Radio continuum size evolution of star-forming galaxies over 0.35 < z < 2.25. (arXiv:1903.12217v1 [astro-ph.GA]) <a href="http://arxiv.org/find/astro-ph/1/au:+Jimenez_Andrade_E/0/1/0/all/0/1">E.F. Jiménez-Andrade</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Magnelli_B/0/1/0/all/0/1">B. Magnelli</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Karim_A/0/1/0/all/0/1">A. Karim</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:+Schinnerer_E/0/1/0/all/0/1">E. Schinnerer</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Sargent_M/0/1/0/all/0/1">M. Sargent</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Romano_Diaz_E/0/1/0/all/0/1">E. Romano-Díaz</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:+Lang_P/0/1/0/all/0/1">P. Lang</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Bertoldi_F/0/1/0/all/0/1">F. Bertoldi</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Vardoulaki_E/0/1/0/all/0/1">E. Vardoulaki</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Toft_S/0/1/0/all/0/1">S. Toft</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Smolcic_V/0/1/0/all/0/1">V. Smolčić</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Harrington_K/0/1/0/all/0/1">K. Harrington</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Leslie_S/0/1/0/all/0/1">S. Leslie</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:+Liu_D/0/1/0/all/0/1">D. Liu</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Karoumpis_C/0/1/0/all/0/1">C. Karoumpis</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Kartaltepe_J/0/1/0/all/0/1">J. Kartaltepe</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Koekemoer_A/0/1/0/all/0/1">A.M. Koekemoer</a>
We present the first systematic study of the radio continuum size evolution We present the first systematic study of the radio continuum size evolution http://arxiv.org/icons/sfx.gif
of star-forming galaxies (SFGs) over the redshift range $0.35
of star-forming galaxies (SFGs) over the redshift range $0.35<z<2.25$. We use
the VLA COSMOS 3GHz map (noise $rm rms=2.3,mu Jy ,beam^{-1}$, $theta_{rm
beam}=0.75,rm arcsec$) to construct a mass-complete sample of 3184
radio-selected SFGs that reside on and above the main-sequence (MS) of SFGs. We
find no clear dependence between the radio size and stellar mass, $M_{star}$,
of SFGs with $10.5lesssimlog(M_star/rm M_odot)lesssim11.5$. Our analysis
suggests that MS galaxies are preferentially extended, while SFGs above the MS
are always compact. The median effective radius of SFGs on (above) the MS of
$R_{rm eff}=1.5pm0.2$ ($1.0pm0.2$) kpc remains nearly constant with cosmic
time; a parametrization of the form $R_{rm eff}propto(1+z)^alpha$ yields a
shallow slope of only $alpha=-0.26pm0.08,(0.12pm0.14)$ for SFGs on (above)
the MS. The size of the stellar component of galaxies is larger than the extent
of the radio continuum emission by a factor $sim$2 (1.3) at $z=0.5,(2)$,
indicating star formation is enhanced at small radii. The galactic-averaged
star formation rate surface density $(Sigma_{rm SFR})$ scales with the
distance to the MS, except for a fraction of MS galaxies ($lesssim10%$) that
harbor starburst-like $Sigma_{rm SFR}$. These “hidden” starbursts might have
experienced a compaction phase due to disk instability and/or merger-driven
burst of star formation, which may or may not significantly offset a galaxy
from the MS. We thus propose to jointly use $Sigma_{rm SFR}$ and distance to
the MS to better identify the galaxy population undergoing a starbursting
phase.
