M. Paolillo

Agn host galaxies at z ∼ 0.4-1.3 : Bulge-dominated and lacking merger-agn connection

We investigate morphological structure parameters and local environments of distant moderate-luminosity active galactic nucleus (AGN) host galaxies in the overlap between the HST/ACS observations of the Great Observatories Origins Deep Survey (GOODS) and the two Chandra Deep Fields. We compute near-neighbor counts and BViz asymmetry (A) and concentration (C) indices for ≈35,500 GOODS/ACS galaxies complete to , including z850 ≈ 26.6 the resolved hosts of 322 X-ray–selected AGNs. Distributions of (1) asymmetry for 130 AGN hosts z z 850 850 ! 23 and (2) near-neighbor counts for 173 AGN hosts are both consistent with non-AGN control samples. z850 ! 24 This implies no close connection between recent galaxy mergers and moderate-luminosity AGN activity out to appreciable look-back times ( ), approaching the epoch of peak AGN activity in the universe. The distri- z 1.3 bution of z850 C for the AGN hosts is offset by compared to the non-AGN, a 6.4 DC ≈ 0.5 j discrepancy much larger than can be explained by the possible influence of unresolved emission from the AGN or a circumnuclear starburst. The local universe association between AGN and bulge-dominated galaxies thus persists to substantial look-back time. We discuss implications in the context of the low-redshift supermassive central black hole mass correlation with host galaxy properties, including concentration.

THE 4 Ms CHANDRA DEEP FIELD-SOUTH NUMBER COUNTS APPORTIONED BY SOURCE CLASS: PERVASIVE ACTIVE GALACTIC NUCLEI AND THE ASCENT OF NORMAL GALAXIES

This article presents cumulative and differential number-count measurements for the recently completed 4 Ms Chandra Deep Field-South survey.

High-Redshift Extremely Red Objects in the Hubble Space Telescope Ultra Deep Field Revealed by the GOODS Infrared Array Camera Observations

Using early data from the Infrared Array Camera (IRAC) on the Spitzer Space Telescope, taken for the Great Observatories Origins Deep Survey (GOODS), we identify and study objects that are well detected at 3.6 μm but are very faint (and in some cases, invisible) in the Hubble Ultra Deep Field (HUDF) ACS and NICMOS images and in very deep VLT Ks-band imaging. We select a sample of 17 objects with fν(3.6 μm)/fν(z850) > 20. The analysis of their spectral energy distributions (SEDs) from 0.4 to 8.0 μm shows that the majority of these objects cannot be satisfactorily explained without a well-evolved stellar population. We find that most of them can be well fitted by a simple two-component model, where the primary component represents a massive, old population that dominates the strong IR emission, while the secondary component represents a low-amplitude, on-going star formation process that accounts for the weak optical fluxes. Their estimated photometric redshifts (zp) range from 1.6 to 2.9 with the median at zp = 2.4. For the simple star formation histories considered here, their corresponding stellar masses range from (0.1-1.6)×1011 M☉ for a Chabrier initial mass function (IMF). Their median rest-frame Ks-band absolute magnitude is -22.9 mag in the AB system, or 1.5 × L*(K) for present-day elliptical galaxies. In the scenario of pure luminosity evolution, such objects may be direct progenitors for at least 14%-51% of the local population of early type galaxies. Because of the small cosmic volume of the HUDF, however, this simple estimate could be affected by other effects, such as cosmic variance and the strong clustering of massive galaxies. A full analysis of the entire GOODS area is now under way to assess such effects.

The XMM Deep survey in the CDF-S

We present the first results of the spectroscopy of distant, o bscured AGN as obtained with the ultra‐deep (�3.3 Ms) XMM‐Newton survey in the Chandra Deep Field South (CDF‐S). One of the primary goals of the project is to characterize the X‐ray spectral properties of obscured and heavily obscured Compton‐thick AGN over the range of redhifts and luminosities that are relevant in terms of their contribution to the X‐ray background. The ultra‐deep exposure, coupled with the XMM detector’s spectral throughput, allowed us to accumulate good quality X‐ray spectra for a large number of X‐ray sources and, in particular, for heavily obscured AGN at cosmological redshifts. Specifically we present the X ‐ray spectral properties of two high‐redshift ‐ z= 1.53 and z=3.70 ‐

The XMM Deep survey in the CDF-S - I. First results on heavily obscured AGN

We present the first results of the spectroscopy of distant, o bscured AGN as obtained with the ultra‐deep (�3.3 Ms) XMM‐Newton survey in the Chandra Deep Field South (CDF‐S). One of the primary goals of the project is to characterize the X‐ray spectral properties of obscured and heavily obscured Compton‐thick AGN over the range of redhifts and luminosities that are relevant in terms of their contribution to the X‐ray background. The ultra‐deep exposure, coupled with the XMM detector’s spectral throughput, allowed us to accumulate good quality X‐ray spectra for a large number of X‐ray sources and, in particular, for heavily obscured AGN at cosmological redshifts. Specifically we present the X ‐ray spectral properties of two high‐redshift ‐ z= 1.53 and z=3.70 ‐

PREVALENCE OF X-RAY VARIABILITY IN THE CHANDRA DEEP FIELD-SOUTH

We studied the X-ray variability of sources detected in the Chandra Deep Field-South, nearly all of which are low- to moderate-z active galactic nuclei (AGNs). We find that 45% of the sources with more than 100 counts exhibit significant variability on timescales ranging from a day up to a year. The fraction of sources found to be variable increases with observed flux, suggesting that more than 90% of all AGNs possess intrinsic variability. We also find that the fraction of variable sources appears to decrease with increasing intrinsic absorption; a lack of variability in hard, absorbed AGNs could be due to an increased contribution of reflected X-rays to the total flux. We do not detect significant spectral variability (ΔΓ > 0.2) in the majority (~70%) of our sources. In half of the remaining 30%, the hardness ratio is anticorrelated with flux, mimicking the high/soft-low/hard states of galactic sources. The X-ray variability appears anticorrelated with the luminosity of the sources, in agreement with previous studies. High-redshift sources, however, have larger variability amplitudes than expected from extrapolations of their low-z counterparts, suggesting a possible evolution in the accretion rate and/or size of the X-ray-emitting region. Finally, we discuss some effects that may produce the observed decrease in the fraction of variable sources from z = 0.5 out to z = 2.

Luminosity function of clusters of galaxies

The composite galaxy luminosity function (hereafter LF) of 39 Abell clusters of galaxies is derived by computing the statistical excess of galaxy counts in the cluster direction with respect to control elds. Due to the wide eld coverage of the digitised POSS-II plates, we can measure eld counts around each cluster in a fully homogeneous way. Furthermore, the availability of virtually unlimited sky coverage allows us to directly compute the LF errors without having to rely on the estimated variance of the background. The wide eld coverage also allows us to derive the LF of the whole cluster, including galaxies located in the cluster outskirts. The global composite LF has a slope 1:1 0:2 with minor variations from blue to red lters, and M 21:7; 22:2; 22: 4m ag (H0 =5 0 km s 1 Mpc 1 )i ng;r and i lters, respectively (errors are detailed in the text). These results are in quite good agreement with several previous determinations and in particular with the LF determined for the inner region of a largely overlapping set of clusters, but derived making use of a completely dierent method for background subtraction. The similarity of the two LFs suggests the existence of minor dierences between the LF in the cluster outskirts and in the central region, or a negligible contribution of galaxies in the cluster outskirts to the global LF.

X-RAY SPECTRAL CONSTRAINTS FOR z ≈ 2 MASSIVE GALAXIES: THE IDENTIFICATION OF REFLECTION-DOMINATED ACTIVE GALACTIC NUCLEI

We use the 4Ms CDF-S survey to place direct X-ray constraints on the ubiquity of z~2 heavily obscured AGNs in K 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.

VARIABILITY-SELECTED LOW-LUMINOSITY ACTIVE GALACTIC NUCLEI IN THE 4 Ms CHANDRA DEEP FIELD-SOUTH

The 4 Ms Chandra Deep Field-South (CDF-S) and other deep X-ray surveys have been highly effective at selecting active galactic nuclei (AGNs). However, cosmologically distant low-luminosity AGNs (LLAGNs) have remained a challenge to identify due to significant contribution from the host galaxy. We identify long-term X-ray variability (~month-years, observed frame) in 20 of 92 CDF-S galaxies spanning redshifts z ≈ 0.08-1.02 that do not meet other AGN selection criteria. We show that the observed variability cannot be explained by X-ray binary populations or ultraluminous X-ray sources, so the variability is most likely caused by accretion onto a supermassive black hole (SMBH). The variable galaxies are not heavily obscured in general, with a stacked effective power-law photon index of Γstack ≈ 1.93 ± 0.13, and are therefore likely LLAGNs. The LLAGNs tend to lie a factor of ≈6-80 below the extrapolated linear variability-luminosity relation measured for luminous AGNs. This may be explained by their lower accretion rates. Variability-independent black hole mass and accretion-rate estimates for variable galaxies show that they sample a significantly different black hole mass-accretion-rate space, with masses a factor of 2.4 lower and accretion rates a factor of 22.5 lower than variable luminous AGNs at the same redshift. We find that an empirical model based on a universal broken power-law power spectral density function, where the break frequency depends on SMBH mass and accretion rate, roughly reproduces the shape, but not the normalization, of the variability-luminosity trends measured for variable galaxies and more luminous AGNs.

UNVEILING A RICH SYSTEM OF FAINT DWARF GALAXIES IN THE NEXT GENERATION FORNAX SURVEY

We report the discovery of 158 previously undetected dwarf galaxies in the Fornax cluster central regions using a deep coadded