J/ApJS/255/30 VLASS QL Ep.1 Catalog, CIRADA version (Gordon+, 2021)
A Quick Look at the 3GHz Radio Sky.
I. Source Statistics from the Very Large Array Sky Survey.
Gordon Y.A., Boyce M.M., O'Dea C.P., Rudnick L., Andernach H.,
Vantyghem A.N., Baum S.A., Bui J.-P., Dionyssiou M., Safi-Harb S., Sander I.
<Astrophys. J. Suppl. Ser. 255, 30 (2021)>
=2021ApJS..255...30G 2021ApJS..255...30G (SIMBAD/NED BibCode)
ADC_Keywords: Surveys ; Radio sources
Keywords: radio astronomy - radio galaxies - radio source catalogs -
sky surveys
Abstract:
The Very Large Array Sky Survey (VLASS) is observing the entire sky
north of -40° in the S-band (2-4GHz), with the highest angular
resolution (2.5") of any all-sky radio continuum survey to date.
VLASS will cover its entire footprint over three distinct epochs, the
first of which has now been observed in full. Based on Quick Look
images from this first epoch, we have created a catalog of 1.9x10^6
reliably detected radio components. Due to the limitations of the
Quick Look images, component flux densities are underestimated by ∼15%
at S>3mJy/beam and are often unreliable for fainter components. We
use this catalog to perform statistical analyses of the 3GHz radio
sky. Comparisons with the Faint Images of the Radio Sky at Twenty cm
survey (FIRST) show the typical 1.4-3GHz spectral index to be -0.71.
The radio color-color distribution of point and extended components is
explored by matching with FIRST and the LOFAR Two Meter Sky Survey. We
present the VLASS source counts, dN/dS, which are found to be
consistent with previous observations at 1.4 and 3GHz. Resolution
improvements over FIRST result in excess power in the VLASS two-point
correlation function at angular scales <7", and in 18% of active
galactic nuclei associated with a single FIRST component being split
into multi-component sources by VLASS.
Description:
The main table (Components) provides measurements and properties for
3.4x10^6 VLASS detections. This includes duplicate and lower
confidence detections that can be identified using the flags provided.
The 1.9x106 components analysed in the paper can be selected using
the main_sample column. As this catalog is based on limited quality
'Quick Look' (QL) images, the flux density measurements are likely
underestimated by an average of ∼15%. A correction for this has NOT
been applied to this data and is left at the discretion of the end
user. Additionally the astrometry is typically only accurate to
∼0.25". The secondary table (SubtileSummary) provides metadata (such
as observation date, beam geometry etc.) and basic source statistics
for each of the individual images (or Subtiles) used to produce this
catalog.
It should be noted that no effort was made to avoid Solar System
objects in VLASS Epoch 1, resulting in 9 observations of major Solar
System bodies. Explicitly,
Mars is detected 3 times at:
J033146.2+195836
J040448.9+214607
J144827.5-151626
Jupiter is detected 3 times at:
J145832.7-155039
J151720.4-170227
J170158.8-221409
Saturn is detected at:
J191537.4-215806
Uranus is detected at:
J013728.4+092953
and the Moon covers a ∼15 arcmin radius centred on:
J085124.7+190327
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
comp.dat 881 3381277 Detected components and properties
subtile.dat 427 35285 Subtile metadata
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Byte-by-byte Description of file: comp.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 31 A31 --- CompName IAU name of the component,
VLASS1QLCIR JHHMMSS.ss+DDMMSS.s
(Component) (1)
33- 36 I4 --- CompId [-588/218] The PyBDSF ID of the
component in the subtile
(Component) (2)
38- 40 I3 --- IslId [0/624] The PyBDSF ID of the flux island
in the subtile (Isl_id) (2)
42- 53 F12.8 deg RAdeg [0.0/360.0] Right Ascension (J2000) (RA)
55- 66 F12.8 deg DEdeg [-40.02/89.83] Declination (J2000) (DEC)
68- 79 F12.8 deg e_RAdeg ?=-99 1-sigma uncertainty in RA
(E_RA) (3)
81- 92 F12.8 deg e_DEdeg ?=-99 1-sigma uncertainty in DEC
(E_DEC) (3)
94-102 F9.3 mJy Ftot The integrated flux density of the
component in the S-band (2-4GHz)
(Total_flux) (3)
104-110 F7.3 mJy e_Ftot 1-sigma uncertainty in total flux
(ETotalf) (3)
112-119 F8.3 mJy/beam Fpeak Peak brightness of the component
in the S-band (2-4GHz) (Peak_flux) (3)
121-126 F6.3 mJy/beam e_Fpeak 1-sigma uncertainty in peak flux
(EPeakfl) (3)
128-136 F9.4 arcsec Maj ?=-99 Major axis of the component fit
(Maj) (3)
138-145 F8.4 arcsec e_Maj ?=-99 1-sigma uncertainty in Maj
(E_Maj) (3)
147-155 F9.4 arcsec Min ?=-99 Minor axis of the component fit
(Min) (3)
157-164 F8.4 arcsec e_Min ?=-99 1-sigma uncertainty in Min
(E_Min) (3)
166-174 F9.4 deg PA ?=-99 Position angle of the component
fit (PA) (3)
176-184 F9.4 deg e_PA ?=-99 1-sigma uncertainty in PA
(E_PA) (3)
186-194 F9.3 mJy FtotIsl Integrated flux density of the entire
flux island (Isl_Total)
196-202 F7.3 mJy e_FtotIsl 1-sigma uncertainty in FtotIsl
(EIslTot)
204-209 F6.3 mJy/beam Islrms Local rms noise of the flux island
(Isl_rms)
211-216 F6.3 mJy/beam Islmean Mean value of the flux island
(Isl_mean)
218-224 F7.3 mJy/beam ResIdIslrms Local rms noise of the residual for
the flux island (Resid_Isl) (3)
226-233 F8.3 mJy/beam ResidIslmean Mean value of the residual for the
flux island (Resid_Isl) (3)
235-246 F12.8 deg RAMdeg Right Ascension (J2000) of the
component peak brightness (RA_max)
248-259 F12.8 deg DEMdeg Declination (J2000) of the component
peak brightness (DEC_max)
261-272 F12.8 deg e_RAMdeg ?=-99 1-sigma uncertainty in RAMdeg
(ERAmax) (3)
274-285 F12.8 deg e_DEMdeg ?=-99 1-sigma uncertainty in DEMdeg
(EDECmax) (3)
287 A1 --- SCode [SCME] Component type (S_Code) (4)
289-299 F11.5 pix Xposn X-pixel coordinate of the component
in the subtile (Xposn)
301-309 F9.5 pix e_Xposn ?=-99 1-sigma uncertainty in Xposn
(E_Xposn) (3)
311-321 F11.5 pix Yposn Y-pixel coordinate of the component
in the subtile (Yposn)
323-331 F9.5 pix e_Yposn ?=-99 1-sigma uncertainty in Yposn
(E_Yposn) (3)
333-343 F11.5 pix XposnMax X-pixel coordinate of the component
peak brightness in the subtile
(Xposn_max)
345-353 F9.5 pix e_XposnMax ?=-99 1-sigma uncertainty in Xposn_max
(EXposnm) (3)
355-363 F9.4 pix YposnMax Y-pixel coordinate of the component
peak brightness in the subtile
(Yposn_max)
365-373 F9.4 pix e_YposnMax ?=-99 1-sigma uncertainty in Yposn_max
(EYposnm) (3)
375-382 F8.4 arcsec MajImgPlane ?=-99 Major axis of the component fit
in the image plane (Majimgp) (3)
384-391 F8.4 arcsec e_MajImgPlane ?=-99 1-sigma uncertainty in
Majimgplane (EMajimg) (3)
393-400 F8.4 arcsec MinImgPlane ?=-99 Minor axis of the component fit
in the image plane (Minimgp)
402-409 F8.4 arcsec e_MinImgPlane ?=-99 1-sigma uncertainty in
Minimgplane (EMinimg) (3)
411-419 F9.4 deg PAImgPlane ?=-99 Position angle of the component
fit in the image plane (PAimgpl) (3)
421-428 F8.4 deg e_PAImgPlane ?=-99 1-sigma uncertainty in
PAimgplane (EPAimg_) (3)
430-437 F8.4 arcsec DCMaj ?=-99 Major axis of the component fit
after deconvolution from the VLASS
beam (DC_Maj) (3)
439-446 F8.4 arcsec e_DCMaj ?=-99 1-sigma uncertainty in DC_Maj
(EDCMaj) (3)
448-455 F8.4 arcsec DCMin ?=-99 Minor axis of the component fit
after deconvolution from the VLASS
beam (DC_Min) (3)
457-464 F8.4 arcsec e_DCMin ?=-99 1-sigma uncertainty in DC_Min
(EDCMin) (3)
466-473 F8.4 deg DCPA ?=-99 Position angle of the component
fit after deconvolution from the
VLASS beam (DC_PA) (3)
475-482 F8.4 deg e_DCPA ?=-99 1-sigma uncertainty in DC_PA
(EDCPA) (3)
484-491 F8.4 arcsec DCMajImgPlane ?=-99 Major axis of the component fit in
the image plane after deconvolution
from the VLASS beam (DCMajim) (3)
493-500 F8.4 arcsec e_DCMajImgPlane ?=-99 1-sigma uncertainty in
DCMajimg_plane (EDCMaj_) (3)
502-509 F8.4 arcsec DCMinImgPlane ?=-99 Minor axis of the component fit in
the image plane after deconvolution
from the VLASS beam (DCMinim) (3)
511-518 F8.4 arcsec e_DCMinImgPlane ?=-99 1-sigma uncertainty in
DCMinimg_plane (EDCMin_) (3)
520-527 F8.4 deg DCPAImgPlane ?=-99 Position angle of the component
fit in the image plane after
deconvolution from the VLASS beam
(DCPAimg) (3)
529-536 F8.4 deg e_DCPAImgPlane ?=-99 1-sigma uncertainty in
DCPAimg_plane (EDCPA_i)
538-543 A6 --- Tile VLASS tile (Tile) (5)
545-558 A14 --- Subtile Name of the Subtile the component was
detected in (Subtile)
560-568 F9.5 deg RASdeg Right Ascension (J2000) of the Subtile
(QLimage)
570-578 F9.5 deg DESdeg Declination (J2000) of the Subtile
(QLimage)
580-589 F10.5 arcsec NVSSdist Angular separation from the nearest
NVSS source (NVSS_dist) (6)
591-602 F12.5 arcsec FIRSTdist Angular separation from the nearest
FIRST source (FIRST_dis) (7)
604-612 F9.4 --- PeakToRing ?=-99 Ratio of maximum brightness within
5" of the component to the maximum
brightness in an annulus centred on the
component with inner and outer radii
of 5" and 10" (Peaktor) (8)
614 I1 --- DupFlag [0/2] Flag to identify duplicate
detections (Duplicate) (9)
616 I1 --- QualFlag [0/7] Flag to denote the Quality of the
detection (Quality_f) (10)
618-627 F10.5 arcsec NNdist ?=-99 Angular separation from nearest
other fitted component in the catalog
after accounting for duplicates
(NN_dist) (3)
629-632 F4.2 arcsec BMaj Major axis of the VLASS beam (BMAJ)
634-637 F4.2 arcsec BMin Minor axis of the VLASS beam (BMIN)
639-641 I3 deg BPA [-90/90]? Position angle of the VLASS
beam (BPA)
643 I1 --- MainSample [0/1] Part of the main sample used for
the scientific analyses presented in
the paper (main_samp) (11)
645-881 A237 --- QLcutout Link to a 3 arcminute square cutout of
the component (QL_cutout)
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Note (1): see http://cdsweb.u-strasbg.fr/cgi-bin/Dic?/17662036
Note (2): The PyBDSF IDs are unique only for components in the same Subtile
Note (3): Only available for fitted components, not empty flux islands
Note (4): Component type as follows:
S = Single-Gaussian fit
C = Single-Gaussian fit in an island with other components
M = Multi-Gaussian fit
E = Empty island (no components fit to the island)
Note (5): A description of the VLASS tiling strategy is given in VLASS Memo
#7 (https://library.nrao.edu/public/memos/vla/vlass/VLASS_007.pdf)
Note (6): see NVSS catalog, Cat. VIII/65 (Condon et al., 1998AJ....115.1693C 1998AJ....115.1693C).
Note (7): As FIRST only covers a subset of the VLASS footprint this metric
should only be considered to be useful within the FIRST footprint, see
VIII/92, 1997ApJ...475..479W 1997ApJ...475..479W and 2015ApJ...801...26H 2015ApJ...801...26H
Note (8): Peaktoring may be especially useful for detecting potential
spurious detections due to sidelobes and is incorporated in our
Quality_flag to this end, see also Note (10)
Note (9): Duplicate detections resulting from image overlaps are identified
using a 2" search radius, with the highest signal-to-noise component
prioritised. Possible values are as follows:
0 = Component is not duplicated,
1 = Component is duplicated and this is the preferred entry,
2 = Component is duplicates and this is not the preferred entry
Note (10): Components start with a Quality_flag of 0 which is added to
based on the outcome of a number of tests
+1 if Peaktoring < 2 and NN_dist > 20",
+2 if Peakflux/Islrms < 5,
+4 if Peak_flux > Total_flux.
Components with Quality_flag = 0 are considered to have the most
reliable detections and measurements.
Note (11): Suitable for most users, satisfies Duplicate_flag < 2,
Quality_flag ≡ (0|4), S_Code != E
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Byte-by-byte Description of file: subtile.dat
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Bytes Format Units Label Explanations
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1- 14 A14 --- Subtile Name of the Quick Look image,
JHHMMSS+DDMMSS (Subtile)
16 I1 --- Imagever [1/5] Version of the image produced by
NRAO (Image_version)
18- 23 A6 --- Tile The VLASS tile that this subtile is
taken from (Tile) (1)
25- 27 F3.1 --- Epoch The epoch and sub-epoch of VLASS this
Subtile is taken from (Epoch)
29- 37 F9.4 deg Bmaj Major axis of the VLASS beam in this
subtile (BMAJ)
39- 47 F9.4 deg Bmin Minor axis of the VLASS beam in this
subtile (BMIN)
49- 57 F9.4 deg BPA [-90/90] Position angle of the VLASS beam
in this subtile (BPA)
59- 63 F5.1 --- LatPole Latitude of pole in coordinate system
(LATPOLE)
65- 69 F5.1 --- LonPole Longitude of pole in coordinate system
(LONPOLE)
71- 77 F7.3 deg Crval1 Reference pixel Right Ascension (CRVAL1)
79- 85 F7.3 deg Crval2 Reference pixel Declination (CRVAL2)
87-112 A26 "datime" Obs.date Date and time of observation (DATE-OBS)
114-125 F12.8 deg RAdeg Observation Right Ascension,
at epoch Obs.date (OBSRA)
127-138 F12.8 deg DEdeg Observation Declination,
at epoch Obs.date (OBSDEC)
140-144 I5 --- Field NRAO name of VLASS field (FIELD)
146-171 A26 --- DateImg Date that the image file was produced
(DATE) (2)
173-187 A15 --- Origin Software (CASA) and version used to
produce the image file (ORIGIN)
189-194 F6.4 mJy/beam MeanIslrms Mean Isl_rms of components in this subtile
(Meanislrms)
196-201 F6.4 mJy/beam SDIslrms Standard deviation of the Isl_rms of
components in this subtile (SDislrms)
203-208 F6.4 mJy/beam Fp25 25th percentile of the Peak_flux
distribution for components in this
subtile (Peakfluxp25)
210-215 F6.4 mJy/beam Fp50 50th percentile of the Peak_flux
distribution for components in this
subtile (Peakfluxp50)
217-223 F7.4 mJy/beam Fp75 75th percentile of the Peak_flux
distribution for components in this
subtile (Peakfluxp75)
225-233 F9.4 mJy/beam Fpmax Peak flux of the brightest component in
this subtile (Peakfluxmax)
235-237 I3 --- Ncomp [11/219] Number of fitted components in
this subtile (N_components)
239-241 I3 --- NemptyIsl [10/218] Number of empty flux islands
detected in this subtile
(Nemptyislands) (3)
243-427 A185 --- Subtileurl Link to the Subtile image file
(Subtile_url)
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Note (1): A description of the VLASS tiling strategy is given in VLASS Memo
#7 (https://library.nrao.edu/public/memos/vla/vlass/VLASS_007.pdf)
Note (2): This is distinct from the observation date and people interested
in when the observation was undertaken should use DATE-OBS
Note (3): Empty flux islands are low confidence detections that fail to
meet the signal-to-noise threshold required to be fit as a component (for
more information please see https://www.astron.nl/citt/pybdsf/)
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Acknowledgements:
Yjan Gordon, Yjan.Gordon(at)umanitoba.ca
History:
18-Aug-2021: on-line version
09-Sep-2021: revised version
09-Feb-2022: urls updated
(End) Patricia Vannier [CDS] 13-Aug-2021