J/A+A/673/A113 MALS ten pointings continuum catalogue (Wagenveld+ 2023)
The MeerKAT Absorption Line Survey: Homogeneous continuum catalogues towards a
measurement of the cosmic radio dipole.
Wagenveld J.D., Kloeckner H.-R., Gupta N., Deka P.P., Jagannathan P.,
Sekhar S., Balashev S.A., Boettcher E., Combes F., Emig K.L., Hilton M.,
Jozsa G.I.G., Kamphuis P., Klutse D.Y., Knowles K., Krogager J.-K.,
Mohapatra A., Momjian E., Moodley K., Muller S., Petitjean P., Salas P.,
Sikhosana S., Srianand R.
<Astron. Astrophys. 673, A113 (2023)>
=2023A&A...673A.113W 2023A&A...673A.113W (SIMBAD/NED BibCode)
ADC_Keywords: Surveys ; Galaxies, radio ; Morphology
Keywords: surveys - galaxies: statistics - radio continuum: galaxies
Abstract:
The number counts of homogeneous samples of radio sources are a tried
and true method of probing the large-scale structure of the Universe,
as most radio sources outside the Galactic plane are at cosmological
distances. As such, they are expected to trace the cosmic radio
dipole, an anisotropy analogous to the dipole seen in the cosmic
microwave background (CMB). Results have shown that although the
cosmic radio dipole matches the direction of the CMB dipole, it has a
significantly larger amplitude. This unexplained result challenges our
assumption of the Universe being isotropic, which can have large
repercussions for the current cosmological paradigm. Though
significant measurements have been made, sensitivity to the radio
dipole is generally hampered by systematic effects that can cause
large biases in the measurement. Here we assess these systematics with
data from the MeerKAT Absorption Line Survey (MALS), a blind search
for absorption lines with pointings centred on bright radio sources.
With the sensitivity and field of view of MeerKAT, thousands of
sources are observed in each pointing, allowing for the possibility of
measuring the cosmic radio dipole given enough pointings. We present
the analysis of ten MALS pointings, focusing on systematic effects
that could lead to an inhomogeneous catalogue. We describe the
calibration and creation of full band continuum images and catalogues,
producing a combined catalogue containing 16307 sources and covering
37.5 square degrees of sky down to a sensitivity of 10uJy/beam. We
measure the completeness, purity, and flux recovery statistics for
these catalogues using simulated data. We investigate different source
populations in the catalogues by looking at flux densities and
spectral indices and how they might influence source counts. Using the
noise characteristics of the pointings, we find global measures that
can be used to correct for the incompleteness of the catalogue,
producing corrected number counts down to 100-200uJy. We show that
we can homogenise the catalogues and properly account for systematic
effects. We determine that we can measure the dipole to 3σ
significance with 100 MALS pointings.
Description:
Catalogue of the wideband continuum images of ten pointings of the
MeerKAT Absorption Line Survey (MALS) containing 16307 sources
covering 37.5 square degrees of sky. Sensitivity and resolution vary
throughout the pointings, as described in the accompanying paper.
Catalogues are based on PyBDSF output with additional information
added where needed. Sources that have been fit with multiple Gaussian
components by PyBDSF are visually inspected and have additional
information extracted from cutouts.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
mals-ten.dat 460 16307 MALS 10 pointings catalogue
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Byte-by-byte Description of file: mals-ten.dat
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Bytes Format Units Label Explanations
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1- 13 A13 --- PointID Pointing where the source is found
(Pointing_id)
16- 34 A19 --- Name Source name following IAU convention
(JHHMMSS.ss+DDMMSS.s) (Source_name)
37- 40 I4 --- SourceId [0/2619] PyBDSF source ID (Source_id)
43- 46 I4 --- IslId [0/2630] PyBDSF island ID (Isl_id)
49- 58 F10.6 deg RAdeg Right Ascension (J2000) (RA)
61- 68 F8.6 deg e_RAdeg Error in Right Ascension (E_RA)
71- 80 F10.6 deg DEdeg Declination (J2000) (DEC)
83- 90 F8.6 deg e_DEdeg Error in Declination (E_DEC)
93- 99 F7.5 deg Sep-PC Distance from pointing centre (Sep_PC)
102-111 F10.5 mJy Ftot Total flux density at 1.27GHz
(Total_flux)
114-121 F8.5 mJy e_Ftot Error on total flux density
(ETotalflux)
124-133 F10.5 mJy/beam Fpeak Peak flux density at 1.27GHz (Peak_flux)
136-142 F7.5 mJy/beam e_Fpeak Error on peak flux density (EPeakflux)
145-152 F8.5 --- SpIndex ? Spectral index (Spectral_index)
155-161 F7.5 --- SpIndexCorr Correction factor for residual primary
beam effects spectral index
(Spectralindexcorrection)
164-170 F7.5 --- e_SpIndex ? Error on spectral index
(ESpectralindex)
173-182 F10.6 deg RAmdeg Right Ascension of maximum (J2000)
(RA_max)
185-192 F8.6 deg e_RAmdeg Error on right ascension of maximum
(ERAmax)
195-204 F10.6 deg DEmdeg Declination of maximum (J2000) (DEC_max)
207-214 F8.6 deg e_DEmdeg Error on declination of maximum
(EDECmax)
217-224 F8.5 arcsec Maj Major axis (Maj)
227-234 F8.5 arcsec e_Maj Error on major axis (E_Maj)
237-244 F8.5 arcsec Min Minor axis (Min)
247-254 F8.5 arcsec e_Min Error on minor axis (E_Min)
257-265 F9.5 deg PA Position angle (PA)
268-276 F9.5 deg e_PA Error on position angle (E_PA)
279-286 F8.5 arcsec DCMaj Deconvolved major axis (DC_Maj)
289-296 F8.5 arcsec e_DCMaj Error on deconvolved major axis
(EDCMaj)
299-306 F8.5 arcsec DCMin Deconvolved minor axis (DC_Min)
309-316 F8.5 arcsec e_DCMin Error on deconvolved minor axis
(EDCMin)
319-327 F9.5 deg DCPA Deconvolved position angle (DC_PA)
330-338 F9.5 deg e_DCPA Error on deconvolved position angle
(EDCPA)
341-350 F10.5 mJy FtotIsl Total flux of island at 1.27GHz
(IslTotalflux)
353-359 F7.5 mJy e_FtotIsl Error on total flux of island
(EIslTotal_flux)
362-368 F7.5 mJy/beam Islrms Average background RMS noise of island
(Isl_rms)
371-378 F8.5 mJy/beam Islmean Average background mean of island
(Isl_mean)
381-387 F7.5 mJy/beam ResIslrms Average residual background RMS noise of
island (ResidIslrms)
390-397 F8.5 mJy/beam ResIslmean Average residual background mean of
island (ResidIslmean)
400 A1 --- SCode [SMC] PyBDSF source flag (S_Code) (1)
403-404 I2 --- NGaus Number of Gaussians fit to source
(N_Gaus)
407 I1 --- Res [0/1] Resolved flag
(0: unresolved, 1: resolved) (Resolved)
410 I1 --- Artifact [0/1] Artifact flag
(0: ok, 1: artifact) (Flag_Artifact)
413-422 F10.6 deg RAImdag ? Intensity weighted mean right ascension
of island from cutout (RA_mean)
425-434 F10.6 deg DEImdag ? Intensity weighted mean declination
of island from cutout (DEC_mean)
437-443 F7.5 mJy CutFtot ? Total flux density at 1.27GHz of island
from cutout (CutoutTotalflux)
446-453 F8.5 --- CutSpIndex ? Intensity weighted mean spectral index
from cutout (CutoutSpectralindex)
456-457 A2 --- CutFlag Cutout flag(s) (Cutout_flag) (2)
460 A1 --- CutClass [GIPA] Classification from visual
inspection of cutout (Cutout_class) (3)
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Note (1): PyBDSF source flag as follows:
S = fit with a single Gaussian
M = fit with multiple Gaussians
C = one of multiple sources on the same island
Note (2): Cutout flag as follows:
M = mean position falls outside the island
C = position of the brightest pixel does not correspond to the maximum
position from PyBDSF
F = difference between CutFtot (Cutouttotalflux) and
FtotIsl (IslTotalflux) more than 20%
Note (3): Classification from visual inspection of cutout as follows:
G = well described by the Gaussian model
I = well described by the island characteristics
P = well described by a single Gaussian component
A = artefact
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Acknowledgements:
Jonah Wagenveld, wagenveld(at)mpifr-bonn.mpg.de
(End) J. Wagenveld [MPI for Radio Astronomy], P. Vannier [CDS] 30-Mar-2023