J/ApJ/923/31 CHILES VERDES: COSMOS radio variability (Sarbadhicary+, 2021)
CHILES VERDES: radio variability at an unprecedented depth and cadence in the
COSMOS field.
Sarbadhicary S.K., Tremou E., Stewart A.J., Chomiuk L., Peters C.,
Hales C., Strader J., Momjian E., Fender R., Wilcots E.M.
<Astrophys. J., 923, 31 (2021)>
=2021ApJ...923...31S 2021ApJ...923...31S
ADC_Keywords: Radio continuum; Active gal. nuclei; Surveys; Redshifts;
X-ray sources
Keywords: Radio continuum emission ; Radio active galactic nuclei ;
Time domain astronomy ; Time series analysis
Abstract:
Although it is well established that some extragalactic radio sources
are time-variable, the properties of this radio variability, and its
connection with host galaxy properties, remain to be
explored-particularly for faint sources. Here we present an analysis
of radio variable sources from the CHILES Variable and Explosive Radio
Dynamic Evolution Survey (CHILES VERDES)-a partner project of the
1.4GHz COSMOS HI Large Extragalactic Survey. CHILES VERDES provides an
unprecedented combination of survey depth, duration, and cadence, with
960hr of 1-2GHz continuum VLA data obtained over 209 epochs between
2013 and 2019 in a 0.44deg2 section of the well-studied
extragalactic deep field, COSMOS. We identified 18 moderate-variability
sources (showing 10%-30% flux density variation) and 40 lower-variability
sources (2%-10% flux density variation). They are mainly active
galactic nuclei (AGNs) with radio luminosities in the range of
1022-1027W/Hz, based on cross-matching with COSMOS multiwavelength
catalogs. The moderate-variability sources span redshifts z=0.22-1.56,
have mostly flat radio spectra (α>-0.5), and vary on
timescales ranging from days to years. The lower-variability sources
have similar properties, but generally have higher radio luminosities
than the moderate-variability sources, extending to z=2.8, and have
steeper radio spectra (α<-0.5). No star-forming galaxy showed
statistically significant variability in our analysis. The observed
variability likely originates from scintillation on short (∼week)
timescales, and Doppler-boosted intrinsic AGN variability on long
(month-year) timescales.
Description:
The COSMOS HI Legacy Extragalactic Survey (CHILES) Variable and
Explosive Radio Dynamic Evolution Survey (VERDES), designed to look
for variable phenomena within a single VLA pointing observed at L-band
(1-2GHz), using nearly 1000hr of observations obtained between
2013 and 2019. The data were taken as part of the CHILES, a survey of
neutral hydrogen traced by the 21cm emission line in the COSMOS field
out to an unprecedented depth of z∼0.5. The CHILES pointing was chosen
to be in the COSMOS field where it can enjoy significant
multiwavelength supporting data. The single L-band pointing yields a
field of view 0.5° in diameter (half-power beamwidth) at 1.5GHz.
The data were obtained in the VLA's B-configuration, which yields a
resolution of 4.3" at 1.5GHz. See Section 2.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table2.dat 90 18 Multi-band and multi-wavelength properties of our
18 CHILES VERDES moderate-variability sources
table3.dat 90 40 Multi-band and multi-wavelength properties of our
40 CHILES VERDES low-variability sources
fig8.dat 38 3096 Light curves for sources designated
"moderate-variability"
fig9.dat 38 6880 Light curves of the 40 low-variability sources
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See also:
II/284 : COSMOS Multi-Wavelength Photometry Catalog (Capak+, 2007)
VIII/65 : 1.4GHz NRAO VLA Sky Survey (NVSS) (Condon+ 1998)
VIII/87 : The Allen Telescope Array 20cm Survey (ATATS). I. (Croft+ 2010)
VIII/103 : Herschel Multi-tiered Extragalactic Survey (Oliver+, 2012)
VIII/95 : Herschel Multi-tiered Extragalactic Survey (Oliver+, 2012)
J/AJ/127/2565 : Faint FIRST variable radio sources (De Vries+, 2004)
J/ApJS/155/271 : CDF-South: Optical spectroscopy (Szokoly+, 2004)
J/MNRAS/385/2225 : AzTEC millimetre survey of COSMOS field (Scott+, 2008)
J/ApJ/690/20 : Models of AGN & black hole populations (Shankar+, 2009)
J/ApJ/699/L43 : FIRST-NVSS-SDSS AGN sample catalog (Smolcic+, 2009)
J/ApJS/188/384 : The VLA-COSMOS survey. IV. (Schinnerer+, 2010)
J/MNRAS/415/3831 : AzTEC/ASTE source catalogue (Aretxaga+, 2011)
J/ApJ/739/76 : Pi GHz Sky Survey (PiGSS). II. (Bower+, 2011)
J/ApJ/740/65 : VLA search for 5GHz radio transients (Ofek+, 2011)
J/ApJ/742/49 : Var. & transient radio sources in FIRST (Thyagarajan+, 2011)
J/MNRAS/436/1919 : SCUBA observations of COSMOS galaxies (Casey+, 2013)
J/ApJ/762/93 : PiGSS. III. ELAIS-N1, Coma & Lockman fields (Croft+, 2013)
J/ApJ/769/125 : 1.4GHz radio var. in FIRST & SDSS Stripe 82 (Hodge+, 2013)
J/AJ/147/143 : MOJAVE. XI. Spectral distributions (Hovatta+, 2014)
J/ApJ/819/62 : The COSMOS-Legacy Survey (CLS) catalog (Civano+, 2016)
J/ApJS/224/24 : The COSMOS2015 catalog (Laigle+, 2016)
J/ApJ/817/34 : C-COSMOS Legacy multiwavelength cat. (Marchesi+, 2016)
J/ApJ/818/105 : CNSS pilot survey (Mooley+, 2016)
J/A+A/607/A132 : VLBA observations of the COSMOS field (Herrera Ruiz+, 2017)
J/ApJS/230/7 : Spectral flux densities from 50MHz to 50GHz (Perley+, 2017)
J/A+A/602/A2 : VLA-COSMOS 3 GHz Large Project. II. (Smolcic+, 2017)
J/A+A/602/A1 : VLA-COSMOS 3 GHz Large Project (Smolcic+, 2017)
J/MNRAS/474/4396 : MASIV Survey. IV. Radio AGNs variability (Koay+, 2018)
J/ApJ/874/13 : 24yr of radio observations of V404 Cygni (Plotkin+, 2019)
Byte-by-byte Description of file: table[23].dat
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Bytes Format Units Label Explanations
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1- 4 A4 --- ID CHILES VERDES identifier
6- 12 A7 --- TRAP Internal ID used by TraP algorithm for source
14- 22 F9.5 deg RAdeg [149.9/150.7] Right Ascension (J2000)
24- 30 F7.5 deg DEdeg [2/2.7] Declination (J2000)
32- 36 F5.2 mJy Flux [0.09/10.4] Median integrated flux density
38- 42 F5.3 --- Var [0.01/0.3] Coefficient of variability
44- 50 F7.3 --- eta [1/804] Reduced chi-squared statistic
52- 56 F5.2 [W/Hz] logL1.4 [22.17/26.4]? Log 1.4GHz luminosity (1)
58 A1 --- l_logLx Limit flag on logLx
59- 63 F5.2 [10-7W] logLx [41/44.5]? Log 0.5-8keV X-ray luminosity
from Marchesi+ 2016, J/AJ/817/34 ;
in units of erg/s
65- 70 F6.3 --- alpha [-1.9/1]? The 1-4GHz spectral index
72- 77 F6.3 --- e_alpha [0.07/0.6]? Uncertainty in alpha
79- 84 F6.3 --- zbest [0.12/2.7]? Best available redshift
measurement from Marchesi+ 2016, J/AJ/817/34
86- 90 A5 --- Class Classification (2)
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Note (1): From Smolcic+ 2017, J/A+A/602/A1
Note (2): From Marchesi+ 2016, J/AJ/817/34 -- Code as follows:
HLAGN = high-to-moderate luminosity AGN
MLAGN = moderate-to-low luminosity AGN
See Section 5.
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Byte-by-byte Description of file: fig[89].dat
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Bytes Format Units Label Explanations
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1- 4 A4 --- ID CHILES VERDES identifier
6- 13 E8.2 Jy Flux [6.5e-6/0.013] Integrated flux density
16- 23 E8.2 Jy e_Flux [1.4e-5/0.01] Uncertainty in Flux
26- 38 F13.5 d JD Julian Date
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History:
From electronic version of the journal
(End) Prepared by [AAS], Emmanuelle Perret [CDS] 15-May-2023