THE SPITZER HIGH-REDSHIFT RADIO GALAXY SURVEY

Journal Article · Fri Dec 10 04:00:00 EST 2010 · Astrophysical Journal

DOI:https://doi.org/10.1088/0004-637X/725/1/36· OSTI ID:21474453

De Breuck, Carlos; Galametz, Audrey; Vernet, Joel ^[1]; Seymour, Nick ^[2]; Stern, Daniel; Eisenhardt, P R. M. ^[3]; Willner, S P; Fazio, G G ^[4]; Lacy, Mark ^[5]; Rettura, Alessandro ^[6]; Rocca-Volmerange, Brigitte ^[7]

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1. European Southern Observatory, Karl Schwarzschild Strasse 2, 85748 Garching (Germany)
2. Mullard Space Science Laboratory, University College London, Holmbury St Mary, Dorking, Surrey, RH5 6NT (United Kingdom)
3. Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, CA 91109 (United States)
4. Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States)
5. National Radio Astronomy Observatory, 520 Edgemont Road, Charlottesville, VA 22903 (United States)
6. Department of Physics and Astronomy, University of California, Riverside, CA 92521 (United States)
7. Institut d'Astrophysique de Paris, UMR7095 CNRS, Universite Pierre et Marie Curie, Paris 6, 98bis boulevard Arago, 75014 Paris (France)

We present results from a comprehensive imaging survey of 70 radio galaxies at redshifts 1 < z < 5.2 using all three cameras on board the Spitzer Space Telescope. The resulting spectral energy distributions unambiguously show a stellar population in 46 sources and hot dust emission associated with the active nucleus in 59. Using a new rest-frame S{sub 3{sub {mu}m}}/S{sub 1.6{sub {mu}m}} versus S{sub 5{sub {mu}m}}/S{sub 3{sub {mu}m}} criterion, we identify 42 sources where the rest-frame 1.6 {mu}m emission from the stellar population can be measured. For these radio galaxies, the median stellar mass is high, 2 x 10{sup 11} M{sub sun}, and remarkably constant within the range 1 < z < 3. At z>3, there is tentative evidence for a factor of two decrease in stellar mass. This suggests that radio galaxies have assembled the bulk of their stellar mass by z {approx} 3, but confirmation by more detailed decomposition of stellar and active galactic nucleus (AGN) emission is needed. The rest-frame 500 MHz radio luminosities are only marginally correlated with stellar mass but are strongly correlated with the rest-frame 5 {mu}m hot dust luminosity. This suggests that the radio galaxies have a large range of Eddington ratios. We also present new Very Large Array 4.86 and 8.46 GHz imaging of 14 radio galaxies and find that radio core dominance-an indicator of jet orientation-is strongly correlated with hot dust luminosity. While all of our targets were selected as narrow-lined, type 2 AGNs, this result can be understood in the context of orientation-dependent models if there is a continuous distribution of orientations from obscured type 2 to unobscured type 1 AGNs rather than a clear dichotomy. Finally, four radio galaxies have nearby (<6'') companions whose mid-IR colors are suggestive of their being AGNs. This may indicate an association between radio galaxy activity and major mergers.

• OSTI ID: 21474453
• Journal Information: Astrophysical Journal, Journal Name: Astrophysical Journal Journal Issue: 1 Vol. 725; ISSN ASJOAB; ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
COSMIC RADIO SOURCES
DUSTS
EMISSION
ENERGY SPECTRA
EVOLUTION
GALACTIC EVOLUTION
GALAXIES
LUMINOSITY
MASS
OPTICAL PROPERTIES
PHYSICAL PROPERTIES
RADIO GALAXIES
RED SHIFT
SPECTRA
TELESCOPES