The VLA-COSMOS 3 GHz Large Project: Average radio spectral energy distribution of highly star-forming galaxies. (arXiv:1812.03392v1 [astro-ph.GA])
<a href="http://arxiv.org/find/astro-ph/1/au:+Tisanic_K/0/1/0/all/0/1">K. Tisani&#x107;</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Smolcic_V/0/1/0/all/0/1">V. Smol&#x10d;i&#x107;</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Delhaize_J/0/1/0/all/0/1">J. Delhaize</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Novak_M/0/1/0/all/0/1">M. Novak</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Intema_H/0/1/0/all/0/1">H. Intema</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Delvecchio_I/0/1/0/all/0/1">I. Delvecchio</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Schinnerer_E/0/1/0/all/0/1">E. Schinnerer</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Zamorani_G/0/1/0/all/0/1">G. Zamorani</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Bondi_M/0/1/0/all/0/1">M. Bondi</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Vardoulaki_E/0/1/0/all/0/1">E. Vardoulaki</a>

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 VLA observations of the COSMOS field at 1.4 GHz and 3 GHz with
unpublished GMRT observations at 325 MHz and 610 MHz by employing survival
analysis to account for non-detections in the GMRT maps. We selected a sample
of HSFGs in a broad redshift range (0.3100M0/yr) and constructed the
average radio SED. By fitting a broken power-law, we find that the spectral
index changes from $alpha_1=0.42pm0.06$ below a rest-frame frequency of 4.3
GHz to $alpha_2=0.94pm0.06$ above 4.3 GHz. Our results are in line with
previous low-redshift studies of HSFGs (SFR>10M0/yr) that show the SED of HSFGs
to differ from the SED found for normal SFGs (SFR<10M0/yr). The difference is mainly in a steeper spectrum around 10 GHz, 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.

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 VLA observations of the COSMOS field at 1.4 GHz and 3 GHz with
unpublished GMRT observations at 325 MHz and 610 MHz by employing survival
analysis to account for non-detections in the GMRT maps. We selected a sample
of HSFGs in a broad redshift range (0.3<z<4,SFR>100M0/yr) and constructed the
average radio SED. By fitting a broken power-law, we find that the spectral
index changes from $alpha_1=0.42pm0.06$ below a rest-frame frequency of 4.3
GHz to $alpha_2=0.94pm0.06$ above 4.3 GHz. Our results are in line with
previous low-redshift studies of HSFGs (SFR>10M0/yr) that show the SED of HSFGs
to differ from the SED found for normal SFGs (SFR<10M0/yr). The difference is
mainly in a steeper spectrum around 10 GHz, 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.

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