J/A+A/702/A232 SDSS low z quasar companion galaxies (Bettoni+, 2025)
SDSS low z quasar companion galaxies.
Bettoni D., Falomo R., Paiano S.
<Astron. Astrophys. 702, A232 (2025)>
=2025A&A...702A.232B 2025A&A...702A.232B (SIMBAD/NED BibCode)
ADC_Keywords: Galaxies ; QSOs ; Redshifts ; Photometry ; Optical
Keywords: galaxies: active - galaxies: evolution - quasars: absorption lines -
quasars: emission lines - quasars: general
Abstract:
We investigate the relationship between quasars and close companion
galaxies using photometry and spectroscopy from the large data set of
the SDSS DR16 survey. From the SDSS-QSO catalog of quasars, we
selected objects with 0.1<z≤0.35 and absolute magnitude M(r)
←21.3. For all these targets, we searched for candidate companion
galaxies that have a projected distance from the target <700kpc and
a radial velocity difference from the QSO ΔV<1000km/s. We find
that in 447 QSO at least one companion galaxy is associated. A total
of 691 associated galaxies are found in these QSO fields. In the
majority of them there is just one associated galaxy but in few cases,
many companions are also discovered and in two cases the QSO is found
in rich galaxy environments. The possible contamination due to a
chance projection of the companion galaxies is found less than 5%.
Based on the available data we expect on average to find ∼2
associated companion galaxies for each QSO. A small fraction (13%) of
the companion galaxies exhibits [OII] emission lines as signature of
recent star formation. However a similar fraction (16%) of
unassociated galaxies in the same QSO fields show [OII] emission.
This study suggests that there is no significant link between the
presence of these close companion galaxies or the signature of recent
star formation and the QSO nuclear activity.
Description:
We searched the SDSS DR16 database for companion galaxy candidates
residing in the vivinity of low-redshift (0.1<z<0.35) QSOs. The
association between the QSO and the galaxy is based on the spectrum
and a projected distance of less than 700kpc from the QSO with a
radial velocity difference of ΔV<1000km/s between the QSO and
galaxy. Under these conditions (and after discarding a number of
objects with poor quality spectra), we found 650 companions for 446
QSO fields.
The catalog of QSO and associated companion galaxies. There are 446
QSO in the range of redshift 0.1<z≤0.35 and there are 650 associated
companion galaxies in these QSO fields.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
qso.dat 65 446 List of position and magnitudes of QSO
comp.dat 54 650 Position magnitude redshift and projected
distance for 650 companion objects
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Byte-by-byte Description of file: qso.dat
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Bytes Format Units Label Explanations
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1- 7 A7 --- QSO QSO designation (QSO_NNN)
9- 26 A18 --- SDSS SDSS designation (HHMMSS.ss+DDMMSS.s)
28- 37 F10.6 deg RAdeg Right ascension (J2000.0)
39- 48 F10.6 deg DEdeg Declination (J2000.0)
50- 57 F8.6 --- z Redshift of the QSO
59- 65 F7.4 mag rmag r magnitude of the QSO
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Byte-by-byte Description of file: comp.dat
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Bytes Format Units Label Explanations
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1- 11 A11 --- Name Designation for the companion, ANQSONNN
13- 22 F10.6 deg RAdeg Right Ascension (J2000)
24- 33 F10.6 deg DEdeg Declination (J2000)
35- 40 F6.4 --- zcomp Redshift of companion galaxy
42- 47 F6.3 mag rmagcomp r band magnitude of companion galaxy
49- 54 F6.2 kpc PDist Projected distance from the QSO
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Acknowledgements:
Daniela Bettoni, daniela.bettoni(at)inaf.it
(End) Daniela Bettoni [INAF OAPD], Patricia Vannier [CDS] 09-Oct-2025