J/ApJ/835/L30 Dislodged AGNs (Makarov+, 2017)
Astrometric evidence for a population of dislodged AGNs.
Makarov V.V., Frouard J., Berghea C.T., Rest A., Chambers K.C., Kaiser N.,
Kudritzki R.-P., Magnier E.A.
<Astrophys. J. 835, L30 (2017)>
=2017ApJ...835L..30M 2017ApJ...835L..30M (SIMBAD/NED BibCode)
ADC_Keywords: Positional data ; QSOs
Keywords: astrometry - galaxies: nuclei - quasars: general - reference systems
Abstract:
We investigate a sample of 2293 ICRF2 extragalactic radio-loud sources
with accurate positions determined by VLBI, mostly active galactic
nuclei (AGNs) and quasars, which are cross-matched with optical
sources in the first Gaia release (Gaia DR1). The distribution of
offsets between the VLBI sources and their optical counterparts is
strongly non-Gaussian, with powerful wings extending beyond 1 arcsec.
Limiting our analysis to only high-confidence difference detections,
we find (and publish) a list of 188 objects with normalized variances
above 12 and offsets below 1 arcsec. Pan-STARRS stacked and
monochromatic images resolve some of these sources, indicating the
presence of double sources, confusion sources, or pronounced extended
structures. Some 89 high-quality objects, however, do not show any
perturbations and appear to be star-like single sources, yet they are
displaced by multiples of the expected error from the radio-loud AGN.
We conclude that a fraction of luminous AGNs (more than 4%) can be
physically dislodged from the optical centers of their parent
galaxies.
Description:
We performed a cone search of Gaia DR1 objects within 1" of each
ICRF2 source, which at the time of writing included more than 3400
entries. Counting only the closest counterparts, this resulted in 2293
tentative matches. The positional matching is straightforward, as the
extragalactic AGNs are believed to represent a quasi-inertial,
non-rotating reference frame, thus no epoch transformations are
needed. There is a small number of possible matches with separations
greater than 1", but those are deemed almost certainly confusion
sources.
The entire statistical selection of extreme outliers comprise 188
sources.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 124 188 List of 188 objects with normalized variances
above 12 and offsets below 1 arcsec
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See also:
I/323 : International Celestial Reference Frame 2, ICRF2 (Ma+, 2009)
I/337 : Gaia DR1 (Gaia Collaboration, 2016)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 13 F13.9 mas Delta [0.461/936.284] Absolute difference in
position between Gaia and VLBI
15- 30 A16 --- ICRF ICRF2 name (JHHMMSS.s+DDMMSS)
32- 44 F13.9 deg RAdeg ICRF2 right ascension (J2000)
46- 58 F13.9 deg DEdeg ICRF2 declination (J2000)
60 A1 --- Disp [DVN] ICRF2 type (1)
62- 72 F11.8 mag Gmag [14/22] Gaia DR1 magnitude in G band
74- 79 F6.4 --- z ?=- Redshift from OCARS
81- 82 A2 --- AGNtype Morphological type from OCARS (2)
84- 88 I5 --- Nconf [0/30000] Number of Gaia sources
within 10 arcmin
90 I1 % Pneib [0/7] Probability of a chance neighbor
within 1 arcsec
92-124 A33 --- Notes Notes (3)
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Note (1): ICRF2 type as follows:
D = defining
V = VCS
N = non-VCS
Note (2): Morphological type from OCARS as follows:
AB = blazar (replaced by other AGN class when known)
AL = BL Lac type
AQ = quasar
AR = LINER-type AGN
AS = Seyfert galaxy
G = galaxy
R = radio source
S = star or stellar object
V = visual source; this code is also set for all sources having optical
measurements if they are classified as radio source in NED and SIMBAD
Note (3): an asterisk * stands for a star-like image, and galaxy stands for
obviously extended objects.
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Acknowledgements:
Valeri Makarov, valeri.makarov(at)usno.navy.mil
(End) Patricia Vannier [CDS] 10-Feb-2017