We study an early dark energy (EDE) model as a K-essence scalar field in the framework of FLRW universe using an effective parametrization of the state equation as a function of the redshift $z$ with the tracker condition during radiation domination, but also demanding an accelerated expansion of the universe at late times emulating cosmological constant. We found all the dynamical variables of the EDE system. We use the luminosity distances of the SNIA to get the best estimations for the free parameters of the model and also, we constrain the model using primordial abundances of light nuclei in BBN theory. We summarize the necessary conditions to achieve BBN predictions and the accelerated expansion of the universe at late times.
We present an intermediate inflationary stage in a Jordan-Brans-Dicke theory. In this scenario we analyze the quantum fluctuations corresponding to adiabatic and isocurvature modes. The model is compared to that described by using the intermediate model in Einstein General Relativity theory. We assess the status of this model in light of the WMAP7 data.
We present measurements of the galaxy cluster X-ray Luminosity Function (XLF) from the Wide Angle ROSAT Pointed Survey (WARPS) and quantify its evolution. WARPS is a serendipitous survey of the central region of ROSAT pointed observations and was carried out in two phases (WARPS-I and WARPS-II). The results here are based on a final sample of 124 clusters, complete above a flux limit of 6.5 10E-15 erg/s/cm2, with members out to redshift z ~ 1.05, and a sky coverage of 70.9 deg2. We find significant evidence for negative evolution of the XLF, which complements the majority of X-ray cluster surveys. To quantify the suggested evolution, we perform a maximum likelihood analysis and conclude that the evolution is driven by a decreasing number density of high luminosity clusters with redshift, while the bulk of the cluster population remains nearly unchanged out to redshift z ~ 1.1, as expected in a low density Universe. The results are found to be insensitive to a variety of sources of systematic uncertainty that affect the measurement of the XLF and determination of the survey selection function. We perform a Bayesian analysis of the XLF to fully account for uncertainties in the local XLF on the measured evolution, and find that the detected evolution remains significant at the 95% level. We observe a significant excess of clusters in the WARPS at 0.1 < z < 0.3 and LX ~ 2 10E42 erg/s compared with the reference low-redshift XLF, or our Bayesian fit to the WARPS data. We find that the excess cannot be explained by sample variance, or Eddington bias, and is unlikely to be due to problems with the survey selection function.
In order to understand the nature of the sources producing the recently uncovered CIB fluctuations, we study cross-correlations between the fluctuations in the source-subtracted Cosmic Infrared Background (CIB) from Spitzer/IRAC data and the unresolved Cosmic X-ray Background (CXB) from deep Chandra observations. Our study uses data from the EGS/AEGIS field, where both datasets cover an ~8'x45' region of the sky. Quantitatively, our measurement is the cross-power spectrum between the IR and X-ray data which we detect to be statistically significant and positive at angular scales >20" where the source-subtracted CIB fluctuations in the Spitzer data are dominated by the clustering component. The cross-power signal between the IRAC maps at 3.6 um and 4.5 um and the Chandra [0.5-2] keV data has been detected with the overall significance of ~3.5 sigma and ~5 sigma respectively. At the same time we find no evidence of significant cross-correlations at the harder Chandra bands. The cross-correlation signal is produced by individual IR sources with 3.6 um and 4.5 um magnitudes m_AB>25-26 and [0.5-2] keV X-ray fluxes <<7x10^-17 cgs. We determine that at least 15-25% of the large scale power of CIB fluctuations is correlated with the spatial power spectrum of the X-ray fluctuations. If this correlation is attributed to emission from accretion processes at both IR and X-ray wavelengths, this implies a much higher fraction of the accreting black holes than among the known populations. We discuss the various possible low- and high-z suspects for the discovered cross-power and show that neither local foregrounds, nor the known remaining normal galaxies and active galactic nuclei (AGN) can reproduce the measurements. These observational results are an important new constraint on theoretical modeling of the near-IR CIB fluctuations.
In this paper, we propose a new unified dark fluid (UDF) model with equation of state (EoS) $w(a)=-\alpha/(\beta a^{-n}+1)$, which includes the generalized Chaplygin gas model (gGg) as its special case, where $\alpha$, $\beta$ and $n$ are three positive numbers. It is clear that this model reduces to the gCg model with EoS $w(a)=-B_s/(B_s+(1-B_s)a^{-3(1+\alpha)})$, when $\alpha=1$, $\beta=(1-B_s)/B_s$ and $n=3(1+\alpha)$. By combination the cold dark matter and the cosmological constant, one can coin a EoS of unified dark fluid in the form of $w(a)=-1/(1+(1-\Omega_{\Lambda})a^{-3}/\Omega_{\Lambda})$. With this observations, our proposed EoS provides a possible deviation from $\Lambda$CDM model when the model parameters $\alpha$ and $n$ deviate from 1 and 3 respectively. By using the currently available cosmic observations from type Ia supernovae (SN Ia) Union2.1, baryon acoustic oscillation (BAO) and cosmic microwave background radiation (CMB), we test the viability of this model and detect the possible devotion from the $\Lambda$CDM model. The results show that the new UDF model fits the cosmic observation as well as that of the $\Lambda$CDM model and no deviation is found from the $\Lambda$CDM model in $3\sigma$ confidence level. However, our new UDF model can give a non-zero sound speed, as a contrast, which is zero for the $\Lambda$CDM model. We expect the large structure formation information can distinct the new UDF model from the $\Lambda$CDM model.
Evolution of galaxies is one of the most actual topics in astrophysics. Among the most important factors determining the evolution are two galactic components which are difficult or even impossible to detect optically: the gaseous disks and the dark matter halo. We use deep Hubble Space Telescope images to construct a two-component (bulge + disk) model for stellar matter distribution of galaxies. Properties of the galactic components are derived using a three-dimensional galaxy modeling software, which also estimates disk thickness and inclination angle. We add a gas disk and a dark matter halo and use hydrodynamical equations to calculate gas rotation and dispersion profiles in the resultant gravitational potential. We compare the kinematic profiles with the Team Keck Redshift Survey observations. In this pilot study, two galaxies are analyzed deriving parameters for their stellar components; both galaxies are found to be disk-dominated. Using the kinematical model, the gas mass and stellar mass ratio in the disk are estimated.
Luminous and Ultra-Luminous Infrared Galaxies (U/LIRGs) do also radiate copious amounts of radio emission, both thermal (free-free) and non-thermal (mainly synchrotron). This is very handy since, unlike optical and infra-red observations, radio is not obscured by the ubiquitous dust present in U/LIRGs, which allows a direct view of the ongoing activity in the hearts of those prolific star-forming galaxies. Here, I first justify the need for this high-angular resolution radio studies of local U/LIRGs, discuss the energy budget and the magnetic field, as well as IC and synchrotron losses in U/LIRGs, and present some selected results obtained by our team on high-angular resolution radio continuum studies of U/LIRGs. Among other results, I show the impressive discovery of an extremely prolific supernova factory in the central ~150 pc of the galaxy Arp 299-A (D=45 Mpc) and the monitoring of a large number of very compact radio sources in it, the detection and precise location of the long-sought AGN in Arp 299-A. A movie showing the appearance and disappearance of new SNe in Arp 299A can be found at this http URL All those results demonstrate that very-high angular resolution studies of nearby U/LIRGs are of high relevance for the comprehension of both local and high-z starbursting galaxies.
This talk is an attempt to combine recent insights into the nature of the nuclear star clusters in galaxies of various morphologies into a coherent (albeit simplistic) picture for their formation, growth, and eventual destruction.
We show how the Zel'dovich approximation and the second order displacement field of Lagrangian perturbation theory can be obtained from a general relativistic gradient expansion in \Lambda{}CDM cosmology. The displacement field arises as a result of a second order non-local coordinate transformation which brings the synchronous/comoving metric into a Newtonian form. We find that, with a small modification, the Zel'dovich approximation holds even on scales comparable to the horizon. The corresponding density perturbation is not related to the Newtonian potential via the usual Poisson equation but via a modified Helmholtz equation. This is a consequence of causality not present in the Newtonian theory. The second order displacement field receives relativistic corrections that are subdominant on short scales but are comparable to the second order Newtonian result on scales approaching the horizon. The corrections are easy to include when setting up initial conditions in large N-body simulations.
We derive a constraint on patchy screening of the cosmic microwave background from inhomogeneous reionization, using off-diagonal TB and TT correlations in WMAP-7 temperature/polarization data. We interpret this as a constraint on the rms optical-depth fluctuation \Delta\tau\ as a function of a coherence multipole Lc. We relate these parameters to a comoving coherence scale, of bubble size Rc, in a phenomenological model where reionization is instantaneous but occurs on a crinkly surface, and also to the bubble size in a model of "Swiss cheese" reionization where bubbles of fixed size are spread over some range of redshifts. The current WMAP data are still too weak, by several orders of magnitude, to constrain reasonable models, but forthcoming Planck and future EPIC data should begin to approach interesting regimes of parameter space. We also present constraints on the parameter space imposed by the recent results from the EDGES experiment.
Significative developments on the primordial black hole quantization seem to indicate that the structure formation in the universe behaves under a unified scheme. This leads to the existence of scaling relations, whose validity could offer insights on the process of unification between quantum mechanics and gravity. Encouraging results have been obtained in order to recover the observed magnitudes of angular momenta, peculiar radii and virialized times for large and small structures. In the cosmological regime, we show that it seems possible to infer the magnitude of the cosmological constant in terms of the matter density, in agreement with the observed values.
We address the issue of constraining the class of $f(\mathcal{R})$ able to reproduce the observed cosmological acceleration, by using the so called cosmography of the universe. We consider a model independent procedure to build up a $f(z)$-series in terms of the measurable cosmographic coefficients; we therefore derive cosmological late time bounds on $f(z)$ and its derivatives up to the fourth order, by fitting the luminosity distance directly in terms of such coefficients. We perform a Monte Carlo analysis, by using three different statistical sets of cosmographic coefficients, in which the only assumptions are the validity of the cosmological principle and that the class of $f(\mathcal{R})$ reduces to $\Lambda$CDM when $z\ll1$. We use the updated union 2.1 for supernovae Ia, the constrain on the $H_0$ value imposed by the measurements of the Hubble space telescope and the Hubble dataset, with measures of $H$ at different $z$. We find a statistical good agreement of the $f(\mathcal{R})$ class under exam, with the cosmological data; we thus propose a candidate of $f(\mathcal{R})$, which is able to pass our cosmological test, reproducing the late time acceleration in agreement with observations.
For simulations that deal only with dark matter or stellar systems, the
conventional N-body technique is fast, memory efficient, and relatively simple
to implement. However when including the effects of gas physics, mesh codes are
at a distinct disadvantage compared to SPH. Whilst implementing the N-body
approach into SPH codes is fairly trivial, the particle-mesh technique used in
mesh codes to couple collisionless stars and dark matter to the gas on the
mesh, has a series of significant scientific and technical limitations. These
include spurious entropy generation resulting from discreteness effects, poor
load balancing and increased communication overhead which spoil the excellent
scaling in massively parallel grid codes.
We propose the use of the collisionless Boltzmann moment equations as a means
to model collisionless material as a fluid on the mesh, implementing it into
the massively parallel FLASH AMR code. This approach, which we term
"collisionless stellar hydrodynamics" enables us to do away with the
particle-mesh approach. Since the parallelisation scheme is identical to that
used for the hydrodynamics, it preserves the excellent scaling of the FLASH
code already demonstrated on peta-flop machines.
We find the classic hydrodynamic equations and Boltzmann moment equations can
be reconciled under specific conditions, allowing us to generate analytic
solutions for collisionless systems using conventional test problems. We
confirm the validity of our approach using a suite of demanding test problems,
including the use of a modified Sod shock test. We conclude by demonstrating
the ability of our code to model complex phenomena by simulating the evolution
of a spiral galaxy whose properties agree with those predicted by swing
amplification theory. (Abridged)
The 2012 International Pulsar Timing Array (IPTA) Mock Data Challenge (MDC) is designed to test current Gravitational Wave (GW) detection algorithms. Here we will briefly outline two detection algorithms for a stochastic background of gravitational waves, namely, a first-order likelihood method and an optimal statistic method and present our results from the closed MDC data sets.
We consider a model of inflation which has recently been proposed in the literature and where inflation is induced by corrections to the energy density coming from the non-commutativity of spacetime. We show that the very rapid inflationary expansion typical of this model is responsible for a burst of particle production which ends inflation and leads to a radiation-dominated phase. We analytically estimate the energy density of these particles and we confront the results with more precise numerical calculations. We estimate the number of inflationary e-folds before the back-reaction of the radiation energy density overcomes the non-commutative effects and terminate inflation naturally.
The ghost free massive gravity modified Friedmann equations at cosmic scale and provided an explanation of cosmic acceleration without dark energy. We analyzed the cosmological solutions of the massive gravity in detail and confronted the cosmological model with current observational data. We found that the model parameters $\alpha_3$ and $\alpha_4$ which are the coefficients of the third and fourth order nonlinear interactions cannot be constrained by current data at the background level. The mass of graviton is found to be the order of current Hubble constant if $\alpha_3=\alpha_4=0$, and the mass of graviton can be as small as possible in the most general case.
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There is a well known correlation between the mass and metallicity of star-forming galaxies. Because mass is correlated with luminosity, this relation is often exploited, when spectroscopy is not available, to estimate galaxy metallicities based on single band photometry. However, we show that galaxy color is typically more effective than luminosity as a predictor of metallicity. This is a consequence of the correlation between color and the galaxy mass-to-light ratio and the recently discovered correlation between star formation rate (SFR) and residuals from the mass-metallicity relation. Using Sloan Digital Sky Survey spectroscopy of 148,021 nearby galaxies, we derive "LZC relations," empirical relations between metallicity (in nine common strong line diagnostics), luminosity, and color (in three filter pairs). We show that these relations allow photometric metallicity estimates, based on luminosity and a single optical color, that are 40% more precise than those made based on luminosity alone; galaxy metallicity can be estimated to within 0.06 - 0.1 dex of the spectroscopically-derived value depending on the metallicity diagnostic used. Including color information in metallicity estimates also reduces systematic biases for populations skewed toward high or low SFR environments, as we illustrate using the host galaxy of the supernova SN 2010ay. This new tool will lend more statistical power to studies of galaxy populations, such as supernova and gamma-ray burst (GRB) host environments, in ongoing and future wide field imaging surveys.
We present a new approach to study galaxy evolution in a cosmological context. We combine cosmological merger trees and semi-analytic models of galaxy formation to provide the initial conditions for multi-merger hydrodynamic simulations. In this way we exploit the advantages of merger simulations (high resolution and inclusion of the gas physics) and semi-analytic models (cosmological background and low computational cost), and integrate them to create a novel tool. This approach allows us to study the evolution of various galaxy properties, including the treatment of the hot gaseous halo from which gas cools and accretes onto the central disc, which has been neglected in many previous studies. This method shows several advantages over other methods. As only the particles in the regions of interest are included, the run time is much shorter than in traditional cosmological simulations, leading to greater computational efficiency. Using cosmological simulations, we show that multiple mergers are expected to be more common than sequences of isolated mergers, and therefore studies of galaxy mergers should take this into account. In this pilot study, we present our method and illustrate the results of simulating ten Milky Way-like galaxies since z=1. We find good agreement with observations for the total stellar masses, star formation rates, cold gas fractions and disc scale length parameters. We expect that this novel numerical approach will be very useful for pursuing a number of questions pertaining to the transformation of galaxy internal structure through cosmic time.
We present the Combined Array for Research in Millimeter Astronomy (CARMA) ATLAS3D molecular gas imaging survey, a systematic study of the distribution and kinematics of molecular gas in CO-rich early-type galaxies. Our full sample of 40 galaxies (30 newly mapped and 10 taken from the literature) is complete to a 12CO(1-0) integrated flux of 18.5 Jy km/s, and it represents the largest, best-studied sample of its type to date. A comparison of the CO distribution of each galaxy to the g-r color image (representing dust) shows that the molecular gas and dust distributions are in good agreement and trace the same underlying interstellar medium. The galaxies exhibit a variety of CO morphologies, including discs (50%), rings (15%), bars+rings (10%), spiral arms (5%), and mildly (12.5%) and strongly (7.5%) disrupted morphologies. There appear to be weak trends between galaxy mass and CO morphology, whereby the most massive galaxies in the sample tend to have molecular gas in a disc morphology. We derive a lower limit to the total accreted molecular gas mass across the sample of 2.48x10^10 Msuns, or approximately 8.3x10^8 Msuns per minor merger within the sample, consistent with minor merger stellar mass ratios.
NGC 604 is the second most massive H II region in the Local Group, thus an important laboratory for massive star formation. Using a combination of observational and analytical tools that include Spitzer spectroscopy, Herschel photometry, Chandra imaging, and Bayesian Spectral Energy Distribution fitting, we investigate the physical conditions in NGC 604, and quantify the amount of massive star formation currently taking place. We derive an average age of 4 +/- 1 Myr and a total stellar mass of 1.6 (+1.6)(-1.0) x 10^5 M_sun for the entire region, in agreement with previous optical studies. Across the region we find an effect of the X-ray field on both the abundance of aromatic molecules and the [Si II] emission. Within NGC 604 we identify several individual bright infrared sources with diameters of about 15 pc and luminosity weighted masses between 10^3 M_sun and 10^4 M_sun. Their spectral properties indicate that some of these sources are embedded clusters in process of formation, which together account for ~8% of the total stellar mass in the NGC 604 system. The variations of the radiation field strength across NGC 604 are consistent with a sequential star formation scenario, with at least two bursts in the last few million years. Our results indicate that massive star formation in NGC 604 is still ongoing, likely triggered by the earlier bursts.
Tachyonic scalar field-driven late universe with dust matter content is
considered. The cosmic expansion is modeled with power-law and phantom
power-law expansion at late time ($z < 2$ for power-law and $z<0.45$ for
phantom power-law). WMAP7 and its combined data are used to constraint the
model.
For quintessence and tachyonic field, forms of the equation of state do not
depends on type of the scalar field but depend only on scale factor function.
However the forms of potential and the field solution are different in
quintessence and tachyonic cases. Power-law cosmology model (driven with either
quintessence or tachyonic field) predicts equation of state unmatched to the
observational value, hence the model is excluded for quintessence and tachyonic
field. The phantom power-law cosmology model predicts values of equation of
state which agree with observational data (true for both quintessence and
tachyonic cases), i.e. $w_{\phi, 0} = -1.49^{+11.64}_{-4.08}$ (WMAP7+BAO+$H_0$)
and $ w_{\phi, 0} = -1.51^{+3.89}_{-6.72} $ (WMAP7). The phantom-power law
exponent $\b$ must be less than -6, so that the $-2 < w_{\phi, 0} < -1$. The
phantom power-law tachyonic potential is reconstructed. The dimensionless
potential slope variable $\Gamma$ at present is about 1.5. The potential
reduced to $V= V_0\phi^{-2}$ in the limit $\Omega_{\m, 0} \rightarrow 0$.
We make the first detailed MCMC likelihood study of cosmological constraints that are expected from some of the largest, ongoing and proposed, cluster surveys in different wave-bands and compare the estimates to the prevalent Fisher matrix forecasts. Mock catalogs of cluster counts expected from the surveys -- eROSITA, WFXT, RCS2, DES and Planck, along with a mock dataset of follow-up mass calibrations are analyzed for this purpose. A fair agreement between MCMC and Fisher results is found only in the case of minimal models. However, for many cases, the marginalized constraints obtained from Fisher and MCMC methods can differ by factors of 30-100%. The discrepancy can be alarmingly large for a time dependent dark energy equation of state, $w(a)$; the Fisher methods are seen to under-estimate the constraints by as much as a factor of 4--5. Typically, Fisher estimates become more and more inappropriate as we move away from $\Lambda$CDM, to a constant-$w$ dark energy to varying-$w$ dark energy cosmologies. Fisher analysis, also, predicts incorrect parameter degeneracies. From the point of mass-calibration uncertainties, a high value of unknown scatter about the mean mass-observable relation, and its redshift dependence, is seen to have large degeneracies with the cosmological parameters $\sigma_8$ and $w(a)$ and can degrade the cosmological constraints considerably. We find that the addition of mass-calibrated cluster datasets can improve dark energy and $\sigma_8$ constraints by factors of 2--3 from what can be obtained compared to CMB+SNe+BAO only. Since, details of future cluster surveys are still being planned, we emphasize that optimal survey design must be done using MCMC analysis rather than Fisher forecasting. (abridged)
It was recently suggested that, compared to its stellar mass (M*), the central stellar velocity dispersion (sigma*) of a galaxy might be a better indicator for its host dark matter halo mass. Here we test this hypothesis by estimating the dark matter halo mass for central alaxies in groups as function of M* and sigma*. For this we have estimated the redshift-space cross-correlation function (CCF) between the central galaxies at given M* and sigma* and a reference galaxy sample, from which we determine both the projected CCF, w_p(r_p), and the velocity dispersion profile (VDP) of satellites around the centrals. A halo mass is then obtained from the average velocity dispersion within the virial radius. At fixed M*, we find very weak or no correlation between halo mass and sigma*. In contrast, strong mass dependence is clearly seen even when sigma* is limited to a narrow range. Our results thus firmly demonstrate that the stellar mass of central galaxies is still a good (if not the best) indicator for dark matter halo mass, better than the stellar velocity dispersion. The dependence of galaxy clustering on sigma* fixed M*, as recently discovered by Wake et al. (2012), may be attributed to satellite galaxies, for which the tidal stripping occurring within halos has stronger effect on stellar mass than on central stellar velocity dispersion.
Arguments are given that at least a fraction of molecular clouds may live much longer time that it is usually assumed, without the transition into diffuse atomic gas (HI). We propose that star formation in these clouds may be strongly delayed and weakened by the magnetic field.
Abell 1995 is a puzzling galaxy cluster hosting a powerful radio halo, but it has not yet been recognized as a obvious cluster merger, as usually expected for clusters with diffuse radio emission. We aim at an exhaustive analysis of the internal structure of Abell 1995 to verify if this cluster is really dynamically relaxed, as reported in previous studies. We base our analysis on new and archival spectroscopic and photometric data for 126 galaxies in the field of Abell 1995. The study of the hot intracluster medium was performed on X-ray archival data. Based on 87 fiducial cluster members, we have computed the average cluster redshift <z>=0.322 and the global radial velocity dispersion ~1300 km/s. We detect two main optical subclusters separated by 1.5 arcmin that cause the known NE-SW elongation of the galaxy distribution and a significant velocity gradient in the same direction. As for the X-ray analysis, we confirm that the intracluster medium is mildly elongated, but we also detect three X-ray peaks. Two X-ray peaks are offset with respect to the two galaxy peaks and lie between them, thus suggesting a bimodal merger caught in a phase of post core-core passage. The third X-ray peak lies between the NE galaxy peak and a third, minor galaxy peak suggesting a more complex merger. Simple analytical arguments suggest a merging scenario for Abell 1995, where two main subsystems are seen just after the collision with an intermediate projection angle. The high mass of Abell 1995 and the evidence of merging suggest it is not atypical among clusters with known radio halos. Interestingly, our findings reinforce the previous evidence for the peculiar dichotomy between the dark matter and galaxy distributions observed in this cluster.
The cosmic microwave background (CMB) provides us with our most direct observational window to the early universe. Observations of the temperature and polarization anisotropies in the CMB have played a critical role in defining the now-standard cosmological model. In this contribution we review some of the basics of CMB science, highlighting the role of observations made with ground-based and balloon-borne Antarctic telescopes. Most of the ingredients of the standard cosmological model are poorly understood in terms of fundamental physics. We discuss how current and future CMB observations can address some of these issues, focusing on two directly relevant for Antarctic programmes: searching for gravitational waves from inflation via B-mode polarization, and mapping dark matter through CMB lensing.
In this work we present for the first time an analytic framework for
calculating the individual and joint distributions of the n-th most massive or
n-th highest redshift galaxy cluster for a given survey characteristic allowing
to formulate LCDM exclusion criteria. We show that the cumulative distribution
functions steepen with increasing order, giving them a higher constraining
power with respect to the extreme value statistics. Additionally, we find that
the order statistics in mass (being dominated by clusters at lower redshifts)
is sensitive to the matter density and the normalisation of the matter
fluctuations, whereas the order statistics in redshift is particularly
sensitive to the geometric evolution of the Universe. For a fixed cosmology,
both order statistics are efficient probes of the functional shape of the mass
function at the high mass end. To allow a quick assessment of both order
statistics, we provide fits as a function of the survey area that allow
percentile estimation with an accuracy better than two per cent. Furthermore,
we discuss the joint distributions in the two-dimensional case for different
combinations of order.
Having introduced the theory, we apply the order statistical analysis to the
SPT massive cluster sample and MCXC catalogue and find that the ten most
massive clusters in the sample are consistent with LCDM and the Tinker mass
function. In turn, by assuming the LCDM reference cosmology, order statistics
can also be utilised for consistency checks of the completeness of the observed
sample and of the modelling of the survey selection function. [abridged]
Due to a large mass-to-light ratio and low astrophysical backgrounds, dwarf spheroidal galaxies (dSphs) are considered to be one of the most promising targets for dark matter searches via gamma rays. The Fermi LAT Collaboration has recently reported robust constraints on the dark matter annihilation cross section from a combined analysis of 10 dSphs. These constraints have been applied to experimentally valid, super-symmetric particle models derived from a phenomenological scan of the Minimal Supersymmetric Standard Model (the pMSSM). Additionally, the LAT Collaboration has searched for spatially extended, hard-spectrum gamma-ray sources lacking counterparts in other wavelengths, since they may be associated with dark matter substructures predicted from simulations.
This is a brief introduction to the closing discussion of the IAU Symposium 295, "The Intriguing Life of Massive Galaxies", that was held in Beijing from August 27 through 31, 2012. The discussion was focused on only four hot items, namely 1) the redshift evolution of the size of passively evolving galaxies, 2) the evolution with redshift of the specific star formation rate, 3) quenching of star formation in galaxies and dry merging, and 4) the IMF.
We present a complete update of the analysis of electron neutrino and antineutrino disappearance experiments in terms of neutrino oscillations in the framework of 3+1 neutrino mixing, taking into account the Gallium anomaly, the reactor anomaly, solar neutrino data and nu_e-C scattering data. We discuss the implications of a recent 71Ga(3He,3H)71Ge measurement which give information on the neutrino cross section in Gallium experiments. We discuss the solar bound on active-sterile mixing and present our numerical results. We discuss the connection between the results of the fit of neutrino oscillation data and the heavy neutrino mass effects in beta-decay experiments (considering new Mainz data) and neutrinoless double-beta decay experiments (considering the recent EXO results).
We analyze residual spectra of 3 K blackbody radiation (CMB) using non-extensive thermostatistics with a parameter q-1. The limits of |q-1|<1.2x10^{-5} and the temperature fluctuation |delta T|<(1.6-4.3)x10^{-5} are smaller than those by Tsallis et al. Moreover, analyzing the monopole spectrum by a formula including the chemical potential mu, we obtain the limits |q-1|<2.3x10^{-5} and |mu|<1.6x10^{-4}. |q-1| is comparable with the Sunyaev-Zeldovich effect y.
Results from a large, multi-J CO, {13}CO, and HCN line survey of Luminous Infrared Galaxies (L_{IR}>=10^{10} L_{\odot}) in the local Universe (z<=0.1), complemented by CO J=4--3 up to J=13--12 observations from the Herschel Space Observatory (HSO), paints a new picture for the average conditions of the molecular gas of the most luminous of these galaxies with turbulence and/or large cosmic ray (CR) energy densities U_{CR} rather than far-UV/optical photons from star-forming sites as the dominant heating sources. Especially in ULIRGs (L_{IR}>10^{12} L_{\odot}) the Photon Dominated Regions (PDRs) can encompass at most \sim few% of their molecular gas mass while the large U_{CR} and the strong turbulence in these merger/starbursts, can volumetrically heat much of their molecular gas to T_{kin}\sim(100-200)K, unhindered by the high dust extinctions. Moreover the strong supersonic turbulence in ULIRGs relocates much of their molecular gas at much higher average densities than in isolated spirals. This renders low-J CO lines incapable of constraining the properties of the bulk of the molecular gas in ULIRGs, with substantial and systematic underestimates of its mass possible when only such lines are used. A comparative study of multi-J HCN lines and CO SLEDs from J=1--0 up to J=13--12 of NGC 6240 and Arp 193 offers a clear example of two merger/starbursts whose similar low-J CO SLEDs, and L_{IR}/L_{CO,1-0}, L_{HCN, 1-0}/L_{CO,1-0} ratios, yield no indications about their strongly diverging CO SLEDs beyond J=4--3, and ultimately the different physical conditions in their molecular ISM. The much larger sensitivity of ALMA and its excellent site in the Atacama desert now allows the observations necessary to ....
We describe an analysis of the First International Pulsar Timing Array Data Challenge. We employ a robust, unbiased Bayesian framework developed by van Haasteren to study the three Open and Closed datasets, testing various models for each dataset and using MultiNest to recover the evidence for the purposes of Bayesian model-selection. The parameter constraints of the favoured model are confirmed using an adaptive MCMC technique. Our results for Closed1 favoured a gravitational-wave background with strain amplitude at f=1 yr-1, A, of (1.1 +/- 0.1) x 10^{-14}, power spectral-index gamma=4.30 +/- 0.15 and no evidence for red-timing noise or single-sources. The evidence for Closed2 favours a gravitational-wave background with A=(6.1 +/- 0.3) x 10^{-14}, gamma=4.34 +/- 0.09 with no red-timing noise or single-sources. Finally, the evidence for Closed3 favours the presence of red-timing noise and a gravitational-wave background, with no single-sources. The properties of the background were A=(5 +/- 1) x 10^{-15} and gamma=4.23 +/- 0.35, while the properties of the red-noise were N_{red}=(12 +/- 4) ns and gamma_{red}=1.5 +/- 0.3. In all cases the redness of the recovered background is consistent with a source-population of inspiraling supermassive black-hole binaries. We also investigate the effect that down-sampling of the datasets has on parameter constraints and run-time. Finally we provide a proof-of-principle study of the ability of the Bayesian framework used in this paper to reconstruct the angular correlation of gravitational-wave background induced timing-residuals, comparing this to the Hellings and Downs curve.
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Unresolved near-infrared background anisotropies are expected to have contributions from the earliest galaxies during reionization and faint, dwarf galaxies at intermediate redshifts. Previous measurements were unable to conclusively pinpoint the dominant origin because they did not sample spatial scales that were sufficiently large to distinguish between these two possibilities. Here we report a measurement of the anisotropy power spectrum from sub-arcminute to one degree angular scales and find the clustering amplitude to be larger than the model predictions involving the two existing explanations. As the shot-noise level of the power spectrum is consistent with that expected from faint galaxies, a new source population on the sky is not necessary to explain the observations. A physical mechanism that increases the clustering amplitude, however, is needed. Motivated by recent results related to the extended stellar light profile in dark matter halos, we consider the possibility that the fluctuations originate from diffuse intrahalo stars of all galaxies. We find that the measured power spectrum can be explained by an intrahalo light fraction of 0.07 to 0.2 % relative to the total luminosity in dark matter halos of masses log(M/M_Sun) ~ 9 to 12 at redshifts of ~ 1 to 4.
We examine the cosmic evolution of a stellar initial mass function (IMF) in galaxies that varies with the Jeans mass in the interstellar medium, paying particular attention to the K-band stellar mass to light ratio (M/L_K) of present-epoch massive galaxies. We calculate the typical Jeans mass using high-resolution hydrodynamic simulations coupled with a fully radiative model for the ISM, which yields a parameterisation of the IMF characteristic mass as a function of galaxy star formation rate (SFR). We then calculate the star formation histories of galaxies utilising an equilibrium galaxy growth model coupled with constraints on the star formation histories set by abundance matching models. Our main result is that at early times, energetic coupling between dust and gas drive warm conditions in the ISM, and hence bottom-light/top-heavy IMFs associated with large ISM Jeans masses for massive star-forming galaxies. At late times, lower cosmic ray fluxes allow for cooler ISM temperatures in massive galaxies, and hence bottom-heavy IMFs. Because the massive stars (M >~ 1 Msun) formed during the top-heavy phases at early times have all disappeared by today, the resultant M/L_K ratios in massive galaxies at the present epoch is increased relative to the non-varying IMF case. A key result is that a given galaxy may go through both top-heavy and bottom-heavy phases during its lifetime. Quantitatively, the variations in M/L_K with galaxy mass are slightly smaller than what is observed. Nonetheless, these results are encouraging because they can, at least qualitatively, reconcile a bottom-light IMF that would help explain a number of observations of massive high-z galaxies with the bottom-heavy IMF inferred for the descendants of those galaxies today.
We present a new determination of the distance to M101, host of the type Ia SN 2011fe, based on the tip of the red giant branch method (TRGB). Our determination is based on {\it Hubble Space Telescope} archival $F555W$ and $F814W$ images of nine fields within the galaxy. Color-magnitude diagrams of arm-free regions in all fields show a prominent red giant branch (RGB). We measure the $I$-band magnitudes of the TRGB, obtaining a mean value of $I_{\rm TRGB}=25.28\pm0.01$ (where the error is a standard error), using an edge-detection method. We derive a weighted mean value of distance modulus $(m-M)_0=29.30\pm0.01 ({\rm random})\pm0.12 ({\rm systematic})$, corresponding to a linear distance of $7.24\pm0.03\pm0.40 $ Mpc. While previous estimates for M101 show a large range (TRGB distances of $(m-M)_0=29.05$ to 29.42 and Cepheid distances of $(m-M)_0=29.04$ to 29.71), our measurements of the TRGB distances for nine fields show a small dispersion of only 0.02. We combine our distance estimate and photometry in the literature to derive absolute peak magnitudes in optical and near-infrared bands of SN 2011fe. Absolute maximum magnitudes of SN 2011fe are $\sim0.2$ mag brighter in the optical band and much more in the NIR than the current calibrations of SNe Ia in the literature. From the optical maximum magnitudes of SN 2011fe we obtain a value of the Hubble constant, $H_0=65.0\pm0.5({\rm random})\pm5.7({\rm systematic})$ \kmsMpc, slightly smaller than other recent determinations of $H_0$.
We combine our Hubble Space Telescope measurement of the proper motion of the Leo I dwarf spheroidal galaxy (presented in a companion paper) with the highest resolution numerical simulations of Galaxy-size dark matter halos in existence to constrain the mass of the Milky Way's dark matter halo (M_MW). Despite Leo I's large Galacto-centric space velocity (200 km/s) and distance (261 kpc), we show that it is extremely unlikely to be unbound if Galactic satellites are associated with dark matter substructure, as 99.9% of subhalos in the simulations are bound to their host. The observed position and velocity of Leo I strongly disfavor a low mass Milky Way: if we assume that Leo I is the least bound of the Milky Way's classical satellites, then we find that M_MW > 10^{12} M_sun at 95% confidence for a variety of Bayesian priors on M_MW. In lower mass halos, it is vanishingly rare to find subhalos at 261 kpc moving as fast as Leo I. Should an additional classical satellite be found to be less bound than Leo I, this lower limit on M_MW would increase by 30%. Imposing a mass weighted LCDM prior, we find a median Milky Way virial mass of M_MW=1.6 x 10^{12} M_sun, with a 90% confidence interval of [1.0-2.4] x 10^{12} M_sun. We also confirm a strong correlation between subhalo infall time and orbital energy in the simulations and show that proper motions can aid significantly in interpreting the infall times and orbital histories of satellites.
In this work we investigate the effect on weak-lensing shear and convergence measurements due to distortions from the Lorentz boost induced by our Galaxy's motion. While no ellipticity is induced in an image from the Lorentz boost to first order in beta = v/c, the image is magnified. This affects the inferred convergence at a 10 per cent level and is most notable for low multipoles in the convergence power spectrum, C {\kappa}{\kappa}, and for surveys with large sky coverage like LSST. Experiments which image only small fractions of the sky and convergence power spectrum determinations at l > 5 can safely neglect the boost effect to first order in beta.
UV observations in the local universe have uncovered a population of early-type galaxies with UV flux consistent with low-level recent or ongoing star formation. We present resolved UV-optical photometry of a sample of 19 SDSS early-type galaxies at z~0.1 drawn from the sample originally selected by Salim & Rich (2010) to lie in the bluer part of the green valley in the UV-optical color-magnitude diagram as measured by GALEX. Utilizing high-resolution HST far-UV imaging provides unique insight into the distribution of UV light in these galaxies, which we call "extended star-forming early-type galaxies" (ESF-ETGs) because of extended UV emission that is indicative of recent star formation. The UV-optical color profiles of all ESF-ETGs show red centers and blue outer parts. Their outer colors require the existence of a significant underlying population of older stars in the UV-bright regions. Analysis of stacked SDSS spectra reveals weak LINER-like emission in their centers. Using a cross-matched SDSS DR7/GALEX GR6 catalog, we search for other green valley galaxies with similar properties to these ESF-ETGs and estimate that ~13% of dust-corrected green valley galaxies of similar stellar mass and UV-optical color are likely ESF-candidates, i.e., ESF-ETGs are not rare. Our results are consistent with star formation that is gradually declining in existing disks, i.e., the ESF-ETGs are evolving onto the red sequence for the first time, or with rejuvenated star formation due to accreted gas in older disks provided that the gas does not disrupt the structure of the galaxy and the resulting star formation is not too recent and bursty. ESF-ETGs may typify an important subpopulation of galaxies that can linger in the green valley for up to several Gyrs, based on their resemblance to nearby gas-rich green valley galaxies with low-level ongoing star formation. (abridged)
We present the preliminary analysis of clustering of a sample of 1157 radio-identified galaxies from Machalski & Condon (1999). We found that for separations $2-15 h^{-1}$Mpc their redshift space autocorrelation function $\xi(s)$ can be approximated by the power law with the correlation length $\sim 3.75h^{-1}$Mpc and slope $\gamma \sim 1.8$. The correlation length for radiogalaxies is found to be lower and the slope steeper than the corresponding parameters of the control sample of optically observed galaxies. Analysis the projected correlation function $\Xi(r)$ displays possible differences in the clustering properties between active galactic nuclei (AGN) and starburst (SB) galaxies.
We discuss the non-perturbative effects on the annihilation cross section of an Electro-Weak Dark Matter (EWDM) particle belonging to an electroweak multiplet when the splittings between the masses of the DM component and the other charged or neutral component(s) of the multiplet are treated as free parameters. Our analysis shows that EWDM exhibits not only the usual Sommerfeld enhancement with resonance peaks but also dips where the cross section is suppressed. Moreover, we have shown that the non-perturbative effects become important even when the EWDM mass is below the TeV scale, provided that some of the mass splitting are reduced to the order of a few MeV. This extends the possibility of observing sizeable non-perturbative effects in the dark matter annihilation to values of the dark matter mass significantly smaller than previously considered, since only electroweak--induced mass splittings larger than 100 MeV have been discussed in the literature so far. We have then used the available experimental data on the cosmic antiproton flux to constrain the EWDM parameter space. In our calculation of the expected signal we have included the effect of the convolution of the cross section with the velocity distribution of the dark matter particles in the Galaxy, showing that it can alter the non--perturbative effects significantly. In the case of EWDM with non-zero hypercharge, we have shown that the mass splitting in the Dirac dark matter fermion can be chosen so that the inelastic cross section of the EWDM off nuclei is allowed by present direct detection constraints and at the same time is within the reach of future experiments.
We have searched for dust in an optical sample of 910 Early-Type Galaxies (ETG) in the Virgo cluster (447 of which are optically complete at m_pg <= 18.0), extending also to the dwarf ETG, using Herschel images at 100, 160, 250, 350 and 500 microns. Dust was found in 52 ETG (46 are in the optically complete sample), including M87 and another 3 ETG with strong synchrotron emisssion. Dust is detected in 17% of ellipticals, 41% of lenticulars, and in about 4% of dwarf ETG. The dust-to-stars mass ratio increases with decreasing optical luminosity, and for some dwarf ETG reaches values similar to those of the dusty late-type galaxies. Slowly rotating ETG are more likely to contain dust than fast rotating ones. Only 8 ETG have both dust and HI, while 39 have only dust and 8 have only HI, surprisingly showing that only rarely dust and HI survive together. ETG with dust appear to be concentrated in the densest regions of the cluster, while those with HI tend to be at the periphery. ETG with an X-ray active SMBH are more likely to have dust and vice versa the dusty ETG are more likely to have an active SMBH.
We perform a quantitative morphological comparison between the hosts of Active Galactic Nuclei (AGN) and quiescent galaxies at intermediate redshifts (z~0.7). The imaging data are taken from the large HST/ACS mosaics of the GEMS and STAGES surveys. Our main aim is to test whether nuclear activity at this cosmic epoch is triggered by major mergers. Using images of quiescent galaxies and stars, we create synthetic AGN images to investigate the impact of an optical nucleus on the morphological analysis of AGN hosts. Galaxy morphologies are parameterized using the asymmetry index A, concentration index C, Gini coefficient G and M20 index. A sample of ~200 synthetic AGN is matched to 21 real AGN in terms of redshift, host brightness and host-to-nucleus ratio to ensure a reliable comparison between active and quiescent galaxies. The optical nuclei strongly affect the morphological parameters of the underlying host galaxy. Taking these effects into account, we find that the morphologies of the AGN hosts are clearly distinct from galaxies undergoing violent gravitational interactions. In fact, the host galaxies' distributions in morphological descriptor space are more similar to undisturbed galaxies than major mergers. Intermediate-luminosity (Lx < 10^44 erg/s) AGN hosts at z~0.7 show morphologies similar to the general population of massive galaxies with significant bulges at the same redshifts. If major mergers are the driver of nuclear activity at this epoch, the signatures of gravitational interactions fade rapidly before the optical AGN phase starts, making them undetectable on single-orbit HST images, at least with usual morphological descriptors. This could be investigated in future synthetic observations created from numerical simulations of galaxy-galaxy interactions.
A major uncertainty in models for photoionised outflows in AGN is the
distance of the gas to the central black hole. We present the results of a
massive multiwavelength monitoring campaign on the bright Seyfert 1 galaxy Mrk
509 to constrain the location of the outflow components dominating the soft
X-ray band.
Mrk 509 was monitored by XMM-Newton, Integral, Chandra, HST/COS and Swift in
2009. We have studied the response of the photoionised gas to the changes in
the ionising flux produced by the central regions. We were able to put tight
constraints on the variability of the absorbers from day to year time scales.
This allowed us to develop a model for the time-dependent photoionisation in
this source.
We find that the more highly ionised gas producing most X-ray line opacity is
at least 5 pc away from the core; upper limits to the distance of various
absorbing components range between 20 pc up to a few kpc. The more lowly
ionised gas producing most UV line opacity is at least 100 pc away from the
nucleus.
These results point to an origin of the dominant, slow (v<1000 km/s) outflow
components in the NLR or torus-region of Mrk 509. We find that while the
kinetic luminosity of the outflow is small, the mass carried away is likely
larger than the 0.5 Solar mass per year accreting onto the black hole.
We also determined the chemical composition of the outflow as well as
valuable constraints on the different emission regions. We find for instance
that the resolved component of the Fe-K line originates from a region 40-1000
gravitational radii from the black hole, and that the soft excess is produced
by Comptonisation in a warm (0.2-1 keV), optically thick (tau~10-20) corona
near the inner part of the disk.
The masses of 68 supermassive black holes (SMBHs) in nearby (z<0.15) active galactic nuclei (AGNs) detected by the INTEGRAL observatory in the hard X-ray energy band (17-60 keV) outside the Galactic plane (|b| > 5 degrees) have been estimated. Well-known relations between the SMBH mass and (1) the infrared luminosity of the stellar bulge (from 2MASS data) and (2) the characteristics of broad emission lines (from RTT-150 data) have been used. A comparison with the more accurate SMBH mass estimates obtained by the reverberation-mapping technique and from direct dynamical measurements is also made for several objects. The SMBH masses derived from the correlation with the bulge luminosity turn out to be systematically higher than the estimates made by other methods. The ratio of the bolometric luminosity to the critical Eddington luminosity has been found for all AGNs. It ranges from 1 to 100% for the overwhelming majority of objects.
We describe the experimental design of C-4, an expansion of the CoGeNT dark matter search to four identical detectors each approximately three times the mass of the p-type point contact germanium diode presently taking data at the Soudan Underground Laboratory. Expected reductions of radioactive backgrounds and energy threshold are discussed, including an estimate of the additional sensitivity to low-mass dark matter candidates to be obtained with this search.
We derive the redshift drift formula for the inhomogeneous pressure spherically symmetric Stephani universes which are complementary to inhomogeneous density Lema\^itre-Tolman-Bondi (LTB) models. We show that there is a clear difference between the redshift drift predictions for these two models. The Stephani models have positive drift values at small redshift and behave qualitatively as the $\Lambda$CDM models while the drift for LTB models is always negative. This prediction can be tested in future space experiments such as E-ELT, TMT, GMT or CODEX.
We present a No-Go theorem for keV sterile neutrino Dark Matter: if sterile neutrinos at the keV scale play the role of Dark Matter, they are typically unstable and their decay produces an astrophysical monoenergetic X-ray line. It turns out that the observational bound on this line is so strong that it contradicts the existence of a quasi-degenerate spectrum of active neutrinos in a seesaw type I framework where the Casas-Ibarra matrix R is real. This is the case in particular for models without CP violation. We give a general proof of this theorem. While the theorem (like every No-Go theorem) relies on certain assumptions, the situation under which it applies is still sufficiently general to lead to interesting consequences for keV neutrino model building. In fact, depending on the outcome of the next generation experiments, one might be able to rule out whole classes of models for keV sterile neutrinos.
We present a model of the gravitational field based on two symmetric tensors. Gravity is affected by the new field, but outside matter the predictions of the model coincide exactly with general relativity, so all classical tests are satisfied. We find that massive particles do not follow a geodesic while massless particles trajectories are null geodesics of an effective metric. We study the Cosmological case, where we get an accelerated expansion of the universe without dark energy. We also introduce the possibility to explain dark matter with $\tilde{\delta}$ gravity.
Approximately 10% of active galactic nuclei exhibit relativistic jets, which are powered by accretion of matter onto super massive black holes. While the measured width profiles of such jets on large scales agree with theories of magnetic collimation, predicted structure on accretion disk scales at the jet launch point has not been detected. We report radio interferometry observations at 1.3mm wavelength of the elliptical galaxy M87 that spatially resolve the base of the jet in this source. The derived size of 5.5 +/- 0.4 Schwarzschild radii is significantly smaller than the innermost edge of a retrograde accretion disk, suggesting that the M87 jet is powered by an accretion disk in a prograde orbit around a spinning black hole.
We present non-LTE time-dependent radiative-transfer simulations of pair-instability supernovae (PISNe) stemming from red-supergiant (RSG), blue-supergiant (BSG) and Wolf-Rayet (WR) star rotation-free progenitors born in the mass range 160-230Msun, at 10^-4 Zsun. Although subject to uncertainties in convection and stellar mass-loss rates, our initial conditions come from physically-consistent models that treat evolution from the main-sequence, the onset of the pair-production instability, and the explosion phase. With our set of input models characterized by large 56Ni and ejecta masses, and large kinetic energies, we recover qualitatively the Type II-Plateau, II-peculiar, and Ib/c light-curve morphologies, although they have larger peak bolometric luminosities (~10^9 to 10^10 Lsun) and a longer duration (~200d). We discuss the spectral properties for each model during the photospheric and nebular phases, including Balmer lines in II-P and II-pec at early times, the dominance of lines from intermediate-mass-elements (IMEs) near the bolometric maximum, and the strengthening of metal line blanketing thereafter. Having similar He-core properties, all models exhibit similar post-peak spectra that are strongly blanketed by FeII and FeI lines, characterized by red colors, and that arise from photospheres/ejecta with a temperature of <4000K. Combined with the modest line widths after bolometric peak, these properties contrast with those of known super-luminous SNe suggesting that PISNe are yet to be discovered. Being reddish, PISNe will be difficult to observe at high redshift except when they stem from RSG explosions, in which case they could be used as metallicity probes and distance indicators.
Composite Higgs Models are very appealing candidates for a natural realization of electroweak symmetry breaking. Non minimal models could explain the recent Higgs data from ATLAS, CMS and Tevatron experiments, including the excess in the amount of diphoton events, as well as provide a natural dark matter candidate. In this article, we study a Composite Higgs model based on the coset $SO(7)/G2$. In addition to the Higgs doublet, one $SU(2)_L$ singlet of electric charge one, $\kappa^\pm$, as well as one singlet $\eta$ of the whole Standard Model group arise as pseudo-Goldstone bosons. $\kappa^\pm$ and $\eta$ can be responsible of the diphoton excess and dark matter respectively.
Many sources in the fourth INTEGRAL/IBIS catalogue are still unidentified, since they lack an optical counterpart. An important tool that can help in identifying/classifying these sources is the cross-correlation with radio catalogues, which are very sensitive and positionally accurate. Moreover, the radio properties of a source, such as the spectrum or morphology, could provide further insight into its nature. Flat-spectrum radio sources at high Galactic latitudes are likely to be AGN, possibly associated to a blazar or to the compact core of a radio galaxy. Here we present a small sample of 6 sources extracted from the fourth INTEGRAL/IBIS catalogue that are still unidentified/unclassified, but which are very likely associated with a bright, flat-spectrum radio object. To confirm the association and to study the source X-ray spectral parameters, we performed X-ray follow-up observations with Swift/XRT. We report the results obtained from this search and discuss the nature of each source. 5 of the 6 radio associations are also detected in X-rays; in 3 cases they are the only counterpart found. IGR J06073--0024 is a flat-spectrum radio quasar at z=1.08, IGR J14488--4008 is a newly discovered radio galaxy, while IGR J18129--0649 is an AGN of a still unknown type. The nature of IGR J07225--3810 and IGR J19386--4653 is less well defined, since in both cases we find another X-ray source in the INTEGRAL error circle; nevertheless, the flat-spectrum radio source, likely to be a radio loud AGN, remains a viable and more convincing association in both cases. Only for IGR J11544--7618 could we not find any convincing counterpart since the radio association is not an X-ray emitter.
As a first step toward understanding a lanscape of vacua in a theory of non-linear massive gravity, we consider a landscape of a single scalar field and study tunneling between a pair of adjacent vacua. We study the Hawking-Moss (HM) instanton that sits at a local maximum of the potential, and evaluate the dependence of the tunneling rate on the parameters of the theory. It is found that provided with the same physical HM Hubble parameter $H_{HM}$, depending on the values of parameters $\alpha_3$ and $\alpha_4$ in the action, the corresponding tunneling rate can be either enhanced or suppressed when compared to the one in the context of General Relativity (GR). Furthermore, we find the constraint on the ratio of the physical Hubble parameter to the fiducial one, which constrains the form of potential. This result is in sharp contrast to GR where there is no bound on the minimum value of the potential.
This review article considers some of the most common methods used in astronomy for regressing one quantity against another in order to estimate the model parameters or to predict an observationally expensive quantity using trends between object values. These methods have to tackle some of the awkward features prevalent in astronomical data, namely heteroscedastic (point-dependent) errors, intrinsic scatter, non-ignorable data collection and selection effects, data structure and non-uniform population (often called Malmquist bias), non-Gaussian data, outliers and mixtures of regressions. We outline how least square fits, weighted least squares methods, Maximum Likelihood, survival analysis, and Bayesian methods have been applied in the astrophysics literature when one or more of these features is present. In particular we concentrate on errors-in-variables regression and we advocate Bayesian techniques.
We report the results of our observations of the 12CO (J=1-0) and 12CO (J=3-2) line emission of 74 major giant molecular clouds (GMCs) within the galactocentric distance of 5.1 kpc in the Local Group galaxy M33. The observations have been conducted as part of the Nobeyama Radio Observatory M33 All-disk survey of Giant Molecular Clouds project (NRO MAGiC). The spatial resolutions are 80 pc for 12CO (J=1-0) and 100 pc for 12CO (J=3-2). We detect 12CO (J=3-2) emission of 65 GMCs successfully. Furthermore, we find that the correlation between the surface density of the star formation rate, which is derived from a linear combination of Halpha and 24um emissions, and the 12CO (J=3-2) integrated intensity still holds at this scale. This result show that the star-forming activity is closely associated with warm and dense gases that are traced with the 12CO (J=3-2) line, even in the scale of GMCs. We also find that the GMCs with a high star-forming activity tend to show a high integrated intensity ratio (R3-2/1-0). Moreover, we also observe a mass-dependent trend of R3-2/1-0 for the GMCs with a low star-forming activity. From these results, we speculate that the R3-2/1-0 values of the GMCs with a low star-forming activity mainly depend on the dense gas fraction and not on the temperature, and therefore, the dense gas fraction increases with the mass of GMCs, at least in the GMCs with a low star-forming activity.
Deep Very Large Array imaging of the quasar 3C\,345 at 4.86 and 8.44 GHz has
been used to study the structure and linear polarization of its radio jet on
scales ranging from 2 to 30 kpc. There is a 7--8 Jy unresolved core with
spectral index $\alpha \simeq -0.24$ ($I_\nu \propto \nu^{\alpha}$). The jet
(typical intensity 15 mJy/beam) consists of a $2.5\arcsec$ straight section
containing two knots, and two additional non-co-linear knots at the end. The
jet's total projected length is about 27 kpc. The spectral index of the jet
varies over $-1.1 \lesssim \alpha \lesssim -0.5$. The jet diverges with a
semi-opening angle of about $9^\circ$, and is nearly constant in integrated
brightness over its length. A faint feature north-east of the core does not
appear to be a true counter-jet, but rather an extended lobe of this FR-II
radio source seen in projection. The absence of a counter-jet is sufficient to
place modest constraints on the speed of the jet on these scales, requiring
$\beta \ga 0.5$. Despite the indication of jet precession in the total
intensity structure, the polarization images suggest instead a jet re-directed
at least twice by collisions with the external medium.
Surprisingly, the electric vector position angles in the main body of the jet
are neither longitudinal nor transverse, but make an angle of about $55^\circ$
with the jet axis in the middle while along the edges the vectors are
transverse, suggesting a helical magnetic field. There is no significant
Faraday rotation in the source, so that is not the cause of the twist. The
fractional polarization in the jet averages 25% and is higher at the edges. In
a companion paper it is shown that differential Doppler boosting in a diverging
relativisitic velocity field can explain the electric vector pattern in the
jet.
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We analyze the link between active galactic nuclei (AGN) and mid-infrared flux using dust radiative transfer calculations of starbursts realized in hydrodynamical simulations. Focusing on the effect of galaxy dust, we evaluate diagnostics commonly used to disentangle AGN and star formation in ultraluminous infrared galaxies (ULIRGs). We examine these quantities as a function of time, viewing angle, dust model, AGN spectrum, and AGN strength in merger simulations meant to bracket the properties of ULIRGs. Our more obscured starburst begins SF-dominated with significant PAH emission, and ends with a ~10^9 year period of red near-IR colors. At coalescence, when the AGN is most luminous, dust obscures the near-infrared AGN signature, reduces the relative emission from polycyclic aromatic hydrocarbons (PAHs), and enhances the 9.7 micron absorption by silicate grains. Although generally consistent with previous interpretations, our results imply none of these indicators can unambiguously estimate the AGN luminosity fraction in all cases. Some identify relatively unobscured AGN where the direct torus emission is observed, while others indicate more highly obscured AGN. We show that a combination of the extinction feature at 9.7 microns, the PAH strength, and a near-infrared slope can simultaneously constrain the AGN fraction and dust grain distribution for a wide range of obscuration. We find that this procedure, accessible to the James Webb Space Telescope, may estimate the AGN power as tightly as the hard X-ray flux alone, thereby providing a valuable future cross-check and constraint for large samples of distant ULIRGs.
We report systematic variations in the CO(2-1)/CO(1-0) line ratio (R) in M51. The ratio shows clear evidence for the evolution of molecular gas from the upstream interarm regions, passage into the spiral arms and back into the downstream interarm regions. In the interarm regions, R is typically low <0.7 (and often 0.4-0.6); this is similar to the ratios observed in Galactic giant molecular clouds (GMCs) with low far-IR luminosities. However, the ratio rises to >0.7 (often 0.8-1.0) in the spiral arms, particularly at their leading (downstream) edge. R is also high, 0.8-1.0, in the central region. An LVG calculation provides insight into the changes in the gas physical conditions between the arm and interarm regions: cold and low density gas (~10K, ~300cm-3) is required for the interarm GMCs, but this gas must become warmer and/or denser in the more active star forming spiral arms. R is higher in areas of high 24micron brightness (an approximate tracer of star formation rate surface density) and high CO(1-0) integrated intensity (a well-calibrated tracer of total molecular gas surface density). The systematic enhancement of the CO(2-1) line relative to CO(1-0) in luminous star forming regions suggests that some caution is needed when using CO(2-1) as a tracer of bulk molecular gas mass.
We study the effects of gravitational lensing by galaxy clusters of the background of dusty star-forming galaxies (DSFGs) and the Cosmic Microwave Background (CMB), and examine the implications for Sunyaev-Zel'dovich-based (SZ) galaxy cluster surveys. At the locations of galaxy clusters, gravitational lensing modifies the probability distribution of the background flux of the DSFGs as well as the CMB. We find that, in the case of a single-frequency 150 GHz survey, lensing of DSFGs leads to both a slight increase (~10%) in detected cluster number counts (due to a ~ 50% increase in the variance of the DSFG background, and hence an increased Eddington bias), as well as to a rare (occurring in ~2% of clusters) "filling-in" of SZ cluster signals by bright strongly lensed background sources. Lensing of the CMB leads to a ~55% reduction in CMB power at the location of massive galaxy clusters in a spatially-matched single-frequency filter, leading to a net decrease in detected cluster number counts. We find that the increase in DSFG power and decrease in CMB power due to lensing at cluster locations largely cancel, such that the net effect on cluster number counts for current SZ surveys is sub-dominant to Poisson errors.
We discuss the properties of subhalos in cluster-size halos, using a high-resolution statistical sample: the Rhapsody simulations introduced in Wu et al. (2012). We demonstrate that the criteria applied to select subhalos have significant impact on the inferred properties of the sample, including the scatter in the number of subhalos, the correlation between the subhalo number and formation time, and the shape of subhalos' spatial distribution and velocity structure. We find that the number of subhalos, when selected using the peak maximum circular velocity in their histories (a property expected to be closely related to the galaxy luminosity), is uncorrelated with the formation time of the main halo. This is in contrast to the previously reported correlation from studies where subhalos are selected by the current maximum circular velocity; we show that this difference is a result of the tidal stripping of the subhalos. We also find that the dominance of the main halo and the subhalo mass fraction are strongly correlated with halo concentration and formation history. These correlations are important to take into account when interpreting results from cluster samples selected with different criteria. Our sample also includes a fossil cluster, which is presented separately and placed in the context of the rest of the sample.
We present Herschel observations at 70, 160, 250, 350 and 500 micron of the environment of the radio galaxy 4C+41.17 at z = 3.792. About 65% of the extracted sources are securely identified with mid-IR sources observed with the Spitzer Space Telescope at 3.6, 4.5, 5.8, 8 and 24 micron. We derive simple photometric redshifts, also including existing 850 micron and 1200 micron data, using templates of AGN, starburst-dominated systems and evolved stellar populations. We find that most of the Herschel sources are foreground to the radio galaxy and therefore do not belong to a structure associated with 4C+41.17. We do, however, find that the SED of the closest (~ 25" offset) source to the radio galaxy is fully consistent with being at the same redshift as 4C+41.17. We show that finding such a bright source that close to the radio galaxy at the same redshift is a very unlikely event, making the environment of 4C+41.17 a special case. We demonstrate that multi-wavelength data, in particular on the Rayleigh-Jeans side of the spectral energy distribution, allow us to confirm or rule out the presence of protocluster candidates that were previously selected by single wavelength data sets.
We study the spectral properties of the unresolved cosmic X-ray background (CXRB) in the 1.5-7.0 keV energy band with the aim of providing an observational constraint on the statistical properties of those sources that are too faint to be individually probed. We made use of the Swift X-ray observation of the Chandra Deep Field South complemented by the Chandra data. Exploiting the lowest instrument background (Swift) together with the deepest observation ever performed (Chandra) we measured the unresolved emission at the deepest level and with the best accuracy available today. We find that the unresolved CXRB emission can be modeled by a single power law with a very hard photon index Gamma=0.1+/-0.7 and a flux of 5(+/-3)E-12 cgs in the 2.0-10 keV energy band (1 sigma error). Thanks to the low instrument background of the Swift-XRT, we significantly improved the accuracy with respect to previous measurements. These results point towards a novel ingredient in AGN population synthesis models, namely a positive evolution of the Compton-thick AGN population from local Universe to high redshift.
We present a new measurement of the optical Quasar Luminosity Function (QLF), using data from the Sloan Digital Sky Survey-III: Baryon Oscillation Spectroscopic Survey (SDSS-III: BOSS). From the SDSS-III Data Release Nine (DR9), we select a uniform sample of 22,301 i<=21.8 quasars over an area of 2236 sq. deg with confirmed spectroscopic redshifts between 2.2<z<3.5, filling in a key part of the luminosity-redshift plane for optical quasar studies. We derive the completeness of the survey through simulated quasar photometry, and check this completeness estimate using a sample of quasars selected by their photometric variability within the BOSS footprint. We investigate the level of systematics associated with our quasar sample using the simulations, in the process generating color-redshift relations and a new quasar k-correction. We probe the faint end of the QLF to M_i(z=2.2) = -24.5 and see a clear break in the QLF at all redshifts up to z=3.5. We find that a log-linear relation (in log[Phi*] - M*) for a luminosity and density evolution (LEDE) model adequately describes our data within the range 2.2<z<3.5; across this interval the break luminosity increases by a factor of ~2.3 while Phi* declines by a factor of ~6. At z<2.2 our data is reasonably well fit by a pure luminosity evolution (PLE) model. We see only a weak signature of "AGN downsizing", in line with recent studies of the hard X-ray luminosity function. We compare our measured QLF to a number of theoretical models and find that models making a variety of assumptions about quasar triggering and halo occupation can fit our data over a wide range of redshifts and luminosities.
We present the optical narrow line ratios in an SDSS based sample of 3,175 broad Ha selected type 1 AGN, and explore their positions in the BPT diagrams as a function of the AGN and the host properties. We find the following: 1. The luminosities of all measured narrow lines (Ha, Hb, [OIII], [NII], [SII], [OI]) show a Baldwin relation relative to the broad Ha luminosity L_bHa, with slopes in the range of 0.53-0.72. 2. About 20% of the type 1 AGN reside within the `Composite' and `SF' regions of the BPT diagrams. These objects also show excess narrow Ha and UV luminosities, for their L_bHa, consistent with contribution from star formation which dominates the narrow lines emission, as expected from their positions in the BPT diagrams. 3. The type 1 which reside within the AGN region in the BPT diagrams, are offset to lower [SII]/Ha and [NII]/Ha luminosity ratios, compared to type 2 AGN. This offset is a selection effect, related to the lower AGN/host luminosity selection of the type 2 AGN selected from the SDSS galaxy sample. 4. The [NII]/Ha and [NII]/[SII] ratios in type 1 AGN increase with the host mass, as expected if the mass-metallicity relation of quiescent galaxies holds for the AGN narrow line region. 5. The broad lines optical FeII is higher for a higher [NII]/Ha, at a fixed L_Bol and Eddington ratio L/L_Edd. This suggests that the broad line region metallicity is also related to the host mass. 6. The fraction of AGN which are LINERs increases sharply with decreasing L/L_Edd. This fraction is the same for type 1 and type 2 AGN. 7. The BPT position is unaffected by the amount of dust extinction of the optical-UV continuum, which suggests the extincting dust resides on scales larger than the NLR.
We demonstrate that massive simulated galaxies assemble in two phases, with the initial growth dominated by compact in situ star formation, whereas the late growth is dominated by accretion of old stars formed in subunits outside the main galaxy. We also show that 1) gravitational feedback strongly suppresses late star formation in massive galaxies contributing to the observed galaxy colour bimodality that 2) the observed galaxy downsizing can be explained naturally in the two-phased model and finally that 3) the details of the assembly histories of massive galaxies are directly connected to their observed kinematic properties.
Recent observations have discovered a population of extended Lya sources, dubbed Lyman-alpha blobs (LABs), at high redshift z ~ 3 - 6.6. These LABs typically have a luminosity of L ~ 10^{42-44} erg/s, and a size of tens of kiloparsecs, with some giant ones reaching up to D ~ 100 kpc. However, the origin of these LABs is not well understood. In this paper, we investigate a merger model for the formation of LABs by studying Lya emission from interacting galaxies at high redshifts by means of a combination of hydrodynamics simulations with three dimensional radiative transfer calculations. Our galaxy simulations focus on a set of binary major mergers of galaxies with a mass range of 3-7 *10^{12} Msun in the redshift range of z\sim3 -7, and we use the newly improved ART^2 code to perform the radiative transfer calculations which couple multi-wavelength continuum, ionization of hydrogen, and Lya line emission. We find that intense star formation and enhanced cooling induced by gravitational interaction produce strong Lya emission from these merging galaxies. The Lya emission appears to be extended due to the extended distribution of sources and gas. During the close encounter of galaxy progenitors when the star formation rate peaks at ~ 10^3 Msun/yr, our model produces Lya blobs with luminosity of L\sim 10^{42-44} erg/s, and size of D\sim 10-20 kpc at z>6 and D\sim 20-50 kpc at z ~ 3, in broad agreement with observations in the same redshift range. Our results suggest that merging galaxies may produce some typical LABs as observed, but the giant ones may be produced by mergers more massive than those in our model, or a combination of mergers and cold accretion from filaments on a large scale.
X-ray observations of galaxy clusters reveal a large range of morphologies with various degrees of disturbance, showing that the assumptions of hydrostatic equilibrium and spherical shape which are used to determine the cluster mass from X-ray data are not always satisfied. It is therefore important for the understanding of cluster properties as well as for cosmological applications to detect and quantify substructure in X-ray images of galaxy clusters. Two promising methods to do so are power ratios and center shifts. Since these estimators can be heavily affected by Poisson noise and X-ray background, we performed an extensive analysis of their statistical properties using a large sample of simulated X-ray observations of clusters from hydrodynamical simulations. We quantify the measurement bias and error in detail and give ranges where morphological analysis is feasible. A new, computationally fast method to correct for the Poisson bias and the X-ray background contribution in power ratio and center shift measurements is presented and tested for typical XMM-Newton observational data sets. We studied the morphology of 121 simulated cluster images and establish structure boundaries to divide samples into relaxed, mildly disturbed and disturbed clusters. In addition, we present a new morphology estimator - the peak of the 0.3-1 r500 P3/P0 profile to better identify merging clusters. The analysis methods were applied to a sample of 80 galaxy clusters observed with XMM-Newton. We give structure parameters (P3/P0 in r500, w and P3/P0_max) for all 80 observed clusters. Using our definition of the P3/P0 (w) substructure boundary, we find 41% (47%) of our observed clusters to be disturbed.
In this paper we present a new method to extract cosmological parameters using the radial scale of the Baryon Acoustic Oscillations as a standard ruler in deep galaxy surveys. The method consists in an empirical parametrization of the radial 2-point correlation function, which provides a robust and precise extraction of the sound horizon scale. Moreover, it uses data from galaxy surveys in a manner that is fully cosmology independent and therefore, unbiased. A study of the main systematic errors and the validation of the method in cosmological simulations are also presented, showing that the measurement is limited only by cosmic variance. We then study the full information contained in the Baryon Acoustic Oscillations, obtaining that the combination of the radial and angular determinations of this scale is a very sensitive probe of cosmological parameters, able to set strong constraints on the dark energy properties, even without combining it with any other probe.
We develop a theory of nonlinear cosmological perturbations on superhorizon scales for a multi-component scalar field with a general kinetic term and a general form of the potential in the context of inflationary cosmology. We employ the ADM formalism and the spatial gradient expansion approach, characterised by O(\epsilon^2), where \epsilon=1/(HL) is a small parameter representing the ratio of the Hubble radius to the characteristic length scale L of perturbations. We provide a formalism to obtain the solution in the multi-field case. This formalism can be applied to the superhorizon evolution of a primordial non-Gaussianity beyond the so-called \delta N formalism which is equivalent to O(\epsilon^0) of the gradient expansion. In doing so, we also derive fully nonlinear gauge transformation rules valid through O(\epsilon^2). These fully nonlinear gauge transformation rules can be used to derive the solution in a desired gauge from the one in a gauge where computations are much simpler. As a demonstration, we consider an analytically solvable model and construct the solution explicitly.
The first detection of the silicate absorption feature in AGNs was made at 9.7 micrometer for the prototypical Seyfert 2 galaxy NGC 1068 over 30 years ago, indicating the presence of a large column of silicate dust in the line-of-sight to the nucleus. It is now well recognized that type 2 AGNs exhibit prominent silicate absorption bands, while the silicate bands of type 1 AGNs appear in emission. More recently, using the Mid-Infrared Interferometric Instrument on the Very Large Telescope Interferometer, Jaffe et al. (2004) by the first time spatially resolved the parsec-sized dust torus around NGC 1068 and found that the 10 micrometer silicate absorption feature of the innermost hot component exhibits an anomalous profile differing from that of the interstellar medium and that of common olivine-type silicate dust. While they ascribed the anomalous absorption profile to gehlenite (Ca_2Al_2SiO_7, a calcium aluminum silicate species), we propose a physical dust model and argue that, although the presence of gehlenite is not ruled out, the anomalous absorption feature mainly arises from silicon carbide.
This paper is the first of a series considering the properties of distribution of nearby galaxies in the low density regions. Among 7596 galaxies with radial velocities V_{LG}<3500 km/s, absolute magnitudes M_K<-18.4^m$, and Galactic latitudes |b| >15 degr there are 3168 field galaxies (i.e. 42%) that do not belong to pairs, groups or clusters in the Local universe. Applying to this sample the percolation method with a radius of r_0=2.8 Mpc, we found 226 diffuse agglomerates with n>=4 number of members. The structures of eight most populated objects among them (n>=25) are discussed. These non-virialized agglomerates are characterized by a median dispersion of radial velocities of about 170 km/s, the linear size of around 6 Mpc, integral K-band luminosity of 3*10^{11} L_sun, and a formal virial-mass-to-luminosity ratio of about 700 M_sun/L_sun. The mean density contrast for the considered agglomerates is only <Delta n/\bar{n}\gtrsim 5, and their crossing time is about 30-40 Gyr.
Several approaches exist to model gravitational lens systems. In this study, we apply global optimization methods to find the optimal set of lens parameters using a genetic algorithm. We treat the full optimization procedure as a two-step process: an analytical description of the source plane intensity distribution is used to find an initial approximation to the optimal lens parameters. The second stage of the optimization uses a pixelated source plane with the semilinear method to determine an optimal source. Regularization is handled by means of an iterative method and the generalized cross validation (GCV) and unbiased predictive risk estimator (UPRE) functions that are commonly used in standard image deconvolution problems. This approach simultaneously estimates the optimal regularization parameter and the number of degrees of freedom in the source. Using the GCV and UPRE functions we are able to justify an estimation of the number of source degrees of freedom found in previous work. We test our approach by applying our code to a subset of the lens systems included in the SLACS survey.
Reconstruction of the CMB in the Galactic plane is extremely difficult due to the dominant foreground emissions such as Dust, Free-Free or Synchrotron. For cosmological studies, the standard approach consists in masking this area where the reconstruction is not good enough. This leads to difficulties for the statistical analysis of the CMB map, especially at very large scales (to study for e.g., the low quadrupole, ISW, axis of evil, etc). We investigate in this paper how well some inpainting techniques can recover the low-$\ell$ spherical harmonic coefficients. We introduce three new inpainting techniques based on three different kinds of priors: sparsity, energy and isotropy, and we compare them. We show that two of them, sparsity and energy priors, can lead to extremely high quality reconstruction, within 1% of the cosmic variance for a mask with Fsky larger than 80%.
We study non-Gaussianity of density perturbations generated by an axionic curvaton, focusing on the case that the curvaton sits near the hilltop of the potential during inflation. Such hilltop curvatons can generate a red-tilted density perturbation spectrum without invoking large-field inflation. We show that, even when the curvaton dominates the Universe, the non-Gaussianity parameter fNL is positive and mildly increases towards the hilltop of the curvaton potential, and that fNL = O(10) is a general and robust prediction of such hilltop axionic curvatons. In particular, we find that the non-Gaussianity parameter is bounded as fNL <~ 30 - 40 for a range of the scalar spectral index, ns = 0.94 - 0.99, and that fNL = 20 - 40 is realized for the curvaton mass m_\sigma = 10 - 10^6 GeV and the decay constant f = 10^{12} - 10^{17} GeV. One of the plausible candidates for the axionic curvaton is an imaginary component of a modulus field with mass of order 10 - 100 TeV and decay constant of 10^{16} - 10^{17} GeV. We also discuss extreme cases where the curvaton drives a second inflation and find that fNL is typically smaller compared to non-inflating cases.
We investigate direct determination of expansion history using redshift distortions without plugging into detailed cosmological parameters. The observed spectra in redshift space include a mixture of information: fluctuations of density-density and velocity-velocity spectra, and distance measures of perpendicular and parallel components to the line of sight. Unfortunately it is hard to measure all the components simultaneously without any specific prior assumption. Common prior assumptions include a linear/quasi-linear model of redshift distortions or a model for the shape of the power spectra, which eventually breaks down on small scales at later epochs where nonlinear structure formation disturbs coherent growth. The degeneracy breaking between the effect of cosmic distances and redshift distortions for example depends on the prior we assume. As an alternative approach is to utilize the cosmological principle inscribed in the heart of the Friedmann-Lema\^itre-Robertson-Walker (hereafter FLRW) universe, that is, the specific relation between the angular diameter distance and the Hubble parameter, in this degeneracy breaking. We show that utilizing this FLRW prior early in the step of distinguishing the distance effect from redshift distortions help us improve the detectability of power spectra and distance measures with no leaning on combination of other experiments.
Recent cosmological data favour additional relativistic degrees of freedom beyond the three active neutrinos and photons, often referred to as "dark radiation". Extensions of the SM involving TeV-scale Z' gauge bosons generically contain superweakly interacting light right-handed neutrinos which can constitute this dark radiation. In this letter we confront the requirement on the parameters of the E6 Z' models to account for the present evidence of dark radiation with the already existing constraints from searches for new neutral gauge bosons at LHC7.
Combined gravitational-wave (GW) and electromagnetic (EM) observations of compact binary mergers should enable detailed studies of astrophysical processes in the strong-field gravity regime. Networks of GW interferometers have poor angular resolution on the sky and their EM signatures are predicted to be faint. Therefore, a challenging goal will be to unambiguously pinpoint the EM counterparts to GW mergers. We perform the first comprehensive end-to-end simulation that focuses on: i) GW sky localization, distance measures and volume errors with two compact binary populations and four different GW networks, ii) subsequent detectability by a slew of multiwavelength telescopes and, iii) final identification of the merger counterpart amidst a sea of possible astrophysical false-positives. First, we find that double neutron star (NS) binary mergers can be detected out to a maximum distance of 400 Mpc (or 750 Mpc) by three (or five) detector GW networks respectively. NS -- black-hole (BH) mergers can be detected a factor of 1.5 further out. The sky localization uncertainties for NS-BH mergers are 50--170 sq. deg. (or 6--65 sq. deg.) for a three (or five detector) GW network respectively. Second, we quantify relative fractions of optical counterparts that are detectable by different size telescopes. Third, we present five case studies to illustrate the diversity of challenges in secure identification of the EM counterpart at low and high Galactic latitudes. For the first time, we demonstrate how construction of low-latency GW volumes in conjunction with local universe galaxy catalogs can help solve the problem of false positives.
Using a simple model of photodissociated atomic hydrogen on a galactic scale, it is possible to derive total hydrogen volume densities. These densities, obtained through a combination of atomic hydrogen, far-ultraviolet and metallicity data, provide an independent probe of the combined atomic and molecular hydrogen gas in galactic disks. We present a new, flexible and fully automated procedure using this simple model. This automated method will allow us to take full advantage of a host of available data on galaxies in order to calculate total hydrogen volume densities of giant molecular clouds surrounding sites of recent star formation. So far this was only possible on a galaxy-by-galaxy basis using by-eye analysis of candidate photodissociation regions. We test the automated method by adopting different models for the dust-to-gas ratio and comparing the resulting densities for M74, including a new metallicity map of M74 produced by integral field spectroscopy. We test the procedure against previously published M83 volume densities based on the same method and find no significant differences. The range of total hydrogen volume densities obtained for M74 is approximately 5-700 cm-3 . Different dust-to-gas ratio models do not result in measurably different densities. The cloud densities presented here add M74 to the list of galaxies analyzed using the assumption of photodissociated atomic hydrogen occurring near sites of recent star formation and further solidify the method. For the first time, full metallicity maps were included in the analysis as opposed to metallicity gradients. The results will need to be compared to other tracers of the interstellar medium and photodissociation regions, such as CO and CII, in order to test our basic assumptions, specifically, our assumption that the HI we detect originates in photodissociation regions.
The amount of H$_2$ present in spiral galaxies remains uncertain, particularly in the dim outer regions and in low-metallicity environments. We present high-resolution CO(1--0) observations with the Plateau de Bure interferometer of the most distant molecular cloud in the local group galaxy M 33. The cloud is a single entity rather than a set of smaller clouds within the broad beam of the original single-dish observations. The interferometer and single-dish fluxes are very similar and the line widths are indistinguishable, despite the difference in beamsize. At a spatial resolution of 10 pc, beyond the optical radius of the M 33, the CO brightness temperature reaches 2.4 Kelvins. A virial mass estimate for the cloud yields a mass of $4.3 \times 10^4$ \msun and a ratio $\ratio \simeq 3.5 \times 10^{20} \Xunit$. While no velocity gradient is seen where the emission is strong, the velocity is redshifted to the extreme SW and blue-shifted to the far NE. If the orientation of the cloud is along the plane of the disk (i.e. not perpendicular), then these velocities correspond to slow infall or accretion. The rather modest infall rate would be about $2 \times 10^{-4}$\moyr.
We have recently proposed that the Standard Model Higgs might be responsible for generating the cosmological perturbations of the universe by acting as an isocurvature mode during a de Sitter inflationary stage. In this paper we study the level of non-Gaussianity in the cosmological perturbations which are inevitably generated due to the non-linearities of the Standard Model Higgs potential. In particular, for the current central value of the top mass, we find that a future detection of non-Gaussianity would exclude the detection of tensor modes by the PLANCK satellite.
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(Abridged) The growing role played by numerical N-body simulations in cosmological studies as a fundamental connection between theoretical modeling and direct observations has led to impressive advancements also in the development and application of specific algorithms designed to probe a wide range of Dark Energy scenarios. Over the last decade, a large number of independent and complementary investigations have been carried out in the field of Dark Energy N-body simulations, starting from the simplest case of homogeneous Dark Energy models up to the recent development of highly sophisticated iterative solvers for a variety of Modified Gravity theories. In this Review - which is meant to be complementary to the general Review by Kuhlen et al. published in this Volume - I will discuss the range of scenarios for the cosmic acceleration that have been successfully investigated by means of dedicated N-body simulations, and I will provide a broad summary of the main results that have been obtained in this rather new research field. I will focus the discussion on a few selected studies that have led to particularly significant advancements in the field, and I will provide a comprehensive list of references for a larger number of related works. Due to the vastness of the topic, the discussion will not enter into the finest details of the different implementations and will mainly focus on the outcomes of the various simulations studies. Although quite recent, the field of Dark Energy simulations has witnessed huge developments in the last few years, and presently stands as a reliable approach to the investigation of the fundamental nature of Dark Energy.
Motivated by the desire to test modified gravity theories exhibiting the Vainshtein mechanism, we solve in various physically relevant limits, the retarded Galileon Green's function (for the cubic theory) about a background sourced by a massive spherically symmetric static body. The static limit of our result will aid us, in a forthcoming paper, in understanding the impact of Galileon fields on the problem of motion in the solar system. In this paper, we employ this retarded Green's function to investigate the emission of Galileon radiation generated by the motion of matter lying deep within the Vainshtein radius r_v of the central object: acoustic waves vibrating on its surface, and the motion of compact bodies gravitationally bound to it. If \lambda is the typical wavelength of the emitted radiation, and r_0 is the typical distance of the source from the central mass, with r_0 << r_v, then, compared to its non-interacting massless scalar counterpart, we find that the Galileon radiation rate is suppressed by the ratio (r_v/\lambda)^{-3/2} at the monopole and dipole orders at high frequencies r_v/\lambda >> 1. However, at high enough multipole order, the radiation rate is enhanced by powers of r_v/r_0. At low frequencies r_v/\lambda << 1, and when the motion is non-relativistic, Galileon waves yield a comparable rate for the monopole and dipole terms, and are amplified by powers of the ratio r_v/r_0 for the higher multipoles.
Recently, we have shown how current cosmological N-body codes already follow the fine grained phase-space information of the dark matter fluid. Using a tetrahedral tesselation of the three-dimensional manifold that describes perfectly cold fluids in six-dimensional phase space, the phase-space distribution function can be followed throughout the simulation. This allows one to project the distribution function into configuration space to obtain highly accurate densities, velocities, and velocity dispersions. Here, we exploit this technique to show first steps on how to devise an improved particle-mesh technique. At its heart, the new method thus relies on a piecewise linear approximation of the phase space distribution function rather than the usual particle discretisation. We use pseudo-particles that approximate the masses of the tetrahedral cells up to quadrupolar order as the locations for cloud-in-cell (CIC) deposit instead of the particle locations themselves as in standard CIC deposit. We demonstrate that this modification already gives much improved stability and more accurate dynamics of the collisionless dark matter fluid at high force and low mass resolution. We demonstrate the validity and advantages of this method with various test problems as well as hot/warm-dark matter simulations which have been known to exhibit artificial fragmentation. This completely unphysical behaviour is much reduced in the new approach. The current limitations of our approach are discussed in detail and future improvements are outlined.
We present the first sample of spectroscopically confirmed heavily reddened broad-line quasars selected using the new near infra-red VISTA Hemisphere Survey and \textit{WISE} All-Sky Survey. Observations of four candidates with $(J-K)>2.5$ and $K\le16.5$ over $\sim$180 deg$^2$, leads to confirmation that two are highly dust-reddened broad-line Type 1 quasars at z$\sim$2. The typical dust extinctions are A$_V\sim$2--2.5 mags. We measure black-hole masses of $\sim10^{9}$M$_\odot$ and extinction corrected bolometric luminosities of $\sim10^{47}$ erg/s, making these among the brightest Type 1 quasars currently known. Despite this, these quasars lie well below the detection limits of wide-field optical surveys like the SDSS with $i_{AB}>22$. We also present \textit{WISE} photometry at 3--22$\mu$m, for our full sample of spectroscopically confirmed reddened quasars including those selected from the UKIDSS Large Area Survey (Banerji et al. 2012a). We demonstrate that the rest-frame infrared SEDs of these reddened quasars are similar to UV-luminous Type 1 quasars with significant hot dust emission and starburst quasar hosts like Mrk231. The average 12$\mu$m flux density of our reddened quasars is similar to that of the recently discovered HyLIRG \textit{WISE}1814+3412 ($z=2.452$) at similar redshifts, with two of our reddened quasars also having comparable 22$\mu$m flux densities to this extreme HyLIRG. These optically faint, heavily reddened broad-line quasars are therefore among the most mid infrared luminous galaxies at $z\sim2$, now being discovered using \textit{WISE}
We present DEEP2 galaxy clustering measurements at z~1 as a function of stellar mass, star formation rate (SFR), and specific SFR (sSFR). We find a strong positive correlation between stellar mass and clustering amplitude on 1-10 h^-1 Mpc scales for blue, star-forming galaxies with 9.5 < log(M_*/M_sun) < 11 and no dependence for red, quiescent galaxies with 10.5 < log(M_*/M_sun) < 11.5. Using recently re-calibrated DEEP2 SFRs from restframe B-band magnitude and optical colors, we find that within the blue galaxy population at z~1, the clustering amplitude increases strongly with increasing SFR and decreasing sSFR. For red galaxies there is no significant correlation between clustering amplitude and either SFR or sSFR. Blue galaxies with high SFR or low sSFR are as clustered on large scales as red galaxies. We find that the clustering trend observed with SFR can be explained mostly, but not entirely, by the correlation between stellar mass and clustering amplitude for blue galaxies. We also show that galaxies above the star-forming "main sequence" are less clustered than galaxies below the main sequence, at a given stellar mass. These results are not consistent with the high sSFR population being dominated by major mergers. We also measure the clustering amplitude of our samples on small scales (< 0.3 h^-1 Mpc) and find an enhanced clustering signal relative to the best-fit large-scale power law for red galaxies with high stellar mass, blue galaxies with high SFR, and both red and blue galaxies with high sSFR. The increased small-scale clustering for galaxies with high sSFRs is likely linked to triggered star formation in interacting galaxies. These measurements provide strong constraints on galaxy evolution and halo occupation distribution models at z~1.
We perform a joint fit to differential number counts from Spitzer's MIPS and Herschel's SPIRE instruments, and angular power spectra of cosmic infrared background (CIB) anisotropies from SPIRE, Planck, the Atacama Cosmology Telescope, and the South Pole Telescope, which together span 220 < \nu / GHz < 4300 (70 < \lambda / \mu m < 1400). We simultaneously constrain the dust luminosity function, thermal dust spectral energy distribution (SED) and clustering properties of CIB sources, and the evolution of these quantities over cosmic time. We find that the data strongly require redshift evolution in the thermal dust SED. In our adopted parametrization, this evolution takes the form of an increase in graybody dust temperature at high redshift, but it may also be related to a temperature - dust luminosity correlation or evolution in dust opacity. The counts and spectra together constrain the evolution of the thermal dust luminosity function up to z ~ 2.5-3, complementing approaches relying on rest-frame mid-infrared observations of the rarest bright objects. We are able to fit the power spectra without requiring a complex halo model approach, and show that neglecting scale-dependent halo bias may be impairing analyses that do use this framework. Our model has considerable predictive power and can be used to calculate any one- or two-point statistic of the CIB over a wide range of frequency and angular scale.
On the basis of a new photometric analysis of the Local Group Dwarf Irregular Galaxy NCG 6822 based on observations obtained with Advanced Camera for Surveys on board of the the Hubble Space Telescope, we have obtained a new estimate of the extinction of two fields located in the southeast region of the galaxy. Due to the presence of significant differences in the distance estimates to NGC 6822 available in literature, we have decided to provide an independent determination of the distance to this galaxy based on an updated and self-consistent theoretical calibration of the tip of the Red Giant Branch (TRGB) brightness. As a result we have obtained a new determination of the distance to NGC 6822 equal to ${\rm(m-M)}_0=23.54\pm 0.05$, and compared our measurement with the most recent determinations of this distance.
Unveiling the nature of cosmic dark matter is an urgent issue in cosmology. Here we make use of a strategy based on the search for the imprints left on the CMB temperature and polarization spectra by the energy deposition due to annihilations of the most promising dark matter candidate, a stable WIMP of mass 1-20 GeV. A major improvement with respect to previous similar studies is a detailed treatment of the annihilation cascade and its energy deposition in the cosmic gas. This is vital as this quantity is degenerate with the annihilation cross-section <{\sigma}v>. The strongest constraints are obtained from Monte Carlo Markov Chains analysis of the combined WMAP7 and SPT datasets up to lmax = 3100. If annihilation occurs via the e+e- channel, a light WIMP can be excluded at 2-{\sigma} c.l. as a viable DM candidate in the above mass range. However, if annihilation occurs via {\mu}+{\mu}- or {\tau}+{\tau}- channels instead we find that WIMPs with mass > 5 GeV might represent a viable cosmological DM candidate. We compare the results obtained in the present work with those obtained adopting an analytical simplified model for the energy deposition process widely used in literature, and we found that realistic energy deposition descriptions can influence the resulting constrains up to 60%.
Aims. We present results of a comprehensive spectral study on the large-scale environment of AGNs based on Sloan Spectroscopic Survey data. Methods. We analyzed the spectra of galaxies in the environment of AGN and other activity classes up to distances of 1 Mpc. Results. The mean H{\alpha} and [OIII] {\lambda}5007 line luminosities in the environmental galaxies within a projected radius of 1 Mpc are highest around Seyfert 1 galaxies, with decreasing luminosities for Seyfert 2 and HII galaxies, and lowest for absorption line galaxies. Furthermore, there is a trend toward H{\alpha} and [OIII] luminosities in the environmental galaxies increasing as a function of proximity to the central emission line galaxies. There is another clear trend toward a neighborhood effect within a radius of 1000 kpc for the AGN and non-AGN types: Seyfert galaxies tend to have the highest probability of having another Seyfert galaxy in the neighborhood. HII galaxies tend to have the highest probability of having another HII galaxy in the neighborhood, etc. The number of companions within 1000 kpc is inversely correlated with the H{\alpha}, [OIII] {\lambda}5007, as well as with the continuum luminosities of the central galaxies, regardless of whether they are of Seyfert, HII, or absorption line types.
The dying radio sources represent a very interesting and largely unexplored stage of the active galactic nucleus (AGN) evolution. They are considered to be very rare, and almost all of the few known ones were found in galaxy clusters. However, considering the small number detected so far, it has not been possible to draw any firm conclusions about their X-ray environment. We present X-ray observations performed with the Chandra satellite of the three galaxy clusters Abell 2276, ZwCl 1829.3+6912, and RX J1852.1+5711, which harbor at their center a dying radio source with an ultra-steep spectrum that we recently discovered. We analyzed the physical properties of the X-ray emitting gas surrounding these elusive radio sources. We determined the global X-ray properties of the clusters, derived the azimuthally averaged profiles of metal abundance, gas temperature, density, and pressure. Furthermore, we estimated the total mass profiles. The large-scale X-ray emission is regular and spherical, suggesting a relaxed state for these systems. Indeed, we found that the three clusters are also characterized by significant enhancements in the metal abundance and declining temperature profiles toward the central region. For all these reasons, we classified RX J1852.1+5711, Abell 2276, and ZwCl 1829.3+6912 as cool-core galaxy clusters.
We examine the accuracy of the quasi-static approximation and a parametric form commonly employed for evolving linear perturbations in f(R) gravity theories and placing cosmological constraints. In particular, we analyze the nature and the importance of the near horizon effects that are often neglected. We find that for viable models, with a small present value of the scalaron field, such corrections are entirely negligible with no impact on observables. We also find that the one-parameter form, commonly used to represent the modified equations for linear perturbations in f(R), leads to theoretical systematic errors that are relatively small and, therefore, is adequate for placing constraint on f(R) models.
The OTELO project is the extragalactic survey currently under way using the tunable filters of the OSIRIS instrument at the GTC. OTELO is already providing the deepest emission line object survey of the universe up to a redshift 7. In this contribution, the status of the survey and the first results obtained are presented.
Primordial magnetic fields of cosmologically interesting field strengths can be generated from gravitationally coupled electrodynamics during inflation. As the cosmological constraints require this to be power law inflation it is not possible to generate at the same time the curvature perturbation from inflation. Therefore here a completion is considered whereby the large scale magnetic field is generated during inflation and the primordial curvature mode in a subsequent era from a curvaton field. It is found that constraints on the model to obtain strong magnetic fields and those to suppress the amplitude of the curvature perturbation generated during inflation can be simultaneously satisfied for magnetic seed fields $B_s\stackrel{>}{\sim}10^{-30}$ G.
We present observations of SDF-05M05, an unusual optical transient discovered in the Subaru Deep Field (SDF). The duration of the transient is > ~800 d in the observer frame, and the maximum brightness during observation reached approximately 23 mag in the i' and z' bands. The faint host galaxy is clearly identified in all 5 optical bands of the deep SDF images. The photometric redshift of the host yields z~0.6 and the corresponding absolute magnitude at maximum is ~-20. This implies that this event shone with an absolute magnitude brighter than -19 mag for approximately 300 d in the rest frame, which is significantly longer than a typical supernova and ultra-luminous supernova. The total radiated energy during our observation was 1x10^51 erg. The light curves and color evolution are marginally consistent with some of luminous IIn supernova. We suggest that the transient may be a unique and peculiar supernova at intermediate redshift.
We present a new method to identify and characterize the structure of the intracluster medium (ICM) in simulated galaxy clusters. The method uses the median of gas properties, such as density and pressure, which we show to be very robust to the presence of gas inhomogeneities. In particular, we show that the radial profiles of median gas properties are smooth and do not exhibit fluctuations at locations of massive clumps in contrast to mean and mode properties. It is shown that distribution of gas properties in a given radial shell can be well described by a log-normal PDF and a tail. The former corresponds to a nearly hydrostatic bulk component, accounting for ~99% of the volume, while the tail corresponds to high density inhomogeneities. We show that this results in a simple and robust separation of the diffuse and clumpy components of the ICM. The FWHM of the density distribution grows with radius and varies from ~0.15 dex in cluster centre to ~0.5 dex at 2r_500 in relaxed clusters. The small scatter in the width between relaxed clusters suggests that the degree of inhomogeneity is a robust characteristic of the ICM. It broadly agrees with the amplitude of density perturbations in the Coma cluster. We discuss the origin of ICM density variations in spherical shells and show that less than 20% of the width can be attributed to the triaxiality of the cluster gravitational potential. As a link to X-ray observations of real clusters we evaluated the ICM clumping factor with and without high density inhomogeneities. We argue that these two cases represent upper and lower limits on the departure of the observed X-ray emissivity from the median value. We find that the typical value of the clumping factor in the bulk component of relaxed clusters varies from ~1.1-1.2 at r_500 up to ~1.3-1.4 at r_200, in broad agreement with recent observations.
We derived a post-Newtonian (PN) inspiral only gravitational waveform for unequal mass, spinning black hole binaries. Towards the end of the inspiral the larger spin dominates over the orbital angular momentum (while the smaller spin is negligible), hence the name Spin-Dominated Waveforms (SDW). Such systems are common sources for future gravitational wave detectors and during the inspiral the largest amplitude waves are emitted exactly in its last part. The SDW waveforms emerge as a double expansion in the PN parameter and the ratio of the orbital angular momentum to the dominant spin.
Bose-Einstein condensate dark matter model and Randall-Sundrum type 2 brane-world theory are tested with galactic rotation curves. Analytical expressions are derived for the rotational velocities of test particles around the galactic center in both cases. The velocity profiles are fitted to the observed rotation curve data of high surface brightness and low surface brightness galaxies. The brane-world model fits better the rotation curves with asymptotically flat behaviour.
We consider an extension of the nuMSM in which sterile neutrino masses originate from the VEV of a Higgs singlet phi and dark matter is produced through the decays of phi rather than through active-sterile neutrino oscillations. This model, which we refer to as the nuNMSM, can readily satisfy constraints on warm dark matter from the Lyman-alpha forest. We show that the hierarchical parameters of the nuNMSM can arise from symmetries broken at or near the Planck scale for two specific models of the scalar sector: one in which phi stabilizes the electroweak vacuum and one in which phi is the inflaton. These models have several experimental signatures that are distinct from the nuMSM, including additional dark radiation that is relativistic at both primordial nucleosynthesis and CMB decoupling and, for the former, a large invisible branching ratio of the Higgs.
Random fields in nature often have, to a good approximation, Gaussian characteristics. We present the mathematical framework for a new and simple method for investigating the non-Gaussian contributions, based on counting the maxima and minima of a scalar field. We consider a random surface, whose height is given by a nonlinear function of a Gaussian field. We find that, as a result of the non-Gaussianity, the density of maxima and minima no longer match and calculate the relative imbalance between the two. Our approach allows to detect and quantify non-Gaussianities present in any random field that can be represented as the height of a smooth two-dimensional surface.
In this work we study rotation curves of spiral galaxies using a model of dark matter based on a scalar-tensor theory of gravity. We show how to estimate the scalar field dark matter parameters using a sample of observed rotation curves.
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