اشترك بالحزمة الذهبية واحصل على وصول غير محدود شمرا أكاديميا
تسجيل مستخدم جديدAGN Unification at z ~ 1: u - R Colors and Gradients in X-ray AGN Hosts
192
0
0.0
(
0
)
تأليف
S. Mark Ammons
اسأل ChatGPT حول البحث
ﻻ يوجد ملخص باللغة العربية
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.
قيم البحث
اقرأ أيضاً
Using data from the DEEP2 galaxy redshift survey and the All Wavelength Extended Groth Strip International Survey we obtain stacked X-ray maps of galaxies at 0.7 < z < 1.0 as a function of stellar mass. We compute the total X-ray counts of these gala
xies and show that in the soft band (0.5--2,kev) there exists a significant correlation between galaxy X-ray counts and stellar mass at these redshifts. The best-fit relation between X-ray counts and stellar mass can be characterized by a power law with a slope of 0.58 +/- 0.1. We do not find any correlation between stellar mass and X-ray luminosities in the hard (2--7,kev) and ultra-hard (4--7,kev) bands. The derived hardness ratios of our galaxies suggest that the X-ray emission is degenerate between two spectral models, namely point-like power-law emission and extended plasma emission in the interstellar medium. This is similar to what has been observed in low redshift galaxies. Using a simple spectral model where half of the emission comes from power-law sources and the other half from the extended hot halo we derive the X-ray luminosities of our galaxies. The soft X-ray luminosities of our galaxies lie in the range 10^39-8x10^40, ergs/s. Dividing our galaxy sample by the criteria U-B > 1, we find no evidence that our results for X-ray scaling relations depend on optical color.
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 (AEG
IS). 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 study of Spitzer/IRAC and X-ray active galactic nuclei (AGNs) selection techniques in order to quantify the overlap, uniqueness, contamination, and completeness of each. We investigate how the overlap and possible contamination of the sa
mples depends on the IR and X-ray depths. We use Spitzer/IRAC imaging, Chandra and XMM X-ray imaging, and PRism MUlti-object Survey (PRIMUS) spectroscopic redshifts to construct galaxy and AGN samples at 0.2<z<1.2 over 8 deg^2. We construct samples over a wide range of IRAC flux limits (SWIRE to GOODS depth) and X-ray flux limits (10 ks to 2 Ms). We compare IR-AGN samples defined using the IRAC color selection of Stern et al. and Donley et al. with X-ray detected AGN samples. For roughly similar depth IR and X-ray surveys, we find that ~75% of IR-AGN are identified as X-ray AGN. This fraction increases to ~90% when comparing against the deepest X-ray data, indicating that only ~10% of IR-selected AGN may be heavily obscured. The IR-AGN selection proposed by Stern et al. suffers from contamination by star-forming galaxies at various redshifts when using deeper IR data, though the selection technique works well for shallow IR data. While similar overall, the IR-AGN samples preferentially contain more luminous AGN, while the X-ray AGN samples preferentially contain lower specific accretion rate AGN, where the host galaxy light dominates at IR wavelengths. The host galaxy populations of the IR and X-ray AGN samples have similar restframe colors and stellar masses; both selections identify AGN in blue, star-forming and red, quiescent galaxies.
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 c
ross-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.
We present a photometric and spectroscopic study of galaxies at 0.5<z<1 as a function of environment based on data from the zCOSMOS survey. There is a fair amount of evidence that galaxy properties depend on mass of groups and clusters, in the sense
that quiescent galaxies prefer more massive systems. We base our analysis on a mass-selected environment using X-ray groups of galaxies and define the group membership using a large number of spectroscopic redshifts from zCOSMOS. We show that the fraction of red galaxies is higher in groups than in the field at all redshifts probed in our study. Interestingly, the fraction of [OII] emitters on the red sequence increases at higher redshifts in groups, while the fraction does not strongly evolve in the field. This is due to increased dusty star formation activities and/or increased activities of active galactic nuclei (AGNs) in high redshift groups. We study these possibilities using the 30-band photometry and X-ray data. We find that the stellar population of the red [OII] emitters in groups is old and there is no clear hint of dusty star formation activities in those galaxies. The observed increase of red [OII] emitters in groups is likely due to increased AGN activities. However, our overall statistics is poor and any firm conclusions need to be drawn from a larger statistical sample of z~1 groups.
سجل دخول لتتمكن من نشر تعليقات
التعليقات
جاري جلب التعليقات
سجل دخول لتتمكن من متابعة معايير البحث التي قمت باختيارها
