Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userMeasuring the Dark Matter Halo Mass of X-ray AGN at z~1 using photometric redshifts
142
0
0.0
(
0
)
Added by
Georgios Mountrichas
Publication date
2012
fields
Physics
and research's language is
English
Ask ChatGPT about the research
No Arabic abstract
Data from the AEGIS, COSMOS and ECDFS surveys are combined to infer the bias and dark matter halo mass of moderate luminosity [LX(2-10 keV) = 42.9 erg s-1] X-ray AGN at z~1 via their cross-correlation function with galaxies. In contrast to standard cross-correlation function estimators, we present a method that requires spectroscopy only for the AGN and uses photometric redshift probability distribution functions for galaxies to determine the projected real-space AGN/galaxy cross-correlation function. The estimated dark matter halo mass of X-ray AGN in the combined AEGIS, COSMOS and ECDFS fields is ~13h-1M_solar, in agreement with previous studies at similar redshift and luminosity ranges. Removing from the sample the 5 per cent of the AGN associated with X-ray selected groups results in a reduction by about 0.5 dex in the inferred AGN dark matter halo mass. The distribution of AGN in dark matter halo mass is therefore skewed and the bulk of the population lives in moderate mass haloes. This result favour cold gas accretion as the main channel of supermassive black hole growth for most X-ray AGN.
rate research
Read More
We present evidence that AGN do not reside in ``special environments, but instead show large-scale clustering determined by the properties of their host galaxies. Our study is based on an angular cross-correlation analysis applied to X-ray selected AGN in the COSMOS and UDS fields, spanning redshifts from $zsim4.5$ to $zsim0.5$. Consistent with previous studies, we find that AGN at all epochs are on average hosted by galaxies in dark matter halos of $10^{12}-10^{13}$ M$_{odot}$, intermediate between star-forming and passive galaxies. We find, however, that the same clustering signal can be produced by inactive (i.e. non-AGN) galaxies closely matched to the AGN in spectral class, stellar mass and redshift. We therefore argue that the inferred bias for AGN lies in between the star-forming and passive galaxy populations because AGN host galaxies are comprised of a mixture of the two populations. Although AGN hosted by higher mass galaxies are more clustered than lower mass galaxies, this stellar mass dependence disappears when passive host galaxies are removed. The strength of clustering is also largely independent of AGN X-ray luminosity. We conclude that the most important property that determines the clustering in a given AGN population is the fraction of passive host galaxies. We also infer that AGN luminosity is likely not driven by environmental triggering, and further hypothesise that AGN may be a stochastic phenomenon without a strong dependence on environment.
We combine multiwavelength data in the AEGIS-XD and C-COSMOS surveys to measure the typical dark matter halo mass of X-ray selected AGN [Lx(2-10keV)>1e42 erg/s] in comparison with far-infrared selected star-forming galaxies detected in the Herschel/PEP survey (PACS Evolutionary Probe; Lir>1e11 solar) and quiescent systems at z~1. We develop a novel method to measure the clustering of extragalactic populations that uses photometric redshift Probability Distribution Functions in addition to any spectroscopy. This is advantageous in that all sources in the sample are used in the clustering analysis, not just the subset with secure spectroscopy. The method works best for large samples. The loss of accuracy because of the lack of spectroscopy is balanced by increasing the number of sources used to measure the clustering. We find that X-ray AGN, far-infrared selected star-forming galaxies and passive systems in the redshift interval 0.6<z<1.4 are found in halos of similar mass, $log M_{DMH}/(M_{odot},h^{-1})approx13.0$. We argue that this is because the galaxies in all three samples (AGN, star-forming, passive) have similar stellar mass distributions, approximated by the J-band luminosity. Therefore all galaxies that can potentially host X-ray AGN, because they have stellar masses in the appropriate range, live in dark matter haloes of $log M_{DMH}/(M_{odot},h^{-1})approx13.0$ independent of their star-formation rates. This suggests that the stellar mass of X-ray AGN hosts is driving the observed clustering properties of this population. We also speculate that trends between AGN properties (e.g. luminosity, level of obscuration) and large scale environment may be related to differences in the stellar mass of the host galaxies.
We explore the role of the group environment in the evolution of AGN at the redshift interval 0.7<z<1.4, by combining deep Chandra observations with extensive optical spectroscopy from the All-wavelength Extended Groth strip International Survey (AEGIS). The sample consists of 3902 optical sources and 71 X-ray AGN. Compared to the overall optically selected galaxy population, X-ray AGN are more frequently found in groups at the 99% confidence level. This is partly because AGN are hosted by red luminous galaxies, which are known to reside, on average, in dense environments. Relative to these sources, the excess of X-ray AGN in groups is significant at the 91% level only. Restricting the sample to 0.7<z<0.9 and M_B<-20mag in order to control systematics we find that X-ray AGN represent (4.7pm1.6) and (4.5pm1.0)% of the optical galaxy population in groups and in the field respectively. These numbers are consistent with the AGN fraction in low redshift clusters, groups and the field. The results above, although affected by small number statistics, suggest that X-ray AGN are spread over a range of environments, from groups to the field, once the properties of their hosts (e.g. colour, luminosity) are accounted for. There is also tentative evidence, significant at the 98% level, that the field produces more X-ray luminous AGN compared to groups, extending similar results at low redshift to z~1. This trend may be because of either cold gas availability or the nature of the interactions occurring in the denser group environment (i.e. prolonged tidal encounters).
We present a new cosmological probe for galaxy clusters, the halo sparsity. This characterises halos in terms of the ratio of halo masses measured at two different radii and carries cosmological information encoded in the halo mass profile. Building upon the work of Balmes et al. (2014) we test the properties of the sparsity using halo catalogs from a numerical N-body simulation of ($2.6$ Gpc/h)$^3$ volume with $4096^3$ particles. We show that at a given redshift the average sparsity can be predicted from prior knowledge of the halo mass function. This provides a quantitative framework to infer cosmological parameter constraints using measurements of the sparsity of galaxy clusters. We show this point by performing a likelihood analysis of synthetic datasets with no systematics, from which we recover the input fiducial cosmology. We also perform a preliminary analysis of potential systematic errors and provide an estimate of the impact of baryonic effects on sparsity measurements. We evaluate the sparsity for a sample of 104 clusters with hydrostatic masses from X-ray observations and derive constraints on the cosmic matter density $Omega_m$ and the normalisation amplitude of density fluctuations at the $8$ Mpc h$^{-1}$ scale, $sigma_8$. Assuming no systematics, we find $Omega_m=0.42pm 0.17$ and $sigma_8=0.80pm 0.31$ at $1sigma$, corresponding to $S_8equiv sigma_8sqrt{Omega_m}=0.48pm 0.11$. Future cluster surveys may provide opportunities for precise measurements of the sparsity. A sample of a few hundreds clusters with mass estimate errors at a few percent level can provide competitive cosmological parameter constraints complementary to those inferred from other cosmic probes.
We present uncontaminated rest-frame u - R colors of 78 X-ray-selected AGN hosts at 0.5 < z < 1.5 in the Chandra Deep Fields measured with HST/ACS/NICMOS and VLT/ISAAC imaging. We also present spatially-resolved NUV - R color gradients for a subsample of AGN hosts imaged by HST/WFC3. Integrated, uncorrected photometry is not reliable for comparing the mean properties of soft and hard AGN host galaxies at z ~ 1 due to color contamination from point-source AGN emission. We use a cloning simulation to develop a calibration between concentration and this color contamination and use this to correct host galaxy colors. The mean u - R color of the unobscured/soft hosts beyond ~6 kpc is statistically equivalent to that of the obscured/hard hosts (the soft sources are 0.09 +/- 0.16 magnitudes bluer). Furthermore, the rest-frame V - J colors of the obscured and unobscured hosts beyond ~6 kpc are statistically equivalent, suggesting that the two populations have similar distributions of dust extinction. For the WFC3/IR sample, the mean NUV - R color gradients of unobscured and obscured sources differ by less than ~0.5 magnitudes for r > 1.1 kpc. These three observations imply that AGN obscuration is uncorrelated with the star formation rate beyond ~1 kpc. These observations favor a unification scenario for intermediate-luminosity AGNs in which obscuration is determined geometrically. Scenarios in which the majority of intermediate-luminosity AGN at z ~ 1 are undergoing rapid, galaxy-wide quenching due to AGN-driven feedback processes are disfavored.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
