A survey of high-$z$ galaxies: SERRA simulations

TL;DR

The SERRA simulations provide high-resolution models of galaxies at redshifts 6 to 15, revealing their physical properties, star formation behaviors, and emission line characteristics, and comparing these with observational data to enhance understanding of early galaxy formation.

Contribution

This paper introduces the SERRA suite of high-resolution cosmological simulations including detailed chemistry and radiative transfer, specifically analyzing the $z=7.7$ galaxy population.

Findings

Galaxies at $z=7.7$ are bursty with high specific star formation rates.

SERRA galaxies are above the Schmidt-Kennicutt relation by a factor of about 3.

Early galaxies follow the standard [CII]-SFR relation and can reproduce observed [OIII]/[CII] ratios.

Abstract

We introduce SERRA, a suite of zoom-in high-resolution ($\sim 10\,\rm pc$) cosmological simulations including non-equilibrium chemistry and on-the-fly radiative transfer. The outputs are post-processed to derive galaxy UV+FIR continuum and emission line properties. Results are compared with available multi-wavelength data to constrain the physical properties (e.g., star formation rates, stellar/gas/dust mass, metallicity) of high-redshift $6 \lesssim z \lesssim 15$ galaxies. This flagship paper focuses on the $z=7.7$ sub-sample, including 202 galaxies with stellar mass $10^7 M_\odot \lesssim M_\star \lesssim 5\times 10^{10}M_\odot$, and specific star formation ranging from ${\rm sSFR} \sim 100\,{\rm Gyr}^{-1}$ in young, low-mass galaxies to $\sim 10\,{\rm Gyr}^{-1}$ for older, massive ones. At this redshift, SERRA galaxies are typically bursty, i.e. they are located above the Schmidt-Kennicutt relation by a factor $\kappa_s = 3.03^{+4.9}_{-1.8}$, consistent with recent findings for [OIII] and [CII] emitters at high-$z$. They also show relatively large ${\rm IRX} = L_{\rm FIR}/L_{\rm UV}$ values as a result of their compact/clumpy morphology effectively blocking the stellar UV luminosity. Note that this conclusion might be affected by insufficient spatial resolution at the molecular cloud level. We confirm that early galaxies lie on the standard $\rm [CII]-SFR$ relation; their observed $L_{\rm [OIII]}/L_{\rm [CII]} \simeq 1-10$ ratios can be reproduced by a part of the SERRA galaxies without the need of a top-heavy IMF and/or anomalous C/O abundances. [OI] line intensities are similar to local ones, making ALMA high-$z$ detections challenging but feasible ($\sim 6\,\rm hr$ for a SFR of $50\,M_\odot\,{\rm yr}^{-1}$).