Chandra's First Decade of Discovery

AGN Evolution

BH activity and star formation at z+0.6-4 in the CDFS

Marcella Brusa, MPE/Garching & UMBC
Fiore F. (INAF -OARoma)

The co-evolution of host galaxies and the active black holes which reside in their centre is one of the most important topics in modern observational cosmology. Here we present a study of the properties of obscured Active Galactic Nuclei (AGN) detected in the CDFS 1Ms Chandra observation and their host galaxies. We found that X-ray selected (LX>1042 erg/s) AGN show Spitzer colors consistent with both AGN and starburst dominated infrared continuum; the latter would not have been selected as AGN from infrared diagnostics. The host galaxies of X-ray selected obscured AGN are all massive (M*>1010 Msun) and, in 50% of the cases, are also actively forming stars (1/SSFR<tHubble) in dusty environments. The median L/LEdd value of the active nucleus is between 3% and 10% depending on the assumed MBH/M* ratio. Finally, we found that the X-ray selected AGN fraction increases with the stellar mass up to a value of ~30% at z>1 and M*>3 x 1011 Msun, a fraction significantly higher than in the local Universe for AGN of similar luminosities.

Finding Goodies in the COSMOS survey

Francesca Civano, SAO
Elvis M. (SAO), Lanzuisi G. (SAO, Rome University) and COSMOS team

We present the discovery in the Chandra COSMOS survey of the only clear double nucleus detected at substantial redshift (z=0.359) and the only one (out of ~2600 X-ray sources) to have an unprecedented broad redshifted absorption and emission iron lines, drawing a kind of inverted P-Cygni profile in its X-ray spectrum. That these two unique features occur in the same source is unlikely to be a co-incidence. The two nuclei, 2.5 kpc apart, are likely to be a Type 1 and a Type 2 AGN from X-ray (Chandra and XMM-Newton) and optical(HST/ACS and VLT/Vimos) imaging and spectroscopic analysis. The broadening of the redshifted absorption iron line is the result of the superimposition of narrow lines redshifted by different velocities in 5 years of XMM and Chandra observations. This z=0.359 merger may broadening our view on the AGN-mergers connection. An intriguing explanation of the system, a “Backlit wind”, is that we are looking through a BAL-like outflow from the nearer nucleus (the type 2) at the rear nucleus(the Type 1), giving us a truly “new angle” on AGN outflows and so on “feedback”.

Optimized UV and X-ray Background Source Samples for WHIM Detection

Maria Laura Conciatore, SAO
F. Nicastro (SAO/FORTH), M. Elvis (SAO), S. Mathur (Ohio State University), Y. Krongold (IA-UNAM)

Cosmological simulations imply that 50% of the baryonic matter in the Local Universe (z≤0.5) resides in a filamentary Warm-Hot Intergalactic Medium (WHIM). The WHIM filaments are intrinsically difficult to detect. The search for observational evidence for the WHIM has only produced statistically limited and/or highly controversial results. The most promising approach to detect and study the WHIM is to search for absorption features from the WHIM in both X-ray and Far UV in the spectra of bright background AGNs. However, extremely long observations with major observatories (Hubble, Chandra, XMM) are required. This investment requires that target selection be carefully optimized. Here we present the results of a search for optimal targets in the UV and X-ray bands. We establish that there is one extremely bright target and a smaller sample of 17 sources practical to use for WHIM studies with current X-ray and FUV spectrographs and deeper WHIM studies with future X-ray facilities (IXO, Pharos).


Heng Hao, SAO
Martin Elvis (SAO), Francesca Civano (SAO)

A detailed study of the evolution of the Spectral Energy Distribution (SED) shapes near 1μm of 324 Type 1 AGNs in the wide-field “Cosmological Evolution Survey” (COSMOS) as a function of luminosity, redshift and Eddington ratio is presented. We study the mean SEDs in redshift bins and bolometric luminosity bins and compare them with Elvis et al. 1994 Type 1 AGN mean SED (E94). We also study the position of our sources in the slope plot relative to the quasar-host galaxy mixing curve and dust reddening curve. We found that E94 is remarkably good in describing the SED shape near 1μm even for high luminosity, redshift and Eddington ratio Type 1 AGNs. We also show examples of some outliers which might be AGNs in different evolution stages compared to normal AGNs.

The Chandra 3C Snapshot Survey for Sources with z<0.3

D. E. Harris, SAO
F. Massaro (SAO), D. Axon (RIT), S. A. Baum (RIT), A. Capetti (INAF), M. Chiaberge (STScI), R. Gilli (INAF), G. Giovannini (INAF), P. Grandi (INAF-IASF), F. D. Macchetto (STScI), C. P. O'Dea (RIT), G. Risaliti (INAF), and W. Sparks (STScI)

We report on our Chandra Cycle 9 program to observe half of the 60 (as yet) unobserved 3C radio sources at z<0.3 for 8 ksec each. We compare the Chandra observations with VLA radio maps and HST data to search for extended emission from jets and hot spots. A comparison of X-ray flux maps in different energy bands provides photometry, an estimate of intrinsic absorption of nuclear emission and information on the emission of extended regions: diffuse emission around the nucleus, jets, and hot spots. We have found X-ray counterparts to 5radio hot spots; 2 knots in the curved jet of 3C17; and X-ray nuclear emission from all the radio galaxies in our sample with only one exception. Included in our sample are 3 Compact Steep Spectrum (CSS) radio galaxies and in one of these we studied the extended X-ray emission spatially associated with the optical emission line region. The work at SAO is supported by NASA grant GO8-9114A.

Optically Obscured Accretion in z 0.5 Galaxies

Ryan Hickox, Harvard-Smithsonian Center for Astrophysics
Roberto Assef, Christopher Kochanek (Ohio State), Stephen Murray, Christine Jones, William Forman (SAO), and the XBootes, AGES, NDWFS, IRAC Shallow Survey, Bootes/MIPS, and FLAMEX Teams

We explore the accretion modes and galaxy properties of X-ray AGN at 0.25 < z < 0.8 that show weak or absent optical signatures (XBONGs), using data from the Bootes 9 deg2 multiwavelength survey. We derive the average spatial clustering, X-ray spectra, and UV-optical-IR SEDs of these objects as a function of host galaxy parameters. We find evidence for a significant population of highly absorbed X-ray AGN in luminous, strongly clustered galaxies with relatively old stellar populations. These objects may represent a “maintenance” phase of X-ray bright accretion that helps prevent star formation in massive red galaxies, as predicted by some galaxy evolution models.

The X-ray properties of Type II Quasars from the Sloan Digital Sky Survey

Jianjun Jia, Johns Hopkins University
Andrew Ptak (JHU), Stephanie LaMassa (JHU), Timothy Heckman (JHU)

65 Type II quasars were found to be covered by Chandra (35) and XMM-Newton (32) archival observations by correlating with the largest catalog of Type II quasars to date selected from Sloan Digital Sky Survey (SDSS). We studied the X-ray properties of these Type II quasars systematically and statistically, and spectra were fitted to characterize the spectral properties of each source. We find that the mean of the column density and photon index of our sample are NH = 1.78E23 cm-2 and γ = 1.79. Our sample are selected from their bright [OIII]5007 optical emission lines, which are formed in the Narrow Line Region (NLR) far away from the central engine. Unlike the X-ray emission, the [OIII] line is typically only moderately affected by the obscuration, and could be used as an indicator of the intrinsic AGN luminosity. The ratio of hard X-ray to [OIII] luminosity shows that the majority of our sample are significantly obscured, and approximately half of the sources are underestimated in the absorbing column density by the power-law continuum model spectral fitting. We thus run a simulation of a more physically realistic model which accounts for the partial covering and Compton scattering to predict the true columns, and the result is consistent with the data. In addition to the “traditional” spectral analysis, we also performed the Markov Chain Monte Carlo (MCMC) simulations to check the consistency of our spectral fits.

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SED and Emission Line Properties of Red 2MASS AGN

Joanna Kuraszkiewicz, Harvard-Smithsonian Center for Astrophysics
Belinda J. Wilkes (CfA), Gary Schmidt (Steward Observ.), Himel Ghosh (Ohio State),

Radio and far-IR surveys, and modeling of the cosmic X-ray background suggest that a large population of obscured AGN has been missed by traditional, optical surveys. The Two Micron All-Sky Survey (2MASS) has revealed a large population (surface density comparable to that of optically selected AGN with Ks<14.5mag) of mostly nearby (median z=0.25), red, moderately obscured AGN, among which 75% are previously unidentified emission-line AGN, with 85% showing broad emission lines. We present the SED and emission line properties of 44 such red (J-Ks>2) 2MASS AGN observed with Chandra. They lie at z<0.37, span a full range of spectral types (Type 1, intermediate, Type 2),Ks-to-X-ray slopes, and polarization (<13%). Their IR-to-X-ray spectral energy distributions (SEDs) are red in the near-IR/opt/UV showing little or no blue bump. The optical colors are affected by reddening, host galaxy emission, redshift, and in few, highly polarized objects, also by scattered AGN light. The levels of obscuration obtained from optical, X-rays, and far-IR imply N_H <few x 1022 cm-2. This, combined with the distribution of [OIII]5007 emission line equivalent widths, suggest a predominance of inclined objects in which obscuration/inclination allows us to see and study weaker emission components which are generally swamped by the direct AGN light. PCA analysis of the IR-X-ray SED and emission line properties shows that, while obscuration/inclination is important, the dominant cause of variance in the sample (eigenvector 1) is the L/Ledd ratio (perhaps because the red near-IR selection limits the range of inclination/obscuration values in our sample). This analysis also distinguishes two sources of obscuration: the host galaxy and circumnuclear absorption.

XMM-Newton Observations of a Complete Sample of Optically Selected Type 2 Seyfert Galaxies

Stephanie LaMassa, The Johns Hopkins University
Timothy Heckman (The Johns Hopkins University), Andrew Ptak (The Johns Hopkins University), Ann Hornschemeier (NASA Goddard Space Flight Center), Lucimara Martins (NAT - Universidade Cruzeiro do Sul), Paule Sonnentrucker (The Johns Hopkins University), Christy Tremonti (Max-Planck Institute for Astronomy)

A majority of Active Galactic Nuclei (AGN) are significantly obscured. Compton-thick AGN (where the column density of the obscuring material exceeds 1024 cm-2) are under-represented in X-ray surveys as the 2-10 keV emission is severely attenuated. However, optical and infrared emission lines, such as the [OIII]λ5007 and [OIV]25.89μm lines, are not affected by this obscuration as they form hundreds of parsecs from the torus in the Narrow Line region, though the [OIII] line suffers some extinction due to the host galaxy (by about a factor of 2) whereas the extinction for the [OIV] line is negligible. Comparison of the X-ray luminosity, which suffers from attenuation, with the [OIII] and [OIV] luminosity can then indicate the amount of obscuration present and whether a source is Compton-thick or Compton-thin.Here we present the results of a sample of 17 Seyfert 2 galaxies selected based on their high [OIII] flux. X-ray follow-up observations with XMM-Newton were undertaken to assess the amount of obscuration present. We find that 11 out of 17 have observed 2-10 keV emission depressed by an order-of-magnitude or more in comparison to isotropic indicators of AGN luminosity. Along with the Fe Kα equivalent width measurements, these results indicate that these targets are likely Compton-thick. We find no correlation between the amount of X-ray obscuration and other properties of the AGN or its host galaxy, indicating that Compton-thick AGN may not trace a distinct population from Compton-thin sources. We are currently supplementing this sample with the original 12 μm sample of Seyfert 2 galaxies, using XMM-Newton and Chandra observations to perform a similar analysis as the [OIII]-selected sample.

X-ray selected Type-2 QSOs: ongoing star formation and obscured accretion.

Vincenzo Mainieri, ESO
COSMOS collaboration

Although the fraction of obscured AGN is found to decrease with luminosity from several studies, a non-negligible population of obscured QSOs is still required by the X-ray background synthesis models. We present a large sample (121 objects) of X-ray selected Type-2 QSOs from the XMM-COSMOS survey: sources with high X-ray luminosity (LX>1044 erg s-1) and heavy obscuration (NH>1022 cm-2), as derived from a detailed X-ray spectral analysis (see Mainieri et al.,2007, ApJS, 172, 368) of the ~1800 X-ray point-like sources in this survey. Few (~5%) of the Type-2 QSOs are best fitted with a pure reflection model. We have performed optical spectroscopy for ~30% of the sample and for the remaining sources we have derived accurate photometric redshifts. The redshift range covered is wide, 0.3<z<3.9 (95% at z>0.8). We compare the general properties of the host galaxies with the ongoing accretion in their nuclei. Morphology: using five non-parametric diagnostics (asymmetry, concentration, Gini coefficient, M20, ellipticity) we found that ~10% of the Type-2 QSOs are in elliptical galaxies, ~55% in disk galaxies and ~35% in irregular galaxies. The majority of the irregular hosts can be described as undergoing merger activity or show tidal debris. Stellar masses have been derived from SED fitting to the observed photometry(from 0.3 to 4.5 micron) and star formation rates from the [OII] or Hα line fluxes. The majority (~75%) of QSO-2 host galaxies have stellar masses above log(Mstar)~10.5 MSun and have ongoing star formation (<SFR> ~100 MSun/yr). The value of 10.5 MSun is similar to the characteristic mass for obscured AGN (Kauffmann et al. 2003) and radio-loud AGN (Best et al. 2005) in the SDSS. It is also consistent with the more general result that the fraction of galaxies hosting AGN increases with the stellar mass.

AGN Feedback in Galaxy Groups: joint X-ray and radio studies

Jan M. Vrtilek, Center for Astrophysics
E. O'Sullivan (CfA), S. Giacintucci (CfA), L. David (CfA), S. Raychaudhury (U. Birmingham), C. Jones (CfA), W. Forman (CfA)

Elliptical galaxies with powerful radio sources frequently occupy the central regions of galaxy groups and clusters. The interactions of these radio sources with the hot X-ray emitting gas, visible through cavities and edges often spatially correlated with radio emission, form part of the motivation for the growing acceptance of AGN feedback as a principal mechanism for the regulation of cooling flows. Galaxy groups, the principal reservoir of baryons in the present Universe, are - with their shallow potentials that easily reveal disturbances, frequent galaxy interactions and mergers, and highly diverse structures - an excellent target for studies aimed at a better understanding of the feedback process, the mechanisms and timescales of energy injection, and the effects on galaxy and group evolution. We survey the scope and results of a study of 18 X-ray bright, elliptical-dominated galaxy groups, for which we have combined deep archival Chandra and XMM-Newton X-ray data with radio continuum imaging of high quality at multiple low frequencies from the GMRT. This combination of data reveals the morphological properties and histories of these sources and the highly diverse types of AGN/hot gas interaction, including the feedback heating by jet-inflated cavities that is common in clusters, but also exhibiting contributions from non-central galaxies, sources in which mixing of X-ray and radio plasma may be important, and cases where AGN-driven gas motions may help distribute heat through the group core. These examples demonstrate the worth of groups as a laboratory for feedback studies, and the insights to be gained from a combined radio/X-ray approach, with the X-ray data showing the geometry, physical state, and energetics of the hot gas and the radio data providing the loci of energy injection and the history of AGN outbursts through the spectral aging of electron populations.

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