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Publication Details
AFRICAN RESEARCH NEXUS
SHINING A SPOTLIGHT ON AFRICAN RESEARCH
earth and planetary sciences
Galaxy clusters around radio-loud active galactic nuclei at 1.3 < z < 3.2 as seen by spitzer
Astrophysical Journal, Volume 769, No. 1, Article 79, Year 2013
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Description
We report the first results from the Clusters Around Radio-Loud AGN program, a Cycle 7 and 8 Spitzer Space Telescope snapshot program to investigate the environments of a large sample of obscured and unobscured luminous radio-loud active galactic nuclei (AGNs) at 1.2 < z < 3.2. These data, obtained for 387 fields, reach 3.6 and 4.5 μm depths of [3.6]AB = 22.6 and [4.5]AB = 22.9 at the 95% completeness level, which is two to three times fainter than L* in this redshift range. By using the color cut [3.6]-[4.5] > -0.1 (AB), which efficiently selects high-redshift (z > 1.3) galaxies of all types, we identify galaxy cluster member candidates in the fields of the radio-loud AGN. The local density of these Infrared Array Camera (IRAC)-selected sources is compared to the density of similarly selected sources in blank fields. We find that 92% of the radio-loud AGN reside in environments richer than average. The majority (55%) of the radio-loud AGN fields are found to be overdense at a ≥2σ level; 10% are overdense at a ≥5σ level. A clear rise in surface density of IRAC-selected sources toward the position of the radio-loud AGN strongly supports an association of the majority of the IRAC-selected sources with the radio-loud AGN. Our results provide solid statistical evidence that radio-loud AGN are likely beacons for finding high-redshift galaxy (proto-)clusters. We investigate how environment depends on AGN type (unobscured radio-loud quasars versus obscured radio galaxies), radio luminosity and redshift, finding no correlation with either AGN type or radio luminosity. We find a decrease in density with redshift, consistent with galaxy evolution for this uniform, flux-limited survey. These results are consistent with expectations from the orientation-driven AGN unification model, at least for the high radio luminosity regimes considered in this sample. © 2013. The American Astronomical Society. All rights reserved.
Authors & Co-Authors
Wylezalek, Dominika
United States, Pasadena
Jet Propulsion Laboratory
Germany, Garching Bei Munchen
European Southern Observatory
Galametz, Audrey
Italy, Rome
Istituto Nazionale Di Astrofisica, Rome
Stern, Daniel K.
United States, Pasadena
Jet Propulsion Laboratory
Vernet, Jöel D.R.
Germany, Garching Bei Munchen
European Southern Observatory
de Breuck, Carlos A.
Germany, Garching Bei Munchen
European Southern Observatory
Seymour, Nick
Australia, Sydney
Cass
Brodwin, Mark
United States, Kansas City
University of Missouri-kansas City
Eisenhardt, Peter R.M.
United States, Pasadena
Jet Propulsion Laboratory
González, Anthony H.
United States, Gainesville
University of Florida
Hatch, N.
United Kingdom, Nottingham
University of Nottingham
Jarvis, Matthew J.
United Kingdom, Hatfield
University of Hertfordshire
South Africa, Bellville
University of the Western Cape
Rettura, Alessandro
United States, Pasadena
California Institute of Technology
Stanford, Spencer Adam
United States, Davis
University of California, Davis
United States, Livermore
Lawrence Livermore National Laboratory
Stevens, Jason A.
United Kingdom, Hatfield
University of Hertfordshire
Statistics
Citations: 14
Authors: 14
Affiliations: 12
Identifiers
Doi:
10.1088/0004-637X/769/1/79
ISSN:
0004637X
e-ISSN:
15384357
Study Design
Cross Sectional Study
Study Approach
Quantitative