J/ApJ/964/98 Recognizing blazars from VLASS radio morphology (Xie+, 2024)
Recognizing blazars using radio morphology from the VLA Sky Survey.
Xie Z.-L., Banados E., Belladitta S., Mazzucchelli C., Schindler J.-T.,
Davies F., Venemans B.P.
<Astrophys. J., 964, 98 (2024)>
=2024ApJ...964...98X 2024ApJ...964...98X
ADC_Keywords: Active gal. nuclei; BL Lac objects; Morphology; Radio sources;
Surveys
Keywords: Blazars ; Active galactic nuclei ; Radio jets
Abstract:
Blazars are radio-loud active galactic nuclei whose jets have a very
small angle to our line of sight. Observationally, the radio emissions
are mostly compact or compact-core with a one-sided jet. With 2.5"
resolution at 3GHz, the Very Large Array Sky Survey (VLASS) enables us
to resolve the structure of some blazar candidates in the sky north of
decl. -40°. We introduce an algorithm to classify radio sources as
either blazar-like or non-blazar-like based on their morphology in the
VLASS images. We apply our algorithm to three existing catalogs,
including one of the known blazars (Roma-BzCAT) and two blazar
candidates identified by Wide-field Infrared Survey Explorer colors
and radio emission (WIBRaLS, KDEBLLACS). We show that in all three
catalogs, there are objects with morphologies inconsistent with being
blazars. Considering all the catalogs, more than 12% of the candidates
are unlikely to be blazars, based on this analysis. Notably, we show
that 3% of the Roma-BzCAT confirmed blazars could be a
misclassification based on their VLASS morphology. The resulting table
with all sources and their radio morphological classification is
available online.
Description:
Our data set comprises a combination of three catalogs: Roma-BzCAT
(Massaro+ 2015, VII/274), WIBRaLS (D'Abrusco+ 2014, J/ApJS/215/14 and
2019, J/ApJS/242/4), and KDEBLLACS (D'Abrusco+ 2019). WIBRaLS and
KDEBLLACS contain blazar candidates, while Roma-BzCAT consists of
confirmed blazars. We download all available epochs of the Very Large
Array Sky Survey (VLASS; Lacy+ 2020PASP..132c5001L 2020PASP..132c5001L;
Gordon+ 2021, J/ApJS/255/30) Quick Look Images for the sources in this
data set.
VLASS1.1 corresponds to the first epoch of the first half of the sky,
and VLASS1.2 is the first epoch of the second part of the sky. The
first epoch is completed in 2019, while the second epoch, VLASS2.1 and
VLASS2.2, is completed in June 2022.
The Monitoring Of Jets in Active galactic nuclei with Very Long
Baseline Array (VLBA) Experiments (MOJAVE; Lister+ 2021, J/ApJ/923/30)
survey focuses on obtaining high-resolution images of AGN radio jets
using VLBA observations, providing detailed images at the parsec
level. We ran our VLASS classifier algorithm in 320 MOJAVE sources
that are identified as blazars. See Section 5.2.
File Summary:
--------------------------------------------------------------------------------
FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
table1.dat 99 3134 Sources from the Roma-BzCAT catalog
classified using our algorithm
table2.dat 99 9821 Sources from WIBRaLS
classified using our algorithm
table3.dat 99 4996 Sources from KDEBLLACS
classified using our algorithm
table5.dat 75 321 Sources from MOJAVE
classified using our algorithm
--------------------------------------------------------------------------------
See also:
VIII/65 : 1.4GHz NRAO VLA Sky Survey (NVSS) (Condon+ 1998)
VII/274 : The Roma BZCAT - 5th edition (Massaro+, 2015)
J/A+AS/132/341 : ROSAT GPS optical identification (Motch+ 1998)
J/ApJS/123/79 : Third EGRET catalog (3EG) (Hartman+, 1999)
J/ApJS/129/547 : RBSC-NVSS sample. I. (Bauer+, 2000)
J/A+A/470/787 : High energy peaked BL Lacs optical sp. (Piranomonte+, 2007)
J/A+A/495/691 : Multifrequency catalog of blazars, Roma-BZCAT (Massaro+, 2009)
J/ApJ/716/30 : SED of Fermi bright blazars (Abdo+, 2010)
J/ApJ/710/764 : Extended radio emission in MOJAVE blazars (Kharb+, 2010)
J/ApJ/748/68 : WISE IR colors of gamma-ray blazars (D'Abrusco+, 2012)
J/ApJ/748/49 : Optical spectroscopy of 1LAC broad-line blazars (Shaw+, 2012)
J/ApJS/215/14 : WISE cand. γ-ray blazar radio sources (D'Abrusco+, 2014)
J/ApJS/234/12 : MOJAVE XV. VLBA 15GHz obs. of AGN jets (Lister+, 2018)
J/ApJS/242/4 : Two new catalogs of blazar candidates (D'Abrusco+, 2019)
J/ApJ/874/43 : MOJAVE. XVII. pc-scale jet kinematics of AGNs (Lister+, 2019)
J/ApJ/892/105 : 4th catalog of Fermi LAT-detected AGNs (4LAC) (Ajello+, 2020)
J/ApJS/255/30 : VLASS QL Ep.1 Catalog, CIRADA version (Gordon+, 2021)
J/ApJ/923/30 : MOJAVE. XVIII. Bright radio-loud active AGNs (Lister+, 2021)
Byte-by-byte Description of file: table1.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 4 I4 --- Seq [1/3134] Result catalog number
6- 25 A20 --- Name Source name (JHHMMSS.ss+DDMMSS.ss)
27- 41 F15.11 deg RAdeg Right Ascension in decimal degrees (J2000)
43- 58 F16.12 deg DEdeg [-40/86.3] Declination in decimal degrees (J2000)
60- 75 A16 --- Class Morphological classification from algorithm
77- 77 I1 --- Vis [0/1] Visual flag (1=visually inspected)
79- 94 A16 --- VClass Visual classification (G1)
96- 99 A4 --- Epoch VLASS image epoch for source (G2)
--------------------------------------------------------------------------------
Byte-by-byte Description of file: table2.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 4 I4 --- Seq [1/9821] Result catalog number
6- 25 A20 --- Name Source name (JHHMMSS.ss+DDMMSS.ss)
27- 41 F15.11 deg RAdeg Right Ascension in decimal degrees (J2000)
43- 58 F16.12 deg DEdeg [-40/89.4] Declination in decimal degrees (J2000)
60- 75 A16 --- Class Morphological classification from algorithm
77- 77 I1 --- Vis [0/1] Visual flag (1=visually inspected)
79- 94 A16 --- VClass Visual classification (G1)
96- 99 A4 --- Epoch VLASS image epoch for source (G2)
--------------------------------------------------------------------------------
Byte-by-byte Description of file: table3.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 4 I4 --- Seq [1/4996] Result catalog number
6- 25 A20 --- Name Source name (JHHMMSS.ss+DDMMSS.ss)
27- 41 F15.11 deg RAdeg Right Ascension in decimal degrees (J2000)
43- 58 F16.12 deg DEdeg [-40/88.8] Declination in decimal degrees (J2000)
60- 75 A16 --- Class Morphological classification from algorithm
77- 77 I1 --- Vis [0/1] Fisual flag (1=visually inspected)
79- 94 A16 --- VClass Visual classification (G1)
96- 99 A4 --- Epoch VLASS image epoch for source (G2)
--------------------------------------------------------------------------------
Byte-by-byte Description of file: table5.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 3 I3 --- Seq [1/321] Result catalog number
5- 23 A19 --- Name Source name
25- 33 F9.5 deg RAdeg Right Ascension in decimal degrees (J2000)
35- 43 F9.5 deg DEdeg [-30/86.3] Declination in decimal degrees (J2000)
45- 60 A16 --- Class Morphological classification from algorithm
62- 62 I1 --- Vis [0/1] Visual flag (1=visually inspected)
64- 70 A7 --- VClass Visual classification (G1)
72- 75 A4 --- Epoch VLASS image epoch for source (G2)
--------------------------------------------------------------------------------
Global notes:
Note (G1): Assigned by human eyes if the algorithm classification is wrong,
this entry is left empty if the source is not visually inspected or
the algorithm classification is correct when "Vis" flag is 1.
The VLASS images are categorized into six distinct morphological
classes, grouped into two sets. Blazar-like morphologies include
COMPACT, OFFSET, 1-SIDE EXTENDED, and 1-SIDE SEPARATED, while
non-blazar-like morphologies comprise 2-SIDE EXTENDED and 2-SIDE
SEPARATED. See Section 3.2.
Note (G2): If the source has two epochs available, this column is left empty,
otherwise it will denote which epoch of VLASS images is available for
the source, EP01: VLASS 1 (completed in 2019), EP02: VLASS 2
(completed in 2022).
--------------------------------------------------------------------------------
History:
From electronic version of the journal
License: CC-BY-4.0
(End) Prepared by [AAS], Emmanuelle Perret [CDS] 02-Jul-2026