J/A+A/621/A139 VLA-COSMOS 3GHz sources average radio SED (Tisanic+, 2019)
The VLA-COSMOS 3 GHz Large Project:
Average radio spectral energy distribution of highly star-forming galaxies.
Tisanic K., Smolcic V., Delhaize J., Novak M., Intema H., Delvecchio I.,
Schinnerer E., Zamorani G., Bondi M., Vardoulaki E.
<Astron. Astrophys. 621, A139 (2019)>
=2019A&A...621A.139T 2019A&A...621A.139T (SIMBAD/NED BibCode)
ADC_Keywords: Galaxies, radio ; Radio continuum
Keywords: galaxies: evolution - galaxies: statistics -
radio continuum: galaxies - galaxies: star formation
Abstract:
We construct the average radio spectral energy distribution (SED) of
highly star-forming galaxies (HSFGs) up to z∼4. Infrared and radio
luminosities are bound by a tight correlation that is defined by the
so-called q parameter. This infrared-radio correlation provides the
basis for the use of radio luminosity as a star-formation tracer.
Recent stacking and survival analysis studies find q to be decreasing
with increasing redshift. It was pointed out that a possible cause of
the redshift trend could be the computation of rest-frame radio
luminosity via a single power-law assumption of the star-forming
galaxies' (SFGs) SED. To test this, we constrained the shape of the
radio SED of a sample of HSFGs. To achieve a broad rest-frame
frequency range, we combined previously published Very Large Array
observations of the COSMOS field at 1.4GHz and 3GHz with unpublished
Giant Meterwave Radio Telescope (GMRT) observations at 325MHz and
610MHz by employing survival analysis to account for non-detections
in the GMRT maps. We selected a sample of HSFGs in a broad redshift
range (z∈[0.3,4], SFR≥100M☉/yr) and constructed the
average radio SED. By fitting a broken power-law, we find that the
spectral index changes from σ1=0.42±0.06 below a rest-frame
frequency of 4.3GHz to σ2=0.94±0.06 above 4.3GHz. Our
results are in line with previous low-redshift studies of HSFGs
(SFR>10M☉/yr) that show the SED of HSFGs to differ from the SED
found for normal SFGs (SFR<10M_☉/yr). The difference is mainly in
a steeper spectrum around 10GHz, which could indicate a smaller
fraction of thermal free-free emission. Finally, we also discuss the
impact of applying this broken power-law SED in place of a simple
power-law in K-corrections of HSFGs and a typical radio SED for normal
SFGs drawn from the literature. We find that the shape of the radio
SED is unlikely to be the root cause of the q-z trend in SFGs.
Description:
The table of cross-matched fluxes in the COSMOS field for the analysis
presented in the paper.
The flux densities at 325MHz, 610MHz, 1.4GHz and 3GHz are given in uJy
and are rounded to 1uJy (which is less than the respective RMS
values). The fluxes are given without errors, since the errors were
not used in the analysis and will be published separately in the
325MHz and 610MHz catalogs. In case a source was not detected at
325MHz or 610MHz, the value given in the table is 5x the local RMS
value at its position.
File Summary:
--------------------------------------------------------------------------------
FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
matched.dat 55 306 Table of cross-matched fluxes
--------------------------------------------------------------------------------
See also:
J/ApJS/188/384 : The VLA-COSMOS survey. IV. (Schinnerer+, 2010)
J/A+A/602/A1 : VLA-COSMOS 3 GHz Large Project (Smolcic+, 2017)
Byte-by-byte Description of file: matched.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 10 A10 --- --- [COSMOSVLA3]
12- 30 A19 --- COSMOSVLA3 VLA-COSMOS name of the source,
JHHMMSS.ss+DDMMSS.s
32- 35 I4 uJy F325MHz 325MHz flux density
36- 39 A4 --- l_F325MHz [Det Ulim] Detection or upper limit at 325MHz
41- 43 I3 uJy F610MHz 610MHz flux density
44- 47 A4 --- l_F610MHz [Det Ulim] Detection or upper limit at 610MHz
49- 51 I3 uJy F1.4GHz 1.4GHz flux density (1)
53- 55 I3 uJy F3GHz 3 GHz flux density (2)
--------------------------------------------------------------------------------
Note (1): Flux densities from Schinnerer et al. (2010, Cat. J/ApJS/188/384)
Note (2): Flux densities from Smolcic et al. (2017, Cat. J/A+A/602/A1)
--------------------------------------------------------------------------------
Acknowledgements:
Kresimir Tisanic, ktisanic(at)phy.hr
(End) Patricia Vannier [CDS] 30-Nov-2018