J/A+A/644/A17 Astrometrically-selected QSO candidates (Heintz+, 2020)
Spectroscopic classification of a complete sample of astrometrically-selected
quasar candidates using Gaia DR2.
Heintz K.E., Fynbo J.P.U., Geier S.J., Moller P., Krogager J.-K.,
Konstantopoulou C., De Burgos A., Christensen L., Steinhardt C.L.,
Milvang-jensen B., Jakobsson P., Hog E., Arvedlund B.E.H.K.,
Christiansen C.R., Hansen T.B., Henriksen P.D., Kuszon K.B., Mckenzie I.B.,
Mosekjaer K.A., Paulsen M.F.K., Sukstorf M.N., Wilson S.N., Orgaard S.K.K.
<Astron. Astrophys., 644, A17 (2020)>
=2020A&A...644A..17H 2020A&A...644A..17H (SIMBAD/NED BibCode)
ADC_Keywords: QSOs
Keywords: astrometry - quasars: general
Abstract:
Here we explore the efficiency and fidelity of a purely astrometric
selection of quasars as point sources with zero proper motions in the
Gaia data release 2 (DR2). We have built a complete candidate sample
including 104 Gaia-DR2 point sources, which are brighter than 20th
magnitude in the Gaia G-band within one degree of the north Galactic
pole (NGP); all of them have proper motions that are consistent with
zero within 2σ uncertainty. In addition to pre-existing spectra,
we have secured long-slit spectroscopy of all the remaining candidates
and find that all 104 stationary point sources in the field can be
classified as either quasars (63) or stars (41). One of the new
quasars that we discover is particularly interesting as the
line-of-sight to it passes through the disc of a foreground (z=0.022)
galaxy, which imprints both NaD absorption and dust extinction on the
quasar spectrum. The selection efficiency of the zero-proper-motion
criterion at high Galactic latitudes is thus ≃60%. Based on this
complete quasar sample, we examine the basic properties of the
underlying quasar population within the imposed limiting magnitude. We
find that the surface density of quasars is 20deg-2 (at G<20mag),
the redshift distribution peaks at z∼1.5, and only eight systems
(13-3+5%) show significant dust reddening. We then explore the
selection efficiency of commonly used optical, near-, and mid-infrared
quasar identification techniques and find that they are all complete
at the 85-90% level compared to the astrometric selection. Finally, we
discuss how the astrometric selection can be improved to an efficiency
of ≃70% by including an additional cut requiring parallaxes of the
candidates to be consistent with zero within 2σ. The selection
efficiency will further increase with the release of future, more
sensitive astrometric measurements from the Gaia mission. This type of
selection, which is purely based on the astrometry of the quasar
candidates, is unbiased in terms of colours and intrinsic emission
mechanisms of the quasars and thus provides the most complete census
of the quasar population within the limiting magnitude of Gaia.
Description:
We present a spectroscopically complete sample of quasar candidates,
which have been identified purely from their apparent zero proper
motion on the sky. The targets were extracted from the Gaia-DR2
catalogue, and we find a total of 104 sources to be brighter than
G=20mag within a 3.14 square degree survey area around the NGP.
Based on spectroscopic data of the full set of candidates, we
classified 63 of the sources as quasars and 41 as stars.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
tableb1.dat 73 78 Observing log ordered by telescope and date
(72 sources)
tableb2.dat 71 63 *Classification of the stationary sources
identified as quasars
tableb3.dat 50 41 *Classification of the stationary sources
identified as stars
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Note on tableb3.dat: We have ordered the objects by the stellar classifications.
Note on tableb2.dat: We have ordered the sources by redshift and separated the
quasars that were observed spectroscopically by previous surveys and this work.
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See also:
I/345 : Gaia DR2 (Gaia Collaboration, 2018)
Byte-by-byte Description of file: tableb1.dat
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Bytes Format Units Label Explanations
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1- 15 A15 --- Source Source Name, GQHHMMSS+DDMMSS
17- 18 I2 h RAh Right ascension (J2000)
20- 21 I2 min RAm Right ascension (J2000)
23- 26 F4.1 s RAs Right ascension (J2000)
28 A1 --- DE- Declination sign (J2000)
29- 30 I2 deg DEd Declination (J2000)
32- 33 I2 arcmin DEm Declination (J2000)
35- 38 F4.1 arcsec DEs Declination (J2000)
40- 43 F4.1 mag rmag r magnitude (AB)
45- 55 A11 --- Tel Telescope/Instrument
57- 66 A10 "date" Obs.date Observation date
68- 73 A6 s ExpTime Exposure time
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Byte-by-byte Description of file: tableb2.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 15 A15 --- Source Source Name, GQHHMMSS+DDMMSS
17- 20 F4.2 --- S/N Signal-to-noise
22- 26 F5.2 --- S/N-Plx Measurement of the signal-to-noise of the
proper motions and parallaxes as reported in
the Gaia-DR2 catalogue
28- 32 F5.2 mag u-g ?=- u-g colour index
34- 37 F4.2 mag J-K ?=- J-K colour index
39- 42 F4.2 mag W1-W2 ?=- W1-W2 colour index
44- 48 F5.3 --- zprev Previous redshift (1)
49 A1 --- n_zprev [P] P for photometric redshift
51- 55 F5.3 --- z ?=- This work redshift
57- 61 F5.2 mag AV Absorption in V band
63- 71 A9 --- Survey Survey
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Note (1): The redshifts from the SDSS archive is from the most recent DR14Q
compilation (Paris et al., 2018, Cat. VII/286 ) and the redshifts from the CFHT
survey are from Crampton et al. (1987ApJ...314..129C 1987ApJ...314..129C). For the objects
identified as quasars as part of this work, we also provide the photometric
redshifts from Richards et al. (2009m Cat. J/ApJS/180/67).
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Byte-by-byte Description of file: tableb3.dat
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Bytes Format Units Label Explanations
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1- 15 A15 --- Source Source Name, GQHHMMSS+DDMMSS
17- 20 F4.2 --- S/N-PM Measurements of the signal-to-noise of the
proper motions as reported in the Gaia-DR2
catalogue
22- 26 F5.2 --- S/N-Plx Measurements of the signal-to-noise of the
parallaxes as reported in the Gaia-DR2
catalogue
28- 31 F4.2 mag u-g ?=- u-g colour index
33- 36 F4.2 mag J-K ?=- J-K colour index
38- 42 F5.2 mag W1-W2 ?=- W1-W2 colour index
44- 50 A7 --- Type MK spectral type
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History:
From electronic version
(End) Patricia Vannier [CDS] 28-Jan-2021