxy shapes can be reliably measured from the ground. Our ground-based shear catalog achieves sub-percent calibration bias compared to high resolution space-based data, for galaxies brighter than i'~24.5 and with half-light radii larger than 1.8". This selection corresponds to a surface density of ~15 galaxies per sq arcmin compared to ~71 per sq arcmin from space. On the other hand the survey speed of current ground-based facilities is much faster than that of HST, although this gain is mitigated by the increased depth of space-based imaging desirable for tomographic (3D) analyses. As an independent experiment, we also reconstruct the projected mass distribution in the COSMOS field using both data sets, and compare the derived cluster catalogs with those from X-ray observations. The ground-based catalog achieves a reasonable degree of completeness, with minimal contamination and no detected bias, for massive clusters at redshifts 0.2<z<0.5. The space-based data provide improved precision and a greater sensitivity to clusters of lower mass or at higher redshift.
We review recent results of SPH simulations of gravitational instability in gaseous protoplanetary disks,emphasizing the role of thermodynamics in both isolated and binary systems. Contradictory results appeared in the literature regarding disk fragmentation at tens of AU from the central star are likely due to the different treatment of radiation physics as well as reflecting different initial conditions. Further progress on the subject requires extensive comparisons between different codes with the requirement that the same initial conditions are adopted. It is discussed how the local conditions of the disks undergoing fragmentation at $R < 25$ AU in recent SPH simulations are in rough agreement with the prediction of analytical models, with small differences being likely related to the inability of analytical models to account for the dynamics and thermodynamics of three-dimensional spiral shocks. We report that radically different adaptive hydrodynamical codes, SPH and adaptive mesh refinement (AMR), yield very similar results on disk fragmentation at comparable resolution in the simple case of an isothermal equation of state. A high number of refinements in AMR codes is necessary but not sufficient to correctly follow fragmentation, rather an initial resolution of the grid high enough to capture the wavelength of the strongest spiral modes when they are still barely nonlinear is essential. These tests represent a useful benchmark and a starting point for a forthcoming code comparison with realistic radiation physics.
The near-infrared spectrum of (50000) Quaoar obtained at the Keck Observatory shows distinct absorption features of crystalline water ice, solid methane and ethane, and possibly other higher order hydrocarbons. Quaoar is only the fifth Kuiper belt object on which volatile ices have been detected. The small amount of methane on an otherwise water ice dominated surface suggests that Quaoar is a transition object between the dominant volatile-poor small Kuiper belt objects (KBOs) and the few volatile-rich large KBOs such as Pluto and Eris.
The Hamburg/ESO quasar HE 1113-0641 is found to be a quadruple gravitational lens, based on observations with the twin 6.5m Magellan telescopes at the Las Campanas Observatory, and subsequently with the Hubble Space Telescope. The z_S=1.235 quasar appears in a cross configuration, with i' band magnitudes ranging from 18.0 to 18.8. With a maximum image separation of 0.67'', this is the smallest-separation quadruple ever identified using a ground-based optical telescope. PSF subtraction reveals a faint lensing galaxy. A simple lens model succeeds in predicting the observed positions of the components, but fails to match their observed flux ratios by up to a magnitude. We estimate the redshift of the lensing galaxy to be z_L~0.7. Time delay estimates are on the order of a day, suggesting that the flux ratio anomalies are not due to variability of the quasar, but may result from substructure or microlensing in the lens galaxy.
Two separate statistical tests are described and developed in order to test un-binned data sets for adherence to the power-law form. The first test employs the TP-statistic, a function defined to deviate from zero when the sample deviates from the power-law form, regardless of the value of the power index. The second test employs a likelihood ratio test to reject a power-law background in favor of a model signal distribution with a cut-off.
We present here the orbital elements of pair BC of visual binary star WDS 18253+4846 (ADS 11344 = HD 170109) and ephemerides for the period 2008-2014 are presented as well. As the orbital elements of pair AB already existed we analyze mass ratio between this two pairs and concluded that components C is the biggest one in this triple system. keywords: visual: binaries
Ultraviolet, optical and near infrared images of the nearby (D ~ 5.5 Mpc) SBm galaxy NGC 1311, obtained with the Hubble Space Telescope, reveal a small population of 13 candidate star clusters. We identify candidate star clusters based on a combination of their luminosity, extent and spectral energy distribution. The masses of the cluster candidates range from ~1000 up to ~100000 Solar masses, and show a strong positive trend of larger mass with increasing with cluster age. Such a trend follows from the fading and dissolution of old, low-mass clusters, and the lack of any young super star clusters of the sort often formed in strong starbursts. The cluster age distribution is consistent with a bursting mode of cluster formation, with active episodes of age ~10 Myr, ~100 Myr and ~1 Gyr. The ranges of age and mass we probe are consistent with those of the star clusters found in quiescent Local Group dwarf galaxies.
A rare coincidence of scales in standard particle physics is needed to explain why $\Lambda$ or the negative pressure of cosmological dark energy (DE) coincides with the positive pressure $P_0$ of random motion of dark matter (DM) in bright galaxies. Recently Zlosnik et al. (2007) propose to modify the Einsteinian curvature by adding a non-linear pressure from a medium flowing with a four-velocity vector field $U^\mu$. We propose to check whether a smooth extension of GR with a simple kinetic Lagrangian of $U^\mu$ can be constructed, and whether the pressure can bend space-time sufficiently to replace the roles of a $w=-1$ DE, $w=0$ Cold DM and heavy neutrinos in explaining anomalous accelerations at all scales. As a specific proof of concept we find a Vector-for-$\Lambda$ model (${\mathbf V\Lambda}$-model) and its variants. With essentially {\it no free parameters}, these appear broadly consistent with the solar system, gravitational potentials in dwarf spiral galaxies and the bullet cluster of galaxies, early universe with inflation, structure formation and BBN, and late acceleration with a 1:3 ratio of DM:DE.
Two new algorithms are described for matching two dimensional coordinate lists of point sources that are signifcantly faster than previous methods. By matching rarely occurring triangles (or more complex shapes) in the two lists, and by ordering searches by decreasing probability of success, it is demonstrated that very few candidates need be considered to find a successful match. Moreover, by immediately testing the suitability of a potential match using an efficient mechanism, the need to process the entire candidate set is avoided, yielding considerable performance improvements. Triangles are described by a cosine metric that reduces the density of triangle space, permitting efficient searches. An alternative shape characterization method that reduces computational overhead in the construction phase is discussed. The algorithms are tested on a set of 10 063 wide-field survey images, with fields-of-view up to 4.8 x 3.6 deg, successfully matching 100% of the images in a mean elapsed time of 6 ms (2.4 GHz Athlon CPU). The elapsed time of the searching phase is shown to vary by less than 1 ms for list sizes between 10 and 200 points, demonstrating that fast, robust searches may be completed in nearly constant time, independent of list size.
Globular clusters produce orders of magnitude more millisecond pulsars per unit mass than the Galactic disk. Since the first cluster pulsar was uncovered twenty years ago, at least 138 have been identified - most of which are binary millisecond pulsars. Because of their origins involving stellar encounters, many of these systems are exotic objects that would never be observed in the Galactic disk. Examples include pulsar-main sequence binaries, extremely rapid rotators (including the current record holder), and millisecond pulsars in highly eccentric orbits. These systems are allowing new probes of the interstellar medium, the equation of state of material at supra-nuclear density, the mass distribution of neutron stars, and the dynamics of globular clusters.
We use high-resolution, three-dimensional hydrodynamics simulations to study the hydrodynamic and gravitational interaction between stellar companions embedded within a differentially rotating common envelope. Specifically, we evaluate the contributions of the non-axisymmetric gravitational tides and pressure forces to the drag force and, hence, to the dissipation rate and the mass accumulated onto the stellar companion. We find that the gravitational drag dominates the hydrodynamic drag during the spiral in phase, leading to the result that a simple prescription based on a gravitational capture radius formalism significantly underestimates the dissipation rate and overestimates the spiral in decay timescale. Although the rate of mass accretion fluctuates significantly, we observe a secular trend leading to an effective rate of mass accretion which is significantly less than the rate based on a gravitational capture radius. The implications of these results are discussed within the context of accretion of compact objects in the common envelope phase.
$UBVRI$ photometry and medium resolution optical spectroscopy of peculiar Type Ia supernova SN 2005hk are presented and analysed, covering the premaximum phase to around 400 days after explosion. The supernova is found to be underluminous compared to "normal" Type Ia supernovae. The photometric and spectroscopic evolution of SN 2005hk is remarkably similar to the peculiar Type Ia event SN 2002cx. The expansion velocity of the supernova ejecta is found to be lower than normal Type Ia events. The late time spectra of SN 2005hk do not show the presence of forbidden [\ion{Fe}{ii}], [\ion{Fe}{iii}] and [\ion{Co}{iii}] lines, but are dominated by narrow, permitted \ion{Fe}{ii}, NIR \ion{Ca}{ii} and \ion{Na}{i} lines with P-Cygni profiles. Light curve modeling indicates SN 2005hk to be a thermonuclear explosion with the Chandrasekhar mass ejecta, but with a smaller kinetic energy ($\KE = 0.3 \times 10^{51} {\rm ergs}$) than that of canonical Type Ia supernovae. The mass of \Nifs\ synthesized in this explosion is $0.18 \Msun$. The early spectra are successfully modeled with this less energetic model with some modifications of the abundance distribution. The late spectrum is explained as a combination of a photospheric component together with a nebular component.
Aims. Qualitative analysis of key (but yet unappreciated) linear phenomena in stratified hydrodynamic Keplerian flows: (i) the occurrence of a vortex mode, as a consequence of strato-rotational balance, with its transient dynamics; (ii) the generation of spiral-density waves (also called inertia-gravity or $g\Omega$ waves) by the vortex mode through linear mode coupling in shear flows. Methods. Non-modal analysis of linearized Boussinesq equations written in the shearing sheet approximation of accretion disk flows. Results. It is shown that the combined action of rotation and stratification introduces a new degree of freedom -- vortex mode perturbation -- which is linearly coupled with the spiral-density waves. These two modes are jointly able to extract energy from the background flow and they govern the disk dynamics in the small-scale range. The transient behavior of these modes is determined by the non-normality of the Keplerian shear flow. Tightly leading vortex mode perturbations undergo substantial transient growth, then, becoming trailing, inevitably generate trailing spiral-density waves by linear mode coupling. This course of events -- transient growth plus coupling -- is particularly pronounced for perturbation harmonics with comparable azimuthal and vertical scales and it renders the energy dynamics similar to the 3D unbounded plane Couette flow case. Conclusions. Our investigation strongly suggests that the so-called bypass concept of turbulence, which has been recently developed by the hydrodynamic community for spectrally stable shear flows, can also be applied to Keplerian disks. This conjecture may be confirmed by appropriate numerical simulations that take in account the vertical stratification and consequent mode coupling in the high Reynolds number regime.
We examine the use of the CMB's TE cross correlation power spectrum as a complementary test for detection of primordial gravitational waves (PGWs). The method used in this paper is based on the determination of the lowest multipole, $\ell_0$, where the TE power spectrum, $C_{\ell}^{TE}$, first changes sign. We examine two toy experiments (one ideal and another more realistic) to see how well they could constrain PGWs using the TE power spectrum alone. The proposed test is useful in providing insurance against false detection of B-modes, and in cases where improper subtraction of systematic effects, such as polarized foregrounds, leave residual B-modes of non-cosmological origin. We found that an ideal experiment limited only by cosmic variance can detect PGWs with a ratio of tensor to scalar metric perturbation power spectra $r=0.3$ at 99.9% confidence level using only the TE correlation. This value is comparable with current constraints obtained by WMAP based on the $2\sigma$ upper limits to the amplitudes of the B-modes. We demonstrate that to measure PGWs by their contribution to the TE cross correlation power spectrum in a realistic ground based experiment when real instrumental noise is taken into account, the amplitude parameter, $r$, should be about a factor 3 larger.
In this paper we continue analysis of CMB TE cross correlation as a source of information about primordial gravitational waves. In our first paper we considered the zero multipole method. In this paper, we use Wiener filtering of the CMB TE data to remove the contribution to the TE power spectrum from density perturbations, leaving only the contribution of PGWs. We examine the same two toy experiments (one ideal and one more realistic), to see how well they could constrain PGWs using the TE power spectrum. We consider three tests applied to a combination of observational data and data sets generated by Monte Carlo simulations: (1) $S/N$ test, (2) sign test, and (3) Wilcoxon rank sum test. Then we compare all these tests with each other and with the zero multipole method (see PMK). Then, we compare signal-to-noise ratio of TE correlation measurements with corresponding signal-to-noise ratios for BB ground based measurements and with current and future TE correlation space measurements. We found that an ideal TE correlation experiment limited only by cosmic variance can detect PGWs with a ratio of tensor to scalar metric perturbation power spectra $r=0.3$ at 98% confidence level with the $S/N$ test, 93% confidence level with the sign test, and 80% confidence level for the Wilcoxon rank sum test. We also compare all results with corresponding results obtained in PMK. We demonstrate that to measure PGWs by their contribution to the TE cross correlation power spectrum in a realistic ground based experiment when real instrumental noise is taken into account, the amplitude parameter, $r$, should be about a factor 4 larger.
51757 objects, which were primarily identified as quasars in SDSS DR5 and have spectroscopic redshifts were used to study the luminosity dependence of the quasar clustering with the help of two different techniques. The obtained results reveal that brighter quasars are more clustered, but this dependence is quite weak, which is in agreement with the results by Porciani & Norberg, 2006 and theoretical predictions by Lidz et al., 2006.
We report on the latest (2007 Jan) observations of supernova remnant (SNR) 1987A from the XMM-Newton mission. Since the 2003 May observations of Haberl et al. (2006), 11 emission lines have experienced increases in flux by factors ~ 3 to 10, with the 775 eV line of O VIII showing the greatest increase; we have observed 6 lines of Fe XVII and Fe XVIII previously unreported by XMM-Newton. A two-shock model representing plasmas in non-equilibrium ionization is fitted to the EPIC-pn spectra, yielding temperatures of ~ 0.4 and ~ 3 keV, as well as elemental abundances for N, O, Ne, Mg, Si, S and Fe. We demonstrate that the abundance ratio of N and O can be constrained to less than ~20% accuracy. Within the same confidence interval, the same analysis suggests that the C+N+O abundance varies from ~ 1.1 to 1.4 X 10^-4. Normalizing our obtained abundances by the Large Magellanic Cloud (LMC) values of Hughes, Hayashi & Koyama (1998), we find that O, Ne, Mg and Fe are under-abundant, while Si and S are over-abundant, consistent with the findings of Aschenbach (2007). Such a result has implications for both the single-star and binary accretion/merger models for the progenitor of SNR 1987A. In the context of the binary merger scenario proposed by Morris & Podsiadlowski (2006, 2007), material forming the inner, equatorial ring was expelled after the merger, implying that either our derived Fe abundance is inconsistent with typical LMC values or that iron is under-abundant at the site of the progenitor star of SNR 1987A.
We analyze the rotation curves of 10 spiral galaxies with a newtonian potential corrected with an extra logarithmic term, using a disc modelization for the spiral galaxies. There is a new constant associated with the extra term in the potential. The rotation curve of the chosen sample of spiral galaxies is well reproduced for a given range of the new constant. It is argued that this correction can have its origin from string configurations. The compatibility of this correction with local physics is discussed.
Relic neutralinos produced after the Big Bang are favoured candidates for Dark Matter. They can accumulate at the centre of massive celestial objects like our Sun. Their annihilation can result in a high-energy neutrino flux that could be detectable as a localised emission with earth-based neutrino telescopes like ANTARES. In this paper a brief overview of the prospects of the indirect search for Dark Matter particles with the ANTARES detector will be given. The analysis method and expected performance for the detection of the expected neutrinos will be discussed.
We developed a source detection algorithm based on the Minimal Spanning Tree (MST), that is a graph-theoretical method useful for finding clusters in a given set of points. This algorithm is applied to gamma-ray bidimensional images where the points correspond to the arrival direction of photons, and the possible sources are associated with the regions where they clusterize. Some filters to select these clusters and to reduce the spurious detections are introduced. An empirical study of the statistical properties of MST on random fields is carried in order to derive some criteria to estimate the best filter values. We introduce also two parameters useful to verify the goodness of candidate sources. To show how the MST algorithm works in the practice, we present an application to an EGRET observation of the Virgo field, at high galactic latitude and with a low and rather uniform background, in which several sources are detected.
The cosmological evolution of X-ray-selected and optically selected Active Galactic Nuclei (AGNs) show different behaviours interpreted in terms of two different populations. The difference is evident mainly for low luminosity AGNs (LLAGNs), many of which are lost by optical photometric surveys. We are conducting a spectroscopical study of a composite sample of AGN candidates selected in SA57 following different searching techniques, to identify low luminosity AGNs and break down the sample into different classes of objects. AGN candidates were obtained through optical variability and/or X-ray emission. Of special interest are the extended variable objects, which are expected to be galaxies hosting LLAGNs. Among the 26 classified objects a fair number (9) show typical AGN spectra. 10 objects show Narrow Emission Line Galaxy spectra, and in most of them (8/10) optical variability suggests the presence of LLAGNs.
The physical processes that define the spine of the galaxy cluster X-ray luminosity -- temperature (L-T) relation are investigated using a large hydrodynamical simulation of the Universe. This simulation models the same volume and phases as the Millennium Simulation and has a linear extent of 500 h^{-1} Mpc. We demonstrate that mergers typically boost a cluster along but also slightly below the L-T relation. Due to this boost we expect that all of the very brightest clusters will be near the peak of a merger. Objects from near the top of the L-T relation tend to have assembled much of their mass earlier than an average halo of similar final mass. Conversely, objects from the bottom of the relation are often experiencing an ongoing or recent merger.
We study the evolution of the galaxy population up to z\sim3 as a function of its colour properties. In particular, luminosity functions and luminosity densities have been derived as a function of redshift for the blue/late and red/early populations. We use data from the GOODS-MUSIC catalogue which have typical magnitude limits z<26 and Ks<23.5 for most of the sample. About 8% of the galaxies have spectroscopic redshifts; the remaining have well calibrated photometric redshifts derived from the extremely wide multi-wavelength coverage in 14 bands (from the U band to the Spitzer 8 \mu m band). We have derived a catalogue of galaxies complete in rest-frame B-band, which has been divided in two subsamples according to their rest-frame U-V colour (or derived specific star formation rate, SSFR) properties. We confirm a bimodality in the U-V colour and SSFR of the galaxy sample up to z\sim 3. This bimodality is used to compute the LFs of the blue/late and red/early subsamples. The LFs of the blue/late and total samples are well represented by steep Schechter functions evolving in luminosity with increasing redshifts. The volume density of the LFs of the red/early populations decreases with increasing redshift. The shape of the red/early LFs shows an excess of faint red dwarfs with respect to the extrapolation of a flat Schechter function and can be represented by the sum of two Schechter functions. Our model for galaxy formation in the hierarchical clustering scenario, which also includes external feedback due to a diffuse UV background, shows a general broad agreement with the LFs of both populations, the larger discrepancies being present at the faint end for the red population. Hints on the nature of the red dwarf population are given on the basis of their stellar mass and spatial distributions.
The Magellanic System represents one of the best places to study the formation and evolution of galaxies. Photometric surveys of various depths, areas and wavelengths have had a significant impact on our understanding of the system; however, a complete picture is still lacking. VMC (the VISTA near-infrared YJKs survey of the Magellanic System) will provide new data to derive the spatially resolved star formation history and to construct a three-dimensional map of the system. These data combined with those from other ongoing and planned surveys will give us an absolutely unique view of the system opening up the doors to truly new science!
We apply a wind model, driven by combined cosmic-ray and thermal-gas pressure, to the Milky Way, and show that the observed Galactic diffuse soft X-ray emission can be better explained by a wind than by previous static gas models. We find that cosmic-ray pressure is essential to driving the observed wind. Having thus defined a "best-fit" model for a Galactic wind, we explore variations in the base parameters and show how the wind's properties vary with changes in gas pressure, cosmic-ray pressure and density. We demonstrate the importance of cosmic rays in launching winds, and the effect cosmic rays have on wind dynamics. In addition, this model adds support to the hypothesis of Breitschwerdt and collaborators that such a wind may help explain the relatively small gradient observed in gamma-ray emission as a function of galactocentric radius.
The energetics and emission mechanism of GRBs are not well understood. Here we demonstrate that the instantaneous peak flux or equivalent isotropic peak luminosity, L_iso ergs s^-1, rather than the integrated fluence or equivalent isotropic energy, E_iso ergs, underpins the known high-energy correlations. Using new spectral/temporal parameters calculated for 101 bursts with redshifts from BATSE, BeppoSAX, HETE-II and Swift we describe a parameter space which characterises the apparently diverse properties of the prompt emission. We show that a source frame characteristic-photon-energy/peak luminosity ratio, K_z, can be constructed which is constant within a factor of 2 for all bursts whatever their duration, spectrum, luminosity and the instrumentation used to detect them. The new parameterization embodies the Amati relation but indicates that some correlation between E_peak and E_iso follows as a direct mathematical inference from the Band function and that a simple transformation of E_iso to L_iso yields a universal high energy correlation for GRBs. The existence of K_z indicates that the mechanism responsible for the prompt emission from all GRBs is probably predominantly thermal.
Models of terrestrial planet formation in the presence of a migrating giant planet have challenged the notion that hot-Jupiter systems lack terrestrial planets. We briefly review this issue and suggest that hot-Jupiter systems should be prime targets for future observational missions designed to detect Earth-sized and potentially habitable worlds.
Edge-on spiral galaxies offer a unique perspective on disks. One can accurately determine the height distribution of stars and ISM and the line-of-sight integration allows for the study of faint structures. The Spitzer IRAC camera is an ideal instrument to study both the ISM and stellar structure in nearby galaxies; two of its channels trace the old stellar disk with little extinction and the 8 micron channel is dominated by the smallest dust grains (Polycyclic Aromatic Hydrocarbons, PAHs). Dalcanton et al. (2004) probed the link between the appearance of dust lanes and the disk stability. In a sample of bulge-less disks they show how in massive disks the ISM collapses into the characteristic thin dust lane. Less massive disks are gravitationally stable and their dust morphology is fractured. The transition occurs at 120 km/s for bulgeless disks. Here we report on our results of our Spitzer/IRAC survey of nearby edge-on spirals and its first results on the NIR Tully-Fischer relation, and ISM disk stability.
We use the very large Millennium Simulation of the concordance $\Lambda$CDM cosmogony to calibrate the bias and error distribution of Timing Argument estimators of the masses of the Local Group and of the Milky Way. From a large number of isolated spiral-spiral pairs similar to the Milky Way/Andromeda system, we find the interquartile range of the ratio of timing mass to true mass to be a factor of 1.8, while the 5% and 95% points of the distribution of this ratio are separated by a factor of 5.7. Here we define true mass as the sum of the ``virial'' masses $M_{200}$ of the two dominant galaxies. For current best values of the distance and approach velocity of Andromeda this leads to a median likelihood estimate of the true mass of the Local Group of $5.27\times 10^{12}\msun$, or $\log M_{LG}/M_\odot = 12.72$, with an interquartile range of $[12.58, 12.83]$ and a 5% to 95% range of $[12.26, 13.01]$. Thus a 95% lower confidence limit on the true mass of the Local Group is $1.81\times 10^{12}\msun$. A timing estimate of the Milky Way's mass based on the large recession velocity observed for the distant satellite Leo I works equally well, although with larger systematic uncertainties. It gives an estimated virial mass for the Milky Way of $2.43 \times 10^{12}\msun$ with a 95% lower confidence limit of $0.80 \times 10^{12}\msun$.
We used multiwavelength data (HI, FUV, NUV, R) to search for evidence of star formation in the intragroup medium of the Hickson Compact Group 100. We find that young star-forming regions are located in the intergalactic HI clouds of the compact group which extend to over 130 kpc away from the main galaxies. A tidal dwarf galaxy candidate is located in the densest region of the HI tail, 61 kpc from the brightest group member and its age is estimated to be only 3.3 Myr. Fifteen other intragroup HII regions and TDG candidates are detected in the GALEX FUV image and within a field 10'x10' encompassing the HI tail. They have ages <200 Myr, HI masses of 10^(9.2-10.4) Msun, 0.001< SFR <0.01 Msun yr^-1, and stellar masses 10^4.3--10^6.5 Msun. The HI clouds to which many of them are associated have column densities about one order of magnitude lower than N(HI)~10^21 cm^-2.
We present the design of the Fabry-Perot system of the Robert Stobie Spectrograph on the 11m Southern African Large Telescope and its characterization as measured in the laboratory. This system provides spectroscopic imaging at any desired wavelength spanning a bandpass 430 - 860 nm, at four different spectral resolving powers ranging from 300 to 9000. Our laboratory tests revealed a wavelength dependence of the etalon gap and parallelism with a maximum variation between 600 - 720 nm that arises because of the complex structure of the broadband multi-layer dielectric coatings. We also report an unanticipated optical effect of this multi-layer coating structure that produces a significant, and wavelength dependent, change in the apparent shape of the etalon plates. This change is caused by two effects: the physical non-uniformities or thickness variations in the coating layers, and the wavelength dependence of the phase change upon refection that can amplify these non-uniformities. We discuss the impact of these coating effects on the resolving power, finesse, and throughput of the system. This Fabry-Perot system will provide a powerful tool for imaging spectroscopy on one of the world's largest telescopes.
An anomalous transient in the early Hubble-type (S0) galaxy Messier 85 (M85) in the Virgo cluster was discovered by Kulkarni et al. (2007) on 7 January 2006 that had very low luminosity (peak absolute R-band magnitude MR of about -12) that was constant over more than 80 days, red colour and narrow spectral lines, which seem inconsistent with those observed in any known class of transient events. Kulkarni et al. (2007) suggest an exotic stellar merger as the possible origin. An alternative explanation is that the transient in M85 was a type II-plateau supernova of extremely low luminosity, exploding in a lenticular galaxy with residual star-forming activity. This intriguing transient might be the faintest supernova that has ever been discovered.
We present arcsecond-scale mid-ir photometry (in the 10.5 micron N band and at 24.8 microns), and low resolution spectra in the N band (R~100) of a candidate high mass protostellar object (HMPO) in IRAS 18151-1208 and of two HMPO candidates in IRAS 20343+4129, IRS 1 and IRS 3. In addition we present high resolution mid-ir spectra (R~80000) of the two HMPO candidates in IRAS 20343+4129. These data are fitted with simple models to estimate the masses of gas and dust associated with the mid-ir emitting clumps, the column densities of overlying absorbing dust and gas, the luminosities of the HMPO candidates, and the likely spectral type of the HMPO candidate for which [Ne II] 12.8 micron emission was detected (IRAS 20343+4129 IRS 3). We suggest that IRAS 18151-1208 is a pre-ultracompact HII region HMPO, IRAS 20343+4129 IRS 1 is an embedded young stellar object with the luminosity of a B3 star, and IRAS 20343+4129 IRS 3 is a B2 ZAMS star that has formed an ultracompact HII region and disrupted its natal envelope.
To measure the supernova (SN) rates at intermediate redshift we performed the Southern inTermediate Redshift ESO Supernova Search (STRESS). Unlike most of the current high redshift SN searches, this survey was specifically designed to estimate the rate for both type Ia and core collapse (CC) SNe. We counted the SNe discovered in a selected galaxy sample measuring SN rate per unit blue band luminosity. Our analysis is based on a sample of ~43000 galaxies and on 25 spectroscopically confirmed SNe plus 64 selected SN candidates. Our approach is aimed at obtaining a direct comparison of the high redshift and local rates and at investigating the dependence of the rates on specific galaxy properties, most notably their colour. The type Ia SN rate, at mean redshift z=0.3, amounts to 0.22^{+0.10+0.16}_{-0.08 -0.14} h_{70}^2 SNu, while the CC SN rate, at z=0.21, is 0.82^{+0.31 +0.30}_{-0.24 -0.26} h_{70}^2 SNu. The quoted errors are the statistical and systematic uncertainties. With respect to local value, the CC SN rate at z=0.2 is higher by a factor of ~2 already at redshift, whereas the type Ia SN rate remains almost constant. This implies that a significant fraction of SN Ia progenitors has a lifetime longer than 2-3 Gyr. We also measured the SN rates in the red and blue galaxies and found that the SN Ia rate seems to be constant in galaxies of different colour, whereas the CC SN rate seems to peak in blue galaxies, as in the local Universe. SN rates per unit volume were found to be consistent with other measurements showing a steeper evolution with redshift for CC SNe with respect to SNe Ia. Finally we have exploited the link between star formation (SF) and SN rates to predict the evolutionary behaviour of the SN rates and compare it with the path indicated by observations.
We investigate gravitino dark matter scenarios in which the primordial ^6Li production is catalyzed by bound-state formation of long-lived negatively charged particles X^- with ^4He. In the constrained minimal supersymmetric Standard Model (CMSSM) with the stau^- as the X^-, the observationally inferred bound on the primordial ^6Li abundance allows us to derive a rigid lower limit on the gaugino mass parameter. This limit can have severe implications for supersymmetry searches at the Large Hadron Collider and for the reheating temperature after inflation.
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Procyon A is a bright F5IV star in a binary system. Although the distance, mass and angular diameter of this star are all known with high precision, the exact evolutionary state is still unclear. Evolutionary tracks with different ages and different mass fractions of hydrogen in the core pass, within the errors, through the observed position of Procyon A in the Hertzsprung-Russell diagram. For more than 15 years several different groups have studied the solar-like oscillations in Procyon A to determine its evolutionary state. Although several studies independently detected power excess in the periodogram, there is no agreement on the actual oscillation frequencies yet. This is probably due to either insufficient high-quality data (i.e. aliasing) or due to intrinsic properties of the star (i.e. short mode lifetimes). Now a spectroscopic multi-site campaign using 10 telescopes world-wide (minimising aliasing effects) with a total time span of nearly 4 weeks (increase the frequency resolution) is performed to identify frequencies in this star and finally determine its properties and evolutionary state.
The opacity of a spiral disk due to dust absorption influences every measurement we make of it in the UV and optical. Two separate techniques directly measure the total absorption by dust in the disk: calibrated distant galaxy counts and overlapping galaxy pairs. The main results from both so far are a semi-transparent disk with more opaque arms and a relation between surface brightness and disk opacity. In the Spitzer era, SED models of spiral disks add a new perspective on the role of dust in spiral disks. Combined with the overall opacity from galaxy counts, we can derive a typical optical depth of the dusty ISM clouds: 0.4 which implies a size of ~60 pc. Current work on galaxy counts is in the ACS fields of M51, M101 and M81. Occulting galaxies offer the possibility of probing the history of disk opacity from higher redshift occulting pairs. Evolution in disk opacity could influence distance measurements (SN1a, Tully-Fisher relation). Here, we present first results from spectroscopically selected occulting pairs in the SDSS. The redshift range for this sample is limited but does offer a first insight into disk opacity evolution as well as a reference for higher redshift measurements.
Imaging data from the Sloan Digital Sky Survey are used to characterize the population of galaxies in groups and clusters detected with the MaxBCG algorithm. We investigate the dependence of Brightest Cluster Galaxy (BCG) luminosity, and the distributions of satellite galaxy luminosity and satellite color, on cluster properties over the redshift range 0.1 < z < 0.3. The size of the dataset allows us to make measurements in many bins of cluster richness, radius and redshift. We find that, within r_200 of clusters with mass above 3e13 h-1 M_sun, the luminosity function of both red and blue satellites is only weakly dependent on richness. We further find that the shape of the satellite luminosity function does not depend on cluster-centric distance for magnitudes brighter than ^{0.25}M_i - 5log(h) < -19. However, the mix of faint red and blue galaxies changes dramatically. The satellite red fraction is dependent on cluster-centric distance, galaxy luminosity and cluster mass, and also increases by ~5% between redshifts 0.28 and 0.2, independent of richness. We find that BCG luminosity is tightly correlated with cluster richness, scaling as L_{BCG} ~ M_{200}^{0.3}, and has a Gaussian distribution at fixed richness, with sigma_{log L} ~ 0.17 for massive clusters. The ratios of BCG luminosity to total cluster luminosity and characteristic satellite luminosity scale strongly with cluster richness: in richer systems, BCGs contribute a smaller fraction of the total light, but are brighter compared to typical satellites. This study demonstrates the power of cross-correlation techniques for measuring galaxy populations in purely photometric data.
In order to distinguish between the various components of massive star forming regions (i.e. infalling, outflowing and rotating gas structures) within our own Galaxy, we require high angular resolution observations which are sensitive to structures on all size scales. To this end, we present observations of the molecular and ionized gas towards massive star forming regions at 230 GHz from the SMA (with zero spacing from the JCMT) and at 22 and 23 GHz from the VLA at arcsecond or better resolution. These observations (of sources such as NGC7538, W51e2 and K3-50A) form an integral part of a multi-resolution study of the molecular and ionized gas dynamics of massive star forming regions (i.e. Klaassen & Wilson 2007). Through comparison of these observations with 3D radiative transfer models, we hope to be able to distinguish between various modes of massive star formation, such as ionized or halted accretion (i.e Keto 2003 or Klaassen et al. 2006 respectively).
Massive black hole binary coalescences are prime targets for space-based gravitational-wave (GW) observatories. GW measurements can localize the position of a coalescing binary on the sky to an ellipse with major axis ${a few} \times 10$ arcminutes to a few degrees, depending on source redshift, and a minor axis which is $2 - 4$ times smaller. Neglecting weak gravitational lensing, GWs would also determine the source's luminosity distance to better than percent accuracy for close sources, degrading to several percent for more distant sources. Assuming a well-measured cosmology, the source's redshift could be inferred with similar accuracy. GWs alone can thus pinpoint a binary to a 3-dimensional ``pixel,'' guiding searches for the hosts of these events. We examine the time evolution of this pixel, studying it at merger and at several intervals before merger. One day before merger, the major axis of the error ellipse is typically larger than its final value by a factor $\sim 1.5-6$. The minor axis is larger by $\sim 2-9$, and the error in the luminosity distance is larger by a factor $\sim 1.5-7$. This large change over short time is due to spin-induced precession, which is strongest in the final days before merger. The evolution is slower as we go back further in time. For $z = 1$, we find that GWs will localize a binary to within $\sim 10$ square degrees as early as a month prior to merger and determine distance (and hence redshift) to several percent. [Abridged]
We present interferometric observations of $^{12}$CO and $^{13}$CO $J$=2$-$1 emission from the butterfly-shaped, young planetary nebula NGC 6302. The high angular resolution and high sensitivity achieved in our observations allow us to resolve the nebula into two distinct kinematic components: (1) a massive expanding torus seen almost edge-on and oriented in the North-South direction, roughly perpendicular to the optical nebula axis. The torus exhibits very complex and fragmentated structure; (2) high velocity molecular knots moving at high velocity, higher than 20 \kms, and located in the optical bipolar lobes. These knots show a linear position-velocity gradient (Hubble-like flow), which is characteristic of fast molecular outflow in young planetary nebulae. From the low but variable $^{12}$CO/$^{13}$CO $J$=2$-$1 line intensity ratio we conclude that the $^{12}$CO $J$=2$-$1 emission is optically thick over much of the nebula. Using the optically thinner line $^{13}$CO $J$=2$-$1 we estimate a total molecular gas mass of $\sim$ 0.1 M$_\odot$, comparable to the ionized gas mass; the total gas mass of the NGC 6302 nebula, including the massive ionized gas from photon dominated region, is found to be $\sim$ 0.5 M$_\odot$. From radiative transfer modelling we infer that the torus is seen at inclination angle of 75$^\circ$ with respect to the plane of the sky and expanding at velocity of 15 \kms. Comparison with recent observations of molecular gas in NGC 6302 is also discussed.
Cherenkov Telescopes (as Magic, Hess and Veritas), while pointing horizontally should reveal also the fluorescence flare tails of nearby down-going air-showers. Such air-showers, born at higher (tens km) altitudes, are growing and extending up to lowest atmospheres (EeVs) or up to higher (few km) quotas (PeVs). Viceversa, as it has been foreseen and only recently observed, the opposite takes place. Fluorescence Telescopes made for UHECR detection may be blazed by inclined Cherenkov lights. The geomagnetic splitting may tag the energy as well as the inclined shower footprint as seen in a recent peculiar event in AUGER. Additional stereoscopic detection may define the event origination distance and its consequent primary composition, extending our understanding on UHECR composition, while unveling a novel tau Neutrino Astronomy.
We present a ballistic description of the formation and propagation of the working surface of a relativistic jet. Using simple laws of conservation of mass and linear momentum at the working surface, we obtain a full description of the working surface flow parametrised by the initial velocity and mass injection. This allows us to compute analytically the energy release at any time in the working surface. We compare this model with a new numerical code used for the propagation of a relativistic fluid in one dimension. We finally use this code to test the limits of our study.
The bipolar morphology of the planetary nebula (PN) K 3-35 observed in radio-continuum images was modelled with 3D hydrodynamic simulations with the adaptive grid code yguazu-a. We find that the observed morphology of this PN can be reproduced considering a precessing jet evolving in a dense AGB circumstellar medium, given by a mass loss rate \dot{M}_{csm}=5x10^{-5}M_{\odot}/yr and a terminal velocity v_{w}=10 km/s. Synthetic thermal radio-continuum maps were generated from numerical results for several frequencies. Comparing the maps and the total fluxes obtained from the simulations with the observational results, we find that a model of precessing dense jets, where each jet injects material into the surrounding CSM at a rate \dot{M}_j=2.8x10^{-4} {M_{\odot}/yr (equivalent to a density of 8x10^{4} {cm}^{-3}, a velocity of 1500 km/s, a precession period of 100 yr, and a semi-aperture precession angle of 20 degrees agrees well with the observations.
The Newtonian solid-mechanical theory of nodeless spheroidal and torsional seismic elastic vibrations trapped in the crust of quaking neutron star is outlined. The spectral equations for the frequency of these modes are obtained and applied to the modal classification of the quasi-periodic oscillations of X-ray luminosity in the aftermath of giant flares in SGR 1806-20 and SGR 1900+14. The presented analysis is heavily relied on the currently accepted identification of the QPOs frequency from the range [30-200] Hz with those for torsional nodeless vibrations. Based on this identification, which is used to fix the input parameters entering the obtained spectral formulae, we compute frequency spectrum of nodeless spheroidal elastic vibrations. Focus is placed on the low-frequency QPOs in the data for SGR 1806-20 whose physical origin has been called into question. Our calculations suggest that QPOs with frequencies 18 Hz and 26 Hz are due to dipole spheroidal and dipole torsional shear vibrations of the crust against unperturbed by starquake core, respectively. The uncertainties in association of the high-frequency QPOs with nodeless elastic shear vibrations are briefly discussed.
We report results of spectral studies of steady emission and short bursts for magnetar candidates using data obtained by the XMM-Newton, Chandra and Swift spacecrafts. The spectra of the steady emission and the short bursts for most magnetar candidates are represented by a two blackbody function with an absorption (2BB). Three AXPs (4U 0142+614, 1RXS J170849.0-400910 and 1E 2259+586) seem to have an excess above ~7 keV in their soft X-ray spectra. The excess could be related to a non-thermal hard component discovered by the International Gamma-Ray Astrophysics Laboratory. For the magnetar candidates of which the spectra are well reproduced by 2BB, there is a strong linear correlation between lower blackbody temperatures (kT_LT) and higher blackbody temperatures (kT_HT), and between squares of lower blackbody radii (R_LT^2) and squares of higher blackbody radii (R_HT^2). The ratio of kT_LT/kT_HT ~ 0.4 is almost constant independently with magnetar candidates and/or emission types (the steady emission and the short bursts). This would imply a common emission mechanism among the magnetar candidates. The relationship between the steady emission and the short bursts might be analogous to a relationship between microflares and solar flares of the Sun.
The role of torsion and a scalar field $\phi$ in gravitation in the background of a particular class of the Riemann-Cartan geometry is considered here. Some times ago, a Lagrangian density with Lagrange multipliers has been proposed by the author which has been obtained by picking some particular terms from the SO(4,1) Pontryagin density, where the scalar field $\phi$ causes the de Sitter connection to have the proper dimension of a gauge field. Here it has been shown that the divergence of the axial torsion gives the Newton's constant and the scalar field becomes a function of the Ricci scalar $\mathcal{R}$. The starting Lagrangian then reduces to a Lagrangian representing the metric $f(\mathcal{R})$ gravity theory.
A theory of collisionless fluids is developed in a unified picture, where nonrotating figures with anisotropic random velocity component distributions and rotating figures with isotropic random velocity component distributions, make adjoints configurations to the same system. R fluids are defined and mean and rms angular velocities and mean and rms tangential velocity components are expressed, by weighting on the moment of inertia and the mass, respectively. The definition of figure rotation is extended to R fluids. The generalized tensor virial equations are formulated for R fluids and further attention is devoted to axisymmetric configurations where, for selected coordinate axes, a variation in figure rotation has to be counterbalanced by a variation in anisotropy excess and vice versa. A microscopical analysis of systematic and random motions is performed under a few general hypotheses, by reversing the sign of tangential or axial velocity components of an assigned fraction of particles, leaving the distribution function and other parameters unchanged (Meza 2002). The application of the reversion process to tangential velocity components, implies the conversion of random motion rotation kinetic energy into systematic motion rotation kinetic energy. The application of the reversion process to axial velocity components, implies the conversion of random motion translation kinetic energy into systematic motion translation kinetic energy, and the loss related to a change of reference frame is expressed in terms of systematic (imaginary) motion rotation kinetic energy. A procedure is sketched for deriving the spin parameter distribution (including imaginary rotation) from a sample of observed or simulated large-scale collisionless fluids i.e. galaxies and galaxy clusters.
We derive a simple consistency relation from the running of the tensor-to-scalar ratio. From this, for single field models we can determine whether the potential belongs to hybrid type or not. Multi-field cases in general give non-trivial contributions dependent on the geometry of the field space and the inflationary dynamics, which can enable us to distinguish single and multi-field inflation models observationally.
The first map of interstellar acetylene (C2H2) has been obtained with the infrared spectrograph onboard the Spitzer Space Telescope. A spectral line map of the $\nu_5$ vibration-rotation band at 13.7 microns carried out toward the star-forming region Cepheus A East, shows that the C2H2 emission peaks in a few localized clumps where gas-phase CO2 emission was previously detected with Spitzer. The distribution of excitation temperatures derived from fits to the C2H2 line profiles ranges from 50 to 200 K, a range consistent with that derived for gaseous CO2 suggesting that both molecules probe the same warm gas component. The C2H2 molecules are excited via radiative pumping by 13.7 microns continuum photons emanating from the HW2 protostellar region. We derive column densities ranging from a few x 10^13 to ~ 7 x 10^14 cm^-2, corresponding to C2H2 abundances of 1 x 10^-9 to 4 x 10^-8 with respect to H2. The spatial distribution of the C2H2 emission along with a roughly constant N(C2H2)/N(CO2) strongly suggest an association with shock activity, most likely the result of the sputtering of acetylene in icy grain mantles.
We investigate the evolution of the properties of model populations of ultraluminous X-ray sources (ULXs) consisting of a black-hole accretor in a binary with a donor star. We have computed models corresponding to three different populations of black-hole binaries; two invoke stellar-mass (~10 Msun) black hole accretors, and the third utilizes intermediate-mass (~1000 Msun) black holes (IMBHs). For each of the three populations, we computed 30,000 binary evolution sequences using a full Henyey stellar evolution code. The optical flux from the model ULXs includes contributions from the accretion disk, due to x-ray irradiation as well as intrinsic viscous heating, and that due to the donor star. We present "probability images" for the ULX systems in planes of color-magnitude, orbital period vs. X-ray luminosity, and luminosity vs. evolution time. Estimates of the numbers of ULXs in a typical galaxy as functions of time and of X-ray luminosity are also presented. Our model CMDs are compared with six ULX counterparts that have been discussed in the literature. Overall, the observed systems seem more closely related to model systems with very high-mass donors (> ~25 Msun) in binaries with IMBH accretors. However, significant difficulties remain with both the IMBH and stellar-mass black hole models.
We present here X-ray spectra of the HMXB SMC X-1 obtained in an observation with the XMM observatory beginning before eclipse and ending near the end of eclipse. With the Reflection Grating Spectrometers (RGS) on board XMM, we observe emission lines from hydrogen-like and helium-like ions of nitrogen, oxygen, neon, magnesium, and silicon. Though the resolution of the RGS is sufficient to resolve the helium-like n=2->1 emission into three line components, only one of these components, the intercombination line, is detected in our data. The lack of flux in the forbidden lines of the helium-like triplets is explained by pumping by ultraviolet photons from the B0 star and, from this, we set an upper limit on the distance of the emitting ions from the star. The lack of observable flux in the resonance lines of the helium-like triplets indicate a lack of enhancement due to resonance line scattering and, from this, we derive a new observational constraint on the distribution of the wind in SMC X-1 in velocity and coordinate space. We find that the solid angle subtended by the volume containing the helium-like ions at the neutron star multiplied by the velocity dispersion of the helium-like ions must be less than 4pi steradians km/s. This constraint will be satisfied if the helium-like ions are located primarily in clumps distributed throughout the wind or in a thin layer along the surface of the B0 star.
High speed collisions, although current in clusters of galaxies, have long been neglected, as they are believed to cause little damages to galaxies, except when they are repeated, a process called harassment. In fact, they are able to produce faint but extended gaseous tails. Such low-mass, starless, tidal debris may become detached and appear as free floating clouds in the very deep HI surveys that are currently being carried out. We show in this paper that these debris possess the same apparent properties as the so-called "Dark Galaxies", objects originally detected in HI, with no optical counterpart, and presumably dark matter dominated. We present a numerical model of the prototype of such Dark Galaxies - VirgoHI21 -, that is able to reproduce its main characteristics: the one-sided tail linking it to the spiral galaxy NGC 4254, the absence of stars, and above all the reversal of the velocity gradient along the tail originally attributed to rotation motions caused by a massive dark matter halo and which we find to be consistent with simple streaming motions plus projection effects. According to our numerical simulations, this tidal debris was expelled 750 Myr ago during a fly-by at 1100 km/s of NGC 4254 by a massive companion which should now lie at a projected distance of about 400 kpc. A candidate for the intruder is discussed. The existence of galaxies that have never been able to form stars had already been challenged based on theoretical and observational grounds. Tidal collisions, in particular those occurring at high speed, provide a much more simple explanation for the origin of such putative Dark Galaxies.
Two dimensional hydrodynamical disks are nonlinearly unstable to the formation of vortices. Once formed, these vortices essentially survive forever. What happens in three dimensions? We show with pseudospectral simulations that in 3D a vortex in a short box forms and survives just as in 2D. But a vortex in a tall box is unstable and is destroyed. In our simulation, the unstable vortex decays into a transient turbulent-like state that transports angular momentum outward at a nearly constant rate for hundreds of orbital times. The 3D instability that destroys vortices is a generalization of the 2D instability that forms them. We derive the conditions for these nonlinear instabilities to act by calculating the coupling between linear modes, and thereby derive the criterion for a vortex to survive in 3D as it does in 2D: the azimuthal extent of the vortex must be larger than the scale height of the accretion disk. When this criterion is violated, the vortex is unstable and decays. Because vortices are longer in azimuthal than in radial extent by a factor that is inversely proportional to their excess vorticity, a vortex with given radial extent will only survive in a 3D disk if it is sufficiently weak. This counterintuitive result explains why previous 3D simulations always yielded decaying vortices: their vortices were too strong. We conclude that in protoplanetary disks weak vortices can trap dust and serve as the nurseries of planet formation. Decaying strong vortices might be responsible for the outwards transport of angular momentum that is required to make accretion disks accrete.
Three-flavor crystalline color superconducting (CCS) phase of quantum chromodynamics (QCD) is a candidate phase for the ground state of cold matter at moderate densities above the density of deconfinement phase transition. Apart from being a superfluid, the CCS phase has solid state properties, such as lattice structure and shear modulus, hence the ability to sustain multipolar deformations in gravitational equilibrium. We construct equilibrium configurations of hybrid stars composed of nuclear matter at low and CCS quark matter at high densities. Phase equilibrium between these phases is possible only for rather stiff equations of state of nuclear matter and large couplings in the effective Nambu--Jona-Lasinio Lagrangian describing the CCS state. We identify a new branch of stable CCS hybrid stars within a broad range of central densities which, depending on the details of the equations of state, either bifurcate from the nuclear sequence of stars when the central density exceeds that of the deconfinement phase transition or form a separate class of twin configurations separated from the purely nuclear sequence by an instability region. The maximal masses of our non-rotating hybrid configurations are consistent with the presently available astronomical bounds. The sequencies of hybrid configurations that rotate near the mass-shedding limit are found to be more compact and thus support substantially larger spins than their same mass nuclear counterparts.
We describe a new wave mode similar to the acoustic wave in which both density and velocity fluctuate. Unlike the acoustic wave in which the underlying distribution is Maxwellian, this new wave mode occurs when the underlying distribution is a suprathermal kappa function and involves fluctuations in the power law index, kappa. This wave mode always propagates faster than the acoustic wave with an equivalent effective temperature and becomes the acoustic wave in the Maxwellian limit as kappa goes to infinity.
The observed cosmic acceleration today could be due to an unknown energy component (dark energy), or a modification to general relativity (modified gravity). If dark energy models and modified gravity models are required to predict the same cosmic expansion history H(z), they will predict different growth rate for cosmic large scale structure, f_g(z)=d\ln \delta/d\ln a (\delta=(\rho_m-\bar{\rho_m})/\bar{\rho_m}), a is the cosmic scale factor). If gravity is not modified, the measured H(z) leads to a unique prediction for f_g(z), f_g^H(z). Comparing f_g^H(z) with the measured f_g(z) provides a transparent and straightforward test of gravity. We show that a simple \chi^2 test provides a general figure-of-merit for our ability to distinguish between dark energy and modified gravity given the measured H(z) and f_g(z). We study a magnitude-limited NIR galaxy redshift survey covering >10,000 (deg)^2 and the redshift range of 0.5<z<2. The resultant data can be divided into 7 redshift bins, and yield the measurement of H(z) to the accuracy of 1-2% via baryon acoustic oscillation measurements, and f_g(z) to the accuracy of a few percent via the measurement of redshift space distortions and the bias factor which describes how light traces mass. We find that if the H(z) data are fit by both a DGP gravity model and an equivalent dark energy model that predict the same expansion history, a survey area of 11,931 (deg)^2 is required to rule out the DGP gravity model at the 99.99% confidence level. It is feasible for such a galaxy redshift survey to be carried out by the next generation space missions from NASA and ESA, and it will revolutionize our understanding of the universe by differentiating between dark energy and modified gravity.
Neutrinos heavier than $M_Z/2\sim 45$ GeV are not excluded by particle physics data. Stable neutrinos heavier than this might contribute to the dark matter content of the universe as well as to the cosmic gamma ray background through annihilation in galaxies. We calculate the evolution of the heavy neutrino density in the universe as a function of their mass, $M_N$ and then the subsequent gamma ray spectrum from annihilation of distant $N\bar{N}$ (from $0<z<5$). This includes estimating the enhancement of the signal due to dark matter clumping. The evolution of the heavy neutrino density in the universe is calculated numerically. In order to obtain the enhancement due to the increased density within galaxies, we approximate the distribution of $N$ to be proportional to that of dark matter in the GalICS model. The calculated gamma ray spectrum is compared to the measured EGRET data. Heavy neutrinos of mass $120\lesssim M_N \lesssim 155$ GeV could account for the entire dark matter content of the universe. Furthermore, these neutrinos would be detectable with precision gamma ray measurements.
We analyze the mean rest-frame ultraviolet (UV) spectrum of Type Ia Supernovae (SNe Ia) and its dispersion using high signal-to-noise Keck-I/LRIS-B spectroscopy for a sample of 36 events at intermediate redshift (z=0.5) discovered by the Canada-France-Hawaii Telescope Supernova Legacy Survey (SNLS). We introduce a new method for removing host galaxy contamination in our spectra, exploiting the comprehensive photometric coverage of the SNLS SNe and their host galaxies, thereby providing the first quantitative view of the UV spectral properties of a large sample of distant SNe Ia. Although the mean SN Ia spectrum has not evolved significantly over the past 40% of cosmic history, precise evolutionary constraints are limited by the absence of a comparable sample of high quality local spectra. Within the high-redshift sample, we discover significant UV spectral variations and exclude dust extinction as the primary cause by examining trends with the optical SN color. Although progenitor metallicity may drive some of these trends, the variations we see are much larger than predicted in recent models and do not follow expected patterns. An interesting new result is a variation seen in the wavelength of selected UV features with phase. We also demonstrate systematic differences in the SN Ia spectral features with SN light curve width in both the UV and the optical. We show that these intrinsic variations could represent a statistical limitation in the future use of high-redshift SNe Ia for precision cosmology. We conclude that further detailed studies are needed, both locally and at moderate redshift where the rest-frame UV can be studied precisely, in order that future missions can confidently be planned to fully exploit SNe Ia as cosmological probes [ABRIDGED].
The MOdified Newtonian Dynamics (MOND) is presented here, as well as a theory that can be linked to it: the theory of the Aether, a four-vector field breaking Lorentz invariance. The form of its Lagrangian is studied, then basic equations of the theory are rederived in a detailed way, and calculated for different metrics, exploring the impact of non-zero spatial terms of the Aether. A brief attempt of making the Aether Lagrangian depend on a scalar field is presented. An analytic solving of a galaxy model with an external field is described, which highlights the MONDian external field effect that breaks the strong equivalence principle.
We model the thermal effect of young stars on their surrounding environment in order to understand clustered star formation. We take radiative heating of dust, dust-gas collisional heating, cosmic-ray heating, and molecular cooling into account. Using Dusty, a spherical continuum radiative transfer code, we model the dust temperature distribution around young stellar objects with various luminosities and surrounding gas and dust density distributions. We have created a grid of dust temperature models, based on our modeling with Dusty, which we can use to calculate the dust temperature in a field of stars with various parameters. We then determine the gas temperature assuming energy balance. Our models can be used to make large-scale simulations of clustered star formation more realistic.
We follow the evolution of helium stars of initial mass $(2.2 - 2.5) M_\odot$, and show that they undergo off-center carbon burning, which leaves behind ${\mathbf \sim 0.01 M_\odot}$ of unburnt carbon in the inner part of the core. When the carbon-oxygen core grows to Chandrasekhar mass, the amount of left-over carbon is sufficient to ignite thermonuclear runaway. At the moment of explosion, the star will possess an envelope of several $0.1 M_{\odot}$, consisting of He, C, and possibly some H, perhaps producing a kind of peculiar SN. Based on the results of Waldman and Barkat (2007) for accreting white dwarfs, we expect to get thermonuclear runaway at a broad range of $\rho_c \approx (1 - 6) \times 10^9 \mathrm{g cm^{-3}}$, depending on the amount of residual carbon. We verified the feasibility of this scenario by showing that in a close binary system with initial masses $(8.5 + 7.7) M_{\odot}$ and initial period of 150 day the primary produces a helium remnant of $2.3 M_{\odot}$ that evolves further like the model we considered.
A review of recent studies on a new mechanism of generation of large-scale magnetic field in a sheared turbulent plasma is presented. This mechanism is associated with the shear-current effect which is related to the W x J-term in the mean electromotive force. This effect causes the generation of the large-scale magnetic field even in a nonrotating and nonhelical homogeneous sheared turbulent convection whereby the alpha effect vanishes. It is found that turbulent convection promotes the shear-current dynamo instability, i.e., the heat flux causes positive contribution to the shear-current effect. However, there is no dynamo action due to the shear-current effect for small hydrodynamic and magnetic Reynolds numbers even in a turbulent convection, if the spatial scaling for the turbulent correlation time is k^{-2}, where k is the small-scale wave number. We discuss here also the nonlinear mean-field dynamo due to the shear-current effect and take into account the transport of magnetic helicity as a dynamical nonlinearity. The magnetic helicity flux strongly affects the magnetic field dynamics in the nonlinear stage of the dynamo action. When the magnetic helicity flux is not small, the saturated level of the mean magnetic field is of the order of the equipartition field determined by the turbulent kinetic energy. The obtained results are important for elucidation of origin of the large-scale magnetic fields in astrophysical and cosmic sheared turbulent plasma.
We present a model to explain the mass segregation and shallow mass functions observed in the central parts of dense and young starburst stellar clusters. The model assumes that the initial pre-stellar cores mass function resulting from the turbulent fragmentation of the proto-cluster cloud is significantly altered by the cores coalescence before they collapse to form stars. With appropriate, yet realistic parameters, this model based on the competition between cores coalescence and collapse reproduces the mass spectra of the well studied Arches cluster. Namely, the slopes at the intermediate and high mass ends are reproduced, as well as the peculiar bump observed at 6 M_sol. This coalescence-collapse process occurs on short timescale of the order of one fourth the free fall time of the proto-cluster cloud (i.e., a few 10^{4} years), suggesting that mass segregation in Arches and similar clusters is primordial. The best fitting model implies the total mass of the Arches cluster is 1.45 10^{5} M_sol, which is slightly higher than the often quoted, but completeness affected, observational value of a few 10^{4} M_sol. The derived star formation efficiency is ~30 percent which implies that the Arches cluster is likely to be gravitationally bound.
SPACE (SPectroscopic All-sky Cosmic Explorer) is a class-M mission proposed to ESA for the Cosmic Vision 2015-2025 call and recently promoted to the next assessment study phase. SPACE will produce the first all-sky spectroscopic survey of the Universe, taking spectra of more than 500 million galaxies over a wide range of redshifts. SPACE will operate in slit mode (MEMS) at R~400 between 0.8 and 1.8micron down to AB~23, providing redshifts to an accuracy of Delta z~0.001, regardless on the presence of bright emission lines, together with the most relevant physical and evolutionary properties. The catalog of spectroscopic redshift will allow to place the ultimate constraints on the Baryon Acoustic Oscillations and the nature of Dark Energy. By obtaining the first 3-D all-sky map of the Universe at z~2 and beyond, SPACE will trace the growth rate of cosmic structures, the large scale structure of luminous baryons and its cosmic evolution. Besides the all-sky survey, SPACE will carry out a deep extragalactic survey over an area of ~10 sq. deg., enabling a most powerful supernova search program, and a galactic plane survey in integral field mode. Approximately 30% of the time will be open. Due to its versatility, SPACE is a ``self-sufficient'' observatory which can attack and solve the most compelling questions on the nature of the Dark Energy without complementary data from the Earth or space. Its unique wide-field capabilities in the near-IR make SPACE the ideal complement to JWST, ALMA, and the future 25-50 m telescopes.
We argue that giant flares in SGRs can be associated to the core conversion of an isolated neutron star having a subcritical magnetic field $\sim 10^{12}$ G and a fallback disk around it. We show that, in a timescale of $\lesssim 10^5$ yrs, accretion from the fallback disk can increase the mass of the central object up to the critical mass for the conversion of the core of the star into quark matter. A small fraction of the neutrino-antineutrino emission from the just-converted quark-matter hot core annihilates into $e^+e^-$ pairs above the neutron star surface originating the gamma emission of the spike while the further cooling of the heated neutron star envelope originates the tail of the burst. We show that several characteristics of the giant flare of the SGR 1806-20 of 27 December 2004 (spike and tail energies, timescales, and spectra) can be explained by this mechanism.
The scattering of electromagnetic radiation by the particle gyrating in an external magnetic field is considered. Particular attention is paid to the low-frequency case, when the frequencies of incident radiation are much less than the electron gyrofrequency. The spectral and polarization features of the scattering cross-section are analyzed in detail. It is found that the scattering transfers the low-frequency photons to high harmonics of the gyrofrequency, into the range of the synchrotron emission of the electron. The total scattering cross-section appears much larger than that for the particle at rest. The problem studied is directly applicable to the radio wave scattering in the magnetosphere of a pulsar. The particles acquire relativistic rotational energies as a result of resonant absorption of the high-frequency radio waves and concurrently scatter the low-frequency radio waves, which are still below the resonance. It is shown that the scattering can affect the radio intensity and polarization at the lowest frequencies and can compete with the resonant absorption in contributing to the low-frequency turnover in the pulsar spectrum. Moreover, the scattering can be an efficient mechanism of the pulsar high-energy emission, in addition to the synchrotron re-emission of the particles. Other astrophysical applications of the scattering by gyrating particles are pointed out as well.
We study how the determination of the Hubble constant from cosmological distance measures is affected by models of dark energy and vice versa. For this purpose, constraints on the Hubble constant and dark energy are investigated using the cosmological observations of cosmic microwave background, baryon acoustic oscillations and type Ia suprenovae. When one investigates dark energy, the Hubble constant is often a nuisance parameter, thus it is usually marginalized over. On the other hand, when one focuses on the Hubble constant, simple dark energy models such as a cosmological constant and a constant equation of state are usually assumed. Since we do not know the nature of dark energy yet, it is interesting to investigate the Hubble constant assuming some types of dark energy and see to what extent the constraint on the Hubble constant is affected by the assumption concerning dark energy. We show that the constraint on the Hubble constant is not affected much by the assumption for dark energy. We furthermore show that this holds true even if we remove the assumption that the universe is flat. We also discuss how the prior on the Hubble constant affects the constraints on dark energy and/or the curvature of the universe.
G39-27/289 is a common proper motion pair formed by a white dwarf (WD0433+270) and a main-sequence star (BD+26 730) that apparently has been classified as a member of the Hyades open cluster. Previous studies of the white dwarf component yielded a cooling time of ~4 Gyr. Although it has not been pointed out before explicitly, this result is 6 times larger than the age of the Hyades cluster, giving rise to an apparent conflict between the physics of white dwarfs and cluster main-sequence fitting. We investigate whether this system belongs to the Hyades cluster and, accordingly, give a plausible explanation to the nature of the white dwarf member. From kinematic and chemical composition considerations we believe that the system was a former member of the Hyades cluster and therefore has an evolutionary link with it. However, the evidence is not conclusive. With regards to the nature of the white dwarf component, we find that two core compositions (C/O and Fe) are compatible with the observed effective temperature and radius. These compositions yield very different cooling times of ~4 Gyr and ~1 Gyr, respectively. We distinguish two posssible scenarios. If the pair does not belong to the Hyades cluster but only to the Hyades stream, this would indicate that such stream contains rather old objects and definitely not coeval with the cluster. This has interesting consequences for Galactic dynamics. On the contrary, if the white dwarf has an Fe core, it will have a cooling time compatible with the Hyades age. This is a tantalizing result that would have implications for the thermonuclear explosion of white dwarfs and explosion theories of degenerate nuclei.
The stellar evolution code YREC is outlined with emphasis on its applications to helio- and asteroseismology. The procedure for calculating calibrated solar and stellar models is described. Other features of the code such as a non-local treatment of convective core overshoot, and the implementation of a parametrized description of turbulence in stellar models, are considered in some detail. The code has been extensively used for other astrophysical applications, some of which are briefly mentioned at the end of the paper.
Principal Component Analysis (PCA) is a well-known technique used to decorrelate a set of vectors. It has been applied to explore the star formation history of galaxies or to determine distances of mass-lossing stars. Here we apply PCA to the optical data of Planetary Nebulae (PNe) with the aim of extracting information about their morphological differences. Preliminary analysis of a sample of 55 PNe with known abundances and morphology shows that the second component (PC2), which results from a relation produced by the parameters log(N/O), initial and final mass of PNe, is depending on the morphology of PNe. It has been found that when log(N/O) < -0.18 the PNe's nitrogen is low independently on the oxygen abundance for either Bipolar (B), Elliptical (E) or Round (R) PNe. An interesting result is that both E and R PNe have log(N/O) < 0 while only B PNe show negative and positive values. Consequently, B PNe are expected to have higher nitrogen values than the E and R PNe. Following that and a second sample of 35 PNe, n_{e} is also found to be higher in B PNe. Also, in all PNe morphologies PC2 appears to have a minimum at 0.89 and PNe's initial mass at 2.6 solar masses. 5-D diagrams between PCAs components and physical parameters are also presented. More results will follow while simple models will be applied in order to try to give a physical meaning to the components.
The pulse sequence is interpreted as a realization of a random electron discharge process in a vacuum gap over the polar cap (PC) - the open magnetic force line region on the neutron star surface. This point of view is illustrated by an example based on the dice. The generators of the random numbers are a cube and a coin. Throwing of dice and coin tossing determine the discharge places on the "light" and "dark" sides of PC, and correspondingly - the "shape" of the individual pulses and their statistical properties The physical mechanism giving such discharge scheme is shortly discussed. It may be a charge drained down from a sharp top of surface waves in a parallel electric field on the liquid PC surface of a neutron star.
The cold dark matter (CDM) scenario generically predicts the existence of
triaxial dark matter haloes which contain notable amounts of substructure.
However, analytical halo models with smooth, spherically symmetric density
profiles are routinely adopted in the modelling of light propagation effects
through such objects. In this paper, we address the biases introduced by this
procedure by comparing the surface mass densities of actual N-body haloes
against the widely used analytical model suggested by Navarro, Frenk and White
(1996) (NFW).
We conduct our analysis in the redshift range of 0.0 - 1.5. In cluster sized
haloes, we find that triaxiality can cause scatter in the surface mass density
of the haloes up to sigma_+ = +60% and sigma_- = -70%, where the 1-sigma limits
are relative to the analytical NFW model given value. Subhaloes can increase
this scatter to sigma_+ = +70% and sigma_- = -80%. In galaxy sized haloes, the
triaxial scatter can be as high as sigma_+ = +80% and sigma_- = -70%, and with
subhaloes the values can change to sigma_+ = +40% and sigma_- = -80%.
We present an analytical model for the surface mass density scatter as a
function of distance to the halo centre, halo redshift and halo mass. The
analytical description enables one to investigate the reliability of results
obtained with simplified halo models. Additionally, it provides the means to
add simulated surface density scatter to analytical density profiles. As an
example, we discuss the impact of our results on the calculation of
microlensing optical depths for MACHOs in CDM haloes.
We present near-infrared (H- and K-band) integral-field observations of the circumnuclear star formation rings in five nearby spiral galaxies. The data, obtained at the Very Large Telescope with the SINFONI spectrograph, are used to construct maps of various emission lines that reveal the individual star forming regions ("hot spots") delineating the rings. We derive the morphological parameters of the rings, and construct velocity fields of the stars and the emission line gas. We propose a qualitative, but robust, diagnostic for relative hot spot ages based on the intensity ratios of the emission lines Brackett gamma, HeI, and [FeII]. Application of this diagnostic to the data presented here provides tentative support for a scenario in which star formation in the rings is triggered predominantly at two well-defined regions close to, and downstream from, the intersection of dust lanes along the bar with the inner Lindblad resonance.
The X-ray source SAXJ1712.6-3739 is a very weak Low Mass X-ray Binary discovered in 1999 with BeppoSAX and located in the Galactic Center. This region has been deeply investigated by the INTEGRAL satellite with an unprecedented exposure time, giving us an unique opportunity to study the hard X-ray behavior also for weak objects. The spectral results are based on the systematic analysis of all INTEGRAL observations covering the source position performed between February 2003 and October 2006. SAXJ1712.6-3739 did not shows any flux variation along this period as well as compared to previous BeppoSAX observation. Hence, to better constrain the physical parameters we combined both instrument data. Long INTEGRAL monitoring reveals, for the first time, that this X-ray burster is a weak persistent source, displaying a X-ray spectrum extended to high energy and spending most of the time in a low luminosity hard state. The broad-band spectrum is well modeled with a simple Comptonized model with a seed photons temperature of ~0.5keV and an electron temperature of ~24keV. The low mass accretion rate (~2x10^{-10} Msun/yr), the long bursts recurrence time, the small sizes of the region emitting the seed photons consisting with the inner disk radius and the high luminosity ratio in the 40-100keV and 20-40keV band, are all features common to the Ultra Compact source class.
For Seyfert galaxies, the AGN unification model provides a simple and well
established explanation of the Type 1/Type 2 dichotomy through orientation
based effects. The generalization of this unification model to the higher
luminosity AGNs that are the quasars remains a key question. The recent
detection of Type 2 Radio-Quiet quasars seems to support such an extension. We
propose to further test this scenario.
On the basis of a compilation of quasar host galaxy position angles
consisting of previously published data and of new measurements performed using
HST Archive images, we investigate the possible existence of a correlation
between the linear polarization position angle and the host galaxy/extended
emission position angle of quasars.
We find that the orientation of the rest-frame UV/blue extended emission is
correlated to the direction of the quasar polarization. For Type 1 quasars, the
polarization is aligned with the extended UV/blue emission while these two
quantities are perpendicular in Type 2 objects. This result is independent of
the quasar radio-loudness. We interpret this (anti-)alignment effect in terms
of scattering in a two-component polar+equatorial model which applies to both
Type 1 and Type 2 objects. Moreover the orientation of the polarization -and
then of the UV/blue scattered light- does not appear correlated to the major
axis of the stellar component of the host galaxy measured from near-IR images.
Boxy/peanut bulges in disk galaxies have been associated to stellar bars. In this talk, we discuss the different properties of such bulges and their relation with the corresponding bar, using a very large sample of a few hundred numerical N-body simulations. We present and inter-compare various methods of measuring the boxy/peanut bulge properties, namely its strength, shape and possible asymmetry. Some of these methods can be applied to both simulations and observations. Our final goal is to get correlations that will allow us to obtain information on the boxy/peanut bulge for a galaxy viewed face-on as well as information on the bars of galaxies viewed edge-on.
The contributions of the H.E.S.S. collaboration to the ICRC 2007 in Merida, Mexico. All proceedings papers are compiled in a single source file.
The turbulent magnetic diffusivity tensor is determined in the presence of rotation or shear and the question is addressed whether dynamo action from the shear--current effect can explain large-scale magnetic field generation found in simulations with shear. For this purpose a set of evolution equations for the response to imposed test fields is solved simultaneously with the momentum and continuity equations. The corresponding results for the electromotive force are used to calculate turbulent transport coefficients. The diagonal components of the turbulent magnetic diffusivity tensor are found to be equal, but their values increase slightly with increasing shear and decrease with increasing rotation rate. In the presence of shear, the sign of the two off-diagonal components of the turbulent magnetic diffusion tensor is the same and opposite to the sign of the shear such that dynamo action from the shear--current effect is impossible. However, even though there is no alpha effect on the average, the components of the alpha tensor display gaussian fluctuations about zero that are strong enough to drive an incoherent alpha--shear dynamo. The incoherent shear--current effect is found to be subdominant.
The majority of X-ray burst sources do not display a burst rate that increases with luminosity as expected, but this is seen in the two clocked bursters XB1323-619 and GS1826-24. We present a detailed investigation of these two sources which in the case of the first source, spans 18 years. Based on measurements of the burst rate, X-ray luminosity, the alpha-parameter and the two time constants generally present in the burst decays, we demonstrate the importance of the rp nuclear burning process. A detailed comparison with theory shows that although the burst rate in each source agrees well with the theoretical value, there is a difference of more than a factor of 5 in the burst rate at a given luminosity between the sources. We show that the main reason for this is that the two sources have substantially different emitting areas on the neutron star in non-burst emission, a factor often neglected. Variation of this area may explain the inverse relation of burst rate with luminosity in the majority of burst sources.
To optimise the science results of the asteroseismic part of the CoRoT satellite mission a complementary simultaneous ground-based observational campaign is organised for selected CoRoT targets. The observations include both high-resolution spectroscopic and multi-colour photometric data. We present the preliminary results of the analysis of the ground-based observations of three targets. A line-profile analysis of 216 high-resolution FEROS spectra of the delta Sct star HD 50844 reveals more than ten pulsation frequencies in the frequency range 5-18 c/d, including possibly one radial fundamental mode (6.92 c/d). Based on more than 600 multi-colour photometric datapoints of the beta Cep star HD180642, spanning about three years and obtained with different telescopes and different instruments, we confirm the presence of a dominant radial mode nu1=5.48695 c/d, and detect also its first two harmonics. We find evidence for a second mode nu2=0.3017 c/d, possibly a g-mode, and indications for two more frequencies in the 7-8 c/d domain. From Stromgren photometry we find evidence for the hybrid delta Sct/gamma Dor character of the F0 star HD 44195, as frequencies near 3 c/d and 21 c/d are detected simultaneously in the different filters.
We investigate how different models that have been proposed for solving the dark matter problem can fit the velocity dispersion observed around elliptical galaxies, on either a small scale (~ 20kpc) with stellar tracers, such as planetary nebulae, or large scale (~ 200kpc) with satellite galaxies as tracers. Predictions of Newtonian gravity, either containing pure baryonic matter, or embedded in massive cold dark matter (CDM) haloes, are compared with predictions of the modified gravity of MOND. The standard CDM model has problems on a small scale, and the Newtonian pure baryonic model has difficulties on a large scale, while a fit with MOND is possible on both scales.
We investigate correlations between the optical linear polarization position angle and the orientation of the host galaxy/extended emission of Type 1 and Type 2 Radio-Loud (RL) and Radio-Quiet (RQ) quasars. We have used high resolution Hubble Space Telescope (HST) data and deconvolution process to obtain a good determination of the host galaxy orientation. With these new measurements and a compilation of data from the literature, we find a significant correlation between the polarization position angle and the position angle of the major axis of the host galaxy/extended emission. The correlation appears different for Type 1 and Type 2 objects and depends on the redshift of the source. Interpretations in the framework of the unification model are discussed.
We have used the Novikov-Thorne thin disk model to fit the continuum X-ray spectra of three transient black hole X-ray binaries in the thermal state. From the fits we estimate the dimensionless spin parameters of the black holes to be: 4U 1543-47, a* = a/M = 0.7-0.85; GRO J1655-40, a* = 0.65-0.8; GRS 1915+105, a* = 0.98-1. We plan to expand the sample of spin estimates to about a dozen over the next several years. Some unresolved theoretical issues are briefly discussed.
Motivated by the emergence of multicore architectures, and the reality that parallelism is rarely used for analysis in observational astronomy, we demonstrate how general users may employ tightly-coupled multiprocessors in scriptable research calculations while requiring no special knowledge of parallel programming. Our method rests on the observation that much of the appeal of high-level vectorized languages like IDL or MatLab stems from relatively simple internal loops over regular array structures, and that these loops are highly amenable to automatic parallelization with OpenMP. We discuss how ISIS, an open-source astrophysical analysis system embedding the S-Lang numerical language, was easily adapted to exploit this pattern. Drawing from a common astrophysical problem, model fitting, we present beneficial speedups for several machine and compiler configurations. These results complement our previous efforts with PVM, and together lead us to believe that ISIS is the only general purpose spectroscopy system in which such a range of parallelism -- from single processors on multiple machines to multiple processors on single machines -- has been demonstrated.
Accurate alignment of the radio and optical celestial reference frames requires detailed understanding of physical factors that may cause offsets between the positions of the same object measured in different spectral bands. Opacity in compact extragalactic jets (due to synchrotron self-absorption and external free-free absorption) is one of the key physical phenomena producing such an offset, and this effect is well-known in radio astronomy ("core shift"). We have measured the core shifts in a sample of 29 bright compact extragalactic radio sources observed using very long baseline interferometry (VLBI) at 2.3 and 8.6 GHz. We report the results of these measurements and estimate that the average shift between radio and optical positions of distant quasars would be of the order of 0.1-0.2 mas. This shift exceeds positional accuracy of GAIA and SIM. We suggest two possible approaches to carefully investigate and correct for this effect in order to align accurately the radio and optical positions. Both approaches involve determining a Primary Reference Sample of objects to be used for tying the radio and optical reference frames together.
Based on the results of applying the extended ADC emission model to three Z-track sources: GX340+0, GX5-1 and CygX-2, we propose an explanation of the Z-track sources in which the Normal and Horizontal Branches are dominated by the increasing radiation pressure of the neutron star. The emitted flux becomes several times super-Eddington at the Hard Apex and Horizontal Branch and we suggest that the inner accretion disk is disrupted by this and that part of the accretion flow is diverted vertically. This position on the Z-track is exactly the position where radio emission is detected showing the presence of jets. We thus propose that high radiation pressure is a necessary condition for the launching of jets. We also show that flaring must consist of unstable nuclear burning and that the mass accretion rate per unit emitting area of the neutron star mdot at the onset of flaring agrees well with the critical theoretical value at which burning becomes unstable.
A subgroup of dwarf galaxies have characteristics of a possible evolutionary transition between star-forming systems and dwarf ellipticals. These systems host significant starbursts in combination with smooth, elliptical outer envelopes and small HI content; they are low on gas and unlikely to sustain high star formation rates over significant cosmic time spans. We explore possible origins of such starburst "transition" dwarfs using moderately deep optical images. While galaxy-galaxy interactions could produce these galaxies, no optical evidence exists for tidal debris or other outer disturbances, and they also lack nearby giant neighbors which could supply recent perturbations. Colors of the outer regions indicate that star formation ceased > 1 Gyr in the past, a longer time span than can be reasonably associated with the current starbursts. We consider mechanisms where the starbursts are tied either to interactions with other dwarfs or to the state of the interstellar medium, and discuss the possibility of episodic star formation events associated with gas heating and cooling in low specific angular momentum galaxies.
We present new estimates of ages and metallicities, based on FORS/VLT optical (4400-5500A) spectroscopy, of 16 dwarf elliptical galaxies (dE's) in the Fornax Cluster and in Southern Groups. These dE's are more metal-rich and younger than previous estimates based on narrow-band photometry and low-resolution spectroscopy. For our sample we find a mean metallicity [Z/H] = -0.33 dex and mean age 3.5 Gyr, consistent with similar samples of dE's in other environments (Local Group, Virgo). Three dE's in our sample show emission lines and very young ages. This suggests that some dE's formed stars until a very recent epoch and were self-enriched by a long star formation history. Previous observations of large near-infrared (~8500A) Ca II absorption strengths in these dE's are in good agreement with the new metallicity estimates, solving part of the so-called Calcium puzzle.
We computed the chemical evolution of spiral bulges hosting Seyfert nuclei, based on updated chemical and spectro-photometrical evolution models for the bulge of our Galaxy, made predictions about other quantities measured in Seyferts, and modeled the photometry of local bulges. The chemical evolution model contains detailed calculations of the Galactic potential and of the feedback from the central supermassive black hole, and the spectro-photometric model covers a wide range of stellar ages and metallicities. We followed the evolution of bulges in the mass range 10^9 - 10^{11} Msun by scaling the star formation efficiency and the bulge scalelength as in the inverse-wind scenario for elliptical galaxies, and considering an Eddington limited accretion onto the central supermassive black hole. We successfully reproduced the observed black hole-host bulge mass relation. The observed nuclear bolometric luminosity is reproduced only at high redshift or for the most massive bulges; in the other cases, at z = 0 a rejuvenation mechanism is necessary. The black hole feedback is in most cases not significant in triggering the galactic wind. The observed high star formation rates and metal overabundances are easily achieved, as well as the constancy of chemical abundances with redshift and the bulge present-day colours. Those results are not affected if we vary the index of the stellar IMF from x=0.95 to x=1.35; a steeper IMF is instead required in order to reproduce the colour-magnitude relation and the present K-band luminosity of the bulge.
A fundamental bound on the relaxation time \tau of a perturbed thermodynamical system has recently been derived, \tau \geq \hbar/\pi T, where $T$ is the system's temperature. We demonstrate analytically that black holes saturate this bound in the extremal limit and for large values of the azimuthal number m of the perturbation field.
We consider the quasinormal spectrum of a charged scalar field in the (charged) Reissner-Nordstrom spacetime, which has two horizons. The spectrum is characterized by two distinct families of asymptotic resonances. We suggest and demonstrate the according to Bohr's correspondence principle and in agreement with the Bekenstein-Mukhanov quantization scheme, one of these resonances corresponds to a fundamental change of Delta A=4hbar ln2 in the surface area of the black-hole outer horizon. The second asymptotic resonance is associated with a fundamental change of Delta Atot=4hbar ln3 in the total area of the black hole (in the sum of the surface areas of the inner and outer horizons), in accordance with a suggestion of Makela and Repo.
After a period of inflationary expansion, the
Universe reheated and reached full thermal equilibrium at the reheating
temperature T_R. In this work we point out that, in the context of effective
low-energy supersymmetric models, LHC measurements may allow one to determine
T_R as a function of the mass of the dark matter particle assumed to be either
an axino or a gravitino. An upper bound on their mass may also be derived.
The majority of models of inflation in string theory predict an absence of measurable gravitational waves, r << 10^{-3}. The most promising proposals for making string theoretic models that yield measurable tensor fluctuations involve axion fields with slightly broken shift symmetry. We consider such models in detail, with a particular focus on the N-flation scenario and on axion valley/natural inflation models. We find that in Calabi-Yau threefold compactifications with logarithmic Kahler potentials K it appears to be difficult to meet the conditions required for axion inflation in the supergravity regime. However, in supergravities with an (approximately) quadratic shift-symmetric K, axion inflation may be viable. Such Kahler potentials do arise in some string models, in specific limits of the moduli space. We describe the most promising classes of models; more detailed study will be required before one can conclude that working models exist.
We discuss a general fourth-order theory of gravity on the brane. In general, the formulation of the junction conditions (except for Euler characteristics such as Gauss-Bonnet term) leads to the higher powers of the delta function and requires regularization. We suggest the way to avoid such a problem by imposing the metric and its first derivative to be regular at the brane, while the second derivative to have a kink, the third derivative of the metric to have a step function discontinuity, and no sooner as the fourth derivative of the metric to give the delta function contribution to the field equations. Alternatively, we discuss the reduction of the fourth-order gravity to the second-order theory by introducing an extra tensor field. We formulate the appropriate junction conditions on the brane. We prove the equivalence of both theories. In particular, we prove the equivalence of the junction conditions with different assumptions related to the continuity of the metric along the brane.
We argue that the Higgs boson of the Standard Model can lead to inflation and produce cosmological perturbations in accordance with cosmological observations. An essential requirement is the non-minimal coupling of the Higgs scalar field to gravity; no new particle besides already present in the electroweak theory is required.
We describe a broad class of time-dependent exact wave solutions to 6D gauged chiral supergravity with two compact dimensions. These 6D solutions are nontrivial warped generalizations of 4D pp-waves and Kundt class solutions and describe how a broad class of previously-static compactifications from 6D to 4D (sourced by two 3-branes) respond to waves moving along one of the uncompactified directions. Because our methods are generally applicable to any higher dimensional supergravity they are likely to be of use for finding the supergravity limit of time-dependent solutions in string theory. The 6D solutions are interesting in their own right, describing 6D shock waves induced by high energy particles on the branes, and as descriptions of the near-brane limit of the transient wavefront arising from a local bubble-nucleation event on one of the branes, such as might occur if a tension-changing phase transition were to occur.
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Using a uniform analysis procedure, we measure spatially resolved weak gravitational lensing and hydrostatic X-ray masses for a sample of 18 clusters of galaxies. We find a radial trend in the X-ray to lensing mass ratio: at r2500 we obtain a ratio MX/ML=1.03+/-0.07 which decreases to MX/ML=0.78+/-0.09 at r500. This difference is significant at 3 sigma once we account for correlations between the measurements. We show that correcting the lensing mass for excess correlated structure outside the virial radius slightly reduces, but does not eliminate this trend. An X-ray mass underestimate, perhaps due to nonthermal pressure support, can explain the residual trend. We also examine the cluster gas fraction and find no correlation with ML, an important result for techniques that aim to determine cosmological parameters using the gas fraction.
If light scalar fields are present at the end of inflation, their non-equilibrium dynamics such as parametric resonance or a phase transition can produce non-Gaussian density perturbations. We show how this non-Gaussianity can be calculated using non-linear lattice field theory simulations and the separate universe approximation. Our numerical results for the massless preheating model rule out large parts of the parameter space, and suggest that any inflationary model in which preheating is dominated by the homogeneous mode may be in conflict with observations.
Since 1999, a radial velocity survey of 179 red giant stars is ongoing at Lick Observatory with a one month cadence. At present ~20-100 measurements have been collected per star with an accuracy of 5 to 8 m/s. Of the stars monitored, 145 (80%) show radial velocity (RV) variations at a level >20 m/s, of which 43 exhibit significant periodicities. Here, we investigate the mechanism causing the observed radial velocity variations. Firstly, we search for a correlation between the radial velocity amplitude and an intrinsic parameter of the star, in this case surface gravity (log g). Secondly, we investigate line profile variations and compare these with theoretical predictions.
We present an analysis of the optical colors of 413 Virgo cluster early-type dwarf galaxies (dEs), based on Sloan Digital Sky Survey imaging data. Our study comprises (1) a comparison of the color-magnitude relation (CMR) of the different dE subclasses that we identified in Paper III of this series, (2) a comparison of the shape of the CMR in low and high-density regions, (3) an analysis of the scatter of the CMR, and (4) an interpretation of the observed colors with ages and metallicities from population synthesis models. We find that the CMRs of nucleated (dE(N)) and non-nucleated dEs (dE(nN)) are significantly different from each other, with similar colors at fainter magnitudes (r > 17 mag), but increasingly redder colors of the dE(N)s at brighter magnitudes. We interpret this with older ages and/or higher metallicities of the brighter dE(N)s. The dEs with disk features have similar colors as the dE(N)s and seem to be only slightly younger and/or less metal-rich on average. Furthermore, we find a small but significant dependence of the CMR on local projected galaxy number density, consistently seen in all of u-r, g-r, and g-i, and weakly i-z. We deduce that a significant intrinsic color scatter of the CMR is present, even when allowing for a distance spread of our galaxies. No increase of the CMR scatter at fainter magnitudes is observed down to r = 17 mag (Mr = -14 mag). The color residuals, i.e., the offsets of the data points from the linear fit to the CMR, are clearly correlated with each other in all colors for the dE(N)s and for the full dE sample. We conclude that there must be at least two different formation channels for early-type dwarfs in order to explain the heterogeneity of this class of galaxy. (Abridged)
The cosmic gamma-ray background (CGB) is a very promising channel to look for signatures of dark matter annihilation. Indeed, if gamma-rays from dark matter constitute a relevant fraction of the CGB, then, together with an imprint in the energy spectrum, peculiar angular signatures are also expected. In particular, the expected anisotropies differ significantly compared to the anisotropies from emission of astrophysical sources only, provided that annihilation in sub-galactic clumps and/or in cuspy haloes gives only a moderate enhancement in the dark matter signal. In this scenario the differences are at a level detectable with the forthcoming GLAST observatory. As complementary observables we further introduce the cross-correlation between surveys of galaxies and the CGB and the cross-correlation between different energy bands of the CGB and we study their sensitivity to the dark matter angular signatures. We find that a combined analysis of all the anisotropy observables provides a powerful tool to investigate the dark matter signal.
The median observed velocity width v_90 of low-ionization species in damped Ly-alpha systems is close to 90 km/s, with approximately 10% of all systems showing v_90 > 210 km/s at z=3. We show that a relative shortage of such high-velocity neutral gas absorbers in state-of-the-art galaxy formation models is a fundamental problem, present both in grid-based and particle-based numerical simulations. Using a series of numerical simulations of varying resolution and box size to cover a wide range of halo masses, we demonstrate that energy from gravitational infall alone is insufficient to produce the velocity dispersion observed in damped Ly-alpha systems, nor does this dispersion arise from an implementation of star formation and feedback in our highest resolution (~ 45 pc) models, if we do not put any galactic winds into our models by hand. We argue that these numerical experiments highlight the need to separate dynamics of different components of the multiphase interstellar medium at z=3.
(Abridged) We present a detailed analysis of week-long simultaneous observations of the blazar Mrk421 at 2-60 keV X-rays (RXTE) and TeV gamma-rays (Whipple and HEGRA) in 2001. The unprecedented quality of this dataset enables us to establish firmly the existence of the correlation between the TeV and X-ray luminosities, and to start unveiling some of its more detailed characteristics, in particular its energy dependence, and time variability. The source shows strong, highly correlated variations in X-ray and gamma-ray. No evidence of X-ray/gamma-ray interband lag is found on the full week dataset (<3 ks). However, a detailed analysis of the March 19 flare reveals that data are not consistent with the peak of the outburst in the 2-4 keV X-ray and TeV band being simultaneous. We estimate a 2.1+/-0.7 ks TeV lag. The amplitudes of the X-ray and gamma-ray variations are also highly correlated, and the TeV luminosity increases more than linearly w.r.t. the X-ray one. The strong correlation supports the standard model in which a unique electrons population produces the X-rays by synchrotron radiation and the gamma-ray component by inverse Compton scattering. However, for the individual best observed flares the gamma-ray flux scales approximately quadratically w.r.t. the X-ray flux, posing a serious challenge to emission models for TeV blazars. Rather special conditions and/or fine tuning of the temporal evolution of the physical parameters of the emission region are required in order to reproduce the quadratic correlation.
We infer the large-scale source parameters of dusty galaxies from their observed spectral energy distributions (SEDs) using the analytic radiative transfer methodology presented in Chakrabarti & McKee (2005). For local ultra-luminous infrared galaxies (ULIRGs), we show that the millimeter to far-infrared (FIR) SEDs can be well fit using the standard dust opacity index of 2 when self-consistent radiative transfer solutions are employed, indicating that the cold dust in local ULIRGs can be described by a single grain model. We develop a method for determining photometric redshifts of ULIRGs and sub-mm galaxies from the millimeter-FIR SED; the resulting value of $1+z$ is typically accurate to about 10%. As such, it is comparable to the accuracy of near-IR photometric redshifts and provides a complementary means of deriving redshifts from far-IR data, such as that from the upcoming $\it{Herschel Space Observatory}$. Since our analytic radiative transfer solution is developed for homogeneous, spherically symmetric, centrally heated, dusty sources, it is relevant for infrared bright galaxies that are primarily powered by compact sources of luminosity that are embedded in a dusty envelope. We discuss how deviations from spherical symmetry may affect the applicability of our solution, and we contrast our self-consistent analytic solution with standard approximations to demonstrate the main differences.
The gravitational magnification and demagnification of Type Ia supernovae (SNe) modify their positions on the Hubble diagram, shifting the distance estimates from the underlying luminosity-distance relation. This can introduce a systematic uncertainty in the dark energy equation of state (EOS) estimated from SNe, although this systematic is expected to average away for sufficiently large data sets. Using mock SN samples we quantify the lensing bias. We find that the bias on the dark energy EOS is less than half a percent for large datasets ($\gtrsim$ 2,000 SNe). However, if highly magnified events (SNe deviating by more than 2.5$\sigma$) are systematically removed from the analysis, the bias increases to $\sim$ 0.8%. Given that the EOS parameters measured from such a sample have a 1$\sigma$ uncertainty of 10%, the systematic bias related to lensing in SN data can be safely ignored in future cosmological measurements.
Precision infrared photometry from Spitzer has enabled the first direct studies of light from extrasolar planets, via observations at secondary eclipse in transiting systems. Current Spitzer results include the first longitudinal temperature map of an extrasolar planet, and the first spectra of their atmospheres. Spitzer has also measured a temperature and precise radius for the first transiting Neptune-sized exoplanet, and is beginning to make precise transit timing measurements to infer the existence of unseen low mass planets. The lack of stellar limb darkening in the infrared facilitates precise radius and transit timing measurements of transiting planets. Warm Spitzer will be capable of a precise radius measurement for Earth-sized planets transiting nearby M-dwarfs, thereby constraining their bulk composition. It will continue to measure thermal emission at secondary eclipse for transiting hot Jupiters, and be able to distinguish between planets having broad band emission versus absorption spectra. It will also be able to measure the orbital phase variation of thermal emission for close-in planets, even non-transiting planets, and these measurements will be of special interest for planets in eccentric orbits. Warm Spitzer will be a significant complement to Kepler, particularly as regards transit timing in the Kepler field. In addition to studying close-in planets, Warm Spitzer will have significant application in sensitive imaging searches for young planets at relatively large angular separations from their parent stars.
Motivated by the increasing use of the Kennicutt-Schmidt (K-S) star formation law to interpret observations of high redshift galaxies, the importance of gas accretion to galaxy formation, and the recent observations of chemical abundances in galaxies at z~2-3, I use simple analytical models to assess the consistency of these processes of galaxy evolution with observations and with each other. I derive the time dependence of star formation implied by the K-S law, and show that the sustained high star formation rates observed in galaxies at z~2-3 require the accretion of additional gas. A model in which the gas accretion rate is approximately equal to the combined star formation and outflow rates broadly reproduces the observed trends of star formation rate with galaxy age. Using an analytical description of chemical evolution, I also show that this model, further constrained to have an outflow rate roughly equal to the star formation rate, reproduces the observed mass-metallicity relation at z~2.
The Solar Tower Atmospheric Cherenkov Effect Experiment (STACEE) is an atmospheric Cherenkov telescope (ACT) that uses a large mirror array to achieve a relatively low energy threshold. For sources with Crab-like spectra, at high elevations, the detector response peaks near 100 GeV. Gamma-ray burst (GRB) observations have been a high priority for the STACEE collaboration since the inception of the experiment. We present the results of 20 GRB follow-up observations at times ranging from 3 minutes to 15 hours after the burst triggers. Where redshift measurements are available, we place constraints on the intrinsic high-energy spectra of the bursts.
We report new L and T dwarfs found in a cross-match of the SDSS Data Release 1 and 2MASS. Our simultaneous search of the two databases effectively allows us to relax the criteria for object detection in either survey and to explore the combined databases to a greater completeness level. We find two new T dwarfs in addition to the 13 already known in the SDSS DR1 footprint. We also identify 22 new candidate and bona-fide L dwarfs, including a new young L2 dwarf and a peculiar L2 dwarf with unusually blue near-IR colors: potentially the result of mildly sub-solar metallicity. These discoveries underscore the utility of simultaneous database cross-correlation in searching for rare objects. Our cross-match completes the census of T dwarfs within the joint SDSS and 2MASS flux limits to the 97% level. Hence, we are able to accurately infer the space density of T dwarfs. We employ Monte Carlo tools to simulate the observed population of SDSS DR1 T dwarfs with 2MASS counterparts and find that the space density of T0-T8 dwarf systems is 0.0070 (-0.0030; +0.0032) per cubic parsec (95% confidence interval), i.e., about one per 140 cubic parsecs. Compared to predictions for the T dwarf space density that depend on various assumptions for the sub-stellar mass function, this result is most consistent with models that assume a flat sub-stellar mass function dN/dM ~ M^0. No >T8 dwarfs were discovered in the present cross-match, though less than one was expected in the limited area (2099 sq. degrees) of SDSS DR1.
Measurements of the arrival directions of cosmic rays have not revealed their
sources. High energy neutrino telescopes attempt to resolve the problem by
detecting neutrinos whose directions are not scrambled by magnetic fields. The
key issue is whether the neutrino flux produced in cosmic ray accelerators is
detectable. It is believed that the answer is affirmative, both for the
galactic and extragalactic sources, provided the detector has kilometer-scale
dimensions. We revisit the case for kilometer-scale neutrino detectors in a
model-independent way by focussing on the energetics of the sources. The real
breakthrough though has not been on the theory but on the technology front: the
considerable technical hurdles to build such detectors have been overcome.
Where extragalactic cosmic rays are concerned an alternative method to probe
the accelerators consists in studying the arrival directions of neutrinos
produced in interactions with the microwave background near the source, i.e.
within a GZK radius. Their flux is calculable within large ambiguities but, in
any case, low. It is therefore likely that detectors that are larger yet by
several orders of magnitudes are required. These exploit novel techniques, such
as detecting the secondary radiation at radio wavelengths emitted by neutrino
induced showers.
Estimates of inflationary parameters from the CMB B-mode polarization spectrum on the largest scales depend on knowledge of the reionization history, especially at low tensor-to-scalar ratio. Assuming an incorrect reionization history in the analysis of such polarization data can strongly bias the inflationary parameters. One consequence is that the single-field slow-roll consistency relation between the tensor-to-scalar ratio and tensor tilt might be excluded with high significance even if this relation holds in reality. We explain the origin of the bias and present case studies with various tensor amplitudes and noise characteristics. A more model-independent approach can account for uncertainties about reionization, and we show that parametrizing the reionization history by a set of its principal components with respect to E-mode polarization removes the bias in inflationary parameter measurement with little degradation in precision.
We present the results of a high accuracy ($\sigma \approx 0.005%$) polarization monitoring of the Be Star Achernar that was carried out between July 7th and November 5th, 2006. Our results indicate that, after a near quiescent phase from 1998 to 2002, Achernar is presently in an active phase and has built a circumstellar disk. We detect variations both in the polarization level and position angle in timescales as short as one hour and as long as several weeks. Detailed modeling of the observed polarization strongly suggests that the short-term variations originate from discrete mass ejection events which produce transient inhomogeneities in the inner disk. Long-term variations, on the other hand, can be explained by the formation of an inner ring following one or several mass ejection events.
We have applied the torus fitting procedure described in Ng & Romani (2004) to PWNe observations in the Chandra data archive. This study provides quantitative measurement of the PWN geometry and we characterize the uncertainties in the fits, with statistical errors coming from the fit uncertainties and systematic errors estimated by varying the assumed fitting model. The symmetry axis $\Psi$ of the PWN are generally well determined, and highly model-independent. We often derive a robust value for the spin inclination $\zeta$. We briefly discuss the utility of these results in comparison with new radio and high energy pulse measurements
We present the analysis and results of recent high-energy gamma-ray observations of the high energy-peaked BL Lac (HBL) object 1ES 1218+304 with the Solar Tower Atmospheric Cherenkov Effect Experiment (STACEE). 1ES 1218+304 is an X-ray bright HBL at a redshift z=0.182. It has been predicted to be a gamma-ray emitter above 100 GeV, detectable by ground-based Cherenkov telescopes. Recently this source has been detected by MAGIC and VERITAS, confirming these predictions. STACEE's sensitivity to astrophysical sources at energies above 100 GeV allows it to explore high energy sources such as X-ray bright active galaxies and gamma-ray bursts. We present results from STACEE observations of 1ES 1218+304 in the 2006 and 2007 observing seasons.
Existence of GZK neutrinos (ultra high energy neutrinos) have been justified although the flux is very low. A new method is desired to use a huge mass of a detector medium to detect them. A fundamental study of radar method was carried out to measure microwave reflection from electromagnetic energy deposit by X-ray irradiation in a small rock salt sample. The reflection rate of 1x10^-6 was found at the energy deposit of 1x10^19 eV which was proportional to square of the X-ray intensity suggesting the effect to be coherent scattering. The decay time of the reflection was several seconds. This effect implies a large scale natural rock salt formation could be utilized like a bubble chamber irradiated by radio wave instead of visible light to detect GZK neutrinos.
In paper I of this series we discuss how magnification bias distorts the 3D correlation function by enhancing the observed correlation in the line-of-sight (LOS) orientation, especially on large scales. This lensing anisotropy is distinctive, making it possible to separately measure the galaxy-galaxy, galaxy-magnification and magnification-magnification correlations. Here we extend the discussion to the power spectrum, which has one key qualitative difference from the correlation function. In real space, pairs oriented close to the LOS direction are not protected against nonlinearity even if the pair separation is large; this is because nonlinear fluctuations can enter through gravitational lensing at a small transverse separation (i.e. impact parameter). The situation in Fourier space is different: by focusing on a small wavenumber k, as is usually done, linearity is guaranteed because both the LOS and transverse wavenumbers must be small. This is why magnification distortion of the galaxy correlation appears less severe in Fourier space. Nonetheless, the effect is non-negligible, especially for the transverse Fourier modes, and should be taken into account in interpreting precision measurements of the galaxy power spectrum, for instance those that focus on the baryon oscillations. The lensing induced anisotropy of the power spectrum has a shape that is distinct from the more well known anisotropies due to peculiar motions and the Alcock-Paczynski effect. The lensing anisotropy is highly localized in Fourier space while the latter two anisotropies are more spread out. The implied ability to isolate the magnification bias component means one can perform a gravitational lensing measurement without measuring galaxy shapes.
We have carried out sub-mm 12CO(J=3-2) observations of 6 giant molecular clouds (GMCs) in the Large Magellanic Cloud (LMC) with the ASTE 10m sub-mm telescope at a spatial resolution of 5 pc and very high sensitivity. We have identified 32 molecular clumps in the GMCs and revealed significant details of the warm and dense molecular gas with n(H2) $\sim$ 10$^{3-5}$ cm$^{-3}$ and Tkin $\sim$ 60 K. These data are combined with 12CO(J=1-0) and 13CO(J=1-0) results and compared with LVG calculations. We found that the ratio of 12CO(J=3-2) to 12CO(J=1-0) emission is sensitive to and is well correlated with the local Halpha flux. We interpret that differences of clump propeties represent an evolutionary sequence of GMCs in terms of density increase leading to star formation.Type I and II GMCs (starless GMCs and GMCs with HII regions only, respectively) are at the young phase of star formation where density does not yet become high enough to show active star formation and Type III GMCs (GMCs with HII regions and young star clusters) represents the later phase where the average density is increased and the GMCs are forming massive stars. The high kinetic temperature correlated with \Halpha flux suggests that FUV heating is dominant in the molecular gas of the LMC.
We report on simultaneous optical and X-ray observations of the Seyfert galaxy, NGC3147. The XMM-Newton spectrum shows that the source is unabsorbed in the X-rays ($N_H<5\times10^{20}$ cm$^{-2}$). On the other hand, no broad lines are present in the optical spectrum. The origin of this optical/X-rays misclassification (with respect to the Unification Model) cannot be attributed to variability, since the observations in the two bands are simultaneous. Moreover, a Compton-thick nature of the object can be rejected on the basis of the low equivalent width of the iron K$\alpha$ line ($\simeq130$ eV) and the large ratio between the 2-10 keV and the [OIII] fluxes. It seems therefore inescapable to conclude that NGC3147 intrinsically lacks the Broad Line Region (BLR), making it the first "true" Seyfert 2.
Since most high- and intermediate-mass protostars are at great distance and form in clusters, high linear resolution observations are needed to investigate their physical properties. To study the gas in the innermost region around the protostars in the proto-cluster IRAS 05358+3543, we observed the source in several transitions of methanol and other molecular species with the Plateau de Bure Interferometer and the Submillimeter Array, reaching a linear resolution of 1100 AU. We determine the kinetic temperature of the gas around the protostars through an LVG and LTE analysis of their molecular emission; the column densities of CH3OH, CH3CN and SO2 are also derived. Constrains on the density of the gas are estimated for two of the protostellar cores. We find that the dust condensations are in various evolutionary stages. The powerhouse of the cluster, mm1a, harbours a hot core with T~220 (75<T<330) K. A double-peaked profile is detected in several transitions toward mm1a, and we found a velocity gradient along a linear structure which could be perpendicular to one of the outflows from the vicinity of mm1a. Since the size of the double-peaked emission is less than 1100 AU, we suggest that mm1a might host a massive circumstellar disk. The other sources are in earlier stages of star formation. The least active source, mm3, could be a starless massive core, since it is cold (T<20 K), with a large reservoir of accreting material (M ~ 19 M_\odot), but no molecular emission peaks on it.
We summarise the mathematical foundation of the holographic method of measuring the reflector profile of an antenna or radio telescope. In particular, we treat the case, where the signal source is located at a finite distance from the antenna under test, necessitating the inclusion of the so-called Fresnel field terms in the radiation integrals. We assume a ``full phase'' system with reference receiver to provide the reference phase. We describe in some detail the hardware and software implementation of the system used for the holographic measurement of the 12m ALMA prototype submillimeter antennas. We include a description of the practicalities of a measurement and surface setting. The results for both the VertexRSI and AEC (Alcatel-EIE-Consortium) prototype ALMA antennas are presented.
The INTEGRAL satellite, which studies the Universe in the hard X-ray and soft Gamma-ray domain, has been operational for 5 years now. The X-ray telescopes, which use the coded mask technique, provide unprecedented spectral and imaging resolution. This led to a number of discoveries, such as the distribution of diffuse emission in the Galaxy, the discovery of highly absorbed sources and fast X-ray transients in the Galactic Plane, localization of ~50 Gamma-ray bursts, and the resolution of the cosmic X-ray background around its peak at 30 keV. About 300 previously known X-ray sources have been detected and in addition more than 200 new sources have been discovered. INTEGRAL provides spectra starting at 3 keV and ranging up to several hundred keV. This article gives a brief overview about the major discoveries of INTEGRAL.
The Atacama Large Millimeter Array (ALMA) will consist of up to 64 state-of-the-art sub-mm telescopes, subject to stringent performance specifications which will push the boundaries of the technology, and makes testing of antenna performance a likewise challenging task. Two antenna prototypes were evaluated at the ALMA Test Facility at the Very Large Array site in New Mexico, USA. The dynamic behaviour of the antennas under operational conditions was investigated with the help of an accelerometer system capable of measuring rigid body motion of the elevation structure of the antenna, as well as a few low-order deformation modes, resulting in dynamic performance numbers for pointing stability, reflector surface stability, path length stability, and structure flexure. Special emphasis was given to wind effects, one of the major factors affecting performance on timescales of seconds to tens of minutes. This paper describes the accelerometer system, its capabilities and limitations, and presents the dynamic performance results of the two prototype antennas investigated.
The accuracy of position measurements on stellar targets with the future Space Interferometry Mission (SIM) will be limited not only by photon noise and by the properties of the instrument (design, stability, etc.) and the overall measurement program (observing strategy, reduction methods, etc.), but also by the presence of other "confusing" stars in the field of view (FOV). We use a simple "phasor" model as an aid to understanding the main effects of this "confusion bias" in single observations with SIM. This analytic model has been implemented numerically in a computer code and applied to a selection of typical SIM target fields drawn from some of the Key Projects already accepted for the Mission. We expect that less than 1% of all SIM targets will be vulnerable to confusion bias; we show that for the present SIM design, confusion may be a concern if the surface density of field stars exceeds 0.4 star/arcsec^2. We have developed a software tool as an aid to ascertaining the possible presence of confusion bias in single observations of any arbitrary field. Some a priori knowledge of the locations and spectral energy distributions of the few brightest stars in the FOV is helpful in establishing the possible presence of confusion bias, but the information is in general not likely to be available with sufficient accuracy to permit its removal. We discuss several ways of reducing the likelihood of confusion bias in crowded fields. Finally, several limitations of the present semi-analytic approach are reviewed, and their effects on the present results are estimated. The simple model presented here provides a good physical understanding of how confusion arises in a single SIM observation, and has sufficient precision to establish the likelihood of a bias in most cases.
We performed MHD simulations of very light bipolar jets with density contrasts down to 10^-4 in axisymmetry, which were injected into a medium of constant density and evolved up to 200 kpc (200 r_j) full length. These jets show weak and roundish bow shocks as well as broad cocoons and thermalize their kinetic energy very efficiently. We argue that very light jets are necessary to match low-frequency radio observations of radio lobes as well as the bow shocks seen in X-rays. Due to the slow propagation, the backflows and their turbulent interaction in the midplane are important for a realistic global appearance.
Long Gamma Ray Bursts (GRBs) constitute an important tool to study the Universe near and beyond the epoch of reionization. We delineate here the characteristics of an 'ideal' instrument for the search of GRBs at z>6-10. We find that the detection of these objects requires soft band detectors with a high sensitivity and moderately large FOV. In the light of these results, we compare available and planned GRB missions, deriving conservative predictions on the number of high-z GRBs detectable by these instruments along with the maximum accessible redshift. We show that the Swift satellite will be able to detect various GRBs at z>6, and likely at z>10 if the trigger threshold is decreased by a factor of ~2. Furthermore, we find that INTEGRAL and GLAST are not the best tool to detect bursts at z>6: the former being limited by the small FOV, and the latter by its hard energy band and relatively low sensitivity. Finally, future missions (SVOM, EDGE, but in particular EXIST) will provide a good sample of GRBs at z>6 in a few years of operation.
Charge transfer (or exchange) reactions between hydrogen atoms and protons in shocks of supernova remnants (SNRs) are a natural way of broadening the Balmer and Lyman lines of hydrogen. We present a method to estimate the luminosity of broad (~ 1000$ km/s) Ly-alpha, Ly-beta, Ly-gamma, H-beta and P-alpha lines, as well as the total luminosity of the two-photon continuum, from existing measurements of the H-alpha flux. We consider cases of B=0.1 and 1, where B is the ratio of electron to proton temperatures. We examine a modest sample of 8 proximate, Balmer-dominated SNRs from our Galaxy and the Large Magellanic Cloud. The expected broad Ly-alpha luminosity per object is at most ~ 10^{36} erg/s. The two-photon continuum luminosities is comparable to the broad H-alpha and Ly-alpha ones. Differences in the Ly-alpha/H-alpha and Ly-beta/H-alpha luminosity ratios between the B=0.1 and 1 cases are factors ~ 2 for shock velocities between about 1000 and 4000 km/s, thereby providing a direct and unique way to directly measure B. In principle, broad, ``non-radiative'' Ly-alpha from SNRs in young galaxies can be directly observed in the optical range of wavelengths. However, by taking into consideration the different supernova rates between core collapse and thermonuclear supernovae, as well as the duration we expect to observe non-radiative Ly-alpha emission from SNRs, we expect their contribution to the total Ly-alpha luminosity from young galaxies at z ~ 3 to 5 to be negligibly small (~ 0.001%), compared to the mechanism described by Shull & Silk (1979).
We simulated the long-term collisional depletion of debris disks around solar-type (G2V) stars with our code. The numerical results were supplemented by, and interpreted through, a new analytic model. A few general scaling rules for the disk evolution are suggested. The timescale of the collisional evolution is inversely proportional to the initial disk mass and scales with radial distance as r^4.3 and with eccentricities of planetesimals as e^2.3. Further, we show that at actual ages of debris disks between 10 Myr and 10 Gyr, the decay of the dust mass and the total disk mass follow different laws. The reason is that the collisional lifetime of planetesimals is size-dependent. At any moment, there exists a transitional size, which separates larger objects that still have the ``primordial'' size distribution set in the growth phase from small objects whose size distribution is already set by disruptive collisions. The dust mass and its decay rate evolve as that transition affects objects of ever-larger sizes. Under standard assumptions, the dust mass, fractional luminosity, and thermal fluxes all decrease as t^xi with xi = -0.3...-0.4. Specific decay laws of the total disk mass and the dust mass, including the value of xi, largely depend on a few model parameters, such as the critical fragmentation energy as a function of size, the primordial size distribution of largest planetesimals, as well as the characteristic eccentricity and inclination of their orbits. With standard material prescriptions and a distribution of disk masses and extents, a synthetic population of disks generated with our analytic model agrees quite well with the observed Spitzer/MIPS statistics of 24 and 70 micron fluxes and colors versus age.
We develop a formalism for studying the dynamics of massive black hole binaries embedded in gravitationally-bound stellar cusps, and study the binary orbital decay by three-body interactions, the impact of stellar slingshots on the density profile of the inner cusp, and the properties of the ejected hypervelocity stars (HVSs). We find that the scattering of bound stars shrinks the binary orbit and increases its eccentricity more effectively than that of unbound ambient stars. Binaries with initial eccentricities e>0.3 and/or unequal-mass companions (M_2/M_1<0.1) can decay by three-body interactions to the gravitational wave emission regime in less than a Hubble time. The stellar cusp is significantly eroded, and cores as shallow as \rho\propto r^-0.7 may develop from a pre-existing singular isothermal density profile. A population of HVSs is ejected in the host galaxy halo, with a total mass ~M_2. We scale our results to the scattering of stars bound to Sgr A*, the massive black hole in the Galactic Center, by an inspiraling companion of intermediate mass. Depending on binary mass ratio, eccentricity, and initial slope of the stellar cusp, a core of radius ~0.1 pc typically forms in 1-10 Myr. On this timescale about 500-2500 HVSs are expelled with speeds sufficiently large to escape the gravitational potential of the Milky Way.
In this paper we consider a spatially flat Friedmann-Robertson-Walker (FRW) cosmological model whit cosmological constant, containing a stiff fluid and a classical Dirac field. The proposed cosmological scenario describes the evolution of effective dark matter and dark energy components reproducing, with the help of that effective multifluid configuration, the quintessential behavior. We find the value of the scale factor where the effective dark energy component crosses the phantom divide. The model we introduce, which can be considered as a modified $\La$CDM one, is characterized by a set of parameters which may be constrained by the astrophysical observations available up to date.
The evolution of linear cosmological perturbations in modified theories of gravity is investigated assuming the Palatini formalism. It has been discussed about the stability problem in this model based on the equivalence between f(R) gravity and the scalar tensor theory. However, we study this problem in the physical frame where the matter is minimally coupled. In general, the stability of the superhorizon metric evolution depends on models. We show that the deviation from the superhorizon metric evolution is null for a specific choice for the nonlinear Einstein-Hilbert action, $f(\hat{R}) \sim \hat{R}^{n}$, where $n \neq 0,2,3$. Thus the stability of metric fluctuation is guaranteed in these models. We also study the matter density fluctuation in the general gauge and show the differential equations in super and sub-horizon scales.
We compute the electromagnetic radiative corrections to all leading annihilation processes which may occur in the Galactic dark matter halo, for dark matter in the framework of supersymmetric extensions of the Standard Model (MSSM and mSUGRA), and present the results of scans over the parameter space that is consistent with present observational bounds on the dark matter density of the Universe. Although these processes have previously been considered in some special cases by various authors, our new general analysis shows novel interesting results with large corrections that may be of importance, e.g., for searches at the soon to be launched GLAST gamma-ray space telescope. In particular, it is pointed out that regions of parameter space where there is a near degeneracy between the dark matter neutralino and the tau sleptons, radiative corrections may boost the gamma-ray yield by up to three or four orders of magnitude, even for neutralino masses considerably below the TeV scale, and will enhance the very characteristic signature of dark matter annihilations, namely a sharp step at the mass of the dark matter particle. Since this is a particularly interesting region for more constrained mSUGRA models of supersymmetry, we use an extensive scan over this parameter space to verify the significance of our findings. We also re-visit the direct annihilation of neutralinos into photons and point out that, for a considerable part of the parameter space, internal bremsstrahlung is more important for indirect dark matter searches than line signals.
Modified gravity theory is known to violate Birkhoff's theorem. We explore a key consequence of this violation, the effect of distant matter in an Einstein-de Sitter universe on the motion of test particles. We find that when a particle is accelerated, a force is experienced that is proportional to the particle's mass and acceleration and acts in the direction opposite to that of the acceleration. We identify this force with inertia. At very low accelerations, our inertial law deviates slightly from that of Newton, yielding a testable prediction that may be verified with relatively simple experiments.
We report the first results of the GammeV experiment, a search for milli-eV mass particles with axion-like couplings to two photons. The search is performed using a ``light shining through a wall'' technique where incident photons oscillate into new weakly interacting particles that are able to pass through the wall and subsequently regenerate back into detectable photons. The oscillation baseline of the apparatus is continuously variable, thus allowing probes of different values of particle mass. We find no excess of events above background and are able to constrain the two-photon couplings of possible new scalar (pseudoscalar) particles to be less than $3.2\times 10^{-7} {GeV}^{-1}$ ($3.2\times 10^{-7} {GeV}^{-1}$) in the limit of massless particles.
We study a large-scale instability in a sheared nonhelical turbulence that causes generation of large-scale vorticity. Three types of the background large-scale flows are considered, i.e., the Couette and Poiseuille flows in a small-scale homogeneous turbulence, and the "log-linear" velocity shear in an inhomogeneous turbulence. It is known that laminar plane Couette flow and antisymmetric mode of laminar plane Poiseuille flow are stable with respect to small perturbations for any Reynolds numbers. We demonstrate that in a small-scale turbulence under certain conditions the large-scale Couette and Poiseuille flows are unstable due to the large-scale instability. This instability causes formation of large-scale vortical structures stretched along the mean sheared velocity. The growth rate of the large-scale instability for the "log-linear" velocity shear is much larger than that for the Couette and Poiseuille background flows. We have found a turbulent analogue of the Tollmien-Schlichting waves in a small-scale sheared turbulence. A mechanism of excitation of turbulent Tollmien-Schlichting waves is associated with a combined effect of the turbulent Reynolds stress-induced generation of perturbations of the mean vorticity and the background sheared motions. These waves can be excited even in a plane Couette flow imposed on a small-scale turbulence when perturbations of mean velocity depend on three spatial coordinates. The energy of these waves is supplied by the small-scale sheared turbulence.
We provide a theory of dynamo ($\alpha$ effect) and momentum transport in three-dimensional magnetohydrodynamics. For the first time, we show that the $\alpha$ effect is severely reduced by the shear even in the absence of magnetic field. The $\alpha$ effect is further suppressed by magnetic fields well below equipartition (with the large-scale flow) with different scalings depending on the relative strength of shear and magnetic field. The turbulent viscosity is also found to be significantly reduced by shear and magnetic fields, with positive value. These results suggest a crucial effect of shear and magnetic field on dynamo quenching and momentum transport reduction, with important implications for laboratory and astrophysical plasmas, in particular for the dynamics of the Sun.
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(Abridged) Using ab initio cosmological Eulerian adaptive mesh refinement radiation hydrodynamical calculations, we discuss how very massive stars start the process of cosmological reionization. The models include non-equilibrium primordial gas chemistry and cooling processes and accurate radiation transport in the Case B approximation using adaptively ray traced photon packages, retaining the time derivative in the transport equation. Supernova feedback is modeled by thermal explosions triggered at parsec scales. All calculations resolve the local Jeans length by at least 16 grid cells at all times and as such cover a spatial dynamic range of ~10^6. These first sources of reionization are highly intermittent and anisotropic and first photoionize the small scales voids surrounding the halos they form in, rather than the dense filaments they are embedded in. As the merging objects form larger, dwarf sized galaxies, the escape fraction of UV radiation decreases and the HII regions only break out on some sides of the galaxies making them even more anisotropic. In three cases, SN blast waves induce star formation in overdense regions that were formed earlier from ionization front instabilities. These stars form tens of parsecs away from the center of their parent DM halo. Approximately 5 ionizing photons are needed per sustained ionization when star formation in 10^6 M_sun halos are dominant in the calculation. As the halos become larger than ~10^7 M_sun, the ionizing photon escape fraction decreases, which in turn increases the number of photons per ionization to 15-50, in calculations with stellar feedback only. Supernova feedback in these more massive halos creates a more diffuse medium, allowing the stellar radiation to escape more easily and maintaining the ratio of 5 ionizing photons per sustained ionization.
We present deep WIYN H-alpha imaging of the dwarf irregular starburst galaxy NGC 1569, together with WIYN SparsePak spatially-resolved optical spectroscopy of the galactic outflow. This leads on from our previous detailed analyses of the state of the ISM in the central regions of this galaxy. Our deep imaging reveals previously undetected ionized filaments in the outer halo. Through combining these results with our spectroscopy we have been able to re-define the spatial extent of the previously catalogued superbubbles, and derive estimates for their expansion velocities, which we find to be in the range 50-100 km/s. The implied dynamical ages of <25 Myr are consistent with the recent star- and cluster-formation histories of the galaxy. Detailed decomposition of the multi-component H-alpha line has shown that within a distinct region ~700x500 pc in size, roughly centred on the bright super star cluster A, the profile is composed of a bright, narrow (FWHM <= 70 km/s) feature with an underlying, broad component (FWHM ~ 150 km/s). Applying the conclusions found in our previous work regarding the mechanism through which the broad component is produced, we associate the faint, broad emission with the interaction of the hot, fast-flowing winds from the young star clusters with cool clumps of ISM material. This interaction generates turbulent mixing layers on the surface of the clouds and the evaporation and/or ablation of material into the outflow. Under this interpretation, the extent of the broad component region may indicate an important transition point in the outflow, where ordered expansion begins to dominate over turbulent motion. In this context, we present a multi-wavelength discussion of the evolutionary state of the outflow.
Here we present a brief overview of UC HII regions with EE (UC HII+EE) including our most recent effort aimed at searching for UC HII regions associated with extended emission.
We identified globular clusters and field stars of extragalactic origin and investigated their chemical, physical, and kinematical properties. This objects as supposed was captured by the Galaxy at different times from debris of the dwarf satellite galaxies disrupted by its tidal forces. The results are follows. (1) The majorities of metal-poor stellar objects in the Galaxy have an extragalactic origin. (2) The masses of the accreted globular clusters decrease with the removal from the center and the plane of the Galaxy. (3) The relative abundances of chemical elements in the accreted and genetically connected stars are essentially distinguished. (4) The accreted field stars demonstrate the decrease of the relative magnesium abundanses with an increase in sizes and inclinations of their orbits. (5) The stars of the Centaurus moving group were born from the matter, in which star formation rate was considerably lower than in the early Galaxy. On the base of these properties was made a conclusion that with the decrease of the masses of the dwarf galaxies in them simultaneously decrease the average masses of globular clusters and the maximum masses of supernova SNe II. Namely latter fact leads to the decrease of the relative abundances of \alpha-elements in their metal-poor stars.
Based on a simulation of galaxy formation in the standard cosmological model, we suggest that a consistent picture for Gamma-Ray Bursts and star formation may be found that is in broad agreement with observations: GRBs preferentially form in low metallicity environments and in galaxies substantially less luminous that L*. We find that the computed formation rate of stars with metallicity less than 0.1Zsun agrees remarkably well with the rate evolution of Gamma-Ray Bursts observed by Swift from z=0 to z=4, whereas the evolution of total star formation rate is weaker by a factor of about 4. Given this finding, we caution that any inference of star formation rate based on observed GRB rate may require a more involved exercise than a simple proportionality.
Halo coronal mass ejections (HCMEs) are responsible of the most severe
geomagnetic storms. A prediction of their geoeffectiveness and travel time to
Earth's vicinity is crucial to forecast space weather.
Unfortunately coronagraphic observations are subjected to projection effects
and do not provide true characteristics of CMEs. Recently, Michalek (2006, {\it
Solar Phys.}, {\bf237}, 101) developed an asymmetric cone model to obtain the
space speed, width and source location of HCMEs. We applied this technique to
obtain the parameters of all front-sided HCMEs observed by the SOHO/LASCO
experiment during a period from the beginning of 2001 until the end of 2002
(solar cycle 23). These parameters were applied for the space weather forecast.
Our study determined that the space speeds are strongly correlated with the
travel times of HCMEs within Earth's vicinity and with the magnitudes related
to geomagnetic disturbances.
We discuss the star formation history of the Galaxy, based on the observations of extremely metal-poor stars (EMP) in the Galactic halo, to gain an insight into the evolution and structure formation in the early universe. The initialmass function (IMF) of EMP stars is derived from the observed fraction of carbon-enhanced EXP (CEMP) stars among the EMP survivors, which are thought to originate from the evolution in the close binary systems with mass transfer. Relying upon the theory of the evolution of EMP stars and of their binary evolution, we find that stars of metallicity [Fe/H]<-2.5 were formed at typical mass of ~10M_sun. The top heavy IMF thus obtained is applied to study the early chemical evolution of the Galaxy. We construct the merging history of our Galaxy semi-analytically and derive the metallicity distribution function (MDF) of low-mass EMP stars that survive to date with taking into account the contribution of binary systems. It is shown that the resultant MDF can well reproduce the observed distribution of EMP survivors, and, in particular, that they almost all stem from a less-mass companion in binary systems. We also investigate how first stars affect the MDF of EMP stars.
Models for DM are invoked with various density distributions, to account for flat rotation curves of galaxies. The effect of DE on these profiles for large galaxies and clusters are also studied. The rotation curves are shown to dip at a particular distance, when the effect of DE became significant.
Our purpose is to find which is the most reliable one among various oxygen abundance determination methods. We will test the validity of several different oxygen abundance determination methods using methods of modern statistics. These methods include Bayesian analysis and information scoring. We will analyze a sample of $\sim$6000 $\hii$ galaxies from the Sloan Digital Sky Survey (SDSS) spectroscopic observations data release four. All methods that we used drew the same conclusion that the $T_e$ method is a more reliable oxygen abundance determination methods than the Bayesian metallcity method under the existing telescope ability. The ratios of the likelihoods between the different kinds of methods tell us that the $T_e$, $P$, and $O3N2$ methods are consistent with each other because the $P$ and $O3N2$ method are calibrated by $T_e$-method. The Bayesian and $R_{23}$ method are consistent with each other because both are calibrated by a galaxy model. In either case, the $N2$ method is an {\it unreliable} method.
We describe a finite-volume method for solving the Poisson equation on oct-tree adaptive meshes using direct solvers for individual mesh blocks. The method is a modified version of the method presented by Huang and Greengard (2000), which works with finite-difference meshes and does not allow for shared boundaries between refined patches. Our algorithm is implemented within the FLASH code framework and makes use of the PARAMESH library, permitting efficient use of parallel computers. We describe the algorithm and present test results that demonstrate its accuracy.
Bright HNC 1--0 emission has been found towards several Seyfert galaxies. This is unexpected since traditionally HNC is a tracer of cold (10 K) gas, and the molecular gas of luminous galaxies like Seyferts is thought to have bulk kinetic temperatures surpassing 50 K. In this work we aim to distinguish the cause of the bright HNC and to model the physical conditions of the HNC and HCN emitting gas. We have used SEST, JCMT and IRAM 30m telescopes to observe HNC 3-2 and HCN 3-2 line emission in a selection of 5 HNC-luminous Seyfert galaxies. We estimate and discuss the excitation conditions of HCN and HNC in NGC 1068, NGC 3079, NGC 2623 and NGC 7469, based on the observed 3-2/1-0 line intensity ratios. We also observed CN 1-0 and 2-1 emission and discuss its role in photon and X-ray dominated regions. HNC 3-2 was detected in 3 galaxies (NGC 3079, NGC 1068 and NGC 2623). HCN 3-2 was detected in NGC 3079, NGC 1068 and NGC 1365. The HCN 3-2/1-0 ratio is lower than 0.3 only in NGC 3079, whereas the HNC 3-2/1-0 ratio is larger than 0.3 only in NGC 2623. The HCN/HNC 1-0 and 3-2 line ratios are larger than unity in all the galaxies. The HCN/HNC 3-2 line ratio is lower than unity only in NGC 2623, similar to Arp 220, Mrk 231 and NGC 4418. In three of the galaxies the HNC emissions emerge from gas of densities n<10^5 cm^3, where the chemistry is dominated by ion-neutral reactions. In NGC 1068 the emission of HNC emerges from lower (<10^5 cm^3) density gas than HCN (>10^5 cm^3). Instead, the emissions of HNC and HCN emerge from the same gas in NGC 3079. The observed HCN/HNC and CN/HCN line ratios favor a PDR scenario, rather than an XDR one. However, the N(HNC)/N(HCN) column density ratios obtained for NGC 3079 can be found only in XDR environments.
Numerical simulations of planetesimal accretion in circumprimary and circumbinary orbits are described. The secular perturbations by the com- panion star and gas drag are included in our models. We derive limits on the parameters of the binary system for which accretion and then planetary forma- tion are possible. In the circumbinary case we also outline the radial distance from the baricenter of the stars beyond which accumulation always occurs. Hy- drodynamical simulations are also presented to validate our N-body approach based on the axisymmetric approximation for the gas of the disk.
We investigate numerically the long-time behavior of balanced Alfven wave turbulence forced at intermediate scales. Whereas the usual constant-flux solution is found at the smallest scales, two new scalings are obtained at the forcing scales and at the largest scales of the system. In the latter case we show, in particular, that the spectrum evolves first to a state determined by Loitsyansky invariant and later a state close to the thermodynamic equipartition solution predicted by wave turbulence. The astrophysical implications for galactic magnetic field generation are discussed.
We present the results of a deep (1.1 Ms) observation of the Coma cluster of galaxies in the 18-30 keV band with the IBIS/ISGRI imager on board the INTEGRAL satellite. We show that the source extension in the North-East to South-West (SW) direction ($\sim 17'$) significantly exceeds the size of the point spread function of ISGRI, and that the centroid of the image of the source in the 18-30 keV band is displaced in the SW direction compared to the centroid in the 1-10 keV band. To test the nature of the SW extension we fit the data assuming different models of source morphology. The best fit is achieved with a diffuse source of elliptical shape, although an acceptable fit can be achieved assuming an additional point source SW of the cluster core. In the case of an elliptical source, the direction of extension of the source coincides with the direction toward the subcluster falling onto the Coma cluster. If the SW excess is due to the presence of a point source with a hard spectrum, we show that there is no obvious X-ray counterpart for this additional source, and that the closest X-ray source is the quasar EXO 1256+281, which is located $6.1'$ from the centroid of the excess. Finally, we show that the hard X-ray emission coincides with the 1.4 GHz radio emission, which suggests that the hard X-ray emission comes from the same population of electrons that is responsible for radio haloes through synchrotron emission.
We construct for the first time, the sequences of stable neutron star (NS) models capable of explaining simultaneously, the glitch healing parameters, $Q$, of both the pulsars, the Crab ($Q \geq 0.7$) and the Vela ($Q \leq 0.2$), on the basis of starquake mechanism of glitch generation. These models yield an upper bound on surface redshift of NSs, $z_R \simeq 0.77$. If the lower limit of the observational constraint of (i) $Q \geq 0.7$ for the Crab pulsar and (ii) the recently evaluated value of the moment of inertia for the Crab pulsar, $I_{\rm Crab,45} \geq 3.04$ (where $I_{45}=I/10^{45} {\rm g.cm}^2$), both are imposed together on these models, the models yield the value of matching density, $E_b = 7.0794 \times 10^{14}{\rm g cm}^{-3}$ at the core-envelope boundary. This value of matching density yields a model-independent upper bound on neutron star masses, $M_{\rm max} \leq 2.59 M_\odot$, and the strong lower bounds on surface redshift $z_R \simeq 0.6232$ and mass $M \simeq 2.455 M_\odot$ for the Crab ($Q \simeq 0.7$) and the strong upper bound on surface redshift $z_R \simeq 0.2016 $ and mass $M \simeq 1.142 M_\odot$ for the Vela ($Q \simeq 0.2$) pulsar. However, for the observational constraint of the `central' weighted mean value $Q \approx 0.72$, and $I_{\rm Crab,45} > 3.04$, for the Crab pulsar, the minimum surface redshift and mass of the Crab pulsar are slightly increased to the values $z_R \simeq 0.655$ and $M \simeq 2.5 M_\odot$ respectively, whereas for the central weighted mean value $Q \approx 0.12$ for the Vela pulsar, the maximum surface redshift and mass of the Vela pulsar are slightly decreased to the values $z_R \simeq 0.1645$ and $M \simeq 0.9635 M_\odot$ respectively.
The imaging capabilities of the INTEGRAL and HESS observatories allow the study of hard X-ray and TeV sources with unprecedented positional accuracy. Here I review the multiwavelength followup studies which are currently being performed on the unidentified sources detected by these facilities in order to unveil their actual nature.
The first high resolution Spitzer IRS 9-37um spectra of 29 Seyfert galaxies (about one quarter) of the 12um Active Galaxy Sample are presented and discussed. The high resolution spectroscopy was obtained with corresponding off-source observations. This allows excellent background subtraction, so that the continuum levels and strengths of weak emission lines are accurately measured. The result is several new combinations of emission line ratios, line/continuum and continuum/continuum ratios that turn out to be effective diagnostics of the strength of the AGN component in the IR emission of these galaxies. The line ratios [NeV]/[NeII], [OIV]/[NeII], already known, but also [NeIII]/[NeII] and [NeV]/[SiII] can all be effectively used to measure the dominance of the AGN. We extend the analysis, already done using the 6.2um PAH emission feature, to the equivalent width of the 11.25um PAH feature, which also anti-correlates with the dominance of the AGN. We measure that the 11.25um PAH feature has a constant ratio with the H_2 S(1) irrespective of Seyfert type, approximately 10 to 1. Using the ratio of accurate flux measurements at about 19um with the two spectrometer channels, having aperture areas differing by a factor 4, we measured the source extendness and correlated it with the emission line and PAH feature equivalent widths. The extendness of the source gives another measure of the AGN dominance and correlates both with the EWs of [NeII] and PAH emission. Using the rotational transitions of H$_2$ we were able to estimate temperatures (200-300K) and masses (1-10 x 10^6 M_sun), or significant limits on them, for the warm molecular component in the galaxies observed.
To advance our knowledge of the nature of the central source in LLAGNs and its relation with stellar clusters, we are carrying out several imaging projects with HST at near-UV, optical and near-IR wavelengths. In this paper, we present the first results obtained with observations of the central regions of 57 LLAGNs imaged with the WFPC2 through any of the V (F555W, F547M, F614W) and I (F791W, F814W) filters that are available in the HST archive. The sample contains 34% of the LINERs and 36% of the TOs in the Palomar sample. The mean spatial resolution of these images is 10 pc. With these data we have built an atlas that includes structural maps for all the galaxies, useful to identify compact nuclear sources and, additionally, to characterize the circumnuclear environment of LLAGNs, determining the frequency of dust and its morphology. The main results obtained are: 1) We have not found any correlation between the presence of nuclear compact sources and emission-line type. Thus, nucleated LINERs are as frequent as nucleated TOs. 2) The nuclei of "Young-TOs" are brighter than the nuclei of "Old-TOs" and LINERs. These results confirm our previous results that Young-TOs are separated from other LLAGNs classes in terms of their central stellar population properties and brightness. 3) Circumnuclear dust is detected in 88% of the LLAGNs, being almost ubiquitous in TOs. 4) The dust morphology is complex and varied, from nuclear spiral lanes to chaotic filaments and nuclear disk-like structures. Chaotic filaments are as frequent as dust spirals; but nuclear disks are mainly seen in LINERs. These results suggest an evolutionary sequence of the dust in LLAGNs, LINERs being the more evolved systems and Young-TOs the youngest. The full collection of figures are at this http URL
We study the effect of the neutron star spin -- kick velocity alignment observed in young radio pulsars on the coalescence rate of binary neutron stars. Two scenarios of the neutron star formation are considered: when the kick is always present and when it is small or absent if a neutron star is formed in a binary system due to electron-capture degenerate core collapse. The effect is shown to be especially strong for large kick amplitudes and tight alignments, reducing the expected galactic rate of binary neutron star coalescences compared to calculations with randomly directed kicks. The spin-kick correlation also leads to a much narrower NS spin-orbit misalignment.
To study the effect of metallicity on the mass-loss rate of asymptotic giant
branch (AGB) stars, we have conducted mid-infrared photometric measurements of
such stars in the Sagittarius (Sgr dSph) and Fornax dwarf spheroidal galaxies
with the 10-$\mu$m camera VISIR at the VLT. We derive mass-loss rates for 29
AGB stars in Sgr dSph and 2 in Fornax. The dust mass-loss rates are estimated
from the $K-[9]$ and $K-[11]$ colours. Radiative transfer models are used to
check the consistency of the method. Published IRAS and Spitzer data confirm
that the same tight correlation between $K-[12]$ colour and dust mass-loss
rates is observed for AGB stars from galaxies with different metallicities,
i.e. the Galaxy, the LMC and the SMC.
The derived dust mass-loss rates are in the range 5$\times10^{-10}$ to
3$\times10^{-8}$ M$_{\odot}$yr$^{-1}$ for the observed AGB stars in Sgr dSph
and around 5$\times10^{-9}$ M$_{\odot}$yr$^{-1}$ for those in Fornax; while
values obtained with the two different methods are of the same order of
magnitude. The mass-loss rates for these stars are higher than the nuclear
burning rates, so they will terminate their AGB phase by the depletion of their
stellar mantles before their core can grow significantly. Some observed stars
have lower mass-loss rates than the minimum value predicted by theoretical
models.
We present recent results from the Laboratory for Cosmological Data Mining (this http URL) at the National Center for Supercomputing Applications (NCSA) to provide robust classifications and photometric redshifts for objects in the terascale-class Sloan Digital Sky Survey (SDSS). Through a combination of machine learning in the form of decision trees, k-nearest neighbor, and genetic algorithms, the use of supercomputing resources at NCSA, and the cyberenvironment Data-to-Knowledge, we are able to provide improved classifications for over 100 million objects in the SDSS, improved photometric redshifts, and a full exploitation of the powerful k-nearest neighbor algorithm. This work is the first to apply the full power of these algorithms to contemporary terascale astronomical datasets, and the improvement over existing results is demonstrable. We discuss issues that we have encountered in dealing with data on the terascale, and possible solutions that can be implemented to deal with upcoming petascale datasets.
The dissolution process of star clusters is rather intricate for theory. We investigate it in the context of chaotic dynamics. We use the simple Plummer model for the gravitational field of a star cluster and treat the tidal field of the Galaxy within the tidal approximation. That is, a linear approximation of tidal forces from the Galaxy based on epicyclic theory in a rotating reference frame. The Poincar\'e surfaces of section reveal the effect of a Coriolis asymmetry. The system is non-hyperbolic which has important consequences for the dynamics. We calculated the basins of escape with respect to the Lagrangian points $L_1$ and $L_2$. The longest escape times have been measured for initial conditions in the vicinity of the fractal basin boundaries. Furthermore, we computed the chaotic saddle for the system and its stable and unstable manifolds. The chaotic saddle is a fractal structure in phase space which has the form of a Cantor set and introduces chaos into the system.
We construct evolutionary models of the populations of AGN and supermassive black holes, in which the black hole mass function grows at the rate implied by the observed luminosity function, given assumptions about the radiative efficiency and the Eddington ratio. We draw on a variety of recent X-ray and optical measurements to estimate the bolometric AGN luminosity function and compare to X-ray background data and the independent estimate of Hopkins et al. (2007) to assess remaining systematic uncertainties. The integrated AGN emissivity closely tracks the cosmic star formation history, suggesting that star formation and black hole growth are closely linked at all redshifts. Observational uncertainties in the local black hole mass function remain substantial, with estimates of the integrated black hole mass density \rho_BH spanning the range 3-5.5x10^5 Msun/Mpc^3. We find good agreement with estimates of the local mass function for a reference model where all active black holes have efficiency \eps=0.065 and L_bol/L_Edd~0.4. In this model, the duty cycle of 10^9 Msun black holes declines from 0.07 at z=3 to 0.004 at z=1 and 0.0001 at z=0. The decline is shallower for less massive black holes, a signature of "downsizing" evolution in which more massive black holes build their mass earlier. The predicted duty cycles and AGN clustering bias in this model are in reasonable accord with observational estimates. If the typical Eddington ratio declines at z<2, then the "downsizing" of black hole growth is less pronounced. Matching the integrated AGN emissivity to the local black hole mass density implies \eps=0.075 (\rho_BH/4.5x10^5 Msun/Mpc^3)^{-1} for our standard luminosity function estimate (25% higher for Hopkins et al.'s), lower than the values \eps=0.16-0.20 predicted by MHD simulations of disk accretion.
We present VRIJHK photometry, and optical and near-infrared spectroscopy, of the heavily extinguished Type Ia supernova (SN) 2002cv, located in NGC 3190, which is also the parent galaxy of the Type Ia SN 2002bo. SN 2002cv, not visible in the blue, has a total visual extinction of 8.74 +- 0.21 mag. In spite of this we were able to obtain the light curves between -10 and +207 days from the maximum in the I band, and also to follow the spectral evolution, deriving its key parameters. We found the peak I-band brightness to be Imax = 16.57 +- 0.10 mag, the maximum absolute I magnitude to be MmaxI = -18.79 +- 0.20, and the parameter dm15(B) specifying the width of the B-band light curve to be 1.46 +- 0.17 mag. The latter was derived using the relations between this parameter and dm40(I) and the time interval dtmax(I) between the two maxima in the I-band light curve. As has been found for previously observed, highly extinguished SNe Ia, a small value of 1.59 +- 0.07 was obtained here for the ratio Rv of the total-to-selective extinction ratio for SN 2002cv, which implies a small mean size for the grains along the line of sight toward us. Since it was found for SN 2002bo a canonical value of 3.1, here we present a clear evidence of different dust properties inside NGC 3190.
The hydrogen-deficiency in extremely hot post-AGB stars of spectral class PG1159 is probably caused by a (very) late helium-shell flash or a AGB final thermal pulse that consumes the hydrogen envelope, exposing the usually-hidden intershell region. Thus, the photospheric elemental abundances of these stars allow to draw conclusions about details of nuclear burning and mixing processes in the precursor AGB stars. We compare predicted elemental abundances to those determined by quantitative spectral analyses performed with advanced non-LTE model atmospheres. A good qualitative and quantitative agreement is found for many species (He, C, N, O, Ne, F, Si, Ar) but discrepancies for others (P, S, Fe) point at shortcomings in stellar evolution models for AGB stars. PG1159 stars appear to be the direct progeny of [WC] stars.
We study the evolution of scalar perturbations in the radiation-dominated era of Randall-Sundrum braneworld cosmology by numerically solving the coupled bulk and brane master wave equations. We find that density perturbations with wavelengths less than a critical value (set by the bulk curvature length) are amplified during horizon re-entry. Conversely, we explicitly confirm from simulations that the spectrum is identical to GR on large scales. Although this magnification is not relevant for the cosmic microwave background or measurements of large scale structure, it may have some bearing on the formation of primordial black holes in Randall-Sundrum models.
We present a scheme to solve the nonlinear multigroup radiation diffusion (MGD) equations. The method is incorporated into a massively parallel, multidimensional, Eulerian radiation-hydrodynamic code with adaptive mesh refinement (AMR). The patch-based AMR algorithm refines in both space and time creating a hierarchy of levels, coarsest to finest. The physics modules are time-advanced using operator splitting. On each level, separate level-solve packages advance the modules. Our multigroup level-solve adapts an implicit procedure which leads to a two-step iterative scheme that alternates between elliptic solves for each group with intra-cell group coupling. For robustness, we introduce pseudo transient continuation (PTC). We analyze the magnitude of the PTC parameter to ensure positivity of the resulting linear system, diagonal dominance and convergence of the two-step scheme. For AMR, a level defines a subdomain for refinement. For diffusive processes such as MGD, the refined level uses Dirichet boundary data at the coarse-fine interface and the data is derived from the coarse level solution. After advancing on the fine level, an additional procedure, the sync-solve (SS), is required in order to enforce conservation. The MGD SS reduces to an elliptic solve on a combined grid for a system of G equations, where G is the number of groups. We adapt the partial temperature scheme for the SS; hence, we reuse the infrastructure developed for scalar equations. Results are presented. (Abridged)
A problem of the cosmological evolution of the IGM is recalled and a necessity to find distant (z>0.5) giant radio galaxies (GRGs) with the lobe energy densities lower than about 10^{-14} J m^{-3} to solve this problem is emphasized. Therefore we undertake a search for such GRGs on the southern sky hemisphere using the SALT. In this paper we present a selected sample of the GRG candidates and the first deep detections of distant host galaxies, as well as the low-resolution spectra of the galaxies identified on the DSS frames. The data collected during the Performance Verification (P-V) phase show that 21 of 35 galaxies with the spectroscopic redshift have the projected linear size greater than 1 Mpc (for H_{0}=71 km\s\Mpc). However their redshifts do not exceed the value of 0.4 and the energy density in only two of them is less than 10^{-14} J m^{-3}. A photometric redshift estimate of one of them (J1420-0545) suggests a linear extent larger than 4.8 Mpc, i.e. a larger than that of 3C236, the largest GRG known up to now.
Extragalactic jets are visualized as dynamic erruptive events modelled by time-dependent magnetohydrodynamic (MHD) equations. The jet structure comes through the temporally self-similar solutions in two-dimensional axisymmetric spherical geometry. The two-dimensional magnetic field is solved in the finite plasma pressure regime, or finite $\beta$ regime, and it is described by an equation where plasma pressure plays the role of an eigenvalue. This allows a structure of magnetic lobes in space, among which the polar axis lobe is strongly peaked in intensity and collimated in angular spread comparing to the others. For this reason, the polar lobe overwhelmes the other lobes, and a jet structure arises in the polar direction naturally. Furthermore, within each magnetic lobe in space, there are small secondary regions with closed two-dimensional field lines embedded along this primary lobe. In these embedded magnetic toroids, plasma pressure and mass density are much higher accordingly. These are termed as secondary plasmoids. The magnetic field lines in these secondary plasmoids circle in alternating sequence such that adjacent plasmoids have opposite field lines. In particular, along the polar primary lobe, such periodic plasmoid structure happens to be compatible with radio observations where islands of high radio intensities are mapped.
KPD0005+5106 is the hottest known helium-rich white dwarf. We have identified NeVIII lines in UV and optical spectra and conclude that it is significantly hotter than previously thought, namely Teff=200,000 K instead of 120,000 K. This is a possible explanation for the observed hard X-ray emission as being of photospheric origin. Concerning its evolutionary state, we suggest that KPD0005+5106 is not a descendant of a PG1159 star but more probably related to the O(He) stars and RCrB stars.
We investigate the birth and evolution of isolated radio pulsars using a population synthesis method, modeling the birth properties of the pulsars, their time evolution, and their detection in the Parkes and Swinburne Multibeam (MB) surveys. Together, the Parkes and Swinburne MB surveys have detected nearly 2/3 of the known pulsars and provide a remarkably homogeneous sample to compare with simulations. New proper motion measurements and an improved model of the distribution of free electrons in the interstellar medium, NE2001, also make revisiting these issues particularly worthwhile. We present a simple population model that reproduces the actual observations well, and consider others that fail. We conclude that: pulsars are born in the spiral arms, with the birthrate of 2.8+/-0.5 pulsars/century peaking at a distance ~3 kpc from the Galactic centre, and with mean initial speed of 380^{+40}_{-60} km/s; the birth spin period distribution extends to several hundred milliseconds, with no evidence of multimodality, implying that characteristic ages overestimate the true ages of the pulsars by a median factor >2 for true ages <30,000 yr; models in which the radio luminosities of the pulsars are random generically fail to reproduce the observed P-Pdot diagram, suggesting a relation between intrinsic radio luminosity and (P, Pdot); radio luminosities L Edot^0.5 provide a good match to the observed P-Pdot diagram; for this favored radio luminosity model, we find no evidence for significant magnetic field decay over the lifetime of the pulsars as radio sources ~100 Myr.
In the present paper we report on the difference in angular sizes between radio-loud and radio-quiet CMEs. For this purpose we compiled these two samples of events using Wind/WAVES and SOHO/LASCO observations obtained during 1996-2005. It is shown that the radio-loud CMEs are almost two times wider than the radio-quiet CMEs (considering expanding parts of CMEs). Furthermore we show that the radio-quiet CMEs have a narrow expanding bright part with a large extended diffusive structure. These results were obtained by measuring the CME widths in three different ways.
We directly measure the evolution of the intergalactic Lyman-alpha effective optical depth, tau_eff, over the redshift range 2<z<4.2 from a sample of 86 high-resolution, high-signal-to-noise quasar spectra obtained with Keck/ESI, Keck/HIRES, and Magellan/MIKE. We find that our estimates of the quasar continuum levels in the Ly-alpha forest obtained by spline fitting are systematically biased low, but that this bias can be accounted for using mock spectra. The mean fractional error <Delta C/C_true> is <1% at z=2, 4% at z=3, and 12% at z=4. We provide estimates of the level of absorption arising from metals in the Ly-alpha forest based on both direct and statistical metal removal results in the literature, finding that this contribution is ~6-9% at z=3 and decreases monotonically with redshift. The high precision of our measurement indicates significant departures from the best-fit power-law redshift evolution, particularly near z=3.2.
The solar argon abundance cannot be directly derived by spectroscopic observations of the solar photosphere. The solar Ar abundance is evaluated from solar wind measurements, nucleosynthetic arguments, observations of B stars, HII regions, planetary nebulae, and noble gas abundances measured in Jupiter's atmosphere. These data lead to a recommended argon abundance of N(Ar) = 91,200(+/-)23,700 (on a scale where Si = 10^6 atoms). The recommended abundance for the solar photosphere (on a scale where log N(H) = 12) is A(Ar)photo = 6.50(+/-)0.10, and taking element settling into account, the solar system (protosolar) abundance is A(Ar)solsys = 6.57(+/-)0.10.
It is well know that the coronagraphic observations of halo CMEs are subject to projection effects. Viewing in the plane of the sky does not allow us to determine the crucial parameters defining geoeffectivness of CMEs, such as the velocity, width or source location. We assume that halo CMEs at the beginning phase of propagation have constant velocities, are symmetric and propagate with constant angular widths. Using these approximations and determining projected velocities and difference between times when CME appears on the opposite sides of the occulting disk we are able to get the necessary parameters. We present consideration for the whole halo CMEs from SOHO/LASCO catalog until the end of 2000. We show that the halo CMEs are in average much more faster and wider than the all CMEs from the SOHO/LASCO catalog.
We report a sensitive search for the HCN(J=2-1) emission line towards SDSS J1148+5251 at z=6.42 with the VLA. HCN emission is a star formation indicator, tracing dense molecular hydrogen gas (n(H2) >= 10^4 cm^-3) within star-forming molecular clouds. No emission was detected in the deep interferometer maps of J1148+5251. We derive a limit for the HCN line luminosity of L'(HCN) < 3.3 x 10^9 K km/s pc^2, corresponding to a HCN/CO luminosity ratio of L'(HCN)/L'(CO) < 0.13. This limit is consistent with a fraction of dense molecular gas in J1148+5251 within the range of nearby ultraluminous infrared galaxies (ULIRGs; median value: L'(HCN)/L'(CO) = 0.17 {+0.05/-0.08}) and HCN-detected z>2 galaxies (0.17 {+0.09/-0.08}). The relationship between L'(HCN) and L(FIR) is considered to be a measure for the efficiency at which stars form out of dense gas. In the nearby universe, these quantities show a linear correlation, and thus, a practically constant average ratio. In J1148+5251, we find L(FIR)/L'(HCN) > 6600. This is significantly higher than the average ratios for normal nearby spiral galaxies (L(FIR)/L'(HCN) = 580 {+510/-270}) and ULIRGs (740 {+505/-50}), but consistent with a rising trend as indicated by other z>2 galaxies (predominantly quasars; 1525 {+1300/-475}). It is unlikely that this rising trend can be accounted for by a contribution of AGN heating to L(FIR) alone, and may hint at a higher median gas density and/or elevated star-formation efficiency toward the more luminous high-redshift systems. There is marginal evidence that the L(FIR)/L'(HCN) ratio in J1148+5251 may even exceed the rising trend set by other z>2 galaxies; however, only future facilities with very large collecting areas such as the SKA will offer the sensitivity required to further investigate this question.
Halo coronal mass ejections (HCMEs) originating from regions close to the center of the Sun are likely to be geoeffective. Assuming that the shape of HCMEs is a cone and they propagate with constant angular widths and velocities, at least in their early phase, we have developed a technique (Michalek et al. 2003) which allowed us to obtain the space speed, width and source location. We apply this technique to obtain the parameters of all full HCMEs observed by the Solar and Heliospheric Observatory (SOHO) mission's Large Angle and Spectrometric Coronagraph (LASCO) experiment until the end of 2002. Using this data we examine which parameters determine the geoeffectiveness of HCMEs. We show that in the considered period of time only fast halo CMEs (with the space velocities higher than $\sim 1000{km\over s}$ and originating from the western hemisphere close to the solar center could cause the severe geomagnetic storms. We illustrate how the HCME parameters can be used for space weather forecast. It is also demonstrated that the strength of a geomagnetic storm does not depend on the determined width of HCMEs. This means that HCMEs do not have to be very large to cause major geomagnetic storms.
We present a new version of the compiled catalogue of nearby stars for which was published the spectoscopically determined effective temperatures, surface gravities, and abundances of iron, magnesium, calcium, silicon, and titanium. Distances, velocity components, galactic orbital elements, and ages was calculated for all stars. The atmospheric parameters and iron abundances were found from 4700 values in 136 publications, while relative abundances of alpha-elements were found from 2800 values in 81 publications for ~2000 dwarfs and giants using a three-step iteration averaging procedure, with weights assigned to each source of data as well as to each individual determination and taking into account systematic deviations of each scale relative to the reduced mean scale. The estimated assumed completeness for data sources containing more than five stars, up to late April 2007, exceeds 90%. For the vast majority of stars in the catalogue, the spatial-velocity components were derived from modern high-precision astrometric observations, and their Galactic orbit elements were computed using a three-component model of the Galaxy, consisting of a disk, a bulge, and a massive extended halo. Ages was determined for dwarfs and subgiants using Yale isochrones~2004. For this purpose the original codes was developed, based on interpolation with the 3D-spline functions of theoretical isochrones, and with subsequent interpolation in metallicity and abundances of \alpha-elements.
Luminous blue compact galaxies, common at z~1 but now relatively rare, show disturbed kinematics in emission lines. As part of a program to understand their formation and evolution, we have investigated the stellar dynamics of a number of nearby objects in this class. We have obtained long-slit spectra with VLT/FORS2 in the spectral region covering the near-infrared calcium triplet. In this paper we focus on the well known luminous blue compact galaxy ESO 338-IG04 (Tololo 1924-416). A previous investigation, using Fabry-Perot interferometry, showed that this galaxy has a chaotic H-alpha velocity field, indicating that either the galaxy is not in dynamical equilibrium, or that H-alpha does not trace the gravitational potential due to feedback from star formation. We show that along the apparent major axis, the stellar and ionised gas velocities follow each other closely. Hence, the chaotic velocity field must be attributed to the fact that the young stellar population in ESO 338-IG04 is not in dynamical equilibrium. The most likely explanation, which is also supported by its morphology, is that the galaxy has experienced a merger and that this has triggered the current starburst. We also reanalyse the rotation curve of ESO 400-G43, where the gas and stars are instead decoupled. Summarising the results of our program so far, we note that emission-line velocity fields are not always reliable tracers of stellar motions, and assess the implications for kinematic studies of similar galaxies at intermediate redshift.
Due to projection effects, coronagraphic observations cannot uniquely determine parameters relevant to the geoeffectiveness of CMEs, such as the true propagation speed, width, or source location. The Cone Model for Coronal Mass Ejections (CMEs) has been studied in this respect and it could be used to obtain these parameters. There are evidences that some CMEs initiate from a flux-rope topology. It seems that these CMEs should be elongated along the flux-rope axis and the cross section of the cone base should be rather elliptical than circular. In the present paper we applied an asymmetric cone model to get the real space parameters of frontsided halo CMEs (HCMEs) recorded by SOHO/LASCO coronagraphs in 2002. The cone model parameters are generated through a fitting procedure to the projected speeds measured at different position angles on the plane of the sky. We consider models with the apex of the cone located at the center and surface of the Sun. The results are compared to the standard symmetric cone model.
We present novel evidence for a fine structure observed in the net-circular polarization (NCP) of a sunspot penumbra based on spectropolarimetric measurements utilizing the Zeeman sensitive FeI 630.2 nm line. For the first time we detect a filamentary organized fine structure of the NCP on spatial scales that are similar to the inhomogeneities found in the penumbral flow field. We also observe an additional property of the visible NCP, a zero-crossing of the NCP in the outer parts of the center-side penumbra, which has not been recognized before. In order to interprete the observations we solve the radiative transfer equations for polarized light in a model penumbra with embedded magnetic flux tubes. We demonstrate that the observed zero-crossing of the NCP can be explained by an increased magnetic field strength inside magnetic flux tubes in the outer penumbra combined with a decreased magnetic field strength in the background field. Our results strongly support the concept of the uncombed penumbra.
We present an extensive data set of ~150 localized features from Cassini images of Saturn's Ring A, a third of which are demonstrated to be persistent by their appearance in multiple images, and half of which are resolved well enough to reveal a characteristic "propeller" shape. We interpret these features as the signatures of small moonlets embedded within the ring, with diameters between 40 and 500 meters. The lack of significant brightening at high phase angle indicates that they are likely composed primarily of macroscopic particles, rather than dust. With the exception of two features found exterior to the Encke Gap, these objects are concentrated entirely within three narrow (~1000 km) bands in the mid-A Ring that happen to be free from local disturbances from strong density waves. However, other nearby regions are similarly free of major disturbances but contain no propellers. It is unclear whether these bands are due to specific events in which a parent body or bodies broke up into the current moonlets, or whether a larger initial moonlet population has been sculpted into bands by other ring processes.
We investigate the chemical abundances of NGC 3603 in the Milky Way, of 30 Doradus in the Large Magellanic Cloud, and of N 66 in the Small Magellanic Cloud. The mid-infrared observations with the Infrared Spectrograph onboard the Spitzer Space Telescope allow us to probe spectra toward distinct physical regions within each object, the central ionizing cluster, the surrounding ionized gas, photodissociation-regions, and buried stellar clusters. We detect [SIII], [SIV], [ArIII], [NeII], [NeIII], [FeII], and [FeIII] lines and derive the ionic abundances. Based on the ionic abundance ratio (NeIII/H)/(SIII/H), we find that the gas probed in the MIR is characterized by a higher degree of ionization than the gas probed with optical spectra. We compute the elemental abundances of Ne, S, Ar, and Fe. We find that the alpha-elements Ne, S, and Ar scale with each other. Our determinations agree well with the abundances derived from the optical. The Ne/S ratio is higher than the solar proportion between Ne and S and points toward a moderate depletion of sulfur on dust grains. We find remarkably homogeneous neon and sulfur abundances (0.11 dex in 15 positions in 30 Doradus), suggesting a relatively homogenous ISM. Small-scale mixing cannot be ruled out.
The similarity of the observed mass densities of baryons and cold dark matter may be a sign they have a related origin. The baryon-to-dark matter ratio can be understood in the MSSM with right-handed (RH) neutrinos if CDM is due to a d = 4 flat direction condensate of very weakly coupled RH sneutrino LSPs and the baryon asymmetry is generated by Affleck-Dine leptogenesis along a d = 4 (H_{u}L)^2 flat direction. Observable signatures of the model include CDM and baryon isocurvature perturbations and distinctive long-lived NLSP phenomenology.
The discovery of dark energy (DE) as the physical cause for the accelerated expansion of the Universe is the most remarkable experimental finding of modern cosmology. However, it leads to insurmountable theoretical difficulties from the point of view of fundamental physics. Inflation, on the other hand, constitutes another crucial ingredient, which seems necessary to solve other cosmological conundrums and provides the primeval quantum seeds for structure formation. One may wonder if there is any deep relationship between these two paradigms. In this work, we suggest that the existence of the DE in the present Universe could be linked to the quantum field theoretical mechanism that may have triggered primordial inflation in the early Universe. This mechanism, based on quantum conformal symmetry, induces a logarithmic, asymptotically-free, running of the gravitational coupling. If this evolution persists in the present Universe, and if matter is conserved, the general covariance of Einstein's equations demands the existence of dynamical DE in the form of a running cosmological term whose variation follows a power law of the redshift.
It is shown that nearly-flat 3+1D spacetime emerging from a dual quantum field theory in 2+1D displays quantum fluctuations from classical Euclidean geometry on macroscopic scales. A covariant holographic mapping is assumed, where plane wave states with wavevector k on a 2D surface map onto classical null trajectories in the emergent third dimension at an angle \theta=l_P k relative to the surface element normal, where l_P denotes the Planck length. Null trajectories in the 3+1D world then display quantum uncertainty of angular orientation, with standard deviation \Delta\theta=\sqrt{l_P/z} for longitudinal propagation distance z in a given frame. The quantum complementarity of transverse position at macroscopically separated events along null trajectories corresponds to a geometry that is not completely classical, but displays observable holographic quantum noise. A statistical estimator of the fluctuations from Euclidean behavior is given for a simple thought experiment based on measured sides of triangles. The effect can be viewed as sampling noise due to the limited degrees of freedom of such a theory, consistent with covariant bounds on entropy.
A new formulation of Carter's constant for geodesic motion in Kerr black holes is given. It is shown that Carter's constant corresponds to the total angular momentum plus a precisely defined part which is quadratic in the linear momenta. The characterization is exact in the weak field limit obtained by letting the gravitational constant go to zero. It is suggested that the new form can be useful in current studies of the dynamics of extreme mass ratio inspiral (EMRI) systems emitting gravitational radiation.
We extend previous work on the minimal D-term inflation model modified by Right-Handed (RH) sneutrino fields to include additional inflaton-sector SUGRA corrections and two-field inflation effects. We show that SUGRA corrections simultaneously allow n_{s} to be within 3-year WMAP limits and the cosmic string contribution to the CMB power spectrum to be less than 5%. For gauge coupling g < 1, the CMB contribution from cosmic strings is predicted to be at least 1% while the spectral index is predicted to be less than 0.968 for a CMB string contribution less than 5%. Treating the inflaton-RH sneutrino system as a two-field inflation model, we show that the time-dependence of the RH sneutrino field strongly modifies the single-field results for values of RH sneutrino mass m_{\Phi} > 0.1 H. The running spectral index is \alpha = -0.0002 when m_{\Phi} < 0.1 H but increases to positive values as m_{\Phi}/H increases, with \alpha > 0.008 for m_{\Phi} > 1.0 H.
Weakly interacting massive particles (WIMPs) are one of the leading candidates for Dark Matter. So far we can use direct Dark Matter detection to estimate the mass of halo WIMPs only by fitting predicted recoil spectra to future experimental data. Here we develop a model-independent method for determining the WIMP mass by using experimental data directly. This method is independent of the as yet unknown WIMP density near the Earth as well as of the WIMP-nuclear cross section and can be used to extract information about WIMP mass with O(50) events.
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We have analyzed the redshift-dependent fraction of galactic bars over 0.2<z<0.84 in 2,157 luminous face-on spiral galaxies from the COSMOS 2-square degree field. Our sample is an order of magnitude larger than that used in any previous investigation, and is based on substantially deeper imaging data than that available from earlier wide-area studies of high-redshift galaxy morphology. We find that the fraction of barred spirals declines rapidly with redshift. Whereas in the local Universe about 65% of luminous spiral galaxies contain bars (SB+SAB), at z ~0.84 this fraction drops to about 20%. Over this redshift range the fraction of strong (SB) bars drops from about 30% to under 10%. It is clear that when the Universe was half its present age, the census of galaxies on the Hubble sequence was fundamentally different from that of the present day. A major clue to understanding this phenomenon has also emerged from our analysis, which shows that the bar fraction in spiral galaxies is a strong function of stellar mass, integrated color and bulge prominence. The bar fraction in very massive, luminous spirals is about constant out to z ~ 0.84 whereas for the low mass, blue spirals it declines significantly with redshift beyond z=0.3. There is also a slight preference for bars in bulge dominated systems at high redshifts which may be an important clue towards the co-evolution of bars, bulges and black holes. Our results thus have important ramifications for the processes responsible for galactic downsizing, suggesting that massive galaxies matured early in a dynamical sense, and not just as a result of the regulation of their star formation rate.
We present detailed images of diffuse UV intergalactic light (IGL), situated in a 60kpc halo that surrounds the radio galaxy MRC 1138-262 at z=2. We discuss the nature of the IGL and rule out faint cluster galaxies, nebular continuum emission, synchrotron, inverse Compton emission and scattering of galactic stellar light as possible sources of the IGL. Dust scattered quasar light is an unlikely possibility that cannot be ruled out entirely. We conclude that the source of the IGL is most likely to be a young stellar population distributed in a halo encompassing the radio and satellite galaxies, undergoing star formation at a rate greater than 57 Msun/yr. Within 70kpc of the radio core, approximately 44% of the star formation that is traced by UV light occurs in this diffuse mode. The average UV colour of the IGL is bluer than the average galaxy colour, and there is a trend for the IGL to become bluer with increasing radius from the radio galaxy. Both the galaxies and the IGL show a UV colour--surface brightness relation which can be obtained by variations in either stellar population age or extinction. These observations show a different, but potentially important mode of star formation, that is diffuse in nature. Star formation, as traced by UV light, occurs in two modes in the high redshift universe: one in the usual Lyman break galaxy clump-like mode on kpc scales, and the other in a diffuse mode over a large region surrounding massive growing galaxies. Such a mode of star formation can easily be missed by high angular resolution observations that are well suited for detecting high surface brightness compact galaxies. Extrapolating from these results, it is possible that a significant amount of star formation occurs in large extended regions within the halos of the most massive galaxies forming at high redshift.
We present a detailed analysis of the intrinsic scatter in the integrated SZ effect - cluster mass (Y-M) relation, using semi-analytic and simulated cluster samples. Specifically, we investigate the impact on the Y-M relation of energy feedback, variations in the host halo concentration and substructure populations, and projection effects due to unresolved clusters along the line of sight (the SZ background). Furthermore, we investigate at what radius (or overdensity) one should measure the integrated SZE and define cluster mass so as to achieve the tightest possible scaling. We find that the measure of Y with the least scatter is always obtained within a smaller radius than that at which the mass is defined; e.g. for M_{200} (M_{500}) the scatter is least for Y_{500} (Y_{1100}). The inclusion of energy feedback in the gas model significantly increases the intrinsic scatter in the Y-M relation due to larger variations in the gas mass fraction compared to models without feedback. We also find that variations in halo concentration for clusters of a given mass may partly explain why the integrated SZE provides a better mass proxy than the central decrement. Substructure is found to account for approximately 20% of the observed scatter in the Y-M relation. Above M_{200} = 2x10^{14} h^{-1} msun, the SZ background does not significantly effect cluster mass measurements; below this mass, variations in the background signal reduce the optimal angular radius within which one should measure Y to achieve the tightest scaling with M_{200}.
It has been known for over 30 years that Galactic globular clusters (GCs) are overabundant by orders of magnitude in bright X-ray sources per unit mass relative to the disk population. Recently a quantitative understanding of this phenomenon has developed, with a clear correlation between the number of X-ray sources in a cluster, $N_X$, and the cluster's encounter frequency, $\Gamma$, becoming apparent. We derive a refined version of $\Gamma$ that incorporates the finite lifetime of X-ray sources and the dynamical evolution of clusters. With it we find we are able to explain the few clusters that lie off the $N_X$--$\Gamma$ correlation, and resolve the discrepancy between observed GC core radii and the values predicted by theory. Our results suggest that most GCs are still in the process of core contraction and have not yet reached the thermal equilibrium phase driven by binary scattering interactions.
We present BIMA observations of a 2$\arcmin$ field in the northeastern spiral arm of M31. In this region we find six giant molecular clouds that have a mean diameter of 57$\pm$13 pc, a mean velocity width of 6.5$\pm$1.2 \kms, and a mean molecular mass of 3.0 $\pm$ 1.6 $\times$ 10$^5$\Msun. The peak brightness temperature of these clouds ranges from 1.6--4.2 K. We compare these clouds to clouds in M33 observed by \citet{wilson90} using the OVRO millimeter array, and some cloud complexes in the Milky Way observed by \cite{dame01} using the CfA 1.2m telescope. In order to properly compare the single dish data to the spatially filtered interferometric data, we project several well-known Milky Way complexes to the distance of Andromeda and simulate their observation with the BIMA interferometer. We compare the simulated Milky Way clouds with the M31 and M33 data using the same cloud identification and analysis technique and find no significant differences in the cloud properties in all three galaxies. Thus we conclude that previous claims of differences in the molecular cloud properties between these galaxies may have been due to differences in the choice of cloud identification techniques. With the upcoming CARMA array, individual molecular clouds may be studied in a variety of nearby galaxies. With ALMA, comprehensive GMC studies will be feasible at least as far as the Virgo cluster. With these data, comparative studies of molecular clouds across galactic disks of all types and between different galaxy disks will be possible. Our results emphasize that interferometric observations combined with the use of a consistent cloud identification and analysis technique will be essential for such forthcoming studies that will compare GMCs in the Local Group galaxies to galaxies in the Virgo cluster.
We study the effect of primordial nongaussianity on large-scale structure, focusing upon the most massive virialized objects. Using N-body simulations, we calculate the mass function and clustering of dark matter halos across a range of redshifts and levels of nongaussianity. We propose a simple fitting function for the mass function valid across the entire range of our simulations. We find pronounced effects of nongaussianity on the clustering of dark matter halos, leading to strongly scale-dependent bias. This suggests that the large-scale clustering of rare objects may provide a sensitive probe of primordial nongaussianity. We very roughly estimate that upcoming surveys can constrain nongaussianity at the level |fNL| <~ 10, competitive with forecasted constraints from the microwave background.
Considerable attention has recently focused on gravity theories obtained by extending general relativity with additional scalar, vector, or tensor degrees of freedom. In this paper, we show that the black-hole solutions of these theories are essentially indistinguishable from those of general relativity. Thus, we conclude that a potential observational verification of the Kerr metric around an astrophysical black hole cannot, in and of itself, be used to distinguish between these theories. On the other hand, it remains true that detection of deviations from the Kerr metric will signify the need for a major change in our understanding of gravitational physics.
We construct merger trees from the largest database of dark matter haloes to date provided by the Millennium simulation to quantify the merger rates of haloes over a broad range of descendant halo mass (1e12 < M0 < 1e15 Msun), progenitor mass ratio (1e-3 < xi < 1), and redshift (0 < z < 6). We find the mean merger rate per halo, B/n, to have very simple dependence on M0, xi, and z, and propose a universal fitting form for B/n that is accurate to 10-20%. Overall, B/n depends very weakly on the halo mass (proportional to M0^0.08) and scales as a power law in the progenitor mass ratio (proportional to xi^-2) for minor mergers (xi < 0.1) with a mild upturn for major mergers. As a function of time, we find the merger rate per Gyr to evolve as (1+z)^n with n=2-2.3, while the rate per unit redshift is nearly independent of z. Several tests are performed to assess how our merger rates are affected by, e.g. the time interval between Millennium outputs, binary vs multiple progenitor mergers, and mass conservation and diffuse accretion during mergers. In particular, we find halo fragmentations to be a general issue in merger tree construction from N-body simulations and compare two methods for handling these events. We compare our results with predictions of two analytical models for halo mergers based on the Extended Press-Schechter (EPS) model and the coagulation theory. We find the EPS model to overpredict the major merger rates and underpredict the minor merger rates by up to a factor of a few.
We compare the stellar structure of the isolated, Local Group dwarf galaxy Pegasus (DDO216) with low resolution HI maps from Young et al. (2003). Our comparison reveals that Pegasus displays the characteristic morphology of ram pressure stripping; in particular, the HI has a ``cometary'' appearance which is not reflected in the regular, elliptical distribution of the stars. This is the first time this phenomenon has been observed in an isolated Local Group galaxy. The density of the medium required to ram pressure strip Pegasus is at least $10^{-5} - 10^{-6}$, cm$^{-3}$. We conclude that this is strong evidence for an inter-galactic medium associated with the Local Group.
We construct a physically motivated model for predicting the properties of the remnants of gaseous galaxy mergers, given the properties of the progenitors and the orbit. The model is calibrated using a large suite of SPH merger simulations. It implements generalized energy conservation while accounting for dissipative energy losses and star formation. The dissipative effects are evaluated from the initial gas fractions and from the orbital parameters via an "impulse" parameter, which characterizes the strength of the encounter. Given the progenitor properties, the model predicts the remnant stellar mass, half-mass radius, and velocity dispersion to an accuracy of 25%. The model is valid for both major and minor mergers. We provide an explicit recipe for semi-analytic models of galaxy formation.
Stability properties of magnetic-field configurations containing the toroidal and axial field are considered. The stability is treated by making use of linear analysis. It is shown that the conditions required for the onset of instability are essentially different from those given by the necessary condition $d (s B_{\phi})/ds > 0$, where $s$ is the cylindrical radius. The growth rate of instability is calculated for a wide range of the parameters. We argue that the instability can operate in two different regimes depending on the strength of the axial field and the profile of the toroidal field.
The long, bright gamma-ray burst GRB 070125 was localized by the Interplanetary Network. We present light curves of the prompt gamma-ray emission as observed by Konus-WIND, RHESSI, Suzaku-WAM, and Swift-BAT. We detail the results of joint spectral fits with Konus and RHESSI data. The burst shows moderate hard-to-soft evolution in its multi-peaked emission over a period of about one minute. The total burst fluence as observed by Konus is $1.75 \times 10^{-4}$ erg/cm$^2$ (20 keV-10 MeV). Using the spectroscopic redshift z = 1.547, we find that the burst is consistent with the Amati $E_{peak,i}-E_{iso}$ and the Ghirlanda $E_{peak,i}-E_\gamma$ correlations.
A solution of magnetic Hall equations for plasma filaments in the Coulomb gauge is obtained in the non-holonomic frame. Some physical features of the solution include, the non-conservation of the magnetic helicity and the decay of the magnetic field in the filaments. From the mathematical point of view,the presence of Frenet torsion in the filament is actually shown to be fundamental for the breaking of conservation of magnetic helicity in the case of helicoidal filaments. Since the magnetic helicity is not conserved even in the Coulomb gauge, and the magnetic field decays, one can say that the dynamo action fails. Actually the presence of torsion enhances the breaking of magnetic field helicity conservation. A similar formula of the one obtained here without considering the Hall effect has been obtained by Moffatt and Ricca (PRSA-1992) in the case of holonomic filaments. It is shown that unknotted magnetic filaments may place a lower bound on the magnetic energy. Discussions on the writhe number are also discussed.
We constructed some main-sequence mergers from case A binary evolution and studied their characteristics via Eggleton's stellar evolution code. Both total mass and orbital angular momentum are conservative in our binary evolutions. Some mergers might be on the left of the ZAMS as defined by normal surface composition on a CMD because of enhanced surface helium content. The study also shows that central hydrogen content of the mergers is independent of mass. As a consequence, we fit the formula of magnitude and B-V of the mergers when they return back to thermal equilibrium with maximum error 0.29 and 0.037, respectively. Employing the consequences above, we performed Monte Carlo simulations to examine our models in NGC 2682 and NGC 2660. In NGC 2682, binary mergers from our models cover the region with high luminosity, but its importance is much less than that of AML. Our results are well-matched to the observations of NGC2660 if there is about 0.5Mo of mass loss in the merger process.
We use semi-analytic techniques to evaluate the burst sensitivity of designs for the EXIST hard X-ray survey mission. Applying these techniques to the mission design proposed for the Beyond Einstein program, we find that with its very large field-of-view and faint gamma-ray burst detection threshold, EXIST will detect and localize approximately two bursts per day, a large fraction of which may be at high redshift. We estimate that EXIST's maximum sensitivity will be ~4 times greater than that of Swift's Burst Alert Telescope. Bursts will be localized to better than 40 arcsec at threshold, with a burst position as good as a few arcsec for strong bursts. EXIST's combination of three different detector systems will provide spectra from 3 keV to more than 10 MeV. Thus, EXIST will enable a major leap in the understanding of bursts, their evolution, environment, and utility as cosmological probes.
Detailed physical processes of magnetic field generation from density fluctuations in the pre-recombination era are studied. Solving Maxwell equations and the generalized Ohm's law, the evolutions of the net charge density, the electric current and the electromagnetic field are solved. Unlike most of previous works, we treat electrons and photons as separate components under the assumption of tight coupling. We find that generation of the magnetic field due to density fluctuations takes place only from the second order of both perturbation theory and the tight coupling approximation.
We present the analysis and results of 12.5 hours of high-energy gamma-ray observations of the EGRET-detected pulsar PSR B1951+32 using the Solar Tower Atmospheric Cherenkov Effect Experiment (STACEE). STACEE is an atmospheric Cherenkov detector, in Albuquerque, New Mexico, that detects cosmic gamma rays using the shower-front-sampling technique. STACEE's sensitivity to astrophysical sources at energies around 100 GeV allows it to investigate emission from gamma-ray pulsars with expected pulsed emission cutoffs below 100 GeV. We discuss the observations and analysis of STACEE's PSR 1951+32 data, accumulated during the 2005 and 2006 observing seasons.
To advance from milli-arcsecond to micro-arcsecond astrometry, time keeping capability and its comparison among different stations need to be improved and enhanced. The T2L2 (Time transfer by laser link) experiment under development at OCA and CNES to be launched in 2008 on Jason-2, allows the synchronization of remote clocks on Earth. It is based on the propagation of light pulses in space which is better controlled than the radio waves propagation. In this paper, characteristics are presented for both common view and non-common view T2L2 comparisons of clocks between China and France.
We present a study of large-scale bars in the local Universe, based on a large sample of ~3692 galaxies, with -18.5 <= M_g < -22.0 mag and redshift 0.01 <= z < 0.03, drawn from the Sloan Digitized Sky Survey. Our sample includes many galaxies that are disk-dominated and of late Hubble types. Both color cuts and S\'ersic cuts yield a similar sample of ~2000 disk galaxies. We characterize bars and disks by ellipse-fitting r-band images and applying quantitative criteria. After excluding highly inclined ($>60^{\circ}$) systems, we find the following results. (1) The optical r-band fraction (f_opt-r) of barred galaxies, when averaged over the whole sample, is ~48%-52%. (2)~When galaxies are separated according to half light radius (r_e), or normalized r_e/R_24, which is a measure of the bulge-to-disk (B/D) ratio, a remarkable result is seen: f_opt-r rises sharply, from ~40% in galaxies that have small r_e/R_24 and visually appear to host prominent bulges, to ~70% for galaxies that have large r_e/R_24 and appear disk-dominated. (3)~f_opt-r rises for galaxies with bluer colors, lower masses, or fainter luminosities. (4) While hierarchical $\Lambda$CDM models of galaxy evolution models fail to produce galaxies without classical bulges, our study finds that ~20% of disk galaxies appear to be ``quasi-bulgeless''. (5) After applying the same cutoffs in magnitude (M_V<-19.3 mag), bar size (a_bar >= 1.5 kpc), and bar ellipticity (e_bar >=~0.4) that studies out to z~1 apply to ensure a complete sample, adequate spatial resolution, and reliable bar identification, we obtain an optical r-band bar fraction of 34%. This is comparable to the value reported at z~0.2-1.0, implying that the optical bar fraction does not decline dramatically by an order of magnitude in bright galaxies out to z~1. (abridged)
We derive new limits on the value of the cosmological constant, $\Lambda$, based on the Einstein bending of light by systems where the lens is a distant galaxy or a cluster of galaxies. We use an amended lens equation in which the contribution of $\Lambda$ to the Einstein deflection angle is taken into account and use observations of Einstein radii around several lens systems. Interestingly, we find that the contribution of the cosmological constant to the bending angle can be as big as 27% of the magnitude of the first-order term in the deflection angle and a few orders of magnitude larger than the second-order term. We use these observations of bending-angles to derive limits on the value of $\Lambda$ and find them to be competitive with the value determined from cosmology.
The chromosphere of the quiet Sun is a highly intermittent and dynamic phenomenon. Three-dimensional radiation (magneto-)hydrodynamic simulations exhibit a mesh-like pattern of hot shock fronts and cool expanding post-shock regions in the sub-canopy part of the inter-network. This domain might be called "fluctosphere". The pattern is produced by propagating shock waves, which are excited at the top of the convection zone and in the photospheric overshoot layer. New high-resolution observations reveal a ubiquitous small-scale pattern of bright structures and dark regions in-between. Although it qualitatively resembles the picture seen in models, more observations - e.g. with the future ALMA - are needed for thorough comparisons with present and future models. Quantitative comparisons demand for synthetic intensity maps and spectra for the three-dimensional (magneto-)hydrodynamic simulations. The necessary radiative transfer calculations, which have to take into account deviations from local thermodynamic equilibrium, are computationally very involved so that no reliable results have been produced so far. Until this task becomes feasible, we have to rely on careful qualitative comparisons of simulations and observations. Here we discuss what effects have to be considered for such a comparison. Nevertheless we are now on the verge of assembling a comprehensive picture of the solar chromosphere in inter-network regions as dynamic interplay of shock waves and structuring and guiding magnetic fields.
In this paper, we illustrate the main features of the electronics and data acquisition systems of the ANTARES apparatus, a large volume, deep-sea neutrino telescope under construction in the Mediterranean Sea off the coast of Toulon, France. The apparatus consists of an array of 900 large-area photomultipliers arranged on 12 detection lines, 5 of which are in data acquisition since January 2007. The schedule is to complete the apparatus construction in early 2008.
The proper motion measurements for 143 previously known L and T dwarfs are presented. From this sample we identify and discuss 8 high velocity L dwarfs. We also find 4 new wide common proper motion binaries/multiple systems. Using the moving cluster methods we have also identified a number of L dwarfs that may be members of the Ursa Major (age ~400 Myr), the Hyades (age ~625 Myr) and the Pleiades (age ~125 Myr) moving groups.
Big Bang nucleosynthesis (BBN) is the earliest sensitive probe of the values of many fundamental particle physics parameters. We have found the leading linear dependences of primordial abundances on all relevant parameters of the standard BBN code, including binding energies and nuclear reaction rates. This enables us to set limits on possible variations of fundamental parameters. We find that 7Li is expected to be significantly more sensitive than other species to many fundamental parameters, a result which also holds for variations of coupling strengths in grand unified (GUT) models. Our work also indicates which areas of nuclear theory need further development if the values of ``constants'' are to be more accurately probed.
Many binary stellar systems in which the primary star is beyond the asymptotic giant branch (AGB) evolutionary phase show significant orbital eccentricities whereas current binary interaction models predict their orbits to be circularised. We analyse how the orbital parameters in a system are modified under mass loss and mass exchange among its binary components and propose a model for enhanced mass-loss from the AGB star due to tidal interaction with its companion, which allows a smooth transition between the wind and Roche-lobe overflow mass-loss regimes. We explicitly follow its effect along the orbit on the change of eccentricity and orbital semi-major axis, as well as the effect of accretion by the companion. We calculate timescales for the variation of these orbital parameters and compare them to the tidal circularisation timescale. We find that in many cases, due to the enhanced mass loss of the AGB component at orbital phases closer to the periastron, the net eccentricity growth rate in one orbit is comparable to the rate of tidal circularisation. We show that with this eccentricity enhancing mechanism it is possible to reproduce the orbital period and eccentricity of the Sirius system, which under the standard assumptions of binary interaction is expected to be circularised. We also show that this mechanism may provide an explanation for the eccentricities of most barium star systems, which are expected to be circularised due to tidal dissipation. By proposing a tidally enhanced model of mass loss from AGB stars we find a mechanism which efficiently works against the tidal circularisation of the orbit, which explains the significant eccentricities observed in binary systems containing a white dwarf and a less evolved companion, such as Sirius and systems with barium stars.
The properties of high redshift quasar host galaxies are studied, in order to investigate the connection between galaxy evolution, nuclear activity, and the formation of supermassive black holes. We combine new near-infrared observations of three high redshift quasars (2 < z < 3), obtained at the ESO Very Large Telescope equipped with adaptive optics, with selected data from the literature. For the three new objects we were able to detect and characterize the properties of the host galaxy, found to be consistent with those of massive elliptical galaxies of M(R) ~ -24.7 for the one radio loud quasar, and M(R) ~ -23.8 for the two radio quiet quasars. When combined with existing data at lower redshift, these new observations depict a scenario where the host galaxies of radio loud quasars are seen to follow the expected trend of luminous (~5L*) elliptical galaxies undergoing passive evolution. This trend is remarkably similar to that followed by radio galaxies at z > 1.5. Radio quiet quasars hosts also follow a similar trend but at a lower average luminosity (~0.5 mag dimmer). The data indicate that quasar host galaxies are already fully formed at epochs as early as ~2 Gyr after the Big Bang and then passively fade in luminosity to the present epoch.
We present the detection of low-amplitude, long-period g-modes in two individual sdBV stars which are known to be p-mode pulsators. Only few of these hybrid objects, showing both p- and g-modes, are known today. We resolve the g-mode domain in HS0702+6043 and add HS2201+2610 to the list of hybrid pulsators. To discover the low-amplitude g-modes, a filtering algorithm based on wavelet transformations was applied to denoise observational data.
We have observed 13 methanol maser sources associated with massive star-forming regions; W3(OH), Mon R2, S 255, W 33A, IRAS 18151-1208, G 24.78+0.08, G 29.95-0.02, IRAS 18556+0136, W 48, OH 43.8-0.1, ON 1, Cep A and NGC 7538 at 6.7 GHz using the Japanese VLBI Network (JVN). Twelve of the thirteen sources were detected at our longest baseline of $\sim$50 M$\lambda$, and their images are presented. Seven of them are the first VLBI images at 6.7 GHz. This high detection rate and the small fringe spacing of $\sim$4 milli-arcsecond suggest that most of the methanol maser sources have compact structure. Given this compactness as well as the known properties of long-life and small internal-motion, this methanol maser line is suitable for astrometry with VLBI.
Knowledge of the stellar parameters for the parent stars of transiting exoplanets is pre-requisite for establishing the planet properties themselves, and often relies on stellar evolution models. GJ 436, which is orbited by a transiting Neptune-mass object, presents a difficult case because it is an M dwarf. Stellar models in this mass regime are not as reliable as for higher mass stars, and tend to underestimate the radius. Here we use constraints from published transit light curve solutions for GJ 436 along with other spectroscopic quantities to show how the models can still be used to infer the mass and radius accurately, and at the same time allow the radius discrepancy to be estimated. Similar systems should be found during the upcoming Kepler mission, and could provide in this way valuable constraints to stellar evolution models in the lower main sequence. The stellar mass and radius of GJ 436 are M = 0.452 [-0.012,+0.014] M(Sun) and R = 0.464 [-0.011,+0.009] R(Sun), and the radius is 10% larger than predicted by the standard models, in agreement with previous results from well studied double-lined eclipsing binaries. We obtain an improved planet mass and radius of M = 23.17 +/- 0.79 M(Earth) and R = 4.22 [-0.10,+0.09] R(Earth), a density of rho = 1.69 [-0.12,+0.14] g/cm3, and an orbital semimajor axis of a = 0.02872 +/- 0.00027 AU.
This review presents a personal view of the role that starbursts play in the star formation history of the universe. It is mainly focused on the properties of nearby starburst galaxies selected for their strong UV and/or FIR emission. The similarities between local starbursts and star-forming galaxies at high redshift are also presented. I discuss too the role that LIRGs and ULIRGs and merging systems play in the formation and evolution of galaxies.
There is a large body of work that has used the excellent Chandra observations of nearby galaxies with neglible low mass X-ray binary (LMXB) populations. This has culminated in a ``Universal'' X-ray luminosity function (XLF) for high mass X-ray binaries (HMXBs). However, a number of methods have been used to convert from source intensities to luminosities when creating these XLFs. We have taken advantage of the XMM-Newton observations of the nearby starbursting spiral galaxy NGC 253 to test some of these methods. We find the luminosities derived from these various methods to vary by a factor of $\sim$3. We also find the most influential factor in the conversion from intensity to luminosity to be the absorption. We therefore conclude that a more consistent approach is required for determining the true Universal XLF for HMXBs. Ideally, this would involve individual spectral fitting of each X-ray source. Certainly, the line-of-sight absorption should be determined from the observations rather than assuming Galactic absorption. We find the best approach for obtaining an XLF from low-count data to be the splitting of the X-ray sources into two or more intensity intervals, and obtaining a conversion from intensity to flux for each group from spectral modelling of the summed spectrum of that group.
The origin of galactic cosmic rays is one of the most interesting unsolved problems in astroparticle physics. Experimentally, the problem is attacked by a multi-disciplinary effort, namely by direct measurements of cosmic rays above the atmosphere, by air shower observations, and by the detection of TeV $\gamma$ rays. Recent experimental results are presented and their implications on the contemporary understanding of the origin of galactic cosmic rays are discussed.
We present 2D simulations of the cooling of neutron stars with strong magnetic fields (B \geq 10^{13} G). We solve the diffusion equation in axial symmetry including the state of the art microphysics that controls the cooling such as slow/fast neutrino processes, superfluidity, as well as possible heating mechanisms. We study how the cooling curves depend on the the magnetic field strength and geometry. Special attention is given to discuss the influence of magnetic field decay. We show that Joule heating effects are very large and in some cases control the thermal evolution. We characterize the temperature anisotropy induced by the magnetic field for the early and late stages of the evolution of isolated neutron stars.
We search for a spectral line produced by a dark matter (DM) particle with the mass in the range 40 keV < M_DM < 14 MeV, decaying in the DM halo of the Milky Way, using a high-resolution spectrometer SPI on board of INTEGRAL satellite. To distinguish the DM decay line from numerous instrumental lines, found in the SPI background spectrum, we study the dependence of the intensity of the line signal on the offset of the SPI pointing from the direction toward the Galactic Center (GC). After a critical analysis of the uncertainties of the DM density profile in the inner Galaxy we find that the intensity of the DM decay line should decrease by at least a factor of 3 when the offset from GC increases from 0 to 180 degrees. We find that such a pronounced variation of the line flux across the sky is not observed for any line, detected with the significance higher than 3 sigma in the SPI background spectrum. Possible DM decay origin is not ruled out only for the unidentified spectral lines, having low (~ 3 sigma) significance or coinciding in position with the instrumental ones. In the energy interval 20 keV -- 7 MeV we derive restrictions on the DM decay line flux, implied by the (non)detection of the DM decay line. For a particular DM candidate, the sterile neutrino of mass M_DM, we derive a bound on the mixing angle.
We present the results of the analysis of an archival observation of LMC X-2 performed with XMM/Newton. The spectra taken by high-precision instruments have never been analyzed before. We find an X-ray position for the source that is inconsistent with the one obtained by ROSAT, but in agreement with the Einstein position and that of the optical counterpart. The correlated spectral and timing behaviour of the source suggests that the source is probably in the normal branch of its X-ray color-color diagram. The spectrum of the source can be fitted with a blackbody with a temperature 1.5 keV plus a disk blackbody at 0.8 keV. Photoelectric absorption from neutral matter has an equivalent hydrogen column of 4 x 10^{20} cm^{-2}. An emission line, which we identify as the O VIII Lyman alpha line, is detected, while no feature due to iron is detected in the spectrum. We argue that the emission of this source can be straightforwardly interpreted as a sum of the emission from a boundary layer between the NS and the disc and a blackbody component coming from the disc itself. Other canonical models that are used to fit Z-sources do not give a satisfactory fit to the data. The detection of the O VIII emission line (and the lack of detection of lines in the iron region) can be due to the fact that the source lies in the Large Magellanic Cloud.
Intercluster filaments negligibly contribute to the weak lensing signal in General Relativity (GR), $\gamma_{N}\sim 10^{-4}-10^{-3}$. In the context of relativistic Modified Newtonian Dynamics (MOND) (Bekenstein 2004), however, a single filament inclined by $\approx 45^\circ$ from the line of sight can cause substantial distortion of background sources pointing towards the filament's axis ($\kappa=\gamma=(1-A^{-1})/2\sim 0.01$); this is rigourous for infinitely long uniform filaments, but also qualitatively true for short filaments ($\sim 30$Mpc), and even in regions where the projected matter density of the filament equals to zero. Since galaxies and galaxy clusters are generally embedded in filaments or are projected on such structures, this contribution complicates the interpretation of the weak lensing shear map in the context of MOND. While our analysis is of mainly theoretical interest providing order-of-magnitude estimates only, it seems safe to conclude that when modeling systems with anomalous weak lensing signals, e.g. the "bullet cluster" (Clowe et al. 2006), the "cosmic train wreck" of A520 (Mahdavi et al. 2007) and the "dark clusters" of Erben et al. (2000), filamentary structures might contribute in a significant and likely complex fashion. On the other hand, our predictions of a (conceptual) difference in the weak lensing signal could, in principle, be used to falsify MOND/TeVeS and its variations (Zlosnik et al. 2007; Zhao 2007).
We interpret the recent gravitational lensing observations of Jee et al. \cite{Jee} as first evidence for a {\it caustic} ring of dark matter in a galaxy cluster. A caustic ring unavoidably forms when a cold collisionless flow falls with net overall rotation in and out of a gravitational potential well. Evidence for caustic rings of dark matter was previously found in the Milky Way and other isolated spiral galaxies. We argue that galaxy clusters have at least one and possibly two or three caustic rings. We calculate the column density profile of a caustic ring in a cluster and show that it is consistent with the observations of Jee et al.
The bulk composition of an exoplanet is commonly inferred from its average density. For small planets, however, the average density is not unique within the range of compositions. Variations of a number of important planetary parameters--which are difficult or impossible to constrain from measurements alone--produce planets with the same average densities but widely varying bulk compositions. We find that adding a gas envelope equivalent to 0.1%-10% of the mass of a solid planet causes the radius to increase 5-60% above its gas-free value. A planet with a given mass and radius might have substantial water ice content (a so-called ocean planet) or alternatively a large rocky-iron core and some H and/or He. For example, a wide variety of compositions can explain the observed radius of GJ 436b, although all models require some H/He. We conclude that the identification of water worlds based on the mass-radius relationship alone is impossible unless a significant gas layer can be ruled out by other means.
Gravitational waveforms from the inspiral and ring-down stages of the binary black hole coalescences can be modelled accurately by approximation/perturbation techniques in general relativity. Recent progress in numerical relativity has enabled us to model also the non-perturbative merger phase of the binary black-hole coalescence problem. This enables us to \emph{coherently} search for all three stages of the coalescence of non-spinning binary black holes using a single template bank. Taking our motivation from these results, we propose a family of template waveforms which can model the inspiral, merger, and ring-down stages of the coalescence of non-spinning binary black holes that follow quasi-circular inspiral. This two-dimensional template family is explicitly parametrized by the physical parameters of the binary. We show that the template family is not only \emph{effectual} in detecting the signals from black hole coalescences, but also \emph{faithful} in estimating the parameters of the binary. We compare the sensitivity of a search (in the context of different ground-based interferometers) using all three stages of the black hole coalescence with other template-based searches which look for individual stages separately. We find that the proposed search is significantly more sensitive than other template-based searches for a substantial mass-range, potentially bringing about remarkable improvement in the event-rate of ground-based interferometers. As part of this work, we also prescribe a general procedure to construct interpolated template banks using non-spinning black hole waveforms produced by numerical relativity.
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