J/A+A/700/A63 AGNs as seen by Apertif and LOFAR (Kutkin+, 2025)
Spectral indices in active galactic nuclei as seen by Apertif and LOFAR.
Kutkin A.M., Morganti R., Oosterloo T.A., Adams E.A.K., Denes H.,
van Leeuwen J., Norden M.J., Orru E.
<Astron. Astrophys. 700, A63 (2025)>
=2025A&A...700A..63K 2025A&A...700A..63K (SIMBAD/NED BibCode)
ADC_Keywords: Active gal. nuclei ; Radio sources
Keywords: catalogs - surveys - galaxies: active - radio continuum: galaxies -
radio continuum: general
Abstract:
We present two new radio continuum images obtained with Apertif at
1.4GHz. The images, produced with a direction-dependent calibration
pipeline, cover 136 square degrees of the Lockman Hole and 24 square
degrees of the ELAIS-N fields, with an average resolution of
17x12" and residual noise of 33uJy/beam. With the improved
depth of the images we found in total 63692 radio sources, many of
which are detected for the first time at this frequency. With the
addition of the previously published Apertif catalog for the Bootes
field, we cross-match with the LOFAR deep-fields value-added catalogs
at 150MHz, resulting in a homogeneous sample of 10196 common sources
with spectral index estimates, one of the largest to date. We analyze
and discuss the correlations between spectral index, redshift, linear
sources size, and radio luminosity, taking into account biases of
flux-density-limited surveys. Our results suggest that the observed
correlation between spectral index and redshift of active galactic
nuclei can be attributed to the Malmquist bias reflecting an intrinsic
relation between radio luminosity and the spectral index. We also find
a correlation between spectral index and linear source size with more
compact sources having steeper spectra.
Description:
We processed Apertif observations and presented two new radio
continuum images and catalogs at 1.4GHz. Due to the higher
sensitivity of Apertif compared to previous northern surveys, many
radio sources were detected for the first time at these frequencies.
The images cover more than 150 square degrees within the well-known
fields, ELAIS-N and Lockman Hole, observed at many other facilities at
various frequencies. With the addition of the previously published
catalog for the Bootes field, we cross-matched Apertif source
coordinates with those in LOFAR value-added catalogs to probe spectral
indices and other parameters of radio sources. We compiled and studied
a new sample of common Apertif and LOFAR sources, complete in terms of
spectral index and including enough data for a statistical analysis,
which is especially crucial for high redshift sources. We constrained
and separately studied a subsample of sources free from Malmquist
bias.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1a.dat 94 8526 Apertif source list for the ELAIS-N field
table1b.dat 94 55166 Apertif source list for the Lockman Hole field
table3.dat 75 10196 Spectral indices of sources at 1400-150MHz
list.dat 92 2 List of fits images
fits/* . 2 Individual fits images
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Byte-by-byte Description of file: table1a.dat table1b.dat
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Bytes Format Units Label Explanations
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1- 19 A19 --- Name Source name, APTF_JHHMMSS+DDMMSS
21- 28 F8.4 deg RAdeg Right ascension (ICRS, J2000)
30- 34 F5.2 arcsec e_RAdeg Right ascension error
36- 42 F7.4 deg DEdeg Declination (ICRS, J2000)
44- 48 F5.2 arcsec e_DEdeg Declination error
50- 57 F8.3 mJy Ftot Total flux density at 1350MHz or 1375MHz
59- 65 F7.3 mJy e_Ftot Total flux density error
67- 74 F8.3 mJy/beam Fpeak Peak flux density at 1350MHz or 1375MHz
76- 82 F7.3 mJy/beam e_Fpeak Peak flux density error
84- 89 F6.1 uJy/beam Islrms local background noise RMS
91- 94 A4 --- SCode Source type as classified by PyBDSF (1)
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Note (1): Scode 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
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1- 19 A19 --- Apertif Apertif source name (ICRS, J2000),
APTF_JHHMMSS+DDMMSS
21- 42 A22 --- LOFAR LOFAR HBA source name (ICRS, J2000),
ILTJHHMMSS.ss+DDMMSS.s
44- 48 F5.2 --- SIAptHBA Spectral index between 1400 and 150MHz
50- 53 F4.2 --- e_SIAptHBA Spectral index uncertainty
55- 59 F5.2 --- zbest ? Redshift estimate from the LOFAR
value-added catalog
61- 67 F7.2 [W/Hz] logL150 ? Luminosity density at 150MHz
68 A1 --- n_logL150 [i] i for -∞
70- 75 F6.2 kpc Size150 ? Linear source size at 150MHz
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Byte-by-byte Description of file: list.dat
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Bytes Format Units Label Explanations
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1- 9 F9.5 deg RAdeg Right Ascension of center (J2000)
10- 18 F9.5 deg DEdeg Declination of center (J2000)
20- 24 I5 --- Nx Number of pixels along X-axis
26- 30 I5 --- Ny Number of pixels along Y-axis
32- 38 I7 Kibyte size Size of FITS file
40- 59 A20 --- FileName Name of FITS file, in subdirectory fits
61- 92 A32 --- Title Title of the FITS file
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Acknowledgements:
Alexander Kutkin, kutkin(at)astron.nl
(End) Patricia Vannier [CDS] 24-Jul-2025