Heavy X-ray obscuration in the most luminous galaxies discovered by WISE

Creators: Vito, F.; Brandt, W. N.; Stern, D.; Assef, R. J.; Chen, C.-T. J.; Brightman, M.; Comastri, A.; Eisenhardt, P.; Garmire, G. P.; Hickox, R. C.; Lansbury, G.; Tsai, C.-W.; Walton, D. J.; Wu, J. W.

Abstract

Hot dust-obscured galaxies (DOGs) are hyperluminous (L_(8–1000 μm) > 10^(13) L_⊙) infrared galaxies with extremely high (up to hundreds of K) dust temperatures. The sources powering both their extremely high luminosities and dust temperatures are thought to be deeply buried and rapidly accreting supermassive black holes (SMBHs). Hot DOGs could therefore represent a key evolutionary phase in which the SMBH growth peaks. X-ray observations can be used to study their obscuration levels and luminosities. In this work, we present the X-ray properties of the 20 most luminous (L_(bol) ≳ 10^(14) L_⊙) known hot DOGs at z = 2–4.6. Five of them are covered by long-exposure (10–70 ks) Chandra and XMM–Newton observations, with three being X-ray detected, and we study their individual properties. One of these sources (W0116−0505) is a Compton-thick candidate, with column density N_H = (1.0–1.5) × 10^(24) cm^(−2) derived from X-ray spectral fitting. The remaining 15 hot DOGs have been targeted by a Chandra snapshot (3.1 ks) survey. None of these 15 are individually detected; therefore, we applied a stacking analysis to investigate their average emission. From hardness ratio analysis, we constrained the average obscuring column density and intrinsic luminosity to be log N_H (cm^(−2)) > 23.5 and L_X ≳ 10^(44) erg s^(−1), which are consistent with results for individually detected sources. We also investigated the L_X–L_6 μm and LX–L_(bol) relations, finding hints that hot DOGs are typically X-ray weaker than expected, although larger samples of luminous obscured quasi-stellar objects are needed to derive solid conclusions.

Additional Information

© 2017 The Author(s). Published by Oxford University Press on behalf of the Royal Astronomical Society. Received 24 March 2003. Accepted 30 September 2003. We thank the anonymous referee for useful comments and suggestions, which helped in significantly improving this work. FV, WNB, and C-TJC acknowledge support from the Penn State ACIS Instrument Team Contract SV4-74018 (issued by the Chandra X-ray Center, which is operated by the Smithsonian Astrophysical Observatory for and on behalf of NASA under contract NAS8-03060) and the V.M. Willaman Endowment. RJA was supported by FONDECYT grant number 1151408. PE and DS acknowledge support from Chandra Award Number 17700696 issued by the Chandra X-ray Center. DJW acknowledges support from STFC in the form of an Ernest Rutherford Fellowship. JWW acknowledges support from MSTC through grant 2016YFA0400702. The Guaranteed Time Observations (GTO) included here were selected by the ACIS Instrument Principal Investigator, Gordon P. Garmire, of the Huntingdon Institute for X-ray Astronomy, LLC, which is under contract to the Smithsonian Astrophysical Observatory; Contract SV2-82024. This publication makes use of data products from the Wide-field Infrared Survey Explorer, which is a joint project of the University of California, Los Angeles, and the Jet Propulsion Laboratory/California Institute of Technology, funded by the National Aeronautics and Space Administration, and was supported by NASA under Proposal No. 13-ADAP13-0092 issued through the Astrophysics Data Analysis Program. Based on observations obtained with XMM–Newton, an ESA science mission with instruments and contributions directly funded by ESA Member States and NASA.

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