# The Star Formation Main Sequence in the Hubble Space Telescope Frontier Fields

## TL;DR

This study examines the star formation main sequence in distant galaxies using Hubble data, extending to lower masses and analyzing its slope, scatter, and evolution with redshift.

## Contribution

It provides the first analysis of the MS down to very low stellar masses at high redshift, accounting for observational biases and exploring the mass dependence of scatter.

## Key findings

- The MS slope is approximately linear and does not evolve significantly with redshift.
- Scatter around the MS decreases with increasing stellar mass, indicating more varied star formation histories in low mass galaxies.
- The SFR per unit stellar mass increases with redshift more mildly than models predict.

## Abstract

We investigate the relation between the star formation rate (SFR) and the stellar mass (M), i.e. the Main Sequence (MS) relation of star-forming galaxies, at 1.3<=z<6 in the first four HST Frontier Fields, based on rest-frame UV observations. Gravitational lensing combined with deep HST observations allows us to extend the analysis of the MS down to stellar masses as low as logM/Msun~7.5 at z<~4 and logM/Msun~8 at higher redshifts, a factor of ~10 below most previous results. We perform an accurate simulation to take into account the effect of observational uncertainties on the MS and correct for the Eddington bias. This step allows us to reliably measure the MS and in particular its slope. While the normalization increases with redshift, we fit an unevolving and approximately linear slope. We nicely extend to lower masses the results of brighter surveys. Thanks to the large dynamic range in mass and by making use of the simulation, we analyzed any possible mass dependence of the dispersion around the MS. We find tentative evidence that the scatter decreases with increasing stellar masses, suggesting a larger variety of star formation histories in low mass galaxies. This trend agrees with theoretical predictions, and is explained as either a consequence of the smaller number of progenitors of low mass galaxies in a hierarchical scenario and/or of the efficient but intermittent stellar feedback processes in low mass halos. Finally, we observe an increase in the SFR per unit stellar mass with redshift milder than predicted by theoretical models, implying a still incomplete understanding of the processes responsible for galaxy growth.