We define a sample of 27 radio-excess AGN in the Chandra Deep Field North by selecting galaxies that do not obey the radio/infrared correlation for radio-quiet AGN and star-forming galaxies. Approximately 60% of these radio-excess AGN are X-ray undetected in the 2 Ms Chandra catalog, even at exposures of > 1 Ms; 25% lack even 2-sigma X-ray detections. The absorbing columns to the faint X-ray-detected objects are 10^22 cm^-2 < N_H < 10^24 cm^-2, i.e., they are obscured but unlikely to be Compton thick. Using a local sample of radio-selected AGN, we show that a low ratio of X-ray to radio emission, as seen in the X-ray weakly- and non-detected samples, is correlated with the viewing angle of the central engine, and therefore with obscuration. Our technique can explore the proportion of obscured AGN in the distant Universe; the results reported here for radio-excess objects are consistent with but at the low end of the overall theoretical predictions for Compton-thick objects.
We derive the equations for the propagation of relativistic ionization fronts in both static and moving gases. We focus on the supersonic R-type phase that occurs right after a source turns on, and we compare the nonrelativistic and relativistic solutions for several important cases. Relativistic corrections can be significant up until the light-crossing time of the equilibrium Stromgren sphere. For a static medium, we obtain exact analytical solutions and apply them to the illustrative problems of an O star in a molecular cloud and a starburst in a high-redshift cosmological halo. Relativistic corrections can be important at early times when the H II regions are small, as well as at later times, if a density gradient causes the I-front to accelerate. For the cosmologically-expanding IGM, we derive an analytical solution in the case of a steady source and a constant clumping factor. Here relativistic corrections are significant for short-lived, highly-luminous sources like QSOs at the end of reionization, but negligible for weaker or higher-redshift sources. Finally, we numerically calculate the evolution of relativistic I-fronts in the presence of small-scale structure and infall, for a large galaxy undergoing a starburst and a luminous, high-redshift QSO. For such strong and short-lived sources, the relativistic corrections are quite significant, and small-scale structure can decrease the size of the H II region by up to an additional ~25%. (abridged)
We calculate the redshift-space power spectrum of the Sloan Digital Sky Survey (SDSS) Luminous Red Galaxy (LRG) sample, finding evidence for a full series of acoustic features down to the scales of ~0.25 h Mpc^{-1}. This corresponds up to the 9. peak in the CMB angular power spectrum. The acoustic scale derived, (107.8 +- 4.3) h^{-1}Mpc (k < 0.2 h Mpc^{-1}), agrees very well with the ``concordance'' model prediction and also with the one determined via the analysis of the spatial two-point correlation function by Eisenstein et al.(2005). This is not only an independent confirmation of Eisenstein et al.(2005) results made with different methods and software but also, according to our knowledge, the first determination of the power spectrum of the SDSS LRG sample. By calculating the two-point correlation function using the smooth cubic spline model fitted to the observed bandpowers and comparing with the results of the direct determination we demonstrate the consistency of our results.
We investigate whether ultra--high energy cosmic rays (UHECR) may be preferentially produced in massive galaxy clusters, by looking for correlations between UHECR directions and those of x-ray clusters. We find an excess of highest energy cosmic rays (above 50 EeV) which correlate with massive galaxy cluster positions within an angle of about one degree. The observed correlation has a chance probability of order 0.1 %. Including lower energy cosmic rays in the sample causes the angle where the most significant correlation is found to increase to 2--3 degrees. These results suggest that some UHECR are produced in galaxy clusters, or in objects that preferentially populate galaxy clusters.
Extensive air showers of cosmic rays with energies above 5.10**18 eV registered by the Yakutsk array have been analyzed. The existence of showers without muon component is found. Among them we found 5 clusters and these clusters correlate with nearest pulsars. It is found that there exist 4 classes of showers. Showers with high content of muons are mainly observed at E> 4.10**19 eV and they are formed most likely by heavy nuclei.
It is proposed a new approach for estimating the composition of cosmic rays. It is found that the zenith angle distributions and muon components of EAS for energies E>10^19 eV and E>4.10^19 eV differ from each other. It is shown that the cosmic rays above E>4.10^19 eV is heavier than the cosmic rays at energy E~ 10^19 eV. According to our estimation the SUGAR array detected 8 showers above 10^20 eV. It is concluded that no sign of Greisen-Zatsepin-Kuzmin (GZK) cut off in the spectrum of cosmic rays and all cosmic rays are galactic.
Arrival directions of cosmic rays with the energy E>4.10^19 eV are analyzed on the basis of the Yakutsk and AGASA extensive air shower arrays. It is supposed that the clusters can be formed as a result of fragmentation of superheavy nuclei. The consequences of this supposition compare with experimental data. Part of clusters with E>2.10^19 eV correlate with the nearest pulsars. The new effect is found - clusters intensify a feature of cosmic rays distribution.
Dynamical scalar fields in the framework of loop quantum cosmology have recently risen a considerable amount of attention. This interest relates mainly to the natural way the initial conditions for slow roll inflation are set and the avoidance of a big crunch in closed models. In this work, the evolution of a scalar field is explored taking into account the presence of a background fluid in a positively curved Universe. Though the mechanism that provides the initial conditions for inflation, extensively studied in the literature, is still available, it is somehow constrained on the amount of initial kinetic energy the field must have if the field is initially situated at the minimum of the potential. It is found, however, that for potentials with a minimum such as the chaotic inflation model, there is an additional mechanism that can provide the correct initial conditions for successful inflation even if initially the kinetic energy of the field is subdominant by many orders of magnitude.
Numerical simulations predict the first stars in a LCDM universe formed at z>20 in minihalos with masses ~10^6 M_sun. We have simulated 3D propagation of ionization fronts (I-fronts) created by these stars (M_*=15-500 M_sun) that formed in minihalos at z=20, outward thru the minihalo and beyond. We follow the evolving H II region within the gas density field from a cosmological simulation of primordial star formation. The H II region evolves a ``champagne flow,'' once the D-type I-front, preceded by a shock, moves outward down the density gradient inside the minihalo until it detaches from the shock as a weak R-type I-front. A ray-tracing calculation tracks the I-front during this ``champagne phase,'' taking account of the hydrodynamical back-reaction of the gas by an approximate model of the ionized wind. We find that the escape fraction increases with stellar mass, 0.7<f_esc<0.9 for 80<M_*/M_sun<500. We also quantify the ionizing efficiency of these stars -- the ratio of gas mass ionized to stellar mass. For stars with M_*> 80M_sun, this ratio is ~60,000, roughly half the number of ionizing photons released per stellar baryon during the their lifetimes, independent of stellar mass. In addition, we find that nearby minihalos trap the I-front, so their centers remain neutral. This is contrary to the recent suggestion that these first stars would trigger the formation of a second generation by fully ionizing their neighbor minihalos so as to stimulate molecular hydrogen formation in their cores. Finally, we discuss the effect of evacuating the gas from the host halo on the growth and luminosity of ``miniquasars'' that may form from black holes that are remnants of these stars. (abridged)
A deep mid- and far-infrared survey in the Extended Groth Strip (EGS) area gives 3.6 to 8\micron flux densities or upper limits for 253 Lyman Break Galaxies (LBGs). The LBGs are a diverse population but with properties correlated with luminosity. The LBGs show a factor of 30 range in indicated stellar mass and a factor of 10 in apparent dust content relative to stellar mass. About 5% of LBGs are luminous at all wavelengths with powerful emission at rest 6\micron. In the rest 0.9 to 2\micron spectral range these galaxies have stellar spectral slopes with no sign of an AGN power law component, suggesting that their emission is mainly powered by intensive star formation. Galaxies in this luminous population share the infrared properties of cold SCUBA sources: both are massive and dusty starburst galaxies at $2<z<3$; their stellar mass is larger than $10^{11} M_{\odot}$. We suggest that these galaxies are the progenitors of present-day giant elliptical galaxies, with a substantial fraction of their stars already formed at $z \approx 3$.
We discuss the current understanding of the most basic properties of astrophysical MHD turbulence and trace the origins of the modern views and theoretical uncertainties to the ideas set forth in 1950s and 1960s by Iroshnikov, Kraichnan, Batchelor, Schlueter and Biermann. Universal aspects of the theory are emphasised. Two astrophysical applications are touched upon: turbulence in the solar wind and in clusters of galaxies. These are, in a certain (very approximate) sense, two ``pure'' cases of small-scale turbulence, where theoretical models of the two main regimes of MHD turbulence -- with and without a strong mean magnetic field -- can be put to the test. They are also good examples of a complication that is more or less generic in astrophysical plasmas: the MHD description is, in fact, insufficient for astrophysical turbulence and plasma physics must make an entrance.
Few dozens of young high mass stars orbit Sgr A* at distances as short as 0.1
parsec, where star formation should be quenched by the strong tidal shear from
Sgr A*. The puzzling young stellar population is believed to come into
existence in one of the two ways:
(i) "normal" star formation at several tens of parsec in a very massive star
cluster that then spiraled in, or (ii) star formation in situ in a massive
self-gravitating disk. We propose to constrain these two scenarios via the
expected X-ray emission from young low mass stars that should have formed
alongside the massive stars. To this end we compare the recent Chandra
observations of X-ray emission from young stars in the Orion Nebula, and the
Chandra observations of Sgr A* field. We show that the cluster inspiral model
is ruled out irrespectively of the initial mass function (IMF) of the young
stars. In addition, for the in situ model, we find that no more than few
thousand low-mass stars could have formed alongside the massive stars. This is
more than a factor of ten fewer than expected if these stars were formed with
the standard IMF as elsewhere in the Galaxy. The young stars in the GC are thus
the first solid observational evidence for star formation in AGN disks and also
require the IMF of these stars to be top-heavy. We briefly consider implication
of these results for AGN in general.
It is shown that in the duration-hardness plane the GRBs of the third intermediate subgroup are well defined. Their durations are intermediate (i.e. roughly between 2 and 10 seconds), but their hardnesses are the lowest. They are even softer than the long bursts.
The photometric and spectroscopic observations of nearby type IIP supernova 2004dj are presented. The $^{56}$Ni mass estimated from the light curve is $\approx0.02 M_{\odot}$. This estimate is found to be consistent with the H$\alpha$ luminosity. SN2004dj reveals a strong asymmetry of the H$\alpha$ emission line at the nebular epoch with the shift of the maximum of -1600 km s$^{-1}$. A similar asymmetric component is detected in H$\beta$, [O I] and [Ca II] lines. The line asymmetry is interpreted as a result of the asymmetry of $^{56}$Ni ejecta. The H$\alpha$ profile and its evolution are reproduced in the model of the asymmetric bipolar $^{56}$Ni and spherical hydrogen distributions. The mass of the front $^{56}$Ni jet is comparable to the central component and twice as larger compared to the rear $^{56}$Ni jet. We note that the asymmetric bipolar structure of of $^{56}$Ni ejecta is revealed also by SN1999em, another type IIP supernova.
We have used the Vimos VLT Deep Survey in combination with other spectroscopic, photometric and X-ray surveys from literature to detect several galaxy structures in the Chandra Deep Field South (CDFS). Both a friend-of-friend based algorithm applied to the spectroscopic redshift catalog and an adaptative kernel galaxy density and colour maps correlated with photometric redshift estimates have been used. We mainly detect a chain-like structure at z=0.66 and two massive groups at z=0.735 and 1.098 showing signs of ongoing collapse. We also detect two galaxy walls at z=0.66 and at z=0.735 (extremely compact in redshift space). The first one contains the chain-like structure and the last one contains in its center one of the two massive groups. Finally, other galaxy structures that are probably loose low mass groups are detected. We compare the group galaxy population with simulations in order to assess the richness of these structures and we study their galaxy morphological contents. The higher redshift structures appear to probably have lower velocity dispersion than the nearby ones. The number of moderatly massive structures we detect is consistent with what is expected for an LCDM model, but a larger sample is required to put significant cosmological constraints.
The paper deals with the construction of images from visibilities acquired using aperture synthesis instruments: Fourier synthesis, deconvolution, and spectral interpolation/extrapolation. Its intended application is to specific situations in which the imaged object possesses two superimposed components: ($i$) an extended component together with ($ii$) a set of point sources. It is also specifically designed to the case of positive maps, and accounts for a known support. Its originality lies within joint estimation of the two components, coherently with data, properties of each component, positivity and possible support. We approach the subject as an inverse problem within a regularization framework: a regularized least-squares criterion is specifically proposed and the estimated maps are defined as its minimizer. We have investigated several options for the numerical minimization and we propose a new efficient algorithm based on augmented Lagrangian. Evaluation is carried out using simulated and real data (from radio interferometry) demonstrating the capability to accurately separate the two components.
The loss of linear momentum by gravitational radiation and the resulting gravitational recoil of black-hole binary systems may play an important role in the growth of massive black holes in early galaxies. We calculate the gravitational recoil of non-spinning black-hole binaries at the second post-Newtonian order (2PN) beyond the dominant effect, obtaining, for the first time, the 1.5PN correction term due to tails of waves and the next 2PN term. We find that the maximum value of the net recoil experienced by the binary due to the inspiral phase up to the innermost stable circular orbit (ISCO) is of the order of 22 km/s. We then estimate the kick velocity accumulated during the plunge from the ISCO up to the horizon by integrating the momentum flux using the 2PN formula along a plunge geodesic of the Schwarzschild metric. We find that the contribution of the plunge dominates over that of the inspiral. For a mass ratio m_2/m_1=1/8, we estimate a total recoil velocity (due to both adiabatic and plunge phases) of 100 +/- 20 km/s. For a ratio 0.38, the recoil is maximum and we estimate it to be 250 +/- 50 km/s. In the limit of small mass ratio, we estimate V/c to be approximately 0.043 (1 +/- 20%)(m_2/m_1)^2. Our estimates are consistent with, but span a substantially narrower range than, those of Favata et al. (2004).
The Galactic center harbors some of the most massive star clusters known in the Galaxy: the Arches and the Quintuplet. Based on the Chandra observations of these clusters (PI: Wang) which recently became public, I discuss the X-ray emission from the massive stars in these clusters. Confirming the general trend for Wolf-Rayet (WR) stars being X-ray dim, none of them is detected in the Quintuplet cluster. The most massive star known in the Galaxy, the Pistol star, is also not detected, invoking questions regarding the proposed binary nature of this object. X-ray emission in the Arches cluster is dominated by three stellar point sources. All three sources as well as the cluster's diffuse radiation show strong emission at 6.4-6.7 keV, indicating the presence of fluorescenting cool material. The Arches point sources may be identified as colliding wind binaries, albeit other possibilities cannot be ruled out.
We discuss the extended X-ray emission seen in three archival Chandra observations, and one archival XMM-Newton observation, of the FRII radio galaxy Pictor A. The overall properties of the X-ray lobes are consistent with the conclusions of earlier workers that the extended X-ray emission is largely due to the inverse-Compton process, and the implied departure from equipartition is in the range seen by us in other sources. In detail, we show that the X-ray/radio flux ratio varies quite strongly as a function of position throughout the source, and we discuss possible implications of this observation for the spatial variation of electron energy spectra and magnetic field strength through the lobe. We show that the radio and X-ray properties of the lobe are not consistent with a simple model in which variations in the magnetic field strength alone are responsible for the observed differences between emission at different frequencies. We also discuss the origins of the extended emission seen around the eastern hotspot, arguing that it may be diffuse synchrotron radiation tracing a region of distributed particle acceleration, and the implications of a possible weak X-ray counterjet detection which, taken together with the other properties of the bright X-ray jet, leads us to suggest that the X-ray jet and possible counterjet are also produced by synchrotron emission.
Hipparcos Intermediate Astrometric Data (IAD) have been used to derive
astrometric orbital elements for spectroscopic binaries from the newly released
Ninth Catalogue of Spectroscopic Binary Orbits (SB9). Among the 1374 binaries
from SB9 which have an HIP entry, 282 have detectable orbital astrometric
motion (at the 5% significance level). Among those, only 70 have astrometric
orbital elements that are reliably determined (according to specific
statistical tests discussed in the paper), and for the first time for 20
systems, representing a 10% increase relative to the 235 DMSA/O systems already
present in the Hipparcos Double and Multiple Systems Annex.
The detection of the astrometric orbital motion when the Hipparcos IAD are
supplemented by the spectroscopic orbital elements is close to 100% for
binaries with only one visible component, provided that the period is in the 50
- 1000 d range and the parallax is larger than 5 mas. This result is an
interesting testbed to guide the choice of algorithms and statistical tests to
be used in the search for astrometric binaries during the forthcoming ESA Gaia
mission.
Finally, orbital inclinations provided by the present analysis have been used
to derive several astrophysical quantities. For instance, 29 among the 70
systems with reliable astrometric orbital elements involve main sequence stars
for which the companion mass could be derived. Some interesting conclusions may
be drawn from this new set of stellar masses, like the enigmatic nature of the
companion to the Hyades F dwarf HIP 20935. This system has a mass ratio of 0.98
but the companion remains elusive.
The heating power and stress tensor are calculated for shear flow of turbulent magnetized plasma in the framework of Langevin-Burgers approach to the turbulency. An explicit formula for the effective viscosity is derived. It is shown that the effective viscosity is formally divergent for evanescent bare plasma viscosity. This characteristic feature of the result solves the problem of the missing viscosity in accretion discs and reveals why the quasars are the most powerful sources of light in the universe. The formulae for the heating and stress tensor can be incorporated in global models for accretion discs and also in all other physical conditions where there is shear flow in magnetized turbulent plasma.
We estimate that the vacuum electric field associated with a spinning Magnetospheric Eternally Collapsing Object MECO (www.phys.uni-sofia.bg/~astro/abbrev.html) could be higher by a factor of ~ 10^4 than the corresponding pulsar value because of extreme relativistic Frame Dragging Effect. Thus isolated spinning MECOs could be source of UHE cosmic ray acceleration and VHE gamma-ray production. However because of the steeply varying gravitational field close to the surface of the MECO, any signal generated there would be both extremely redshifted and distorted. As a result, there may not be any significant pulsed X-ray or Radio emission from close to the surface, and consequently, the $\gamma$-ray source may appear as ``Unidentified'' and the particle accelerator may appear as ``Dark''.
New results from the Baikal neutrino telescope NT200, based on the first 5 years of operation (1998-2003), are presented. We derive an all-flavor limit on the diffuse flux of astrophysical neutrinos between 20 TeV and 50 PeV, extract an enlarged sample of high energy muon neutrino events, and obtain limits on the flux of high energy atmospheric muons. In 2005, the upgraded telescope NT200+ will be commissioned: 3 additional distant strings with only 12 photo-multipliers each will rise the effective volume to 20 Mton at 10 PeV for this largest running neutrino telescope in the Northern hemisphere.
We study surface brightness fluctuations (SBF) in a sample of 8 elliptical
galaxies using Advanced Camera for Surveys (ACS) Wide Field Channel (WFC) data
drawn from the Hubble Space Telescope (HST) archive. SBF magnitudes in the
F814W bandpass, and galaxy colors from F814W, F435W, and F606W images -- when
available -- are presented. Galaxy surface brightness profiles are determined
as well. We present the first SBF--broadband color calibration for the ACS/WFC
F814W bandpass, and (relative) distance moduli estimates for 7 of our galaxies.
We detect and study in detail the SBF variations within individual galaxies
as a probe of possible changes in the underlying stellar populations.
Inspecting both the SBF and color gradients in comparison to model predictions,
we argue that SBF, and SBF-gradients, can in principle be used for unraveling
the different evolutionary paths taken by galaxies, though a more comprehensive
study of this issue would be required. We confirm that the radial variation of
galaxy stellar population properties should be mainly connected to the presence
of radial chemical abundance gradients, with the outer galaxy regions being
more metal poor than the inner ones.
It is well-known that gravitational lensing is a powerful tool to investigate matter distributions including DM. Typical angular distances images and typical time scales depend on gravitational lens masses. A launch of space interferometer Radioastron will give new excellent facilities to investigate microlensing in radio band, since in this case there is a possibility not only to resolve microimages but also observe astrometric microlensing.
We review some theoretical and statistical aspects of the origin of the large-scale structure in the Universe, in view of the two most widely known and accepted scenarios: the inflaton and the curvaton scenarios. Among the theoretical aspects, we point out the impossibility of having a low inflationary energy scale in the simplest curvaton model. A couple of modifications to the simplest setup are explored, corresponding to the implementation of a second (thermal) inflationary period whose end makes the curvaton field `heavy', triggering either its oscillations or immediate decay. Low scale inflation is then possible to attain with H_\ast being as low as 1 TeV. Among the statistical aspects, we study the bispectrum B_\zeta(k_1,k_2,k_3) of the primordial curvature perturbation \zeta whose normalisation \fnl gives information about the level of non-gaussianity in \zeta. In connection with \fnl, several conserved and/or gauge invariant quantities described as the second-order curvature perturbation have been given in the literature. We review each of these quantities showing how to interpret one in terms of the others, and analyze the respective expected \fnl in both the inflaton and the curvaton scenarios as well as in other less known models for the generation of primordial perturbations and/or non-gaussianities. The Sasaki and Stewart's \delta N formalism turns out to be a powerful technique to compute \fnl in multi-component slow-roll inflation, as the knowledge of the evolution of some family of unperturbed universes is the only requirement. We present for the first time this formalism and apply it to selected examples.
The dynamical reaction of the particles accelerated at a shock front by the first order Fermi process can be determined within kinetic models that account for both the hydrodynamics of the shocked fluid and the transport of the accelerated particles. These models predict the appearance of multiple solutions, all physically allowed. We discuss here the role of injection in selecting the {\it real} solution, in the framework of a simple phenomenological recipe, which is a variation of what is sometimes referred to as {\it thermal leakage}. In this context we show that multiple solutions basically disappear and when they are present they are limited to rather peculiar values of the parameters.
We present spectra of twelve Type Ia supernovae obtained in 1999 at the William Herschel Telescope and the Nordic Optical Telescope during a search for Type Ia supernovae (SN Ia) at intermediate redshift. The spectra range from z=0.178 to z=0.493, including five high signal-to-noise ratio SN Ia spectra in the still largely unexplored range 0.15 < z < 0.3. Most of the spectra were obtained before or around restframe B-band maximum light. None of them shows the peculiar spectral features found in low-redshift over- or under-luminous SN Ia. Expansion velocities of characteristic spectral absorption features such as SiII at 6355 angs., SII at 5640 angs. and CaII at 3945 angs. are found consistent with their low-z SN Ia counterparts.
We use the 2MASS extended source catalogue to determine angular correlation functions, w_p, to high orders (p<=9). The main sample contains 650,745 galaxies and represents an order of magnitude increase in solid angle over previous samples used in such analysis. The high-order correlation functions are used to determine the projected and real space hierarchical amplitudes, s_p and S_p. In contrast to recent results, for p<=6 these parameters are found to be quite constant over a wide range of scales to r=40 Mpc, consistent with a Gaussian form to the primordial distribution of density fluctuations which has evolved under the action of gravitational instability. We test the sensitivity of our results to the presence of rare fluctuations in the local galaxy distribution by cutting various regions of over-density from the main sample; unlike previous analyses, we find that our results are relatively robust to the removal of the largest superclusters. We use our constraints on the K-band S_p parameters in two ways. First, we examine their consistency with non-Gaussian initial conditions; we are able to rule out strong non-Gaussianity in the primordial density field, as might be seeded by topological defects such as cosmic strings or global textures at the 2.5 sigma confidence level. Second, we investigate the way in which galaxies trace the underlying mass distribution. We find evidence for a non-zero quadratic contribution to the galaxy bias, parameterised by c_2=0.57+/-0.33. This positive result represents a significant difference from the negative values found previously; we examine a possible explanation in the light of recent observations which universally provide negative values for c_2.
We are conducting a survey of several regions of high-mass star formation to assess their content and structure. The observations include Spitzer observations, ground-based optical and near-IR imaging surveys, and optical and IR spectra of objects and locations in the molecular clouds. The goal of the survey is to gain a better understanding of the processes involved in high mass star formation by determining the characteristics of the stars detected in these regions and investigating the properties of the interstellar medium (ISM) environment in which these stars form. In this contribution, we present results on the identification and spatial analysis of young stars in three clusters, W5/AFGL 4029, S255, and S235. First we show how the IRAC data are used to roughly segregate young stars according to their mid-infrared colors, into two groups corresponding the SED Class I and Class II young stellar objects. Then using the IRAC data in combination with 2MASS, we show how more young stars can be identified. Finally, we examine the spatial distributions of young stars in these clusters and find a range of morphologies and of peak surface densities.
Long-slit spectra of several dozen young star clusters have been obtained at three positions in the Antennae galaxies with the Space Telescope Imaging Spectrograph (STIS) and its 52"x0.2" slit. Based on H-alpha emission-line measurements, the average cluster-to-cluster velocity dispersion in 7 different cluster aggregates ("knots") is <10 \kms. The fact that this upper limit is similar to the velocity dispersion of gas in the disks of typical spiral galaxies suggests that the triggering mechanism for the formation of young massive compact clusters ("super star clusters") is unlikely to be high velocity cloud-cloud collisions. On the other hand, models where preexisting giant molecular clouds in the disks of spiral galaxies are triggered into cluster formation are compatible with the observed low velocity dispersions. These conclusions are consistent with those reached by Zhang et al. (2001) based on comparisons between the positions of the clusters and the velocity and density structure of the nearby interstellar medium. We find evidence for systematically lower values of the line ratios [NII]/H-alpha and [SII]/H-alpha in the bright central regions of some of the knots, relative to their outer regions. This suggests that the harder ionizing photons are used up in the regions nearest the clusters, and the diffuse ionized gas farther out is photoionized by 'leakage' of the leftover low-energy photons. The low values of the [SII]/H-alpha line ratio, typically [SII]/H-alpha<0.4, indicates that the emission regions are photoionized rather than shock heated. The absence of evidence for shock-heated gas is an additional indication that high velocity cloud-cloud collisions are not playing a major role in the formation of the young clusters.
The bulk of the extragalactic background between 10 keV and 10 GeV is likely to be explained by the emission of Seyfert galaxies, type Ia supernovae, and blazars. However, as revealed by the INTEGRAL satellite, the bulge of our galaxy is an intense source of a 511 keV gamma-ray line, indicating the production of a large number of annihilating positrons. The origin of the latter is debated, and they could be produced, in particular, by the (S- or P-wave) annihilations of light Dark Matter particles into e+e-. In any case, the cumulated effect of similar sources at all redshifts could lead to a new background of hard X-ray and soft gamma-ray photons. On the basis of the hierarchical model of galaxy formation, we compute analytically the SNIa contribution to the background, and add it to Seyfert and blazars emission models. We find that any extra contribution to this unresolved background at 511 keV should be lower than about 4 keV/cm^2/s/sr. Using the same model of galaxy formation, we also compute the extragalactic background due to Dark Matter annihilation. We obtain a new estimate which is one order of magnitude lower than previous works, because we consider that positrons cannot annihilate in very low mass dark matter halos that are unable to host galaxies. As a result, the hypothesis of light Dark Matter particles remains compatible with the observed extragalactic background.
We present the X-ray afterglow catalog of BeppoSAX from the launch of the satellite to the end of the mission. Thirty-three X-ray afterglows were securely identified based on their fading behavior out of 39 observations. We have extracted the continuum parameters (decay index, spectral index, flux, absorption) for all available afterglows. We point out a possible correlation between the X-ray afterglow luminosity and the energy emitted during the prompt $\gamma$-ray event. We do not detect a significant jet signature within the afterglows, implying a lower limit on the beaming angle, neither a standard energy release when X-ray fluxes are corrected for beaming. Our data support the hypothesis that the burst should be surrounded by an interstellar medium rather than a wind environment, and that this environment should be dense. This may be explained by a termination shock located near the burst progenitor. We finally point out that some dark bursts may be explained by an intrinsic faintness of the event, while others may be strongly absorbed.
The Baikal neutrino telescope NT200 takes data since 1998. In 2005, the deployment of three additional strings for common operation with NT200 was finished. We describe the physics program and the design of the new telescope named NT200+ and present selected physical results obtained with NT200. First results from NT200+ will be presented at the conference.
We present a catalog of XMM-Newton and Chandra observations of Gamma-Ray burst (GRB) afterglows, reduced in a common way using the most up-to-date calibration files and software. We focus on the continuum properties of the afterglows. We derive the spectral and temporal decay indexes for 16 bursts. We put constraints on the burst environment and geometry. A comparison of the fast XMM-Newton follow-up and the late Chandra observations shows a significant difference in those parameters, likely produced by a transition from jet expansion taking place between two and ten days after the burst. We also compare our results with the ones obtained by BeppoSAX and SWIFT, and point out that there is no strong discrepancy between the afterglow fluxes observed with all these satellites when we take carefully into account the different median observation time of each observatory.
This paper describes the fourth data release of the Sloan Digital Sky Survey (SDSS), including all survey-quality data taken through June 2004. The data release includes five-band photometric data for 180 million objects selected over 6670 deg^2, and 673,280 spectra of galaxies, quasars, and stars selected from 4783 deg^2 of that imaging data using the standard SDSS target selection algorithms. These numbers represent a roughly 25% increment over those of the Third Data Release. The Fourth Data Release also includes an additional 131,840 spectra of objects selected using a variety of alternative algorithms, to address scientific issues ranging from the kinematics of stars in the Milky Way thick disk to populations of faint galaxies and quasars.
We present the results of a search for high energy extraterrestrial neutrinos with the Baikal underwater Cherenkov detector NT200, based on data taken in 1998 - 2002 (1038 live days).Upper limits on the diffuse fluxes of \nu_e+\nu_{\mu}+\nu_{\tau}, predicted by several models of AGN-like neutrino sources, are derived. For an E^{-2} behavior of the neutrino spectrum, our limit is E^2 \Phi_{\nu}(E)<8.1 10^{-7} cm^{-2} s^{-1} sr^{-1} GeV over a neutrino energy range 2 10^4 - 5 10^7 GeV covering 90% of expected events. The upper limit on the resonant \bar{\nu}_e diffuse flux is \Phi_{\bar{\nu}_e} < 3.3 10^{-20} cm^{-2}s^{-1}sr^{-1}GeV^{-1}.
We present a limit on the flux of relativistic monopoles obtained during 994 days of operation of the Baikal neutrino telescope NT200. The search for relativistic monopoles is based on the enormous amount of Cherenkov radiation emitted by these particles.
Holographic dark energy models have been recently suggested which most clearly show that accelerating cosmology appears to be incompatible with mathematically consistent formulations of fundamental theories such as string/M theories. In this paper it is however argued that holographic phantom models are no longer incompatible with such theories, provided that we allow for the existence of wormholes and ringholes near the big rip singularity and a quantization condition on the parameter of the equation of state is introduced. It is also seen that such a condition actually implies a quantization of the phantom energy which stabilizes the fluid against decay processes.
The Baikal neutrino telescope NT200, operating since 1998, has been upgraded in spring 2005 to NT200+. This telescope with 3 additional outer strings at 100 m radius from the center encloses a geometric volume of 5 Mtons. We describe the modernized data acquisition and control system, which allows for higher bandwidth, full multiplexing of data and control streams over a single cable to shore, redundant system components and underwater data pre-processing. To calibrate all time offsets between new distant strings and the central telescope on the nsec-scale, a new external laser unit with a powerful N2-Dye laser and a light diffusor, has been developed. This laser is also used to tune reconstruction techniques for pointlike showers with energies from 20 TeV to 10 PeV.
We have conducted a study at radio wavelengths of the spectral behaviour of the supernova remnant (SNR) CTB 80. Based on an homogenised data set of integrated flux densities, we calculated for the whole SNR a radio index -0.36 +/- 0.02. The shape of the global spectrum suggests absorption by ionized gas in the interstellar medium (ISM) along the line of sight. Spatial spectral variations across the SNR are investigated based on high-angular resolution data at 240, 324, 610, and 1380 MHz using different techniques. The three extended arms associated with this SNR, show a clear indication of spectral steepening when moving outwards from the central nebula, with variations of up to - 0.9. However, while the spectral steepening is smooth along the eastern arm, the northern and soutwestern arms include locally flatter structures, which in all cases coincide with radio, IR, and optical emission enhancements. We interpret this spectral property as the result of the combination of two different particle populations: aging relativistic electrons injected by PSR B1951+32 and particles accelerated at the sites where the SNR shock front encounters interstellar gas inhomogeneities. Concerning the central nebula, the angular resolution of the available database does not permit a detailed spectral study of the core region, i.e. the 45'' region around PSR B1951+32, where we can only confirm an average spectral index alpha=0.0. The surrounding 8' plateau nebula has an <alpha> ~ -0.25, with a peak of alpha ~ -0.29 coincident with a secondary maximun located at the termination of a twisted filament that trails to the east, behind the pulsar.
The generalized Chaplygin gas is characterized by the equation of state p = - A/rho^alpha, with alpha > -1 and w > -1. We generalize this model to allow for the cases where alpha < -1 or w < -1. This generalization leads to three new versions of the generalized Chaplygin gas: an early phantom model in which w << -1 at early times and asymptotically approaches w = -1 at late times, a late phantom model with w \approx -1 at early times and w -> - \infty at late times, and a transient model with w \approx -1 at early times and w -> 0 at late times. We consider these three cases as models for dark energy alone and examine constraints from type Ia supernovae and from the subhorizon growth of density perturbations. The transient Chaplygin gas model provides a possible mechanism to allow for a currently accelerating universe without a future horizon, while some of the early phantom models produce w < -1 without either past or future singularities.
This paper presents a detailed statistical determination of the equatorial rotation rates of classical Be stars. The rapid rotation of Be stars is likely to be linked to the ejection of gas that forms dense circumstellar disks. The physical origins of these disks are not understood, though it is generally believed that the ability to spin up matter into a Keplerian disk depends on how close the stellar rotation speed is to the critical speed at which the centrifugal force cancels gravity. There has been recent disagreement between the traditional idea that Be stars rotate between 50 and 80 percent of their critical speeds and new ideas (inspired by the tendency for gravity darkening to mask rapid rotation at the equator) that their rotation may be very nearly critical. This paper utilizes Monte Carlo forward modeling to simulate distributions of the projected rotation speed (v sin i), taking into account gravity darkening, limb darkening, and observational uncertainties. A chi-squared minimization procedure was used to find the distribution parameters that best reproduce observed v sin i distributions from R. Yudin's database. Early-type (O7e-B2e) Be stars were found to exhibit a roughly uniform spread of intrinsic rotation speed that extends from 40 to 60 percent up to 100 percent of critical. Late-type (B3e-A0e) Be stars exhibit progressively narrower ranges of rotation speed as the effective temperature decreases; the lower limit rises to reach critical rotation for the coolest Be stars. The derived lower limits on equatorial rotation speed represent conservative threshold rotation rates for the onset of the Be phenomenon. The significantly subcritical speeds found for early-type Be stars represent strong constraints on physical models of angular momentum deposition in Be star disks.
We study the physical and photometric properties of galaxies at z=4 in cosmological hydrodynamic simulations of a lambda-CDM universe. We focus on galaxies satisfying the GOODS "B-dropout" criteria. Our goals are: (1) to study the nature of high-redshift galaxies; (2) to test the simulations against published measurements of high-redshift galaxies; (3) to find relations between photometric measurements by HST/ACS (0.4 -- 1 micron) and Spitzer/IRAC (3.6 -- 8 micron) and the intrinsic physical properties of GOODS "B-dropouts" such as stellar mass, stellar age, dust reddening, and star-formation rate; and (4) to assess how representative the GOODS survey is at this epoch. Our simulations predict that high-redshift galaxies show strong correlations in star formation rate versus stellar mass, and weaker correlations versus environment and age, such that GOODS galaxies are predicted to be the most massive, most rapidly star-forming galaxies at that epoch, living preferentially in dense regions. The simulated rest-frame UV luminosity function (LF) and integrated luminosity density are in broad agreement with observations at z~4. The predicted rest-frame optical (observed 3.6 micron) LF is similar to the rest-frame UV LF, shifted roughly one magnitude brighter. We predict that GOODS detects less than 50% of the total stellar mass density formed in galaxies more massive than 10^8.7 M_sun by z=4, mainly because of brightness limits in the HST/ACS bands. The most rapidly star forming galaxies in our simulations have rates exceeding 1000 M_sun yr^-1, similar to observed sub-mm galaxies. The star formation rates of these galaxies show at most a mild excess (2--3x) over the rates that would be expected for their stellar mass. Whether these bright galaxies would be observable as LBGs depends on the uncertain effects of dust reddening.
We use new and extant literature spectroscopy to address abundances and membership for UMa moving group stars. We first compare the UMa, Coma, and Hyades H-R diagrams via a homogeneous set of isochrones, and find that these three aggregates are essentially coeval. Our spectroscopy of cool UMa dwarfs reveals striking abundance anomalies--trends with Teff, ionization state, and excitation potential--like those recently seen in young cool M34, Pleaides, and Hyades dwarfs. In particular, the trend of rising 7774 Ang-based OI abundance with declining Teff is markedly subdued in UMa compared to the Pleiades, suggesting a dependence on age or metallicity. Despite disparate sources of Li data,our homogeneous analysis indicates that UMa members evince remarkably small scatter in the Li-Teff plane for Teff>5200 K. Significant star-to-star scatter suggested by previous studies is seen for cooler stars. Comparison with the consistently determined Hyades Li-Teff trend reveals differences qualitatively consistent with this cluster's larger [Fe/H] (and perhaps slightly larger age). However, quantitative comparison with standard stellar models indicates the differences are smaller than expected, suggesting the action of a fourth parameter beyond age, mass, and [Fe/H] controlling Li depletion.
We have analyzed archival HST/ACS images in Sloan g and z of the globular cluster (GC) systems of 53 ellipticals in the Virgo Cluster, spanning massive galaxies to dEs. Among the new results are: (1) In the gEs M87 and NGC 4649, there is a correlation between luminosity and color for individual metal-poor GCs, such that more massive GCs are more metal-rich. A plausible interpretation of this result is self-enrichment, and may suggest that these GCs once possessed dark matter halos. (2) Many dEs have metal-rich GC subpopulations. We also confirm the GC color--galaxy luminosity relations found previously for both metal-poor and metal-rich GC subpopulations. (3) There are large differences in GC specific frequency among dEs. Over -15 < M_B < -18, there is little correlation between specific frequency (S_N)and M_B. But we do find evidence for two separate S_N classes of dEs: those with B-band S_N ~ 2, and others with populous GC systems that have S_N ranging from ~ 5-20 with median S_N ~ 10. Together, these points suggest multiple formation channels for dEs in Virgo. (4) The peak of the GC luminosity function (GCLF) is the same for both gEs and dEs. This is contrary to expectations of dynamical friction on massive GCs, unless the primordial GCLF varies between gEs and dEs. Among gEs the GCLF turnover varies by a surprising small 0.05 mag, an encouraging result for its use as an accurate standard candle. (5) dE,Ns appear bimodal in their nuclear properties: there are small bright red nuclei consistent with formation by dynamical friction of GCs, and larger faint blue nuclei which appear to have formed by a dissipative process with little contribution from GCs. The role of dynamical evolution in shaping the present-day properties of dE GC systems and their nuclei remains ambiguous. (Abridged)
An alternative mechanism that dims high redshift supernovae without cosmic acceleration utilizes an oscillation of photons into a pseudo-scalar particle during transit. Since angular diameter distance measures are immune to the loss of photons, this ambiguity in interpretation can be resolved by combining CMB acoustic peak measurements with the recent baryon oscillation detection in galaxy power spectra. This combination excludes a non-accelerating dark energy species at the 4sigma level regardless of the level of the pseudo-scalar coupling. While solutions still exist with substantial non-cosmological dimming of supernovae, they may be tested with future improvement in baryon oscillation experiments.
We present X-ray and optical spectroscopic observations of twelve galaxy groups and clusters identified within the XMM Large-Scale Structure (LSS) survey. Groups and clusters are selected as extended X-ray sources from a 3.5 deg2 XMM image mosaic above a flux limit 8e-15 ergs/s/cm2 in the [0.5-2] keV energy band. Deep BVRI images and multi-object spectroscopy confirm each source as a galaxy concentration located within the redshift interval 0.29<z<0.56. We combine line-of-sight velocity dispersions with the X-ray properties of each structure computed from a two-dimensional surface brightness model and a single temperature fit to the XMM spectral data. The resulting distribution of X-ray luminosity, temperature and velocity dispersion indicate that the XMM-LSS survey is detecting low-mass clusters and galaxy groups to redshifts z < 0.6. Confirmed systems display little or no evidence for X-ray luminosity evolution at a given X-ray temperature compared to lower redshift X-ray group and cluster samples. A more complete understanding of these trends will be possible with the compilation of a statistically complete sample of galaxy groups and clusters anticipated within the continuing XMM-LSS survey.
We use high S/N, high-resolution Keck/HIRES spectroscopy of 4 solar twin candidates (HIP 71813, 76114, 77718, 78399) from our Hipparcos-based CaII H & K survey to carry out parameter and abundance analyses of these objects. Our spectroscopic Teff estimates are some 100 K hotter than the photometric scale of the recent Geneva-Copenhagen survey; several lines of evidence suggest the photometric temperatures are too cool at solar $T_{\rm eff}$. At the same time, our abundances for the 3 solar twin candidates included in the Geneva-Copenhagen survey are in outstanding agreement with the photometric metallicities; there is no sign of the anomalously low photometric metallicities derived for some late-G UMa group and Hyades dwarfs. A first radial velocity determination is made for HIP 78399, and UVW kinematics derived for all stars. HIP 71813 appears to be a kinematic member of the Wolf 630 moving group (a structure apparently reidentified in a recent analysis of late-type Hipparcos stars), but its metallicity is 0.1 dex higher than the most recent estimate of this group's metallicity. While certainly ``solar-type'' stars, HIP 76114 and 77718 are a few percent less massive, significantly older, and metal-poor compared to the Sun; they are neither good solar twin candidates nor solar analogs providing a look at the Sun at some other point in its evolution. HIP 71813 appears to be an excellent solar analog of age 8 Gyr. Our results for HIP 78399 suggest the promise of this star as a solar twin may be equivalent to the ``closest ever solar twin'' HR 6060; follow up study of this star is encouraged.
Using an updated population synthesis code we study the formation and evolution of black holes (BHs) in young star clusters following a massive starburst. This study continues and improves on the initial work described by Belczynski, Sadowski & Rasio (2004). In our new calculations we account for the possible ejections of BHs and their progenitors from clusters because of natal kicks imparted by supernovae and recoil following binary disruptions. The results indicate that the properties of both retained BHs in clusters and ejected BHs (forming a field population) depend sensitively on the depth of the cluster potential. In particular, most BHs ejected from binaries are also ejected from clusters with central escape speeds Vesc < 100 km/s. Conversely, most BHs remaining in binaries are retained by clusters with Vesc > 10 km/s. BHs from single star evolution are also affected significantly: about half of the BHs originating from primordial single stars are ejected from clusters with Vesc < 50 km/s. Our results lay a foundation for theoretical studies of the formation of BH X-ray binaries, including possible `ultra-luminous'' sources, as well as merging BH--BH binaries detectable with future gravitational-wave observatories.
It has been a persistent question at least for a decade where the
gravitational lens caustics are in the radial direction: whether in front of
the lensing mass, behind the lensing mass, or on the plane normal to the line
of sight that passes through the lensing mass, the radiation source, or the
observer. It is a wrong question. And, the truth angers certain referees who
somehow possess the ability to write lengthy rubbish referee reports and delay
certain papers indefinitely.
General relativity is a metric theory, particularly of Riemannian geometry,
which is characterized by the existence of an inner product -- or, the
invariance of the proper time. According to Einstein field equations, a compact
mass defines a spherical geometry around it and focuses photons from a distant
source to an observer with the source and observer as the two focal points.
When the mass is spherically symmetric, the two dimensional lens equation that
relates the angular positions of a source and its images defines a point
caustic at the angular position of the lensing mass.
The third (radial) position of the point caustic is not defined. For an
arbitrary mass, the caustic extends into a web of piecewise smooth curves
punctuated by cusps and again its notion exists only within the context of the
lens equation. We point out a few errors in a couple of papers, published in
the Astrophysical Journal, which may be influential.
Spectroscopic observations obtained with the VLT of one planetary nebula (PN) in Sextans A and of five PNe in Sextans B and of several HII regions (HII) in these two dwarf irregular galaxies are presented. The extended spectral coverage, from 320.0 to 1000.0nm, and the large telescope aperture allowed us to detect a number of emission lines, covering more than one ionization stage for several elements (He, O, S, Ar). The electron temperature (Te) diagnostic [OIII] line at 436.3 nm was measured in all six PNe and in several HII allowing for an accurate determination of the ionic and total chemical abundances by means of the Ionization Correction Factors method. For the time being, these PNe are the farthest ones where such a direct measurement of the Te is obtained. In addition, all PNe and HII were also modelled using the photoionization code CLOUDY. The physico-chemical properties of PNe and HII are presented and discussed. A small dispersion in the oxygen abundance of HII was found in both galaxies: 12 + $\log$(O/H)=7.6$\pm$0.2 in SextansA, and 7.8$\pm$0.2 in SextansB. For the five PNe of SextansA, we find that 12 + $\log$(O/H)=8.0$\pm$0.3, with a mean abundance consistent with that of HII. The only PN known in SextansA appears to have been produced by a quite massive progenitor, and has a significant nitrogen overabundance. In addition, its oxygen abundance is 0.4 dex larger than the mean abundance of HII, possibly indicating an efficient third dredge-up for massive, low-metallicity PN progenitors. The metal enrichment of both galaxies is analyzed using these new data.
From the damping of the Cosmic Microwave Background Radiation
(CMB) anisotropy power spectrum at large scale and the recent accelerating
expansion of the Universe, we find that, there may be a largest scale which we
can detect in the Universe. From this, we can get the inflation parameters as
spectrum index $n_s$, e-fold
$N$, Hubble parameter $H$, the ratio of tensor and scalar $r$, the lasting
time of reheating time $\alpha$ for special inflation models. We do them in
three inflation models, and find that all the results fit very well with the
observations and the inflation theory.
Rotation periods are now available for ~500 pre-main sequence and recently arrived main sequence stars of solar-like mass (0.4-1.2 M_sun) in five nearby young clusters: the Orion Nebula Cluster, NGC 2264, alpha Per, IC 2602 and the Pleiades. In combination with estimates of stellar radii these data allow us to construct distributions of surface angular momentum per unit mass at three different epochs: nominally, 1, 2 and 50 My. Our main result is illustrated in Fig. 18 and may be summarized as follows: (1) 50-60% of the stars on convective tracks in this mass range are released from any locking mechanism very early on and are free to conserve angular momentum throughout most of their PMS evolution, i.e. to spin up and account for the rapidly rotating young main sequence stars. (2) The other 40-50% lose substantial amounts of angular momentum during the first few million years, and end up as slowly rotating main sequence stars. The duration of the rapid angular momentum loss phase is ~5-6 My, which is roughly consistent with the lifetimes of disks estimated from infrared surveys of young clusters. The rapid rotators of Orion age lose less than 10% of their (surface) specific angular momentum during the next 50 My while the slow rotators lose about two-thirds of theirs. A detectable part of this loss occurs even during the ~1 My interval between the ONC and NGC 2264. The data support the view that interaction between an accretion disk and star is the primary mechanism for evolving the broad, bimodal distribution of rotation rates seen for solar-like stars in the ONC into the even broader distributions seen in the young MS clusters.
We have suggested that the Yang-Mills(YM) field can be a kind of candidate of inflation at high energy scale or dark energy at the very low energy scale, which can naturally give the matter state of $\omega<0$, even it can give $\omega<-1$. In this paper, we discuss the perturbation theory of the YM theory, and give a series of equations which can describe the evolution of the perturbation of YM field in the Robertson-Walker space-time. Then for example we discuss solution of the only "electric" field, we find that this field can not generate the scale-invariant initial scalar perturbation spectrum, so it can not as a kind of inflation field, although it can give a nearly de Sitter expansion. But as a kind of dark energy, we find $\omega+1\propto1/a^2$, so it will give a nearly de Sitter expansion which is same with the observation results. We also research the perturbation of this kind of dark energy, we find that if the there is no field perturbation, then the dark energy will be no perturbation $\delta E$, which is different with the scalar field dark energy, but fit well with the observation. If there are field perturbation, the sound velocity is $c_s^2=-1/3$, which will alter the evolution of the cosmic scalar perturbation, this should have obvious effect on the large scale power spectrum of Cosmic Microwave Background Radiation(CMB).
GRB050223 was discovered by the Swift Gamma-Ray Burst Explorer on 23 February
2005 and was the first Gamma-Ray Burst to be observed by both Swift and
XMM-Newton. At the time of writing (May 2005), it has one of the faintest GRB
afterglows ever observed. The spacecraft could not slew immediately to the
burst, so the first X-ray and optical observations occurred approximately 45
minutes after the trigger. Although no optical emission was found by any
instrument, both Swift and XMM-Newton detected the fading X-ray afterglow.
Combined data from both of these observatories show the afterglow to be fading
monotonically as 0.99 +0.15/-0.12 over a time frame between 45 minutes to 27
hours post-burst. Spectral analysis, allowed largely by the higher through-put
of XMM-Newton, implies a power-law with a slope of Gamma=1.75 +0.19/-0.18 and
shows no evidence for absorption above the Galactic column of 7 x 10^20 cm^-2.
From the X-ray decay and spectral slopes, a low electron power-law index of p
= 1.3-1.9 is derived; the slopes also imply that a jet-break has not occured up
to 27 hours after the burst. The faintness of GRB050223 may be due to a large
jet opening or viewing angle or a high redshift.
Extended halo tidal streams from disrupting Milky Way satellites offer new opportunities for gauging fundamental Galactic parameters without challenging observations of the Galactic center. In the roughly spherical Galactic potential tidal debris from a satellite system is largely confined to a single plane containing the Galactic center, so accurate distances to stars in the tidal stream can be used to gauge the Galactic center distance, R_0, given reasonable projection of the stream orbital pole on the X_GC axis. Alternatively, a tidal stream with orbital pole near the Y_GC axis, like the Sagittarius stream, can be used to derive the speed of the Local Standard of Rest (\Theta_LSR). Modest improvements in current astrometric catalogues might allow this measurement to be made, but NASA's Space Interferometry Mission (SIM PlanetQuest) can definitively obtain both R_0 and \Theta_LSR using tidal streams.
We describe multiwavelength optical, X-ray and radio evidences of energetic mergers in southern galaxy cluster Abell 3376 (A3376, redshift z=0.046, X-ray luminosity $ \rm L_{X}(0.1-2.4 keV)= 2.48 \times 10^{44} erg s^{-1}$). Here we report the rare discovery of gigantic, Mpc-scale non-thermal radio structures (`radio-arcs'), shaped like a pair of bow-shock fronts on the merger axis. We argue for the shock acceleration origin of the radio emission and discuss the possibilty of acceleration of very high energy cosmic ray particles in this and similar clusters.
Results of experiments investigating air showers in the energy region of the
knee are summarized. The all-particle energy spectrum, the mean logarithmic
mass, and the average depth of the shower maximum will be discussed.
Spectra for groups of elements from air shower data are compared to results
from direct measurements.
Two structures in the all-particle energy spectrum of cosmic rays, the knee
at
4 PeV and the second knee around 400 PeV are proposed to be explained by a
phenomenological model, the poly gonato model, connecting direct and indirect
measurements. Within this approach the knee is caused by a successive cut-off
of the flux for individual elements starting with protons at 4.5 PeV. The
second knee is interpreted as the end of the stable nuclei of the periodic
table. To check some key features of this model calculations of the cosmic ray
energy spectrum and the propagation path length at energies from 10^14 to 10^19
eV have been performed within the framework of a combined approach based on the
diffusion model of cosmic rays and a direct simulation of charged-particle
trajectories in the Galaxy.
We analyse the B-R_c colors of galaxies as functions of luminosity and local galaxy density using a large photometric redshift catalog based on the Red-Sequence Cluster Survey. We select two samples of galaxies with a magnitude limit of M_Rc<-18.5 and redshift ranges of 0.2<z< 0.4 and 0.4<z<0.6 containing \~10^5 galaxies each. We model the color distributions of subsamples of galaxies and derive the red galaxy fraction and peak colors of red and blue galaxies as functions of galaxy luminosity and environment. The evolution of these relationships over the redshift range of z~0.5 to z~0.05 is analysed in combination with published results from the Sloan Digital Sky Survey. We find that there is a strong evolution in the restframe peak color of bright blue galaxies in that they become redder with decreasing redshift, while the colors of faint blue galaxies remain approximately constant. This effect supports the ``downsizing'' scenario of star formation in galaxies. While the general dependence of the galaxy color distributions on the environment is small, we find that the change of red galaxy fraction with epoch is a function of the local galaxy density, suggesting that the downsizing effect may operate with different timescales in regions of different galaxy densities.
This paper contains the fifth part of the Catalog of Variable Stars created from the V-band photometric data collected by 9x9 deg camera of the All Sky Automated Survey. Preliminary list of variable stars found in the fields located between declination 0 and +28 deg of the northern hemisphere is presented. 11,509 stars brighter than V=15 were found to be variable (2,482 eclipsing, 1,397 regularly pulsating, 318 Mira and 7,310 other stars). Automated algorithm taking into account light curve properties (period, fourier coefficients) and other available data (2MASS colors, IRAS fluxes) was applied to roughly classify objects. Basic photometric properties are presented in the tables and thumbnail light curves are made available for reference. All the photometric data are available over the INTERNET at this http URL or this http URL
We present a comprehensive study of the stellar population and the interstellar medium in NGC 6822 using high-quality \HI data (obtained with the Australia Telescope Compact Array) and optical broad/narrow-band data (obtained with Subaru and the INT). Our H$\alpha$ observations are an order of magnitude deeper than previous studies and reveal a complex filamentary network covering almost the entire central disk of NGC 6822. We find hitherto unknown HII regions in the outskirts of NGC 6822 and the companion galaxy. The old and intermediate age stellar population can be traced out to radii of over 0.6 deg (> 5 kpc), significantly more extended than the HI disk. In sharp contrast, the distribution of the young, blue stars, closely follows the distribution of the HI disk and displays a highly structured morphology. We find evidence for an older stellar population in the companion galaxy -- the current star formation activity, although likely to have been triggered by the interaction with NGC 6822, is not the first star formation episode in this object. We show that the properties of the giant kpc-sized hole in the outer HI disk of NGC 6822 are consistent with it being formed by the effects of stellar evolution.
In this paper, the dynamical heteroclinic orbit and attractor have been employed to make the late-time behaviors of the model insensitive to the initial condition and thus alleviates the fine tuning problem in cosmological dynamical system of barotropic fluid and quintessence with a double exponential potential. The late-time asymptotic behavior of the double exponential model does not always correspond to the single case. The heteroclinic orbits are the non-stationary solutions and in general they will interpolate between the critical points. Although they can not be shown analytically, yet a numerical calculation can reveal most of their properties. Varied heteroclinic orbits and attractors including tracking attractor and de Sitter attractor have been found.
Large volumes of CCD imaging data that will become available from wide-field cameras at telescopes such as the CFHT, SUBARU, VST, or VISTA in the near future are highly suitable for systematic distance surveys of early-type galaxies using the Surface Brightness Fluctuation (SBF) method. For the efficient processing of such large data sets, we are developing the first semi-automatic SBF analysis pipeline named SAPAC. After a brief description of the SBF method we discuss the image quality needed for a successful distance measurement and give some background information on SAPAC
The highly disturbed hot gas in elliptical galaxies, as revealed in many {\em Chandra} X-ray images, implies a source of energy in the galactic nucleus. In some elliptical galaxies faint X-ray ``ghost'' cavities appear without corresponding radio lobes. It has been suggested that ghost cavities are caused by short-lived activity with a timescale of $\sim 10^3-10^4$ years, but this is difficult to understand within the popular paradigm of active galactic nuclei. We suggest an episode model for ghost cavities, invoking captures of red giant stars by the black hole located at the center of the elliptical galaxies at a typical rate of $10^{-5}$yr$^{-1}$ per galaxy. The accretion of tidally disrupted red giant stars onto the black hole powers activity in a timescale of a few years. The total energy channeled into the jet/outflow during the cooling time of the hot gas is $\sim 10^{56}$ erg, which is the typical work required to form the observed cavities. In this scenario, the faint cavities are produced by the feedback following accretion of the debris of the captured red giant stars onto the black holes. We apply the present model to several elliptical galaxies and find that it can explain the formation of the ghost cavities. This model can be tested in the future by comparisons between radio and X-ray observations.
The observed large rates of spinning down after glitches in some radio pulsars have been previously explained in terms of a long-term spin-up behavior of a superfluid part of the crust of neutron stars. We argue that the suggested mechanism is not viable; being inconsistent with the basic requirements for a superfluid spin-up, in addition to its quantitative disagreement with the data. Hence, the observed post-glitch relaxations may not be interpreted due only to the effects of the stellar crust.
We present an analysis indicating that there is a correlation between the fluences and the durations of gamma-ray bursts, and provide arguments that this reflects a correlation between the total emitted energies and the intrinsic durations. For the short (long) bursts the total emitted energies are roughly proportional to the first (second) power of the intrinsic duration. This difference in the energy-duration relationship is statistically significant, and may provide an interesting constraint on models aiming to explain the short and long gamma-ray bursts.
GRO 1655-40, a well known black hole candidate, showed renewed X-ray activity in March 2005 after being dormant for almost eight years. It showed very prominent quasi-periodic oscillations. We analysed the data of two observations in this {\it Rapid Communication}, one taken on March 2nd, 2005 and the other taken on the March 11th, 2005. On March 2nd, 2005 the shock was weak and the QPO was seen in roughly all energies. On March 11th, 2005 the power density spectra showed that quasi-periodic oscillations (QPOs) were exhibited in harder X-rays. On the first day, the QPO was seen at 0.13Hz and on the second day, the QPO was seen at $\sim 6.5$Hz with a spectral break at $\sim 0.1$Hz. We analysed the QPOs for the period 25th Feb. 2005 to 12th of March, 2005 and showed that the frequency of QPO increased monotonically from 0.088Hz to 15.01Hz. This agrees well if the oscillating shock is assumed to propagate with a constant velocity. On several days we also noticed the presence of very high frequency QPOs and for the first time we detected QPOs in the 600-700Hz range, the highest frequency range so far reported for any black hole candidate.
We present spatially resolved Spitzer imaging of the supergiant shell region of the M81 group dwarf galaxy IC 2574 obtained as part of the Spitzer Infrared Nearby Galaxies Survey. This region harbors one of the best nearby examples of a kinematically distinct HI shell, with an associated remnant stellar cluster; the shell is initiating sequential star formation as it interacts with the surrounding interstellar medium. This region dominates the infrared luminosity of IC 2574 and is spatially resolved in all Spitzer imaging bands. We study the differences in dust temperature as a function of local environment and compare local star formation rates as inferred from H Alpha and total infrared luminosities. We find that the strong H Alpha sources are associated with regions of warm dust; however, the most luminous infrared and H Alpha sources are not necessarilyco-spatial. The coolest dust is found in the regions farthest from the rim of the shell; these regions show the best agreement between star formation rates derived from H Alpha and from total infrared luminosities (although discrepancies at the factor of 3-4 level still exist). There is considerable variation in the radio-far infrared correlation in different regions surrounding the shell. The low dust content of the region may influence the scatter seen in these relations; these data demonstrate that the expanding shell is dramatically affecting its surroundings by triggering star formation and altering the dust temperature.
The formation of molecular hydrogen in the interstellar medium takes place on the surfaces of dust grains. Hydrogen molecules play a role in gas-phase reactions that produce other molecules, some of which serve as coolants during gravitational collapse and star formation. Thus, the evaluation of the roduction rate of hydrogen molecules and its dependence on the physical conditions in the cloud are of great importance. Interstellar dust grains exhibit a broad size distribution in which the small grains capture most of the surface area. Recent studies have shown that the production efficiency strongly depends on the grain composition and temperature as well as on its size. In this paper we present a formula which provides the total production rate of H$_2$ per unit volume in the cloud, taking into account the grain composition and temperature as well as the grain size distribution. The formula agrees very well with the master equation results. It shows that for a physically relevant range of grain temperatures, the production rate of H$_2$ is significantly enhanced due to their broad size distribution.
We present a detailed mid-infrared study of the nearby, face-on spiral galaxy M83 based on ISOCAM data. M83 is a unique case study, since a wide variety of MIR broad-band filters as well as spectra, covering the wavelength range of 4 to 18\mu m, were observed and are presented here. Emission maxima trace the nuclear and bulge area, star-formation regions at the end of the bar, as well as the inner spiral arms. The fainter outer spiral arms and interarm regions are also evident in the MIR map. Spectral imaging of the central 3'x3' (4 kpc x 4 kpc) field allows us to investigate five regions of different environments. The various MIR components (very small grains, polycyclic aromatic hydrocarbon (PAH) molecules, ionic lines) are analyzed for different regions throughout the galaxy. In the total 4\mu m to 18\mu m wavelength range, the PAHs dominate the luminosity, contributing between 60% in the nuclear and bulge regions and 90% in the less active, interarm regions. Throughout the galaxy, the underlying continuum emission from the small grains is always a smaller contribution in the total MIR wavelength regime, peaking in the nuclear and bulge components. The implications of using broad-band filters only to characterize the mid-infrared emission of galaxies, a commonly used ISOCAM observation mode, are discussed. We present the first quantitative analysis of new H-alpha and 6cm VLA+Effelsberg radio continuum maps of M83. The distribution of the MIR emission is compared with that of the CO, HI, R band, H-alpha and 6cm radio. A striking correlation is found between the intensities in the two mid-infrared filter bands and the 6cm radio continuum. To explain the tight mid-infrared-radio correlation we propose the anchoring of magnetic field lines in the photoionized shells of gas clouds.
NainiTal-Cape Survey is a survey started with the aim of searching for new rapidly oscillating Ap stars in the northern hemisphere and has discovered one mono-periodic roAp star HD 12098. The frequency separation of HD 12098 suggests a rotation period of 5.5 day for the star. The discovery of roAp oscillations in HD 12098 and the results of the multi-site observation campaign organized to resolve the ambiguity in the determination of the rotation period of HD 12098 is presented. The results of non oscillating Ap stars discovered in the survey and two promising roAp candidates HD 17431 and HD 207561 are also presented. If confirmed, the variability in HD 207561 will make it the first Am star showing roAp type rapid variability.
For the first time connection between the pulsation and modulation properties of RR Lyrae stars has been detected. Based on the available data it is found that the possible range of the modulation frequencies, i.e, the possible maximum value of the modulation frequency depends on the pulsation frequency. Short period variables (P < 0.4 d) can have modulation period as short as some days, while longer period variables (P > 0.6 d) always exhibit modulation with P_mod > 20 d. We interpret this tendency with the equality of the modulation period with the surface rotation period, because similar distribution of the rotational periods is expected if an upper limit of the total angular momentum of stars leaving the RGB exists. The distribution of the projected rotational velocities of red and blue horizontal branch stars at different temperatures shows a similar behaviour as v_rot derived for RR Lyrae stars from their modulation periods. This common behaviour gives reason to identify the modulation period with the rotational period of the modulated RR Lyrae stars.
We summarize the properties of Infrared Dark Clouds, massive, dense, and cool aggregations of interstellar gas and dust that are found througout the Galaxy in projection against the strong mid-infrared background. We describe their distribution and give an overview of their physical properties and chemistry. These objects appear to be the progenitors of high-mass stars and star cluster, but appear to be largely devoid of star formation, which however appears to take place in localized spots.
New models of rotating and non-rotating stars are computed for initial masses between 25 and 120 Msun and for metallicities Z = 0.004, 0.008, 0.020 and 0.040 with the aim of reexamining the wind contribution of Wolf-Rayet (WR) stars to the F19 enrichment of the interstellar medium. Models with an initial rotation velocity vini = 300 km/s are found to globally eject less F19 than the non-rotating models. We compare our new predictions with those of Meynet & Arnould (2000), and demonstrate that the F19 yields are very sensitive to the still uncertain F19(alpha,p)Ne22 rate and to the adopted mass loss rates. Using the recommended mass loss rate values that take into account the clumping of the WR wind and the NACRE reaction rates when available, we obtain WR F19 yields that are significantly lower than predicted by Meynet & Arnould (2000), and that would make WR stars non-important contributors to the galactic F19 budget. In view, however, of the large nuclear and mass loss rate uncertainties, we consider that the question of the WR contribution to the galactic F19 remains quite largely open.
Integrated optics (IO) is an optical technology that allows to reproduce optical circuits on a planar substrate. Since 1996, we have investigated the potentiality of IO in the framework of astronomical single mode interferometry. We review in this paper the principles of IO, the requirements for interferometry and the corresponding solutions offered by IO, the results of component characterization and the possible fields of application.
The 12C14N/12C15N and 12C14N/13C14N isotopic ratios are determined for the first time in a Jupiter-family comet, 88P/1981 Q1 Howell, and in the chemically peculiar Oort Cloud comet C/1999 S4 (LINEAR). By comparing these measurements to previous ones derived for six other Oort Cloud comets (including one of Halley-type), we find that both the carbon and nitrogen isotopic ratios are constant within the uncertainties. The mean values are 12C/13C ~ 90 and 14N/15N \~ 145 for the eight comets. These results strengthen the view that CN radicals originate from refractory organics formed in the protosolar molecular cloud and subsequently incorporated in comets.
We present a new assessment of the contribution of Blazars to the extragalactic background radiation across the e.m. spectrum. Our calculations rely on deep Blazar radio counts that we derived combining several multifrequency surveys. The integrated Blazar emission yields a broad-band non-thermal background that in some parts of the e.m. spectrum dominates the extragalactic brightness. Blazars are the main point-like contributors to the CMB. Their integrated emission causes an apparent T increase of 5-50 muK in the 50-250 GHz range. The CMB fluctuation spectrum is sensibly contaminated at l>300, for a Poissonian source distribution, or at lower l values if spatial clustering is present. We estimate that well over 100,000 Blazars will produce a significant signal in the PLANCK CMB anisotropy maps. Because of the microwave-Xray flux correlation, these sources are expected to have flux > a few 10^{-15} erg/s in the soft X-ray band. Thus, a large fraction of the foreground sources in CMB anisotropy maps could be identified and removed using a multi frequency approach, provided that a sufficiently deep all sky X-ray survey will be available. We further show that Blazars are a major constituent of all high-E extragalactic backgrounds. Their contribution is 11-12% at X-ray frequencies and possibly 100% in the 0.5-50 MeV band. At E>100 MeV, the Blazar collective emission, obtained extrapolating their integrated micro-wave flux to the gamma-ray band using the SED of EGRET detected sources, over-predicts the extragalactic background by a large factor, implying that Blazars not only dominate the gamma-ray sky but also that their average duty cycle at these frequencies must be rather low. We also find that Blazars of the HBL type may produce a significant amount of flux at TeV energies.
It is now widely recognised that massive black holes must have had a fundamental influence on the formation of galaxies and vice versa. With current and imminent missions we aim to unravel much of this relationship for the last 10 Gyr of cosmic history, while the quasar population waned and star formation died down. The picture at earlier times will be more difficult to reconstruct, but will likely be even more exciting: when the first stars shone, the first dust was formed, and quasars were a vigorously rising population. One of the primary goals of XEUS is to allow us to find and study the earliest quasars, however deeply buried in gas and dust they may be. But to understand fully the astrophysical context of these objects, their significance in the grand picture, we must learn how they relate to their environments and their host galaxies. The ESA future Far-InfraRed Mission (FIRM) will provide much of the data we require, revealing the dust heated by star formation in the host galaxy, the relative evolutionary stages of spheroid and black hole, and the total energy budgets posessed by these first quasars. FIRM will reveal star formation in the immediate proto-cluster environment of the quasar and so tell us how the formation of the first galaxies and quasars coupled to the earliest large scale structures.
A bar rotating in a pressure-supported halo generally loses angular momentum and slows down due to dynamical friction. Valenzuela & Klypin report a counter-example of a bar that rotates in a dense halo with little friction for several Gyr, and argue that their result invalidates the claim by Debattista & Sellwood that fast bars in real galaxies require a low halo density. We show that it is possible for friction to cease for a while should the pattern speed of the bar fluctuate upward. The reduced friction is due to an anomalous gradient in the phase-space density of particles at the principal resonance created by the earlier evolution. The result obtained by Valenzuela & Klypin is probably an artifact of their adaptive mesh refinement method, but anyway could not persist in a real galaxy. The conclusion by Debattista & Sellwood still stands.
Using the IRAM 30m telescope, we report the detection of the CO(3--2), CO(4--3), CO(5--4) and CO(6--5) lines in the gravitational lensed submm galaxy SMM J16359+6612 at z=2.5. The CO lines have a double peak profile in all transitions. From a Gaussian decomposition of the spectra we show that the CO line ratios, and therefore the underlying physical conditions of the gas, are similar for the blue and the redshifted component. The CO line Spectral Energy Distribution (SED; i.e. flux density vs. rotational quantum number) turns over already at the CO(5--4) transition which shows that the molecular gas is less excited than in nearby starburst galaxies and high--z QSOs. This difference mainly arises from a lower average H2 density, which indicates that the gas is less centrally concentrated than in nuclear starburst regions in local galaxies. We suggest that the bulk of the molecular gas in SMM J16359+6612 may arise from an overlap region of two merging galaxies. The low gas density and clear velocity separation may reflect an evolutionary stage of the merger event that is in between those seen in the Antennae and in the more evolved ultraluminous infrared galaxies (ULIRGs) like e.g. Mrk231.
We perform a new study of the chances of the fluorescence detector (FD) at the Pierre Auger Observatory (PAO) to detect the tau leptons produced by Earth-skimming ultra high energy tau neutrinos. We present a new and more detailed evaluation of the effective aperture of the FD that takes into account the real elevation profile of the area near PAO and considers a reliable fiducial volume for the experimental set up. We find a significant increase in the number of expected events with respect to the predictions of a previous semi-analytical determination, and our results show the enhancement effect for neutrino detection from the presence of the near mountains.
We present high-speed, multi-colour optical photometry of the anomalous X-ray pulsar 4U 0142+61, obtained with ULTRACAM on the 4.2-m William Herschel Telescope. We detect 4U 0142+61 at magnitudes of i'=23.7+-0.1, g'=27.2+-0.2 and u'>25.8, consistent with the magnitudes found by Hulleman et al.(2004) and hence confirming their discovery of both a spectral break in the optical and a lack of long-term optical variability. We also confirm the discovery of Kern & Martin (2002) that 4U 0142+61 shows optical pulsations with an identical period (~8.7 s) to the X-ray pulsations. The rms pulsed fraction in our data is 29+-8%, 5-7 times greater than the 0.2-8 keV X-ray rms pulsed fraction. The optical and X-ray pulse profiles show similar morphologies and appear to be approximately in phase with each other, the former lagging the latter by only 0.04+-0.02 cycles. In conjunction with the constraints imposed by X-ray observations, the results presented here favour a magnetar interpretation for the anomalous X-ray pulsars.
There is reason to suspect that about half of the baryons are in pressure-supported plasma in the halos of normal galaxies, drawn in by gravity along with about half of the dark matter. To be consistent with the observations this baryonic component, the corona, would have to be hotter than the kinetic temperature of the dark matter in the halo so as to produce acceptable central electron densities. We ascribe this hotter plasma temperature to the addition of entropy prior to and during assembly of the system, in an analogy to cluster formation. The plasma cooling time would be longer than the gravitational collapse time but, in the inner parts, shorter than the Hubble time, making the corona thermally unstable to the formation of a cloudy structure that may be in line with what is indicated by quasar absorption line systems. The corona of an isolated spiral galaxy would be a source of soft X-ray and recombination radiation, adding to the more commonly discussed effects of stars and supernovae. In this picture the mass in the corona is much larger than the mass in condensed baryons in a spiral galaxy. The corona thus would be a substantial reservoir of diffuse baryons that are settling and adding to the mass in interstellar matter and stars, so that star formation in isolated spirals will continue well beyond the present epoch.
We study the stability of cylindrical Taylor-Couette flow in the presence of combined axial and azimuthal magnetic fields, and show that adding an azimuthal field profoundly alters the previous results for purely axial fields. For small magnetic Prandtl numbers Pm, the critical Reynolds number Re_c for the onset of the magneto-rotational instability becomes independent of Pm, whereas for purely axial fields it scales as Pm^{-1}. For typical liquid metals, Re_c is then reduced by several orders of magnitude, enough that this new design should succeed in realizing this instability in the laboratory.
We have created new dust temperature and column density maps of Perseus, Ophiuchus and Serpens using 60 and 100 micron data from the IRIS recalibration of IRAS data. We describe an optimized method for finding the dust temperature, emissivity spectral index, and optical depth using optical and NIR extinction maps. The creation of these temperature and extinction maps (covering tens of square degrees of molecular clouds) is one of the first results from the ongoing COordinated Molecular Probe Line Extinction Thermal Emission (COMPLETE) Survey of Star Forming regions. However, while the extinctions derived from the IRIS emission maps are globally accurate, we warn that FIR emission is not a good proxy for extinction on the scale of one pixel (5').
The magnetic white dwarf SDSS J121209.31+013627.7 exhibits a weak, narrow Halpha emission line whose radial velocity and strength are modulated on a period of ~90 minutes. Though indicative of irradiation on a nearby companion, no cool continuum component is evident in the optical spectrum, and IR photometry limits the absolute magnitude of the companion to M_J > 13.37. This is equivalent to an isolated L5 dwarf, with T_eff < 1700 K. Consideration of possible evolutionary histories suggests that, until ~0.6 Gyr ago, the brown dwarf orbited a ~1.5 M_sun main seqeunce star with P ~ 1 yr, a ~ 1 AU, thus resembling many of the gaseous superplanets being found in extrasolar planet searches. Common envelope evolution when the massive star left the main sequence reduced the period to only a few hours, and ensuing angular momentum loss has further degraded the orbit. The binary is ripe for additional observations aimed at better studying brown dwarfs and the effects of irradiation on their structure.
We present Hubble Space Telescope/Advanced Camera for Surveys (ACS) weak-lensing and Chandra X-ray analyses of MS 1054-0321 at z=0.83, the most distant and X-ray luminous cluster in the Einstein Extended Medium-Sensitivity Survey (EMSS). The high-resolution mass reconstruction through ACS weak-lensing reveals the complicated dark matter substructure in unprecedented detail, characterized by the three dominant mass clumps with the four or more minor satellite groups within the current ACS field. The direct comparison of the mass map with the Chandra X-ray image shows that the eastern weak-lensing substructure is not present in the X-ray image and, more interestingly, the two X-ray peaks are displaced away from the hypothesized merging direction with respect to the corresponding central and western mass clumps, possibly because of ram pressure. In addition, as observed in our previous weak-lensing study of another high-redshift cluster CL 0152-1357 at z=0.84, the two dark matter clumps of MS 1054-0321 seem to be offset from the galaxy counterparts. We examine the significance of these offsets and discuss a possible scenario, wherein the dark matter clumps might be moving ahead of the cluster galaxies. The non-parametric weak-lensing mass modeling gives a projected mass of M(r<1 Mpc)=(1.02+-0.15)x 10^{15} solar mass, where the uncertainty reflects both the statistical error and the cosmic shear effects. Our temperature measurement of T=8.9_{-0.8}^{+1.0} keV utilizing the newest available low-energy quantum efficiency degradation prescription for the Chandra instrument, together with the isothermal beta description of the cluster (r_c=16"+-15" and beta=0.78+-0.08), yields a projected mass of M(r<1 Mpc)=(1.2+-0.2) x 10^{15} solar mass, consistent with the weak-lensing result.
To measure the column densities of interstellar and intergalactic gas clouds using absorption line spectroscopy, the apparent optical depth technique (AOD) of Savage & Sembach (1991) can be used instead of a curve-of-growth analysis or profile fit. We show that the AOD technique, whilst an excellent tool when applied to data with good S/N, will likely overestimate the true column densities when applied to data with low S/N. This overestimation results from the non-linear relationship between the flux falling on a given detector pixel and the apparent optical depth in that pixel. We use Monte Carlo techniques to investigate the amplitude of this overestimation when working with data from the Far Ultraviolet Spectroscopic Explorer (FUSE) and the Space Telescope Imaging Spectrograph (STIS), for a range of values of S/N, line depth, line width, and rebinning. AOD measurements of optimally sampled, resolved lines are accurate to within 10% for FUSE/LiF and STIS/E140M data with S/N>7 per resolution element.
We simulate the growth of galaxies and their central supermassive black holes by implementing a suite of semi-analytic models on the output of the Millennium Run, a very large simulation of the concordance LCDM cosmogony. Our procedures follow the detailed assembly history of each object and are able to track the evolution of all galaxies more massive than the Small Magellanic Cloud throughout a volume comparable to that of large modern redshift surveys. In this first paper we supplement previous treatments of the growth and activity of central black holes with a new model for `radio' feedback from those AGN that lie at the centre of a quasistatic X-ray emitting atmosphere in a galaxy group or cluster. We show that for energetically and observationally plausible parameters such a model can simultaneously explain: (i) the low observed mass drop-out rate in cooling flows; (ii) the exponential cut-off at the bright end of the galaxy luminosity function; and (iii) the fact that the most massive galaxies tend to be bulge-dominated systems in clusters and to contain systematically older stars than lower mass galaxies. This success occurs because static hot atmospheres form only in the most massive structures, and radio feedback (in contrast, for example, to supernova or starburst feedback) can suppress further cooling and star formation without itself requiring star formation. We discuss possible physical models which might explain the accretion rate scalings required for our phenomenological `radio mode' model to be successful.
[Abridged] We apply the multipole vector framework to full-sky maps derived from the first year WMAP data. We significantly extend our earlier work showing that the two lowest cosmologically interesting multipoles, l=2 and 3, are not statistically isotropic. These results are compared to the findings obtained using related methods. In particular, the planes of the quadrupole and the octopole are unexpectedly aligned. Moreover, the combined quadrupole plus octopole is surprisingly aligned with the geometry and direction of motion of the solar system: the plane they define is perpendicular to the ecliptic plane and to the plane defined by the dipole direction, and the ecliptic plane carefully separates stronger from weaker extrema, running within a couple of degrees of the null-contour between a maximum and a minimum over more than 120deg of the sky. Even given the alignment of the quadrupole and octopole with each other, we find that their alignment with the ecliptic is unlikely at >98% C.L., and argue that it is in fact unlikely at >99.9% C.L. We explore the role of foregrounds showing that the known Galactic foregrounds are unlikely to lead to these correlations. Multipole vectors, like individual a_lm, are very sensitive to sky cuts, and we demonstrate that analyses using cut skies induce relatively large errors, thus weakening the observed correlations but preserving their consistency with the full-sky results. Finally we apply our tests to COBE cut-sky maps and briefly extend the analysis to higher multipoles. If the correlations we observe are indeed a signal of non-cosmic origin, then the lack of low-l power will very likely be exacerbated, with important consequences for our understanding of cosmology on large scales.
Purely baryonic dark matter dominated models like MOND based on modification of Newtonian gravity have been successfully in reproducing some dynamical properties of galaxies. More recently, a relativistic formulation of MOND proposed by Bekenstein seems to agree with cosmological large scale structure formation. In this work, we revise the agreement of MOND with observations in light of the new results on the Cosmic Microwave Anisotropies provided by the 2003 flight of Boomerang. The measurements of the height of the third acoustic peak, provided by several small scale CMB experiments have reached enough sensitivity to severely constrain models without cold dark matter. Assuming that acoustic peak structure in the CMB is unchanged and that local measurements of the Hubble constant can be applied, we find that the cold dark matter is strongly favoured with Bayesian probability ratio of about one in two hundred.
Although a simple argument implies that the distribution of dark matter in galactic halos is characterized by discrete flows and caustics, their presence is often ignored in discussions of galactic dynamics and of dark matter detection strategies. Discrete flows and caustics can in fact be irrelevant if the number of flows is very large. We estimate the number of dark matter flows as a function of galactocentric distance and consider the various ways in which that number can be increased, in particular by the presence of structure on small scales (dark matter clumps) and the scattering of the flows by inhomogeneities in the matter distribution. We find that, when all complicating factors are taken into account, discrete flows and caustics in galactic halos remain a robust prediction of cold dark matter cosmology with extensive implications for observation and experiment.
PSR J0751+1807 is a millisecond pulsar in a circular 6 hr binary system with a helium white dwarf secondary. Through high precision pulse timing measurements with the Arecibo and Effelsberg radio telescopes, we have detected the decay of its orbit due to emission of gravitational radiation. This is the first detection of the relativistic orbital decay of a low-mass, circular binary pulsar system. The measured rate of change in orbital period, corrected for acceleration biases, is dP_b/dt=(-6.4+-0.9)x10^-14. Interpreted in the context of general relativity, and combined with measurement of Shapiro delay, it implies a pulsar mass of 2.1+-0.2 solar masses, the most massive pulsar measured. This adds to the emerging trend toward relatively high neutron star masses in neutron star--white dwarf binaries. Additionally, there is some evidence for an inverse correlation between pulsar mass and orbital period in these systems. We consider alternatives to the general relativistic analysis of the data, and we use the pulsar timing data to place limits on violations of the strong equivalence principle.
We report g, V, and r photometric time series of HD 149026 spanning predicted times of transit of the Saturn-mass planetary companion, which was recently discovered by Sato and collaborators. We present a joint analysis of our observations and the previously reported photometry and radial velocities of the central star. We refine the estimate of the transit ephemeris to Tc [HJD] = 2453527.87455^{+0.00085}_{-0.00091} + N * 2.87598^{+0.00012}_{-0.00017}. Assuming that the star has a radius of 1.45 +/- 0.10 R_Sun and a mass of 1.30 +/- 0.10 M_Sun, we estimate the planet radius to be 0.726 +/- 0.064 R_Jup, which implies a mean density of 1.07^{+0.42}_{-0.30} g/cm^3. This density is significantly greater than that predicted for models which include the effects of stellar insolation and for which the planet has only a small core of solid material. Thus we confirm that this planet likely contains a large core, and that the ratio of core mass to total planet mass is more akin to that of Uranus and Neptune than that of either Jupiter or Saturn.
We present interferometric observations of the Be star 51 Ophiuchi. These observations were obtained during the science demonstration phase of the MIDI instrument at the Very Large Telescope Interferometer (VLTI). Using MIDI, a Michelson 2 beam combiner that operates at the N band (8 to 13 microns), we obtained for the first time observations of 51 Oph in the mid-infrared at high-angular resolution. It is currently known that this object presents a circumstellar dust and gas disk that shows a very different composition from other Herbig Ae disks. The nature of the 51 Oph system is still a mystery to be solved. Does it have a companion? Is it a protoplanetary system? We still don't know. Observations with MIDI at the VLTI allowed us to reach high-angular resolution (20 mas).We have several uv points that allowed us to constrain the disk model. We have modeled 51 Oph visibilities and were able to constrain the size and geometry of the 51 Oph circumstellar disk.
High-resolution LCDM cosmological N-body simulations are used to study the properties of galaxy-size dark halos in different environments (cluster, void, and "field"). Halos in clusters and their surroundings have a median spin parameter ~1.3 times lower, and tend to be more spherical and to have less aligned internal angular momentum than halos in voids and the field. For halos in clusters the concentration parameters decrease on average with mass with a slope of ~0.1; for halos in voids these concentrations do not change with mass. For masses <5 10^11 M_sh^-1, halos in clusters are on average ~30-40% more concentrated and have ~2 times higher central densities than halos in voids. When comparing only parent halos, the differences are less pronounced but they are still significant. The Vmax-and Vrms-mass relations are shallower and more scattered for halos in clusters than in voids, and for a given Vmax or Vrms, the mass is smaller at z=1 than at z=0 in all the environments. At z=1, the differences in the halo properties with environment almost dissapear, suggesting this that the differences were stablished mainly after z~1. The halos in clusters undergo more dramatic changes than those in the field or the voids. The differences with environment are owing to (i) the dependence of halo formation time on environment, and (ii) local effects as tidal stripping and the tumultuos histories that halos suffer in high-density regions. We calculate seminumerical models of disk galaxy evolution in halos with the properties found for the different environments. For a given disk mass, the galaxy disks have higher surface density, larger Vd,max and secular bulge-to-disk ratio, lower gas fraction, and are redder as one goes from cluster to void environments, in rough agreement with observations. (abridged)
We model star formation in a wide range of isolated disk galaxies, using a three-dimensional, smoothed particle hydrodynamics code. The model galaxies include a dark matter halo and a disk of stars and isothermal gas. Absorbing sink particles are used to directly measure the mass of gravitationally collapsing gas. Below the density at which they are inserted, the collapsing gas is fully resolved. The star formation rate measured in our models declines exponentially with time. Radial profiles of atomic and molecular gas and star formation rate reproduce observed behavior. We derive from our models and discuss both the global and local Schmidt laws for star formation: power-law relations between surface densities of gas and star formation rate. The global Schmidt law observed in disk galaxies is quantitatively reproduced by our models. We find that the surface density of star formation rate directly correlates with the strength of local gravitational instability. The local Schmidt laws of individual galaxies in our models show clear evidence of star formation thresholds. The variations in both the slope and the normalization of the local Schmidt laws cover the observed range. The averaged values agree well with the observed average, and with the global law. Our results suggest that the non-linear development of gravitational instability determines the local and global Schmidt laws, and the star formation thresholds. We derive from our models the quantitative dependence of the global star formation efficiency on the initial gravitational instability of galaxies. The more unstable a galaxy is, the quicker and more efficiently it forms stars.
In this third paper in a series presenting observations by the Cassini Ultraviolet Imaging Spectrometer (UVIS) of the Io plasma torus, we show remarkable, though subtle, spatio-temporal variations in torus properties. The Io torus is found to exhibit significant, near-sinusoidal variations in ion composition as a function of azimuthal position. The azimuthal variation in composition is such that the mixing ratio of S II is strongly correlated with the mixing ratio of S III and the equatorial electron density and strongly anti-correlated with the mixing ratios of both S IV and O II and the equatorial electron temperature. Surprisingly, the azimuthal variation in ion composition is observed to have a period of 10.07 hours--1.5% longer than the System III rotation period of Jupiter, yet 1.3% shorter than the System IV period defined by Brown (1995). Although the amplitude of the azimuthal variation of S III and O II remained in the range of 2-5%, the amplitude of the S II and S IV compositional variation ranged between 5-25% during the UVIS observations. Furthermore, the amplitude of the azimuthal variations of S II and S IV appears to be modulated by its location in System III longitude, such that when the region of maximum S II mixing ratio (minimum S IV mixing ratio) is aligned with a System III longitude of ~200 +/- 15 degrees, the amplitude is a factor of ~4 greater than when the variation is anti-aligned. This behavior can explain numerous, often apparently contradictory, observations of variations in the properties of the Io plasma torus with the System III and System IV coordinate systems.
The cooling of a compact star depends very sensitively on the state of dense matter at supranuclear densities, which essentially controls the neutrino emission, as well as on the structure of the stellar outer layers which control the photon emission. Open issues concern the hyperon population, the presence of meson condensates, superfluidity and superconductivity, and the transition of confined hadronic matter to quark matter. This paper describes these issues and presents cooling calculations based on a broad collection of equations of state for neutron star matter and strange matter. These results are tested against the body of observed cooling data.
The purpose of the paper is to predict the temperature at the fundamental
blue edge (FBE) of the instability strip for RR Lyrae (RRL) variables from the
pulsation equation that relates temperature to period, luminosity, and mass.
Modern data for the correlations between period, luminosity, and metallicity at
the FBE for field and cluster RRL are used for the temperature calculation. The
predicted temperatures are changed to B-V colors using an adopted color
transformation. The predicted temperatures at the FBE become hotter as [Fe/H]
changes from 0 to -1.5, and thereafter cooler as the metallicity decreases to
-2.5 and beyond. The temperature range over this interval of metallicity is
$\Delta$log $T_e$ = 0.04, or 640 K at 6900K. The predicted color variation is
at the level of 0.03 mag in B-V. The predictions are compared with the observed
RRL colors at the FBE for both the field and cluster variables, showing general
agreement at the level of 0.02 mag in (B-V)$_o$, which, however, is the
uncertainty of the reddening corrections.
The focus of the problem is then reversed by fitting a better envelope to the
observed FBE relation between color and metallicity for metallicities smaller
than -1.8 which, when inserted in the pulsation equation, gives a non-linear
calibration ....
We use X-ray monitoring data obtained over a broad range of time-scales to measure the broadband power spectral density functions (PSDs) of two Seyfert galaxies, the broad line Seyfert 1 NGC 3227 and the Seyfert 2 NGC 5506, which has recently been identified as an obscured Narrow Line Seyfert 1 (NLS 1). Using a Monte-Carlo fitting technique we demonstrate that both PSDs are reminiscent of the PSD of black hole X-ray binaries (BHXRBs) in the high/soft state, and specifically rule out a low/hard state PSD shape in NGC 3227. This result demonstrates that, at least where variability is concerned, broad line Seyferts with hard X-ray spectra (photon index~1.6) are not simply the analogues of the low/hard state in BHXRBs, and the dichotomy of NLS 1 and broad line Seyferts cannot be simply interpreted in terms of the two states. We show that the PSD normalisation in NGC 3227 is strongly energy dependent, with larger variability amplitudes at lower energies, unlike NGC 5506 which shows little energy-dependence of variability. We demonstrate that this difference is caused by spectral pivoting of the continuum in NGC 3227 at high energies, which is probably also related to the large amplitude of variability seen in the 2-10 keV band in this AGN. Using the new PSD data and new results in the literature, we replot the PSD break time-scale versus mass plot for all AGN with PSD breaks measured so far, and demonstrate that higher accretion-rate AGN appear to have relatively shorter break time-scales for their black hole mass than lower-accretion rate AGN.
We present near infrared broad band and polarimetric images of the compact star forming cluster AFGL437 obtained with the NICMOS instrument aboard HST. Our high resolution images reveal a well collimated bipolar reflection nebulosity in the cluster and allow us to identify WK34 as the illuminating source. The scattered light in the bipolar nebulosity centered on this source is very highly polarized (up to 79%). Such high levels of polarization implies a distribution of dust grains lacking large grains, contrary to the usual dust models of dark clouds. We discuss the geometry of the dust distribution giving rise to the bipolar reflection nebulosity and make mass estimates for the underlying scattering material. We find that the most likely inclination of the bipolar nebulosity, south lobe inclined towards Earth, is consistent with the inclination of the large scale CO molecular outflow associated with the cluster, strengthening the identification of WK34 as the source powering it.
We briefly review the emerging paradigm which links the radio-quiet and radio-loud classes of AGN to the different accretion states observed in stellar mass black hole X-ray binary systems (BHXRBs), and discuss the relevance of the AGN/BHXRB connection to blazar variability.
We present a comprehensive study of the morphological properties of 42 gamma-ray burst (GRB) host galaxies imaged with the Hubble Space Telescope in the optical band. The purpose of this study is to understand the relation of GRBs to their macro-environments, and to compare the GRB-selected galaxies to other high redshift samples. We perform both qualitative and quantitative analyses by categorizing the galaxies according to their visual properties, and by examining their surface brightness profiles. We find that all of the galaxies have approximately exponential profiles, indicative of galactic disks, and have a median scale length of about 1.7 kpc. Inspection of the visual morphologies reveals a high fraction of merging and interacting systems, with \~30% showing clear signs of interaction, and an additional ~30% exhibiting irregular and asymmetric structure which may be the result of recent mergers; these fractions are independent of redshift and galaxy luminosity. On the other hand, the three GRB host galaxies for which submillimeter and radio emission has been detected are isolated and compact, unlike the luminous submillimeter-selected galaxies. The fraction of mergers appears to be elevated compared to other high redshift samples, particularly for the low luminosities of GRB hosts (M_B ~ -16 to -21 mag). This suggests that merging and interacting galaxies undergoing a burst of star formation may be an efficient site for the production of GRB progenitors. Finally, we show that GRB hosts clearly follow the size-luminosity relation present in other galaxy samples, but thanks to absorption redshifts they help extend this relation to lower luminosities.
We present our results of deep 21 cm line (HI) observations of five early and mixed-type dwarf galaxies in the nearby Sculptor group using the ATNF 64m Parkes Radio Telescope. Four of these objects, ESO294-G010, ESO410-G005, ESO540-G030, and ESO540-G032, were detected in HI with neutral hydrogen masses in the range of 2-9x10^5 M_{\odot} ($M_{HI}/L_{B}$ = 0.08, 0.13, 0.16, and 0.18, respectively). These HI masses are consistent with the gas mass expected from stellar outflows over a large period of time. Higher resolution radio data from the Australia Telescope Compact Array were further analysed to measure more accurate positions and the distribution of the HI gas. In the cases of dwarfs ESO294-G010 and ESO540-G030, we find significant offsets of 290 pc and 460 pc, respectively, between the position of the HI peak flux and the center of the stellar component. These offsets are likely to have internal cause such as the winds from star-forming regions. The fifth object, the spatially isolated dwarf elliptical Scl-dE1, remains undetected at our 3\sigma limit of 22.5 mJy km/s and thus must contain less than 10^5 M_{\odot} of neutral hydrogen. This leaves Scl-dE1 as the only Sculptor group galaxy known where no interstellar medium has been found to date. The object joins a list of similar systems including the Local Group dwarfs Tucana and Cetus that do not fit into the global picture of the morphology-density relation where gas-rich dwarf irregulars are in relative isolation and gas-deficient dwarf ellipticals are satellites of more luminous galaxies.
We present non-Local Thermodynamic Equilibrium (non-LTE) calculations for neutral carbon spectral line formation, carried out for a grid of model atmospheres covering the range of late-type stars. The results of our detailed calculations suggest that the carbon non-LTE corrections in these stars are higher than usually adopted, remaining substantial even at low metallicity. For the most metal-poor stars in the sample of Akerman et al. (2004), the non-LTE abundance corrections are of the order of -0.35...-0.45 dex (when neglecting H collisions). Applying our results to those observations, the apparent [C/O] upturn seen in their LTE analysis is no longer present, thus revealing no need to invoke contributions from Pop. III stars to the carbon nucleosynthesis.
We report the detection of the 2P_3/2 -> 2P_1/2 fine-structure line of C+ at 157.74 micron in SDSSJ114816.64+525150.3 (hereafter J1148+5251), the most distant known quasar, at z=6.42, using the IRAM 30-meter telescope. This is the first detection of the [CII] line at high redshift, and also the first detection in a Hyperluminous Infrared Galaxy (L_FIR > 10^13 Lsun). The [CII] line is detected at a significance level of 8 sigma and has a luminosity of 4.4 x 10^9 Lsun. The L_[CII]/L_FIR ratio is 2 x 10^-4, about an order of magnitude smaller than observed in local normal galaxies and similar to the ratio observed in local Ultraluminous Infrared Galaxies. The [CII] line luminosity indicates that the host galaxy of this quasar is undergoing an intense burst of star formation with an estimated rate of ~3000 Msun/yr. The detection of C+ in SDSS J1148+5251 suggests a significant enrichment of metals at z ~ 6 (age of the universe ~870 Myr), although the data are consistent with a reduced carbon to oxygen ratio as expected from chemical evolutionary models of the early phases of galaxy formation.
We present new RATAN-600 data on the synchrotron Galaxy radiation at the PLANCK Mission and WMAP frequencies at high Galactic latitudes upto l=3000. The difference between the standard synchrotron template (l<50) of the WMAP group and RATAN-600 data was detected with the strong synchrotron ``longitude quadrant asymmetry''. It may change the WMAP estimates of z_{reheating} from low l polarization data. The polarized synchrotron noise for very deep observations (<< 1 microK) at the PLANCK HFI was not detected at l>200 scales. ``Sakharov Oscillations'' in the E-mode (500<l<2000) should be well visible even at ~10 GHz. The polarized noise from relic gravitational waves (l~80) may be confused with B-mode of synchrotron Galaxy polarized noise at the frequencies below 100 GHz, but there are no problems at HFI-band.
It is widely accepted that the broad absorption line region (BALR) exists in most (if not all) quasars with a small covering factor. Recent works showed that the BALR is optically thick to soft and even medium energy X-rays, with a typical hydrogen column density of a few 10$^{23}$ to $>$ 10$^{24}$ cm$^{-2}$. The electron scattering in the thick absorber might contribute significantly to the observed continuum polarization for both BAL QSOs and non-BAL QSOs. In this paper, we present a detailed study of the electron scattering in the BALR by assuming an equatorial and axisymmetric outflow model. Monte-Carlo simulations are performed to correct the effect of the radiative transfer. Assuming an average covering factor of 0.2 of the BALR, which is consistent with observations, we find the electron scattering in the BALR with a column density of $\sim$ 4 $\times$ 10$^{23}$ cm$^{-2}$ can successfully produce the observed average continuum polarization for both BAL QSOs and non-BAL QSOs. The observed distribution of the continuum polarization of radio quiet quasars (for both BAL QSOs and non-BAL QSOs) is used to constrain the dispersal distribution of the BALR. We find that, to match the observations, the maximum continuum polarization produced by the BALR (while viewed edge-on) peaks at $P$ = 0.34%, which is much smaller than the average continuum polarization of BAL QSOs ($P$ = 0.93%). The discrepancy can be explained by a selection bias that the BAL with larger covering factor, and thus producing larger continuum polarization, is more likely to be detected. A larger sample of radio quiet quasars with accurate measurement of the continuum polarization will give better constraints to the distribution of the BALR properties.
We present deep 850micron imaging of the z=0.773 strong lensing galaxy cluster RCSJ022434-0002.5 from the Red-Sequence Cluster Survey (RCS). These data are part of a larger submillimeter survey of RCS clusters, with SCUBA on the JCMT. We find five objects at 850micron, all of which are also detected at either 1.4-GHz, 450micron or both. The number density of objects in this field is in general agreement with the blank-field source counts; however, when combined with other cluster surveys a general tendency of cluster fields towards higher submm number densities is seen, which may be the result of unrecognized submillimeter luminous cluster galaxies. Primarily employing optical photometric redshifts we show that two of the five submillimeter galaxies in this field are consistent with being cluster members, while two are more likely background systems.
The near-IR HeI 10830A transition is a highly sensitive diagnostic for non-LTE effects in the helium atom. So far, non-LTE line-formation computations have failed to quantitatively reproduce observations of this line in the entire range of early-A to late-O main sequence stars. It is shown that the non-LTE modelling was insufficient, for the most part either because of inaccurate photoionization cross-sections for the 2s 3S state or the neglect of line blocking. New calculations based on state-of-the-art atomic data give excellent agreement with observation for the HeI 10830 A feature, while profiles of the HeI lines in the visual are retained.
Using the initial peculiar-velocity field, we analytically study the hierarchical formation of gravitationally bound objects. The field is smoothed over a scale that corresponds to the mass of a given class of objects. Through the Zel'dovich approximation, the smoothed field determines how the objects cluster together to form a new class of more massive objects. The standard cosmological parameters lead to the evolution of primordial clouds with 10^6 M(sun) -> galaxies with 10^12 M(sun) -> clusters of galaxies with 10^15 M(sun) -> superclusters of galaxies with 10^16 M(sun). The epochs obtained for the formation of these classes of objects are consistent with observations.
We present Hubble Space Telescope images and 2 years of optical photometry of the quadruple quasar HE0435-1223. The time delays between the intrinsic quasar variations are 14.4+/-0.8 (A-D), 8.0+/-0.8 (A-B) and 2.1+/-0.8 (A-C) days. We also observed non-intrinsic variations of ~0.1 mag/yr that we attribute to microlensing. Instead of the traditional approach of assuming a rotation curve for the lens galaxy and then deriving the Hubble constant (H_0), we assume H_0=(72+/-7) km/s/Mpc and derive constraints on the rotation curve. On the scale over which the lensed images occur (1.2"=5kpc/h=1.5R_e), the lens galaxy must have a rising rotation curve, and it cannot have a constant mass-to-light ratio. These results add to the evidence that the structures of early-type galaxies are heterogeneous.
The Swift Gamma-Ray Explorer is designed to make prompt multiwavelength
observations of Gamma-Ray Bursts (GRBs) and GRB afterglows. The X-ray Telescope
(XRT) enables Swift to determine GRB positions with a few arcseconds accuracy
within 100 seconds of the burst onset.
The XRT utilizes a mirror set built for JET-X and an XMM/EPIC MOS CCD
detector to provide a sensitive broad-band (0.2-10 keV) X-ray imager with
effective area of > 120 cm^2 at 1.5 keV, field of view of 23.6 x 23.6
arcminutes, and angular resolution of 18 arcseconds (HPD). The detection
sensitivity is 2x10^-14 erg cm^-2 s^-1 in 10^4 seconds. The instrument is
designed to provide automated source detection and position reporting within 5
seconds of target acquisition. It can also measure the redshifts of GRBs with
Fe line emission or other spectral features. The XRT operates in an
auto-exposure mode, adjusting the CCD readout mode automatically to optimize
the science return for each frame as the source intensity fades. The XRT will
measure spectra and lightcurves of the GRB afterglow beginning about a minute
after the burst and will follow each burst for days or weeks.
We study the faint end of the HI mass function (HIMF) in order to test the predictions of the CDM theory on the number density of objects with small (dark) masses. The neutral hydrogen is much better tracer of the underlying mass distribution compared to the luminous matter and can be used to test the existence of a population of small galaxies in which the star formation has been partially or completely suppressed during cosmic evolution. Due to technical limitations, the existing HI surveys are not very sensitive to HI masses below 10^8 M_sun. We designed a blind HI survey to be sensitive to objects with small HI masses. The surveyed area is in the Canis Venatici groups of galaxies and covers in total ~ 86 deg^2 of sky, with observed velocities in the range -350 < cz < 1400 km/s. We detected 69 objects, 22 of them for the first time in HI. All new HI detections fall in the lower part of the mass-histogram, confirming our ability to detect galaxies with small HI masses. The calculated HIMF is flat in the faint end regime (slope ~ -1), different from the steep rise predicted by CDM models. Possible effects of the environment on the estimated HIMF parameters are discussed.
The diffuse Extragalactic Background Light (EBL) contains unique information about the epochs of formation and the history of evolution of galaxies. Unfortunately, direct measurements are subject to large systematic uncertainties due to the difficulties in the accurate model-based subtraction of the bright foregrounds. An alternative approach is based on the detection and identification of EBL absorption features in high-energy spectra of objects of known redshift. Here we exploit this method on the blazars H 2356-309 (z=0.165) and 1ES 1101-232 (z=0.186), newly discovered at TeV energies by the H.E.S.S. Collaboration. They are the most distant sources with measured spectra known so far at these energies. Their hard spectra provide the most stringent upper limit to date on the EBL in the Opt--NIR band, which appears significantly lower than expected from the current "direct" estimates and very close to the absolute lower limit represented by the integrated light of resolved galaxies. In addition to important cosmological implications, this result shows that the intergalactic space is more transparent to gamma-rays than previously thought, expanding the horizon of the TeV Universe.
XMM-Newton observed the soft gamma repeater SGR 1806-20 about two months after its 2004 December 27 giant flare. A comparison with the previous observations taken with the same instrument in 2003-2004 shows that the pulsed fraction and the spin-down rate have significantly decreased and that the spectrum slightly softened. These changes may indicate a global reconfiguration of the neutron star magnetosphere. The spectral analysis confirms that the presence of a blackbody component in addition to the power-law is required. Since this additional component is consistent with being constant with respect to the earlier observations, we explore the possibility of describing the long-term spectral evolution as only due to the power-law variations. In this case, the slope of the power-law does not significantly change and the spectral softening following the giant flare is caused by the increase of the relative contribution of the blackbody over the power-law component.
The opacity of spiral galaxy disks, from counts of distant galaxies, is
compared to HI column densities. The opacity measurements are calibrated using
the ``Synthetic Field Method'' from Gonzalez et al (1998) and Holwerda et al.
(2005a).
When compared for individual disks, the HI column density and dust opacity do
not seem to be correlated as HI and opacity follow different radial profiles.
To improve statistics, an average radial opacity profile is compared to an
average HI profile. Compared to dust-to-HI estimates from the literature, more
extinction is found in this profile. This difference may be accounted for by an
underestimate of the dust in earlier measurements due to their dependence on
dust temperature. Since the SFM is insensitive to the dust temperature, the
ratio between the SFM opacity and HI could very well be indicative of the true
ratio.
Earlier claims for a radially extended cold dust disk were based on sub-mm
observations. A comparison between sub-mm observations and counts of distant
galaxies is therefore desirable. We present the best current example of such a
comparison, M51, for which the measurements seem to agree. However, this
remains an area where improved counts of distant galaxies, sub-mm observations
and our understanding of dust emissivity are needed.
We study the dynamics of thermonuclear flames propagating in fuel stirred by
stochastic forcing. The fuel consists of carbon and oxygen in a state which is
encountered in white dwarfs close to the Chandrasekhar limit. The level set
method is applied to represent the flame fronts numerically. The computational
domain for the numerical simulations is cubic, and periodic boundary conditions
are imposed. The goal is the development of a suitable flame speed model for
the small-scale dynamics of turbulent deflagration in thermonuclear supernovae.
Because the burning process in a supernova explosion is transient and spatially
inhomogeneous, the localised determination of subgrid scale closure parameters
is essential. We formulate a semi-localised model based on the dynamical
equation for the subgrid scale turbulence energy $k_{\mathrm{sgs}}$. The
turbulent flame speed $s_{\mathrm{t}}$ is of the order
$\sqrt{2k_{\mathrm{sgs}}}$. In particular, the subgrid scale model features a
dynamic procedure for the calculation of the turbulent energy transfer from
resolved toward subgrid scales, which has been successfully applied to
combustion problems in engineering. The options of either including or
suppressing inverse energy transfer in the turbulence production term are
compared. In combination with the piece-wise parabolic method for the
hydrodynamics, our results favour the latter option. Moreover, different
choices for the constant of proportionality in the asymptotic flame speed
relation,
$s_{\mathrm{t}}\propto\sqrt{2k_{\mathrm{sgs}}}$, are investigated.
The ``Synthetic Field Method'' (SFM) was introduced by Gonzalez et al. (1998) to calibrate numbers of distant galaxies as a probe of extinction in a foreground spiral disk. Gonzalez et al. (2003) studied the effect of the foreground disk on these numbers using simulations of current and future instruments for fields in the LMC, M31 and NGC 4536, a galaxy in Virgo. They concluded that: (1) the brighter centers of disks were unsuitable, (2) the granularity of the disk at a fixed surface brightness is the limiting factor in the detection of distant galaxies, and (3) the optimum distance for measurements would be that of the Virgo cluster for the current instruments on board HST. At this distance the foreground disk is smoothed with distance, improving detection of distant background galaxies. Holwerda et al. (2005a) automated the SFM and Holwerda et al. (2005b) applied it to a large set of WFPC2 fields. In this paper, the quality of the extinction measurement in these fields is compared to their distance, granularity, surface brightness and structure. The average surface brightness of the of a field is shown to directly influence the accuracy of the SFM. This restricts meaningful measurements to the disks of spiral galaxies. Large structures such as spiral arms have a similar effect. The granularity or small scale structure in a field influences the detection of distant galaxies, limiting the SFM measurements in nearby disks. From the trends in the accuracy and maximum practical field-of-view considerations, the minimum and maximum distance for SFM application, approximately 5 and 35 Mpc respectively. Using the same instrument and detection method, the relations with SFM parameters and field characteristics can be used to forgo the synthetic fields altogether.
We present H-like Fe XXVI and He-like Fe XXV charge-exchange spectra resulting from collisions of highly charged iron with N2 gas at an energy of 10 eV/amu in an electron beam ion trap. Although individual high-n emission lines are not resolved in our measurements, we observe that the most likely level for Fe25+ --> Fe24+ electron capture is n~9, in line with expectations, while the most likely value for Fe26+ --> Fe25+ charge exchange is significantly higher. In the Fe XXV spectrum, the K-alpha emission feature dominates, whether produced via charge exchange or collisional excitation. The K-alpha centroid is lower in energy for the former case than the latter (6666 versus 6685 eV, respectively), as expected because of the strong enhancement of emission from the forbidden and intercombination lines, relative to the resonance line, in charge-exchange spectra. In contrast, the Fe XXVI high-n Lyman lines have a summed intensity greater than that of Ly-alpha, and are substantially stronger than predicted from theoretical calculations of charge exchange with atomic H. We conclude that the angular momentum distribution resulting from electron capture using a multi-electron target gas is significantly different from that obtained with H, resulting in the observed high-n enhancement. A discussion is presented of the relevance of our results to studies of diffuse Fe emission in the Galactic Center and Galactic Ridge, particularly with ASTRO-E2/Suzaku.
Low resolution spectra have been used to measure individual metal abundances of RR Lyrae stars in NGC 6441, a Galactic globular cluster known to have very unusual horizontal branch morphology and periods of the RR Lyrae stars for its high metallicity. We find an average metal abundance of [Fe/H]=-0.69 +/- 0.06 (r.m.s.=0.33 dex) and [Fe/H]=-0.41 +/- 0.06 (r.m.s.=0.36 dex) on Zinn & West and Carretta & Gratton metallicity scales, respectively, consistent with the cluster metal abundance derived by Armandroff & Zinn. Most of the metallicities were extrapolated from calibration relations defined for [Fe/H] < -1; however, they are clearly high and contrast with the rather long periods of the NGC 6441 variables, thus confirming that the cluster does not fit in the general Oosterhoff classification scheme. The r.m.s. scatter of the average is larger than observational errors (0.15-0.16 dex) possibly indicating some spread in metallicity. However, even the metal poor variables, if confirmed to be cluster members, are still more metal rich than those commonly found in the Oosterhoff type II globular clusters.
High redshift (z >~ 1) clusters are ideal probes to study the formation and evolution of large scale structures and galaxies in the universe. A 10-m class ground based telescope, X-ray observatories (Chandra, XMM-Newton) and HST/ACS are allowing us to perform an unprecedented study of distant massive clusters of galaxies in the redshift range 0.84<z<1.3, selected from X-rays surveys. In this paper we summarize our results on the structure and dynamics of two of these clusters derived from imaging and spectroscopic data as well as our results on the evolution of early-type galaxies.
We investigate the rate of false planetary transit detection due to blending with eclipsing binaries. Our approach is purely empirical and is based on the analysis of the artificially blended light curves of the eclipsing binary stars in the Large Magellanic Cloud from the archive of the Optical Gravitational Lensing Experiment (OGLE). Employing parameters that characterize the significance of the transit and the amplitude of the variation out of the transit, we can substantially limit the number of potential false positives. Further constraint comes from the expected length of the transit by a possible planetary companion. By the application of these criteria we are left only with 18 candidates from the full sample of 2495 stars. Visual inspection of these remaining variables eliminates all of them for obvious reasons (e.g., for visible fingerprints of orbital eccentricity). We draw the attention to the short-period stars, where the false alarm rate is especially low.
(Abridged) We present near-IR imaging of the nearby L dwarf Kelu-1 obtained with the Keck sodium laser guide star adaptive optics (LGS AO) system as part of a high angular resolution survey for substellar binaries. Kelu-1 was one of the first free-floating L dwarfs identified, and the origin of its overluminosity compared to other similar objects has been a long-standing question. Our images clearly resolve Kelu-1 into a 0.29'' (5.4 AU) binary, and a previous non-detection by HST demonstrates that the system is a true physical pair. Binarity explains the properties of Kelu-1 that were previously noted to be anomalous compared to other early-L dwarfs. We estimate spectral types of L1.5-L3 and L3-L4.5 for the two components, giving model-derived masses of 0.05-0.07 Msun and 0.045-0.065 Msun for an estimated age of 0.3-0.8 Gyr. More distant companions are not detected to a limit of 5-9 Mjup. The presence of lithium absorption indicates that both components are substellar, but the weakness of this feature relative to other L dwarfs may arise from the fact that only Kelu-1B is Li-bearing. Determining if both or if only one of the components possesses lithium could constrain the age of Kelu-1 (and other Li-bearing L binaries) with higher precision than is possible for most ultracool field objects. These results are the first LGS AO observations of brown dwarfs and demonstrate the potential of this new instrumental capability for substellar astronomy.
We report angular correlation function (ACF) of Lyman Break Galaxies (LBGs) with unprecedented statistical quality from a sample of 16,920 galaxies at z=4 detected in the 1 deg^2 field of the Subaru/XMM-Newton Deep Field. The ACF significantly departs from a power law, and shows an excess on small scale. Particularly, the ACF of LBGs with i'<27.5 have a clear break between the small and large-scale regimes at the angular separation of ~7'' whose projected length corresponds to the virial radius of dark halos with a mass of 10^{11-12} Mo, indicating multiple LBGs residing in a single dark halo. Both on small (2''<theta<3'') and large (40''<theta<400'') scales, clustering amplitudes monotonically increase with luminosity for the magnitude range of i'=24.5-27.5, and the small-scale clustering shows a stronger luminosity dependence than the large-scale clustering. The small-scale bias reaches b~10-50, and the outskirts of small-scale excess extend to a larger angular separation for brighter LBGs. The ACF and number density of LBGs are reasonably reproduced by a halo model in the framework of the halo occupation distribution of the Cold Dark Matter model.
The Sun is the closest star to our planet and it is the most studied,
perhaps, there exist too much procesess not-understood. One of the solar
processes that have a direct interaction with the earth is the solar wind. The
solar wind is defined as the plasma expulsed from the solar atmosphere, this
wind was cataloged and is considered that have three components:
- Passive solar wind: Is the constant component of the solar wind. -
Supersonic and quasistady flux. - Sporadic supersonic flux.
We present and brief explanation of the Parker's model of the solar wind and
a correlation analysis between solar micro radio bursts and the change of the
solar wind parameters.
We construct the Numerical Galaxy Catalog ($\nu$GC), based on a semi-analytic model of galaxy formation combined with high-resolution N-body simulations in a $\Lambda$-dominated flat cold dark matter ($\Lambda$CDM) cosmological model. The model includes several essential ingredients for galaxy formation, such as merging histories of dark halos directly taken from N-body simulations, radiative gas cooling, star formation, heating by supernova explosions (supernova feedback), mergers of galaxies, population synthesis, and extinction by internal dust and intervening HI clouds. As the first paper in a series using this model, we focus on basic photometric, structural and kinematical properties of galaxies at present and high redshifts. Two sets of model parameters are examined, strong and weak supernova feedback models, which are in good agreement with observational luminosity functions of local galaxies in a range of observational uncertainty. Both models agree well with many observations such as cold gas mass-to-stellar luminosity ratios of spiral galaxies, HI mass functions, galaxy sizes, faint galaxy number counts and photometric redshift distributions in optical pass-bands, isophotal angular sizes, and cosmic star formation rates. In particular, the strong supernova feedback model is in much better agreement with near-infrared (K'-band) faint galaxy number counts and redshift distribution than the weak feedback model and our previous semi-analytic models based on the extended Press-Schechter formalism. (Abridged)
We present a comprehensive spectral analysis of black hole X-ray binaries, LMC X-1 and LMC X-3, based on BeppoSAX observations. We test both the multi-color disk plus power law (MCD+PL) model and a newly-developed Monte-Carlo simulation- based model for a Comptonized MCD (CMCD) with either a spherical or a slab-like corona, by comparing the inferred parameters with independent direct measurements. While all models give an adequate description of the spectra, we find a significant discrepancy between the MCD+PL inferred X-ray-absorbing gas column density and the absorption-edge measurement based on dispersed X-ray spectra. The MCD+PL fits to the LMC X-1 spectra also require a change in the inner disk radius during the BeppoSAX observation, which may be due to the nonphysical effects inherited in the model. In contrast, the CMCD model with the spheric corona gives the predictions of both the disk inclination angle and the absorption that are consistent with the direct measurements, and only slightly under-predicts the black hole mass of LMC X-3. The model explains the spectral state evolution of LMC X-1 within the BeppoSAX observation as a change in the accretion rate, which leads to an increase in both the inner disk temperature and the Comptonization opacity. On the other hand, the CMCD model with the slab-like corona is more problematic in the test and is thus not recommended.
We calculate the reverse shock (RS) synchrotron emission in the optical and the radio wavelength bands from electron-positron pair enriched gamma-ray burst ejecta with the goal of determining the pair content of GRBs using early time observations. We take into account an extensive number of physical effects that influence radiation from the reverse-shock heated GRB ejecta. We find that optical/IR flux depends very weakly on the number of pairs in the ejecta, and there is no unique signature of ejecta pair enrichment if observations are confined to a single wavelength band. It may be possible to determine if the number of pairs per proton in the ejecta is > 100 by using observations in optical and radio bands; the ratio of flux in the optical and radio at the peak of each respective reverse-shock light curve is dependent on the number of pairs per proton. We also find that over a large parameter space, RS emission is expected to be very weak; GRB 990123 seems to have been an exceptional burst in that only a very small fraction of the parameter space produces optical flashes this bright. Also, it is often the case that the optical flux from the forward shock is brighter than the reverse shock flux at deceleration. This could be another possible reason for the paucity of prompt optical flashes with a rapidly declining light curve at early times as was seen in 990123 and 021211.
We report the detection of a young stellar population ($\leq$100 Myrs) in the ba ckground of 9 young open clusters belonging to a homogenoeous sample of 30 star clusters in the Third Galactic Quadrant (at $217^o \leq l \leq 260^o$). Deep and accurate UBVRI photometry allows us to measure model-independent age and distance for the clusters and the background population with high confidence. This population is exactly the same population (the Blue Plume) recently detected in 3 intermediate-age open clusters and suggested to be a $\leq$ 1-2 Gyr old population belonging to the Canis Major (CMa) over-density (Bellazzini et al. 2004, Mart\'inez-Delgado et al. 2005). However, we find that the young population in those three and in six clusters of our sample follows remarkably well the pattern of the Norma-Cygnus spiral arm as defined by CO clouds, while in the other three program clusters it lies in the Perseus arm. We finally provide one example (out of 21) of a cluster which does not show any background population, demonstrating that this population is not ubiquitous toward CMa.
We discuss the contribution of Population III stars to the near-IR (NIR) cosmic infrared background (CIB) and its effect on spectra of high-$z$ high-energy gamma-ray bursts (GRBs). It is shown that if Population III were massive stars, the claimed NIR CIB excess will be reproduced if only ~ 4+/-2% of all baryons went through these stars. Regardless of the precise value of the NIR CIB produced by them, they would leave enough photons to provide a large optical depth for high-energy photons from high-z GRBs. Observations of such GRBs are expected following the planned launch of NASA's GLAST mission. The presence or absence of such damping in the spectra of high-$z$ GRBs will then provide important information on the emissions from the Population III. The location of this cutoff may also serve as an indicator of the GRB's redshift.
We report on the angular correlation function of Lyman-break galaxies (LBGs) at z~4 and 5 from deep samples obtained from the Great Observatories Deep Origins Survey (GOODS). Similar to LBGs at z~3, the shape of w(theta) of the GOODS LBGs is well approximated by a power-law with slope beta~0.6 at angular separation theta > 10 arcsec. The clustering strength of z~4, 5 LBGs also depends on the rest-frame UV luminosity, with brighter galaxies more strongly clustered than fainter ones, implying a general correlation between halos' mass and LBGs' star-formation rate. At smaller separations, w(theta) of deep samples significantly exceeds the extrapolation of the large-scale power-law fit, implying enhanced spatial clustering at scales r < 1 Mpc. We also find that bright LBGs statistically have more faint companions on scales theta < 20 arcsec than fainter ones, showing that the enhanced small-scale clustering is very likely due to sub-structure, namely the fact that massive halos can host multiple galaxies. A simple model for the halo occupation distribution and the CDM halo mass function reproduce well the observed w(theta). The scaling relationship of the clustering strength with volume density and with redshift is quantitatively consistent with that of CDM halos. A comparison of the clustering strength of three samples of equal luminosity limit at z ~ 3, 4 and 5 shows that the LBGs at z~5 are hosted in halos about one order of magnitude less massive than those in the lower redshift bins, suggesting that star-formation was more efficient at higher-redshift.
(Abridged) We explore the spatial distribution of stars in the Sculptor dwarf spheroidal (dSph) galaxy over an area of 7.82 deg^2. We identify red giant branch (RGB) starts via Washington M, T_2+DDO51 photometry and a blue horizontal branch (BHB) population to map the spatial structure of the dSph. A spectroscopically observed subset of Sculptor candidate stars yield a systemic heliocentric velocity for the system of v_{hel}=110.43 km/s, in good agreement with previous studies, and a global velocity dispersion of sigma_v=8.8 km/s, which may rise slightly past 0.4r_{lim}. To a limit of M~19, we find 94% of the photometrically-selected Sculptor giant star candidates with spectrocopic measurements are kinematically associated with Sculptor, and four of ten stars not selected photometrically are selected kinematically; our candidate samples are likely to be very pure. We take considerable care in assessing the contaminating background level in our photometric sample to ensure accurate density profiles. These assessments verify that we detect a considerable stellar density of Sculptor stars to the limits of our survey area in both the RGB and BHB samples. We find the Sculptor density profile is well-fit by a King profile of limiting radius r_{lim} = 79.6 within ~60 arcmin, beyond which a "break" to a power law profile occurs. This break population must be either a bound group of "halo stars" around the Sculptor dSph or unbound tidal debris. The latter is supported by 2D distribution analyses and, if true, implies a fractional mass-loss rate of ~0.042 Gyr^{-1} for Sculptor. Finally, likely more metal-poor RGB stars (as selected by color and magnitude) are significantly less centrally concentrated and, therefore, constitute the primary contributor to the likely tidally-stripped parts of the dSph.
We report results from a panoramic spectroscopic survey of 955 objects in the field of the rich cluster Cl 0024+1654 (z~0.4), complementing the HST imaging presented in the first paper in this series. Our new spectroscopic sample includes over 200 high quality spectra of cluster members, spread across an area 10 Mpc in diameter. We examine the properties of a large sample of 104 cluster early-types as a function of cluster radius and local density, using them as sensitive tracers of the various physical processes that may be responsible for galaxy evolution. By constructing the Fundamental Plane of Cl 0024, we infer an evolution in the mean mass to light ratio of early-types equal to \Delta<Log (M/L_V)> = -0.14 +- 0.02. In the cluster center, we detect a significantly increased scatter in the relationship compared to that seen in local clusters. Moreover, we observe a clear radial trend in the mass to light ratios of individual early types, with the oldest galaxies located in the cluster core. Galaxies are apparently younger at larger radius, with E+S0s in the periphery having M/L_V ratios that nearly match values seen in the field at a similar redshift. Independent spectral indicators used in combination reveal an abrupt interaction with the cluster environment which occurs near the virial radius of Cl 0024, revealed by small bursts of star formation in a population of dim early-types, as well as by enhanced Balmer absorption for a set of larger E+S0s closer to the cluster core. We construct a simple infall model used to compare the timescales and strengths of the observed interactions in this cluster. We examine the possibility that bursts of star formation are triggered when galaxies suffer shocks as they encounter the intra-cluster medium, or by the onset of galaxy harassment.
Optical CCD imaging and spectroscopic observations of three supernova remnants are presented. Optical emission from G 54.4-0.3 and G 59.8+1.2 is detected for the first time, while the first flux calibrated CCD images of the supernova remnant G 126.2+1.6 were performed in the optical emission lines of Halpha+[N II], [O III] and [S II]. A mixture of filamentary and diffuse structures is observed in G 54.4-0.3 and G 59.8+1.2, mainly in Halpha+[N II], while the deep optical images of G 126.2+1.6 reveal several new filamentary and diffuse structures inside the extent of the remnant as defined by its known radio emission. In all cases, the radio emission is found to be well correlated with the optical filaments. [O III] emission was not detected at G 54.4-0.3 and G 59.8+1.2 while in G 126.2+1.6, significant morphological differences between the low and medium ionization images are present suggesting incomplete shock structures. Deep long-slit spectra were taken at different positions of the remnants. Both the flux calibrated images and the long-slit spectra clearly show that the emission originates from shock-heated gas, while some spectra of G 126.2+1.6 are characterized by large [O III]/Hbeta ratios. This remnant's [O III] flux suggests shock velocities into the interstellar "clouds" between 100 and 120 km/s, while the [O III] absence in the other two remnants indicates slower shock velocities. For all remnants, the [S II]6716/6731 ratio indicates electron densities below 600 cm^{-3} with particularly low densities for G 54.4-0.3 (below 50 cm^{-3}). Finally, the Halpha emission has been measured to be between 3.0 to 15.2x10^{-17} erg/s/cm^2/ arcsec^2, 3.2x10^{-17} erg/s/cm^2/ arcsec^2 and between 6.5 to 16.8x10^{-17} erg/s/cm^2/ arcsec^2 for G 54.4-0.3, G 59.8+1.2 and G 126.2+1.6, respectively.
We study quasi-stationary, two-and-a-half-dimensional magnetic reconnection in the framework of incompressible resistive MHD. We use a new theoretical approach for calculation of the reconnection rate. This approach is based on local analytical derivations in a thin reconnection layer and it allows us to consider the case when resistivity is anomalous and is an arbitrary function of the electric current and the spatial coordinates. We find that a quasi-stationary reconnection rate is fully determined by a particular functional form of the anomalous resistivity and by the local configuration of the magnetic field just outside the reconnection layer in the direction across the layer. We also find that in the special case of constant resistivity reconnection is Sweet-Parker and not Petschek.
We present spectroscopic observations of the black-hole binary V4641 Sagittarii, obtained between 4th July 2004 and 28th March 2005, which cover the minor outburst of the star in early July 2004 and quiescence variations on 19 nights scattered over six months. During the outburst, the star peaked approximately 3 magnitudes brighter than usual, and our spectra were dominated by broad hydrogen, helium and iron emission lines. The very first spectra showed P Cygni profiles, which disappeared within a few hours, indicating rapid changes in matter ejection. The H-alpha line had multiple components, one being a broad blue-shifted wing exceeding 5000 km/s. During a simultaneously observed 10-min photometric flare-up, the equivalent width of the H-alpha line temporarily decreased, implying that it was a flare of the continuum. The overall spectral appearance was similar to that observed in the 1999 September active phase, which suggests that similar mass-ejection processes were associated with both eruptions. In quiescence, the spectra were those of the early-type secondary star showing its orbital motion around the primary. By measuring cross-correlation radial velocities, we give an improved set of spectroscopic elements. Whereas we measure the same velocity amplitude (K_2=211.3+/-1.0 km/s), within errors, as Orosz et al. (2001), our centre-of-mass velocity (v_gamma=72.7+/-3.3 km/s) differs significantly from the previously published value (107.4+/-m2.9 km/s). However, we find evidence that the difference is caused by a systematic error in data reduction in the previous study, rather than by gravitational effects of an invisible third component.
We present an analysis of spectral line bisector variations for a few stars observed in the SARG high precision radial velocity planet survey, and discuss their relationship with differential radial velocities. The spectra we consider are the same used for determining radial velocities. The iodine cell lines employed in the measurement of radial velocities were removed before bisector analysis. The line bisectors were then computed from average absorption profiles obtained by cross correlation of the stellar spectra with a mask made from suitable lines of a solar catalog. Bisector velocity spans were then determined: errors in these quantities compare well with theoretical expectations based on resolution, S/N and line shape. The plot of bisector velocity span against radial velocity was studied to search for correlations between line asymmetries and radial velocity variations. A correlation was seen for HD 166435 due to stellar activity, and for HD 8071B due to spectral contamination by the companion. No correlation was seen for 51 Peg and rho CrB, stars hosting planets. We conclude that this technique may be useful to separate radial velocity variations due to barycenter motion from spurious signals in spectra acquired with the iodine cell.
We have estimated the bulge-to-total ($B/T$) light ratios in the $K_s$-band for a sample of 24 S0, S0/a and Sa galaxies by applying a 2-dimensional multicomponent decomposition method. For the disk an exponential function is used, the bulges are fitted by a S\'ersic's $R^{1/n}$ function and the bars and ovals are described either by a S\'ersic or a Ferrers function. In order to avoid non-physical solutions, preliminary characterization of the structural components is made by inspecting the radial profiles of the orientation parameters and the low azimuthal wavenumber Fourier amplitudes and phases. In order to identify also the inner structures, unsharp masks were created: previously undetected inner spiral arms were found in NGC 1415 and marginally in NGC 3941. Most importantly, we found that S0s have a mean $<B/T>_K$-ratio of 0.24 $\pm$ 0.11, which is significantly smaller than the mean $<B/T>_R$ = 0.6 generally reported in the literature. Also, the surface brightness profiles of the bulges in S0s were found to be more exponential-like than generally assumed, the mean shape parameter of the bulge being $<n>$ = 2.1 $\pm$ 0.7. We did not find examples of barred S0s lacking the disk component, but we found some galaxies (NGC 718, NGC 1452, NGC 4608) having a non-exponential disk in the bar region. To our knowledge our study is the first attempt to apply a multicomponent decomposition method for a moderately sized sample of early-type disk galaxies
The results are presented of a molecular line survey to search for the spectral signature of infall towards 77 850 micron continuum sources believed to be candidate high mass protostellar objects. Up to six different transitions, HCO+ 1-0, 3-2 and 4-3, H2CO 2_12-1_11, N2H+ and H13CO+ 3-2, were observed towards each source. Towards the peak of the 850 micron emission, N2H+ was typically strong, with a peak antenna temperature of ~1.5K, with a typical linewidth of ~2km/s. The good agreement between the velocity and velocity width of the N2H+ and H13CO+ emission suggests that both species are tracing similar material in the sources. With respect to the velocity of the N2H+, there is a statistically significant excess of blue asymmetric line profiles in both the HCO+ 1-0 and H2CO transitions. This excess reaches levels similar to that seen towards samples of low mass protostars, and suggests that the material around these high mass sources is infalling. We identify 22 promising candidate infall sources which show at least one blue asymmetric line profile and no red asymmetric profiles. The infall velocity is estimated to be in the range of 0.1 km/s to 1 km/s with an implied mass accretion rate of between 2x10^{-4} Msol/yr and 10^{-3}Msol/yr.
I present recent observations and analyses of star cluster formation in a wide variety of environments -- from young star clusters and super star clusters in normal actively star-forming spirals and irregulars to starbursting dwarfs and spiral-spiral mergers. Star cluster formation in interacting galaxies can be restricted to central starburst region, extend over the entire body of the merger, or even all along extended tidal structures. I address methods and results for the determination of star cluster ages, metallicities, masses, and sizes and discuss the nature, possible lifetimes and future signatures of these star cluster populations, as well as the relative importance of field star formation vs. star cluster formation.
In a previous paper (Brunetti et al. 2004) we presented the first self-consistent calculations of the time-dependent coupled equations for the electrons, hadrons and Alfv\'en waves in the intracluster medium, which describe the stochastic acceleration of the charged particles and the corresponding spectral modification of the waves. Under viable assumptions, this system of mutually interacting components was shown to accurately describe several observational findings related to the radio halos in clusters of galaxies. In this paper, we add to the self-consistency of the calculations by including the generation and re-energization of secondary electrons and positrons, produced by the inelastic interactions of cosmic rays with the thermal gas in the intracluster medium. The bulk of Cosmic rays is expected to be confined within the cluster volume for cosmological times, so that the rate of production of secondary electrons, as well as gamma rays, may become correspondingly enhanced. If MHD waves are present, as it may be expected in the case of a recent merger event, then the reacceleration of secondary electrons and positrons can significantly affect the phenomenology of the non thermal processes in clusters. We investigate here these effects for the first time.
We present a model atmosphere analysis of ten new DO white dwarfs and five new PG1159 stars discovered in the Sloan Digital Sky Survey DR1, DR2 and DR3. This is a significant increase in the number of known DOs and PG1159 stars. DO white dwarfs are situated on the white dwarf cooling sequence from the upper hot end Teff ~ 120 000 K down to the DB gap (Teff ~ 45 000 K). PG1159 stars on the other hand feature effective temperatures which exceed Teff = 65 000 K with an upper limit of Teff = 200 000 K and are the proposed precursors of DO white dwarfs. Improved statistics are necessary to investigate the evolutionary link between these two types of stars. From optical SDSS spectra effective temperatures, surface gravities and element abundances are determined by means of non-LTE model atmospheres.
The environmental properties of a sample of 31 hard X-ray selected AGN are
investigated, from scales of 500 kpc down to 30 kpc, and are compared to a
control sample of inactive galaxies. The AGN all lie in the redshift range
0.4<z<0.6. The accretion luminosity-density of the Universe peaks close to this
redshift range, and the AGN in the sample have X-ray luminosities close to the
knee in the hard X-ray luminosity function, making them representative of the
population which dominated this important phase of energy conversion.
Using both the spatial clustering amplitude and near neighbour counts it is
found that the AGN have environments that are indistinguishable from normal,
inactive galaxies over the same redshift range and with similar optical
properties. Typically, the environments are of sub-cluster richness, in
contrast to similar studies of high-z quasars, which are often found in
clusters with comparable richness to the Abell R>=0 clusters.
It is suggested that minor mergers with low mass companions is a likely
candidate for the mechanism by which these modest luminosity AGN are fuelled.
Massive young stellar objects (YSOs) are powerful infrared H I line emitters. It has been suggested that these lines form in a outflow from a disk surrounding the YSO. Here, new two-dimensional Monte Carlo radiative transfer calculations are described which test this hypothesis. Infrared spectra are synthesised for a YSO disk wind model based on earlier hydrodynamical calculations. The model spectra are in qualitative agreement with the observed spectra from massive YSOs, and therefore provide support for a disk wind explanation for the H I lines. However, there are some significant differences: the models tend to overpredict the Br alpha/Br gamma ratio of equivalent-widths and produce line profiles which are slightly too broad and, in contrast to typical observations, are double-peaked. The interpretation of these differences within the context of the disk wind picture and suggestions for their resolution via modifications to the assumed disk and outflow structure are discussed.
The entrainment matrix (also termed the Andreev-Bashkin matrix or the mass-density matrix) for a neutron-proton mixture is derived at a finite temperature in a neutron star core. The calculation is performed in the frame of the Landau Fermi-liquid theory generalized to account for superfluidity of nucleons. It is shown, that the temperature dependence of the entrainment matrix is described by a universal function independent on an actual model of nucleon-nucleon interaction employed. The results are presented in the form convenient for their practical use. The entrainment matrix is important, e.g., in kinetics of superfluid nucleon mixtures or in studies of the dynamical evolution of neutron stars (in particular, in the studies of star pulsations and pulsar glitches).
The moment of inertia of the pulsar A in the neutron star binary J0737-3039 will soon be measurable through detailed measurements of the periastron advance. We present the calculation of the moment of inertia of neutron stars with the masses of the components of the binary J0737-3039 for a broad range of equations of state of dense matter and discuss the implications of such measurement for constraining the equation of state. An observational determination of the moment of inertia of the pulsar A in J0737-3039 with the accuracy of 10% shall narrow down considerably the range of viable equations of state. We also show that limits on maximal mass of a neutron star provide a complementary set of constraints on the properties of dense nuclear matter.
A massive black hole resides in the center of most, perhaps all galaxies. The
one in the center of our home galaxy, the Milky Way, provides a uniquely
accessible laboratory for studying in detail the connections and interactions
between a massive black hole and the stellar system in which it grows; for
investigating the effects of extreme density, velocity and tidal fields on
stars; and for using stars to probe the central dark mass and probe
post-Newtonian gravity in the weak- and strong-field limits. Recent results,
open questions and future prospects are reviewed in the wider context of the
theoretical framework and physical processes that underlie them.
Contents: [1] Introduction (1.1) Astrophysical context (1.2) Science
questions (1.3) Scope and connections to related topics [2] Observational
overview: Stars in the Galactic center (2.1) The central 100 parsecs (2.2) The
central parsec [3] Stellar dynamics at extreme densities (3.1) Physical
processes and scales (3.2) The stellar cusp in the Galactic center (3.3) Mass
segregation (3.4) Stellar Collisions [4] Probing the dark mass with stellar
dynamics (4.1) Weighing and pinpointing the dark mass (4.2) Constraints on
non-BH dark mass alternatives (4.3) Limits on MBH binarity (4.4) High-velocity
runaway stars [5] Probing post-Newtonian gravity near the MBH (5.1)
Relativistic orbital effects (5.2) Gravitational lensing [6] Strong star-MBH
interactions (6.1) Tidal disruption (6.2) Dissipative interactions with the MBH
[7] The riddle of the young stars (7.1) The difficulties of forming or
importing stars near a MBH (7.2) Proposed solutions (7.3) Feeding the MBH with
stellar winds [8] Outlook (8.1) Progress report (8.2) Future directions
We present an investigation of the metal enrichment of the intra-cluster medium (ICM) by galactic winds and merger-driven starbursts. We use combined N-body/hydrodynamic simulations with a semi-numerical galaxy formation model. The mass loss by galactic winds is obtained by calculating transonic solutions of steady state outflows, driven by thermal, cosmic ray and MHD wave pressure. The inhomogeneities in the metal distribution caused by these processes are an ideal tool to reveal the dynamical state of a galaxy cluster. We present surface brightness, X-ray emission weighted temperature and metal maps of our model clusters as they would be observed by X-ray telescopes like XMM-Newton. We show that X-ray weighted metal maps distinguish between pre- or post-merger galaxy clusters by comparing the metallicity distribution with the galaxy-density distribution: pre-mergers have a metallicity gap between the subclusters, post-mergers a high metallicity between subclusters. We apply our approach to two observed galaxy clusters, Abell 3528 and Abell 3921, to show whether they are pre- or post-merging systems. The survival time of the inhomogeneities in the metallicity distribution found in our simulations is up to several Gyr. We show that galactic winds and merger-driven starbursts enrich the ICM very efficiently after z=1 in the central (~ 3 Mpc radius) region of a galaxy cluster.
We present new results from our spectral analyses of very hot central stars achieved since the last IAU Symposium on planetary nebulae held in Canberra 2001. The analyses are mainly based on UV and far-UV spectroscopy performed with the Hubble Space Telescope and the Far Ultraviolet Spectroscopic Explorer but also on ground-based observations performed at the Very Large Telescope and other observatories. We report on temperature, gravity, and abundance determinations for the CNO elements of hydrogen-rich central stars. In many hydrogen-deficient central stars (spectral type PG1159) we discovered particular neon and fluorine lines, which are observed for the very first time in any astrophysical object. Their analysis strongly confirms the idea that these stars exhibit intershell matter as a consequence of a late helium-shell flash.
We analyze the respective benefits and drawbacks of ground-based and space-based transit surveys for extrasolar planets. Based on simple but realistic assumptions about the fraction of lower main sequence stars harboring telluric and giant planets within the outer limit of the habitable zone, we predict the harvests of fictitious surveys with three existing wide field optical and near-IR cameras: the CFHT-Megacam, SUBARU-Suprime and VISTA-IR. An additional promising instrument is considered, VISTA-Vis, currently under development. The results are compared with the harvests predicted under exactly the same assumptions, for the space missions COROT and KEPLER. We show that ground-based wide field surveys may discover more giant planets than space missions such as COROT or KEPLER, and that they are as efficient as COROT at detecting telluric planets. The KEPLER mission remains the more promising way of discovering telluric planets, being 50 times more efficient than any of the ground-based surveys considered here. KEPLER might even discover telluric planets in the habitable zone of their host star.
We report on a study of young star cluster complexes in the spiral galaxy M51. Recent studies have confirmed that star clusters do not form in isolation, but instead tend to form in larger groupings or complexes. We use {\it HST} broad and narrow band images (from both {\it WFPC2} and {\it ACS}), along with {\it BIMA}-CO observations to study the properties and investigate the origin of the e complexes. We find that the complexes are all young ($< 10$ Myr), have sizes between $\sim$85 and $\sim$240 pc, and have masses between 3-30 $\times 10^{4} M_{\odot}$. Unlike that found for isolated young star clusters, we find a strong correlation between the complex mass and radius, namely $M\propto R^{2.33 \pm 0.19}$. This is similar to that found for giant molecular clouds (GMCs). By comparing the mass-radius relation of GMCs in M51 to that of the complexes we can estimate the star formation efficiency within the complexes, although this value is heavily dependent on the assumed CO-to-H$_2$ conversion factor. The complexes studied here have the same surface density distribution as individual young star clusters and GMCs. If star formation within the complexes is proportional to the gas density at that point, then the shared mass-radius relation of GMCs and complexes is a natural consequence of their shared density profiles. We briefly discuss possibilities for the lack of a mass-radius relation for young star clusters. We note that many of the complexes show evidence of merging of star clusters in their centres, suggesting that larger star clusters can be produced through the build up of smaller clusters.
Recently, Guidorzi et al. (2005) expanded the size of the sample of GRBs for which variabilities and peak luminosities have been measured, from 11 to 32. They confirm the existence of a correlation, but find a dramatically different relationship between L and V than had originally been found. We find that this is the result of improper statistical methodology. When we fit a model to the data that accommodates both statistical variance (in two dimensions) and sample variance, we find that L ~ V^3.4(+0.9,-0.6) with a sample variance of sigma_logV = 0.20(+0.04,-0.04), which is consistent with the original finding of Reichart et al. (2001) -- L ~ V^3.3(+1.1,-0.9) with a sample variance of sigma_logV = 0.18(+0.07,-0.05) -- and inconsistent with the finding of Guidorzi et al. (2005): L ~ V^1.3(+0.8,-0.4) with sample variance assumed to be zero.
We present results from Chandra observations of 14 ultraluminous infrared galaxies (ULIRGs; log(L_IR/L_Sun) >= 12) with redshifts between 0.04 and 0.16. The goals of the observations were to investigate any correlation between infrared color or luminosity and the properties of the X-ray emission and to attempt to determine whether these objects are powered by starbursts or active galactic nuclei (AGNs). The sample contains approximately the same number of high and low luminosity objects and ``warm'' and ``cool'' ULIRGs. All 14 galaxies were detected by Chandra. Our analysis shows that the X-ray emission of the two Seyfert 1 galaxies in our sample are dominated by AGN. The remaining 12 sources are too faint for conventional spectral fitting to be applicable. Hardness ratios were used to estimate the spectral properties of these faint sources. The photon indices for our sample plus the Chandra-observed sample from Ptak et al.(2003) peak in the range of 1.0-1.5, consistent with expectations for X-ray binaries in a starburst, an absorbed AGN, or hot bremsstrahlung from a starburst or AGN. The values of photon index for the objects in our sample classified as Seyferts (type 1 or 2) are larger than 2, while those classified as HII regions or LINERs tend to be less than 2. The hard X-ray to far-infrared ratios for the 12 weak sources are similar to those of starbursts, but we cannot rule out the possibility of absorbed, possibly Compton-thick, AGNs in some of these objects. Two of these faint sources were found to have X-ray counterparts to their double optical and infrared nuclei.
We present optical and near-infrared finding charts taken from the DSS and 2MASS surveys of 94 IRAS sources selected from the GLMP catalogue (Garc\'{\i}a-Lario 1992), and accurate astrometry (~0.2") for most of them. Selection criteria were very red IRAS colours representative for OH/IR stars with optically thick circumstellar shells and the presence of variability according to the IRAS variability index (VAR>50). The main photometric properties of the stars in this `GLMP sample' are presented, discussed and compared with the correspondent properties of the `Arecibo sample' of OH/IR stars studied in Jim\'enez-Esteban et al. (2005a). We find that 37% of the sample (N=34) have no counterpart in the 2MASS, implying extremely high optical depths of their shells. Most of the sources identified in the 2MASS are faint (K>~8) and of very red colour in the near-infrared, as expected. The brightest 2MASS counterpart (K=5.3mag) was found for IRAS 18299--1705. Its blue colour H--K=1.3 suggests that IRAS 8299--1705 is a post-AGB star. A couple of GLMP sources have faint but relatively blue counterparts. They might be misidentifed field stars or stars hich experienced recently a drop of their mass loss rates. The `GLMP sample' in general is made of oxygen-rich AGB stars, which are highly obscured by their circumstellar shells. They belong to the same population as the reddest OH/IR stars in the `Arecibo sample'.
Observational evidence indicates a mismatch between the shapes of collisionless dark matter (DM) halos and those of observed systems. Using hydrodynamical cosmological simulations we investigate the effect of baryonic dissipation on halo shapes. We show that dissipational simulations produce significantly rounder halos than those formed in equivalent dissipationless simulations. Gas cooling causes an average increase in halo principal axis ratios of ~ 0.2-0.4 in the inner regions and a systematic shift that persists out to the virial radius, alleviating any tension between theory and observations. Although the magnitude of the effect may be overestimated due to overcooling, cluster formation simulations designed to reproduce the observed fraction of cold baryons still produce substantially rounder halos. Subhalos also exhibit a trend of increased axis ratios in dissipational simulations. Moreover, we demonstrate that subhalos are generally rounder than corresponding field halos even in dissipationless simulations. Lastly, we analyze a series of binary, equal-mass merger simulations of disk galaxies. Collisionless mergers reveal a strong correlation between DM halo shape and stellar remnant morphology. In dissipational mergers, the combination of strong gas inflows and star formation leads to an increase of the DM axis ratios in the remnant. All of these results highlight the vital role of baryonic processes in comparing theory with observations and warn against over-interpreting discrepancies with collisionless simulations on small scales.
Despite a rich phenomenology, gamma-ray bursts (GRBs) are divided into two classes based on their duration and spectral hardness -- the long-soft and the short-hard bursts. The discovery of afterglow emission from long GRBs was a watershed event, pinpointing their origin to star forming galaxies, and hence the death of massive stars, and indicating an energy release of about 10^51 erg. While theoretical arguments suggest that short GRBs are produced in the merger of compact object binaries (neutron stars or black holes), the progenitors, energetics, and environments of these events remain elusive despite recent localizations. Here we report the discovery of radio, optical, and infrared afterglow emission from the short-hard GRB 050724, which unambiguously associate it with an elliptical galaxy at a redshift, z=0.257. We show that the energy release is 1-3 orders of magnitude smaller than that of long GRBs, and that the burst ejecta may be collimated in jets. More importantly, the nature of the host galaxy for the first time indicates that short GRBs arise from an old (>1 Gyr) stellar population, thereby providing direct support for coalescing compact object binaries as the progenitors.
We present a study of galaxies and intergalactic gas toward the z=2.73 quasar HS1700+6416, to explore the effects of galaxy formation feedback on the IGM. Our observations and ionization simulations indicate that the volume within 100-200 h_71^{-1} physical kpc of high-redshift galaxies contains very small, dense, and metal-rich absorption-line regions. These systems often contain shock-heated gas seen in OVI, and may exhibit [Si/C] abundance enhancements suggestive of Type II supernova enrichment. We argue that the absorbers resemble thin sheets or bubbles, whose physical properties can be explained with a simple model of radiatively efficient shocks propegating through the IGM. Their high metallicities suggest that these shocks are being expelled from--rather than falling into--star forming galaxies. There is a dropoff in the IGM gas density at galaxy impact parameters beyond ~300 physical kpc that may trace boundaries of gas structures where the galaxies reside. The local heavy-element enhancement covers 100-200 kpc; beyond this the observed abundances blend into the general IGM. Supernova-driven winds or dynamical stripping of interstellar gas appears to affect the IGM near massive galaxies, even at R>~100 kpc. However, these feedback systems represent only a few percent of the Lya forest mass at z~2.5. Their mass could be larger if the more numerous metal-poor CIV systems at >~200 kpc are tepid remnants of very powerful winds. Based on present observations it is not clear that this scenario is to be favored over one involving pre-enrichment by smaller galaxies at z>~6.
We present high resolution CO J=1-0 observations of the molecular gas in the Hickson Compact Group Stephan's Quintet (HCG92). Our observations consist of multiple pointing and mosaics covering all the regions where CO and star formation has been detected. Within the 100'' field of view centered on the eastern-most tidal tail, we detect three clumps of emission that may be partially resolved at our resolution of 8''; two of these are new detections not previously seen in ISM studies of this region. Two of these clumps lie in the optical tidal tail, while the third lies to the southeast and is coincident with a large HI feature, but does not correspond to any features at other wavelengths. We also tentatively detect CO emission from the star forming regions in the ``Old Tail'' corresponding to recent star formation activity detected in recent UV and H$\alpha$ observations. Observations of the rest of the compact group do not show detections even though strong emission was detected with single dish telescopes, which suggests the CO emission originates from a diffuse molecular gas cloud or from more at least three separate clumps with separations of greater than around 3 kpc.
We explore the use of the tangential component of weak lensing shear to characterize the ellipticity of clusters of galaxies. We introduce an ellipticity estimator, and quantify its properties for isolated clusters from LCDM N-body simulations. We compare the N-body results to results from smooth analytic models. The expected distribution of the estimator for mock observations is presented, and we show how this distribution is impacted by contaminants such as noise, line of sight projections, and misalignment of the central galaxy used to determine the orientation of the triaxial halo. We examine the radial profile of the estimator and discuss tradeoffs in the observational strategy to determine cluster shape.
We consider cosmological applications of galaxy number density correlations to be inferred from future deep and wide multi-band optical surveys. We mostly focus on very large scales as a probe of possible features in the primordial power spectrum. We find the proposed survey of the Large Synoptic Survey Telescope may be competitive with future all-sky CMB experiments over a broad range of scales. On very large scales the inferred power spectrum is robust to photometric redshift errors, and, given a sufficient number density of galaxies, to angular variations in dust extinction and photometric calibration errors. We also consider other applications, such as constraining dark energy with the two CMB-calibrated standard rulers in the matter power spectrum, and controlling the effect of photometric redshift errors to facilitate the interpretation of cosmic shear data. We find that deep photometric surveys over wide area can provide constraints that are competitive with spectroscopic surveys in small volumes.
(abridged) We investigate in detail the role of active galactic nuclei on the physical state of the gas in galaxy groups and clusters, and the implications for anisotropy in the CMB from Sunyaev-Zeldovich effect. We include the effect of thermal conduction, and find that the resulting profiles of temperature and entropy are consistent with observations. Unlike previously proposed models, our model predicts that isentropic cores are not an inevitable consequence of preheating. The model also reproduces the observational trend for the density profiles to flatten in lower mass systems. We deduce the energy E_agn required to explain the entropy observations as a function of mass of groups and clusters M_cl and show that E_agn is proportional to M_cl^alpha with alpha~1.5. We demonstrate that the entropy measurements, in conjunction with our model, can be translated into constraints on the cluster--black hole mass relation. The inferred relation is nonlinear and has the form M_bh\propto M_cl^alpha. This scaling is an analog and extension of a similar relation between the black hole mass and the galactic halo mass that holds on smaller scales. We show that the central decrement of the CMB temperature is reduced due to the enhanced entropy of the ICM, and that the decrement predicted from the plausible range of energy input from the AGN is consistent with available data of SZ decrement. We show that AGN heating, combined with the observational constraints on entropy, leads to suppression of higher multipole moments in the angular power spectrum and we find that this effect is stronger than previously thought.
We carried out an unbiased survey for massive dense cores in the giant molecular cloud associated with eta Carinae with the NANTEN telescope in 12CO, 13CO, and C18O 1-0 emission lines. We identified 15 C18O cores. Two of the 15 cores are associated with IRAS point sources whose luminosities are larger than 10^4 Lo, which indicates that massive star formation is occuring within these cores. Five cores including the two with IRAS sources are associated with MSX point sources. We detected H13CO+ (1-0) emission toward 4 C18O cores, one of which is associated with neither IRAS nor MSX point sources. This core shows the presence of a bipolar molecular outflow in 12CO (2-1), which indicates that star formation is also occuring in the core. In total, six C18O cores out of 15 are experienced star formation, and at least 2 of 15 are massive-star forming cores in the eta Car GMC. We found that massive star formation occurs preferentially in cores with larger column density, mass, number density, and smaller ratio of virial mass to LTE mass Mvir/M. We also found that the cores in the eta Car GMC are characterized by large line width and Mvir/M on average compared to the cores in other GMCs. We investigated the origin of a large amount of turbulence in the eta Car GMC. We propose the possibility that the large turbulence was pre-existing when the GMC was formed, and is now dissipating. Mechanisms such as multiple supernova explosions in the Carina flare supershell may have contributed to form a GMC with a large amount of turbulence.
We discuss a new class of solutions to the Einstein equations which describe a primordial black hole in a flat Friedmann background. Such solutions arise if a Schwarzschild black hole is patched onto a Friedmann background via a transition region. They are possible providing the black hole event horizon is larger than the cosmological apparent horizon. Such solutions have a number of strange features. In particular, one has to define the black hole and cosmological horizons carefully and one then finds that the mass contained within the black hole event horizon decreases when it is larger than the Friedmann cosmological apparent horizon, although its area always increases. These solutions involve two distinct future null infinities and are interpreted as the conversion of a white hole into a black hole. Although such solutions may not form from gravitational collapse in the same way as standard primordial black holes, there is nothing unphysical about them, since all energy and causality conditions are satisfied. Their conformal diagram is a natural amalgamation of the Kruskal diagram for the extended Schwarzschild solution and the conformal diagram for a black hole in a flat Friedmann background. In this paper, such solutions are obtained numerically for a spherically symmetric universe containing a massless scalar field, but it is likely that they exist for more general matter fields and less symmetric systems.
(Abridged) We review recent observations that suggest the star formation rate density is declining over 3$<z<$7 and illustrate the challenges that this poses in explaining the assembled stellar mass in z$\sim$6 galaxies deduced from Spitzer data. A plausible conclusion is a vigorous period of earlier star formation. Prior to JWST and TMT, strong lensing offers a unique probe of the extent of this earlier activity. We discuss the first results of a blind spectroscopic survey of lensing clusters for 8.5$<z<$10 Ly$\alpha$ emitters using NIRSPEC which is achieving a limiting star formation rate of 0.1 $M_{\odot}$ yr$^{-1}$. A companion HST/IRAC survey is targeting lensed $z$ and $J$-band dropouts and probes a $\simeq$1 arcmin$^2$ region 1 magnitude deeper than the UDF/NICMOS observations. Both surveys will constrain the contribution of early, low luminosity, sources to cosmic reionization.
The ratio between far-ultraviolet (FUV) and infrared (IR) luminosity densities from z=0 to z=1 is discussed by using the luminosity functions (LFs) of both wavelengths. The FUV LF (z=0-1) based on GALEX has been reported by Arnouts et al. (2005), whilst for the IR LF, we used the IRAS PSCz 60-um LF for the local universe and the Spitzer 15-um LF at higher-z as used by Le Floch et al. (2005). Both luminosity densities show a significant evolutionary trend, but the IR evolves much faster than the FUV. Consequently, the ratio $\rho_{dust}/\rho_{FUV}$ increases toward higher-z, from 4 (local) to 15 (z = 1). It is also shown that more than 70% of the star formation activity in the universe is obscured by dust at 0.5 < z < 1.2.
The early F dwarf star ``J37'' in the open cluster NGC6633 shows an unusual pattern of photospheric abundances, including an order of magnitude enhancement of lithium and iron-peak elements, but an under-abundance of carbon. As a consequence of its thin convection zone these anomalies have been attributed to either radiative diffusion or the accretion of hydrogen-depleted material. By comparing high resolution VLT/UVES spectra of J37 (and other F stars in NGC 6633) with syntheses of the Be ii doublet region at 3131 Ang, we establish that J37 also has a Be abundance (A(Be)=3.0+/-0.5) that is at least ten times the cosmic value. This contradicts radiative diffusion models that produce a Li over-abundance, as they also predict photospheric Be depletion. Instead, since Be is a highly refractory element, it supports the notion that J37 is the first clear example of a star that has accreted volatile-depleted material with a composition similar to chondritic meteorites, although some diffusion may be necessary to explain the low C and O abundances.
Recent gamma-ray burst observations have revealed late-time, highly energetic events which deviate from the simplest expectations of the standard fireball picture. Instead they may indicate that the central engine is active or restarted at late times. We suggest that fragmentation and subsequent accretion during the collapse of a rapidly rotating stellar core offers a natural mechanism for this.
I recall the well-known sufficient conditions for the bound $r<16\epsilon$ on the spectrum of the primordial tensor perturbation. Two recent papers claim a violation of this bound, without stating explicitely any violation of the sufficient conditions.
The Ibis/Isgri imager on Integral detected for the first time a hard X-ray source, IGR J17456-2901, located within 1' of Sgr A* over the energy range 20-100 keV. Here we present the results of a detailed analysis of ~7 Ms of Integral observations of the GC. With an effective exposure of 4.7 Ms we have obtained more stringent positional constraints on this HE source and constructed its spectrum in the range 20-400 keV. Furthermore, by combining the Isgri spectrum with the total X-ray spectrum corresponding to the same physical region around SgrA* from XMM data, and collected during part of the Integral observations, we constructed and present the first accurate wide band HE spectrum for the central arcmins of the Galaxy. Our complete analysis of the emission properties of IGR shows that it is faint but persistent with no variability above 3 sigma contrary to what was alluded to in our first paper. This result, in conjunction with the spectral characteristics of the X-ray emission from this region, suggests that the source is most likely not point-like but, rather, that it is a compact, yet diffuse, non-thermal emission region. The centroid of IGR is estimated to be R.A.=17h45m42.5, decl.=-28deg59'28'', offset by 1' from the radio position of Sgr A* and with a positional uncertainty of 1'. Its 20-400 keV luminosity at 8 kpc is L=5.4x10^35 erg/sec. Very recently, Hess detected of a source of ~TeV g-rays also located within 1' of Sgr A*. We present arguments in favor of an interpretation according to which the photons detected by Integral and Hess arise from the same compact region of diffuse emission near the central BH and that the supernova remnant Sgr A East could play an important role as a contributor of very HE g-rays to the overall spectrum from this region.
We present results of the XMM-Newton observation on the bright X-ray binary Cyg X-2. In our analysis we focus upon the absorption and scattering of the X-ray emission by interstellar dust. The scattering halo around Cyg X-2, observed with the CCD detector EPIC-pn, is well detected up to ~7 arcmin and contributes ~5-7% to the total source emission at 1 keV, depending on the dust size distribution model considered. For the first time spatially resolved spectroscopy of a scattering halo is performed. In the halo spectrum we clearly detect the signature of the interstellar dust elements: O, Mg, and Si. The spectral modeling of the halo shows a major contribution of silicates (olivine and pyroxene). The spatial analysis of the halo shows that the dust is smoothly distributed toward Cyg X-2 at least for ~60% of the path to the source. Within the instrumental limits, the data do not show preference for a specific dust size distribution; namely the Mathis, Rumpl & Nordsieck (1977) or the Weingartner & Draine (2001) model. We used the Mie theory to compute the differential scattering cross section. The RGS data were used to investigate the ISM absorption, in particular the region of the oxygen edge. Combining the RGS results with the information on dust grains provided by the EPIC-pn spectrum of the halo we estimate a column density for dust absorption by oxygen, provided that it is locked in silicate grains (abridged).
We present observations of a new very low mass field binary, discovered during an infrared imaging survey of 250 DENIS L and very late-M dwarfs. DENIS-J055146.0-443412.2 is an M8.5+L0 pair, with a physical separation of over 200 AU. This makes it the widest very low mass binary known in the field, by an order of magnitude. Such a system is fragile, and it would not have survived a close encounter with a third body. Its existence demonstrate that some very low mass stars/brown dwarfs form without ejection from a multiple system, or any other strong dynamical interaction.
We analyse SAURON kinematic maps of the inner kpc of the early-type (Sa) barred spiral galaxy NGC 5448. The observed morphology and kinematics of the emission-line gas is patchy and perturbed, indicating clear departures from circular motion. The kinematics of the stars is more regular, and displays a small inner disk-like system embedded in a large-scale rotating structure. We focus on the [OIII] gas, and use a harmonic decomposition formalism to analyse the gas velocity field. The higher-order harmonic terms and the main kinematic features of the observed data are consistent with an analytically constructed simple bar model, which is derived using linear theory. Our study illustrates how the harmonic decomposition formalism can be used as a powerful tool to quantify non-circular motions in observed gas velocity fields.
We constrain the evolution of the dark energy density from Cosmic Microwave Background, Large Scale Structure and Supernovae Ia measurements. While Supernovae Ia are most sensitive to the equation of state $w_0$ of dark energy today, the Cosmic Microwave Background and Large Scale Structure data best constrains the dark energy evolution at earlier times. For the parametrization used in our models, we find $w_0 < -0.8$ and the dark energy fraction at very high redshift $\Omega_{early} < 0.03$ at 95 per cent confidence level.
The 1 - 5 micron diffuse sky emission from which local foreground emission from the solar system and the Galaxy have been subtracted exceeds the brightness that can be attributed to normal star forming galaxies. The nature of this excess near-infrared background light (NIRBL) is still controversial. On one hand, it has been interpreted as a distinct spectral feature created by the redshifted emission from primordial (Population III) stars that have formed at redshifts > 8. On the other hand, the NIRBL spectrum is almost identical to that of the zodiacal cloud, raising the possibility that it is of local origin. Blazars can, in principle, offer a simple test for the nature and origin of the NIRBL. Very high energy gamma-ray photons emitted by these objects are attenuated on route to earth by photon-photon interactions with the extragalactic background light (EBL). This paper examines whether the extragalactic nature of the NIRBL can be determined from the analysis of the TeV spectra of blazars. (Abridged)
The direction dependence of the WIMP direct detection rate provides a powerful tool for distinguishing a WIMP signal from possible backgrounds. We study the the number of events required to discriminate a WIMP signal from an isotropic background for a detector with 2-d read-out using non-parametric circular statistics. We also examine the number of events needed to i) detect a deviation from rotational symmetry, due to flattening of the Milky Way halo and ii) detect a deviation in the mean direction due to a tidal stream. If the senses of the recoils are measured then of order 20-70 events (depending on the plane of the 2-d read out) will be sufficient to reject isotropy of the raw recoil angles at 90% confidence. If the senses can not be measured these number increase by roughly two orders of magnitude (compared with an increase of one order of magnitude for the case of full 3-d read-out). The distributions of the reduced angles, with the (time dependent) direction of solar motion subtracted, are far more anisotropic, however, and if the isotropy tests are applied to these angles then the numbers of events required are similar to the case of 3-d read-out. A deviation from rotational symmetry will only be detectable if the Milky Way halo is significantly flattened. The deviation in the mean direction due to a tidal stream is potentially detectable, however, depending on the density and direction of the stream.
Carbon fibre composite technology for lightweight mirrors is gaining increasing interest in the space- and ground-based astronomical communities for its low weight, ease of manufacturing, excellent thermal qualities and robustness. We present here first results of a project to design and produce a 27 cm diameter deformable carbon fibre composite mirror. The aim was to produce a high surface form accuracy as well as low surface roughness. As part of this programme, a passive mirror was developed to investigate stability and coating issues. Results from the manufacturing and polishing process are reported here. We also present results of a mechanical and thermal finite element analysis, as well as early experimental findings of the deformable mirror. Possible applications and future work are discussed.
We detect angular galaxy-QSO cross-correlations between the APM Galaxy Catalogue and a preliminary release (consisting of roughly half of the anticipated final catalogue) of the Hamburg-ESO Catalogue of Bright QSOs as a function of source QSO redshift using multiple cross-correlation estimators. Each of the estimators yield very similar results, implying that the APM catalogue and the Hamburg-ESO survey are both fair samples of the respective true galaxy and QSO populations. Though the signal matches the expectations of gravitational lensing qualitatively, the strength of the measured cross-correlation signal is significantly greater than the CDM models of lensing by large scale structure would suggest. This same disagreement between models and observation has been found in several earlier studies. We estimate our confidence in the correlation detections versus redshift by generating 1000 random realizations of the Hamburg-ESO QSO survey: We detect physical associations between galaxies and low-redshift QSOs at 99% confidence and detect lensing associations at roughly 95% confidence for QSOs with redshifts between 0.6 and 1. Control cross-correlations between Galactic stars and QSOs show no signal. Finally, the overdensities (underdensities) of galaxies near QSO positions relative to those lying roughly 135 - 150 arcmin away are uncorrelated with differences in Galactic extinction between the two regions, implying that Galactic dust is not significantly affecting the QSO sample.
We present a study of the in-flight performance of the XMM-Newton EPIC MOS and pn detectors, with focus on the influence of proton flares and vignetting on the data. The very wide range in the conditions of our sample of observations, in terms of exposure length and background intensities, allows the detection of a wide range in the spectra of the proton flares, in contrast to the hard-spectrum flares proposed by Lumb et al.(2002) or Read et al.(2003) We also find an up to now unreported contamination in the low energy regime (E<0.5 keV) of the MOS1 observations, consisting of a significant increase in the measured intensities in two CCDs at the edges of the detector. This contamination yields in "bright CCDs" in the observations. Its effect must be taken into account for the study of sources detected in the affected CCDs. With respect to vignetting, we present in-flight exposure maps and we propose a method to repeat this calculation for user-definable energy bands. All the results presented here, have the goal to enable the study of very faint extended sources with XMM-Newton, like nearby galactic X-ray halos or the soft X-ray background.
I discuss simulations of the coalescence of black hole neutron star binary systems with black hole masses between 14 and 20 \msun. The calculations use a three-dimensional smoothed particle hydrodynamics code, a temperature-dependent, nuclear equation of state and a multi-flavor neutrino scheme. General relativistic effects are mimicked using the \Pacz-Wiita pseudo-potential and gravitational radiation reaction forces. Opposite to previous, purely Newtonian calculations, in none of the explored cases episodic mass transfer occurs. The neutron star is always completely disrupted after most of its mass has been transferred directly into the hole. For black hole masses between 14 and 16 \Msun an accretion disk forms, large parts of it, however, are inside the last stable orbit and therefore falling with large radial velocities into the hole. These disks are (opposite to the neutron star merger case) thin and -apart from a spiral shock- essentially cold. For higher mass black holes ($M_{\rm BH} \ge 18$ \msun) almost the complete neutron star disappears in the hole without forming an accretion disk. In these cases the surviving material is spun up by tidal torques and ejected as a half-ring of neutron-rich matter. None of the investigated systems is a promising GRB central engine. We find between 0.01 and 0.2 \Msun of the neutron star to be dynamically ejected. Like in a type Ia supernova, the radioactive decay of this material will power a light curve with a peak luminosity of a few times $10^{44}$ erg/s. The maximum will be reached about three days after the coalescence and will be mainly visible in the optical/near infrared band. The coalescence itself may produce a precursor pulse with a thermal spectrum of $\sim 10$ ms duration.
We study several quintessence models which are singular at Q=0, and use a simple initial constraint $Q_i\ge H_{inflation}/2\pi$ to see when they enter tracking regime, disregarding the details of inflation. We find it can give strong constraints for the inverse power-law potential $V=V_0Q^{-\alpha}$, which has to enter tracking regime for ${\rm ln}z \sim 10$. While for the supergravity model $V=V_0Q^{-\alpha}{\rm exp}(kQ^2/2)$, the constraint is much weakened. For another kind inverse power-law potential $V=V_0{\rm exp}(\lambda/Q)$, it exhibits no constraints.
Stars on the asymptotic giant branch (AGB) produce dust in their circumstellar shells. The nature of the dust-forming environment is influenced by the evolution of the stars, in terms of both chemistry and density, leading to an evolution in the nature of the dust that is produced. Carbon-rich AGB stars are known to produce silicon carbide (SiC). Furthermore, observations of the ~11um SiC feature show that the spectral features change in a sequence that correlates with stellar evolution. We present new infrared spectra of amorphous SiC and show that the ~9um feature seen in both emission and absorption, and correlated with trends in the ~11um feature, may be due to either amorphous SiC or to nano-crystalline diamond with a high proportion of Si substituting for C. Furthermore, we identify SiC absorption in three ISO spectra of extreme carbon stars, in addition to the four presented by Speck et al. (1997). An accurate description of the sequence in the IR spectra of carbon stars requires accounting for both SiC emission and absorption features. This level of detail is needed to infer the role of dust in evolution of carbon stars. Previous attempts to find a sequence in the infrared spectra of carbon stars considered SiC emission features, while neglecting SiC absorption features, leading to an interpretation of the sequence inadequately describes the role of dust. We show that the evolutionary sequence in carbon star spectra is consistent with a grain size evolution, such that dust grains get progressively smaller as the star evolves. The evolution of the grain sizes provides a natural explanation for the shift of the ~11um SiC feature in emission and in absorption. Further evidence for this scenario is seen in both post-AGB star spectra and in meteoritic studies of presolar grains.
Stable particle dark matter may well originate during the decay of long-lived relic particles, as recently extensively examined in the cases of the axino, gravitino, and higher-dimensional Kaluza-Klein (KK) graviton. It is shown that in much of the viable parameter space such dark matter emerges naturally warm/hot or mixed. %due to the kinetic energy imparted %on the dark matter particles during decay. In particular, decay produced gravitinos (KK-gravitons) may only be considered cold for the mass of the decaying particle in the several TeV range, unless the decaying particle and the dark matter particle are almost degenerate. Such dark matter candidates are thus subject to a host of cosmological constraints on warm and mixed dark matter, such as limits from a proper reionisation of the Universe, the Lyman-alpha forest, and the abundance of clusters of galaxies.. It is shown that constraints from an early reionsation epoch, such as indicated by recent observations, may potentially limit such warm/hot components to contribute only a very small fraction to the dark matter.
Ultrahigh-energy cosmic rays passing through the central region of the Galaxy interact with starlight and the infrared photons. Both nuclei and protons generate secondary fluxes of photons and neutrinos on their passage through the central region. We compute the fluxes of these secondary particles, the observations of which can be used to improve one's understanding of origin and composition of ultrahigh-energy comic rays, especially if the violation of the Greisen--Zatespin--Kuzmin cutoff is confirmed by the future data.
We have analyzed XMM-Newton Optical Monitor (OM) UV (180-400 nm) data for a sample of 33 galaxies, of which 30 are cluster members. Nine of these are central cluster galaxies (CCGs) in cooling flow clusters, having mass deposition rates which span a range of 8 to 525 solar masses per year. Using the ratio of UV to 2MASS J band flux, we find a significant UV excess in many, but not all, cooling flow CCGs. This UV excess is a direct indication of the presence of young massive stars, and therefore recent star formation, in these galaxies. Using the Starburst99 spectral energy distribution (SED) model of continuous star formation over a 900 Myr period, we derive star formation rates of 0.2 to 219 solar masses per year for the cooling flow sample. For 2/3 of this sample it is possible to equate Chandra/XMM cooling flow mass deposition rates with UV inferred star formation rates, for a combination of starburst lifetime and IMF slope. This is a pilot study of the well populated XMM UV cluster archive and a more extensive follow up study is currently underway.