J/A+A/676/A37 Bootes field Apertif 1.4 GHz continuum obs. (Kutkin+, 2023)
Apertif 1.4 GHz continuum observations of the Bootes field and their combined
view with LOFAR.
Kutkin A.M., Oosterloo T.A., Morganti R., Offringa A.R., Adams E.A.K.,
Adebahr B., Denes H., Hess K.M., van der Hulst J.M., de Blok W.J.G.,
Bozkurt A., van Cappellen W.A., Gunst A.W., Holties H.A., van Leeuwen J.,
Loose G.M., Oostrum L.C., Vohl D., Wijnholds S.J., Ziemke J.
<Astron. Astrophys. 676, A37 (2023)>
=2023A&A...676A..37K 2023A&A...676A..37K (SIMBAD/NED BibCode)
ADC_Keywords: Surveys ; Radio sources
Keywords: catalogs - surveys - radio continuum: general
Abstract:
We present a new image of a 26.5 square degree region in the Bootes
constellation obtained at 1.4GHz using the Aperture Tile in Focus
(Apertif) system on the Westerbork Synthesis Radio Telescope. We use a
newly developed processing pipeline which includes direction-dependent
self-calibration which provides a significant improvement of the
quality of the images compared to those released as part of the
Apertif first data release. For the Bootes region, we mosaic 187
Apertif images and extract a source catalog. The mosaic image has an
angular resolution of 27x11.5 arcsec and a median background noise of
40uJy/beam. The catalog has 8994 sources and is complete down to the
0.3mJy level. We combine the Apertif image with LOFAR images of the
Bootes field at 54 and 150MHz to study spectral properties of the
sources. We find a spectral flattening towards low flux density
sources. Using the spectral index limits from Apertif non-detections
we derive that up to 9% of the sources have ultra-steep spectra with a
slope steeper than -1.2. Steepening of the spectral index with
increasing redshift is also seen in the data showing a different
dependency for the low-frequency spectral index and the high frequency
one. This can be explained by a population of sources having concave
radio spectra with a turnover frequency around the LOFAR band.
Additionally, we discuss cases of individual extended sources with an
interesting resolved spectral structure. With the improved pipeline,
we aim to continue processing data from the Apertif wide-area surveys
and release the improved 1.4GHz images of several famous fields.
Description:
We extracted the Apertif source catalog using the Python Blob
Detector and Source Finder (PyBDSF; Mohan & Rafferty 2015). Similar to
Shimwell et al. (2019A&A...622A...1S 2019A&A...622A...1S, Cat. J/A+A/622/A1), we used a
peak and island detection threshold of 5σ and 4σ
respectively, and the size of a sliding box to estimate the local RMS
was set to 30x30xbmaj, where bmaj is the major axis of the
synthesized beam.
We used the publicly available LOFAR HBA and LBA mosaic images and the
corresponding catalogs of the Bootes area (Tasse et al.
2021A&A...648A...1T 2021A&A...648A...1T; Williams et al. 2021A&A...655A..40W 2021A&A...655A..40W, Cat.
J/A+A/655/A40) and present spectral indices of the sources in table3.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 324 8994 Apertif source catalog
table3.dat 130 11689 Spectral indices of the sources
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See also:
J/A+A/655/A40 : LoLSS-Deep Bootes 54MHz catalog (Williams+, 2021)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 19 A19 --- Name Source name (Name)
21- 38 F18.14 deg RAdeg Right ascension (ICRS, J2000) (RA)
40- 57 F18.16 arcsec e_RAdeg Right ascension error (E_RA)
59- 76 F18.15 deg DEdeg Declination (ICRS, J2000) (DEC)
78- 95 F18.16 arcsec e_DEdeg Declination error (E_DEC)
97-116 F20.16 mJy Ftot Total flux density at 1.4GHz (Total_flux)
118-136 F19.16 mJy e_Ftot Total flux density at 1.4GHz error
(ETotalflux)
138-157 F20.16 mJy/beam Fpeak Peak flux density 1.4GHz (Peak_flux)
159-177 F19.16 mJy/beam e_Fpeak Peak flux density 1.4GHz error (EPeakflux)
179-198 F20.16 arcsec DCMaj Deconvolved major source size (DC_Maj)
200-218 F19.16 arcsec e_DCMaj Deconvolved major source size error
(EDCMaj)
220-238 F19.16 arcsec DCMin Deconvolved minor source size (DC_Min)
240-258 F19.16 arcsec e_DCMin Deconvolved minor source size error
(EDCMin)
260-279 F20.16 deg DCPA [-90/90]? Deconvolved position angle of
the source (DC_PA) (1)
281-300 F20.16 deg e_DCPA ? Deconvolved position angle error (EDCPA)
302-319 F18.16 uJy/beam Islrms Local background noise RMS (Isl_rms)
321-324 A4 --- SCode Source type as classified by PyBDSF
(S_Code) (2)
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Note (1): from -90 to 90 measured relative to the north celestial pole,
turning positive into the direction of the right ascension.
Note (2): Source type as follows:
S = an isolated source fitted with a single Gaussian
C = sources that were fit by a single Gaussian but are within an
island of emission that also contains other sources
M = sources fitted with multiple Gaussians
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Byte-by-byte Description of file: table3.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 10 F10.5 deg RAdeg ? Apertif Right ascension (ICRS, J2000)
(RA_apt)
12- 20 F9.5 deg DEdeg ? Apertif Declination (ICRS, J2000) (DEC_apt)
22- 28 F7.2 mJy Ftot ? Apertif total flux density 1.4GHz
(Totalfluxapt)
30- 39 F10.5 deg RAHdeg ? LOFAR HBA Right ascension (ICRS, J2000)
(RA_hba)
41- 49 F9.5 deg DEHdeg ? LOFAR HBA Declination (ICRS, J2000) (DEC_hba)
51- 58 F8.2 mJy FtotHBA ? LOFAR HBA total flux density at 150MHz
(Totalfluxhba)
60- 69 F10.5 deg RALdeg ? LOFAR LBA Right ascension (ICRS, J2000)
(RA_lba)
71- 79 F9.5 deg DELdeg ? LOFAR LBA Declination (ICRS, J2000) (DEC_lba)
81- 89 F9.2 mJy FtotLBA ? LOFAR LBA total flux density at 54MHz
(Totalfluxlba)
91 A1 --- l_SIhigh Limit flag on SIhigh
92- 97 F6.3 --- SIhigh ? Spectral index between 150 and 1400MHz
(SI_high)
99-104 F6.3 --- e_SIhigh ? Error of the spectral index
between 150 and 1400MHz (ESIhigh)
106 A1 --- l_SIlow Limit flag on SIlow
107-112 F6.3 --- SIlow ? Spectral index between 54 and 150MHz
(SI_low)
114-119 F6.3 --- e_SIlow ? Error of the spectral index
between 54 and 150MHz (ESIlow)
121-130 F10.8 --- zbestHBA ? Redshift estimate from Lofar value-added
catalog (zbest_hba)
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Acknowledgements:
Alexander Kutkin, kutkin(at)astron.nl
(End) Patricia Vannier [CDS] 06-Jun-2023