Cosmological shocks are a critical part of large-scale structure formation, and are responsible for heating the intracluster medium in galaxy clusters. In addition, they are also capable of accelerating non-thermal electrons and protons. In this work, we focus on the acceleration of electrons at shock fronts, which is thought to be responsible for radio relics - extended radio features in the vicinity of merging galaxy clusters. By combining high resolution AMR/N-body cosmological simulations with an accurate shock finding algorithm and a model for electron acceleration, we calculate the expected synchrotron emission resulting from cosmological structure formation. We produce synthetic radio maps of a large sample of galaxy clusters and present luminosity functions and scaling relationships. With upcoming long wavelength radio telescopes, we expect to see an abundance of radio emission associated with merger shocks in the intracluster medium. By producing observationally motivated statistics, we provide predictions that can be compared with observations to further our understanding of magnetic fields and electron shock acceleration.
We present an estimate of the black hole mass function (BHMF) of broad line quasars (BLQSOs) that self-consistently corrects for incompleteness and the statistical uncertainty in the mass estimates, based on a sample of 9886 quasars at 1 < z < 4.5 drawn from the Sloan Digital Sky Survey. We find evidence for `cosmic downsizing' of black holes in BLQSOs, where the peak in their number density shifts to higher redshift with increasing black hole mass. The cosmic mass density for black holes seen as BLQSOs peaks at z ~ 2. We estimate the completeness of the SDSS as a function of black hole mass and Eddington ratio, and find that at z > 1 it is highly incomplete at M_BH < 10^9 M_Sun and L / L_Edd < 0.5. We also estimate a lower limit on the lifetime of a single BLQSO phase and we place constraints on the maximum mass of a black hole in a BLQSO. Our estimated distribution of BLQSO Eddington ratios peaks at L / L_Edd ~ 0.05 and has a dispersion of ~ 0.4 dex, implying that most BLQSOs are not radiating at or near the Eddington limit; however the location of the peak is subject to considerable uncertainty. The steep increase in number density of BLQSOs toward lower Eddington ratios is expected if the BLQSO accretion rate monotonically decays with time. Furthermore, our estimated lifetime and Eddington ratio distributions imply that the majority of the most massive black holes spend a significant amount of time growing in an earlier obscured phase, a conclusion which is independent of the unknown obscured fraction. These results are consistent with models for self-regulated black hole growth, at least for massive systems at z > 1, where the BLQSO phase occurs at the end of a fueling event when black hole feedback unbinds the accreting gas, halting the accretion flow.
In this letter we develop a common theoretical framework for the dynamics of thin featureless interfaces. We explicitly demonstrate that the same phase field and velocity-dependent one-scale models characterizing the dynamics of relativistic domain walls, in a cosmological context, can also successfully describe, in a friction dominated regime, the dynamics of non-relativistic interfaces in a wide variety of material systems. We further show that a statistical version of the von-Neumman's law applies in the case of scaling relativistic interface networks implying that, although relativistic and non-relativistic interfaces have very different dynamics, a single simulation snapshot is not able to clearly distinguish the two regimes. We highlight that crucial information characterizing an interface network is contained in a single simulation snapshot and explain why laboratory tests with non-relativistic interfaces can be used to rule out cosmological domain walls as a significant dark energy source.
We describe the effect of AGN light on host galaxy optical and UV-optical colours, as determined from X-ray-selected AGN host galaxies at z~1, and compare the AGN host galaxy colours to those of a control sample matched to the AGN sample in both redshift and stellar mass. We identify as X-ray-selected AGN 8.7 +4/-3 per cent of the red-sequence control galaxies, 9.8 +/-3 per cent of the blue-cloud control galaxies, and 14.7 +4/-3 per cent of the green-valley control galaxies. The nuclear colours of AGN hosts are generally bluer than their outer colours, while the control galaxies exhibit redder nuclei. AGN in blue-cloud host galaxies experience less X-ray obscuration, while AGN in red-sequence hosts have more, which is the reverse of what is expected from general considerations of the interstellar medium. Outer and integrated colours of AGN hosts generally agree with the control galaxies, regardless of X-ray obscuration, but the nuclear colours of unobscured AGN are typically much bluer, especially for X-ray luminous objects. Visible point sources are seen in many of these, indicating that the nuclear colours have been contaminated by AGN light and that obscuration of the X-ray radiation and visible light are therefore highly correlated. Red AGN hosts are typically slightly bluer than red-sequence control galaxies, which suggests that their stellar populations are slightly younger. We compare these colour data to current models of AGN formation. The unexpected trend of less X-ray obscuration in blue-cloud galaxies and more in red-sequence galaxies is problematic for all AGN feedback models, in which gas and dust is thought to be removed as star formation shuts down. A second class of models involving radiative instabilities in hot gas is more promising for red-sequence AGN but predicts a larger number of point sources in red-sequence AGNs than is observed. [See paper for full abstract.]
Knowledge of the supernova (SN) delay time distribution (DTD) - the SN rate versus time that would follow a hypothetical brief burst of star formation - can shed light on SN progenitors and physics. We compile recent measurements of the Type-Ia SN (SN Ia) rate in galaxy clusters at redshifts z=0-1.45. Together with the observed iron-to-stellar mass ratio in clusters, which constrains the time-integrated number of SN Ia events in clusters, we recover the DTD of SNe Ia in cluster environments. The DTD peaks at the shortest time-delay interval we probe, 0<t<2.2 Gyr, with a low tail out to delays of ~10 Gyr, and is remarkably consistent with several recent DTD reconstructions based on different methods, in different environments. We test DTD models from the literature, requiring that they simultaneously reproduce the observed cluster SN rates and the observed iron-to-stellar mass ratios. A power-law DTD of the form t^{-1.1+/-0.1}, extending to a Hubble time, can satisfy both constraints. Shallower power laws, such as t^{-1/2} cannot, assuming a single DTD, and a single star-formation burst (either brief or extended) at high z. This implies 50-85% of SNe Ia explode within 1 Gyr of star formation. DTDs from double-degenerate (DD) models, which generically have ~t^{-1} shapes over a wide range of timescales, match the data, but only if their predictions are scaled up by factors of 5-10. Single degenerate (SD) DTDs always give poor fits to the data, due to a lack of delayed SNe and overall low numbers of SNe. The observations also permit a combination of two SN Ia populations - prompt (e.g. SD) SNe Ia that explode within a few Gyr of star formation, and produce about 60% of the iron mass in clusters, and a DD population that contributes the events seen at z<1.4. Our results support the existence of a DD progenitor channel for SNe Ia, if the overall predicted numbers can be suitably increased.
We study the observational constraints on the Phantom Crossing DGP model. We demonstrate that the crossing of the phantom divide does not occur within the framework of the original Dvali-Gabadadze-Porrati (DGP) model or the DGP model developed by Dvali and Turner. By extending their model in the framework of an extra dimension scenario, we construct a model that realizes crossing of the phantom divide. We investigate the cosmological constraints obtained from the recent observational data of Type Ia Supernovae, Cosmic Microwave Background anisotropies, and Baryon Acoustic Oscillations. The best fit values of the parameters with 1$\sigma$ (68\%) errors for the Phantom Crossing DGP model are $\Omega_{m,0}=0.27^{+0.02}_{-0.02}$, $\beta=0.54^{+0.24}_{-0.30}$. We find that the Phantom Crossing DGP model is more compatible with the observations than the original DGP model or the DGP model developed by Dvali and Turner. Our model can realize late-time acceleration of the universe, similar to that of $\Lambda$CDM model, without dark energy due to the effect of DGP gravity. In our model, crossing of the phantom divide occurs at a redshift of $z \sim 0.2$.
We report detections of three z ~ 2.5 submillimeter-selected galaxies (SMGs) in the lowest rotational transition of the carbon monoxide molecule (CO J = 1-0) and one nondetection. For the three galaxies we detected, we find a line-integrated brightness temperature ratio of 0.53 +/- 0.08. The ratio is lower than the frequent assumption of unity, suggesting that mass estimates for SMGs based on J = 3-2 observations and J = 1-0 column density or mass conversion factors should should be multiplied by a factor of 1.8. Comparison of the 1-0 line intensities with intensities of higher-J transitions indicates that single-component models for the interstellar media in SMGs are incomplete. The small dispersion, along with published detections of CO lines with upper J > 3 in most of the sources, indicates that the molecules are not subthermally excited in most galaxies, but that the emission is from a multi-component interstellar medium with physical structure common to many classes of galaxies. This result tends to rule out the lowest scaling factors between CO luminosity and molecular gas mass and further increases molecular mass estimates calibrated against observations of galaxies in the local universe. We also describe and demonstrate a statistically sound method for finding weak lines in broadband spectra, which will find application in searches for molecular lines from sources at unknown redshifts.
We present and analyse integral-field observations of six type-II QSOs with z=0.3-0.4, selected from the Sloan Digital Sky Survey (SDSS). Two of our sample are found to be surrounded by a nebula of warm ionized gas, with the largest nebula extending across 8" (40 kpc). Some regions of the extended nebulae show kinematics that are consistent with gravitational motion, while other regions show relatively perturbed kinematics: velocity shifts and line widths too large to be readily explained by gravitational motion. We propose that a ~20 kpc x20 kpc outflow is present in one of the galaxies. Possible mechanisms for triggering the outflow are discussed. In this object, we also find evidence for ionization both by shocks and the radiation field of the AGN.
Supernova (SN) rates are potentially powerful diagnostics of metal enrichment and SN physics, particularly in galaxy clusters with their deep, metal-retaining potentials and relatively simple star-formation histories. We have carried out a survey for supernovae (SNe) in galaxy clusters, at a redshift range 0.5<z<0.9, using the Advanced Camera for Surveys (ACS) on the Hubble Space Telescope. We reimaged a sample of 15 clusters that were previously imaged by ACS, thus obtaining two to three epochs per cluster, in which we discovered five likely cluster SNe, six possible cluster SNe Ia, two hostless SN candidates, and several background and foreground events. Keck spectra of the host galaxies were obtained to establish cluster membership. We conducted detailed efficiency simulations, and measured the stellar luminosities of the clusters using Subaru images. We derive a cluster SN rate of 0.35 SNuB +0.17/-0.12 (statistical) \pm0.13 (classification) \pm0.01 (systematic) [where SNuB = SNe (100 yr 10^10 L_B_sun)^-1] and 0.112 SNuM +0.055/-0.039 (statistical) \pm0.042 (classification) \pm0.005 (systematic) [where SNuM = SNe (100 yr 10^10 M_sun)^-1]. As in previous measurements of cluster SN rates, the uncertainties are dominated by small-number statistics. The SN rate in this redshift bin is consistent with the SN rate in clusters at lower redshifts (to within the uncertainties), and shows that there is, at most, only a slight increase of cluster SN rate with increasing redshift. The low and fairly constant SN Ia rate out to z~1 implies that the bulk of the iron mass in clusters was already in place by z~1. The recently observed doubling of iron abundances in the intracluster medium between z=1 and 0, if real, is likely the result of redistribution of existing iron, rather than new production of iron.
The recent detection (Jee etal 2009) of the massive cluster XMMU J2235.3-2557 at a redshift z = 1.4, with an estimated mass M = 6.4 +- 1.2 X 10^14 M_sol, has been claimed to be a possible challenge to the standard LCDM cosmological model. More specifically, the probability to detect such a cluster has been estimated to be 0.005 if a LCDM model with gaussian initial conditions is assumed, resulting in a 3 sigma discrepancy from the standard cosmological model. In this paper we propose to use high redshift clusters as the one detected in Jee etal 2009 to compare the cosmological constant scenario with interacting dark energy models. We show that coupled dark energy models, where an interaction is present between dark energy and cold dark matter, can significantly enhance the probability to observe very massive clusters at high redshift.
We study the topology of cosmic large-scale structure through the genus statistics, using galaxy catalogues generated from the Millennium Simulation and observational data from the latest Sloan Digital Sky Survey Data Release (SDSS DR7). We introduce a new method for constructing galaxy density fields and for measuring the genus statistics of its isodensity surfaces. It is based on a Delaunay tessellation field estimation (DTFE) technique that allows the definition of a piece-wise continuous density field and the exact computation of the topology of its polygonal isodensity contours, without introducing any free numerical parameter. Besides this new approach, we also employ the traditional approaches of smoothing the galaxy distribution with a Gaussian of fixed width, or by adaptively smoothing with a kernel that encloses a constant number of neighboring galaxies. Our results show that the Delaunay-based method extracts the largest amount of topological information. Unlike the traditional approach for genus statistics, it is able to discriminate between the different theoretical galaxy catalogues analyzed here, both in real space and in redshift space, even though they are based on the same underlying simulation model. In particular, the DFTE approach detects with high confidence a discrepancy of one of the semi-analytic models studied here compared with the SDSS data, while the other models are found to be consistent.
Bolometric corrections based on the optical-to-ultraviolet continuum spectrum of quasars are widely used to quantify their radiative output, although such estimates are affected by a myriad of uncertainties, such as the generally unknown line-of-sight angle to the central engine. In order to shed light on these issues, we investigate the state-of-the-art models of Hubeny et al. that describe the continuum spectrum of thin accretion discs and include relativistic effects. We explore the bolometric corrections as a function of mass accretion rates, black hole masses and viewing angles, restricted to the parameter space expected for type-1 quasars. We find that a nonlinear relationship log L_bol=A + B log(lambda L_lambda) with B<=0.9 is favoured by the models and becomes tighter as the wavelength decreases. We calculate from the model the bolometric corrections corresponding to the wavelengths lambda = 1450A, 3000A and 5100A. In particular, for lambda=3000A we find A=9.24 +- 0.77 and B=0.81 +- 0.02. We demonstrate that the often-made assumption that quasars emit isotropically may lead to severe systematic errors in the determination of L_bol, when using the method of integrating the "big blue bump" spectrum. For a typical viewing angle of ~30 degrees to the quasar central engine, we obtain that the value of L_bol resulting from the isotropy assumption has a systematic error of ~30% high compared to the value of L_bol which incorporates the anisotropic emission of the accretion disc. These results are of direct relevance to observational determinations of the bolometric luminosities of quasars, and may be used to improve such estimates.
The Laser Interferometer Space Antenna's (LISA's) observation of supermassive binary black holes (SMBBH) could provide a new tool for precision cosmography. Inclusion of sub-dominant signal harmonics in the inspiral signal allows for high-accuracy sky localization, dramatically improving the chances of finding the host galaxy and obtaining its redshift. A SMBBH merger can potentially have component masses from a wide range ($10^5 - 10^8\,\Ms$) over which parameter accuracies vary considerably. We perform an in-depth study in order to understand (i) what fraction of possible SMBBH mergers allow for sky localization, depending on the parameters of the source, and (ii) how accurately $w$ can be measured when the host galaxy can be identified. We also investigate how accuracies on all parameters improve when a knowledge of the sky position can be folded into the estimation of errors. We find that $w$ can be measured to within a few percent in most cases, if the only error in measuring the luminosity distance is due to LISA's instrumental noise and the confusion background from Galactic binaries. However, weak lensing-induced errors will severely degrade the accuracy with which $w$ can be obtained, emphasizing that methods to mitigate weak lensing effects would be required to take advantage of LISA's full potential.
We study the evolution of the scaling relations between maximum circular velocity, stellar mass and optical half-light radius of star-forming disk-dominated galaxies in the context of LCDM-based galaxy formation models. Using data from the literature combined with new data from the DEEP2 and AEGIS surveys we show that there is a consistent observational and theoretical picture for the evolution of these scaling relations from z\sim 2 to z=0. The evolution of the observed stellar scaling relations is weaker than that of the virial scaling relations of dark matter haloes, which can be reproduced, both qualitatively and quantitatively, with a simple, cosmologically-motivated model for disk evolution inside growing NFW dark matter haloes. In this model optical half-light radii are smaller, both at fixed stellar mass and maximum circular velocity, at higher redshifts. This model also predicts that the scaling relations between baryonic quantities evolve even more weakly than the corresponding stellar relations. We emphasize, though, that this weak evolution does not imply that individual galaxies evolve weakly. On the contrary, individual galaxies grow strongly in mass, size and velocity, but in such a way that they move largely along the scaling relations. Finally, recent observation have claimed surprisingly large sizes for a number of star-forming disk galaxies at z \sim 2, which has caused some authors to suggest that high redshift disk galaxies have abnormally high spin parameters. However, we argue that the disk scale lengths in question have been systematically overestimated by a factor \sim 2, and that there is an offset of a factor \sim 1.4 between H\alpha sizes and optical sizes. Taking these effects into account, there is no indication that star forming galaxies at high redshifts (z\sim 2) have abnormally high spin parameters.
We investigate the formation of caustics in Dirac-Born-Infeld type scalar field systems for generic classes of potentials, viz., massive rolling scalar with potential, $V(\phi)=V_0e^{\pm \frac{1}{2} M^2 \phi^2}$ and inverse power-law potentials with $V(\phi)=V_0/\phi^n,~0<n<2$. We find that in the case of\texttt{} exponentially decreasing rolling massive scalar field potential, there are multi-valued regions and regions of likely to be caustics in the field configuration. However there are no caustics in the case of exponentially increasing potential. We show that the formation of caustics is inevitable for the inverse power-law potentials under consideration in Minkowski space time whereas caustics do not form in this case in the FRW universe.
The Laser Interferometer Space Antenna (LISA) is designed to detect gravitational wave signals from astrophysical sources, including those from coalescing binary systems of compact objects such as black holes. Colliding galaxies have central black holes that sink to the center of the merged galaxy and begin to orbit one another and emit gravitational waves. Some galaxy evolution models predict that the binary black hole system will enter the LISA band with significant orbital eccentricity, while other models suggest that the orbits will already have circularized. Using a full seventeen parameter waveform model that includes the effects of orbital eccentricity, spin precession and higher harmonics, we investigate how well the source parameters can be inferred from simulated LISA data. Defining the reference eccentricity as the value one year before merger, we find that for typical LISA sources, it will be possible to measure the eccentricity to an accuracy of parts in a thousand. The accuracy with which the eccentricity can be measured depends only very weakly on the eccentricity, making it possible to distinguish circular orbits from those with very small eccentricities. LISA measurements of the orbital eccentricity can provide strong constraints on theories of galaxy mergers in the early universe.
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Quillen et al. and O'Dea et al. carried out a Spitzer study of a sample of 62 brightest cluster galaxies (BCGs) from the ROSAT Brightest Cluster Sample chosen based on their elevated H-alpha flux. We present Hubble Space Telescope Advanced Camera for Surveys (ACS) far ultraviolet (FUV) images of the Ly-alpha and continuum emission of the luminous emission-line nebulae in 7 BCGs found to have an infrared excess. We confirm that the BCGs are actively forming stars suggesting that the IR excess seen in these BCGs is indeed associated with star formation. The FUV continuum emission extends over a region of ~7-28 kpc (largest linear size) and even larger in Ly-alpha. The young stellar population required by the FUV observations would produce a significant fraction of the ionizing photons required to power the emission line nebulae. Star formation rates estimated from the FUV continuum range from ~3 to ~14 times lower than those estimated from the IR, however both the Balmer decrement in the central few arcseconds and detection of CO in most of these galaxies imply that there are regions of high extinction that could have absorbed much of the FUV continuum. Analysis of archival VLA observations reveals compact radio sources in all 7 BCGs and kpc scale jets in Abell 1835 and RXJ 2129+00. The four galaxies with archival deep Chandra observations exhibit asymmetric X-ray emission, the peaks of which are offset from the center of the BCGs by ~10 kpc on average. A low feedback state for the AGN could allow increased condensation of the hot gas into the center of the galaxy and the feeding of star formation.
The measurement of Baryonic Acoustic Oscillations from galaxy surveys is well known to be a robust and powerful tool to constrain dark energy. This method relies on the knowledge of the size of the acoustic horizon at radiation drag derived from Cosmic Microwave Background Anisotropy measurements. In this paper we quantify the effect of non-standard initial conditions in the form of an isocurvature component on the determination of dark energy parameters from future BAO surveys. In particular, if there is an isocurvature component (at a level still allowed by present data) but it is ignored in the CMB analysis, the sound horizon and cosmological parameters determination is biased, and, as a consequence, future surveys may incorrectly suggest deviations from a cosmological constant. In order to recover an unbiased determination of the sound horizon and dark energy parameters, a component of isocurvature perturbations must be included in the model when analyzing CMB data. Fortunately, doing so does not increase parameter errors significantly.
I look at the growth of weak density inhomogeneities of nonrelativistic matter, in bimetric-MOND (BIMOND) cosmology. I concentrate on matter-twin-matter-symmetric versions of BIMOND, and assume that, on average, the universe is symmetrically populated in the two sectors. MOND effects are absent in an exactly symmetric universe, apart from the appearance of a cosmological constant, Lambda~(a0/c)^2. MOND effects--local and cosmological--do enter when density inhomogeneities that differ in the two sectors appear and develop. MOND later takes its standard form in systems that are islands dominated by pure matter. I derive the nonrelativistic equations governing small-scale fluctuation growth. The equations split into two uncoupled systems, one for the sum, the other for the difference, of the fluctuations in the two sectors. The former is governed strictly by Newtonian dynamics. The latter is governed by MOND dynamics, which entails stronger gravity, and nonlinearity even for the smallest of perturbations. These cause the difference to grow faster than the sum, conducing to matter-twin-matter segregation. The nonlinearity also causes interaction between nested perturbations on different scales. Because matter and twin matter repel each other in the MOND regime, matter inhomogeneities grow not only by their own self gravity, but also through shepherding by flanking TM overdensitie. The relative importance of gravity and pressure in the MOND system depends also on the strength of the perturbation. The development of structure in the universe, in either sector, thus depends crucially on two initial fluctuation spectra: that of matter alone and that of the matter-TM difference. I also discuss the back reaction on cosmology of BIMOND effects that appear as ``phantom matter'' resulting from inhomogeneity differences between the two sectors. (abridged)
Deep near-infrared images recorded with NICI on Gemini South are used to investigate the evolved stellar content in the outer regions of the south east quadrant of the spiral galaxy M83. A diffuse population of asymptotic giant branch (AGB) stars is detected outside of the previously identified young and intermediate age star clusters in the outer disk. The brightest AGB stars have M_K > -8, and the AGB luminosity function (LF) is well-matched by model LFs that assume ages < 1 Gyr. The specific star formation rate (SFR) during the past few Gyr estimated from AGB star counts is consistent with that computed from mid-infrared observations of star clusters at similar radii, and it is concluded that the disruption timescale for star clusters in the outer disk is << 1 Gyr. The luminosity function and specific frequency of AGB stars varies with radius, in a manner that is indicative of lower luminosity-weighted ages at larger radii. Modest numbers of red supergiants are also found, indicating that there has been star formation during the past 100 Myr, while the ratio of C stars to M giants is consistent with that expected for a solar metallicity system that has experienced a constant SFR for the past few Gyrs.
We investigate the ability of spectroscopic techniques to yield realistic star formation histories (SFHs) for the bulges of spiral galaxies based on a comparison with their observed broadband colors. Full spectrum fitting to optical spectra indicates that recent (within ~1 Gyr) star formation activity can contribute significantly to the V-band flux, whilst accounting for only a minor fraction of the stellar mass budget which is made up primarily of old stars. Furthermore, recent implementations of stellar population (SP) models reveal that the inclusion of a more complete treatment of the thermally pulsating asymptotic giant branch (TP-AGB) phase to SP models greatly increases the NIR flux for SPs of ages 0.2-2 Gyr. Comparing the optical--NIR colors predicted from population synthesis fitting, using models which do not include all stages of the TP-AGB phase, to the observed colors reveals that observed optical--NIR colors are too red compared to the model predictions. However, when a 1 Gyr SP from models including a full treatment the TP-AGB phase is used, the observed and predicted colors are in good agreement. This has strong implications for the interpretation of stellar populations, dust content, and SFHs derived from colors alone.
Galaxy cluster surveys based on the Sunyaev-Zeldovich effect (SZE) mapping are expected from ongoing experiments. Such surveys are anticipated to provide a significant amount of information relevant to cosmology from the number counts redshift distribution. We carry out an estimation of predicted SZE counts and their redshift distribution taking into account the current cosmological constraints and the X-ray cluster temperature distribution functions. Comparison between local and distant cluster temperature distribution functions provides evidence for an evolution in the abundance of X-ray clusters that is not consistent with the use of standard scaling relations of cluster properties in the framework of the current concordance model. The hypothesis of some evolution of the scaling law driven by non-gravitational processes is a natural solution to this problem. We perform a MCMC statistical study using COSMOMC, combining current CMB observations from WMAP, the SNIa Hubble diagram, the galaxy power spectrum data from SDSS and X-ray clusters temperature distributions to predict SZE cluster number counts. Models reproducing well the X-ray cluster temperature distribution function evolution lead to a significantly lower SZE clusters number counts with a distinctive redshift distribution. Ongoing microwave SZE surveys will therefore shed new light on intracluster gas physics and greatly help to identify the role of possible non-gravitational physics in the history of the hot gas component of x-ray clusters.
In this second paper of two analysis, we present near-infrared morphological and asymmetry studies perfomed in sample of 92 galaxies found in different density environments: galaxies in Compact Groups (HCGs), Isolated Pairs of Galaxies (KPGs), and Isolated Galaxies (KIGs). Both studies have proved useful to identify the effect of interactions on galaxies. In the NIR, the properties of the galaxies in HCGs, KPGs and KIGs are more similar than in the optical. This is because the NIR band traces the older stellar populations, which formed earlier and are more relaxed than the younger populations. However, we found asymmetries related to interacions in both, KPG and HCG samples. In HCGs, the fraction of asymmetric galaxies is even higher than what we found in the optical. In the KPGs, the interactions look like very recent events, while in the HCGs, galaxies are more morphologically evolved and show properties suggesting they suffered more frequent interactions. The key difference seems to be the absence of star formation in the HCGs: while interactions produce intense star formation in the KPGs we do not see this effect in the HCGs. This is consistent with the dry merger hypothesis (Coziol & Plauchu-Frayn 2007): the interaction between galaxies in compact groups, (CG), are happening without the presence of gas. If the gas was spent in stellar formation (to build the bulge of the numerous early-type galaxies), then the HCGs possibly started interacting sometime before the KPGs. On the other hand, the dry interaction condition in CGs suggests the galaxies are on merging orbits, and consequently such system cannot be that much older either. [abridge]
We present a novel exact solution to Einstein's General Relativity equations for an ideal fluid and explore the possibility that it could describe the patch of the universe observable to us. We consider a Lorentzian manifold whose metric can be parameterized as $g_{\mu \nu} = diag\left(1, -a^2(t) r_0^2/r^2, -a^2(t) r_0^2/r^2, -a^2(t) r_0^2/r^2\right)$ in a cartesian comoving grid $(t,x,y,z)$ in which the fluid is assumed to be at rest $u^{\mu}=(1,0,0,0)$, $t$ denotes cosmological time, $r=\sqrt{x^2+y^2+z^2}$ is a radial comoving coordinate and $r_0$ is a characteristic $length$ scale. This novel class of solutions fits well with the observational pillars upon which relies the standard FLRW cosmology and, furthermore, it naturally solves some of its most outstanding problems.
Studies of galactic circumnuclear environments is important to our understanding of the feeding and feedback of the central super-massive black hole and in turn the global evolution of the host galaxy. We present an observational overview of the circumnuclear environment in M31 and a tentative understanding of its regulation. Notes on selected open issues, as well as on a comparison with the Galactic Center and other extragalactic circumnuclear environments, are also presented.
We comment on the recent arguments by Senatore and Zaldarriaga that loop corrections to the zeta-zeta correlator cannot grow with time after first horizon crossing. We first emphasize the need to search for such secular dependence in corrections whose in-out matrix elements are infrared singular on an infinite spatial manifold. Then we give examples of such time dependence from pure quantum gravity and from scalar potential models. Finally, we point out that this time dependence arises from inflationary particle production and is therefore unlikely to endanger the preservation of super-horizon correlations as a record of inflation.
We present a study of the motion of compact jet components in quasar B3 1633+382. Through analyzing 14 epochs of VLBI observations of three components (B1, B2, and B3) at 22 GHz, we find two different possibilities of component classification. Thus two corresponding kinematical models can be adopted to explain the evolutionary track of components. One is a linear motion, while another is a helical model. Future observations are needed to provide new kinematical constraints for the motion of these components in this source.
We demonstrate novel features in the behavior of the second and third order non-linearity parameters of the curvature perturbation, namely, $f_{NL}$ and $g_{NL}$, arising from non-linear motion of curvaton field. We investigate two classes of potentials for the curvaton - the first has tiny oscillations super-imposed upon the quadratic potential. The second is characterized by a single 'feature' separating two quadratic regimes with different mass scales. The feature may either be a bump or a flattening of the potential. In the case of the oscillatory potential we find that as the width and height of superimposed oscillations increase, both $f_{NL}$ and $g_{NL}$ deviate strongly from their expected values from a quadratic potential. $f_{NL}$ changes sign from positive to negative as the oscillations in the potential become more prominent. Hence, this model can be severely constrained by convincing evidence from observations that $f_{NL}$ is positive. $g_{NL}$, on the other hand, acquires very large negative values. For the the single feature potential, we find that $f_{NL}$ and $g_{NL}$ exhibit oscillatory behavior as a function of the parameter that controls the feature.
We present an analysis of stellar population gradients in 4,546 Early-Type Galaxies with photometry in $grizYHJK$ along with optical spectroscopy. A new approach is described which utilizes color information to constrain age and metallicity gradients. Defining an effective color gradient, $\nabla_{\star}$, which incorporates all of the available color indices, we investigate how $\nabla_{\star}$ varies with galaxy mass proxies, i.e. velocity dispersion, stellar (M_star) and dynamical (M_dyn) masses, as well as age, metallicity, and alpha/Fe. ETGs with M_dyn larger than 8.5 x 10^10, M_odot have increasing age gradients and decreasing metallicity gradients wrt mass, metallicity, and enhancement. We find that velocity dispersion and alpha/Fe are the main drivers of these correlations. ETGs with 2.5 x 10^10 M_odot =< M_dyn =< 8.5 x 10^10 M_odot, show no correlation of age, metallicity, and color gradients wrt mass, although color gradients still correlate with stellar population parameters, and these correlations are independent of each other. In both mass regimes, the striking anti-correlation between color gradient and alpha-enhancement is significant at \sim 4sigma, and results from the fact that metallicity gradient decreases with alpha/Fe. This anti-correlation may reflect the fact that star formation and metallicity enrichment are regulated by the interplay between the energy input from supernovae, and the temperature and pressure of the hot X-ray gas in ETGs. For all mass ranges, positive age gradients are associated with old galaxies (>5-7 Gyr). For galaxies younger than \sim 5 Gyr, mostly at low-mass, the age gradient tends to be anti-correlated with the Age parameter, with more positive gradients at younger ages.
We analyze the chemical abundances of planetary nebulae and HII regions in the M81 disk for insight on galactic evolution, and compare it with that of other galaxies, including the Milky Way. We acquired Hectospec/MMT spectra of 39 PNe and 20 HII regions, with 33 spectra viable for temperature and abundance analysis. Our PN observations represent the first PN spectra in M81 ever published, while several HII region spectra have been published before, although without a direct electron temperature determination. We determine elemental abundances of helium, nitrogen, oxygen, neon, sulfur, and argon in PNe and HII regions, and determine their averages and radial gradients. The average O/H ratio of PNe compared to that of the HII regions indicates a general oxygen enrichment in M81 in the last ~10 Gyr. The PN metallicity gradient in the disk of M81 is -0.055+-0.02 dex/kpc. Neon and sulfur in PNe have a radial distribution similar to that of oxygen, with similar gradient slopes. If we combine our HII sample with the one in the literature we find a possible mild evolution of the gradient slope, with results consistent with gradient steepening with time. Additional spectroscopy is needed to confirm this trend. There are no Type I PNe in our M81 sample, consistently with the observation of only the brightest bins of the PNLF, the galaxy metallicity, and the evolution of post-AGB shells. Both the young and the old populations of M81 disclose shallow but detectable negative radial metallicity gradient, which could be slightly steeper for the young population, thus not excluding a mild gradients steepening with the time since galaxy formation. During its evolution M81 has been producing oxygen; its total oxygen enrichment exceeds that of other nearby galaxies.
We study the effect of massive neutrinos on the evolution of the early mini-halos (M~10^{6} M_{\odot} at z~20) where the first stars may have formed. In the framework of the extended Press-Schechter formalism, we evaluate analytically the rates of merging of the mini-halos into zero-dimensional larger halos and one dimensional mini-filaments. It is shown that the halo-to-filament merging rate increases sharply with the neutrino mass fraction f_{\nu} while the halo-to-halo merging rate decreases with f_{\nu}. For f_{\nu}\le 0.04, the halo-to-filament merging rate is negligibly low at all filament mass scales while for f_{\nu}\ge0.07 the halo- to-filament merging rate exceeds the halo-to-halo merging rate at the characteristic filament mass scales of 10^{9}-10^{10} M_{\odot}. The distribution of the epochs of the longest-axis collapse of these first filaments is also derived and found to reach a sharp maximum at z~8-9. Once the first mini-filaments form, they would provide bridges along which the matter and gas more rapidly accrete onto the constituent halos, causing the early formation of the first galaxies and rapid growth of their central blackholes. Furthermore, the longest axis collapse of these first mini-filaments would spur the supermassive blackholes to power the ultraluminous high-$z$ quasars. In this scenario, the mass estimate ~3x10^{9}M_{\odot} for the supermassive blackholes in the Sloan quasar detected at $z\approx 6.4$ by Willott et al. in 2003 corresponds to an upper limit of the neutrino neutrino mass, m_{\nu}\le 0.22 eV.
We present the first results from a survey of SDSS quasars selected for strong H I damped Lyman-{\alpha} (DLA) absorption with corresponding low equivalent width absorption from strong low-ion transitions (e.g. C II {\lambda}1334 and Si II {\lambda}1260). These metal-poor DLA candidates were selected from the SDSS DR5 quasar spectroscopic database, and comprise a large new sample for probing low metallicity galaxies. Medium-resolution echellette spectra from the Keck ESI spectrograph for an initial sample of 35 systems were obtained to explore the metal-poor tail of the DLA distribution and to investigate the nucleosynthetic patterns at these metallicities. We have estimated saturation corrections for the moderately under-resolved spectra, and systems with very narrow Doppler parameter (b \le 5 km s-1) will likely have underestimated abundances. For those systems with Doppler parameters b > 5 km s-1, we have measured low metallicity DLA gas with [X/H] < -2.4 for at least one of C, O, Si, or Fe. Assuming non-saturated components, we estimate that several DLA systems have [X/H] < -2.8, including five DLA systems with both low equivalent widths and low metallicity in transitions of both C II and O I. All of the measured DLA metallicities, however, exceed or are consistent with a metallicity of at least 1/1000 of solar, regardless of the effects of saturation in our spectra. Our results indicate that the metal-poor tail of galaxies at z \sim 3 drops exponentially at [X/H]< -3. The observed ratio of [C/O] for values of [O/H] < -2.5 exceeds values seen in moderate metallicity DLA systems, and also exceeds theoretical nucleosynthesis predictions for higher mass Population III stars.
Two field 2-forms on the space-time manifold, in a relationship of duality, are presented and applied to derive the equations of motion for relativistic particles having both electric and magnetic charges. By exterior derivatives, these forms yield the two groups of Maxwell equations, while specific integrality conditions ensure magnetic monopole or electric charge quantization. Some properties of the common characteristic vector of the dual 2-forms are discussed. It is shown that the coupled energy-density continuity equation and the eikonal equation represent a classical, infinite-dimensional Hamiltonian system.
We perform a global analysis of cosmological observables in generalized cosmologies which depart from $\Lambda$CDM models by allowing non-vanishing curvature $\Omega_k\neq 0$, dark energy with equation of state with $\omega\neq -1$, the presence of additional relativistic degrees of freedom $\Delta N_{\rm rel}$, and neutrino masses $\Omega_\nu\neq 0$. By combining the data from cosmic microwave background (CMB) experiments (in particular the latest results from WMAP-7), the present day Hubble constant (H0) measurement, the high-redshift Type-I supernovae (SN) results and the information from large scale structure (LSS) surveys, we determine the parameters in the 10-dimensional parameter space for such models. We present the results from the analysis when the full shape information from the LSS matter power spectrum (LSSPS) is included versus when only the corresponding distance measurement from the baryon acoustic oscillations (BAO) is accounted for. We compare the bounds on the neutrino mass scale in these generalized scenarios with those obtained for the 6+1 parameter analysis in $\Lambda{\rm CDM}+m_\nu$ models and we also study the dependence of those on the set of observables included in the analysis. Finally we combine these results with the information on neutrino mass differences and mixing from the global analysis of neutrino oscillation experiments and derive the presently allowed ranges for the two laboratory probes of the absolute scale of neutrino mass: the effective electron neutrino mass in single beta decay and the effective Majorana neutrino mass in neutrinoless $\beta\beta$ decay.
Variation in high energy cosmic rays (HECRs) has been proposed to explain a 62 My periodicity in terrestrial fossil biodiversity. It has been suggested that the infall of our galaxy toward the Virgo cluster could generate an extragalactic shock, accelerating charged particles and exposing the earth to a flux of high energy cosmic rays (HECRs). The oscillation of the Sun perpendicular to the galactic plane could induce 62 My periodicity in the HECR flux on the Earth, with a magnitude much higher than the Galactic cosmic ray change we see in a solar cycle. This mechanism could potentially explain the observed 62 My periodicity in terrestrial biodiversity over the past 500 My. In addition to direct effects on life from secondaries, HECRs induced air showers ionize the atmosphere leading to changes in atmospheric chemistry and microphysical processes that can lead to cloud formation including low altitude cloud cover. An increase in ionization changes the global electric circuit which could enhance the formation of cloud condensation nuclei (CCN) through microphysical processes such as electroscavenging and ion mediated nucleation, leading to an increase in the cloud cover. This could increase the albedo and reduce the solar flux reaching the ground, reducing the global temperature. Using an existing model, we have calculated the enhancement in atmospheric ionization at low altitudes resulting from exposure to HECRs. We use a conservative model to estimate the change in low altitude cloud cover from this increased ionization.
Spider is a balloon-borne array of six telescopes that will observe the Cosmic Microwave Background. The 2624 antenna-coupled bolometers in the instrument will make a polarization map of the CMB with approximately one-half degree resolution at 145 GHz. Polarization modulation is achieved via a cryogenic sapphire half-wave plate (HWP) skyward of the primary optic. We have measured millimeter-wave transmission spectra of the sapphire at room and cryogenic temperatures. The spectra are consistent with our physical optics model, and the data gives excellent measurements of the indices of A-cut sapphire. We have also taken preliminary spectra of the integrated HWP, optical system, and detectors in the prototype Spider receiver. We calculate the variation in response of the HWP between observing the CMB and foreground spectra, and estimate that it should not limit the Spider constraints on inflation.
This work deals with $F(T)$ gravity models driven by real scalar fields with usual and phantom dynamics. We illustrate the results with examples of current interest, and we find some analytical solutions for scale factors and scalar fields. The results indicate that torsion-scalar models also admit the accelerated expansion of the universe.
We analyse observed fractions of core-collapse SN types from the Lick Observatory SN Search, and we discuss corresponding implications for massive star evolution. For a standard IMF, observed fractions of SN types cannot be reconciled with expectations of single-star evolution. The mass range of WR stars that shed their H envelopes via their own mass loss accounts for less than half the observed fraction of SNeIbc. Progenitors of SNeIbc must extend to a much lower range of initial masses than classical WR stars, and we argue that most SNIbc and SNIIb progenitors must arise from binary Roche-lobe overflow. SNeIc still trace higher mass and metallicity, because line-driven winds in the WR stage remove the He layer and propel the transition from SNIb to Ic. Less massive progenitors of SNeIb and IIb may not be classical WR stars; they may be underluminous with weak winds, possibly hidden by overluminous mass-gainer companions that appear as B[e] supergiants or related objects having aspherical circumstellar material. The remaining SN types (II-P, II-L, and IIn) are redistributed across the full range of initial mass. We consider direct collapse to black holes without visible SNe, but find this problematic. Major areas of remaining uncertainty are (1) the influence of binary separation, rotation, and metallicity, (2) mass differences in progenitors of SNeIIn compared to SNeII-L and II-P, and (3) SNeIc arising from single stars with eruptive mass loss, its dependence on metallicity, and how it relates to diversity within the SNIc subclass. (abridged)
The new 1-m f/4 fast-slew Zadko Telescope was installed in June 2008 about 70 km north of Perth, Western Australia. It is the only metre-class optical facility at this southern latitude between the east coast of Australia and South Africa, and can rapidly image optical transients at a longitude not monitored by other similar facilities. We report on first imaging tests of a pilot program of minor planet searches, and Target of Opportunity observations triggered by the Swift satellite. In 12 months, 6 gamma-ray burst afterglows were detected, with estimated magnitudes; two of them, GRB 090205 (z = 4.65) and GRB 090516 (z = 4.11), are among the most distant optical transients imaged by an Australian telescope. Many asteroids were observed in a systematic 3-month search. In September 2009, an automatic telescope control system was installed, which will be used to link the facility to a global robotic telescope network; future targets will include fast optical transients triggered by highenergy satellites, radio transient detections, and LIGO gravitational wave candidate events. We also outline the importance of the facility as a potential tool for education, training, and public outreach.
We demonstrate that there exists a large class of action functionals of the scalar curvature and of the Gauss-Bonnet invariant which are able to relax dynamically a large cosmological constant (CC), whatever it be its starting value in the early universe. Hence, it is possible to understand, without fine-tuning, the very small current value of the CC as compared to its theoretically expected large value in quantum field theory and string theory. In our framework, this relaxation appears as a pure gravitational effect, where no ad hoc scalar fields are needed. The action involves a positive power of a characteristic mass parameter, M, whose value can be, interestingly enough, of the order of a typical particle physics mass of the Standard Model of the strong and electroweak interactions or extensions thereof, including the neutrino mass. The model universe emerging from this scenario (the ``Relaxed Universe'') falls within the class of the so-called LXCDM models of the cosmic evolution. Therefore, there is a ``cosmon'' entity X (represented by an effective object, not a field), which in this case is generated by the effective functional and is responsible for the dynamical adjustment of the cosmological constant. This model universe successfully mimics the essential past epochs of the standard (or ``concordance'') cosmological model (LCDM). Furthermore, it provides interesting clues to the coincidence problem and it may even connect naturally with primordial inflation.
An exact de Sitter solution of scalar-tensor gravity is found, in which the non-minimal coupling scalar is rolling along a non-constant potential. Based on this solution, a dust-filled FRW universe is explored in frame of scalar-tensor gravity. The effective dark energy induced by the sole non-minimal scalar can be quintessence-like, phantom-like, and more significantly, can cross the phantom divide. The rich and varied properties of scalar-tensor gravity even with only one scalar is shown in this article.
The Fermi Gamma-ray Space Telescope has detected the gamma-ray glow emanating from the giant radio lobes of the radio galaxy Centaurus A. The resolved gamma-ray image shows the lobes clearly separated from the central active source. In contrast to all other active galaxies detected so far in high-energy gamma-rays, the lobe flux constitutes a considerable portion (>1/2) of the total source emission. The gamma-ray emission from the lobes is interpreted as inverse Compton scattered relic radiation from the cosmic microwave background (CMB), with additional contribution at higher energies from the infrared-to-optical extragalactic background light (EBL). These measurements provide gamma-ray constraints on the magnetic field and particle energy content in radio galaxy lobes, and a promising method to probe the cosmic relic photon fields.
We present high- and intermediate resolution radio observations of the central region in the spiral galaxy IC 2497, performed using the European VLBI Network (EVN) at 18 cm, and the Multi-Element Radio Linked Interferometer Network (MERLIN) at 18 cm and 6 cm. We detect two compact radio sources, with brightness temperatures above 10e5 K, suggesting that they are related to AGN activity. We show that the total 18 cm radio emission from the galaxy is dominated neither by these compact sources nor large-scale emission, but extended emission confined within a sub-kpc central region. IC 2497 therefore appears as a typical luminous infrared galaxy that exhibits a nuclear starburst with a massive star formation rate (M > 5M_solar) of 12.4 M_solar/yr. These results are in line with the hypothesis that the ionisation nebula "Hanny's Voorwerp" at a distance of approx. 15-25 kpc from the galaxy is ionised by the radiation cone of the AGN.
We show that most of cutoff measures of the multiverse violate some of the basic properties of probability theory when applied repeatedly to predict the results of local experiments. Starting from minimal assumptions, such as Markov property, we derive a correspondence between cosmological measures and quantum field theories in one lesser dimension. The correspondence allows us to replace the picture of an infinite multiverse with a finite causally connected region accessible by a given observer in conjunction with a Euclidean theory defined on its past boundary.
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We present the final results from a high sampling rate, multi-month, spectrophotometric reverberation mapping campaign undertaken to obtain either new or improved Hbeta reverberation lag measurements for several relatively low-luminosity AGNs. We have reliably measured thetime delay between variations in the continuum and Hbeta emission line in six local Seyfert 1 galaxies. These measurements are used to calculate the mass of the supermassive black hole at the center of each of these AGNs. We place our results in context to the most current calibration of the broad-line region (BLR) R-L relationship, where our results remove outliers and reduce the scatter at the low-luminosity end of this relationship. We also present velocity-resolved Hbeta time delay measurements for our complete sample, though the clearest velocity-resolved kinematic signatures have already been published.
We report the discovery of a six-month-long mid-infrared transient, SDWFS-MT-1, in the Spitzer Deep, Wide-Field Survey of the NOAO Deep Wide-Field Survey Bootes field. The transient, located in a z=0.19 low luminosity (M_[4.5]~-18.6 mag, L/L_MilkyWay~0.01) metal-poor (12+log(O/H)~7.8) irregular galaxy, peaked at a mid-infrared absolute magnitude of M_[4.5]~-24.2 in the 4.5 micron Spitzer/IRAC band and emitted a total energy of at least 10^51 ergs. The optical emission was likely fainter than the mid-infrared, although our constraints on the optical emission are poor because the transient peaked when the source was "behind" the Sun. The Spitzer data are consistent with emission by a modified black body with a temperature of ~1350 K. We rule out a number of scenarios for the origin of the transient such as a Galactic star, AGN activity, GRB, tidal disruption of a star by a black hole and gravitational lensing. The most plausible scenario is a supernova exploding inside a massive, optically thick circumstellar medium, composed of multiple shells of previously ejected material. If the proposed scenario is correct, then a significant fraction (~10%) of the most luminous supernova may be self-enshrouded by dust not only before but also after the supernova occurs. The spectral energy distribution of the progenitor of such a supernova would be a slightly cooler version of eta Carina, peaking at 20-30 microns.
J113924.74+164144.0 is an interesting galaxy at z = 0.0693, i.e. D_L ~ 305 Mpc, with tidal-tail-like extended optical features on both sides. There are two neighbouring galaxies, a spiral galaxy J113922.85+164136.3 which has a strikingly similar 'tidal' morphology, and a faint galaxy J113923.58+164129.9. We report HI 21 cm observations of this field to search for signatures of possible interaction. Narrow HI emission is detected from J113924.74+164144.0, but J113922.85+164136.3 shows no detectable emission. The total HI mass detected in J113924.74+164144.0 is 7.7 x 10^9 M_solar. The HI emission from the galaxy is found to be extended and significantly offset from the optical position of the galaxy. We interpret this as signature of possible interaction with the neighbouring spiral galaxy. There is also a possible detection of HI emission from another nearby galaxy J113952.31+164531.8 at z = 0.0680 at a projected distance of 600 kpc, and with a total HI mass of 5.3 x 10^9 M_solar, suggesting that all these galaxies form a loose group at z ~ 0.069.
Models that lead to a cosmological stiff fluid component, with a density $\rho_S$ that scales as $a^{-6}$, where $a$ is the scale factor, have been proposed recently in a variety of contexts. We calculate numerically the effect of such a stiff fluid on the primordial element abundances. Because the stiff fluid energy density decreases with the scale factor more rapidly than radiation, it produces a relatively larger change in the primordial helium-4 abundance than in the other element abundances, relative to the changes produced by an additional radiation component. We show that the helium-4 abundance varies linearly with the density of the stiff fluid at a fixed fiducial temperature. Taking $\rho_{S10}$ and $\rho_{R10}$ to be the stiff fluid energy density and the standard density in relativistic particles, respectively, at $T = 10$ MeV, we find that the change in the primordial helium abundance is well-fit by $\Delta Y_p = 0.00024(\rho_{S10}/\rho_{R10})$. The changes in the helium-4 abundance produced by additional radiation or by a stiff fluid are identical when these two components have equal density at a ``pivot temperature", $T_*$, where we find $T_* = 0.55$ MeV. Current estimates of the primordial $^4$He abundance give the constraint on a stiff fluid energy density of $\rho_{S10}/\rho_{R10} < 30$.
We present a novel method for computing the Minkowski Functionals from isodensity surfaces extracted directly from the Delaunay tessellation of a point distribution. This is an important step forward compared to the previous cosmological studies when the isodensity surface was built in the field on a uniform cubic grid and therefore having a uniform spatial resolution. The density field representing a particular interest in cosmology is the density of galaxies which is obtained from the highly nonuniform distribution of the galaxy positions. Therefore, the constraints caused by the spatially uniform grid put severe limitations on the studies of the geometry and shapes of the large-scale objects: superclusters and voids of galaxies. Our technique potentially is able to eliminate most of these limitations. The method is tested with some simple geometric models and an application to the density field from an N-body simulation is shown.
A new effect is described by which primordial gravity waves leave a permanent signature in the large scale structure of the Universe. The effect occurs at second order in perturbation theory and is sensitive to the order in which perturbations on different scales are generated. We derive general forecasts for the detectability of the effect with future experiments, and consider observations of the pre-reionization gas through the 21 cm line. It is found that the Square Kilometre Array will not be competitive with current cosmic microwave background constraints. However, a more futuristic experiment could, through this effect, provide the highest ultimate sensitivity to tensor modes and possibly even measure the tensor spectral index. It is thus a potentially quantitative probe of the inflationary paradigm.
In the Friedmann cosmology the deceleration of the expansion $q$ plays a fundamental role. We derive the deceleration as a function of redshift $q(z)$ in two scenarios: $\Lambda$CDM model and modified Chaplygin gas ($MCG$) model. The function for the $MCG$ model is then fitted to the cosmological data in order to obtain the cosmological parameters that minimize $\chi^2$. We use the Fisher matrix to construct the covariance matrix of our parameters and reconstruct the q(z) function. We use Supernovae Ia, WMAP5 and BAO measurements to obtain the observational constraints. We determined the present acceleration as $q_0=-0.60 \pm 0.12$ for the $MCG$ model using the Constitution dataset of SNeIa and BAO, and $q_0=-0.63 \pm 0.17$ for the Union dataset and BAO. The transition redshift from deceleration to acceleration was found to be around $0.6$ for both datasets. We have also determined the dark energy parameter for the $MCG$ model: $\Omega_{X0}=0.834 \pm 0.028$ for the Constitution dataset and $\Omega_{X0}=0.854 \pm 0.036$ using the Union dataset.
In accelerating dark energy models, the estimates of H0 from Sunyaev-Zel'dovich effect (SZE) and X-ray surface brightness of galaxy clusters may depend on the matter content (Omega_M), the curvature (Omega_K) and the equation of state parameter (w). In this article, by using a sample of 25 angular diameter distances from galaxy clusters obtained through SZE/X-ray technique, we constrain H_0 in the framework of a general LCDM models (free curvature) and a flat XCDM model with equation of state parameter, w=p_x/\rho_x (w=constant). In order to broke the degeneracy on the cosmological parameters, we apply a joint analysis involving the baryon acoustic oscillations (BAO) and the CMB Shift Parameter signature. By neglecting systematic uncertainties, for nonflat LCDM cosmologies we obtain $H_0=73.2^{+4.3}_{-3.7}$ km s$^{-1}$ Mpc$^{-1}$ (1sigma) whereas for a flat universe with constant equation of state parameter we find $H_0=71.4^{+4.4}_{-3.4}$ km s$^{-1}$ Mpc$^{-1}$ (1$\sigma$). Such results are also in good agreement with independent studies from the Hubble Space Telescope key project and recent estimates based on Wilkinson Microwave Anisotropy Probe, thereby suggesting that the combination of these three independent phenomena provides an interesting method to constrain the Hubble constant. In particular, comparing these results with a recent determination for a flat LCDM model using only the SZE technique and BAO [Cunha et al. MNRAS 379, L1 2007], we see that the geometry has a very weak influence on H0 estimates for this combination of data.
The structural parameters of the disk of the Large Magellanic Cloud (LMC) are estimated.We used the red clump stars from the VI photometric data of the Optical Gravitational Lensing Experiment (OGLE III) survey and from the Magellanic Cloud Photometric Survey (MCPS) for the estimation of inclination and position angle of line of nodes of the LMC disk. The dereddened peak I magnitude of the red clump stars in each subregion is used to obtain the relative distances and hence the z coordinate. The RA and Dec of each sub-region is converted into x & y cartesian coordinates. A weighted least square plane fitting method is applied to this x,y,z data to estimate the structural parameters of the LMC disk. We find an inclination of i =23.0 plus or minus 0.8 and PAlon = 163.7 plus or minus 1.5 for the LMC disk using the OGLE III data and an inclination of i=37.4 plus or minus 2.3 and PAlon= 141.2 plus or minus 3.7 for the LMC disk using the MCPS data. Extra-planar features which are in front as well as behind the fitted plane are seen in both the data sets. The effect of choice of center, reddening and area covered on the estimated parameters are discussed. Regions in the north west, south west and south east of the LMC disk are warped with respect to the fitted plane. We also identify a symmetric but offcentered warp in the inner LMC.We identify that the structure of the LMC disk inside the 3 degree radius is different from the outside disk such that the inner LMC has relatively less inclination and relatively large PAlon. The 3D plot of the LMC disk suggests an offcentered increase in the inclination for the north-eastern regions which might be due to tidal effects. We suggest that the variation in the planar parameters estimated by various authors as well as in this study is because of the difference in coverage and the complicated inner structure of the LMC disk. In the inner LMC, the stellar and HI disk are found to have similar properties.
Primordial magnetic fields could provide an explanation for the galactic magnetic fields observed today, in which case they may also leave interesting signals in the CMB and the small-scale matter power spectrum. We discuss how to approximately calculate the important non-linear magnetic effects within the guise of linear perturbation theory, and calculate the matter and CMB power spectra including the SZ contribution. We then use various cosmological datasets to constrain the form of the magnetic field power spectrum. Using solely large-scale CMB data (WMAP7, QUaD and ACBAR) we find a 95% CL on the variance of the magnetic field at 1 Mpc of B_\lambda < 6.4 nG. When we include SPT data to constrain the SZ effect, we find a revised limit of B_\lambda < 4.1 nG. The addition of SDSS Lyman-alpha data lowers this limit even further, roughly constraining the magnetic field to B_\lambda < 1.3 nG.
We investigate the scale on which the correlation arises between the 843 MHz radio and the 60 micron far-infrared (FIR) emission from star forming regions in the Milky way. The correlation, which exists on the smallest scales investigated (down to ~4 pc), becomes noticeably tight on fields of size 30', corresponding to physical scales of ~20-50 pc. The FIR to radio flux ratio on this scale is consistent with the radio emission being dominated by thermal emission. We also investigate the location dependence of q_mean, a parameter measuring the mean FIR to radio flux ratio, of a sample of star forming regions. We show that q_mean displays a modest dependence on galactic latitude. If this is interpreted as a dependence on the intensity of star formation activity, the result is consistent with studies of the Large Magellanic Cloud (LMC) and other nearby galaxies that show elevated values for q in regions of enhanced star formation.
Star formation is regulated through a variety of feedback processes. In this study, we treat feedback by metal injection and a UV background as well as by X-ray irradiation. Our aim is to investigate whether star formation is significantly affected when the ISM of a proto-galaxxy enjoys different metallicities and when a star forming cloud resides in the vicinity of a strong X-ray source. We perform cosmological Enzo simulations with a detailed treatment of non-zero metallicity chemistry and thermal balance. We also perform FLASH simulations with embedded Lagrangian sink particles of a collapsing molecular cloud near a massive, 10^{7} M\odot, black hole that produces X-ray radiation. We find that a multi-phase ISM forms for metallicites as small as 10^{-4} Solar at z = 6, with higher (10^{-2}Z\odot) metallicities supporting a cold (< 100 K) and dense (> 10^{3} cm^{-3}) phase at higher (z = 20) redshift. A star formation recipe based on the presence of a cold dense phase leads to a self-regulating mode in the presence of supernova and radiation feedback. We also find that when there is strong X-ray feedback a collapsing cloud fragments into larger clumps whereby fewer but more massive protostellar cores are formed. This is a consequence of the higher Jeans mass in the warm (50 K, due to ionization heating) molecular gas. Accretion processes dominate the mass function and a near-flat, non-Salpeter IMF results.
To investigate the present situation of the merging in the southern outer region of Abell 85, we carried out long (~100 ks) observations with Suzaku, and produced an X-ray hardness ratio map. We found a high hardness ratio peak in the east side of a subcluster located in the south of the cluster; an X-ray spectrum of the region including this peak indicates a high temperature of ~8.5 keV. This hot spot has not been reported so far. We consider that this hot spot is a postshock region produced by the infall of the subcluster from the southwest. By using the Rankine--Hugoniot jump conditions for shocks, the Mach number and the infall velocity of the subcluster are obtained as 1.5 +/- 0.2 and 1950^{+290}_{-280} km s^{-1}, respectively, in the case of merging with the subcluster from the southwest direction. By using the redshift difference between the A 85 and the subcluster obtained from optical observations, the angle between the line of sight and the direction of the motion of the subcluster is estimated to be 75^{+7}_{-8} degrees. We estimate the kinetic energy of the subcluster and the energy used for intracluster medium (ICM) heating to be ~10^{63} and \lesssim 8 \times 10^{60} erg, respectively. This shows that the deceleration of the subcluster by ICM heating has been negligibly small.
We study a simple five-dimensional extension of the Standard Model, compactified on a flat line segment in which there propagate Higgs and gauge bosons of the Standard Model. We impose a Dirichlet boundary condition on the Higgs field to realize its vacuum expectation value. Since a flat Nambu-Goldstone zero-mode of the bulk Higgs is eliminated by the Dirichlet boundary condition, a superposition of the Higgs Kaluza-Klein modes play the role of the Nambu-Goldstone boson except at the boundaries. We discuss phenomenology of our model at the LHC, namely the top Yukawa deviation and the production and invisibly rapid decay of the physical Higgs field, as well as the constraints from the electroweak precision measurements.
The purpose of this paper is to explain clearly why nonlocality must be an essential part of the theory of relativity. In the standard local version of this theory, Lorentz invariance is extended to accelerated observers by assuming that they are pointwise inertial. This locality postulate is exact when dealing with phenomena involving classical point particles and rays of radiation, but breaks down for electromagnetic fields, as field properties in general cannot be measured instantaneously. The problem is corrected in nonlocal relativity by supplementing the locality postulate with a certain average over the past world line of the observer.
We study the stability properties of the Cauchy horizon for two different self-dual black hole solutions obtained in a model inspired by Loop Quantum Gravity. The self-dual spacetimes depend on a free dimensionless parameter called a polymeric parameter P. For the first metric the Cauchy horizon is stable for supermassive black holes only if this parameter is sufficiently small. For small black holes, however the stability is easily implemented. The second metric analyzed is not only self-dual but also "form-invariant" under the transformation r -> r*^2/r and r* = 2 m P. We find that this symmetry protects the Cauchy horizon for any value of the polymeric parameter.
The persistent discrepancy between observations of 7Li with putative primordial origin and its abundance prediction in Big Bang Nucleosynthesis (BBN) has become a challenge for the standard cosmological and astrophysical picture. We point out that the decay of GeV-scale metastable particles X may significantly reduce the BBN value down to a level at which it is reconciled with observations. The most efficient reduction occurs when the decay happens to charged pions and kaons, followed by their charge exchange reactions with protons. Similarly, if X decays to muons, secondary electron antineutrinos produce a similar effect. We consider the viability of these mechanisms in different classes of new GeV-scale sectors, and find that several minimal extensions of the Standard Model with metastable vector and/or scalar particles are capable of solving the cosmological lithium problem. Such light states can be a key to the explanation of recent cosmic ray anomalies and can be searched for in a variety of high-intensity medium-energy experiments.
Particles dropped into a rotating black hole can collide near the inner horizon with enormous energies. The entropy produced by these collisions can be several times larger than the increase in the horizon entropy due to the addition of the particles. In this paper entropy is produced by releasing large numbers of neutrons near the outer horizon of a rotating black hole such that they collide near the inner horizon at energies similar to those achieved at the Relativistic Heavy Ion Collider. The increase in horizon entropy is approximately 80 per dropped neutron pair, while the entropy produced in the collisions is 160 per neutron pair. The collision entropy is produced inside the horizon, so this excess entropy production does not violate Bousso's bound limiting the entropy that can go through the black hole's horizon. The generalized laws of black hole thermodynamics are obeyed. No individual observer inside the black hole sees a violation of the second law of thermodynamics
We give a novel description of the recently proposed theory of new massive gravity (NMG) in three dimensions. We show that in terms of a Dirac type differential operator acting on the traceless Ricci tensor, the field equations of the theory reduce to the massive Klein-Gordon type equation with a curvature-squared source term and to a constraint equation. Under a certain relation between the source tensor and the traceless Ricci tensor, fulfilled for constant scalar curvature, the field equations of topologically massive gravity (TMG) can be thought of as the ``square-root" of the massive Klein-Gordon type equation. Using this fact, we establish a simple framework for mapping all known algebraic types D and N solutions of TMG into NMG. We also present new exact solutions of algebraic types D and N that are only inherent in NMG.
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We present the 24 micron rest-frame luminosity function (LF) of star-forming galaxies in the redshift range 0.0 < z < 0.6 constructed from 4047 spectroscopic redshifts from the AGN and Galaxy Evolution Survey of 24 micron selected sources in the Bootes field of the NOAO Deep Wide-Field Survey. This sample provides the best available combination of large area (9 deg^2), depth, and statistically complete spectroscopic observations, allowing us to probe the evolution of the 24 micron LF of galaxies at low and intermediate redshifts while minimizing the effects of cosmic variance. In order to use the observed 24 micron luminosity as a tracer for star formation, active galactic nuclei (AGNs) that could contribute significantly at 24 micron are identified and excluded from our star-forming galaxy sample based on their mid-IR spectral energy distributions or the detection of X-ray emission. The evolution of the 24 micron LF of star-forming galaxies for redshifts of z < 0.65 is consistent with a pure luminosity evolution where the characteristic 24 micron luminosity evolves as (1+z)^(3.8+/-0.3). We extend our evolutionary study to encompass 0.0 < z < 1.2 by combining our data with that of the Far-Infrared Deep Extragalactic Legacy Survey. Over this entire redshift range the evolution of the characteristic 24 micron luminosity is described by a slightly shallower power law of (1+z)^(3.4+/-0.2). We find a local star formation rate density of (1.09+/-0.21) x 10^-2 Msun/yr/Mpc^-3, and that it evolves as (1+z)^(3.5+/-0.2) over 0.0 < z < 1.2. These estimates are in good agreement with the rates using optical and UV fluxes corrected for the effects of intrinsic extinction in the observed sources. This agreement confirms that star formation at z <~ 1.2 is robustly traced by 24 micron observations and that it largely occurs in obscured regions of galaxies. (Abridged)
(abridged) Using a Lyman-Break technique, we identify 66 z~7 and 47 z~8 candidate galaxies in the ultra-deep (~29 AB mag) WFC3/IR observations over the HUDF and two nearby HUDF09 fields (14 arcmin**2) and the deep (~27.5 AB mag), wide-area (~40 arcmin**2) ERS observations. This 26-29 AB mag sample of 113 galaxies in the reionization epoch is the largest currently available. A contamination rate of <=14% is found after thoroughly assessing the impact of lower redshift sources, photometric scatter, low mass stars, spurious sources, and transients on our selection. Carefully modelling the selection volumes for each of our search fields, we derive luminosity functions for galaxies at z~7 and z~8. The faint-end slopes alpha we find at z~7 and z~8 are alpha = -1.94+/-0.24 and alpha=-2.00+/-0.33, respectively. This provides increasingly strong evidence that the UV LF at z>~6 is at least as steep as at z~4 (alpha=-1.73+/-0.05), with alpha<~-1.7, and that lower luminosity galaxies dominate the galaxy luminosity density during the epoch of reionization. Luminosity densities and SFRs derived from these UV LFs are compared to those derived from recent stellar mass density determinations at z>~4. We find reasonable consistency, with the SFR densities implied from the stellar mass densities being only ~40% higher at z<7. This suggests that (1) the stellar mass densities inferred from the Spitzer IRAC photometry are reasonably accurate and (2) that the IMF at very high redshift may not be that different from later times. Extrapolating these LFs to lower luminosities and higher redshifts show that galaxies contribute substantially to the reionization. Thomson optical depths of 0.056 (0.075), within 2sigma (1sigma) of the latest WMAP values, are obtained for escape fractions of 20% (60%) and clumping factors of 3.
We present results from new Chandra, GMRT, and SOAR observations of NGC 5813, the dominant central galaxy in a nearby galaxy subgroup. The system shows clear signatures from three distinct outbursts of the central AGN, with three pairs of roughly collinear cavities. The inner two cavity pairs are each associated with elliptical surface brightness edges, which we unambiguously identify as shocks with measured temperature jumps and with Mach numbers of M \approx 1.7 and M \approx 1.5 for the inner and outer shocks, respectively. Such clear signatures from three distinct AGN outbursts in an otherwise relaxed system provide a unique opportunity to study AGN feedback and outburst history. The mean power of the two most recent outbursts varies by an order of magnitude, indicating that the mean jet power varies significantly over long (~10^7 yr) timescales. The total energy output of the most recent outburst is also less than the total energy of the previous outburst, which may be a result of the lower mean power, or may indicate that the most recent outburst is ongoing. We directly measure the local heat input into the ICM at the shock fronts, and show that the shock heating balances radiative cooling of the gas locally. The outburst interval implied by both the shock and cavity ages (~10^7 yr) indicates that in this system shock heating alone is sufficient to balance radiative cooling close to the central AGN, which is the relevant region for regulating feedback between the ICM and the central SMBH.
We have measured redshifts for 243 z ~3 quasars in nine VLT VIMOS LBG redshift survey areas, each of which is centred on a known bright quasar. Using spectra of these quasars, we measure the cross-correlation between neutral hydrogen gas causing the Lya forest and 1020 Lyman-break galaxies at z ~3. We find an increase in neutral hydrogen absorption within 5 h^-1 Mpc of a galaxy in agreement with the results of Adelberger et al. (2003, 2005). The Lya-LBG cross-correlation can be described by a power-law on scales larger than 3 h^-1 Mpc. When galaxy velocity dispersions are taken into account our results at smaller scales (<2 h^-1 Mpc) are also in good agreement with the results of Adelberger et al. (2005). There is little immediate indication of a region with a transmission spike above the mean IGM value which might indicate the presence of star-formation feedback. To measure the galaxy velocity dispersions, which include both intrinsic LBG velocity dispersion and redshift errors, we have used the LBG-LBG redshift space distortion measurements of Bielby et al. (2010). We find that the redshift-space transmission spike implied in the results of Adelberger et al. (2003) is too narrow to be physical in the presence of the likely LBG velocity dispersion and is likely to be a statistical fluke. Nevertheless, neither our nor previous data can rule out the presence of a narrow, real-space transmission spike, given the evidence of the increased Lya absorption surrounding LBGs which can mask the spike's presence when convolved with a realistic LBG velocity dispersion. Finally, we identify 176 CIV systems in the quasar spectra and find an LBG-CIV correlation strength on scales of 10 h^-1 Mpc consistent with the relation measured at ~Mpc scales.
The study of linear perturbation theory for general functions of the Ricci and Gauss-Bonnet scalars is done over an empty anisotropic universe, i.e. the Kasner-type background, in order to show that an anisotropic background in general has ghost degrees of freedom, which are absent on Friedmann-Lemaitre-Robertson-Walker (FLRW) backgrounds. The study of the scalar perturbation reveals that on this background the number of independent propagating degrees of freedom is four and reduces to three on FLRW backgrounds, as one mode becomes highly massive to decouple from the physical spectrum. When this mode remains physical, there is inevitably a ghost mode.
Population III star formation during the dark ages shifted from minihalos (~10^6 Msun) cooled via molecular hydrogen to more massive halos (~10^8 Msun) cooled via Ly-alpha as Lyman-Werner backgrounds progressively quenched molecular hydrogen cooling. Eventually, both modes of primordial star formation were suppressed by the chemical enrichment of the IGM. We present a comprehensive model for following the modes of Population III star formation that is based on a combination of analytical calculations and cosmological simulations. We characterize the properties of the transition from metal-free star formation to the first Population II clusters for an average region of the Universe and for the progenitors of the Milky Way. Finally, we highlight the possibility of observing the explosion of Population III stars within Ly-alpha cooled halos at redshift z~6 in future deep all sky surveys such as LSST.
The presence of absorbing gas around the central engine of Active Galactic Nuclei (AGN) is a common feature of these objects. Recent work has looked at the effect of the dust component of the gas, and how it enhances radiation pressure such that dusty gas can have a lower effective Eddington limit than ionised gas. In this work, we use multi-wavelength data and X-ray spectra from the 2 Ms exposures of the Chandra Deep Field North and Chandra Deep Field South surveys, to characterise the AGN in terms of their Eddington ratio and hydrogen column density. Their distributions are then compared with what is predicted when considering the coupling between dust and gas. Our final sample consists of 234 objects from both fields, the largest and deepest sample of AGN for which this comparison has been made up to date. We find that most of the AGN in our sample tend to be found at low Eddington ratios (typically between 1e-4 and 1e-1) and high column density (>1e22 cm^-2), with black hole masses between ~1e8 and 1e9 solar masses. Their distribution is in agreement with that expected from the enhanced radiation pressure model, avoiding the area where we would predict the presence of outflows. We also investigate how the balance between AGN radiation pressure and gravitational potential influences the behaviour of clouds in the galactic bulge, and describe a scenario where an enhanced radiation pressure can lead to the fundamental plane of black hole/galaxy scaling relations.
We analyze the optical-near infrared spectra of 33 quasars with redshifts 3.9 < z < 6.4 with the aim of investigating the properties of dust extinction at these cosmic epochs. The SMC extinction curve has been shown to reproduce the dust reddening of most quasars at z < 2.2; the main goal of this work is to investigate whether this curve provides a good prescription for describing dust extinction also at higher redshifts or not. We fit the observed spectra with synthetic absorbed quasar templates obtained by varying the intrinsic slope (alpha), the absolute extinction (A3000) and by using grid of empirical and theoretical extinction curves. We find that seven quasars in our sample require substantial extinction (A3000 > 0.8), and are characterized by very steep intrinsic slopes (alpha < -2.3). All of the individual quasars require extinction curve deviating from the SMC, with a tendency to flatten at lambda < 2000 A (rest frame). We obtain a mean extinction curve at z>4, both by a simultaneous fit of all quasars and by averaging the extinction curves inferred for individual quasars. In the case of Broad Absorption Line quasars the mean extinction curve deviates from the SMC at a confidence level > 95%. The different extinction curves in quasars at z>4 relative to quasars at lower redshift suggest either a different dust production mechanism at high redshift, or a different mechanism of processing dust into the ISM. We suggest that the same transitions may also apply to normal, star forming galaxies at z>4. In particular, the observed change of the average spectral slope in galaxies at z>4 may be partially ascribed to a variation of the extinction curve, rather than a lower dust content at high redshift. In this scenario, the extinction curve inferred at z>4 would imply a corrected cosmic star formation rate at these epochs a factor of \sim 2 higher than estimated in the past.
We analyse the redshift dependence of space number density of quasars assuming that they are the short-lived active stages of the massive galaxies and arise immediately after the collapse of homogeneous central part of protogalaxy clouds. Obtained dependence fits the observational data ChaMP+CDF+ROSAT (Silverman et al. 2005) very well for protogalaxy clouds of mass $M\approx 8\cdot 10^{11}$ $h^{-1}M_{\odot}$ and ellipticity $e<0.4$. The lifetime of bright X-ray AGNs or QSOs with $L_X>10^{44.5}$ erg$\cdot s^{-1}$ in the range of energies $0.3-8$ keV is $\tau_{QSO}\sim 6\cdot10^6$ years when the mass of supermassive black hole is $M_{SMBH}\sim 10^{9}$ $M_{\odot}$ and the values of other quasar parameters are reasonable. The analysis and all calculations were carried out in the framework of $\Lambda$CDM-model with parameters determined from 5-years WMAP, SNIa and large scale structure data \cite{Komatsu09}. It is concluded, that the halo model of galaxy formation in the $\Lambda$CDM cosmological model matches well observational data on AGNs and QSOs number density coming from current optical and X-ray surveys.
Gamma-ray bursts are usually classified through their high-energy emission into short-duration and long-duration bursts, which presumably reflect two different types of progenitors. However, it has been shown on statistical grounds that a third, intermediate population is needed in this classification scheme, although an extensive study of the properties of this class has so far not been done. The large amount of follow-up studies generated during the Swift era allows us to have a suficient sample to attempt a study of this third population through the properties of their prompt emission and their afterglows. Our study is focused on a sample of GRBs observed by Swift during its first four years of operation. The sample contains those bursts with measured redshift since this allows us to derive intrinsic properties. Intermediate bursts are less energetic and have dimmer afterglows than long GRBs, especially when considering the X-ray light curves, which are on average one order of magnitude fainter than long bursts. There is a less significant trend in the redshift distribution that places intermediate bursts closer than long bursts. Except for this, intermediate bursts show similar properties to long bursts. In particular, they follow the Epeak vs. Eiso correlation and have, on average, positive spectral lags with a distribution similar to that of long bursts. Like long GRBs, they normally have an associated supernova, although some intermediate bursts have shown no supernova component. This study shows that intermediate bursts are different from short bursts and, in spite of sharing many properties with long bursts, there are some differences between them as well. We suggest that the physical difference between intermediate and long bursts could be that for the first the ejecta are thin shells while for the latter they are thick shells.
We perform a uniform, systematic analysis of a sample of 38 X-ray galaxy clusters with three different Chandra calibrations. The temperatures change systematically between calibrations. Cluster temperatures change on average by roughly ~6% for the smallest changes and roughly ~13% for the more extreme changes between calibrations. We explore the effects of the changing cluster spectral properties on Sunyaev-Zel'dovich effect (SZE) and X-ray determinations of the Hubble constant. The Hubble parameter changes by +10% and -13% between the current calibration and two previous Chandra calibrations, indicating that changes in the cluster temperature basically explain the entire change in H_0. Although this work focuses on the difference in spectral properties and resultant Hubble parameters between the calibrations, it is intriguing to note that the newer calibrations favor a lower value of the Hubble constant, H_0 ~ 60 km s-1 Mpc-1, typical of results from SZE/X-ray distances. Both galaxy clusters themselves and the details of the instruments must be known precisely to enable reliable precision cosmology with clusters, which will be feasible with combined efforts from ongoing observations and planned missions and observatories covering a wide range of wavelengths.
Context. Hydrogen ionized by young, high-mass stars in starburst galaxies
radiates radio recombination lines (RRLs), whose strength can be used as a
diagnostic of the ionization rate, conditions and gas dynamics in the
starburst, without problems of dust obscuration. However, the lines are weak
and only few extragalactic starburst systems have been detected.
Aims. We aimed to increase the number of known starburst systems with
detectable RRLs for detailed studies.
Methods. We searched for the RRLs H91alpha and H92alpha at 8 GHz in the
nearby Seyfert galaxy NGC 4945 using the ATCA with resolution of 3". This
yielded a detection from which we derived conditions in the starburst.
Results. We detected RRLs from the nucleus of NGC 4945 with a peak strength
of 17.8 mJy, making it the strongest extragalactic RRL emitter known at this
frequency. The line emission from NGC 4945 can be matched by a model consisting
of a collection of 10 to 300 H II regions with temperatures of 5000 K,
densities of 10^3 cm^-3 to 10^4 cm^-3 and a total effective diameter of 2 pc to
100 pc. The Lyman continuum production rate required to maintain the ionization
requires 2000 to 10000 O5 stars to be produced in the starburst, inferring a
star formation rate of 2 Msun/yr to 8 Msun/yr. We resolved the rotation curve
within the central 70 pc region and this is well described by a set of rotating
rings that were coplanar and edge on with a simple flat rotation curve. The
rotation speed of 120 km/s within the central 1" (19 pc) radius infers an
enclosed mass of 3 x 10^7 Msun.
Conclusion. We discovered RRLs from NGC 4945. It is the strongest known
extragalactic RRL emitter and is suited to high-quality spectroscopic study. We
resolved the dynamics of the ionized gas in the central 70 pc and derived
conditions and star formation rates in the ionized gas.
Understanding the infrared emission of galaxies is critical to observational and theoretical investigations of the condensation of galaxies out of the intergalactic medium and the conversion of gas into stars over cosmic time. From an observational perspective, about half of all photons emitted within galaxies are locally absorbed by dust grains, necessitating a self-consistent analysis of the panchromatic emission of galaxies to quantify star-formation and AGN activity as a function of epoch and environment. From a theoretical perspective, physical processes involving dust are expected to play a major role in regulating the accumulation of baryons in galaxies and their condensation into stars on scales ranging from Mpc down to sub-pc. All this requires a quantitative analysis of the interaction between dust, gas and radiation. Here we review progress in the modelling of some of these processes.
Couplings between the inflaton and any additional fields can lead to isolated bursts of particle production during inflation (for example from parametric resonance or a phase transition). Inflationary particle production leaves localized features in the spectrum and bispectrum of the observable cosmological fluctuations, via the Infra-Red (IR) cascading mechanism. We focus on a simple prototype interaction g^2 (\phi-\phi_0)^2\chi^2 between the inflaton, \phi, and iso-inflaton, \chi; extending previous work on this model in two directions. First, we quantify the magnitude of the produced nongaussianity by extracting the moments of the probability distribution function from lattice field theory simulations. We argue that the bispectrum feature from particle production might be observable for reasonable values of the coupling, g^2. Second, we develop a detailed analytical theory of particle production and IR cascading during inflation, which is in excellent agreement with numerical simulations. Our formalism improves significantly on previous approaches by consistently incorporating both the expansion of the universe and also metric perturbations. We use this new formalism to estimate the shape of the bispectrum from particle production, showing this to be distinguishable from other mechanisms that predict large nongaussianity.
We study superparticle spectra in the superconformal flavor scenario with non-universal gaugino masses. The non-universality of gaugino masses can lead to the wino-like or higgsino-like neutralino LSP. Furthermore, it is shown that the parameter space for the higgsino-like LSP includes the region where the fine-tuning problem can be improved. The degeneracy of soft scalar masses squared does not drastically change by taking ratios of gaugino masses of order one. The degeneracy of scalar masses for squarks and left-handed sleptons would be good to avoid the FCNC problem but that of right-handed slepton masses is weak. However, the overall size of right-handed slepton masses become larger when the bino becomes heavier. It is also pointed out that such region can be realized, and thus, that would be favorable to avoid the FCNC problem for soft scalar masses as well as A-terms.
Adiabatic contraction is frequently used to model the effects of baryon condensation on dark matter halos. However, it has recently been shown that this model is not always accurate; authors including Gnedin et al. (2004) and Gustafsson et al. (2006) have found it to be inaccurate at the level of tens of percent. We have analyzed high resolution N-body simulations of dark matter halos, focusing specifically on the evolution of angular momentum, to assess the accuracy of the assumptions of the adiabatic contraction model. We investigate the validity of the assumptions using dark-matter-only halos, in order to provide a limit on how accurate we may expect the adiabatic contraction model to be once baryons are included. In brief, we find that not only is individual particle angular momentum not conserved, but the radial profile and distribution of angular momentum also varies over the age of the Universe by up to factors of a few. We find that torques from external structure are the most likely cause for this distribution shift. This variation implies that there is a fundamental limit on the possible accuracy of the adiabatic contraction model in modeling the response of DM halos to the growth of galaxies.
Precision tests of gravity can be used to constrain the properties of hypothetical very light scalar fields, but these tests depend crucially on how macroscopic astrophysical objects couple to the new scalar field. We develop quasi-analytic methods for solving the equations of stellar structure using scalar-tensor gravity, with the goal of seeing how stellar properties depend on assumptions made about the scalar coupling at a microscopic level. We illustrate these methods by applying them to Brans-Dicke scalars, and their generalization in which the scalar-matter coupling is a weak function of the scalar field. The four observable parameters that characterize the fields external to a spherically symmetric star (the stellar radius, R, mass, M, scalar `charge', Q, and the scalar's asymptotic value, phi_infty) are subject to two relations because of the matching to the interior solution, generalizing the usual mass-radius, M(R), relation of General Relativity. We identify how these relations depend on the microscopic scalar couplings, agreeing with earlier workers when comparisons are possible. Explicit analytical solutions are obtained for the instructive toy model of constant-density stars, whose properties we compare to more realistic equations of state for neutron star models.
In hybrid inflation, initial field values leading to sufficiently long inflation were thought be fine-tuned in a narrow band along the inflationary valley. A re-analysis of this problem has shown that there exists a non negligible proportion of successful initial conditions exterior to the valley, organized in a complex structure with fractal boundaries, and whose origin has been explained. Their existence in a large part of the parameter space has been demonstrated using a bayesian Monte-Carlo-Markov-Chain (MCMC) method, and natural bounds on potential parameters have been established. Moreover, these results are shown to be valid not only for the original hybrid model, but also for other hybrid realizations in various frameworks.
If neutrino mass is a function of the Higgs potential then minimum of the total thermodynamic potential $\Omega$ (which is the Higgs potential minus the neutrino pressure) can shift from the standard electro-weak vev $v=246.2$ GeV by a small amount which depends on the neutrino pressure. If the neutrino mass is a very steep function of the Higgs field then the equilibrium thermodynamic potential can act like the dark energy with $\omega \simeq -1$. Choosing the neutrino mass as logarithmic function of the Higgs field and a heavy mass scale, we find that the correct magnitude of the cosmological density of the present universe $\rho_\lambda \simeq (0.002 eV)^4$ is obtained by choosing the heavy mass at the GUT scale.
The characterization of a $m$-dimensional internal manifold with metric as having positive, zero or negative curvature is known to be one of the most important aspects of warped compactifications in $(4+m)$-dimensional supergravity models and hence that of matter content in an effective four-dimensional theory. In this context, Douglas and Kallosh in arXiv:1001.4008 argued that string compactifications using manifolds whose scalar curvature is everywhere negative must have significant warping or large stringy corrections, or both. Douglas-Kallosh argument may apply to some particular class of flux compactifications with strong constraints on the warp geometry or standard Kaluza-Klein compactifications (with constant warp factor), but perhaps not to a general class of warped solutions in curved manifolds. For clarity, we first present some explicit examples of 4D de Sitter solutions in ten and eleven dimensions, without source terms (fluxes or objects that violate positivity conditions), but with an arbitrary 6D curvature. We then explore the possibility of obtaining de Sitter solutions by using a 6-dimensional warped manifold ${\cal M}$ by introducing p-form gauge fields. We show that 4D de Sitter solutions can exist with almost any choice of internal space curvature, including manifolds whose 6D Ricci scalar curvature is negative.
By performing a bayesian Monte-Carlo-Markov-Chain analysis, it is shown that a large number of e-folds (more than 60) are generated classically during the waterfall after hybrid inflation in a large part of the parameter space of the model. As a result, the observable perturbation modes leave the Hubble radius during waterfall inflation. The power spectrum of adiabatic perturbations is red, possibly in agreement with CMB constraints. A particular attention has been given to study only the regions for which quantum backreactions do not affect the classical dynamics. Implications concerning the preheating and the absence of topological defects in our universe are discussed.
The X-ray spectrum of the Seyfert 1.5 source NGC 6860 is among the most complex of the sources detected in the Swift Burst Alert Telescope all-sky survey. A short XMM-Newton follow-up observation of the source revealed a flat spectrum both above and below 2 keV. To uncover the complexity of the source, in this paper we analyze both a 40 ks Suzaku and a 100 ks XMM-Newton observation of NGC 6860. While the spectral state of the source changed between the newer observations presented here and the earlier short XMM-Newton spectrum - showing a higher flux and steeper power law component - the spectrum of NGC 6860 is still complex with clearly detected warm absorption signatures. We find that a two component warm ionized absorber is present in the soft spectrum, with column densities of about 10^20 and 10^21 cm$^-2, ionization parameters of xi = 180 and 45 ergs cm s^-1, and outflow velocities for each component in the range of 0-300 km s^-1. Additionally, in the hard spectrum we find a broad (approx 11000 km s^-1) Fe K-alpha emission line, redshifted by approx 2800 km s^-1.
We expand the study of generalized brane cosmologies by allowing for an $f(\tilde{\cal R})$ gravity term on the brane, with $\tilde{\cal R}$ the curvature scalar derived from the induced metric. We also include arbitrary matter components on the brane and in the five-dimensional bulk. At low energies, the effect of the bulk on the brane evolution can be described through a mirage component, termed generalized dark radiation, in the effective four-dimensional field equations. Using the covariant formalism, we derive the exact form of these equations. We also derive an effective conservation equation involving the brane matter and the generalized dark radiation. At low energies the coupled brane-bulk system has a purely four-dimensional description. The applications of the formalism include generalizations of the Starobinsky model and the Dvali-Gabadadze-Porrati cosmology.
This is the first paper of a series in which we present new measurements of the observed rates of supernovae (SNe) in the local Universe, determined from the Lick Observatory Supernova Search (LOSS). We have obtained 2.3 million observations of 14,882 sample galaxies over an interval of 11 years (March 1998 through Dec. 2008). We considered 1036 SNe detected in our sample and used an optimal subsample of 726 SNe (274 SNe~Ia, 116 SNe~Ibc, 324 SNe~II) to determine our SN rates. This is the largest and most homogeneous set of nearby SNe ever assembled for this purpose, and ours is the first local SN rate analysis based on CCD imaging and modern image-subtraction techniques. In this paper, we lay the foundation of the study. We derive the recipe for the control-time calculation for SNe with a known luminosity function, and provide details on the construction of the galaxy and SN samples used in the calculations. Compared with a complete volume-limited galaxy sample, our sample has a deficit of low-luminosity galaxies but still provides enough statistics for a reliable rate calculation. There is a strong Malmquist bias, so the average size (luminosity or mass) of the galaxies increases monotonically with distance, and this trend is used to showcase a correlation between SN rates and galaxy sizes. Very few core-collapse SNe are found in early-type galaxies, providing strong constraints on the amount of recent star formation within these galaxies. The small average observation interval ($\sim 9$ days) of our survey ensures that our control-time calculations can tolerate a reasonable amount of uncertainty in the luminosity functions of SNe. We perform Monte Carlo simulations to determine the limiting magnitude of each image and the SN detection efficiency as a function of galaxy Hubble type ... (abridged)
This is the second paper of a series in which we present new measurements of the observed rates of supernovae (SNe) in the local Universe, determined from the Lick Observatory Supernova Search (LOSS). In this paper, a complete SN sample is constructed, and the observed (uncorrected for host-galaxy extinction) luminosity functions (LFs) of SNe are derived. These LFs solve two issues that have plagued previous rate calculations for nearby SNe: the luminosity distribution of SNe and the host-galaxy extinction. We select a volume-limited sample of 175 SNe, collect photometry for every object, and fit a family of light curves to constrain the peak magnitudes and light-curve shapes. The volume-limited LFs show that they are not well represented by a Gaussian distribution. There are notable differences in the LFs for galaxies of different Hubble types (especially for SNe Ia). We derive the observed fractions for the different subclasses in a complete SN sample, and find significant fractions of SNe II-L (10%), IIb (12%), and IIn (9%) in the SN II sample. Furthermore, we derive the LFs and the observed fractions of different SN subclasses in a magnitude-limited survey with different observation intervals, and find that the LFs are enhanced at the high-luminosity end and appear more "standard" with smaller scatter, and that the LFs and fractions of SNe do not change significantly when the observation interval is shorter than 10 days. We also discuss the LFs in different galaxy sizes and inclinations, and for different SN subclasses. Some notable results are ... (abridged).
This is the third paper of a series in which we present new measurements of the observed rates of supernovae (SNe) in the local Universe, determined from the Lick Observatory Supernova Search (LOSS). We have considered a sample of about 1000 SNe and used an optimal subsample of 726 SNe (274 SNe Ia, 116 SNe Ibc, and 324 SNe II) to determine our rates. We study the trend of the rates as a function of a few quantities available for our galaxy sample, such as luminosity in the B and K bands, stellar mass, and morphological class. We discuss different choices (SN samples, input SN luminosity functions, inclination correction factors) and their effect on the rates and their uncertainties. A comparison between our SN rates and the published measurements shows that they are consistent with each other to within uncertainties when the rate calculations are done in the same manner. Nevertheless, our data demonstrate that the rates cannot be adequately described by a single parameter using either galaxy Hubble types or B - K colours. A secondary parameter in galaxy "size", expressed by luminosity or stellar mass, is needed to adequately describe the rates in the rate-size relation: the galaxies of smaller sizes have higher SN rates per unit mass or per unit luminosity. The trends of the SN rates in galaxies of different Hubble types and colours are discussed. We examine possible causes for the rate-size relation. Physically, such a relation for the core-collapse SNe is probably linked to the correlation between the specific star-formation rate and the galaxy sizes, but it is not clear whether the same link can be established for SNe Ia. We discuss the two-component ("tardy" and "prompt") model for SN Ia rates, and find that the SN Ia rates in young stellar populations might have a strong correlation with the core-collapse SN rates. We derive volumetric and Milky Way rates ... (abridged)
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We present new measurements of the coherent motion of galaxies based on observations of the large-scale redshift--space distortions seen in the two--dimensional two--point correlation function of Luminous Red Galaxies in Data Release Seven of the Sloan Digital Sky Survey. We have developed a new methodology for estimating these coherent motions, which is less dependent on the details of galaxy bias and of the cosmological model to explain the late--time acceleration of the expansion of the Universe. We measure a one--dimensional velocity dispersion of galaxies on large--scales of sigma_v=3.01^{+0.45}_{-0.46} Mpc/h and sigma_v=3.69^{+0.47}_{-0.47} Mpc/h at a mean redshift of z=0.25 and 0.38 respectively. These values are fully consistent with predictions for a WMAP7--normalised LCDM Universe and inconsistent (at >5 sigma) with a Dvali-Gabadadze-Porrati (DGP) model for the Universe. We can convert the units of these sigma_v measurements to 270^{+40}_{-41} km/s and 320^{+41}_{-41} km/s respectively (assuming a LCDM universe), which are much lower than that expected based on recent low redshift (z<0.2) measurements of the peculiar velocity field (or ``bulk flows"), i.e., we would have predicted motions of ~ 600 km/s over our redshift range (0.16<z<0.47) to be consistent with these local measurements. One possible explanation for such a large discrepancy is that our Galaxy is located in unusually over, or under, dense region of the Universe.
One of the strongest arguments against the cosmological constant as an explanation of the current epoch of accelerated cosmic expansion is the existence of an earlier, dynamical acceleration, i.e. inflation. We examine the likelihood that acceleration is an occasional phenomenon, putting stringent limits on the length of any accelerating epoch between recombination and the recent acceleration; such an epoch must last less than 0.05 e-fold (at z>2) or the matter power spectrum is modified by more than 20%.
We present a HST/STIS spectroscopic and optical/radio imaging study of the Seyfert NGC 2110 aiming to measure the dynamics and understand the nature of the nuclear outflow in the galaxy. Previous HST studies have revealed the presence of a linear structure in the Narrow-Line Region (NLR) aligned with the radio jet. We show that this structure is strongly accelerated, probably by the jet, but is unlikely to be entrained in the jet flow. The ionisation properties of this structure are consistent with photoionisation of dusty, dense gas by the active nucleus. We present a plausible geometrical model for the NLR, bringing together various components of the nuclear environment of the galaxy. We highlight the importance of the circum-nuclear disc in determining the appearance of the emission line gas and the morphology of the jet. From the dynamics of the emission line gas, we place constraints on the accelerating mechanism of the outflow and discuss the relative importance of radio source synchrotron pressure, radio jet ram pressure and nuclear radiation pressure in accelerating the gas. While all three mechanisms can account for the energetics of the emission line gas, gravitational arguments support radio jet ram pressure as the most likely source of the outflow.
The spectral energy distribution of galaxies is a complex function of the star formation history and geometrical arrangement of stars and gas in galaxies. The computation of the radiative transfer of stellar radiation through the dust distribution is time-consuming. This aspect becomes unacceptable in particular when dealing with the predictions by semi-analytical galaxy formation models populating cosmological volumes, to be then compared with multi-wavelength surveys. Mainly for this aim, we have implemented an artificial neural network algorithm into the spectro-photometric and radiative transfer code GRASIL in order to compute the spectral energy distribution of galaxies in a short computing time. This allows to avoid the adoption of empirical templates that may have nothing to do with the mock galaxies output by models. The ANN has been implemented to compute the dust emission spectrum (the bottleneck of the computation), and separately for the star-forming molecular clouds and the diffuse dust (due to their different properties and dependencies). We have defined the input neurons effectively determining their emission, which means this implementation has a general applicability and is not linked to a particular galaxy formation model. We have trained the net for the disc and spherical geometries, and tested its performance to reproduce the SED of disc and starburst galaxies, as well as for a semi-analytical model for spheroidal galaxies. We have checked that for this model both the SEDs and the galaxy counts in the Herschel bands obtained with the ANN approximation are almost superimposed to the same quantities obtained with the full GRASIL. We conclude that this method appears robust and advantageous, and will present the application to a more complex SAM in another paper.
We investigate constraints on dark energy fluctuations using type Ia supernovae. If dark energy is not in the form of a cosmological constant, that is if the equation of state is not equal to -1, we expect not only temporal, but also spatial variations in the energy density. Such fluctuations would cause local variations in the universal expansion rate and directional dependences in the redshift-distance relation. We present a scheme for relating a power spectrum of dark energy fluctuations to an angular covariance function of standard candle magnitude fluctuations. The predictions for a phenomenological model of dark energy fluctuations are compared to observational data in the form of the measured angular covariance of Hubble diagram magnitude residuals for type Ia supernovae in the Union2 compilation. The observational result is consistent with zero dark energy fluctuations. However, due to the limitations in statistics, current data still allow for quite general dark energy fluctuations as long as they are in the linear regime.
We show here how Renormalized Perturbation Theory (RPT) calculations applied to the quasi-linear growth of the large-scale structure can be carried on in presence of primordial non-Gaussian (PNG) initial conditions. It is explicitly demonstrated that the series reordering scheme proposed in Bernardeau, Crocce and Scoccimarro (2008) is preserved for non-Gaussian initial conditions. This scheme applies to the power spectrum and higher order spectra and is based on a reorganization of the contributing terms into sum of products of multi-point propagators. In case of PNG new contributing terms appear, the importance of which is discussed in the context of current PNG models. The properties of the building blocks of such resummation schemes, the multi-point propagators, are then investigated. It is first remarked that their expressions are left unchanged at one-loop order irrespectively of statistical properties of the initial field. We furthermore show that the high-momemtum limit of each of these propagators can be explicitly computed even for arbitrary initial conditions. They are found to be damped by an exponential cutoff whose expression is directly related to the moment generating function of the one-dimensional displacement field. This extends what had been established for multi-point propagators for Gaussian initial conditions. Numerical forms of the cut-off are shown for the so-called local model of PNG.
Small fractions of isocurvature perturbations correlated with the dominant adiabatic mode are shown to be a significant primordial systematic for future Baryon Acoustic Oscillation (BAO) surveys, distorting the standard ruler distance by broadening and shifting the peak in the galaxy correlation function. Untreated this systematic leads to biases that can exceed $10\sigma$ in the dark energy parameters even for Planck-level isocurvature constraints. Accounting for the isocurvature modes corrects for this bias but degrades the dark energy figure of merit by at least 50\%. The BAO data in turn provides extremely powerful new constraints on the nature of the primordial perturbations. Future large galaxy surveys will thus be powerful probes of the earliest phase of the universe in addition to helping pin down the nature of dark energy.
The Galaxy Ultraviolet Explorer (GALEX) satellite has recently shown the presence of an extended, outer ring studded with UV-bright knots surrounding the lenticular galaxy NGC 4262. Such a structure---not detected in the optical---is coupled with a ring of atomic (HI) gas. We want to show that both star-forming and HI rings surrounding this SB0 galaxy share the same radial distance from the galaxy center and spatial orientation. We want also to model the kinematics of the ring(s) and of the galaxy body. We make use of archive FUV and NUV GALEX data plus HI observations from the literature. We confirm that the UV-bright and atomic gas rings of NGC 4262 have the same extent and projected spatial orientation. Their kinematics is not coupled with that of the galaxy stars. It is possible that NGC 4262 has undergone a major gas stripping event in the past which gave origin to the present "necklace" of UV-bright knots.
The disk masses of four low surface brightness galaxies (LSB) were estimated using marginal gravitational stability criterion and the stellar velocity dispersion data which were taken from Pizzella et al., 2008 [1]. The constructed mass models appear to be close to the models of maximal disk. The results show that the disks of LSB galaxies may be significantly more massive than it is usually accepted from their brightnesses. In this case their surface densities and masses appear to be rather typical for normal spirals. Otherwise, unlike the disks of many spiral galaxies, the LSB disks are dynamically overheated.
Using the exact Lemaitre-Bondi-Tolman solution with a non-vanishing cosmological constant $\Lambda$, we investigate how the presence of a local spherically-symmetric inhomogeneity can affect apparent cosmological observables, such as the deceleration parameter or the effective equation of state of dark energy (DE), derived from the luminosity distance under the assumption that the real space-time is exactly homogeneous and isotropic. The presence of a local underdensity is found to produce apparent phantom behavior of DE, while a locally overdense region leads to apparent quintessence behavior. Our study shows how observations in an inhomogeneous $\Lambda$CDM universe with initial conditions compatible with the inflationary beginning, if interpreted under the wrong assumption of homogeneity, can lead to the wrong conclusion about the presence of ``fake'' evolving dark energy instead of $\Lambda$.
We present hydrodynamic simulations of a major merger of disk galaxies, and study the ISM dynamics and star formation properties. High spatial and mass resolutions of 12pc and 4x10^4 M_sol allow to resolve cold and turbulent gas clouds embedded in a warmer diffuse phase. We compare to lower resolution models, where the multiphase ISM is not resolved and is modeled as a relatively homogeneous and stable medium. While merger-driven bursts of star formation are generally attributed to large-scale gas inflows towards the nuclear regions, we show that once a realistic ISM is resolved, the dominant process is actually gas fragmentation into massive and dense clouds and rapid star formation therein. As a consequence, star formation is more efficient by a factor of up to 10 and is also somewhat more extended, while the gas density probability distribution function (PDF) rapidly evolves towards very high densities. We thus propose that the actual mechanism of starburst triggering in galaxy collisions can only be captured at high spatial resolution and when the cooling of gas is modeled down to less than 10^3 K. Not only does our model reproduce the properties of the Antennae system, but it also explains the ``starburst mode'' revealed recently in high-redshift mergers compared to quiescent disks.
We investigate the potential of exploiting the Sunyaev-Zeldovich effect (SZE) to study the properties of hot gas in galaxy groups. It is shown that, with upcoming SZE surveys, one can stack SZE maps around galaxy groups of similar halo masses selected from large galaxy redshift surveys to study the hot gas in halos represented by galaxy groups. We use various models for the hot halo gas to study how the expected SZE signals are affected by gas fraction, equation of state, halo concentration, and cosmology. Comparing the model predictions with the sensitivities expected from the SPT, ACT and Planck surveys shows that a SPT-like survey can provide stringent constraints on the hot gas properties for halos with masses M ~> 10^{13} h^{-1}Msun. We also explore the idea of using the cross correlation between hot gas and galaxies of different luminosity to probe the hot gas in dark matter halos without identifying galaxy groups to represent dark halos. Our results show that, with a galaxy survey as large as the Sloan Digital Sky Survey and with the help of the conditional luminosity function (CLF) model, one can obtain stringent constraints on the hot gas properties in halos with masses down to 10^{13} h^{-1}Msun. Thus, the upcoming SZE surveys should provide a very promising avenue to probe the hot gas in relatively low-mass halos where the majority of L*-galaxies reside.
Primordial non-Gaussianity is a potentially powerful discriminant of the physical mechanisms that generated the cosmological fluctuations observed today. Any detection of significant non-Gaussianity would thus have profound implications for our understanding of cosmic structure formation. The large scale mass distribution in the Universe is a sensitive probe of the nature of initial conditions. Recent theoretical progress together with rapid developments in observational techniques will enable us to critically confront predictions of inflationary scenarios and set constraints as competitive as those from the Cosmic Microwave Background. In this paper, we review past and current efforts in the search for primordial non-Gaussianity in the large scale structure of the Universe.
We are constructing the broadband SED catalog of the MOJAVE sample from the radio to the gamma-ray band using MOJAVE, Swift UVOT/XRT/BAT, and Fermi/LAT data, in order to understand the emission mechanism of extragalactic outflows and to investigate the site of high-energy emission in AGN. Since the launch of Fermi gamma-ray Space Telescope in August 2008, two thirds of the MOJAVE sources have been detected by Fermi/LAT. Combining the results of high-resolution VLBI, X-ray, and gamma-ray observations of the jet-dominated AGN sample, we want to pin down the origin of high-energy emission in relativistic jets. Here we present our overall project and preliminary results for 6 selected sources.
Disk galaxies at high redshift (z~2) are characterized by high fractions of cold gas, strong turbulence, and giant star-forming clumps. Major mergers should typically involve such galaxies. High-redshift merger simulations, however, have always modeled the ISM as stable, homogeneous, and thermally pressurized. We present the first high-redshift merger simulations with cold, turbulent, and clumpy gas, and we discuss the major new features of these models compared to models where the gas is artificially stabilized and warmed. Gas turbulence, which is already strong in high-redshift disks, is further enhanced in mergers. Some phases are dispersion-dominated, with most of the gas kinetic energy in the form of velocity dispersion and very chaotic velocity fields, unlike low-redshift mergers. High-redshift mergers are also characterized by highly dissipative gas collapse to the center of mass, with the stellar component following in a global contraction. The final galaxies are early-type with relatively small radii and high Sersic indices, like high-redshift compact spheroids. The mass fraction in a disk component that survives or re-forms after a merger is severely reduced compared to models with stabilized gas, which lends support to cold accretion as the main formation mechanism for massive disks at high redshift .
We compare the model power spectrum, computed based on the perturbation theory (PT) of structure formation, with the power spectrum of luminous red galaxies (LRG) measured from the Sloan Digital Sky Survey Data Release 7 catalog, assuming a flat, cold dark matter-dominated cosmology. The model includes the effects of massive neutrinos, nonlinear matter clustering and nonlinear, scale-dependent galaxy bias in a self-consistent manner. Combining with the recent results from Wilkinson Microwave Background Anisotropy Probe (WMAP), we found that the PT model well matches the LRG power spectrum down to k=0.1 h/Mpc. We then derive a upper limit on the sum of neutrino masses, sigma(m_nu,tot) < 0.81 eV (95% C.L.), marginalized over other parameters including nonlinear bias parameters and dark energy equation of state parameter. The neutrino mass limit is improved by a factor of 1.85 compared to the limit from the WMAP5 alone.
We perform a full perturbative stability analysis of the 6D cascading gravity model in the presence of 3-brane tension. We demonstrate that for sufficiently large tension on the (flat) 3-brane, there are no ghosts at the perturbative level, consistent with results that had previously only been obtained in a specific 5D decoupling limit. These results establish the cascading gravity framework as a consistent infrared modification of gravity.
Assuming that supernovae type Ia (SNe Ia) are standard candles one could use them to test cosmological theories. The Hubble Space Telescope team analyzed 186 SNe Ia\cite{Riess_04} to test the Standard Cosmological model (SC) associated with expanded lengths in the Universe and evaluate its parameters. We use the same sample to determine parameters of Conformal Cosmological model (CC) with relative reference units of intervals, so that conformal quantities of General Relativity are interpreted as observables. We concluded, that really the test is extremely useful and allows to evaluate parameters of the model. From a formal statistical point of view the best fit of the CC model is almost the same quality approximation as the best fit of SC model with $\Omega_\Lambda=0.72, \Omega_m=0.28$. As it was noted earlier, for CC models, a rigid matter component could substitute the $\Lambda$-term (or quintessence) existing in the SC model. We note that a free massless scalar field can generate such a rigid matter. We describe results of our analysis for more recent "gold" data (for 192 SNe Ia).
In this paper we present multiband optical polarimetric observations of the VHE blazar PKS 2155-304 made simultaneously with a H.E.S.S./Fermi high-energy campaign in 2008, when the source was found to be in a low state. The intense daily coverage of the dataset allowed us to study in detail the temporal evolution of the emission and we found that the particle acceleration timescales are decoupled from the changes in the polarimetric properties of the source. We present a model in which the optical polarimetric emission originates at the polarised mm-wave core and propose an explanation for the lack of correlation between the photometric and polarimetric fluxes. The optical emission is consistent with an inhomogeneous synchrotron source in which the large scale field is locally organised by a shock in which particle acceleration takes place. Finally, we use these optical polarimetric observations of PKS 2155-304 at a low state to propose an origin for the quiescent gamma-ray flux of the object, in an attempt to provide clues for the source of its recently established persistent TeV emission.
We consider the presence and evolution of primordial density perturbations in a cosmological model based on a simple ansatz which captures -- by providing a set of effective gravitational field equations -- the strength of the enhanced quantum loop effects that can arise during inflation. After deriving the general equations that perturbations obey, we concentrate on scalar perturbations and show that their evolution is quite different than that of conventional inflationary models but still phenomenologically acceptable. The main reason for this novel evolution is the presence of an oscillating regime after the end of inflation which makes all super-horizon scalar modes oscillate. The same reason allows for a natural and very fast reheating mechanism for the universe.
(shortened) [...] Within the Fireshell model [...] a new family of disguised short bursts has been introduced: long bursts with a protracted low instantaneous luminosity due to a low density CircumBurst Medium (CBM). GRB 071227 presents, in the 15-150 keV energy band, a short duration (about 1.8s) spikelike emission followed by a very soft extended tail up to one hundred seconds after the trigger. It is a low luminous (E_{iso}=5.8x10^{50}) near GRB (z=0.383) and there is not an associated type Ib/c bright Supernova (SN). For these reasons GRB 071227 has been classified as a short burst not fulfilling the Amati relation holding for long burst. We check the classification of GRB 071227 within the fireshell model. In particular, we want to test if this burst is another example of disguised short burst, after GRB 970228 and GRB 060614 and, for this reason, it would indeed fulfill the Amati relation. MWe simulate GRB 071227 light curves in the Swift BAT 15-50 keV bandpass and in the XRT (0.3-10 keV) energy band within the fireshell model. We perform simulations of the tail in the 15-50 keV bandpass, as well as of the first part of the X-ray afterglow. This provides: E_{tot}^{e^\pm}= 5.04x10^{51} erg, B=2.0x10^{-4}, E_{P-GRB}/E_{aft} ~ 0.25 and <n_{cbm}> = 3.33 particles/cm^3. Such values are still well in the range of "long duration" GRBs. We interpret the observed energy of the first hard emission by identifying it with the P-GRB emission. The remaining long soft tail indeed fulfills the Amati relation. CONCLUSIONS: GRB 071227, classified in literature as a short burst, by the analysis made within the fireshell scenario results to be another example of disguised short bursts, after GRB 970228 and GRB 060614. A further confirmation of this result is that the soft tail of GRB 071227 fulfills the Amati relation.
This chapter reviews theoretical work on the stellar dynamics of galaxy disks. All the known collective global instabilities are identified, and their mechanisms described in terms of local wave mechanics. A detailed discussion of warps and other bending waves is also given. The structure of bars in galaxies, and their effect on galaxy evolution, is now reasonably well understood, but there is still no convincing explanation for their origin and frequency. Spiral patterns have long presented a special challenge, and ideas and recent developments are reviewed. Other topics include scattering of disk stars and the survival of thin disks.
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