We present the results of Hubble Space Telescope Wide Field Camera 3 observations of the core of the Phoenix Cluster (SPT-CLJ2344-4243) in five broadband filters spanning rest-frame 1000-5500A. These observations reveal complex, filamentary blue emission, extending for >40 kpc from the brightest cluster galaxy. We observe an underlying, diffuse population of old stars, following an r^1/4 distribution, confirming that this system is somewhat relaxed. The spectral energy distribution in the inner part of the galaxy, as well as along the extended filaments, is a smooth continuum and is consistent with that of a star-forming galaxy, suggesting that the extended, filamentary emission is not due to a large-scale highly-ionized outflow from the central AGN, but rather a massive population of young stars. We estimate an extinction-corrected star formation rate of 798 +/- 42 Msun/yr, consistent with our earlier work based on low spatial resolution ultraviolet, optical, and infrared imaging. We argue that such a high star formation rate is not the result of a merger, as it would require >10 mergers with gas-rich galaxies and there is no evidence for such multiple merger events. Instead, we propose that the high X-ray cooling rate of ~2850 Msun/yr is the origin of the cold gas reservoir. The combination of such a high cooling rate and the relatively weak radio source in the cluster core suggests that feedback has been unable to halt runaway cooling in this system, leading to this tremendous burst of star formation.
The Milky Way (MW) is surrounded by numerous satellite objects: dwarf galaxies, globular clusters and streams of disrupted systems. Together, these form a vast polar structure (VPOS), a thin plane spreading to Galactocentric distances as large as 250 kpc. The orbital directions of satellite galaxies and the preferred alignment of streams with the VPOS demonstrate that the objects orbit within the structure. This strong phase-space correlation is at odds with the expectations from simulations of structure formation based on the cold dark matter cosmology (LCDM). The accretion of sub-halos along filaments has been suggested as the origin of the anisotropic distribution. We have tested this scenario using the results of high-resolution cosmological simulations and found it unable to account for the large degree of correlation of the MW satellite orbits. It is therefore advisable to search for alternative explanations. The formation of tidal dwarf galaxies (TDGs) in the debris expelled from interacting galaxies is a very natural formation scenario of the VPOS. If a number of MW satellites truly are TDGs, mistakenly interpreting them to trace the dark-matter sub-structure of the MW halo would significantly enhance the 'small-scale' problems which are already known to plague the LCDM model.
In this study we investigate the relation between stellar mass, dust extinction and star formation rate (SFR) using ~150,000 star-forming galaxies from the SDSS DR7. We show that the relation between dust extinction and SFR changes with stellar mass. For galaxies at the same stellar mass dust extinction is anti-correlated with the SFR at stellar masses <10^10 M_solar. There is a sharp transition in the relation at a stellar mass of 10^10 M_solar. At larger stellar masses dust extinction is positively correlated with the SFR for galaxies at the same stellar mass. The observed relation between stellar mass, dust extinction and SFR presented in this study helps to confirm similar trends observed in the relation between stellar mass, metallicity and SFR. The relation reported in this study provides important new constraints on the physical processes governing the chemical evolution of galaxies. The correlation between SFR and dust extinction for galaxies with stellar masses >10^10 M_solar is shown to extend to the population of quiescent galaxies suggesting that the physical processes responsible for the observed relation between stellar mass, dust extinction and SFR may be related to the processes leading to the shut down of star formation in galaxies.
We explore systematic biases in the identification of dark matter in future direct detection experiments and compare the reconstructed dark matter properties when assuming a self-consistent dark matter distribution function and the standard Maxwellian velocity distribution. We find that the systematic bias on the dark matter mass and cross-section determination arising from wrong assumptions for its distribution function is of order ~1\sigma. A much larger systematic bias can arise if wrong assumptions are made on the underlying Milky Way mass model. However, in both cases the bias is substantially mitigated by marginalizing over galactic model parameters. We additionally show that the velocity distribution can be reconstructed in an unbiased manner for typical dark matter parameters. Our results highlight both the robustness of the dark matter mass and cross-section determination using the standard Maxwellian velocity distribution and the importance of accounting for astrophysical uncertainties in a statistically consistent fashion.
We develop a novel abundance matching method to construct a mock catalog of luminous red galaxies (LRGs) in the Sloan Digital Sky Survey (SDSS), using catalogs of halos and subhalos in N-body simulations for a Lambda-dominated, cold dark matter model. Motivated by observations suggesting that LRGs are passively-evolving, massive early-type galaxies with a typical age >5Gyr, we assume that simulated halos at z=2 (z2-halo) are progenitors for LRG-host subhalos observed today, we label the most tightly bound particles in each progenitor z2-halo as LRG "stars". We then identify the subhalos containing these stars to z=0.3 (SDSS redshift) in descending order of the masses of z2-halos until the comoving number density of the matched subhalos becomes comparable to the measured number density of SDSS LRGs, n_LRG=10^{-4} (h/Mpc)^3. Our only free parameter is the number density of halos identified at z=2 and this parameter is fixed to match the observed number density at z = 0.3. By tracing subsequent merging and assembly histories of each progenitor z2-halo, we can directly compute, from $N$-body simulations, the distributions of central and satellite LRGs and their internal motions in each host halo at z=0.3. While the SDSS LRGs are galaxies selected by the magnitude and color cuts from the SDSS images and are not necessarily a stellar-mass-selected sample, our mock catalog reproduces a host of SDSS measurements: the halo occupation distribution for central and satellite LRGs, the projected auto-correlation function of LRGs, the cross-correlation of LRGs with shapes of background galaxies (LRG-galaxy weak lensing), and the nonlinear redshift-space distortion effect, the Finger-of-God effect, in the angle-averaged, redshift-space power spectrum.
This article documents our ongoing search for the elusive "intermediate-mass" black holes. These would bridge the gap between the approximately ten solar mass "stellar-mass" black holes that are the end-product of the life of a massive star, and the "supermassive" black holes with masses of millions to billions of solar masses found at the centers of massive galaxies. The discovery of black holes with intermediate mass is the key to understanding whether supermassive black holes can grow from stellar-mass black holes, or whether a more exotic process accelerated their growth only hundreds of millions of years after the Big Bang. Here we focus on searches for black holes with masses of 10^4-10^6 solar masses that are found at galaxy centers. We will refer to black holes in this mass range as "low-mass" black holes, since they are at the low-mass end of supermassive black holes. We review the searches for low-mass black holes to date and show tentative evidence, from the number of low-mass black holes that are discovered today in small galaxies, that the progenitors of supermassive black holes were formed as ten thousand to one-hundred thousand solar mass black holes via the direct collapse of gas.
For nearly a century, more mass has been measured in galaxies than is contained in the luminous stars and gas. Through continual advances in observations and theory, it has become clear that the dark matter in galaxies is not comprised of known astronomical objects or baryonic matter, and that identification of it is certain to reveal a profound connection between astrophysics, cosmology, and fundamental physics. The best explanation for dark matter is that it is in the form of a yet undiscovered particle of nature, with experiments now gaining sensitivity to the most well-motivated particle dark matter candidates. In this article, I review measurements of dark matter in the Milky Way and its satellite galaxies and the status of Galactic searches for particle dark matter using a combination of terrestrial and space-based astroparticle detectors, and large scale astronomical surveys. I review the limits on the dark matter annihilation and scattering cross sections that can be extracted from both astroparticle experiments and astronomical observations, and explore the theoretical implications of these limits. I discuss methods to measure the properties of particle dark matter using future experiments, and conclude by highlighting the exciting potential for dark matter searches during the next decade, and beyond.
The Sunyaev-Zeldovich (SZ) effect is a promising tool to study physical properties of the hot X-ray emitting intracluster medium (ICM) in galaxy clusters. To date, most SZ observations have been interpreted in combination with X-ray follow-up measurements in order to determine the ICM temperature and estimate the cluster mass. Future high-resolution, multifrequency SZ observations promise to enable detailed studies of the ICM structures, by measuring the ICM temperature through the temperature-dependent relativistic corrections. In this work we develop a non-parametric method to derive three-dimensional physical quantities, including temperature, pressure, total mass, and peculiar velocities, of galaxy clusters from SZ observations alone. We test the performance of this method using hydrodynamical simulations of galaxy clusters, in order to assess systematic uncertainties in the reconstructed physical parameters. In particular, we analyze mock Cerro Chajnantor Atacama Telescope (CCAT) SZ observations, taking into account various sources of systematic uncertainties associated with instrumental effects and astrophysical foregrounds. We show that our method enables accurate reconstruction of the three-dimensional ICM profiles, while retaining full information about the gas distribution. We discuss the application of this technique for ongoing and future multifrequency SZ observations.
We report the discovery of Seyfert-2 galaxies in SDSS-DR8 with galaxy-wide, ultra-luminous narrow-line regions (NLRs) at redshifts z=0.2-0.6. With a space density of 4.4 per cubic Gpc at z~0.3, these "Green Beans" (GBs) are amongst the rarest objects in the Universe. We are witnessing an exceptional and/or short-lived phenomenon in the life cycle of AGN. The main focus of this paper is on a detailed analysis of the GB prototype galaxy J2240-0927 (z=0.326). Its NLR extends over 26x44 kpc and is surrounded by an extended narrow-line region (ENLR). With a total [OIII]5008 luminosity of (5.7+/-0.9)x10e43 erg/s, this is one of the most luminous NLR known around any type-2 galaxy. Using VLT/XSHOOTER we show that the NLR is powered by an AGN, and we derive resolved extinction, density and ionization maps. Gas kinematics is disturbed on a global scale, and high velocity outflows are absent or faint. This NLR is unlike any other NLR or extended emission line region (EELR) known. Spectroscopy with Gemini/GMOS reveals extended, high luminosity [OIII] emission also in other GBs. WISE 24micron luminosities are 5-50 times lower than predicted by the [OIII] fluxes, suggesting that the NLRs reflect earlier, very active quasar states that have strongly subsided in less than a galaxies' light crossing time. These light echos are about 100 times more luminous than any other such light echo known to date. X-ray data are needed for photo-ionization modeling and to verify the light echos.
We assume a DE state equation w(a) = w_0+w_a(a_p-a), and study the dependence of the constraints on w_0 and w_a coefficients on the pivoting redshift 1+z_p=1/a_p. The main findings of our analysis are specific differences between the cases when neutrino mass is allowed or disregarded. The set of data used include WMAP7, SNIa (Union 2.1), BAO's (including WiggleZ and SDSS results) and H_0 constraints. The fitting algorithm is CosmoMC. More in detail: (i)we confirm that the inclination of the likelihood ellipse on the w_0-w_a plane depends on z_p. (ii) When we assume massless neutrinos, the constraints on w_0 and w_a are then independent only around z_p~0.35. (iii) On the contrary, when we consider massive neutrinos, the ellipse axes become parallel to the coordinate axes at a lower z_p~0.25. (iv) When we neglect neutrino mass and we marginalize over all other parameters, the expected range of w_0 values gradually increases when greater z_p values are considered; as expected, it becomes narrowest at z_p~0.35, being then (-1.19,-0.93) at 2 sigma; on the contrary, when neutrino mass is allowed, w_0 decreases when z_p increases and it narrowest 2 sigma range, at z_p~0.25 is (-1.31,-0.97).
We describe a general procedure for using number counts of any object to constrain the probability distribution of the primordial fluctuations, allowing for generic weak non-Gaussianity. We apply this procedure to use limits on the abundance of primordial black holes and dark matter ultracompact minihalos (UCMHs) to characterize the allowed statistics of primordial fluctuations on very small scales. We present constraints on the power spectrum and the amplitude of the skewness for two different families of non-Gaussian distributions, distinguished by the relative importance of higher moments. Although primordial black holes probe the smallest scales, ultracompact minihalos provide significantly stronger constraints on the power spectrum and so are more likely to eventually provide small-scale constraints on non-Gaussianity.
We study the probability distribution P(\Lambda) of the cosmological constant \Lambda in a specific set of KKLT type models of supersymmetric IIB vacua. P(\Lambda) is divergent at \Lambda =0^- and the likely value of \Lambda drops exponentially as the number of complex structure moduli h^{2,1} increases. Also, owing to the hierarchical and approximate no-scale structure, the probability of having a positive Hessian (mass squared matrix) approaches unity as h^{2,1} increases.
Chameleon dark energy is a matter-coupled scalar field which hides its fifth forces locally by becoming massive. We estimate torsion pendulum constraints on the residual fifth forces due to models with gravitation-strength couplings. Experiments such as Eot-Wash are on the verge of ruling out "quantum-stable" chameleon models, in which quantum corrections to the chameleon field and mass remain small. We also consider photon-coupled chameleons, which can be tested by afterglow experiments such as CHASE.
Recently, it has been suggested that the metallicity aversion of
long-duration gamma-ray bursts (LGRBs) is not intrinsic to their formation, but
rather a consequence of the anti-correlation between star-formation and
metallicity seen in the general galaxy population. To investigate this
proposal, we compare the metallicity of the hosts of LGRBs, broad-lined Type Ic
(Ic-bl) supernovae (SNe), and Type II SNe to each other and to the metallicity
distribution of star-forming galaxies using the SDSS to represent galaxies in
the local universe and the TKRS for galaxies at intermediate redshifts.
The differing metallicity distributions of the LGRB hosts and the star
formation in local galaxies forces us to conclude that the low-metallicity
preference of LGRBs is not primarily driven by the anti-correlation between
star-formation and metallicity, but rather must be overwhelmingly due to the
astrophysics of the LGRBs themselves. Three quarters of our LGRB sample are
found at metallicities below 12+log(O/H) < 8.6, while less than a tenth of
local star-formation is at similarly low metallicities. However, our SN samples
are statistically consistent with the metallicity distribution of the general
galaxy population. Using the TKRS population of galaxies, we are able to
exclude the possibility that the LGRB host metallicity aversion is caused by
the decrease in galaxy metallicity with redshift. The presence of the strong
metallicity difference between LGRBs and Ic-bl SNe largely eliminates the
possibility that the observed LGRB metallicity bias is a byproduct of a
difference in the initial mass functions of the galaxy populations. Rather,
metallicity below half-solar must be a fundamental component of the
evolutionary process that separates LGRBs from the vast majority of Ic-bl SNe
and from the bulk of local star-formation.
We present results from an extensive study of 83 precessing, equal-mass black-hole binaries with large spins, a/m=0.8, and use these data to model new nonlinear contributions to the gravitational recoil imparted to the merged black hole. We find a new effect, the "cross kick", that enhances the recoil for partially aligned binaries beyond the "hangup kick" effect. This has the consequence of increasing the probabilities (by nearly a factor two) of recoils larger than 2000 km/s, and, consequently, of black holes getting ejected from galaxies and globular clusters, as well as the observation of large differential redshifts/blueshifts in the cores of recently merged galaxies.
Direct dark matter searches are promising techniques to identify the nature of dark matter particles. I describe the future of this field of research, focussing on the question of what can be achieved in the next decade. I will present the main techniques and R&D projects that will allow to build so-called ultimate WIMP detectors, capable of probing spin-independent interactions down to the unimaginably low cross section of 1e-48 cm2, before the irreducible neutrino background takes over. If a discovery is within the reach of a near-future dark matter experiment, these detectors will be able to constrain WIMP properties such as its mass, scattering cross section and possibly spin. With input from the LHC and from indirect searches, direct detection experiments will hopefully allow to determine the local density and to constrain the local phase-space structure of our dark matter halo.
The polarization transfer coefficients of a relativistic magnetized plasma are derived. These results apply to any momentum distribution function of the particles, isotropic or anisotropic. Particles interact with the radiation either in a non resonant mode when the frequency of the radiation exceeds their characteristic synchrotron emission frequency, or quasi resonantly otherwise. These two classes of particles contribute differently to the polarization transfer coefficients. For a given frequency, this dichotomy corresponds to a regime change in the dependence of the transfer coefficients on the parameters of the particle s population. The derivation of the transfer coefficients involves an exact expression of the conductivity tensor of the relativistic magnetized plasma that has not been used hitherto in this context. Suitable expansions valid at frequencies larger than the cyclotron frequency allow us to analytically perform the summation over all resonances at high harmonics of the relativistic gyrofrequency. The transfer coefficients are represented in the form of two variable integrals that can be conveniently computed for any set of parameters by using Olver s expansion of high order Bessel functions. We particularize our results to a number of distribution functions, isotropic, thermal or powerlaw, with different multipolar anisotropies of low order, or strongly beamed. For isotropic distributions, the Faraday coefficients are expressed in the form of a one variable quadrature over energy, for which we provide the kernels in the high-frequency limit and in the asymptotic low-frequency limit. A similar reduction to a one-variable quadrature over energy is derived at high frequency for a large class of anisotropic distribution functions that may form a basis on which any smoothly anisotropic distribution could be expanded.
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We analyze the science reach of a next generation galaxy redshift survey such as BigBOSS to fit simultaneously for time varying dark energy equation of state and time- and scale-dependent gravity. The simultaneous fit avoids potential bias from assuming $\Lambda$CDM expansion or general relativity and leads to only modest degradation in constraints. Galaxy bias, fit freely in redshift bins, is self calibrated by spectroscopic measurements of redshift space distortions and causes little impact. The combination of galaxy redshift, cosmic microwave background, and supernova distance data can deliver 5-10% constraints on 6 model independent modified gravity quantities.
In this paper we investigate how the halo mass function evolves with redshift, based on a suite of very large (with N_p = 3072^3 - 6000^3 particles) cosmological N-body simulations. Our halo catalogue data spans a redshift range of z = 0-30, allowing us to probe the mass function from the dark ages to the present. We utilise both the Friends-of-Friends (FOF) and Spherical Overdensity (SO) halofinding methods to directly compare the mass function derived using these commonly used halo definitions. The mass function from SO haloes exhibits a clear evolution with redshift, especially during the recent era of dark energy dominance (z < 1). We provide a redshift-parameterised fit for the SO mass function valid for the entire redshift range to within ~20% as well as a scheme to calculate the mass function for haloes with arbitrary overdensities. The FOF mass function displays a weaker evolution with redshift. We provide a `universal' fit for the FOF mass function, fitted to data across the entire redshift range simultaneously, and observe redshift evolution in our data versus this fit. The relative evolution of the mass functions derived via the two methods is compared and we find that the mass functions most closely match at z=0. The disparity at z=0 between the FOF and SO mass functions resides in their high mass tails where the collapsed fraction of mass in SO haloes is ~80% of that in FOF haloes. This difference grows with redshift so that, by z>20, the SO algorithm finds a ~50-80% lower collapsed fraction in high mass haloes than does the FOF algorithm, due in part to the significant over-linking effects known to affect the FOF method.
Due to their extreme luminosities, gamma-ray bursts (GRBs) are routinely detected in hostile regions of galaxies, nearby and at very high redshift, making them important cosmological probes. The investigation of galaxies hosting long-duration GRBs (whose progenitor is a massive star) demonstrated their connection to star formation. Still, the link to the total galaxy population is controversial, mainly because of the small-number statistics: ~ 1,100 are the GRBs detected so far, ~ 280 those with measured redshift, and ~ 70 the hosts studied in detail. These are typically low-redshift (z < 1.5), low luminosity, metal poor, and star-forming galaxes. On the other hand, at 1.5< z <4, massive, metal rich and dusty, interacting galaxies are not uncommon. The most distant population (z > 4) is poorly explored, but the deep limits reached point towards very small and star-forming objects, similar to the low-z population. This `back to the future' behavior is a natural consequence of the connection of long GRBs to star formation in young regions of the universe.
In order to study the mechanism of formation of cD galaxies we search for possible dependencies between the K-band luminosity of cDs and the parameters of their host clusters which we select to have a dominant cD galaxy, corresponding to a cluster morphology of Bautz-Morgan (BM) type I. As a comparison sample we use cD galaxies in clusters where they are not dominant, which we define here as non-BMI (NBMI) type clusters. We find that for 71 BMI clusters the absolute K-band luminosity of cDs depends on the cluster richness, but less strongly on the cluster velocity dispersion. Meanwhile, for 35 NBMI clusters the correlation between cD luminosity and cluster richness is weaker, and is absent between cD luminosity and velocity dispersion. In addition, we find that the luminosity of the cD galaxy hosted in BMI clusters tends to increase with the cD's peculiar velocity with respect to the cluster mean velocity. In contrast, for NBMI clusters the cD luminosity decreases with increasing peculiar velocity. Also, the X-ray luminosity of BMI clusters depends on the cluster velocity dispersion, while in NBMI clusters such a correlation is absent. These findings favour the cannibalism scenario for the formation of cD galaxies. We suggest that cDs in clusters of BMI type were formed and evolved preferentially in one and the same cluster. In contrast, cDs in NBMI type clusters were either originally formed in clusters that later merged with groups or clusters to form the current cluster, or are now in the process of merging.
[Abridged] We present an analysis of optical spectroscopically-identified AGN to M*+1 in a sample of 6 self-similar SDSS galaxy clusters at z=0.07. These clusters are specifically selected to lack significant substructure at bright limits in their central regions so that we are largely able to eliminate the local action of merging clusters on the frequency of AGN. We demonstrate that the AGN fraction increases significantly from the cluster centre to 1.5Rvirial, but tails off at larger radii. If only comparing the cluster core region to regions at ~2Rvirial, no significant variation would be found. We compute the AGN fraction by mass and show that massive galaxies (log(stellar mass)>10.7) are host to a systematically higher fraction of AGN than lower mass galaxies at all radii from the cluster centre. We attribute this deficit of AGN in the cluster centre to the changing mix of galaxy types with radius. We use the WHAN diagnostic to separate weak AGN from `retired' galaxies in which the main ionization mechanism comes from old stellar populations. These retired AGN are found at all radii, while the mass effect is much more pronounced: we find that massive galaxies are more likely to be in the retired class. Further, we show that our AGN have no special position inside galaxy clusters - they are neither preferentially located in the infall regions, nor situated at local maxima of galaxy density. However, we find that the most powerful AGN (with [OIII] equivalent widths <-10Ang) reside at significant velocity offsets in the cluster, and this brings our analysis into agreement with previous work on X-ray selected AGN. Our results suggest that if interactions with other galaxies are responsible for triggering AGN activity, the time-lag between trigger and AGN enhancement must be sufficiently long to obfuscate the encounter site and wipe out the local galaxy density signal.
We perform a global fit study on the new agegraphic dark energy (NADE) model in a non-flat universe by using the MCMC method with the full CMB power spectra data from the WMAP 7-yr observations, the SNIa data from Union2.1 sample, BAO data from SDSS DR7 and WiggleZ Dark Energy Survey, and the latest measurements of $H_0$ from HST. We find that the value of $\Omega_{k0}$ is greater than 0 at least at the 3$\sigma$ confidence levels (CLs), which implies that the NADE model distinctly favors an open universe. Besides, our results show that the value of the key parameter of NADE model, $n=2.673^{+0.053+0.127+0.199}_{-0.077-0.151-0.222}$, at the 1--3$\sigma$ CLs, where its best-fit value is significantly smaller than those obtained in previous works. We find that the reason leading to such a change comes from the different SNIa samples used. Our further test indicates that there is a distinct tension between the Union2 sample of SNIa and other observations, and the tension will be relieved once the Union2 sample is replaced by the Union2.1 sample. So, the new constraint result of the NADE model obtained in this work is more reasonable than before.
We have performed stacking image analyses of galaxies over the Galactic extinction map constructed by Schlegel, Finkbeiner & Davis (1998). We select ~10^7 galaxies in total from the Sloan Digital Sky Survey (SDSS) DR7 photometric catalog. We detect clear signatures of the enhancement of the extinction in r-band, $\Delta A_r$, around galaxies, indicating that the extinction map is contaminated by their FIR (far infrared) emission. The average amplitude of the contamination per galaxy is well fitted to $\Delta A_r(m_r) = 0.64 \times 10^{0.17(18-m_r)}$ [mmag]. While this value is very small, it is directly associated with galaxies and may have a systematic effect on galaxy statistics. Indeed this correlated contamination leads to a relatively large anomaly of galaxy surface number densities against the SFD extinction A_SFD discovered by Yahata et al. (2007). We model the radial profiles of stacked galaxy images, and find that the FIR signal around each galaxy does not originate from the central galaxy alone, but is dominated by the contributions of nearby galaxies via galaxy angular clustering. The separation of the single galaxy and the clustering terms enables us to infer the statistical relation of the FIR and r-band fluxes of galaxies and also to probe the flux-weighted cross-correlation of galaxies, down to the magnitudes that are difficult to probe directly for individual objects. We repeat the same stacking analysis for SDSS DR6 photometric quasars and discovered the similar signatures but with weaker amplitudes. The implications of the present results for galaxy and quasar statistics and for correction to the Galactic extinction map are briefly discussed.
We estimate the masses of disks of galaxies using the marginal gravitational stability criterion and compare them with the photometrical disk mass evaluations. The comparison reveals that the stellar disks of most of spiral galaxies we considered cannot be substantially overheated (at least within several radial scalelengths) and are therefore unlikely to have experienced a significant merging event in their history. However, for substantial part of S0- type galaxies a stellar velocity dispersion is well in excess of the gravitational stability threshold suggesting a major merger event in the past. For four low surface brightness galaxies we found that the disk masses corresponding to the marginal stability condition are significantly higher than it may be expected from their brightness. Either their disks are dynamically overheated, or they contain a large amount of non-luminous matter.
We present a detailed study of the environments of a close pair of clusters of galaxies, A3532 and A3530. The Chandra X-ray image of A3532 reveals presence of substructures on scales of 20 arcseconds in its core. XMM-Newton maps of the clusters show excess X-ray emission from an overlapping region between them. Spectrally determined projected temperature and entropy maps do not show any signs of mergers, either in the overlapping region or within A3530. A3532, however, shows many signs of the presence of mergers: anisotropic temperature variations seen in the projected thermodynamic maps, a wide angled tailed (WAT) radio source at its center, and several X-ray candidate cavities near the WAT. A small sized cavity appears coincident with the southern tail of the WAT. Low frequency radio observations show an extension of the WAT radio emission towards the northwest, coinciding with a large scale X-ray cavity. The extension seems either a part of the WAT or an unrelated diffuse source from A3532 itself or from the background. A3530 shows a temperature drop and peak in the abundance at its centre and, therefore, seems to host at least a weak cool core. The cool core in A3532 seems to be disrupted by the ongoing mergers. A reanalysis of the redshifts data reinforces the close proximity of the clusters. The excess emission in the overlapping region seems to be a result of the tidal interactions as the two clusters approach each other for the first time.
Major mergers or/and the repeated minor mergers lead to dynamical heating of disks of galaxies. We analyze the available data on the velocity dispersion of stellar disks of S-S0 galaxies, including the new observational data obtained at 6m telescope of SAO RAS. As a measure of dynamical (over)heating, we use the ratio of the observed velocity dispersion to the minimal dispersion which provides the local stability of the stellar disks with respect to gravitational perturbations. We came to conclusion that stellar disks in a significant part of galaxies (including LSB and some S0 galaxies) are close to the marginal stability condition (or are slightly overheated) -- at least at radial distances $r\sim$ 2-3 radial scalelenghts. It enables to constrain the role of merging in the heating of stellar disks: in many cases it seems to be non-efficient. Marginal stability condition may also be successfully used to estimate the mass of a disk and the midplane volume gas (stars) densities on the basis of kinematic measurements.
We use near-infrared spectroscopic data from the inner few hundred parsecs of a sample of 47 active galaxies to investigate possible correlations between the stellar velocity dispersion (sigma_star), obtained from the fit of the K-band CO stellar absorption bands, and the gas velocity dispersion (sigma) obtained from the fit of the emission-line profiles of [SIII]0.953um, [Fe II]1.257um, [FeII]1.644um and H_2 2.122um. While no correlations with sigma_star were found for H_2 and [SIII], a good correlation was found for the two [Fe II] emission lines, expressed by the linear fit sigma_star = 95.4\pm16.1 + (0.25\pm0.08)sigma_[Fe II]. Excluding barred objects from the sample a better correlation is found between sigma_star and sigma_[FeII], with a correlation coefficient of R=0.80 and fitted by the following relation: sigma_\star = 57.9\pm23.5 + (0.42\pm0.10)sigma_[FeII]. This correlation can be used to estimate $\sigma_\star$ in cases it cannot be directly measured and the [FeII] emission lines are present in the spectra, allowing to obtain the mass of the supermassive black hole (SMBH) from the M-\sigma_\star relation. The scatter from a one-to-one relationship between sigma_star and its value derived from sigma_[FeII] using the equation above for our sample is 0.07dex, which is smaller than that obtained in previous studies which use \sigma_[OIII] in the optical as a proxy for sigma_star. The use of sigma_[Fe\,II] in the near-IR instead of sigma_[OIII] in the optical is a valuable option for cases in which optical spectra are not available or are obscured, as is the case of many AGN.
High redshift quasars can be used to deduce the distribution of dark energy in the Universe, as a complementary tool to SN Ia. The method is based on determination of the size of the Broad Line Region from the emission line delay, determination of the absolute monochromatic luminosity either from the observed statistical relation or from a model of the formation of the Broad Line Region, and determination of the observed monochromatic flux from photometry. This allows to obtain the luminosity distance to a quasar independently from its redshift. The accuracy of the measurements is however, a key issue. We model the expected accuracy of the measurements by creating artificial quasar monochromatic lightcurves and responses from the Broad Line Region under various assumptions about the variability of a quasar, Broad Line Region extension, distribution of the measurements in time, accuracy of the measurements and the intrinsic line variability. We show that the five year monitoring based on Mg II line should give the accuracy of 0.06 - 0.32 magnitude in the distance modulus which allows to put interesting constraints on the cosmological models. Monitoring of higher redshift quasars based on CIV lines is problematic due to much higher level of the intrinsic variability of CIV in comparison with Mg II.
We show that the cusp in the dark matter (DM) distribution required to explain the recently found excess in the gamma-ray spectrum at energies ~130 GeV in terms of the DM annihilations cannot survive the tidal forces if it is offset by ~1.5^\circ from the Galactic centre as suggested by observations.
The formation of the first stars is an exciting frontier area in astronomy. Early redshifts z ~ 20 have become observationally promising as a result of a recently recognized effect of a supersonic relative velocity between the dark matter and gas. This effect produces prominent structure on 100 comoving Mpc scales, which makes it much more feasible to detect 21-cm fluctuations from the epoch of first heating. We use semi-numerical hybrid methods to follow for the first time the joint evolution of the X-ray and Lyman-Werner radiative backgrounds, including the effect of the supersonic streaming velocity on the cosmic distribution of stars. We incorporate self-consistently the negative feedback on star formation induced by the Lyman-Werner radiation, which dissociates molecular hydrogen and thus suppresses gas cooling. We find that the feedback delays the X-ray heating transition by a Delta z ~ 2, but leaves a promisingly large fluctuation signal over a broad redshift range. The large-scale power spectrum is predicted to reach a maximal signal-to-noise ratio of S/N ~ 3-4 at z ~ 18 (for a projected first-generation instrument), with S/N > 1 out to z ~ 22-23. We hope to stimulate additional numerical simulations as well as observational efforts focused on the epoch prior to cosmic reionization.
The number of detections as well as significantly deep non-detections of optical/NIR afterglows of Type I (short-duration population) Gamma-Ray Bursts (GRBs) has become large enough that statistically meaningful samples can now be constructed. I present within some recent results on the luminosity distribution of Type I GRB afterglows in comparison to those of Type II GRBs (collapsar population), the issue of the existence of jet breaks in Type I GRB afterglows, and the discovery of dark Type I GRBs.
We present a theorem which allows one to recognize and classify the asymptotic behavior and causal structure of McVittie metrics for different choices of scale factor, establishing whether a black hole or a couple black-white hole appears in the appropriate limit. Incidentally, the theorem also solves an apparent contradiction present in the literature over the causal structure analysis of the McVittie solution. Although the classification we present is not fully complete, we argue that this result covers most if not all physically relevant scenarios.
Merging binaries of compact relativistic objects (neutron stars and black holes) are thought to be progenitors of short gamma-ray bursts and sources of gravitational waves, hence their study is of great importance for astrophysics. Because of the strong magnetic field of one or both binary members and high orbital frequencies, these binaries are strong sources of energy in the form of Poynting flux (e.g., magnetic-field-dominated outflows, relativistic leptonic winds, electromagnetic and plasma waves). The steady injection of energy by the binary forms a bubble (or a cavity) filled with matter with the relativistic equation of state, which pushes on the surrounding plasma and can drive a shock wave in it. Unlike the Sedov-von Neumann-Taylor blast wave solution for a point-like explosion, the shock wave here is continuously driven by the ever-increasing pressure inside the bubble. We calculate from the first principles the dynamics and evolution of the bubble and the shock surrounding it and predict that such systems can be observed as radio sources a few hours before and after the merger. At much later times, the shock is expected to settle onto the Sedov-von Neumann-Taylor solution, thus resembling an explosion.
That the stellar halo of the Milky Way has a density profile which to first approximation satisfies $\rho \propto r^{-3}$ has been known for a long time. More recently, it has become clear that M31 also has such an extended stellar halo, which approximately follows the same radial scaling. Studies of distant galaxies have revealed the same phenomenology. Also, we now know that the density profiles of the globular cluster systems of our Galaxy and Andromeda to first approximation follow $\rho \propto r^{-3}$, $\Sigma \propto R^{-2}$ in projection. Recently, diffuse populations of stars have been detected spherically surrounding a number of Galactic globular clusters, extending much beyond the Newtonian tidal radii, often without showing any evidence of tidal features. Within the standard Newtonian and GR scenario, numerous and diverse particular explanations have been suggested, individually tailored to each of the different classes of systems described above. Here we show that in a MONDian gravity scenario, any tenuous halo of tracer particles forming a small perturbation surrounding a spherically symmetric mass distribution, will have as an equilibrium configuration precisely a $\rho \propto r^{-3}$ scaling.
Several planets have recently been discovered around old and metal-poor stars, implying that the planets are also old, formed in the early universe. The canonical theory suggests that the conditions for their formation could not have existed at such early epochs. The required conditions such as sufficiently high dust-to-gas ratio, could in fact have existed in the early universe immediately following the first episode of metal production. Metal-rich regions may have existed in multiple isolated pockets of enriched and weakly-mixed gas close to the massive stars. Observations of quasars and gamma-ray bursts show a very wide spread of metals in absorption from $\rm [X/H] \simeq -3$ to $\simeq -0.5$. This suggests that physical conditions in the metal-abundant clumps could have been similar to where protoplanets form today. However, planets could have formed even in low-metallicity environments, where formation of stars is expected to proceed at higher densities. In such cases, the circumstellar accretion disks are expected to rotate faster than their high-metallicity analogues. This in turn can result in the enhancement of dust particles at the disk periphery. Radiation from the central protostar can also act to drive small-scale instabilities with masses in the earth to jupiter mass range. Discoveries of planets with low-metallicity hosts show that planets did indeed form in the early universe, which may require modification of our understanding of the physical processes that produce them. This work is an attempt to provide one such heuristic scenario for the physical basis for their existence.
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We present FitSKIRT, a method to efficiently fit radiative transfer models to UV/optical images of dusty galaxies. These images have the advantage that they have better spatial resolution compared to FIR/submm data. FitSKIRT uses the GAlib genetic algorithm library to optimize the output of the SKIRT Monte Carlo radiative transfer code. Genetic algorithms prove to be a valuable tool in handling the multi- dimensional search space as well as the noise induced by the random nature of the Monte Carlo radiative transfer code. FitSKIRT is tested on artificial images of a simulated edge-on spiral galaxy, where we gradually increase the number of fitted parameters. We find that we can recover all model parameters, even if all 11 model parameters are left unconstrained. Finally, we apply the FitSKIRT code to a V-band image of the edge-on spiral galaxy NGC4013. This galaxy has been modeled previously by other authors using different combinations of radiative transfer codes and optimization methods. Given the different models and techniques and the complexity and degeneracies in the parameter space, we find reasonable agreement between the different models. We conclude that the FitSKIRT method allows comparison between different models and geometries in a quantitative manner and minimizes the need of human intervention and biasing. The high level of automation makes it an ideal tool to use on larger sets of observed data.
Luminous X-ray gas coronae in the dark matter halos of massive spiral galaxies are a fundamental prediction of structure formation models, yet such coronae remained essentially unexplored. In this paper, for the very first time, we detect and characterize extended hot X-ray coronae beyond the optical disks of two normal massive spiral galaxies, NGC1961 and NGC6753. Based on XMM-Newton X-ray observations, we detect hot gaseous emission extending out to ~60 kpc around both galaxies - well beyond their optical radii. The hot gas, whose best-fit temperature is kT~0.6 keV and abundance is ~0.1 Solar, appears to have a fairly uniform distribution, hinting that the quasi-static gas resides in hydrostatic equilibrium in the potential well of the galaxies. The bolometric luminosity of the hot gas in the (0.05-0.15)r_200 region, where r_200 is the virial radius, is ~6e40 erg/s for both NGC1961 and NGC6753. We derive the baryon mass fractions of NGC1961 and NGC6753 and obtain f_b~0.1, which values fall short of the cosmic baryon fraction. The detected X-ray coronae around NGC1961 and NGC6753 offer an excellent basis to probe structure formation simulations. To this end, the observations are confronted with the recently developed moving mesh code AREPO and the traditionally used smoothed particle hydrodynamics code GADGET. The implemented subresolution physics and the gravity solver are identical in the two codes, but they use different methods to solve the hydrodynamical equations. We conclude that, while neither model gives a perfect description, the observed luminosities, gas masses, and abundances favor the AREPO code. Moreover, the shape of the observed density profiles are also well reproduced by AREPO within ~0.4r_200. However, neither model incorporates efficient feedback from supermassive black holes or supernovae, which could alter the simulated properties of the X-ray coronae. (abridged)
We present a spherically symmetric model for the origin and evolution of the temperature profiles in the hot plasma filling galaxy groups and clusters. We find that the gas in clusters is generically not isothermal, and that the temperature declines with radius at large distances from the cluster center (outside the core- and scale radii). This temperature profile is determined by the accretion history of the halo, and is not quantitatively well-described by a polytropic model. We explain quantitatively how the large-scale temperature gradient persists in spite of thermal conduction and convection. These results are a consequence of the cosmological assembly of clusters and cannot be reproduced with non-cosmological simulations of isolated halos. We show that the variation in halo assembly histories produces a ~10% scatter in temperature at fixed mass. On top of this scatter, conduction decreases the temperature of the gas near the scale radius in massive clusters, which may bias hydrostatic mass estimates inferred from x-ray and SZ observations. As an example application of our model profiles, we use mixing-length theory to estimate the turbulent pressure support created by the magnetothermal instability (MTI): in agreement with our earlier MHD simulations, we find that the convection produced by the MTI can provide ~5% non-thermal pressure support near r_500. The magnitude of this turbulent pressure support is likely to be non-monotonic in halo mass, peaking in ~10^14.5 M_sun halos.
We present the first quantified, statistical map of broad-line active galactic nucleus (AGN) frequency with host galaxy color and stellar mass in nearby (0.01 < z < 0.11) galaxies. Aperture photometry and z-band concentration measurements from the Sloan Digital Sky Survey (SDSS) are used to dis- entangle AGN and galaxy emission, resulting in estimates of uncontaminated galaxy rest-frame color, luminosity, and stellar mass. Broad-line AGNs are distributed throughout the blue cloud and green valley at a given stellar mass, and are much rarer in quiescent (red sequence) galaxies. This is in contrast to the published host galaxy properties of weaker narrow-line AGNs, indicating that broad-line AGNs occur during a different phase in galaxy evolution. More luminous broad-line AGNs have bluer host galaxies, even at fixed mass, suggesting that the same processes that fuel nuclear activity also efficiently form stars. The data favor processes that simultaneously fuel both star formation activity and rapid supermassive black hole accretion. If AGNs cause feedback on their host galaxies in the nearby universe, the evidence of galaxy-wide quenching must be delayed until after the broad-line AGN phase.
In typical astrophysical environments, the abundance of heavy elements ranges from 0.001 to 2 times the solar concentration. Lower abundances have been seen in select stars in the Milky Way's halo and in two quasar absorption systems at redshift z=3. These are widely interpreted as relics from the early universe, when all gas possessed a primordial chemistry. Before now there have been no direct abundance measurements from the first Gyr after the Big Bang, when the earliest stars began synthesizing elements. Here we report observations of hydrogen and heavy element absorption in a quasar spectrum at z=7.04, when the universe was just 772 Myr old (5.6% its present age). We detect a large column of neutral hydrogen but no corresponding heavy elements, limiting the chemical abundance to less than 1/10,000 the solar level if the gas is in a gravitationally bound protogalaxy, or less than 1/1,000 solar if it is diffuse and unbound. If the absorption is truly intergalactic, it would imply that the universe was neither ionized by starlight nor chemically enriched in this neighborhood at z~7. If it is gravitationally bound, the inferred abundance is too low to promote efficient cooling, and the system would be a viable site to form the predicted but as-yet unobserved massive population III stars in the early universe.
We present the equivalent width and column density measurements for low and intermediate ionization states of the circumgalactic medium (CGM) surrounding 44 low-z, L ~ L* galaxies drawn from the COS-Halos survey. These measurements are derived from far-UV transitions observed in HST/COS and Keck/HIRES spectra of background quasars within an impact parameter R < 160 kpc to the targeted galaxies. The data show significant metal-line absorption for 33 of the 44 galaxies, including quiescent systems, revealing the common occurance of a cool (T ~ 10^{4 - 5} K), metal-enriched CGM. The detection rates and column densities derived for these metal lines decrease with increasing impact parameter, a trend we interpret as a declining metal surface density profile for the CGM. A comparison of the relative column densities of adjacent ionization states indicates the gas is predominantly ionized. The large surface density in metals demands a large reservoir of metals and gas in the cool CGM (very conservatively, M_ CGMcool > 10^9 MSun), which likely traces a distinct density and/or temperature regime from the highly-ionized CGM traced by OVI absorption. The large dispersion in absorption strengths (including non-detections) suggests the cool CGM traces a wide range of densities or a mix of local ionizing conditions. Lastly, the kinematics inferred from the metal-line profiles are consistent with the cool CGM being bound to the dark matters halos hosting the galaxies; this gas may serve as fuel for future star-formation. Future work will leverage this dataset to provide estimates on the mass, metallicity, dynamics, and origin of the cool CGM in low-z, L* galaxies.
Using the chiral representation for spinors we present a particularly transparent way to generate the most general spinor dynamics in a theory where gravity is ruled by the Einstein-Cartan-Holst action. In such theories torsion need not vanish, but it can be re-interpreted as a 4-fermion self-interaction within a torsion-free theory. The self-interaction may or may not break parity invariance, and may contribute positively or negatively to the energy density, depending on the couplings considered. We then examine cosmological models ruled by a spinorial field within this theory. We find that while there are cases for which no significant cosmological novelties emerge, the self-interaction can also turn a mass potential into an upside-down Mexican hat potential. Then, as a general rule, the model leads to cosmologies with a bounce, for which there is a maximal energy density, and where the cosmic singularity has been removed. These solutions are stable, and range from the very simple to the very complex.
We consider the evolution of primordial magnetic fields generated during cosmological, electroweak or QCD, phase transitions. We assume that the magnetic field generation can be described as an injection of magnetic energy to cosmological plasma at a given scale determined by the moment of magnetic field generation. A high Reynolds number ensures strong coupling between magnetic field and fluid motions. The subsequent evolution of the magnetic field is governed by decaying hydromagnetic turbulence. Both our numerical simulations and a phenomenological description allow us to recover "universal" laws for the decay of magnetic energy and the growth of magnetic correlation length in the turbulent (low viscosity) regime. In particular, we show that during the radiation dominated epoch, energy and correlation length of non-helical magnetic fields scale as conformal time to the powers -1/2 and +1/2, respectively. For helical magnetic fields, energy and correlation length scale as conformal time to the powers -1/3 and +2/3, respectively. The universal decay law of the magnetic field implies that the strength of magnetic field generated during the QCD phase transition could reach $\sim 10^{-9}$\,G with the present day correlation length $\sim 50$ kpc. The fields generated at the electroweak phase transition could be as strong as $\sim 10^{-10}$ G with correlation lengths reaching $\sim 0.3$\,kpc. These values of the magnetic fields are consistent with the lower bounds of the extragalactic magnetic fields. {abstract}
The luminosity function of planetary nebulae populations in galaxies within 10-15 Mpc distance has a cut-off at bright magnitudes and a functional form that is observed to be invariant in different galaxy morphological types. Thus it is used as a secondary distance indicator in both early and late-type galaxies. Recent deep surveys of planetary nebulae populations in brightest cluster galaxies (BCGs) seem to indicate that their luminosity functions deviate from those observed in the nearby galaxies. We discuss the evidence for such deviations in Virgo, and indicate which physical mechanisms may alter the evolution of a planetary nebula envelope and its central star in the halo of BCGs. We then discuss preliminary results for distances for the Virgo, Hydra I and Coma clusters based on the observed planetary nebulae luminosity functions.
We investigate the dependence of the Fanaroff-Riley (FR) I/II dichotomy of radio galaxies on their luminosities and redshifts. Because of a very strong redshift-luminosity correlation (Malmquist bias) in a flux-limited sample, any redshift-dependent effect could appear as a luminosity related effect and vice versa. A question could then arise - do all the morphological differences seen in the two classes (FR I and II types) of sources, usually attributed to the differences in their luminosities, could these all as well be a result of mainly a cosmological evolutionary effect (e.g., due to the changing ambient density) with cosmic epoch? Even a sharp break in luminosity, seen among the two classes, could after all reflect a rather critical ambient density value. A doubt on these lines does not seem to have been raised in past and things have never been examined keeping this particular aspect in mind. We want to ascertain the customary prevalent view in the literature that the systematic differences in the two broad morphology types of FR I and II radio galaxies are indeed due to the differences in their luminosities, and not a manifestation of an evolutionary effect of the cosmic epoch. Here we investigate the dependence of FR I and II dichotomy of radio galaxies on luminosity and redshift by using the 3CR sample, where the FR I and II dichotomy was first seen, supplemented by data from two additional samples (MRC and B3-VLA), which go about a factor of 5 or more deeper in flux-density than the original 3CR sample. This lets us compare sources with similar luminosities but at different redshifts as well as examine sources at similar redshifts but with different luminosities, thereby allowing us a successful separation of the otherwise two intricately entangled effects.
The density profile of cool core of intracluster gas is investigated, for a cluster of galaxies that is initially in the virial equilibrium state and then undergoes radiative cooling. The initial gas profile is derived under the assumption that the gas is hydrostatic within the dark matter potential presented by so-called NFW or King model and has a polytropic profile. The contribution from masses of gas and galaxies to the potential is ignored compared to the dark matter in the calculation. The temperature and density profiles of gas in its quasi-hydrostatic cooling phase, which is expected to last for ~Gyr, is then calculated for different initial gas profiles. It is found that in the quasi-hydrostatic cooling phase, while the temperature decreases to be about one-third, the density increases by a factor of 4-6 at the cluster center in comparison with their initial polytropic values, though the profiles over the core depend on the dark matter potential. Hence, the core radius in the quasi hydrostatic cooling gas appears smaller than the initial polytropic one. We compare the density profile of the cool core with observations to find that while the initial density is around the upper bounds of large-core (>100 kpc) clusters, likely most relaxed but cooling is not yet significant, the central density under quasi-hydrostatic cooling falls between the mid- and high-values of small-core (<100 kpc) or cool-core clusters. It is also found for the quasi-hydrostatic cooling gas that the entropy profile roughly agrees with the best-fit model for the ACCEPT cluster sample with a low central entropy, and the pressure gradient in the inner core is close to that of the REXCESS sample. X-ray surface brightness calculated for the quasi-hydrostatic cooling gas is well represented by the conventional double beta-model, giving a physical basis of applying the double beta-model to cool core clusters.
We present a study of a comparison of spin distributions of subhaloes found associated with a host halo. The subhaloes are found within two cosmological simulation families of Milky Way-like galaxies, namely the Aquarius and GHALO simulations. These two simulations use different gravity codes and cosmologies. We employ ten different substructure finders, which span a wide range of methodologies from simple overdensity in configuration space to full 6-d phase space analysis of particles.We subject the results to a common post-processing pipeline to analyse the results in a consistent manner, recovering the dimensionless spin parameter. We find that spin distribution is an excellent indicator of how well the removal of background particles (unbinding) has been carried out. We also find that the spin distribution decreases for substructure the nearer they are to the host halo's, and that the value of the spin parameter rises with enclosed mass towards the edge of the substructure. Finally subhaloes are less rotationally supported than field haloes, with the peak of the spin distribution having a lower spin parameter.
We investigate the prospects for constraining alternative theories of gravity with a typical near-term low-budget 21 cm intensity mapping experiment. We derive the 21 cm brightness temperature perturbation consistently in linear theory including all line-of-sight and relativistic effects. We uncover new terms that are a small correction on large scales, analogous to those recently found in the context of galaxy surveys. We then perform a Fisher matrix analysis of the B_0 parametrization of f(R) gravity, where B_0 is proportional to the square of Compton wavelength of the scalaron. We find that our 21 cm survey, in combination with CMB information from Planck, will be able to place a 95% upper limit of 7 x 10^{-5} on B_0 in flat models with a LCDM expansion history, improving on current cosmological constraints by several orders of magnitude. We argue that this constraint is limited by our ability to model the mildly non-linear regime of structure formation in modified gravity. We also perform a model-independent principal component analysis on the free functions introduced into the field equations by modified gravity, mu and Sigma. We find that 20--30 modes of the free functions will be `well-constrained' by our combination of observables, the lower and upper limits dependent on the criteria used to define the `goodness' of the constraint. Our analysis reveals that our observables are sensitive primarily to temporal variations in Sigma and scale variations in mu. We argue that the inclusion of 21 cm intensity maps will significantly improve constraints on any cosmological deviations from General Relativity in large-scale structure in a very cost-effective manner.
A detection of the stacked integrated Sachs-Wolfe (ISW) signal in the CMB of rare superstructures identified in the SDSS Luminous Red Galaxy catalogue has been reported at very high statistical significance. The magnitude of the observed signal has previously been argued to be more than 3 standard deviations larger than the theoretical \Lambda CDM expectation. However, this calculation was made in the linear approximation, and relied on assumptions that may potentially have caused the \Lambda CDM expectation to be underestimated. Here we update the theoretical model calculation and compare it with an analysis of ISW maps obtained from N-body simulations of a \Lambda CDM universe. The differences between model predictions and the map analyses are found to be small and cannot explain the discrepancy with observation, which remains at >3 s.d. significance. We discuss the cosmological significance of this anomaly and speculate on the potential of alternative models to explain it.
It is known that modeling uncertainties and astrophysical foregrounds can potentially introduce appreciable bias in the deduced values of cosmological parameters. While it is commonly assumed that these uncertainties will be accounted for to a sufficient level of precision, the level of bias has not been properly quantified in most cases of interest. We show that the requirement that the bias in derived values of cosmological parameters does not surpass nominal statistical error, translates into a maximal level of overall error $O(N^{-1/2})$ on $|\Delta P(k)|/P(k)$ and $|\Delta C_{l}|/C_{l}$, where $P(k)$, $C_{l}$, and $N$ are the matter power spectrum, angular power spectrum, and number of (independent Fourier) modes at a given scale $l$ or $k$ probed by the cosmological survey, respectively. This required level has important consequences on the precision with which cosmological parameters are hoped to be determined by future surveys: In virtually all ongoing and near future surveys $N$ typically falls in the range $10^{6}-10^{9}$, implying that the required overall theoretical modeling and numerical precision is already very high. Future redshifted-21-cm observations, projected to sample $\sim 10^{14}$ modes, will require knowledge of the matter power spectrum to a fantastic $10^{-7}$ precision level. We conclude that realizing the expected potential of future cosmological surveys, which aim at detecting $10^{6}-10^{14}$ modes, sets the formidable challenge of reducing the overall level of uncertainty to $10^{-3}-10^{-7}$.
We collected data on radial velocities and distances of galaxies to elucidate structure and kinematics of the filament attached to the Virgo cluster from south. In the region RA = [12.5 - 13.5]h, Dec = [-20 - 0]deg there are 171 galaxies with radial velocities VLG < 2000 km/s, and 98 of them have distance estimates. This galaxy cloud, called as "Virgo Southern Extension", is situated just on the edge of the Virgo "zero-velocity surface". The mean distance to Virgo SEx, 17pm2 Mpc, and the average radial velocity, 1172pm23 km/s, are very close to the Virgo cluster ones. In Supergalactic coordinates the Virgo SEx dimensions are 15x7x2 Mpc, where the major axis is directed along the line of sight, the second-major axis looks towards the Virgo core and the minor one is perpendicular to the Supergalactic plane. This flattened cloud consists of a dozen virialized groups with the total K-band luminosity of 1.7cdot10^12 Lsol and the total virial mass of 6.3cdot10^13 Msol, having a typical dark matter-to-stellar matter ratio of 37. The Hubble diagram for Virgo SEx galaxies exhibits a tendency of Z-shape wave with a velocity amplitude of ~250 km/s that may be caused by a mass overdensity of ~6cdot10^13 Msol, and in order of magnitude agrees with the sum of virial masses of the groups.
The discovery of the accelerating expansion of the Universe, thought to be driven by a mysterious form of `dark energy' constituting most of the Universe, has further revived the interest in testing Einstein's theory of General Relativity. At the very foundation of Einstein's theory is the geodesic motion of a small, structureless test-particle. Depending on the physical context, a star, planet or satellite can behave very nearly like a test-particle, so geodesic motion is used to calculate the advance of the perihelion of a planet's orbit, the dynamics of a binary pulsar system and of an Earth orbiting satellite. Verifying geodesic motion is then a test of paramount importance to General Relativity and other theories of fundamental physics. On the basis of the first few months of observations of the recently launched satellite LARES, its orbit shows the best agreement of any satellite with the test-particle motion predicted by General Relativity. That is, after modelling its known non-gravitational perturbations, the LARES orbit shows the smallest deviations from geodesic motion of any artificial satellite. LARES-type satellites can thus be used for accurate measurements and for tests of gravitational and fundamental physics. Already with only a few months of observation, LARES provides smaller scatter in the determination of several low-degree geopotential coefficients (Earth gravitational deviations from sphericity) than available from observations of any other satellite or combination of satellites.
An analysis of the Fermi gamma ray space telescope data has recently revealed a resolved gamma-ray feature close to the galactic center which is consistent with monochromatic photons at an energy of about 130 GeV. If interpreted in terms of dark matter (DM) annihilating into \gamma\gamma (\gamma Z, \gamma h), this would correspond to a DM particle mass of roughly 130 GeV (145 GeV, 155 GeV). The rate for these loop-suppressed processes, however, is larger than typically expected for thermally produced DM. Correspondingly, one would generically expect even larger tree level production rates of standard model fermions or gauge bosons. Here, we quantify this expectation in a rather model-independent way by relating the tree level and loop amplitudes with the help of the optical theorem. As an application, we consider bounds from continuum gamma rays, radio and antiproton data on the tree level amplitudes and translate them into constraints on the loop amplitudes. We find that, independently of the DM production mechanism, any DM model aiming at explaining the line signal in terms of charged standard model particles running in the loop is in rather strong tension with at least one of these constraints, with the exception of loops dominated by top quarks. We stress that attempts to explain the 130 GeV feature with internal bremsstrahlung do not suffer from such difficulties.
We investigate a new class of twisting type N vacuum solutions with nonzero (positive) cosmological constant Lambda by studying the equations of geodesic deviations along the privileged radial timelike geodesics, generalizing J. Bicak and J. Podolsky's results on non-twisting type N solutions. It is shown that these twisting radiative spacetimes can be interpreted as exact transverse gravitational waves propagating in the de-Sitter universe, with a distinctive feature that all the wave amplitudes are proportional to Lambda. Moveover, we demonstrate the cosmic no-hair conjecture in these spacetimes and discuss their Killing horizons.
Light bosonic degrees of freedom have become a serious candidate for dark matter. The evolution of these fields around curved spacetimes is poorly understood but is expected to display interesting effects. In particular, the interaction of light bosonic fields with supermassive black holes, key players in most galaxies, could provide colourful examples of superradiance and nonlinear bosenova-like collapse. In turn, the observation of spinning black holes is expected to impose stringent bounds on the mass of putative massive bosonic fields in our universe. Our purpose here is to present a comprehensive study of the evolution of linearized massive scalar and vector fields in the vicinities of rotating black holes. For a certain boson field mass range, the field can become trapped in a potential barrier outside the horizon and transition to a bound state. Because there are a number of such quasi-bound states, the generic outcome is an amplitude modulated sinusoidal, or beating, signal. We believe that the appearance of such beatings has gone unnoticed in the past, and in fact mistaken for exponential growth. The amplitude modulation of the signal depends strongly on the relative excitation of the overtones, which in turn is strongly tied to the bound-state geography. For the first time we explore massive vector fields in generic BH background which are hard, if not impossible, to separate in the Kerr background. Our results show that spinning BHs are generically strongly unstable against massive vector fields.
Using N-body simulations we study the evolution of separate stellar populations in dwarf galaxies in the context of the tidal stirring scenario for the formation of dwarf spheroidal (dSph) galaxies in the Local Group. The dwarf galaxies, initially composed of a stellar disk and a dark matter halo, are placed on seven different orbits around the Milky Way. The stars are divided into two populations, within and outside the half-light radius, and their positions are followed for 10 Gyr. We find that the populations retain different density distributions even over such long timescales. Some of the stars of the outer population migrate to the central part of the dwarf forming an extended core while the stars of the inner population develop a tail in the outer parts. In addition, the outer population is more heavily stripped by tidal forces from the Milky Way and may become subdominant at all radii on tight enough orbits. We conclude that the tidal stirring model is fully compatible with the presence of multiple stellar populations in dSph galaxies.
Massive gravity, galileon and braneworld models that modify gravity to explain cosmic acceleration utilize the nonlinear field interactions of the Vainshtein mechanism to screen fifth forces in high density regimes. These source-dependent interactions cause apparent equivalence principle violations. In the weakly-screened regime violations can be especially prominent since the fifth forces are at near full strength. Since they can also be calculated perturbatively, we derive analytic solutions for illustrative cases: the motion of massive objects in compensated shells and voids and infall toward halos that are spherically symmetric. Using numerical techniques we show that these solutions are valid until the characteristic scale becomes comparable to the Vainshtein radius. We find a relative acceleration of more massive objects toward the center of a void and a reduction of the infall acceleration that increases with the mass ratio of the halos which can in principle be used to test the Vainshtein screening mechanism.
We present a model for the inspiral, merger, and ringdown of highly eccentric compact binaries. We map the binary to an effective single black hole system described by a Kerr metric, thereby including certain relativistic effects not incorporated in existing post-Newtonian approximations. The resultant geodesics source quadrupolar radiation and in turn are evolved under its dissipative effects. At the light ring, we attach a merger model that was previously developed for quasicircular mergers but also performs well for eccentric mergers with little modification. We apply our model to assess the detectability of these sources for initial, Enhanced, and Advanced LIGO across the parameter space of nonspinning close capture compact binaries. We conclude that, should these systems exist in nature, the vast majority will be missed by conventional burst searches or by quasicircular waveform templates in the advanced detector era. Other methods, such as eccentric templates or, more practically, a stacked excess power search, must be developed to avoid losing these sources. These systems would also have been missed frequently in the initial LIGO data analysis. Thus, previous null coincidence results with detected GRBs can not exclude the possibility of coincident gravitational wave signals from eccentric binaries.
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The baryonic acoustic peak in the correlation function of galaxies and galaxy clusters provides a standard ruler to probe the space-time geometry of the Universe, jointly constraining the angular diameter distance and the Hubble expansion rate. Moreover, non-linear effects can systematically shift the peak position, giving us the opportunity to exploit this clustering feature also as a dynamical probe. We investigate the possibility of detecting interactions in the dark sector through an accurate determination of the baryonic acoustic scale. Making use of the public halo catalogues extracted from the CoDECS simulations -- the largest suite of N-body simulations of interacting dark energy models to date -- we determine the position of the baryonic scale fitting a band-filtered correlation function, specifically designed to amplify the signal at the sound horizon. We analyze the shifts due to non-linear dynamics, redshift-space distortions and Gaussian redshift errors, in the range 0 < z < 2. Since the coupling between dark energy and dark matter affects in a particular way the clustering properties of haloes and, specifically, the amplitude and location of the baryonic acoustic oscillations, the cosmic evolution of the baryonic peak position might provide a direct way to discriminate interacting dark energy models from the standard \Lambda CDM framework. To maximize the efficiency of the baryonic peak as a dynamic probe, the correlation function has to be measured in redshift-space, where the baryonic acoustic shift due to non-linearities is amplified. The typical redshift errors of spectroscopic galaxy surveys do not significantly impact these results.
We investigate the nature of high-z host galaxies of long Gamma-Ray Bursts (LGRBs) by means of state-of-the-art numerical simulations of cosmic structure formation and evolution of galaxies. We combine results from different runs with various box sizes and resolutions. By assigning to each simulated galaxy the probability to host a LGRB, assumed to be proportional to the mass of young stars, we provide a full description of the physical properties of high-z LGRB host galaxy population. We find that LGRBs at z>6 are hosted in galaxies with typical star formation rates SFR \sim 0.03-0.3 Msun yr^{-1}, stellar masses M \sim 10^{6-8} Msun, and metallicities Z \sim 0.01-0.1 Zsun. Furthermore, the ratio between their doubling time and the corresponding cosmic time seems to be universally equal to ~0.1-0.3, independently from the redshift. The distribution of their UV luminosity places LGRB hosts in the faint-end of the galaxy luminosity function, well below the current capabilities of space- or ground-based optical facilities. This is in line with recent reports of non-detection of LGRB hosts using extremely deep HST and VLT observations. In conclusion, high-z LGRBs are found to trace the position of those faint galaxies that are thought to be the major actors in the re-ionization of the Universe.
In this paper, we introduce PICACS, a physically-motivated, internally consistent model of scaling relations between galaxy cluster masses and their observable properties. This model can be used to constrain simultaneously the form, scatter (including its covariance) and evolution of the scaling relations, as well as the masses of the individual clusters. In this framework, scaling relations between observables (such as that between X-ray luminosity and temperature) are modelled explicitly in terms of the fundamental mass-observable scaling relations, and so are fully constrained without being fit directly. We apply the PICACS model to several observational datasets, and show that it performs as well as traditional regression methods for simply measuring scaling relation parameters, but presents several significant advantages. For clusters with available X-ray hydrostatic masses, PICACS gives a modest improvement of the precision of the mass estimates, while consistently constraining the mass-observable scaling relations. For a sample of clusters without prior mass estimates, we derive self-consistent constraints on the cluster masses and scaling relations, and find a minor improvement in precision on cluster mass estimates compared with a single scaling relation. We are also able to deconstruct the slope of the luminosity-temperature (LT) relation and show that the steepening compared to self-similar expectations is due to contributions from heating and depletion of the gas within the reference radius R500, and not due to a mass dependence of the gas structure within that radius. Finally, we use PICACS to illustrate the dependence of the expected self-similar evolution of the LT relation on the slopes of the mass scaling relations, and show that our self-consistent modelling predicts self-similar evolution significantly weaker than is commonly assumed.
The population of low-luminosity (< 10^35 erg/s) X-Ray Binaries (XRBs) has been investigated in our Galaxy and M31 but not further. To address this problem, we have used data from the Chandra X-Ray Observatory and the Hubble Space Telescope to investigate the faint population of XRBs in the grand-design spiral galaxy M51. A matching analysis found 25 star clusters coincident with 20 X-ray point sources within 1.5" (60 pc). From X-ray and optical color-color plots we determine that this population is dominated by high-mass XRBs. A stacking analysis of the X-ray data at the positions of optically-identified star clusters was completed to probe low-luminosity X-ray sources. No cluster type had a significant detection in any X-ray energy band. An average globular cluster had the largest upper limit, 9.23 x 10^34 erg/s, in the full-band (0.3 - 8 keV) while on average the complete sample of clusters had the lowest upper limit, 6.46 x 10^33 erg/s in the hard-band (2 - 8 keV). We determined average luminosities of the young and old star cluster populations and compared the results to those from the Milky Way. We conclude that deeper X-ray data is required to identify faint sources with a stacking analysis.
We use the new ultra-deep, near-infrared imaging of the Hubble Ultra-Deep Field (HUDF) provided by our UDF12 HST WFC3/IR campaign to explore the rest-frame UV properties of galaxies at redshifts z > 6.5. We present the first unbiased measurement of the average UV power-law index, beta, for faint galaxies at z ~ 7, the first meaningful measurements of beta at z ~ 8, and tentative estimates for a new sample of galaxies at z ~ 9. Utilising galaxy selection in the new F140W imaging to minimize colour bias, and applying both colour and power-law estimators of beta, we find beta = -2.1 (+/-0.2) at z ~ 7 for galaxies with M_UV ~ -18. This means that the faintest galaxies uncovered at this epoch have, on average, UV colours no more extreme than those displayed by the bluest star-forming galaxies at low redshift. At z ~ 8 we find a similar value, beta = -1.9 (+/-0.3). At z ~ 9, we find beta = -1.8 (+/-0.6), essentially unchanged from z ~ 6 - 7 (albeit highly uncertain). Finally, we show that there is as yet no evidence for a significant intrinsic scatter in beta within our new, robust z ~ 7 galaxy sample. Our results are most easily explained by a population of steadily star-forming galaxies with either ~ solar metallicity and zero dust, or moderately sub-solar (~ 10-20%) metallicity with modest dust obscuration (A_V ~ 0.1-0.2). This latter interpretation is consistent with the predictions of a state-of-the-art galaxy-formation simulation, which also suggests that a significant population of very-low metallicity, dust-free galaxies with beta ~ -2.5 may not emerge until M_UV > -16, a regime likely to remain inaccessible until the James Webb Space Telescope.
We present a derivation of two-point correlations of general tracers in the peak-background split (PBS) framework by way of a rigorous definition of the PBS argument. Our expressions only depend on connected matter correlators and "renormalized" bias parameters with clear physical interpretation, and are independent of any coarse-graining scale. This result should be contrasted with the usual expression derived from a local bias expansion of the tracer number density with respect to the matter density perturbation \delta_L coarse-grained on a scale R_L. In the latter case, the predicted tracer correlation function receives contributions of order <\delta_L^n> at each perturbative order n, whereas, in our formalism, these are absorbed in the PBS bias parameters at all orders. Further, this approach naturally predicts both a scale-dependent bias ~ k^2 such as found for peaks of the density field, and the scale-dependent bias induced by primordial non-Gaussianity in the initial conditions. The only assumption made about the tracers is that their abundance at a given position depends solely on the matter distribution within a finite region around that position.
We revisit the formation and evolution of the first galaxies using new hydrodynamic cosmological simulations with the ART code. Our simulations feature a recently developed model for H2 formation and dissociation, and a star formation recipe that is based on molecular rather than atomic gas. Here, we develop and implement a new recipe for the formation of metal-free Population III stars. We find the epoch during which Pop III stars dominated the energy and metal budget of the first galaxies to be short-lived. Galaxies which host Pop III stars do not retain dynamical signatures of their thermal and radiative feedback for more than 10^8 yr after the lives of the stars end in pair-instability supernovae, even when we consider the maximum reasonable efficiency of the feedback. Though metals ejected by the supernovae can travel well beyond the virial radius of the host galaxy, they will typically begin to fall back quickly, and do not enrich a large fraction of the intergalactic medium. Galaxies more massive than 3 x 10^6 Msun re-accrete most of their baryons and transition to metal-enriched Pop II star formation.
We examine the two-point correlation function (TPCF) of local maxima in temperature fluctuations at the last scattering surface when this stochastic field is modified by the additional fluctuations produced by straight cosmic strings via the Kaiser-Stebbins effect. We demonstrate that one can detect the imprint of cosmic strings with tension $G\mu \gtrsim 1.2 \times 10^{-8}$ on noiseless $1^\prime$ resolution CMB maps at 95% confidence interval. Including the effects of foregrounds and anticipated systematic errors increases the lower bound to $G\mu \gtrsim 9.0\times 10^{-8}$ at $2\sigma$ confidence level. Smearing by beams of order 4' degrades the bound further to $G\mu \gtrsim 1.6 \times 10^{-7}$. Our results indicate that 2-point statistics are more powerful than 1-point statistics (e.g. number counts) for identifying the non-Gaussianity in the CMB due to straight cosmic strings.
Large surveys for Lyman-alpha emitting (LAE) galaxies have been proposed as a new method for measuring clustering of the galaxy population at high redshift with the goal of determining cosmological parameters. However, Lyman-alpha radiative transfer effects may modify the observed clustering of LAE galaxies in a way that mimics gravitational effects, potentially reducing the precision of cosmological constraints. For example, the effect of the linear redshift-space distortion on the power spectrum of LAE galaxies is potentially degenerate with Lyman-alpha radiative transfer effects owing to the dependence of observed flux on intergalactic medium velocity gradients. In this paper, we show that the three-point function (bispectrum) can distinguish between gravitational and non-gravitational effects, and thus breaks these degeneracies, making it possible to recover cosmological parameters from LAE galaxy surveys. Constraints on the angular diameter distance and the Hubble expansion rate can also be improved by combining power spectrum and bispectrum measurements.
We present the results of a study of a statistically significant sample of galaxies which clearly demonstrate that supermassive black holes are generically present in all morphological types. Our analysis is based on the quantitative morphological classification of 1.12 million galaxies in the SDSS DR7 and on the detection of black hole activity via two different methods, the first one based on their X-ray/radio emission and the second one based on their mid-infrared colors. The results of the first analysis confirm the correlation between black hole and total stellar mass for 8 galaxies and includes one galaxy classified as bulgeless. The results of our second analysis, consisting of 15,991 galaxies, show that galaxies hosting a supermassive black hole follow the same morphological distribution as the general population of galaxies in the same redshift range. In particular, the fraction of bulgeless galaxies, 1,450 galaxies or 9 percent, is found to be the same as in the general population. We also present the correlation between black hole and total stellar mass for 6,247 of these galaxies. Importantly, whereas previous studies were limited to primarily bulge-dominated systems, our study confirms this relationship to all morphological types, in particular, to 530 bulgeless galaxies. Our results indicate that the true correlation that exists for supermassive black holes and their host galaxies is between the black hole mass and the total stellar mass of the galaxy and hence, we conclude that the previous assumption that the black hole mass is correlated with the bulge mass is only approximately correct.
Our aim is to explore the nature of emission line galaxies by combining
high-resolution observations obtained in different bands to understand which
objects are powered by an Active Galactic Nucleus(AGN). From the spectroscopic
Palomar survey of nearby bright galaxies, we selected a sample of 18 objects
observed with HST, Chandra, and VLA.
No connection is found between X-ray and emission line luminosities from
ground-based data, unlike what is found for brighter AGN. Conversely, a strong
correlation emerges when using the HST spectroscopic data, which are extracted
on a much smaller aperture. This suggests that the HST data better isolate the
AGN component when one is present, while ground-based line measurements are
affected by diffuse emission from the host galaxies.
The sample separates into two populations. The 11 objects belonging to the
first class have an equivalent width of the [OIII] emission line measured from
HST data EW([OIII])>~2 A and are associated with an X-ray nuclear source; in
the second group we find seven galaxies with EW([OIII])<~1 A that generally do
not show any emission related to an active nucleus (emission lines, X-ray, or
radio sources). This latter group includes about half of the Low Ionization
Nuclear Emission-line region (LINERs) or transition galaxies of the sample, all
of which are objects of low [OIII] line luminosity (<~1E38 erg s-1) and low
equivalent width (<~1 A) in ground-based observations. These results strengthen
the suggestion that the EW([OIII]) value is a robust predictor of the nature of
an emission line galaxy.
We make use of publicly available results from N-body Millennium Simulation to create mock samples of lensed supernovae type Ia and core-collapse. Simulating galaxy-galaxy lensing we derive the rates of lensed supernovae and find than at redshifts higher that 0.5 about 0.06 per cent of supernovae will be lensed by a factor two or more. Future wide field surveys like Gaia or LSST should be able to detect lensed supernovae in their unbiased sky monitoring. Gaia (from 2013) will detect at least 2 cases whereas LSST (from 2018) will see more than 500 a year. Large number of future lensed supernovae will allow to verify results of cosmological simulations. The strong galaxy- galaxy lensing gives an opportunity to reach high-redshift supernovae type Ia and extend the Hubble diagram sample.
We propose a new method to probe for variations in the fine structure constant alpha using clusters of galaxies, opening up a window on a new redshift range for such constraints. Hot clusters shine in the X-ray mainly due to bremsstrahlung, while they leave an imprint on the CMB frequency spectrum through the Sunyaev-Zel'dovich effect. These two physical processes can be characterized by the integrated Comptonization parameter Y_SZ DA^2 and its X-ray counterpart, the Y_X parameter. The ratio of these two quantities is expected to be constant from numerical simulations and current observations. We show that this fact can be exploited to constrain alpha, as the ratio of the two parameters depends on the fine structure constant as alpha^{3.5}. We determine current constraints from a combination of Planck SZ and XMM-Newton data, testing different models of variation of alpha. When fitting for a constant value of alpha, we find that current constraints are at the 1% level, comparable with current CMB constraints. We discuss strategies for further improving these constraints by almost an order of magnitude.
There exists the entropy problem of the early universe, that is, why did the universe begin with an extremely low entropy and how did it evolve into such high entropy at late times? To address this problem, we invoke the nonlinear generalized Chaplygin gas (GCG) as a toy model to compute the evolution of the cosmological entanglement entropy in the early universe before the matter dominant era. GCG has the advantage of providing a smooth and unitary transition between the inflation epoch and the radiation dominant era, which makes the effective calculation possible. We found that soon after the onset of the inflation, the total entanglement entropy rapidly decreases to a minimum, and after that it rises monotonically throughout the remainder of the inflation and the radiation epochs. This indicates that the universe does not need to begin with an extremely low entropy; its smallness can be naturally induced by the dynamics of inflation itself. We believe that our computation largely captures the essential feature of entropy evolution and can provide us insights beyond the toy model.
Assuming that observers located inside the Universe measure a proper time which is different from the time appearing in the Friedmann-Lemaitre equation, and determining this proper time such that the Universe always appears flat to these observers, we derive a simple cosmological model which allows to explain the velocity dispersions of galaxies in galaxy clusters without introducing dark matter. It also explains the present acceleration of the expansion without any resort to dark energy and provides a good fit to the observations of distant supernovae. Depending on the present value of the matter-energy density, we calculate an age of the Universe between 15.4 and 16.5 billion years, significantly larger than the 13.7 billion years of the standard LambdaCDM model. Our model has a slower expansion rate in the early epochs, thus leaving more time for the formation of structures such as stars and galaxies.
Isolated compact groups of galaxies (CGs) present a range of dynamical states, group velocity dispersions, and galaxy morphologies with which to study galaxy evolution, particularly the properties of gas both within the galaxies and in the intragroup medium. As part of a large, multiwavelength examination of CGs, we present an archival study of diffuse X-ray emission in a subset of nine Hickson compact groups observed with the Chandra X-ray Observatory. We find that seven of the groups in our sample exhibit detectable diffuse emission. However, unlike large-scale emission in galaxy clusters, the diffuse features in the majority of the detected groups are linked to the individual galaxies, in the form of both plumes and halos likely as a result of star formation or AGN activity, as well as in emission from tidal features. Unlike previous studies from earlier X-ray missions, HCGs 31, 42, 59, and 92 are found to be consistent with the Lx-T relationship from clusters within the errors, while HCGs 16 and 31 are consistent with the cluster Lx-sigma relation, though this is likely coincidental given that the hot gas in these two systems is largely due to star formation. We find that Lx increases with decreasing group HI to dynamical-mass ratio with tentative evidence for a dependance in X-ray luminosity on HI morphology whereby systems with intragroup HI indicative of strong interactions are considerably more X-ray luminous than passively evolving groups. We also find a gap in the Lx of groups as a function of the total group specific star formation rate. Our findings suggest that the hot gas in these groups is not in hydrostatic equilibrium and these systems are not low-mass analogs of rich groups or clusters, with the possible exception of HCG 62.
Does the "blazar sequence" exist, or is it a result of a selection effect, due to the difficulty in measuring the redshifts of blazars with both high synchrotron peak frequencies (\gtrsim 10^{15} Hz) and luminosities (\gtrsim 10^{46} erg s^{-1})? We explore this question with a sample of blazars from the Second Catalog of Active Galactic Nuclei (AGN) from the Fermi Large Area Telescope (LAT). The Compton dominance, the ratio of the peak of the Compton to the synchrotron peak luminosities, is essentially a redshift-independent quantity, and thus crucial to answering this question. We find that a correlation exists between Compton dominance and the peak frequency of the synchrotron component for all blazars in the sample, including ones with unknown redshift. We then construct a simple model to explain the blazar properties in our sample, where the difference between sources is due to only the magnetic field of the blazar jet emitting region, the external radiation field energy density, and the jet angle to the line of sight, with the magnetic field strength and external energy density being correlated. This model can reproduce the trends of the blazars in the sample, and predicts blazars may be discovered in the future with high synchrotron peak frequencies and luminosities. At the same time the simple model reproduces the lack of high-synchrotron peaked blazars with high Compton dominances (\gtrsim 1).
We argue using simple models that all successful practical uses of probabilities originate in quantum fluctuations in the microscopic physical world around us, often propagated to macroscopic scales. Thus we claim there is no physically verified fully classical theory of probability. We comment on the general implications of this view, and specifically question the application of classical probability theory to cosmology in cases where key questions are known to have no quantum answer.
We investigate the turbulence effect in dark fluid universe with linear inhomogeneous equation of state. Attention is attached to two physical situations. First, we perform the perturbative analysis of turbulence and check its effects around the Big Rip. Later, treating the turbulence energy density as a part of total dark fluid, we study the stability of the system. The result shows that the stability is achieving as the energy density of turbulence decreases, changing into heat (the radiation), in perfect agreement with the avoidance of the Big Rip.
To explore possibilities of avoiding coincidence problem in $f(R)$ gravity we consider models in Einstein conformal frame which are equivalent to Einstein gravity with a minimally coupled scalar field. As the conformal factor determines the coupling term and hence the interaction between matter and dark energy, the function $f(R)$ can in principle be determined by choosing an appropriate function for the deceleration parameter only. Possible behavior of $f(R)$ to avoid coincidence problem are investigated in two such cases.
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We investigate the transition from primordial Pop III star formation to normal Pop II star formation in the first galaxies using new cosmological hydrodynamic simulations. We find that while the first stars seed their host galaxies with metals, they cannot sustain significant outflows to enrich the intergalactic medium, even assuming a top-heavy initial mass function. This means that Pop III star formation could potentially continue until z~6 in different unenriched regions of the universe, before being ultimately shut off by cosmic reionization. Within an individual galaxy, Pop II stars overtake Pop III stars in 20-200 Myr, based on the amount of stellar feedback and metal production.
We quantify the presence of Active Galactic nuclei (AGN) in a mass-complete (M_* >5e10 M_sun) sample of 123 star-forming and quiescent galaxies at 1.5 < z < 2.5, using X-ray data from the 4 Ms Chandra Deep Field-South (CDF-S) survey. 41+/-7% of the galaxies are detected directly in X-rays, 22+/-5% with rest-frame 0.5-8 keV luminosities consistent with hosting luminous AGN (L_0.5-8keV > 3e42 ergs/s). The latter fraction is similar for star-forming and quiescent galaxies, and does not depend on galaxy stellar mass, suggesting that perhaps luminous AGN are triggered by external effects such as mergers. We detect significant mean X-ray signals in stacked images for both the individually non-detected star-forming and quiescent galaxies, with spectra consistent with star formation only and/or a low luminosity AGN in both cases. Comparing star formation rates inferred from the 2-10 keV luminosities to those from rest-frame IR+UV emission, we find evidence for an X-ray excess indicative of low-luminosity AGN. Among the quiescent galaxies, the excess suggests that as many as 70-100% of these contain low- or high-luminosity AGN, while the corresponding fraction is lower among star-forming galaxies (43-65%). The ubiquitous presence of AGN in massive, quiescent z ~ 2 galaxies that we find provides observational support for the importance of AGN in impeding star formation during galaxy evolution.
We present observations of the molecular gas in the nuclear environment of three prototypical low luminosity AGN (LLAGN), based on VLT/SINFONI AO-assisted integral-field spectroscopy of H2 1-0 S(1) emission at angular resolutions of ~0.17". On scales of 50-150 pc the spatial distribution and kinematics of the molecular gas are consistent with a rotating thin disk, where the ratio of rotation (V) to dispersion (sigma) exceeds unity. However, in the central 50 pc, the observations reveal a geometrically and optically thick structure of molecular gas (V/sigma<1 and N_H>10^{23} cm^{-2}) that is likely to be associated with the outer extent of any smaller scale obscuring structure. In contrast to Seyfert galaxies, the molecular gas in LLAGN has a V/sigma<1 over an area that is ~9 times smaller and column densities that are in average ~3 times smaller. We interpret these results as evidence for a gradual disappearance of the nuclear obscuring structure. While a disk wind may not be able to maintain a thick rotating structure at these luminosities, inflow of material into the nuclear region could provide sufficient energy to sustain it. In this context, LLAGN may represent the final phase of accretion in current theories of torus evolution. While the inflow rate is considerable during the Seyfert phase, it is slowly decreasing, and the collisional disk is gradually transitioning to become geometrically thin. Furthermore, the nuclear region of these LLAGN is dominated by intermediate-age/old stellar populations (with little or no on-going star formation), consistent with a late stage of evolution.
The excursion set approach provides a framework for predicting how the abundance of dark matter halos depends on the initial conditions. A key ingredient of this formalism comes from the physics of halo formation: the specification of a critical overdensity threshold (barrier) which protohalos must exceed if they are to form bound virialized halos at a later time. Another ingredient is statistical, as it requires the specification of the appropriate statistical ensemble over which to average when making predictions. The excursion set approach explicitly averages over all initial positions, thus implicitly assuming that the appropriate ensemble is that associated with randomly chosen positions in space, rather than special positions such as peaks of the initial density field. Since halos are known to collapse around special positions, it is not clear that the physical and statistical assumptions which underlie the excursion set approach are self-consistent. We argue that they are, and illustrate by comparing our excursion set predictions with numerical data from the DEUS simulations.
Through a large ensemble of Gaussian simulations and a suite of large-volume $N$-body simulations, we show that in a standard LCDM scenario, supervoids and superclusters in the redshift range (0.4<z<0.7) should leave a small signature on the Integrated Sachs Wolfe (ISW) effect of the order ~2 \mu K. We perform aperture photometry on WMAP data, centred on such superstructures identified from SDSS LRG data, and find amplitudes at the level of 8 -- 11 \mu K -- thus confirming the earlier work of (Granett et al. 2008). If we focus on apertures of the size ~3.6 degrees, then our simulations indicate that LCDM is discrepant at the level of ~4 \sigma. However, if we combine all aperture scales considered, ranging from 1--20 degrees, then the discrepancy becomes ~2 \sigma. Full-sky ISW maps generated from our N-body simulations show that this discrepancy cannot be alleviated by appealing to Rees-Sciama (RS) mechanisms, since their impact on the scales probed by our filters is negligible. We perform a series of tests on the WMAP data for systematics. We check for foreground contaminants and show that the signal does not display the correct dependence on the aperture size expected for a residual foreground tracing the density field. The signal also proves robust against rotation tests of the CMB maps, and seems to be spatially associated to the angular positions of the supervoids and superclusters. We explore whether the signal can be explained by the presence of primordial non-Gaussianities of the local type. We show that for models with f_NL=+/-100, whilst there is a change in the pattern of temperature anisotropies, all amplitude shifts are well below <1 \mu K. If primordial non-Gaussianity were to explain the result, then f_NL would need to be several times larger than currently permitted by WMAP constraints.
One of the most pernicious theoretical systematics facing upcoming gravitational lensing surveys is the uncertainty introduced by the effects of baryons on the power spectrum of the convergence field. One method that has been proposed to account for these effects is to allow several additional parameters (that characterize dark matter halos) to vary and to fit lensing data to these halo parameters concurrently with the standard set of cosmological parameters. We test this method. In particular, we use this technique to model convergence power spectrum predictions from a set of cosmological simulations. We estimate biases in dark energy equation of state parameters that would be incurred if one were to fit the spectra predicted by the simulations either with no model for baryons, or with the proposed method. We show that neglecting baryonic effect leads to biases in dark energy parameters that are several times the statistical errors for a survey like the Dark Energy Survey. The proposed method to correct for baryonic effects renders the residual biases in dark energy equation of state parameters smaller than the statistical errors. These results suggest that this mitigation method may be applied to analyze convergence spectra from a survey like the Dark Energy Survey. For significantly larger surveys, such as will be carried out by the Large Synoptic Survey Telescope, the biases introduced by baryonic effects are much more significant. We show that this mitigation technique significantly reduces the biases for such larger surveys, but that a more effective mitigation strategy will need to be developed in order ensure that the residual biases in these surveys fall below the statistical errors.
We discuss the relationship between a standard Shakura & Sunyaev (1973) accretion disk model and the Big Blue Bump (BBB) observed in Type 1 AGN, and propose a new method to estimate black hole masses. We apply this method to a sample of 23 radio-loud narrow-line Seyfert 1 (RL-NLS1) galaxies, using data from WISE (Wide-field Infrared Survey Explorer), SDSS (Sloan Digital Sky Survey) and GALEX. Our black hole mass estimates are at least a factor $\sim$6 above previous results based on single epoch virial methods, while the Eddington ratios are correspondingly lower. Hence, the black hole masses of RL-NLS1 galaxies are typically above $10^8 M_{\sun}$, in agreement with the typical black hole mass of blazars.
A sample of 10 nearby intermediate-type active galactic nuclei (AGN) drawn from the Sloan Digital Sky Survey (SDSS-DR7) is presented. The aim of this work is to provide estimations of the black hole mass for the sample galaxies from the dynamics of the broad line region. For this purpose, a detailed spectroscopic analysis of the objects was done. Using BPT diagnostic diagrams we have carefully classified the objects as true intermediate-type AGN and found that 80%$^{+7.2%}_{-17.3%}$ are composite AGN. The black hole mass estimated for the sample is within 6.54$\pm$0.16\,$<$\,log\,$M_{\rm BH}$\,$<$\,7.81$\pm$0.14. Profile analysis show that five objects (\object{J120655.63+501737.1}, \object{J121607.08+504930.0}, \object{J141238.14+391836.5}, \object{J143031.18+524225.8} and \object{J162952.88+242638.3}) have narrow double-peaked emission lines in both the red (H$\alpha$, [\ion{N}{2}]$\lambda\lambda$6548,6583 and [\ion{S}{2}]$\lambda\lambda$6716,6731) and the blue (H$\beta$ and [\ion{O}{3}]$\lambda\lambda$4959,5007) region of the spectra, with velocity differences ($\Delta V$) between the double peaks within 114\,$<\Delta V\,<$\,256 km s$^{-1}$. Two of them, \object{J121607.08+504930.0} and \object{J141238.14+391836.5} are candidates for dual AGN since their double-peaked emission lines are dominated by AGN activity. In searches of dual AGN; Type 1, Type 1I and intermediate-type AGN should be carefully separated, due to the high serendipitous number of narrow double-peaked sources (50%$\pm$14.4%) found in our sample.
We present maps of the CO-to-H2 conversion factor (alpha_co) and dust-to-gas ratio (DGR) in 26 nearby, star-forming galaxies with ~kiloparsec spatial resolution. We have simultaneously solved for alpha_co and DGR by assuming that the DGR is approximately constant on kpc scales. With this assumption, we can combine maps of dust mass surface density, CO integrated intensity and HI column density to solve for both alpha_co and DGR with no assumptions about their value or dependence on metallicity or other parameters. Such a study has just become possible with the availability of high resolution far-IR maps from the Herschel key program KINGFISH, 12CO J=(2-1) maps from the IRAM 30m large program HERACLES and HI 21-cm line maps from THINGS. We use a fixed ratio between the (2-1) and (1-0) lines to present our alpha_co results on the more typically used 12CO J=(1-0) scale and show using literature measurements that variations in the line ratio do not effect our results. In total, we derive 782 individual solutions for alpha_co and DGR. On average, alpha_co = 3.1 Msun pc^-2 (K km s^-1)^-1 for our sample with a standard deviation of 0.3 dex. Within galaxies we observe a generally flat profile of alpha_co as a function of galactocentric radius. However, most galaxies exhibit a lower alpha_co in the central kiloparsec---a factor of ~2 below the galaxy mean, on average. In some cases, the central alpha_co value can be factors of 5 to 10 below the standard MW value of alpha_co,MW = 4.4 Msun pc^-2 (K km s^-1)^-1. While for alpha_co we find only weak correlations with metallicity, DGR is well-correlated with metallicity, with an approximately linear slope. Finally, we present several recommendations for choosing an appropriate alpha_co for studies of nearby galaxies.
We measure the luminosity and color dependence and the redshift evolution of galaxy clustering in the Sloan Digital Sky Survey-III Baryon Oscillation Spectroscopic Survey Ninth Data Release. We focus on the projected two-point correlation function (2PCF) of subsets of its CMASS sample, which includes about 260,000 galaxies over ~3,300 sq. deg in the redshift range 0.43<z<0.7. To minimize the selection effect on galaxy clustering, we construct well-defined luminosity and color subsamples by carefully accounting for the CMASS galaxy selection cuts. The 2PCF of the whole CMASS sample, if approximated by a power-law, has a correlation length of r_0=7.93\pm0.06Mpc/h and an index of \gamma=1.85\pm0.01. Clear dependences on galaxy luminosity and color are found for the projected 2PCF in all redshift bins, with more luminous and redder galaxies generally exhibiting stronger clustering and steeper 2PCF. The color dependence is also clearly seen for galaxies within the red sequence, consistent with the behavior of SDSS-II main sample galaxies at lower redshifts. At a given luminosity (k+e corrected), no significant evolution of the projected 2PCFs with redshift is detected for red sequence galaxies. We also construct galaxy samples of fixed number density at different redshifts, using redshift-dependent magnitude thresholds. The clustering of these galaxies in the CMASS redshift range is found to be consistent with that predicted by passive evolution. Our measurements of the luminosity and color dependence and redshift evolution of galaxy clustering will allow for detailed modeling of the relation between galaxies and dark matter halos and new constraints on galaxy formation and evolution.
We present a multi-wavelength study of a 3.6 $\mu$m-selected galaxy sample in the Extended Groth strip. The sample is complete for galaxies with stellar mass $>10^{9.5}$ \Msun and redshift $0.4<z<1.2$. In this redshift range, the IRAC 3.6 $\mu$m band measures the rest-frame near-infrared band, permitting nearly unbiased selection with respect to both quiescent and star-forming galaxies. The numerous spectroscopic redshifts available in the EGS are used to train an Artificial Neural Network to estimate photometric redshifts. The distribution of photometric redshift errors is Gaussian with standard deviation ${\sim}0.025(1+z)$, and the fraction of redshift failures (${>}3\sigma$ errors) is about 3.5%. A new method of validation based on pair statistics confirms the estimate of standard deviation even for galaxies lacking spectroscopic redshifts. Basic galaxy properties measured include rest-frame $U-B$ colors, $B$- and $K$-band absolute magnitudes, and stellar masses. We divide the sample into quiescent and star-forming galaxies according to their rest-frame $U-B$ colors and 24 to 3.6 \micron\ flux density ratios and derive rest $K$-band luminosity functions and stellar mass functions for quiescent, star forming, and all galaxies. The results show that massive, quiescent galaxies were in place by $z\approx1$, but lower mass galaxies generally ceased their star formation at later epochs.
We examine the velocity width of cool X-ray emitting material using XMM-Newton Reflection Grating Spectrometer (RGS) spectra of a sample of clusters and group of galaxies and elliptical galaxies. Improving on our previous analyses, we apply a spectral model which accounts for broadening due to the spatial extent of the source. With both conventional and Markov Chain Monte Carlo approaches we obtain limits, or in a few cases measurements, of the velocity broadening of the coolest X-ray material. In our sample, we include new observations targeting objects with compact, bright, line-rich cores. One of these, MACSJ2229.7-2755, gives a velocity limit of 280 km/s at the 90 per cent confidence level. Other systems with limits close to 300 km/s include A1835, NGC4261 and NGC4472. For more than a third of the targets we find limits better than 500 km/s. HCG62, NGC1399 and A3112 show evidence for ~400 km/s velocity broadening. For a smaller sample of objects, we use continuum-subtracted emission line surface brightness profiles to account for the spatial broadening. Although there are significant systematic errors associated with the technique (~150 km/s), we find broadening at the level of 280 to 500 km/s in A3112, NGC1399 and NGC4636.
We compare two different probes of the expansion history of the universe, namely, luminosity distances from type Ia supernovae and angular diameter distances from galaxy clusters, using the Bayesian interpretation of Crossing statistic [1,2] in conjunction with the cosmic duality relation. Our analysis is conducted independently of any a-priori assumptions about the nature of dark energy. The model independent method which we invoke searches for inconsistencies between SNIa and galaxy cluster data sets. If detected such an inconsistency would imply the presence of systematics in either of the two data sets. Simulating observations based on expected JDEM supernovae data and X-ray eROSITA + SZ Planck cluster data, we show that our method allows one to detect systematics with high precision and without advancing any hypothesis about the nature of dark energy.
We study inflationary universe models that are characterized by a single scalar inflaton field. The study of these models are based on two dynamical equations; one corresponding to the Klein-Gordon equation for the inflaton field, and the other, to a generalized Friedmann equation. After describing the kinematics and dynamics of the models, we determine in some detail scalar density perturbations and relic gravitational waves. We apply this approach to the Friedmann-Chern-Simons and the brane-world inflationary models.
MASSIV (Mass Assembly Survey with SINFONI in VVDS) is a sample of 84 distant star-forming galaxies observed with the SINFONI Integral Field Unit (IFU) on the VLT. These galaxies are selected inside a redshift range of 0.8 < z < 1.9, i.e. where they are between 3 and 5 billion years old. The sample aims to probe the dynamical and chemical abundances properties of representative galaxies of this cosmological era. On the one hand, close environment study shows that about a third of the sample is involved in major mergers. On the other hand, kinematical analysis revealed that 42% of the sample is rotating disks, in accordance with higher redshift samples. The remaining 58% show complex kinematics, suggesting a dynamical support based on dispersion, and about half of these galaxies is involved in major mergers. Spheroids, unrelaxed merger remnants, or extremely turbulent disks might be an explanation for such a behavior. Furthermore, the spatially resolved metallicity analysis reveals positive gradients, adding a piece to the puzzle of galaxies evolution scenarios.
MASSIV (Massiv Assembly Survey with SINFONI in VVDS) is an ESO large program which consists of 84 star-forming galaxies, spanning in a wide range of stellar masses, observed with the IFU SINFONI on the VLT, in the redshift range 1 < z < 2. To be representative of the normal galaxy population, the sample has been selected from a well-defined, complete and representative parent sample. The kinematics of individual galaxies reveals that 58% of the galaxies are slow rotators, which means that a high fraction of these galaxies should probably be formed through major merger processes which might have produced gaseous thick or spheroidal structures supported by velocity dispersion rather than by rotation. Computations on the major merger rate from close pairs indicate that a typical star-forming galaxy underwent ~0.4 major mergers since ~9.5 Gyr, showing that merging is a major process driving mass assembly into the red sequence galaxies. These objects are also intriguing due to the fact that more than one galaxy over four is more metal-rich in its outskirts than in its center.
We study lepton asymmetry evolution in plasma of the early Universe before the electroweak phase transition (EWPT) accounting for chirality flip processes via Higgs decays (inverse decays) entering equilibrium at temperatures below T_RL ~ 10 TeV, T_EW < T < T_RL. We solve appropriate kinetic equations for leptons and Higgs bosons taking into account the lepton number violation due to Abelian anomalies for right- and left electrons and neutrinos in the self-consistent hypercharge field obeying Maxwell equations modified by the contribution of the Standard Model of electroweak interactions. The violation of left lepton numbers and corresponding violation of the baryon number due to sphaleron processes in symmetric phase is taken into account as well. Assuming the Chern-Simons (CS) wave configuration of the seed hypercharge field, we get the estimates of baryon and lepton asymmetries evolved from the primordial right electron asymmetry existing alone as partial asymmetry at T > T_RL. One finds a strong dependence of the asymmetries on the CS wave number. We predict a non-zero chiral asymmetry \Delta \mu = \mu_e_R - \mu_e_L \neq 0 in this scenario evolved down to the EWPT moment that can be used as an initial value for the Maxwellian field evolution after EWPT.
We present the 2012 Hubble Ultra Deep Field campaign (UDF12), a large 128-orbit Cycle 19 \HST\ program aimed at extending previous WFC3/IR observations of the UDF by quadrupling the exposure time in the F105W filter, imaging in an additional F140W filter, and extending the F160W exposure time by 50%. The principal scientific goal of this project is to determine whether galaxies reionized the universe; our observations are designed to provide a robust determination of the star formation density at $z$$\,\gtrsim\,$8, improve measurements of the ultraviolet continuum slope at $z$$\,\sim\,7\,-\,$8, facilitate the construction of new samples of $z$$\,\sim\,9\,-\,$10 candidates, and enable the detection of sources up to $z$$\,\sim\,$12. For this project we committed to combining these and other WFC3/IR imaging observations of the UDF area into a single homogeneous dataset, to provide the deepest near-infrared observations of the sky currently achievable. In this paper we present the observational overview of the project, motivated by its scientific goals, and describe the procedures used in reducing the data as well as the final products that are produced. We have used the most up up-to-date methods for calibrating and combining the images, in particular paying attention to correcting several instrumental effects. We release the full combined mosaics, comprising a single, unified set of mosaics of the UDF, providing the deepest near-infrared blank-field view of the universe obtained to date, reaching magnitudes as deep as AB$\,\sim\,$30 in the near-infrared, and yielding a legacy dataset on this field of lasting scientific value to the community.
We study the effects of non-trivial initial quantum states for inflationary fluctuations within the context of the effective field theory for inflation constructed by Cheung et al. which allows us to discriminate between different initial states in a model-independent way. We develop a Green's function/path integral based formulation that incorporates initial state effects and use it to address questions such as how state-dependent is the consistency relation for the bispectrum, how many e-folds beyond the minimum required to solve the cosmological fine tunings of the big bang are we allowed so that some information from the initial state survives until late times, among others. We find that the so-called consistency condition relating the local limit of the bispectrum and the slow-roll parameter is a state-dependent statement that can be avoided for physically consistent initial states either with or without initial non-Gaussianities.
We present the results of spectroscopic observations of three S0-Sa galaxies: NGC338, NGC 3245, and NGC 5440 at the SAO RAS 6-m BTA telescope. The radial distributions of the line-of-sight velocities and radial velocity dispersions of stars and ionized gas were obtained, and rotation curves of galaxies were computed. We construct the numerical dynamic N-body galaxy models with N > 10^6 point masses. The models include three components: a "live" bulge, a collisionless disk, dynamically evolving to the marginally stable state, and a pseudo-isothermal dark halo. The estimates of radial velocities and velocity dispersions of stars obtained from observations are compared with model estimates, projected onto the line of sight. We show that the disks of NGC 5440 and the outer regions of NGC 338 are dynamically overheated. Taking into account the previously obtained observations, we conclude that the dynamic heating of the disk is present in a large number of early-type disk galaxies, and it seems to ensue from the external effects. The estimates of the disk mass and relative mass of the dark halo are given for seven galaxies, observed at the BTA.
f(R) gravity theories in the Palatini formalism has been recently used as an alternative way to explain the observed late-time cosmic acceleration with no need of invoking either dark energy or extra spatial dimension. However, its applications have shown that some subtleties of these theories need a more profound examination. Here we are interested in the conformal aspects of the Palatini approach in extended theories of gravity. As is well known, extremization of the gravitational action a la Palatini, naturally "selects" a new metric h related to the metric g of the subjacent manifold by a conformal transformation. The related conformal function is given by the derivative of f(R). In this work we examine the conformal symmetries of the flat (k=0) FLRW spacetime and find that its Conformal Killing Vectors are directly linked to the new metric h and also that each vector yields a different conformal function.
We present mid infrared (MIR) spectra of the Seyfert 2 (Sy 2) galaxy NGC 1808, obtained with the Gemini's Thermal-Region Camera Spectrograph (T-ReCS) at a spatial resolution of 26 pc. The high spatial resolution allowed us to detect bright polycyclic aromatic hydrocarbons (PAHs) emissions at 8.6micron and 11.3micron in the galaxy centre (26 pc) up to a radius of 70 pc from the nucleus. The spectra also present [Ne ii]12.8micron ionic lines, and H2 S(2)12.27micron molecular gas line. We found that the PAHs profiles are similar to Peeters's A class, with the line peak shifted towards the blue. The differences in the PAH line profiles also suggests that the molecules in the region located 26 pc NE of the nucleus are more in the neutral than in the neutral state, while at 26 pc SW of the nucleus, the molecules are mainly in ionised state. After removal of the underlying galaxy contribution, the nuclear spectrum can be represented by a Nenkova's clumpy torus model, indicating that the nucleus of NGC 1808 hosts a dusty toroidal structure with an angular cloud distribution of sigma = 70degree, observer's view angle i = 90degree, and an outer radius of R0 = 0.55 pc. The derived column density along the line of sight is NH = 1.5 x 10^24 cm-2, which is sufficient to block the hard radiation from the active nucleus, and would explain the presence of PAH molecules near to the NGC 1808's active nucleus.
Lundmark established observational evidence that the Universe is expanding. Lema\^itre established theoretical evidence. Hubble established observational proof.
We propose a new framework for explaining the proximity of the baryon and dark matter relic densities \Omega_{DM} \approx 5\Omega_B. The scenario assumes that the number density of the observed dark matter states is generated due to decays from a second hidden sector which simultaneously generates the baryon asymmetry. In contrast to asymmetric dark matter models, the dark matter can be a real scalar or Majorana fermion and thus presents distinct phenomenology. We discuss aspects of model building and general constraints in this framework. We present a simple supersymmetric implementation of this mechanism and show that it can be used to obtain the correct dark matter relic density for a bino LSP.
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