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Chandra X-ray observations of the hyper-luminous infrared galaxy IRAS F15307+3252.

Hlavacek-Larrondo, J. and Gandhi, P. and Hogan, M. T. and Gendron-Marsolais, M.-L. and Edge, A. C. and Fabian, A. C. and Russell, H. R. and Iwasawa, K. and Mezcua, M. (2017) 'Chandra X-ray observations of the hyper-luminous infrared galaxy IRAS F15307+3252.', Monthly notices of the Royal Astronomical Society., 464 (2). pp. 2223-2233.


Hyper-luminous infrared galaxies (HyLIRGs) lie at the extreme luminosity end of the IR galaxy population with LIR > 1013 L⊙. They are thought to be closer counterparts of the more distant sub-millimeter galaxies, and should therefore be optimal targets to study the most massive systems in formation. We present deep Chandra observations of IRAS F15307+3252 (100 ks), a classical HyLIRG located at z = 0.93 and hosting a radio-loud AGN (L1.4 GHz ∼ 3.5 × 1025 W Hz−1). The Chandra images reveal the presence of extended (r = 160 kpc), asymmetric X-ray emission in the soft 0.3–2.0 keV band that has no radio counterpart. We therefore argue that the emission is of thermal origin originating from a hot intragroup or intracluster medium virializing in the potential. We find that the temperature (∼2 keV) and bolometric X-ray luminosity (∼3 × 1043 erg s−1) of the gas follow the expected LX-ray–T correlation for groups and clusters, and that the gas has a remarkably short cooling time of 1.2 Gyr. In addition, VLA radio observations reveal that the galaxy hosts an unresolved compact steep-spectrum (CSS) source, most likely indicating the presence of a young radio source similar to 3C186. We also confirm that the nucleus is dominated by a redshifted 6.4 keV Fe Kα line, strongly suggesting that the AGN is Compton-thick. Finally, Hubble images reveal an overdensity of galaxies and sub-structure in the galaxy that correlates with soft X-ray emission. This could be a snapshot view of on-going groupings expected in a growing cluster environment. IRAS F15307+3252 might therefore be a rare example of a group in the process of transforming into a cluster.

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Publisher statement:This article has been accepted for publication in Monthly notices of the Royal Astronomical Society ©: 2016 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.
Date accepted:27 September 2016
Date deposited:04 May 2017
Date of first online publication:28 September 2016
Date first made open access:04 May 2017

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