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Register a new userX-ray Surface Brightness Profiles of Active Galactic Nuclei in the Extended Groth Strip: Implications for AGN Feedback
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Suchetana Chatterjee
Publication date
2013
fields
Physics
and research's language is
English
Authors
Suchetana Chatterjee
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Using data from the All Wavelength Extended Groth Strip International Survey (AEGIS) we statistically detect the extended X-ray emission in the interstellar medium (ISM)/intra-cluster medium (ICM) in both active and normal galaxies at 0.3 <= z <= 1.3. For both active galactic nuclei (AGN) host galaxy and normal galaxy samples that are matched in restframe color, luminosity, and redshift distribution, we tentatively detect excess X-ray emission at scales of 1--10 arcsec at a few sigma significance in the surface brightness profiles. The exact significance of this detection is sensitive to the true characterization of Chandras point spread function. The observed excess in the surface brightness profiles is suggestive of lower extended emission in AGN hosts compared to normal galaxies. This is qualitatively similar to theoretical predictions of the X-ray surface brightness profile from AGN feedback models, where feedback from AGN is likely to evacuate the gas from the center of the galaxy/cluster. We propose that AGN that are intrinsically under-luminous in X-rays, but have equivalent bolometric luminosities to our sources will be the ideal sample to study more robustly the effect of AGN feedback on diffuse ISM/ICM gas.
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We use data from the All Wavelength Extended Groth Strip International Survey to construct stacked X-ray maps of optically bright active galaxies (AGN) and an associated control sample of galaxies at high redshift (z less than 0.6). From our analysis of the surface brightness profiles obtained from these X-ray maps, we find evidence of feedback from the active nuclei. We find that excluding galaxies and AGN, residing in group environments, from our samples enhances the significance of our detection. Our results support the tentative findings of Chatterjee et al. who use X-ray selected AGN for their analysis. We discuss the implications of these results in the context of quantifying AGN feedback and show that the current method can be used to extract X-ray source population in high redshift galaxies.
Recent time-resolved spectral studies of a few Active Galactic Nuclei in hard X-rays revealed occultations of the X-ray primary source probably by Broad Line Region (BLR) clouds. An important open question on the structure of the circumnuclear medium of AGN is whether this phenomenon is common, i.e. whether a significant fraction of the X-ray absorption in AGN is due to BLR clouds. Here we present the first attempt to perform this kind of analysis in a homogeneous way, on a statistically representative sample of AGN, consisting of the ~40 brightest sources with long XMM-Newton and/or Suzaku observations. We describe our method, based on a simple analysis of hardness-ratio light curves, and its validation through a complete spectroscopic analysis of a few cases. We find that X-ray eclipses, most probably due to clouds at the distance of the BLR, are common in sources where the expected occultation time is compatible with the observation time, while they are not found in sources with longer estimated occultation times. Overall, our results show that occultations by BLR clouds may be responsible for most of the observed X-ray spectral variability at energies higher than 2 keV, on time scales longer than a few ks.
We present $ugR$ optical images taken with the MMT/Megacam and the Subaru/Suprime of the Extended Groth Strip survey. The total survey covers an area of about $sim 1$ degree$^2$, including four sub-fields and is optimized for the study of galaxies at $zsim3$. Our methods for photometric calibration in AB magnitudes, the limiting magnitude and the galaxy number count are described. A sample of 1642 photometrically selected candidate LBGs to an apparent $R_{AB}$ magnitude limit of 25.0 is present. The average sky surface density of our LBGs sample is $sim$ 1.0 arcmin$^{-2}$, slightly higher than the previous finding.
We investigate galactic-scale outflowing winds in 72 star-forming galaxies at z~1 in the Extended Groth Strip. Galaxies were selected from the DEEP2 survey and follow-up LRIS spectroscopy was obtained covering SiII, CIV, FeII, MgII, and MgI lines in the rest-frame ultraviolet. Using GALEX, HST, and Spitzer imaging, we examine galaxies on a per-object basis in order to understand both the prevalence of galactic winds at z~1 and the star-forming and structural properties of objects experiencing outflows. Gas velocities, measured from the centroids of FeII interstellar absorption lines, span the interval [-217, +155] km/s. We find that ~40% (10%) of the sample exhibits blueshifted FeII lines at the 1-sigma (3-sigma) level. We also measure maximal outflow velocities using the profiles of the FeII and MgII lines, and show that MgII frequently traces higher velocity gas than FeII. Quantitative morphological parameters derived from the HST imaging suggest that mergers are not a prerequisite for driving outflows. More face-on galaxies also show stronger winds than highly-inclined systems, consistent with the canonical picture of winds emanating perpendicular to galactic disks. Using star-formation rates calculated from GALEX data, and areas estimated from HST imaging, we detect a ~3-sigma correlation between outflow velocity and star-formation rate surface density, but only a weak (~1-sigma) trend between outflow velocity and star-formation rate. Higher resolution data are needed in order to test the scaling relations between outflow velocity and both star-formation rate and star-formation rate surface density predicted by theory.
We use the 4Ms CDF-S survey to place direct X-ray constraints on the ubiquity of z~2 heavily obscured AGNs in K<22 BzK galaxies. Forty seven of the 222 BzK galaxies in the central region of the CDF-S are detected at X-ray energies, 11 of which have hard X-ray spectral slopes (Gamma<1) indicating the presence of heavily obscured AGN activity. The other 36 X-ray detected BzK galaxies appear to be relatively unobscured AGNs and starburst galaxies; we use X-ray variability analyses over a rest-frame baseline of ~3 years to further confirm the presence of AGN activity in many of these systems. The majority (7 out of 11) of the heavily obscured AGNs have excess IR emission over that expected from star formation (termed IR-excess galaxies). However, we find that X-ray detected heavily obscured AGNs only comprise ~25% of the IR-excess galaxy population, which is otherwise composed of relatively unobscured AGNs and starburst galaxies. We find that the typical X-ray spectrum of the heavily obscured AGNs is better characterized by a pure reflection model than an absorbed power-law model, suggesting extreme Compton-thick absorption in some systems. We verify this result by producing a composite rest-frame 2-20 keV spectrum, which has a similar shape as a reflection-dominated X-ray spectrum and reveals an emission feature at rest-frame energy ~6.4 keV, likely to be due to Fe K. These heavily obscured AGNs are likely to be the distant analogs of the reflection-dominated AGNs recently identified at z~0 with >10 keV observatories. On the basis of these analyses we estimate the space density for typical (intrinsic X-ray luminosities of L_X>1E43 erg/s) heavily obscured and Compton-thick AGNs at z~2. Our space-density constraints are conservative lower limits but they are already consistent with the range of predictions from X-ray background models.
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