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Galaxy Clusters around Radio-loud Active Galactic Nuclei at 1.3 < z < 3.2 as Seen by Spitzer

Wylezalek, Dominika and Galametz, Audrey and Stern, Daniel and Vernet, Joël and de Breuck, Carlos and Seymour, Nick and Brodwin, Mark and Eisenhardt, Peter R. M. and Gonzalez, Anthony H. and Hatch, Nina and Jarvis, Matt and Rettura, Alessandro and Stanford, Spencer A. and Stevens, Jason A. (2013) Galaxy Clusters around Radio-loud Active Galactic Nuclei at 1.3 < z < 3.2 as Seen by Spitzer. Astrophysical Journal, 769 (1). Art. No. 79. ISSN 0004-637X. doi:10.1088/0004-637X/769/1/79.

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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.

Item Type:Article
Related URLs:
URLURL TypeDescription
Wylezalek, Dominika0000-0003-2212-6045
Galametz, Audrey0000-0002-1504-8117
Stern, Daniel0000-0003-2686-9241
de Breuck, Carlos0000-0002-6637-3315
Seymour, Nick0000-0003-3506-5536
Brodwin, Mark0000-0002-4208-798X
Gonzalez, Anthony H.0000-0002-0933-8601
Jarvis, Matt0000-0001-7039-9078
Rettura, Alessandro0000-0002-5615-256X
Additional Information:© 2013 American Astronomical Society. Received 2013 February 11; accepted 2013 April 1; published 2013 May 6. We gratefully acknowledge James Falder and Conor Mancone who were involved in the initial CARLA proposals. N.S. is the recipient of an ARC Future Fellowship. This work is based on observations made with the Spitzer Space Telescope, which is operated by the Jet Propulsion Laboratory, California Institute of Technology under a contract with NASA.
Funding AgencyGrant Number
Australian Research CouncilUNSPECIFIED
Subject Keywords: galaxies: active; galaxies: clusters: general; galaxies: high-redshift; infrared: galaxies; techniques: photometric
Issue or Number:1
Record Number:CaltechAUTHORS:20130718-145023922
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Official Citation:Galaxy Clusters around Radio-loud Active Galactic Nuclei at 1.3 < z < 3.2 as Seen by Spitzer Dominika Wylezalek, Audrey Galametz, Daniel Stern, Joël Vernet, Carlos De Breuck, Nick Seymour, Mark Brodwin, Peter R. M. Eisenhardt, Anthony H. Gonzalez, Nina Hatch, Matt Jarvis, Alessandro Rettura, Spencer A. Stanford, and Jason A. Stevens doi:10.1088/0004-637X/769/1/79
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:39454
Deposited By: Ruth Sustaita
Deposited On:19 Jul 2013 14:33
Last Modified:09 Nov 2021 23:45

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