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Active Galaxies Newsletter

An electronic publication dedicated to the observations and theory of active galaxies
Edited by Megan Argo

The Active Galaxies Newsletter is an electronic publication dedicated to the observation and theory of active galaxies. It is intended to be used to notify others in the field of recently accepted papers, conference proceedings and dissertations, and also contains announcements of jobs and conferences. It is produced monthly and sent to over 600 subscribers.

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Latest Issue:

New job: Post-doctoral position, University of Sheffield, deadline January 15th. See details.

Active An electronic publication dedicated to
Galaxies the observation and theory of
Newsletter active galaxies
No. 206 -- December 2014 Editor: Megan Argo (

Accepted Abstracts - Submitted Abstracts - Thesis Abstracts
Jobs Adverts - Meetings Adverts - Special Announcements

From the Editor

Welcome to all the new subscribers, and thanks to everyone who contributed to this issue of the Active Galaxies Newsletter. This newsletter is intended to disseminate paper abstracts, meeting announcements, job adverts and other information which may be of interest to the active galaxies community. It is produced monthly and, whilst the deadline for contributions is the last day of the month, contributions may be submitted at any time.

The Latex macros for submitting abstracts and dissertation abstracts are appended to each issue of the newsletter and are also available on the web page. Please note that the editor may reject submissions which do not use the template. As always, any suggestions or feedback regarding the newsletter are welcome.

Many thanks for your continued subscription.

Megan Argo

Abstracts of recently accepted papers

Active galactic nuclei at z~1.5: I. Spectral energy distribution and accretion discs

D. M. Capellupo1, H. Netzer1, P. Lira2, B. Trakhtenbrot3, J. Mejía-Restrepo2

1. School of Physics and Astronomy, Tel Aviv University, Tel Aviv 69978, Israel
2. Departamento de Astronomía, Universidad de Chile, Camino del Observatorio 1515, Santiago, Chile
3. Institute for Astronomy, Dept. of Physics, ETH Zurich, Wolfgang-Pauli-Strasse 27, CH-8093 Zurich, Switzerland

The physics of active super massive black holes (BHs) is governed by their mass (MBH), spin (a*) and accretion rate (Ṁ). This work is the first in a series of papers with the aim of testing how these parameters determine the observable attributes of active galactic nuclei (AGN). We have selected a sample in a narrow redshift range, centered on z ∼1.55, that covers a wide range in MBH and Ṁ, and are observing them with X-shooter, covering rest wavelengths ∼1200-9800 Å. The current work covers 30 such objects and focuses on the origin of the AGN spectral energy distribution (SED). After estimating MBH and Ṁ based on each observed SED, we use thin AD models and a Bayesian analysis to fit the observed SEDs in our sample. We are able to fit 22/30 of the SEDs. Out of the remaining 8 SEDs, 3 can be fit by the thin AD model by correcting the observed SED for reddening within the host galaxy and 4 can be fit by adding a disc wind to the model. In four of these 8 sources, Milky Way-type extinction, with the strong 2175Å feature, provides the best reddening correction. The distribution in spin parameter covers the entire range, from -1 to 0.998, and the most massive BHs have spin parameters greater than 0.7. This is consistent with the "spin-up" model of BH evolution. Altogether, these results indicate that thin ADs are indeed the main power houses of AGN, and earlier claims to the contrary are likely affected by variability and a limited observed wavelength range.

Accepted by MNRAS

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Differences between CO- and calcium triplet-derived velocity dispersions in spiral galaxies: evidence for central star formation?

Rogemar A. Riffel1, Luis C. Ho2,3, Rachel Mason4, Alberto Rodríguez-Ardila5, Lucimara Martins6, Rogério Riffel7, Ruben Diaz8, Luis Colina9, Almudena Alonso-Herrero10, Helene Flohic11, Omaira Gonzalez Martin12,13,19, Paulina Lira14, Richard McDermid4,15, Cristina Ramos Almeida12,13, Ricardo Schiavon2,16, Karun Thanjavur17, Daniel Ruschel Dutra7,12, Claudia Winge8, Eric Perlman18

1. Universidade Federal de Santa Maria, Departamento de Física/CCNE, 97105-900, Santa Maria, RS, Brazil
2. Kavli Institute for Astronomy and Astrophysics, Peking University, Beijing, China
3. Department of Astronomy, School of Physics, Peking University, Beijing, China
4. Gemini Observatory, Northern Operations Center, 670 N. A'ohoku Place, Hilo, HI 96720, USA
5. Laboratório Nacional de Astrofísica/MCT, Rua dos Estados Unidos 154, Itajubá, MG, Brazil
6. NAT - Universidade Cruzeiro do Sul, Rua Galvão Bueno, 868, São Paulo, SP, Brazil
7. Universidade Federal do Rio Grande do Sul, Instituto de Física, CP 15051, Porto Alegre 91501-970, RS, Brazil
8. Gemini Observatory, Southern Operations Center, Casilla 603, La Serena, Chile
9. Astrophysics Department, Center for Astrobiology (CSIC-INTA), Torrejon de Ardoz, 28850 Madrid, Spain
10. Instituto de Fisica de Cantabria, CSIC-UC, 39005 Santander, Spain
11. University of the Pacific, Department of Physics, 3601 Pacific Avenue, Stockton, CA 95211, USA
12. Instituto de Astrofísica de Canarias, Calle Vía Láctea, s/n, E-38205, La Laguna, Tenerife, Spain
13. Departamento de Astrofísica, Universidad de La Laguna, E-38205, La Laguna, Tenerife, Spain
14. Departamento de Astronomía, Universidad de Chile, Casilla 36-D, Santiago, Chile
15. Department of Physics and Astronomy, Macquarie University, NSW 2109, Australia
16. Astrophysics Research Institute, Liverpool John Moores University, IC2, Liverpool Science Park 146 Brownlow Hill, Liverpool L3 5RF, United Kingdom
17. Departament of Physics & Astronomy, University of Victoria, PO Box 1700, STN CSC Victoria, BC, V8W 2Y2, CANADA
18. Department of Physics and Space Sciences, Florida Insitute of Technology, 150 West University Boulevard, Melbourne, FL 32901, USA
19. Centro de Radioastronomia y Astrofisica (UNAM), Apartado Postal 3-72 (Xangari), 58089 Morelia, Mexico

We examine the stellar velocity dispersions (σ) of a sample of 48 galaxies, 35 of which are spirals, from the Palomar nearby galaxy survey. It is known that for ultra-luminous infrared galaxies (ULIRGs) and merger remnants the σ derived from the near-infrared CO band-heads is smaller than that measured from optical lines, while no discrepancy between these measurements is found for early-type galaxies. No such studies are available for spiral galaxies - the subject of this paper. We used cross-dispersed spectroscopic data obtained with the Gemini Near-Infrared Spectrograph (GNIRS), with spectral coverage from 0.85 to 2.5 μm, to obtain σ measurements from the 2.29 μm CO band-heads (σCO), and the 0.85 μm calcium triplet (σCaT). For the spiral galaxies in the sample, we found that σCO is smaller than σCaT, with a mean fractional difference of 14.3%. The best fit to the data is given by σopt = (46.0±18.1) + (0.85±0.12)σCO. This "σ discrepancy" may be related to the presence of warm dust, as suggested by a slight correlation between the discrepancy and the infrared luminosity. This is consistent with studies that have found no σ-discrepancy in dust-poor early-type galaxies, and a much larger discrepancy in dusty merger remnants and ULIRGs. That σCO is lower than σopt may also indicate the presence of a dynamically cold stellar population component. This would agree with the spatial correspondence between low σCO and young/intermediate-age stellar populations that has been observed in spatially-resolved spectroscopy of a handful of galaxies.

Accepted by MNRAS

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Triggering optical AGN: the need for cold gas, and the indirect roles of galaxy environment and interactions

J. Sabater1, P. N. Best1 and T. M. Heckman2

1. Institute for Astronomy (IfA), University of Edinburgh, Royal Observatory, Blackford Hill, EH9 3HJ Edinburgh, U.K.
2. Center for Astrophysical Sciences, Department of Physics & Astronomy, The Johns Hopkins University, Baltimore, MD 21218

We present a study of the prevalence and luminosity of Active Galactic Nuclei (AGN; traced by optical spectra) as a function of both environment and galaxy interactions. For this study we used a sample of more than 250000 galaxies drawn from the Sloan Digital Sky Survey and, crucially, we controlled for the effect of both stellar mass and central star formation activity. Once these two factors are taken into account, the effect of the local density of galaxies and of one-on-one interactions is minimal in both the prevalence of AGN activity and AGN luminosity. This suggests that the level of nuclear activity depends primarily on the availability of cold gas in the nuclear regions of galaxies and that secular processes can drive the AGN activity in the majority of cases. Large scale environment and galaxy interactions only affect AGN activity in an indirect manner, by influencing the central gas supply.

Accepted by MNRAS

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Feedback from Mass Outflows in Nearby Active Galactic Nuclei. II. Outflows in the Narrow-Line Region of NGC 4151

D.M. Crenshaw1, T.C. Fischer1, S.B. Kraemer2, and H.R. Schmitt3

1. Department of Physics and Astronomy, Georgia State University, 25 Park Place, Suite 605, Atlanta, GA 30303
2. Institute for Astrophysics and Computational Sciences, Department of Physics, The Catholic University of America, Washington, DC 20064
3. Naval Research Laboratory, Washington, DC 20375, USA

We present a detailed study of AGN feedback in the narrow-line region (NLR) of the Seyfert 1 galaxy NGC 4151. We illustrate the data and techniques needed to determine the mass outflow rate (Ṁout) and kinetic luminosity (LKE) of the outflowing ionized gas as a function of position in the NLR. We find that Ṁout peaks at a value of 3.0 M yr-1 at a distance of 70 pc from the central supermassive black hole (SMBH), which is about 10 times the outflow rate coming from inside 13 pc, and 230 times the mass accretion rate inferred from the bolometric luminosity of NGC 4151. Thus, most of the outflow must arise from "in situ" acceleration of ambient gas throughout the NLR. LKE peaks at 90 pc and drops rapidly thereafter, indicating that most of the kinetic energy is deposited within about 100 pc from the SMBH. Both values exceed the Ṁout and LKE determined for the UV/X-ray absorber outflows in NGC 4151, indicating the importance of NLR outflows in providing feedback on scales where circumnuclear star formation and bulge growth occur.

Accepted by The Astrophysical Journal

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An embedded active nucleus in the OH megamaser galaxy IRAS16399-0937

Dinalva A. Sales1,2, A. Robinson2, D. J. Axon2,3,†, J. Gallimore4, P. Kharb5, R. L. Curran2, C. O'Dea2, S. Baum6, M. Elitzur7, R. Mittal2

1. Departamento de Astronomia, Universidade Federal do Rio Grande do Sul. 9500 Bento Gonçalves, Porto Alegre, 91501-970, Brazil
2. School of Physics and Astronomy, Rochester Institute of Technology, 84 Lomb Memorial Drive, Rochester, NY 14623, USA
3. School of Mathematical & Physical Sciences, University of Sussex, Falmer, Brighton, BN2 9BH, UK
† 1951-2012
4. Department of Physics, Bucknell University, Lewisburg, PA 17837, USA
5. Indian Institute of Astrophysics, II Block, Koramangala, Bangalore 560034, India
6. Chester F. Carlson Center for Imaging Science, Rochester Institute of Technology, 54 Lomb Memorial Drive, Rochester, NY 14623, USA
7. Physics & Astronomy Department, University of Kentucky, Lexington, KY 40506-0055

We present a multiwavelength study of the OH Megamaser galaxy (OHMG) IRAS16399-0937, based on new HST/ACS F814W and Hα+[NII] images and archive data from HST, 2MASS, Spitzer, Herschel and the VLA. This system has a double nucleus, whose northern (IRAS16399N) and southern (IRAS16399S) components have a projected separation of ∼6" (3.4kpc) and have previously been identified based on optical spectra as a Low Ionization Nuclear Emission Line Region (LINER) and starburst nucleus, respectively. The nuclei are embedded in a tidally distorted common envelope, in which star formation is mostly heavily obscured. The infrared spectrum is dominated by strong polycyclic aromatic hydrocarbon (PAH), but deep silicate and molecular absorption features are also present, and are strongest in the IRAS16399N nucleus. The 0.435-500μm SED was fitted with a model including stellar, ISM and AGN torus components using our new MCMC code, CLUMPYDREAM. The results indicate that the IRAS16399N contains an AGN (Lbol∼1044 ergs/s) deeply embedded in a quasi-spherical distribution of optically-thick clumps with a covering fraction ≈1. We suggest that these clumps are the source of the OHM emission in IRAS16399-0937. The high torus covering fraction precludes AGN-photoionization as the origin of the LINER spectrum, however, the spectrum is consistent with shocks (v∼100-200 kms-1). We infer that the ∼108M black-hole in IRAS16399N is accreting at a small fraction (∼1%) of its Eddington rate. The low accretion-rate and modest nuclear SFRs suggest that while the gas-rich major merger forming the IRAS16399-0937 system has triggered widespread star formation, the massive gas inflows expected from merger simulations have not yet fully developed.

Accepted by ApJ 2014

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The dust masses of powerful radio galaxies: clues to the triggering of their activity

C. Tadhunter1, D. Dicken2, R. Morganti3,4, V. Konyves2, N. Ysard5, N. Nesvadba5, and C. Ramos Almeida6,7

1. Department of Physics & Astronomy, University of Sheffield, Sheffield S3 7RH
2. Laboratoire AIM-Paris-Saclay, CEA/DSM/Irfu, Orme des Merisiers, Bat 709, 91191 Gif sur Yvette, France
3. ASTRON, P.O. Box 2, 7990 AA Dwingeloo, The Netherlands
4. Kapteyn Astronomical Institute, University of Groningen, P.O. Box 800, 9700 AV Groningen, The Netherlands
5. Institut d'Astrophysique Spatiale (IAS), Universit?? Paris-Sud, 91405, Orsay, France
6. Instituto de Astrofísica de Canarias, C/ Via Láctea, E38205 - La Laguna,Tenerife, Spain
7. Departamento de Astrofísica, Universidad de La Laguna, E-38205, La Laguna, Tenerife, Spain

We use deep Herschel Space Observatory observations of a 90% complete sample of 32 intermediate-redshift 2Jy radio galaxies (0.05 < z < 0.7) with strong emission lines to estimate the dust masses of their host galaxies and thereby investigate the triggering mechanisms for their quasar-like AGN. The dust masses derived for the radio galaxies (7.2 × 105 < Md < 2.6 × 108 M) are intermediate between those of quiescent elliptical galaxies on the one hand, and ultra luminous infrared galaxies (ULIRGs) on the other. Consistent with simple models for the co-evolution of supermassive black holes and their host galaxies, these results suggest that most radio galaxies represent the late time re-triggering of AGN activity via mergers between the host giant elliptical galaxies and companion galaxies with relatively low gas masses. However, a minority of the radio galaxies in our sample (∼20%) have high, ULIRG-like dust masses, along with evidence for prodigious star formation activity. The latter objects are more likely to have been triggered in major, gas-rich mergers that represent a rapid growth phase for both their host galaxies and their supermassive black holes.

Accepted by Monthly Notices of the Royal Astronomical Society.

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Extended warm gas in the ULIRG Mrk273: Galactic outflows and tidal debris

J. Rodríguez Zaurín1,2, C.N. Tadhunter3, D.S.N. Rupke4, S. Veilleux5, H.W.W. Spoon6, M. Chiaberge7, C. Ramos Almeida1,2, D. Batcheldor8, and W.B. Sparks7

1. Instituto de Astrofísica de Canarias, E-38205, La Laguna, Tenerife, Spain
2. Departamento de Astrofísica, Universidad de La Laguna, Tenerife, Spain
3. Department of Physics and Astronomy, University of Sheffield, Sheffield S3 7RH, UK
4. Department of Physics, Rhodes College, Memphis, TN 38112, USA
5. Department of Astronomy, University of Maryland, College Park, MD 20742, USA
6. Cornell University, CRSR, Space Sciences Building, Ithaca, NY 14853, USA
7. Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, USA
8. Physics and Space Sciences Department, Florida Institute of Technology, 150 West University Boulevard, Melbourne, FL 32901, USA

We present new HST ACS medium- and narrow-band images and optical Isaac Newton Telescope (INT) long-slit spectra of the merging system Mrk273. The HST observations sample the [OIII]λλ4959,5007 emission from the galaxy and the nearby continuum. These data were taken as a part of a larger study of ultraluminous infrared galaxies (ULIRGs) with the aim of investigating the importance of the warm, AGN induced outflows in such objects. The HST images show that the morphologies of the extended continuum and the ionised gas emission from the galaxy are decoupled, extending almost perpendicular to each other. In particular, we detect for the first time a spectacular structure of ionised gas in the form of filaments and clumps that extend ∼23kpc to the east of the nuclear region. The quiescent ionised gas kinematics at these locations suggests that these filaments are tidal debris left over from a secondary merger event that are illuminated by an AGN in the nuclear regions. The images also reveal a complex morphology in the nuclear region of the galaxy for both the continuum and the [OIII] emission. Consistent with this complexity, we find a wide diversity of emission line profiles in these regions. Kinematic disturbance in the form of broad (FWHM > 500 km s-1) and/or strongly shifted (|ΔV| >150 km s-1 ) emission line components is found at almost all locations in the nuclear regions, but confined to a radius of ∼4 kpc to the east and west of the northern nucleus. In most cases, we are able to fit the profiles of all the emission lines of different ionisation with a kinematic model using two or three Gaussian components. From these fits, we derive diagnostic line ratios that are used to investigate the ionisation mechanisms at the different locations in the galaxy. We show tha these line ratios are generally consistent with photoionisation by an AGN as the main ionisation mechanism. Finally, the highest surface brightness [OIII] emission is found in a compact region that is coincident with the so-called SE nuclear component. The compactness, kinematics, and emission line ratios of this component suggest that it is a separate nucleus with its own AGN. At this stage, further observations are required to confirm the dual (or multiple?) AGN nature of Mrk273.

Accepted by A&A.

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Imprints of the quasar structure in time-delay light curves: Microlensing-aided reverberation mapping

D. Sluse1, M. Tewes1

1. Argelander-Institut fur Astronomie, Auf dem Hugel 71, 53121, Bonn, Germany

The advent of large area photometric surveys has raised a great deal of interest in the possibility of using broadband photometric data, instead of spectra, to measure the size of the broad line region of active galactic nuclei. We describe here a new method that uses time-delay lensed quasars where one or several images are affected by microlensing due to stars in the lensing galaxy. Because microlensing decreases (or increases) the flux of the continuum compared to the broad line region, it changes the contrast between these two emission components. We show that this effect can be used to effectively disentangle the intrinsic variability of those two regions, offering the opportunity to perform reverberation mapping based on single-band photometric data. Based on simulated light curves generated using a damped random walk model of quasar variability, we show that measurement of the size of the broad line region can be achieved using this method, provided one spectrum has been obtained independently during the monitoring. This method is complementary to photometric reverberation mapping and could also be extended to multi-band data. Because the effect described above produces a variability pattern in difference light curves between pairs of lensed images that is correlated with the time-lagged continuum variability, it can potentially produce systematic errors in measurement of time delays between pairs of lensed images. Simple simulations indicate that time-delay measurement techniques that use a sufficiently flexible model for the extrinsic variability are not affected by this effect and produce accurate time delays.

Published in Astronomy and Astrophysics, 571, A60

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Short-Timescale monitoring of the X-ray, UV and broad double-peak emission line of the nucleus of NGC1097

Jaderson S. Schimoia1,8, Thaisa Storchi-Bergmann1,9, Dirk Grupe2,10, Michael Eracleous3,11,12, Bradley M. Peterson4, Jack A. Baldwin5, Rodrigo S. Nemmen6,13,14 and Cláudia Winge7

1. Instituto de Física, Universidade Federal do Rio Grande do Sul, Campus do Vale, Porto Alegre, RS, Brazil
2. Space Science Center, Morehead State University, 235 Martindale Dr.Morehead, KY 40351
3. Department of Astronomy and Astrophysics and Institute for Gravitation and the Cosmos, Pennsylvania State University, 525 Davey Lab, University Park, PA 16802, USA
4. Department of Astronomy, 140 West 18th Avenue, and the Center for Cosmology and AstroParticle Physics, 191 West Woodruff Avenue, The Ohio State University, Columbus, OH 43210, USA
5. Department of Physics and Astronomy, Michigan State University, East Lansing, MI 48864, USA
6. Instituto de Astronomia, Geofísica e Ciências Atmosféricas, Universidade de São Paulo, São Paulo, SP 05508-090, Brazil
7. Gemini South Observatory, c/o AURA Inc., Casilla 603, La Serena, Chile
8. Also at Department of Astronomy, The Ohio State University, 140 West 18th Avenue, Columbus, OH 43210, USA
9. Also at Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA
10. Also at Swift Mission Operation Center, 2582 Gateway Dr., State College, PA 16801, USA
11. Also at Center for Relativistic Astrophysics, Georgia Institute of Tchnology, Atlanta, GA 30332, USA
12. Also at Department of Astronomy, University of Washington, Seattle, WA 98195, USA
13. Also at NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA
14. Also at Center for Research and Exploration in Space Science & Technology (CRESST)
15. Also at Department of Physics, University of Maryland, Baltimore County, 1000 Hilltop Circle, Baltimore, MD 21250, USA

Recent studies have suggested that the short-timescale (≲7 days) variability of the broad (∼10,000kms-1) double-peaked Hα profile of the LINER nucleus of NGC1097 could be driven by a variable X-ray emission from a central radiatively inefficient accretion flow (RIAF). To test this scenario, we have monitored the NGC1097 nucleus in X-ray and UV continuum with Swift and the Hα flux and profile in the optical spectrum using SOAR and Gemini-South from 2012 August to 2013 February. During the monitoring campaign, the Hα flux remained at a very low level - 3 times lower than the maximum flux observed in previous campaigns and showing only limited (∼20%) variability. The X-ray variations were small, only ∼13% throughout the campaign, while the UV did not show significant variations. We concluded that the timescale of the Hα profile variation is close to the sampling interval of the optical observations, which results in only marginal correlation between the X-ray and Hα fluxes. We have caught the AGN in NGC1097 in a very low activity state, in which the ionizing source was very weak and capable of ionizing just the innermost part of the gas in the disk. Nonetheless, the data presented here still support the picture in which the gas that emits the broad double-peaked Balmer lines is illuminated/ionized by a source of high-energy photons which is located interior to the inner radius of the line-emitting part of the disk.

Accepted by The Astrophysical Journal

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The host galaxies of X-ray selected Active Galactic Nuclei to z=2.5: Structure, star-formation and their relationships from CANDELS and Herschel/PACS

David Rosario1, Dan McIntosh2, Arjen van der Wel3 et al.

1. Max-Planck-Institut für Extraterrestrische Physik (MPE), Garching, Germany
2. Department of Physics & Astronomy, University of Missouri- Kansas City, Kansas City, MO, USA
3. Max-Planck Institut für Astronomie (MPIA), Heidelberg, Germany

We study the relationship between the structure and star-formation rate (SFR) of X-ray selected low and moderate luminosity active galactic nuclei (AGNs) in the two Chandra Deep Fields, using Hubble Space Telescope imaging from the Cosmic Assembly Near Infrared Extragalactic Legacy Survey (CANDELS) and deep far-infrared maps from the PEP+GOODS-Herschel survey. We derive detailed distributions of structural parameters and FIR luminosities from carefully constructed control samples of galaxies, which we then compare to those of the AGNs. At z∼1, AGNs show slightly diskier light profiles than massive inactive (non-AGN) galaxies, as well as modestly higher levels of gross galaxy disturbance (as measured by visual signatures of interactions and clumpy structure). In contrast, at z∼2, AGNs show similar levels of galaxy disturbance as inactive galaxies, but display a red central light enhancement, which may arise due to a more pronounced bulge in AGN hosts or due to extinguished nuclear light. We undertake a number of tests of these alternatives, but our results do not strongly favour one interpretation over the other. The mean SFR and its distribution among AGNs and inactive galaxies are similar at z>1.5. At z<1, however, clear and significant enhancements are seen in the SFRs of AGNs with bulge-dominated light profiles. These trends suggest an evolution in the relation between nuclear activity and host properties with redshift, towards a minor role for mergers and interactions at z>1.5.

In press at Astronomy & Astrophysics, Main Journal

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X-ray polarization fluctuations induced by cloud eclipses in active galactic nuclei

F. Marin and M. Dovciak

Astronomical Institute of the Academy of Sciences, Bocní II 1401, CZ-14100 Prague, Czech Republic

Context: A fraction of active galactic nuclei (AGN) show dramatic X-ray spectral changes on the day-to-week time scales associated with variation in the line of sight of the cold absorber. Aims: We intend to model the polarization fluctuations arising from an obscuration event, thereby offering a method of determining whether flux variations are due to occultation or extreme intrinsic emission variability. Methods: Undertaking 1 - 100 keV polarimetric simulations with the Monte Carlo code STOKES, we simulated the journey of a variety of cold gas clouds in front of an extended primary source. We varied the hydrogen column density nH and size of the absorber, as well as the initial polarization state of the emitting source, to cover a wide range of scenarios. Results: Simulations indicate that different results are expected according to the initial polarization of the extended continuum source. For unpolarized primary fluxes, large (∼50°) variations of the polarization position angle ψ are expected before and after an occultation event, which is associated with very low residual polarization degrees (P≪1%). In the case of an emitting disk with intrinsic, position-independent polarization, and for a given range of parameters, X-ray eclipses significantly alter the observed polarization spectra, with most of the variations seen in ψ. Finally, non-uniformly polarized emitting regions produce very distinctive polarization variations due to the successive covering and uncovering of different portions of the disk. Plotted against time, variations in P and ψ form detectable P Cygni type profiles that are distinctive signatures of non-axisymmetric emission. Conclusions: We find that X-ray polarimetry is particularly adapted to probing X-ray eclipses due to Compton-thin and Compton-thick gas clouds. Polarization measurements would distinguish between intrinsic intensity fluctuations and external eclipsing events, constrain the geometry of the covering medium, and test the hypothesis of non-uniformly emitting disks predicted by general relativity.

Accepted by A&A

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Selection of AGN candidates in the GOODS-South Field through SPITZER/MIPS 24μm variability

Judit García-González1, Almudena Alonso-Herrero1,2, Pablo G. Pérez-González3, Antonio Hernán-Caballero1, Vicki L. Sarajedini4 and Víctor Villar3

1. Instituto de Física de Cantabria, CSIC-UC, Avenida de los Castros s/n, 39005 Santander, Spain
2. Augusto González Linares Senior Research Fellow
3. Departamento de Astrofísica, Facultad de CC. Físicas, Universidad Complutense de Madrid, 28040 Madrid, Spain
4. Departament of Astronomy, University of Florida, Gainesville, FL 32611, USA

We present a study of galaxies showing mid-infrared variability in data taken in the deepest Spitzer/MIPS 24μm surveys in the GOODS-South field. We divide the dataset in epochs and subepochs to study the long-term (months-years) and the short-term (days) variability. We use a χ2-statistics method to select AGN candidates with a probability ≤1% that the observed variability is due to statistical errors alone. We find 39 (1.7% of the parent sample) sources that show long-term variability and 55 (2.2% of the parent sample) showing short-term variability. That is, 0.03 sources × arcmin-2 for both, long-term and short-term variable sources. After removing the expected number of false positives inherent to the method, the estimated percentages are 1.0% and 1.4% of the parent sample for the long-term and short-term respectively. We compare our candidates with AGN selected in the X-ray and radio bands, and AGN candidates selected by their IR emission. Approximately, 50% of the MIPS 24 μm variable sources would be identified as AGN with these other methods. Therefore, MIPS 24 μm variability is a new method to identify AGN candidates, possibly dust obscured and low luminosity AGN, that might be missed by other methods. However, the contribution of the MIPS 24 μm variable identified AGN to the general AGN population is small (≤13%) in GOODS-South.

Accepted by MNRAS

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X-ray constraints on the local supermassive black hole occupation fraction

Brendan P. Miller1,2, Elena Gallo1, Jenny E. Greene3, Brandon C. Kelly4, Tommaso Treu4, Jong-Hak Woo5, and Vivienne Baldassare1

1. Department of Astronomy, University of Michigan, Ann Arbor, MI 48109, USA
2. Department of Physics and Astronomy, Macalester College, Saint Paul, MN 55105, USA
3. Department of Astrophysics, Princeton University, Princeton, NJ 08544, USA
4. Physics Department, University of California, Santa Barbara, CA 93106, USA
5. Astronomy Program, Department of Physics and Astronomy, Seoul National University, Seoul, Korea

Distinct seed formation mechanisms are imprinted upon the fraction of dwarf galaxies currently containing a central supermassive black hole. Seeding by Pop III remnants is expected to produce a higher occupation fraction than is generated with direct gas collapse precursors. Chandra observations of nearby early-type galaxies can directly detect even low-level supermassive black hole activity, and the active fraction immediately provides a firm lower limit to the occupation fraction. Here, we use the volume-limited AMUSE surveys of ∼200 optically-selected early-type galaxies to characterize simultaneously, for the first time, the occupation fraction and the scaling of LX with Mstar, accounting for intrinsic scatter, measurement uncertainties, and X-ray limits. For early-type galaxies with Mstar<1010 M, we obtain a lower limit to the occupation fraction of >20% (at 95% confidence), but full occupation cannot be excluded. The preferred dependence of log LX upon log Mstar has a slope of ∼0.7-0.8, consistent with the "downsizing" trend previously identified from the AMUSE dataset, and a uniform Eddington efficiency is disfavored at ∼2σ. We provide guidelines for the future precision with which these parameters may be refined with larger or more sensitive samples.

Accepted by ApJ

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Compton Thick AGN in the XMM-COSMOS survey

G. Lanzuisi1,2, P. Ranalli1, I. Georgantopoulos1 et al

1. Institute of Astronomy & Astrophysics, National Observatory of Athens, Palaia Penteli, 15236, Athens, Greece
2. INAF - Osservatorio Astronomico di Bologna, Via Ranzani 1, 40127, Bologna, Italy

Heavily obscured, Compton Thick (CT, NH>1024 cm-2) Active Galactic Nuclei (AGN) may represent an important phase in AGN/galaxy co-evolution and are expected to provide a significant contribution to the cosmic X-ray background at its peak. However, unambiguously identifying CT AGN beyond the local Universe is a challenging task even in the deepest X-ray surveys, and given the expected low spatial density of these sources in the 2-10 keV band, large area surveys are needed to collect sizable samples. Through direct X-ray spectra analysis, we selected 39 heavily obscured AGN (NH > 3×1023 cm-2) at bright xray fluxes (F2-10 ≳ 10-14 erg s-1 cm-2) in the 2 deg2 XMM-COSMOS survey. After selecting CT AGN based on the fit of a simple absorbed two power law model to the shallow XMM data, the presence of bona-fide CT AGN was confirmed in 80% of the sources using deeper Chandra data and more complex models. The final sample comprises 10 CT AGN (6 of them also have a detected Fe Kα line with EW ∼ 1 keV), spanning a large range of redshift (z ∼ 0.1-2.5) and luminosity (L2-10 ∼ 1043.5-1045 ergs) and is complemented by 29 heavily obscured AGN spanning the same redshift and luminosity range. We collected the rich multi-wavelength information available for all these sources, in order to study the distribution of SMBH and host properties, such as BH mass (MBH), Eddington ratio (λEdd), stellar mass (M*), specific star formation rate (sSFR) in comparison with a sample of unobscured AGN. We find that highly obscured sources tend to have significantly smaller MBH and higher λEdd with respect to unobscured sources, while a weaker evolution in M* is observed. The sSFR of highly obscured sources is consistent with the one observed in the main sequence of star forming galaxies, at all redshift. We also present and briefly discuss optical spectra, broad band spectral energy distribution (SED) and morphology for the sample of 10 CT AGN. Both the optical spectra and SED agree with the classification as highly obscured sources: all the available optical spectra are dominated by the stellar component of the host galaxy, and to reproduce the broad band SED, an highly obscured torus component is needed for all the CT sources. Exploiting the high resolution Hubble-ACS images available, we are able to show that these highly obscured sources have a significantly larger merger fraction with respect to other xray selected samples of AGN. Finally we discuss the implications of our findings in the context of AGN/galaxy co-evolutionary models, and compare our results with the predictions of xray background synthesis models.

Accepted by A&A on 25 November 2014.

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Postdoctoral Research Associate in AGN Triggering and Feedback
Department of Physics & Astronomy, University of Sheffield
Deadline: 12th January 2015

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Applications are invited for a 3 year postdoctoral position to carry forward a broad-based programme of research that aims to accurately quantify the feedback effect of the AGN in some of the most rapidly evolving galaxies in the local Universe, and also to investigate the triggering of the AGN activity. The project will involve the analysis and interpretation of existing high-quality data obtained using the HST/ACS, VLT/XSHOOTER and WHT/ISIS instruments. Observations with ALMA are also anticipated.

The successful applicant will join the Astrophysics Group at the University of Sheffield, which has research interests in the fields of active galaxies, quasars, galaxy evolution, massive stars, star clusters, star formation, supernovae, interacting binary star systems and time domain astrophysics.

Applicants should have (or be about to obtain) a PhD in astrophysics or a related area. Experience in the analysis of optical/IR spectroscopic data is essential, and background knowledge of the AGN field is desirable.

For informal enquiries about this position please contact Prof Clive Tadhunter (Tel: +44-(0)114-2224300,

Applications (application form, CV including publication list, brief research statement, and contact details for up to 3 referees) should be submitted via the online application system at by 15th January 2015.