J/A+A/627/A33 Optically variable AGN in COSMOS field (De Cicco+, 2019)
Optically variable AGN in the three-year VST survey of the COSMOS field.
De Cicco D., Paolillo M., Falocco S., Poulain M., Brandt W.N., Bauer F.E.,
Vagnetti F., Longo G., Grado A., Ragosta F., Botticella M.T., Pignata G.,
Vaccari M., Radovich M., Salvato M., Covone G., Napolitano N.R.,
Marchetti L., Schipani P.
<Astron. Astrophys. 627, A33 (2019)>
=2019A&A...627A..33D 2019A&A...627A..33D (SIMBAD/NED BibCode)
ADC_Keywords: Active gal. nuclei ; Magnitudes ; Redshifts
Keywords: galaxies: active - quasars: general - X-rays: galaxies - surveys
Abstract:
The analysis of the variability of active galactic nuclei (AGNs) at
different wavelengths and the study of possible correlations among
different spectral windows are nowadays a major field of inquiry.
Optical variability has been largely used to identify AGNs in
multivisit surveys. The strength of a selection based on optical
variability lies in the chance to analyze data from surveys of large
sky areas by ground-based telescopes. However the effectiveness of
optical variability selection, with respect to other multiwavelength
techniques, has been poorly studied down to the depth expected from
next generation surveys.
Here we present the results of our r-band analysis of a sample of 299
optically variable AGN candidates in the VST survey of the COSMOS
field, counting 54 visits spread over three observing seasons spanning
>3yr. This dataset is >3 times larger in size than the one presented
in our previous analysis (De Cicco et al., 2015, Cat. J/A+A/574/A112),
and the observing baseline is 8 times longer.
We push towards deeper magnitudes (r(AB)∼23.5mag) compared to past
studies; we make wide use of ancillary multiwavelength catalogs in
order to confirm the nature of our AGN candidates, and constrain the
accuracy of the method based on spectroscopic and photometric
diagnostics. We also perform tests aimed at assessing the relevance of
dense sampling in view of future wide-field surveys.
We demonstrate that the method allows the selection of high-purity
(>86%) samples. We take advantage of the longer observing baseline to
achieve great improvement in the completeness of our sample with
respect to X-ray and spectroscopically confirmed samples of AGNs (59%,
vs. ∼15% in our previous work), as well as in the completeness of
unobscured and obscured AGNs.
The effectiveness of the method confirms the importance to develop
future, more refined techniques for the automated analysis of larger
datasets.
Description:
The VST, located at Cerro Paranal Observatory, is a 2.65m optical
telescope with a 0.938 m-diameter secondary mirror, a modified
Ritchey-Chretien configuration, and an alt-azimuth mount. Its
detector,
In the present work we focus on r-band data only, which have a
three-day observing cadence, while for the g and i bands the cadence
is 10 days; in each case there are several gaps, depending on a number
of observational constraints. In the following, magnitudes are quoted
in the AB system, unless otherwise stated.
File Summary:
--------------------------------------------------------------------------------
FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
table3.dat 59 299 List of the 299 optically variable sources
in the robust sample
--------------------------------------------------------------------------------
See also:
J/A+A/574/A112 : COSMOS field variability-selected AGN nuclei (De Cicco+, 2015)
Byte-by-byte Description of file: table3.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 3 I3 --- ID [1/299] Sequential identification number
5- 13 F9.5 deg RAdeg Right ascension (J2000)
15- 23 F9.7 deg DEdeg Declination (J2000)
25- 29 F5.2 mag rmagavg average VST r(AB) magnitude
31- 34 F4.2 mag ltcrms r.m.s. of the light curve
36- 39 F4.2 --- S/G SExtractor stellarity index
41 I1 --- Qual [1/2] Quality label (1)
43- 44 I2 --- Percent Percentile: the number indicates that the
light curve r.m.s. of the source is above the
threshold of the corresponding percentile
46- 51 F6.4 --- z ? redshift: mostly spectroscopic redshifts
from Marchesi et al. (2016, J/ApJ/817/34),
else reference code in r_z
53 A1 --- r_z [*BDT] Reference on z (2)
55- 56 I2 --- Nvisit Number of visits where the source is detected
58- 59 I2 --- Class Source classification (3)
--------------------------------------------------------------------------------
Note (1): Quality label as follows:
1 = strong candidate; no problems or defects detected (232 sources)
2 = likely variable candidate; neighbor potentially affecting the source,
or minor problems detected (67 sources)
Note (2): Reference for redshift when not from Marchesi et al.
(2016, J/ApJ/817/34), as follows:
* = spectroscopic redshift from Hasinger et al. (2018, J/ApJ/858/77)
B = spectroscopic redshift from Lilly et al. (2007, J/ApJS/172/70)
D = photometric redshift from Marchesi et al. (2016, J/ApJ/817/34)
T = photometric redshift from Ilbert et al. (2009, J/ApJ/690/1236)
Note (3): The classification index is the sum of different numbers corresponding
to the following key:
1 = confirmed AGN through spectroscopy/SED
2 = confirmed AGN through X/O diagram
4 = confirmed AGN through IRAC color diagram, Lacy region
8 = confirmed AGN through IRAC color diagram, Donley region
0 = non-classified
-1 = star
--------------------------------------------------------------------------------
Acknowledgements:
Demetra De Cicco, ddecicco(at)astro.puc.cl
(End) Patricia Vannier [CDS] 29-May-2019