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

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

Research output: Contribution to journalArticle

16 Scopus citations

Abstract

Hot dust-obscured galaxies (DOGs) are hyperluminous (L8-1000 μm > 1013L) 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 (Lbol ≳ 1014 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 NH = (1.0-1.5) × 1024 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 NH (cm-2) > 23.5 and LX ≳ 1044 erg s-1, which are consistent with results for individually detected sources. We also investigated the LX-L6 μm and LX-Lbol 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.

Original languageEnglish (US)
Pages (from-to)4528-4540
Number of pages13
JournalMonthly Notices of the Royal Astronomical Society
Volume474
Issue number4
DOIs
StatePublished - Mar 1 2018

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science

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    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., Lansbury, G., Tsai, C. W., Walton, D. J., & Wu, J. W. (2018). Heavy X-ray obscuration in the most luminous galaxies discovered by WISE. Monthly Notices of the Royal Astronomical Society, 474(4), 4528-4540. https://doi.org/10.1093/mnras/stx3120