Ionized gas kinematics and chemical abundances of low-mass star-forming galaxies at $z\sim 3$

Abstract

We selected 35 low-mass SFGs (7.9<log(M${}_{\ast }$/M${}_{\odot }$)<10.3) from deep spectroscopic surveys based on their CIII]1908 emission. We used follow-up NIR observations to examine their rest-optical emission lines and identify ionized outflow signatures through broad emission wings detected after Gaussian modeling of [OIII]4959,5007 profiles. We characterized the galaxies' gas-phase metallicity and carbon-to-oxygen (C/O) abundance using a Te-based method via the OIII]1666/[OIII]5007 ratio and photoionization models. We find line ratios and rest-frame EWs characteristic of high-ionization conditions powered by massive stars. Our sample displays mean rest-frame EW([OIII]5007)~560Ã while 15% of them show EW([OIII]4959,5007)>1000Ã and EW(CIII])>5Ã , closely resembling those now seen in EoR galaxies with JWST. We find low gas-phase metallicities 12+log(O/H)~7.5-8.5 and C/O abundances from 23%-128% solar, with no apparent increasing trend with metallicity. From our [OIII]4959,5007 profile modeling, we find that 65% of our sample shows an outflow component, which is shifted relative to the ionized gas systemic velocity, with mean $v_{max}$~280 km/s which correlates with the $\hat{I}{\pounds }_{SFR}$. We find that the mass-loading factor $\hat{I}¼$ of our sample is typically lower than in more massive galaxies from literature but higher than in typical local dwarf galaxies. In the stellar mass range covered, we find that $\hat{I}¼$ increases with $\hat{I}{\pounds }_{SFR}$ thus suggesting that for a given stellar mass, denser starbursts in low-mass galaxies produce stronger outflows. Our results complement the picture drawn by similar studies at lower redshift, suggesting that the removal of ionized gas in low-mass SFGs driven by stellar feedback is regulated by their stellar mass and by the strength and concentration of their star formation, i.e. $\hat{I}{\pounds }_{\mathrm{SFR}}$.

Accepted for publication in A&A. We updated the manuscript following referee's suggestions. We updated the estimations of C/O by not including CIV flux since it is not detected in most of our sample. No major changes in our results compared with previous version