2006/06/13 by Samuel J. Schmidt, S. J. Schmidt, Andrew J. Connolly +3
Physics and Astronomy · #Active galactic nucleus #Astronomy #Astrophysics #Astrophysics and Cosmic Phenomena #Galaxies: Formation, Evolution, Phenomena #Galaxy #Physics #Population #Radio Astronomy Observations and Technology #Radio galaxy #Redshift #X-shaped radio galaxy #astro-ph
paper · pdf · doi:10.1086/506444
published as Astrophys.J.649:63-78,2006 · Accepted for pulication in the Astrophysical Journal, 19 pages, 16 figures, 6 tables. A version with full resolution figures is available at http://lahmu.phyast.pitt.edu/dragons/dragons.ps.gz
arxiv created 2006/06/13 · openalex publication_date 2006/09/18 · arxiv updated 2009/12/01 · openalex created_date 2016/06/24 · openalex updated_date 2026/08/05
We present the first results from the Distant Radio Galaxies Optically Non-detected in the SDSS (DRaGONS) survey. Using a novel selection technique for identifying high-redshift radio galaxy (HzRG) candidates, a large sample is compiled using bright ( S 1.4 GHz > 100 mJy) radio sources from the FIRST survey having no optical counterpart in the SDSS. Near-IR K -band imaging for 96 targets allows preliminary identification of HzRG candidates through the well-known K - z relation, for subsequent spectroscopic observation. We measure magnitudes brighter than K ≈ 19.5 for 70 of the 96, and limiting magnitudes for the remainder. Redshifts based on a linear fit to the K - z diagram give a mean = 2.5 and median z = 2.0, showing that this method should be efficient at identifying a large number of HzRGs. This selection is also sensitive to a previously unseen population of anomalously red radio galaxies ( r - K > 6.5-7), which may indicate significant obscuration at moderate redshifts. These account for >10% of our sample and may represent a sizable radio-loud population missing from current optically selected AGN samples. We also identify 479 EROs to K = 17.5 in the fields surrounding our HzRG candidates, in a noncontiguous area of 2.38 deg 2 . There is a small overdensity of EROs surrounding the radio galaxy candidates over random fields and some evidence for a physical association of the EROs with the radio galaxies. The clustering of all K ≤ 19.0 galaxies around the radio targets, however, reveals no evidence of a global galaxy excess, strengthening our conclusion that the EROs trace an overdensity not evident in the overall galaxy population.