J/A+A/664/A83 Nearby galaxies in LoTSS-DR2 (Heesen+, 2022)
Nearby galaxies in the LOFAR Two-metre Sky Survey.
I. Insights into the non-linearity of the radio-SFR relation.
Heesen V., Staffehl M., Basu A., Beck R., Stein M., Tabatabaei F.S.,
Hardcastle M.J., Chyzy K.T., Shimwell T.W., Adebahr B., Beswick R.,
Bomans D.J., Botteon A., Brinks E., Brueggen M., Dettmar R.-J., Drabent A.,
de Gasperin F., Guerkan G., Heald G.H., Horellou C., Nikiel-Wroczynski B.,
Paladino R., Piotrowska J., Roettgering H.J.A., Smith D.J.B., Tasse C.
<Astron. Astrophys. 664, A83 (2022)>
=2022A&A...664A..83H 2022A&A...664A..83H (SIMBAD/NED BibCode)
ADC_Keywords: Surveys ; Radio continuum ; Galaxies, nearby
Keywords: cosmic rays - galaxies: magnetic fields -
galaxies: fundamental parameters - galaxies: halos -
radio continuum: galaxies
Abstract:
Cosmic rays and magnetic fields are key ingredients in galaxy
evolution, regulating both stellar feedback and star formation. Their
properties can be studied with low-frequency radio continuum
observations, free from thermal contamination.
We define a sample of 76 nearby (<30Mpc) galaxies, with rich
ancillary data in the radio continuum and infrared from the CHANG-ES
and KINGFISH surveys, which will be observed with the LOFAR Two-metre
Sky Survey (LoTSS) at 144 MHz. Methods. We present maps for 45 of them
as part of the LoTSS data release 2 (LoTSS-DR2), where we measure
integrated flux densities and study integrated and spatially resolved
radio spectral indices. We investigate the radio-SFR relation, using
star-formation rates (SFR) from total infrared and Hα+24-um
emission.
The radio-SFR relation at 144 MHz is clearly super-linear with
L144∝=SFR1.4-1.5. The mean integrated radio spectral index
between 144 and ∼1400MHz is <α≥-0.56±0.14, in agreement with
the injection spectral index for cosmic ray electrons (CRE). However,
the radio spectral index maps show a variation of spectral indices
with flatter spectra associated with star-forming regions and steeper
spectra in galaxy outskirts and, in particular, in extra-planar
regions. We found that galaxies with high star-formation rates (SFR)
have steeper radio spectra; we find similar correlations with galaxy
size, mass, and rotation speed.
Galaxies that are larger and more massive are better electron
calorimeters, meaning that the CRE lose a higher fraction of their
energy within the galaxies. This explains the super-linear radio-SFR
relation, with more massive, star-forming galaxies being radio bright.
We propose a semi-calorimetric radio-SFR relation, which employs the
galaxy mass as a proxy for the calorimetric efficiency.
Description:
The LOw-Frequency ARray (LOFAR) Two-metre Sky Survey (LoTSS) Second
data release contains 120-168MHz images covering 27% of the northern
sky. This work presents a sample of 45 nearby galaxies within 30-Mpc
distance. We present integrated flux densities at 144-MHz using our
20-arcsec maps including the size of the elliptical integration
regions which approximate the extent of the 3-sigma contour lines. We
also present the full set of 6- and 20-arcsec LOFAR 144-MHz maps as
FITS files of the 45 galaxies. These maps were mostly obtained by
re-imaging the (u,v) data that has been re-processed with the
re-calibration pipeline.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
flux.dat 52 45 Integrated 144-MHz flux densities of the 45
galaxies in LoTSS-DR2
list.dat 111 90 List of fits maps
fits/* . 90 Individual fits maps
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See also:
J/A+A/659/A1 : LOFAR Two-metre Sky Survey (LoTSS) DR2 (Shimwell+, 2022)
J/A+A/660/A78 : LoTSS-DR2 sample overview release (Botteon+, 2022)
J/ApJS/257/30 : BL Lac morphologies with LoTSS-DR2 144MHz data (Mooney+, 2021)
Byte-by-byte Description of file: flux.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 8 A8 --- Name Catalog name of the galaxy
10- 19 F10.6 deg RAdeg Right ascension (J2000)
21- 29 F9.6 deg DEdeg Declination (J2000)
31- 34 F4.1 arcmin a Semi-major axis of the integration ellipse
for the 20" map
36- 39 F4.1 arcmin b Semi-minor axis of the integration ellipse
for the 20" map
41- 45 F5.3 Jy S144 Integrated radio flux density at 144MHz
47- 52 F6.4 Jy e_S144 Error of flux density
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Byte-by-byte Description of file: list.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 8 A8 --- Name Catalog name of the galaxy
10- 18 F9.5 deg RAdeg Right Ascension of center (J2000)
19- 27 F9.5 deg DEdeg Declination of center (J2000)
29- 32 I4 --- Nx Number of pixels along X-axis
34- 37 I4 --- Ny Number of pixels along Y-axis
39- 59 A21 "datime" Obs.date Observation date
61- 65 I5 Kibyte size Size of FITS file
67- 88 A22 --- FileName Name of FITS file, in subdirectory fits
90-111 A22 --- Title Title of the FITS file
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Acknowledgements:
Volker Heesen, heesen(at)hs.uni-hamburg.de
(End) Patricia Vannier [CDS] 25-May-2022