J/ApJ/769/79 Spitzer observations of radio-loud AGNs (CARLA) (Wylezalek+, 2013)
Galaxy clusters around radio-loud active galactic nuclei at 1.3 < z < 3.2
as seen by Spitzer.
Wylezalek D., Galametz A., Stern D., Vernet J., De Breuck C., Seymour N.,
Brodwin M., Eisenhardt P.R.M., Gonzalez A.H., Hatch N., Jarvis M.,
Rettura A., Stanford S.A., Stevens J.A.
<Astrophys. J., 769, 79 (2013)>
=2013ApJ...769...79W 2013ApJ...769...79W
ADC_Keywords: Active gal. nuclei ; Infrared sources ; Galaxies, radio ;
Redshifts ; QSOs
Keywords: galaxies: active; galaxies: clusters: general;
galaxies: high-redshift; infrared: galaxies; techniques: photometric
Abstract:
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 4.5µm
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.
Description:
In this paper, we describe the first results from our ∼400hr Warm
Spitzer snapshot program called Clusters Around Radio-Loud AGN, or
CARLA, a Cycle 7 and Cycle 8 program which takes advantage of
Spitzer's impressive sensitivity to identify massive galaxies at high
redshift. To date, CARLA has targeted nearly 400 radio-loud AGN,
including 187 radio-loud quasars (RLQs) and 200 high-redshift radio
galaxies (HzRGs) (sample size as of 2013 February 20).
CARLA observed the lower redshift (1.3<z<2) sources with the Spitzer
IRAC camera at 3.6 and 4.5um (referred to as IRAC1 and IRAC2) during
Cycle 7 with total exposure times of 800s in IRAC1 and 2000s in IRAC2.
Slightly deeper observations were obtained for the higher redshift
(2<z<3.2) portion of the sample during Cycle 8 with total exposure
times of 1000s in IRAC1 and 2100s in IRAC2.
The HzRGs were selected from the updated compendium of Miley & De
Breuck (2008A&ARv..15...67M 2008A&ARv..15...67M). To create the RLQ sample, we selected
all optically bright (MB←26.5) quasars in the Sloan Digitized Sky
Survey (SDSS; Schneider et al. 2010, VII/260) and the 2dF QSO Redshift
Survey (Croom et al. 2004, VII/241), where the spectroscopy-based
classifications were taken from the original catalogs.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 64 387 The CARLA sample of radio-loud AGNs
(Clusters Around Radio-Loud AGNs)
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See also:
VII/260 : The SDSS-DR7 quasar catalog (Schneider+, 2010)
VIII/79 : The VLA Low-frequency Sky Survey at 74MHz (Cohen+ 2007)
VII/241 : The 2dF QSO Redshift Survey (Croom+ 2004)
VIII/65 : 1.4GHz NRAO VLA Sky Survey (NVSS) (Condon+ 1998)
J/MNRAS/438/1149 : WISE data for radio-loud AGN samples (Gurkan+, 2014)
J/A+A/567/A76 : COSMOS field radio-loud AGN population at z>1 (Baldi+, 2014)
J/ApJ/763/127 : Galaxy clusters discovered in the SPT survey (Reichardt+, 2013)
J/ApJ/746/85 : THe HST Cluster Supernova Survey. V. (Suzuki+, 2012)
J/MNRAS/416/2041 : Hα emitters at z=2.23 (Matsuda+, 2011)
J/AJ/140/533 : Morphologies of selected AGN (Griffith+, 2010)
J/ApJ/716/530 : Mid-IR variability from the SDWFS (Kozlowski+, 2010)
J/ApJ/684/905 : Galaxy clusters from IRAC Shallow Survey (Eisenhardt+, 2008)
J/ApJ/658/815 : Radio loudness of active galactic nuclei (Sikora+, 2007)
J/A+A/461/823 : Candidate Lyα emitting galaxies (Venemans+, 2007)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 19 A19 --- Name Source name (sorted by increasing RA)
21- 22 I2 h RAh Hour of Right Ascension (J2000)
24- 25 I2 min RAm Minute of Right Ascension (J2000)
27- 31 F5.2 s RAs Second of Right Ascension (J2000)
33 A1 --- DE- Sign of the Declination (J2000)
34- 35 I2 deg DEd Degree of Declination (J2000)
37- 38 I2 arcmin DEm Arcminute of Declination (J2000)
40- 43 F4.1 arcsec DEs Arcsecond of Declination (J2000)
45- 48 F4.2 --- z [1.3/4.2] Redshift
50- 54 F5.2 [W/Hz] logL [0/29.5] log of rest-frame 500MHz luminosity
56- 59 F4.1 arcmin-2 Sigma [4.5/22.6]?=0 Surface density Σ of
IRAC-selected sources in the CARLA field
61- 64 A4 --- Type AGN type (HzRGs=high-redshift radio galaxies;
RLQ=radio-loud quasars)
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History:
From electronic version of the journal
(End) Greg Schwarz [AAS], Emmanuelle Perret [CDS] 09-Dec-2014