DISCOVERY OF STRONG IRON Kα EMITTING COMPTON THICK QUASARS AT z = 2.5 AND 2.9

2011/01/18 by C. Feruglio, E. Daddi, F. Fiore +4 · 2 citations
Physics and Astronomy · #Active galactic nucleus #Astronomy #Astrophysical Phenomena and Observations #Astrophysics #Astrophysics and Star Formation Studies #Doubly ionized oxygen #Emission spectrum #Equivalent width #Galaxies: Formation, Evolution, Phenomena #Galaxy #Luminous infrared galaxy #Physics #Quasar #Redshift #Rest frame #Spectral line #Star formation #astro-ph.CO #astro-ph.HE

paper · pdf · doi:10.1088/2041-8205/729/1/l4

ApJ Letters, in press. 6 pages, 3 figures

arxiv created 2011/01/18 · openalex publication_date 2011/02/08 · arxiv updated 2015/05/27 · openalex created_date 2016/06/24 · openalex updated_date 2026/08/05

Abstract

We report the detection of the 6.4 keV iron Kα emission line in two infrared-luminous, massive, star-forming BzK galaxies at z = 2.578 and z = 2.90 in the CDF-S. The Chandra 4 Ms spectra of BzK 4892 and BzK 8608 show a reflection-dominated continuum with strong iron lines, with rest-frame equivalent widths EW ∼ 2.3 keV and 1.2 keV, respectively, demonstrating Compton thick (CT) obscuration of the central active galactic nucleus (AGN). For BzK 8608, the line identification closely matches the existing photometric redshift derived from the stellar emission. We use the observed luminosities of the iron Kα line, of the rest-frame mid-IR continuum and of the UV rest-frame narrow emission lines to infer intrinsic L 2–10 keV ≳ 10 44 erg s −1 , about 1.0–2.5 dex larger than the observed ones, hence confirming the presence of an absorber with N H >10 24 cm −2 . The two BzK galaxies have stellar masses of 5 × 10 10 M ☉ and, based on Very Large Array 1.4 GHz and submillimeter 870 μm observations, they appear to host vigorous starburst activity with star formation rate ∼ 300–700 M ☉ yr −1 that is also optically thick. We estimate that the AGN might also conceivably account for an important fraction of the bolometric far-IR emission of the galaxies. The implied volume density of CT AGN with L 2–10 keV >10 44 erg s −1 is in agreement with predictions from X-ray background synthesis models. These sources provide one of the first clear-cut observations of the long-sought phase of simultaneous, heavily obscured quasar and star formation activity, predicted by models of massive galaxy evolution at high redshifts.

Citations

• IDENTIFICATIONS AND PHOTOMETRIC REDSHIFTS OF THE 2 Ms CHANDRA DEEP FIELD-SOUTH SOURCES
• A Thermal Wind Model for the X-Ray Outflow in GRO J1655-40
• The synthesis of the cosmic X-ray background in the Chandra and XMM-Newton era
• The XMM-Newton and BeppoSAX view of the Ultra Luminous Infrared Galaxy MKN 231
• Spitzer’sContribution to the AGN Population
• Energy input from quasars regulates the growth and activity of black holes and their host galaxies
• Reliable Identification of Compton‐thick Quasars atz≈ 2:SpitzerMid‐Infrared Spectroscopy of HDF‐oMD49
• The great observatories origins deep survey
• The Chandra Deep Field–South: Optical Spectroscopy. I.
• Revealing X-ray obscured quasars in SWIRE sources with extreme mid-IR/optical flux ratios
• Searching for mid-IR obscured AGN in the Chandra deep field North

Cited by

• X-ray observations of dust obscured galaxies in theChandradeep field south
• The XMM deep survey in the CDF-S II. a 9-20 keV selection of heavily obscured active galaxies at z>1.7