Chandra's First Decade of Discovery

Session 13: Normal Galaxies

X-raying galaxies: A Chandra Legacy

Q. Daniel Wang, University of Massachusetts

I will review major advances made with Chandra observations on nearby galaxies, particularly in the context of galaxy structure and evolution.

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Chandra observations of AGN Outbursts in “normal” Early-type Galaxies

Christine Jones, SAO
W. Forman (SAO), E. Churazov (MAP,IKI), R. Kraft (SAO), P. Nulsen (SAO), D. Lal (SAO), S. Murray (SAO)

Most galaxies harbor a supermassive black hole at their center. At high redshifts, these galaxies experienced a very active phase, when these black holes produced enormous amounts of energy, likely fueled through galaxy mergers. Today, some of these supermassive black holes still undergo occasional outbursts that are seen through spectacular jets, cavities and buoyant bubbles and shocks in the surrounding X-ray gas. This paper describes Chandra results for a sample of ~200 galaxies for which we measure the X-ray properties, including the X-ray emission from the supermassive black hole at the nucleus, as well as emission from the diffuse gas, stars and LMXB's. We compare the X-ray and radio emission from the nucleus to the kinetic power of the outbursts as measured from the X-ray cavities found in the diffuse gas.

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NGC7618 and UGC12491: Gas-Dynamics in the Nearby Merger of Two Sub-groups

Marie Machacek, SAO
R.P. Kraft (SAO), C. Jones (SAO), W.R. Forman (SAO), P.E.J. Nulsen (SAO), S.S. Murray (SAO), M.J. Hardcastle (Univ. of Hertfordshire)

Most galaxy evolution is found to occur in moderately massive galaxy groups, that, in hierarchical models of structure formation, may themselves be merging along filaments to form more massive structures. The study of nearby examples of galaxy and subgroup mergers, where Chandra's high angular resolution allows us to directly observe X-ray edges, outflows, and tails detailing the dynamical processes at work, is key to understanding the properties of galaxies, their central supermassive black holes, and the surrounding intracluster medium observed today. We present results from two ~30 ks Chandra observations of NGC7618 and UGC12491, respectively, and a 25 ks XMM-Newton MOS+pn observation of the NGC7618/UGC12491 system, together tracing gas dynamical interactions in one of the best examples of an ongoing subgroup-subgroup merger in the local universe. We find X-ray surface brightness discontinuities and temperature asymmetries around the two dominant subgroup galaxies, NGC7618 and UGC12491, but with strikingly different morphologies. We discuss the likely origin of these gas morphologies. We use imaging and spectral analyses of the observed surface brightness and temperature features to measure the density, pressure and entropy in and surrounding NGC7618 and UGC12491 to constrain the kinematics of the merger and test models for gas stripping, “sloshing” and entropy evolution in the sub-group gas, and possible feedback from AGN activity that may have been triggered by the merger.

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AGN on the color-magnitude diagram: Results from a Deep Medium Band Survey with the Subaru Telescope in the MUSYC-ECDFS Region

Carolin Cardamone, Yale University
Urry, C. Megan (Yale), van Dokkum, P. (Yale), Schawinski, Kevin (Yale), Gawiser, E. (Rutgers), Brammer, G. (Yale), Taylor, N. (leiden), Treister, E. (Hawaii), Taniguchi, Y. (Ehime University), Virani, S. (Yale)

We investigate the host galaxy colors of X-ray detected AGN in the Extended Chandra Deep Field South.We have conducted deep medium-band imaging with the Subaru telescope, in 18 filters from 427 nm to 856 nm, of the MUSYC survey field. We detect 80,000 galaxies to equivalent magnitude R 27 mag, of which approximately 1,000 are X-ray-detected AGN observed with Chandra and XMM. Combining the Subaru data with optical, IR data and IRAC photometry we obtain photometric redshifts using EAZY, a fast public photometric redshift code, in the range 0<z<6. We find dz/(1+ z) < 0.01, with fewer than 10% outliers. We describe the colors of AGN host galaxies as a function of host galaxy mass to determine their roll in the evolution of galaxies.

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Beyond the Unification Models in AGN: the BLR in the X-rays

Stefano Bianchi, Università degli Studi di Roma Tre

Different flavors of the Unification Model have been largely successful in explaining most of the complex phenomenology observed in active galactic nuclei (AGN). However, several deviations from the standard scenario have been found, requiring a new view of the role of other parameters, besides the line of sight to the object. In this talk, we will present some recent results on the X-ray “activity” of the broad line region (BLR), which appears to be an important absorbing or emitting medium also in this energy band, and may be completely absent in some sources.

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New Perspectives on Compton-thick AGN

Tahir Yaqoob, Johns Hopkins University
Kendrah Murphy (MIT, Kavli Institute)

Obscured AGN are now recognized as playing a major role in the population of accreting supermassive black holes. We present new results from theoretical calculations that reveal some rather surprising characteristics of Compton-thick AGN. Our findings have a direct impact on the interpretation of existing data, as well as data from the upcoming missions NuSTAR and Astro-H. We show calculations of the dependence of the Fe K line EW, flux, and observed to intrinsic continuum luminosity ratios on the reprocessor column density, geometry, and orientation. We find that, whilst a large EW Fe K emission line is traditionally thought to be a hallmark for identifying Compton-thick AGN, there is a large part of parameter space in which the Fe K line may not even be detectable due to a small EW. We also show that the soft and hard reprocessed X-ray continua differ significantly from those based on models that are currently used to deduce column density distributions of AGN found in surveys, such as those with Chandra, XMM, and the Swift-BAT. The origin of the differences can be attributed to the inclusion of more realistic assumptions in our models compared to those currently in use. These results also impact synthesis models of the CXRB since our model can be used to derive more realistic column density distributions for AGN. The intrinsic continuum luminosity in Compton-thick AGN is a critical quantity that cannot be directly measured and there is no proxy for estimating it in a trivial manner. However, we show how a robust lower limit on the intrinsic luminosity may be inferred. When applied to Swift-BAT AGN, our calculations show that the BAT survey is actually more biased towards Compton-thick type 1 AGN than Compton-thin type 2 OR type 1 AGN.

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