The talks are in the same order as the Program Schedule.
Brusa, Marcella - Stacking photons in deep and large X-ray surveys
Mathur, Smita - Demographics of black holes in nearby galaxies.
Gallo, Elena - AMUSE-Virgo: on the survival of super-massive black holes in faint spheroids
Sivakoff, Gregory - Searching for AGN in the Outskirts of Clusters
Marcella Brusa (Max Planck Institut fuer Extraterrestrische Physik (MPE - Garching), UMBC)
Using the stacking technique, it is possible to study, at least in a statistical sense, the X-ray properties of sources individually undetected even in the deepest observations and down to extremely faint fluxes. Given the very low background of the Chandra satellite, such a technique has been routinely adopted in Chandra works since the beginning of the mission, and successfully used in a variety of studies. Here we present an overview of a few selected results, focused on: 1) the average X-ray properties of the sources responsible for the XRB; 2) the detection of a sizable poulation of Compton Thick AGN at z 2; and 3) the study of the intensity and profile of the 6.4 keV iron line and its evolution with redshift. We also briefly outline the perspectives for these studies for the Chandra mission, and for other present and future X-ray facilities, in the framework of the deepest (Chandra Deep Fields) and largest (e.g. COSMOS) surveys.
Simonetta Puccetti (ASI Science Data Center (ASDC)-INAF) , on behalf of the C-Cosmos collaboration
The 1.8 Msec Chandra COSMOS Survey (C-COSMOS) is the largest Chandra GO program at the time of award. COSMOS is a pan-chromatic survey of the extragalactic sky designed to be both large and deep enough to study galaxy and quasar evolution in typical environments with minimal 'cosmic bias'. The location of COSMOS near the equator (10h +02deg) allows all major and future facilities (esp. EVLA, ALMA) to target this 2 sq. deg.region. Both space - HST, Spitzer, GALEX, XMM - and ground-based - VLA, Subaru, CTIO, KPNO, CFHT, Magellan, VLT - have already surveyed the area to faint limits. The central region of the COSMOS field observed in C-COSMOS is now the target of deeper surveys by the VLA and VLT, and proposed for GALEX and VISTA. We present the current status of the analysis of the C-COSMOS dataset. We focus on source detection and validation, which are complicated by the offset tiling structure of the survey. The 6x6 array of 50ksec observations gives a uniform 200ksec exposure, and a well-defined cut-off in flux. The depth of C-COSMOS was chosen to detect significant numbers of galaxies, up to z 0.9, comparable with the depth of the COSMOS galaxy surveys. About 2000 sources have been detected using both a wavelet algorithm and a PSF fitting algorithm. The present catalog includes about 100 sources with 0.5-2 keV flux smaller that 3E-16 cgs, one of the largest sample of faint X-ray sources so far. Particular care was put in the detection, validation and identification of sources with a separation <12" right down to the limit imposed by the Chandra PSF. This will allow us to put robust constraints on the X-ray source correlation function down to tens of kpc (for a typical z=1). Preliminary results on source number counts, cosmic variace and source clustering will be presented.
Smita Mathur (The Ohio State University) , Himel Ghosh (Ohio State)
The cumulative mass function needed to explain the energetics of high redshift quasars implies that all galaxies in the local universe should host supermassive black holes (SBHs). Low-mass SBHs, however, are impossible to detect dynamically because their sphere of influence cannot be resolved with current telescopes. On the other hand, the "downsizing" of AGN activity with cosmic epoch suggests that the lowest-mass SBHs should be active now, and therefore should be X-ray sources. Given the M_BH - M_Bulge relationship, we expect the low-mass SBHs to be in late-type spirals. We present results from a Chandra archival study - preliminary to an ongoing bigger Chandra survey - of six nearby "quiescent" spirals that shows that all six indeed harbor nuclear X-ray sources. We use available multiwavelength data to weigh the arguments for and against each object being in fact an accreting SBH. We show how X-ray observations are effective in uncovering hidden SBHs.
Elena Gallo (UCSB) , T. Treu, J.-H. Woo, J. Jacob, P. Marshall, R. Antonucci (UCSB)
I will present the first Chandra results from the AGN Multiwavelength Survey of Early-type galaxies in the Virgo cluster (AMUSE-Virgo). This large program targets 100 early-type Virgo galaxies with Chandra ACIS-S and Spitzer MIPS, with the aim to provide an unbiased census of super-massive black hole (SMBH) activity in the local universe. The sample covers over 4 orders of magnitude in black hole mass as estimated from the mass-velocity dispersion relation, large enough that it can be divided in SMBH mass bins to test whether the nuclear activity duty cycle is mass dependent. I will report on the Chandra observations of the first 16 targets, combined with results from archival data of other, more massive, 16 targets. Hard X-ray emission from a position coincident with the galaxy nucleus is detected in 50 per cent of the galaxies, and ascribed to low-level accretion-powered activity from a SMBH. Two of the detected nuclei are hosted in galaxies with absolute B magnitudes fainter than -18, indicating that SMBHs are still being harbored in such faint, low-mass objects.
Gregory Sivakoff (The Ohio State University) , Paul Martini (OSU), Daniel D. Kelson, John Mulchaey (Carnegie Observatories), Ann Zabludoff (Steward Observatories)
With the Chandra X-ray Observatory, it is possible to identify AGN down to low X-ray luminosities. While optical emission-line surveys of clusters of galaxies indicate a low fraction of AGN (1
Paul Martini (The Ohio State University) , G. Sivakoff (OSU), J. Mulchaey (OCIW), D. Kelson (OCIW)
We have studied the evolution of the AGN population in clusters of galaxies with spectroscopic observations of X-ray sources in archival Chandra data. Our low-redshift sample of eight z=0.06-0.3 clusters of galaxies contains only one AGN more luminous than 10^43 erg/s in the hard X-ray band, while in contrast there are eight AGN above this luminosity range in a sample of four clusters at z=0.6. This is strong evidence for a pronounced increase in the fraction of AGN in higher-redshift clusters of galaxies, analogous to the increase in the number of blue galaxies in clusters at higher redshift known as the Butcher-Oemler effect. The AGN evolution is clusters is also more rapid than observed for field AGN, which indicates differential evolution in the cluster AGN population relative to the field, and not merely a different normalization in the number of AGN per galaxy.