J/A+A/579/A115 SUDARE-VOICE variability-selection of AGN (Falocco+, 2015)
SUDARE-VOICE variability-selection of active galaxies in the Chandra Deep
Field-South and the SERVS/SWIRE region.
Falocco S., Paolillo M., Covone G., De Cicco D., Longo G., Grado A.,
Limatola L., Vaccari M., Botticella M.T., Pignata G., Cappellaro E.,
Trevese D., Vagnetti F., Salvato M., Radovich M., Hsu L., Capaccioli M.,
Napolitano N., Brandt W.N., Baruffolo A., Cascone E., Schipani P.
<Astron. Astrophys., 579, A115-115 (2015)>
=2015A&A...579A.115F 2015A&A...579A.115F (SIMBAD/NED BibCode)
ADC_Keywords: Active gal. nuclei ; Photometry, SDSS ; Galaxies, IR
Keywords: galaxies: active - surveys - infrared: galaxies
Abstract:
One of the most peculiar characteristics of active galactic nuclei
(AGNs) is their variability over all wavelengths. This property has
been used in the past to select AGN samples and is foreseen to be one
of the detection techniques applied in future multi-epoch surveys,
complementing photometric and spectroscopic methods. In this paper, we
aim to construct and characterise an AGN sample using a multi-epoch
dataset in the r band from the SUDARE-VOICE survey. Our work makes use
of the VST monitoring programme of an area surrounding the Chandra
Deep Field South to select variable sources. We use data spanning a
six-month period over an area of 2 square degrees, to identify AGN
based on their photometric variability. The selected sample includes
175 AGN candidates with magnitude r<23mag. We distinguish different
classes of variable sources through their lightcurves, as well as
X-ray, spectroscopic, SED, optical, and IR information overlapping
with our survey. We find that 12% of the sample (21/175) is
represented by supernovae (SN). Of the remaining sources, 4% (6/154)
are stars, while 66% (102/154) are likely AGNs based on the available
diagnostics. We estimate an upper limit to the contamination of the
variability selected AGN sample ≃34%, but we point out that
restricting the analysis to the sources with available
multi-wavelength ancillary information, the purity of our sample is
close to 80% (102 AGN out of 128 non-SN sources with multi-wavelength
diagnostics). Our work thus confirms the efficiency of the variability
selection method, in agreement with our previous work on the COSMOS
field. In addition we show that the variability approach is roughly
consistent with the infrared selection.
Description:
This work is based on data in the r band from the SUDARE-VOICE survey
performed with the VST telescope (Botticella et al.,
2013Msngr.151...29B 2013Msngr.151...29B; Cappellaro et al., in prep.; Vaccari et al., in
prep.). The data are centred on the Chandra Deep Field South, covering
an area of 2deg2, in the u, g, r, i bands.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table3.dat 64 175 Results on the selected sample
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See also:
II/326 : Revised SWIRE photometric redshifts (Rowan-Robinson+, 2013)
Byte-by-byte Description of file: table3.dat
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Bytes Format Units Label Explanations
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1- 6 I6 --- ID Optical ID
8- 9 I2 h RAh Right ascension (J2000)
11- 12 I2 min RAm Right ascension (J2000)
14- 18 F5.2 s RAs Right ascension (J2000)
20 A1 --- DE- Declination sign (J2000)
21- 22 I2 deg DEd Declination (J2000)
24- 25 I2 arcmin DEm Declination (J2000)
27- 30 F4.1 arcsec DEs Declination (J2000)
32- 36 F5.2 mag Average r band magnitude
38- 41 F4.2 --- Stell Stellarity index (from Sextractor, see text)
43- 46 F4.1 --- signi Significance of variability in rms units
48 I1 --- Qual [1/2] Quality flag defined in Sect. 4 (1)
50 I1 --- SN [0/1] SN (identified by their LC and confirmed
in SUDARE-I, see Sect. 5.1)
52 I1 --- Star [0/1]?=- Stars identified with the diagnostic
using r-i versus the 3.6um to r band flux
ratio (see Sect. 5.3.1)
54 I1 --- AGNx [0/1]?=- X-ray detected/non-detected
sources (2)
56 I1 --- AGNsp [0/1]?=- AGN validation by optical spectroscopy
(Boutsia et al., 2009, Cat. J/A+A/497/81)
58 I1 --- AGNir [0/1]?=- Sources matching the Lacy et al.
(2004ApJS..154..166L 2004ApJS..154..166L) IR criterion for AGN
selection (see Sect. 5.3.2)
60 I1 --- AGNsed [0/1]?=- AGN validation by multi-wavelength
SED fitting (3)
61 A1 --- n_AGNsed [*+] Note on AGNsed (4)
63- 64 I2 --- Class [-2/4]?=- Final source classification (5)
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Note (1): Quality flag as follows:
1 = candidate is robust, with no evident photometric or aesthetic problems
(60% of the 235 candidates)
2 = candidate is likely to be variable, and the photometry may be slightly
affected by the presence of a nearby companion or by minor aesthetic
defects (e.g. faint satellite tracks) (15%)
3 = candidate is very likely spurious, and its variability is uncertain
(the remaining 25%)
Note (2): Sources flagged with 1 (X-ray detected) and 0 (X-ray non-detected)
(see Sect. 5.2)
Note (3): from Rowan-Robinson et al. 2013MNRAS.428.1958R 2013MNRAS.428.1958R, Cat. II/326;
Hsu et al., 2014ApJ...796...60H 2014ApJ...796...60H.
Sources fitted by an AGN template are flagged with 1, otherwise with 0
Note (4): Flag as follows:
* = sources in Rowan-Robinson et al. (2013MNRAS.428.1958R 2013MNRAS.428.1958R, Cat. II/326)
+ = sources in Hsu et al. (2014ApJ...796...60H 2014ApJ...796...60H)
Note (5): This flag is obtained summing the individual AGN flags reported in
Cols. (9)-(12). It is, thus, a positive number for AGN. The SN are indicated
with flag -2 and the stars with flag 1.
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History:
From electronic version of the journal
(End) Patricia Vannier [CDS] 06-Oct-2015