A strongly starforming group: three massive galaxies associated with a QSO

Abstract

We present here photometric redshift confirmation of the presence of large scale structure around the z=1.82 QSO RXJ0941, which shows an overdensity of submm sources. Radio imaging confirms the presence of the submm sources and pinpoints their likely optical-NIR counterparts. Four of the five submm sources present in this field (including the QSO) have counterparts with redshifts compatible with z=1.82. We show that our photometric redshifts are robust against the use of different spectral templates. We have measured the galaxy stellar mass of the submm galaxies from their rest-frame K-band luminosity obtaining log(M*/Msun)~11.5+-0.2, slightly larger than the Schechter mass of present day galaxies, and hence indicating that most of the stellar mass is already formed. We present optical-to-radio spectral energy distributions (SEDs) of the five SCUBA sources. The emission of RXJ0941 is dominated by reprocessed AGN emission in the observed MIR range, while the starburst contribution completely dominates in the submm range. The SEDs of the other three counterparts are compatible with a dominant starburst contribution above ~24um, with star formation rates SFR~2000Msun/yr, central dust masses log(Mdust/Msun)~9+-0.5 and hence central gas masses log(Mgas/Msun)~10.7. There is very little room for an AGN contribution. From X-ray upper limits and the observed 24um flux, we derive a maximum 2-10keV X-ray luminosity of 1e44 erg/s for any putative AGN, even if they are heavily obscured. This in turn points to relatively small black holes with log(MBH/Msun)<~8 and hence stellar-to-black hole mass ratios about one order of magnitude higher than those observed in the present Universe: most of their central black hole masses are still to be accreted. Local stellar-to-black hole masses ratios can be reached if ~1.3% of the available nuclear gas mass is accreted.

18 pages, 8 figures, 5 tables. Accepted for publication in MNRAS

References in corpus (18)

• The synthesis of the cosmic X-ray background in the Chandra and XMM-Newton era
• The stellar mass assembly of galaxies from z=0 to z=4. Analysis of a sample selected in the rest-frame near-infrared with Spitzer
• Piecing Together the X-ray Background: Bolometric Corrections for Active Galactic Nuclei
• The Galaxy Mass Function up to z=4 in the GOODS-MUSIC sample: into the epoch of formation of massive galaxies
• 350 Micron Dust Emission from High Redshift Quasars
• SHARC-2 350 Micron Observations of Distant Submillimeter Selected Galaxies
• Protoclusters associated with z > 2 radio galaxies. I. Characteristics of high redshift protoclusters
• Weighing the Black Holes in z~2 Submillimeter-Emitting Galaxies Hosting Active Galactic Nuclei
• Photometric redshifts in the SWIRE Survey
• Testing the Evolutionary Link Between Submillimetre Galaxies and Quasars: CO Observations of QSOs at z~2
• A Hubble Space Telescope NICMOS and ACS Morphological Study of z~2 Submillimetre Galaxies
• The XMM-Newton Serendipitous Survey V. Optical identification of the XMM-Newton Medium sensitivity Survey (XMS)
• On the X-ray properties of submm-selected galaxies
• A multi-wavelength study of the proto-cluster surrounding the z=4.1 radio galaxy TN J1338-1942
• A z=1.82 Analog of Local Ultra-massive Elliptical Galaxies
• The XMM-Newton serendipitous survey IV. The AXIS X-ray source counts and angular clustering
• Environments of z>5 quasars: searching for protoclusters at submillimetre wavelengths
• Millimetre observations of a sample of high-redshift obscured quasars

Cited by in corpus (11)

• Coevolution (Or Not) of Supermassive Black Holes and Host Galaxies
• What Drives the Growth of Black Holes?
• The realm of the galaxy protoclusters
• The LABOCA Survey of the Extended Chandra Deep Field South: Clustering of submillimetre galaxies
• An excess of dusty starbursts related to the Spiderweb galaxy
• The Coevolution of Supermassive Black Holes and Massive Galaxies at High Redshift
• Accounting for selection effects in the BH-bulge relations: No evidence for cosmological evolution
• The Main Sequences of Starforming Galaxies and Active Galactic Nuclei at High Redshift
• ASW${}^2$DF: Census of the obscured star formation in a galaxy cluster in formation at $z=2.2$
• Submillimetre observations of X-ray active galactic nuclei in the William Herschel Deep Field
• Submm-bright X-ray absorbed QSOs at z~2: insights into the co-evolution of AGN and star-formation