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Infrared Excess sources: Compton thick QSOs, low-luminosity Seyferts or starbursts?

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2010-07-21
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Georgakakis, A.
Rowan-Robinson, M.
Nandra, K.
Digby-North, J.
Barro, G.
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Wiley
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We explore the nature of Infrared Excess sources (IRX), which are proposed as candidates for luminous [L_X(2–10 keV) > 10^43 erg s^−1] Compton thick (NH > 2 × 1024 cm−2) QSOs at z≈ 2. Lower redshift, z≈ 1, analogues of the distant IRX population are identified by first redshifting to z= 2 the spectral energy distributions (SEDs) of all sources with secure spectroscopic redshifts in the AEGIS (6488) and the GOODS-North (1784) surveys and then selecting those that qualify as IRX sources at that redshift. A total of 19 galaxies are selected. The mean redshift of the sample is z≈ 1. We do not find strong evidence for Compton thick QSOs in the sample. For nine sources with X-ray counterparts, the X-ray spectra are consistent with Compton thin active galactic nucleus (AGN). Only three of them show tentative evidence for Compton thick obscuration. The SEDs of the X-ray undetected population are consistent with starburst activity. There is no evidence for a hot dust component at the mid-infrared associated with AGN heated dust. If the X-ray undetected sources host AGN, an upper limit of L_X(2–10 keV) = 10^43 erg s^−1 is estimated for their intrinsic luminosity. We propose that a large fraction of the z≈ 2 IRX population is not Compton thick quasi-stellar objects (QSOs) but low-luminosity [L_X(2–10 keV) < 10^43 erg s^−1], possibly Compton thin, AGN or dusty starbursts. It is shown that the decomposition of the AGN and starburst contribution to the mid-IR is essential for interpreting the nature of this population, as star formation may dominate this wavelength regime.
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© 2010 The Authors. Journal compilation, © 2010 RAS. The authors wish to thank the anonymous referee for constructive suggestions that improved the paper and Alison Coil for useful comments. AG acknowledges financial support from the Marie-Curie Reintegration Grant PERG03-GA-2008-230644. PGP-G acknowledges support from the Spanish Ministry of Science and Innovation under grants AYA 2006-02358, AYA 2006-15698-C02-02 and CSD2006-100070, and from the Ramón y Cajal Program financed by the Spanish Government and the European Union. This study makes use of data from AEGIS, a multiwavelength sky survey conducted with the Chandra, GALEX, Hubble, Keck, CFHT, MMT, Subaru, Palomar, Spitzer, VLA and other telescopes and supported in part by the NSF, NASA and the STFC.
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Akylas A., Georgantopoulos I., Georgakakis A., Kitsionas S., Hatziminaoglou E., 2006, A&A, 459, 693 Alonso Herrero A. et al., 2006, ApJ, 640, 167 Babbedge T. S. R. et al., 2004, MNRAS, 353, 654 Barger A. J. et al., 2003, AJ, 126, 632 Barger A. J., Cowie L. L., Mushotzky R. F., Yang Y., Wang W.-H., Steffen A. T., Capak P., 2005, AJ, 129, 578 Barmby P., Huang J., Ashby M. L. N., Eisenhardt P. R. M., Fazio G. G., Willner S. P., Wright E. L., 2008, ApJS, 177, 431 Brodwin M. et al., 2008, ApJ, 687, L65 Bauer F. E., Yan L., Sajina A., Alexander D. M., 2010, AJ, 710, 212 Broos P., Townsley L., Getman K., Bauer F., 2002, ACIS Extract, An ACIS Point Source Extraction Package. Pennsylvania State University Brusa M. et al., 2005, A&A, 432, 69 Bussmann R. S. et al., 2009a, ApJ, 693, 750 Bussmann R. S. et al., 2009b, ApJ, 705, 184 Capak P. et al., 2004, AJ, 127, 180 Coil A. L., Newman J. A., Kaiser N., Davis M., Ma C., Kocevski D. D., Koo D. C., 2004, ApJ, 617, 765 Cowie L. L., Barger A. J., Bautz M. W., Brandt W. N., Garmire G. P., 2003, ApJ, 584, L57 Daddi E. et al., 2007, ApJ, 670, 173 Davis M. et al., 2003, in Guhathakurta P., ed., Society of Photo-Optical Instrumentation Engineers (SPIE) Conference Series Vol. 4834, Science Objectives and Early Results of the DEEP2 Redshift Survey. SPIE, Bellingham, WA, p. 161 Davis M. et al., 2007, ApJ, 660, L1 Dey A. et al., 2008, ApJ, 677, 943 Donley J. L., Rieke G. H., Pérez González P. G., Rigby J. R., Alonso Herrero A., 2007, ApJ, 660, 167 Donley J. L., Rieke G. H., Pérez González P. G., Barro G., 2008, ApJ, 687, 111 Draper A. R., Ballantyne D. R., 2009, ApJ, 707, 778 Efstathiou A., Rowan-Robinson M., 1995, MNRAS, 273, 649 Efstathiou A., Rowan-Robinson M., 2003, MNRAS, 343, 322 Efstathiou A., Rowan-Robinson M., Siebenmorgen R., 2000, MNRAS, 313, 734 Elvis M. et al., 1994, ApJS, 95, 1 Fiore F. et al., 2008, ApJ, 672, 94 Fiore F. et al., 2009, ApJ, 693, 447 Georgakakis A., Rowan-Robinson M., Babbedge T. S. R., Georgantopoulos I., 2007, MNRAS, 377, 203 Georgakakis A., Nandra K., Laird E. S., Aird J., Trichas M., 2008, MNRAS, 388, 1205 Georgakakis A. et al., 2009, MNRAS, 397, 623 Georgantopoulos I., Georgakakis A., Rowan-Robinson M., Rovilos E., 2008, A&A, 484, 671 Georgantopoulos I., Akylas A., Georgakakis A., Rowan-Robinson M., 2009, A&A, 507, 747 George I. M., Turner T. J., Netzer H., Nandra K., Mushotzky R. F., Yaqoob T., 1998, ApJS, 114, 73 Getman K. V. et al., 2005, ApJS, 160, 319 Ghisellini G., Haardt F., Matt G., 1994, MNRAS, 267, 743 Gilli R., Comastri A., Hasinger G., 2007, A&A, 463, 79 Gondek D., Zdziarski A. A., Johnson W. N., George I. M., McNaron-Brown K., Magdziarz P., Smith D., Gruber D. E., 1996, MNRAS, 282, 646 Hatziminaoglou E. et al., 2005, AJ, 129, 1198 Hickox R. C., Markevitch M., 2006, ApJ, 645, 95 Ilbert O. et al., 2006, A&A, 457, 841 Lacy M. et al., 2004, ApJS, 154, 166 Laird E. S. et al., 2009, ApJS, 180, 102 Lutz D., Maiolino R., Spoon H. W. W., Moorwood A. F. M., 2004, A&A, 418, 465 Marshall F. E., Boldt E. A., Holt S. S., Miller R. B., Mushotzky R. F., Rose L. A., Rothschild R. E., Serlemitsos P. J., 1980, ApJ, 235, 4 Matt G. et al., 1999, A&A, 341, L39 Morrison R., McCammon D., 1983, ApJ, 270, 119 Mullaney J. R., Alexander D. M., Huynh M., Goulding A. D., Frayer D., 2009, MNRAS, 1649 Murphy E. J., Chary R., Alexander D. M., Dickinson M., Magnelli B., Morrison G., Pope A., Teplitz H. I., 2009, ApJ, 698, 1380 Nandra K., Pounds K. A., 1994, MNRAS, 268, 405 Nandra K. et al., 2007a, ApJ, 660, L11 Nandra K., O’Neill P. M., George I. M., Reeves J. N., 2007b, MNRAS, 382, 194 Narayanan D. et al., 2009, preprint (ArXiv0910.2234) Pérez González P. G. et al., 2005, ApJ, 630, 82 Pérez González P. G. et al., 2008, ApJ, 675, 234 Polletta M. d. C., et al., 2006, ApJ, 642, 673 Pope A. et al., 2008, ApJ, 689, 127 Prieto M. A., Reunanen J., Tristram K. R. W., Neumayer N., Fernández Ontiveros J. A., Orienti M., Meisenheimer K., 2010, MNRAS, 402, 724 Ranalli P., Comastri A., Setti G., 2003, A&A, 399, 39 Risaliti G., Elvis M., 2004, in Barger A. J., ed., Supermassive Black Holes in the Distant Universe Vol. 308 of Astrophysics and Space Science Library, A Panchromatic View of AGN. p. 187 Rowan-Robinson M., 1995, MNRAS, 272, 737 Rowan-Robinson M. et al., 2005, AJ, 129, 1183 Rowan-Robinson M. et al., 2008, MNRAS, 386, 697 Rowan-Robinson M., Valtchanov I., Nandra K., 2009, MNRAS, 397, 1326 Sajina A. et al., 2008, ApJ, 683, 659 Sazonov S., Revnivtsev M., Krivonos R., Churazov E., Sunyaev R., 2007, A&A, 462, 57 Stern D. et al., 2005, ApJ, 631, 163 Sutherland W., Saunders W., 1992, MNRAS, 259, 413 Terashima Y. et al., 2002, ApJ, 139, 1 Townsley L. K., Feigelson E. D., Montmerle T., Broos P. S., Chu Y., Garmire G. P., 2003, ApJ, 593, 874 Tozzi P. et al., 2006, A&A, 451, 457 Treister E. et al., 2009a, ApJ, 706, 535 Treister E., Urry C. M., Virani S., 2009b, ApJ, 696, 110 Weiner B. J. et al., 2005, ApJ, 620, 595 Wirth G. D. et al., 2004, AJ, 127, 3121 Worsley M. A. et al., 2005, MNRAS, 357, 1281 Yan L. et al., 2007, ApJ, 658, 778
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