J/A+A/699/A52 VCV10 and Quaia samples IR-selec var. QSOs (Zaharieva+, 2025)
Identification of quasars variable over long time scales from infrared surveys.
Ensemble variability and structure function properties.
Zaharieva E.A., Ivanov V.D., Ovcharov E.P., Stanchev O.I.
<Astron. Astrophys. 699, A52 (2025)>
=2025A&A...699A..52Z 2025A&A...699A..52Z (SIMBAD/NED BibCode)
ADC_Keywords: Surveys ; QSOs ; Photometry, infrared
Keywords: catalogs - galaxies: active - quasars: general
Abstract:
Quasars are variable and their variability can both constrain their
physical properties and help to identify them.
We aim to look for ways to efficiently identify quasars exhibiting
consistent variability over multi-year time-scales, based on a small
number of epochs. Using infrared (IR) is desirable to avoid bias
against reddened objects.
We compare the apparent brightness of known quasars that have been
observed with two IR surveys, covering up to a twenty-year baseline:
the Two Micron All Sky Survey (2MASS; 1997-2001) and the VISTA
Hemisphere Survey (VHS; 2009-2017).
We look at the previous studies of the selected variable quasars to
see if their variable behaviour is known and when available we use
multi-epoch monitoring with the Zwicky Transient Facility (ZTF) to
obtain a measure of optical variability of individual objects.
We build a sample of nearly 2500 quasars that show statistically
significant variability between the 2MASS and VHS. About 1500 of these
come from the new Quaia sample based on Gaia spectra and about 1/3 of
these have hardly been studied. The Quaia sample constitutes the main
product of this work. Based on ensemble variability and structure
function analysis we demonstrate that the selected objects in our
sample are representative of the typical quasar population and show
behaviour, consistent with other quasar samples. Our analysis
strengthens previous results, for example that variability decreases
with the rest-frame wavelength and that it exhibits peaks for certain
absolute magnitudes of the quasars. Similarly, the structure function
shows an increase in variability for rest-frame time lags below ∼1500d
and a decrease for longer lags, just like in previous studies.
Our selection, even though it is based on two epochs only, seems to be
surprisingly robust, showing up to ∼11% contamination by quasars that
show stable non-variable behaviour in ZTF.
Description:
This data release contains two tables listing quasars selected based
on significant infrared variability between the 2MASS and VHS surveys.
- Table2.dat: List of 952 objects, selected from the VCV10
(Veron-Cetty & Veron, 2010, Cat. VII/224) sample, with photometry from
2MASS and VHS surveys, that show statistically significant variability
in both J and K bands. The columns contain position, 2MASS ID and
magnitudes, VHS magnitudes, and statistical significances of the 2MASS
vs. VHS magnitude differences for J and K separately, as well as the
average.
- Table3.dat: The 1493 objects listed here are selected from the Quaia
(Storey-Fisher et al., 2024ApJ...964...69S 2024ApJ...964...69S) sample, which show
statistically significant variability in both J and K bands. The table
follows the structure of Table2.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table2.dat 112 952 Variable quasars from VCV10 sample
table3.dat 112 1493 Variable quasars from Quaia sample
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See also:
VII/258 : Quasars and Active Galactic Nuclei (13th Ed.) (Veron-Cetty+ 2010)
Byte-by-byte Description of file: table2.dat table3.dat
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Bytes Format Units Label Explanations
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1- 2 I2 h RAh Right ascension (J2000)
4- 5 I2 min RAm Right ascension (J2000)
7- 11 F5.2 s RAs Right ascension (J2000)
13 A1 --- DE- Declination sign (J2000)
14- 15 I2 deg DEd Declination (J2000)
17- 18 I2 arcmin DEm Declination (J2000)
20- 23 F4.1 arcsec DEs Declination (J2000)
25- 41 A17 --- 2MASS 2MASS source identifier (JHHMMSSss+DDMMSSs)
43- 48 F6.3 mag J2MASS 2MASS J-band magnitude
50- 54 F5.3 mag e_J2MASS Error in 2MASS J-band magnitude
56- 61 F6.3 mag K2MASS 2MASS K-band magnitude
63- 67 F5.3 mag e_K2MASS Error in 2MASS K-band magnitude
69- 74 F6.3 mag JVHS VHS J-band magnitude
76- 80 F5.3 mag e_JVHS Error in VHS J-band magnitude
82- 87 F6.3 mag KVHS VHS K-band magnitude
89- 93 F5.3 mag e_KVHS Error in VHS K-band magnitude
95- 99 F5.2 --- SNRJ Signal-to-noise ratio for J-band variability
101-106 F6.2 --- SNRK Signal-to-noise ratio for K-band variability
108-112 F5.2 --- SNRJK Mean signal-to-noise ratio (J and K bands)
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History:
From E. Zaharieva, ezaharieva(at)phys.uni-sofia.bg
Acknowledgements:
We acknowledge the use of data from the Two Micron All Sky Survey
(2MASS) and the VISTA Hemisphere Survey (VHS).
References:
Veron-Cetty & Veron (2010A&A...518A..10V 2010A&A...518A..10V), VCV10 catalog, Cat. VII/258
Storey-Fisher et al. (2024ApJ...964...69S 2024ApJ...964...69S), Quaia catalog
(End) Patricia Vannier [CDS] 29-Apr-2025