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The Deep Swire Field. IV. First Properties of the sub-mJy Galaxy Population: Redshift Distribution, AGN Activity, and Star Formation

Strazzullo, Veronica and Pannella, Maurilio and Owen, Frazer N. and Bender, Ralf and Morrison, Glenn E. and Wang, Wei-Hao and Shupe, David L. (2010) The Deep Swire Field. IV. First Properties of the sub-mJy Galaxy Population: Redshift Distribution, AGN Activity, and Star Formation. Astrophysical Journal, 714 (2). pp. 1305-1323. ISSN 0004-637X.

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We present a study of a 20 cm selected sample in the Deep Spitzer Wide-area InfraRed Extragalactic Legacy Survey Very Large Array Field, reaching a 5σ limiting flux density at the image center of S_(1.4 GHz) ~ 13.5 μJy. In a 0.6 × 0.6 deg^2 field, we are able to assign an optical/IR counterpart to 97% of the radio sources. Up to 11 passbands from the NUV to 4.5 μm are then used to sample the spectral energy distribution (SED) of these counterparts in order to investigate the nature of the host galaxies. By means of an SED template library and stellar population synthesis models, we estimate photometric redshifts, stellar masses, and stellar population properties, dividing the sample into three sub-classes of quiescent, intermediate, and star-forming galaxies. We focus on the radio sample in the redshift range 0.3 < z < 1.3 where we estimate to have a redshift completeness higher than 90% and study the properties and redshift evolution of these sub-populations. We find that, as expected, the relative contributions of active galactic nuclei (AGNs) and star-forming galaxies to the μJy population depend on the flux density limit of the sample. At all flux levels, a significant population of "green-valley" galaxies is observed. While the actual nature of these sources is not definitely understood, the results of this work may suggest that a significant fraction of faint radio sources might be composite (and possibly transition) objects, thus a simple "AGN versus star-forming" classification might not be appropriate to fully understand what faint radio populations really are.

Item Type:Article
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Wang, Wei-Hao0000-0003-2588-1265
Shupe, David L.0000-0003-4401-0430
Additional Information:© 2010 American Astronomical Society. Received 2009 July 20; accepted 2010 March 21; published 2010 April 19. We are grateful to Niv Drory for sharing the SED-fitting code used to estimate galaxy stellar masses. We thank the referee, Paolo Padovani, for his careful reading of this manuscript, and for his detailed comments and suggestions which helped us improve the clarity and presentation of this work. Based on observations of the SWIRE Lockman Hole field taken on the NRAO VLA, Spitzer Space Telescope, KPNO Mayall telescope, UKIRT, and CFHT. The National Radio Astronomy Observatory is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc. The Spitzer Space Telescope is operated by the Jet Propulsion Laboratory, California Institute of Technology under a contract with NASA. The United Kingdom Infrared Telescope is operated by the Joint Astronomy Centre on behalf of the Science and Technology Facilities Council of the U.K. The Canada–France–Hawaii Telescope is operated by the National Research Council (NRC) of Canada, the Institut National des Science de l’Univers of the Centre National de la Recherche Scientifique (CNRS) of France, and the University of Hawaii. This research used the facilities of the Canadian Astronomy Data Centre operated by the National Research Council of Canada with the support of the Canadian Space Agency. F.N.O. and G.E.M. were visiting astronomers at the Kitt Peak National Observatory, National Optical Astronomy Observatory, operated by AURA, Inc., under cooperative agreement with the National Science Foundation. This work was supported by NASA through Jet Propulsion Laboratory contract No.1289215. V.S. and M.P. acknowledge support from the Max-Planck Society and the Alexander von Humboldt Foundation. W.H.W. was a Jansky Fellow of the National Radio Astronomy Observatory while contributing to this work.
Funding AgencyGrant Number
NASA through JPL1289215
Max-Planck SocietyUNSPECIFIED
Alexander von Humboldt FoundationUNSPECIFIED
Subject Keywords:cosmology: observations; galaxies: active; galaxies: evolution; galaxies: starburst; radio continuum: galaxies
Issue or Number:2
Classification Code:PACS: 98.54.Ep; 98.62.Ai; 98.62.Py; 95.85.Bh; 98.62.Lv; 98.54.Cm.
Record Number:CaltechAUTHORS:20100526-154509152
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Official Citation:Veronica Strazzullo et al 2010 ApJ 714 1305 doi: 10.1088/0004-637X/714/2/1305
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:18467
Deposited By: Jason Perez
Deposited On:02 Jun 2010 18:49
Last Modified:03 Oct 2019 01:43

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