The ISM of high-redshift galaxies: clues from C III] and [C II] lines

Kavli Affiliate: Roberto Maiolino

| First 5 Authors: Vladan Markov, Stefano Carniani, Livia Vallini, Andrea Ferrara, Andrea Pallottini

| Summary:

A tight relation between [C II] $ 158 {rm{mu m}}$ line luminosity and
star formation rate (SFR) is observed in local galaxies. At $z > 5$, galaxies
instead deviate downwards from the local $Sigma_{rm{[C
II]}}-Sigma_{rm{SFR}}$ relation. This deviation might be caused by different
interstellar medium (ISM) properties in galaxies at early epochs. We combine
the [C II] and SFR data with C III] $lambda1909$ line observations and our
physical models. We additionally investigate how the ISM properties: burstiness
$kappa_s$, total gas density $n$, and metallicity $Z$, affect the deviation
from the $Sigma_{rm{[C II]}}-Sigma_{rm{SFR}}$ relation in these sources. We
present the VLT/X-SHOOTER observations targeting the C III] $lambda1909$ line
emission in three galaxies at $5.5<z<7.0$. We extend our sample of galaxies by
including archival X-SHOOTER and MUSE data of eight sources at $2<z<7$ and
eleven star-forming systems at $6 < z< 7.5$ with C III] or [C II] data reported
in the literature. We detect C III] $lambda lambda1907, 1909$ line emission
in HZ10 and derive the intrinsic flux of the C III] $ lambda1909$ line. We
constrain the ISM properties of our sample of galaxies: $kappa_s$, $n$, and
$Z$, by applying our physically motivated model based on the MCMC algorithm.
For the most part, high-$z$, star-forming galaxies show subsolar metallicities.
The majority of the sources have $log{(kappa_s)} gtrsim 1$, i.e., they
overshoot the Kennicutt-Schmidt relation by about one order of magnitude. This
suggests that the whole KS relation might be shifted upwards at early times.
Next, all the high-$z$ galaxies of our sample lie below the $Sigma_{rm{[C
II]}}-Sigma_{rm{SFR}}$ local relation. The total gas density $n$ shows the
strongest correlation with the deviation from the local $Sigma_{rm{[C
II]}}-Sigma_{rm{SFR}}$ relation, in agreement with theoretical models.

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