DISCOVERY OF STRONG IRON K{alpha} EMITTING COMPTON THICK QUASARS AT z = 2.5 AND 2.9

Journal Article · Tue Mar 01 04:00:00 EST 2011 · Astrophysical Journal Letters

DOI:https://doi.org/10.1088/2041-8205/729/1/L4· OSTI ID:21560466

Feruglio, C; Daddi, E ^[1]; Fiore, F; Piconcelli, E ^[2]; Alexander, D M ^[3]; Malacaria, C ^[4]

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1. Laboratoire AIM, CEA/DSM-CNRS-Universite Paris Diderot, Irfu/Service d'Astrophysique, CEA Saclay, Orme des Merisiers, 91191 Gif-sur-Yvette Cedex (France)
2. INAF-Osservatorio Astronomico di Roma, via Frascati 33, 00040 Monteporzio Catone (Italy)
3. Department of Physics, Durham University, South Road, DH1 3LE (United Kingdom)
4. Universita' La Sapienza, Piazzale Aldo Moro 5, 00185 Roma (Italy)

We report the detection of the 6.4 keV iron K{alpha} 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 {approx} 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 K{alpha} line, of the rest-frame mid-IR continuum and of the UV rest-frame narrow emission lines to infer intrinsic L{sub 2-10}{sub keV} {approx}> 10{sup 44} erg s{sup -1}, about 1.0-2.5 dex larger than the observed ones, hence confirming the presence of an absorber with N{sub H}>10{sup 24} cm{sup -2}. The two BzK galaxies have stellar masses of 5 x 10{sup 10} M{sub sun} and, based on Very Large Array 1.4 GHz and submillimeter 870 {mu}m observations, they appear to host vigorous starburst activity with star formation rate {approx} 300-700 M{sub sun} yr{sup -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{sub 2-10}{sub keV}>10{sup 44} erg s{sup -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.

• OSTI ID: 21560466
• Journal Information: Astrophysical Journal Letters, Journal Name: Astrophysical Journal Letters Journal Issue: 1 Vol. 729; ISSN 2041-8205
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
COSMIC RADIO SOURCES
DETECTION
ELEMENTS
EMISSION
EVOLUTION
GALAXIES
IRON
METALS
QUASARS
TRANSITION ELEMENTS