The Massive Hosts of Radio Galaxies across Cosmic Time

August 2007 • 2007ApJS..171..353S

Authors • Seymour, Nick • Stern, Daniel • De Breuck, Carlos • Vernet, Joel • Rettura, Alessandro • Dickinson, Mark • Dey, Arjun • Eisenhardt, Peter • Fosbury, Robert • Lacy, Mark • McCarthy, Pat • Miley, George • Rocca-Volmerange, Brigitte • Röttgering, Huub • Stanford, S. Adam • Teplitz, Harry • van Breugel, Wil • Zirm, Andrew

Abstract • We present the results of a comprehensive Spitzer survey of 69 radio galaxies across 1<z<5.2. Using IRAC (3.6-8.0 μm), IRS (16 μm), and MIPS (24-160 μm) imaging, we decompose the rest-frame optical to infrared spectral energy distributions into stellar, AGN, and dust components and determine the contribution of host galaxy stellar emission at rest-frame H band. Stellar masses derived from rest-frame near-IR data, where AGN and young star contributions are minimized, are significantly more reliable than those derived from rest-frame optical and UV data. We find that the fraction of emitted light at rest-frame H band from stars is >60% for ~75% of the high-redshift radio galaxies. As expected from unified models of AGNs, the stellar fraction of the rest-frame H-band luminosity has no correlation with redshift, radio luminosity, or rest-frame mid-IR (5 μm) luminosity. In addition, while the stellar H-band luminosity does not vary with stellar fraction, the total H-band luminosity anticorrelates with the stellar fraction as would be expected if the underlying hosts of these radio galaxies comprise a homogeneous population. The resultant stellar luminosities imply stellar masses of 10¹¹-10^11.5 M_solar even at the highest redshifts. Powerful radio galaxies tend to lie in a similar region of mid-IR color-color space as unobscured AGNs, despite the stellar contribution to their mid-IR SEDs at shorter wavelengths. The mid-IR luminosities alone classify most HzRGs as LIRGs or ULIRGs with even higher total-IR luminosities. As expected, these exceptionally high mid-IR luminosities are consistent with an obscured, highly accreting AGN. We find a weak correlation of stellar mass with radio luminosity.

Links

• PREPRINT http://arxiv.org/abs/astro-ph/0703224
• NED https://ned.ipac.caltech.edu/uri/NED::InRefcode/2007ApJS..171..353S
• ELECTR https://doi.org/10.1086%2F517887
• SIMBAD http://simbad.u-strasbg.fr/simbo.pl?bibcode=2007ApJS..171..353S
• PDF https://stacks.iop.org/0067-0049/171/353/pdf
• DATA https://irsa.ipac.caltech.edu/bibdata/2007/S/2007ApJS..171..353S.html
• SPIRES http://inspirehep.net/search?p=find+eprint+astro-ph/0703224