# The main sequence of star forming galaxies I. The local relation and its bending

## TL;DR

This study investigates the slope and bending of the local star-forming galaxy main sequence using multiple SFR indicators, revealing a mass-dependent bending and increased scatter at higher stellar masses linked to galaxy environment and merger activity.

## Contribution

It provides new insights into the mass-dependent shape and scatter of the galaxy main sequence, highlighting the roles of mergers and hot halo gas in high-mass galaxy evolution.

## Key findings

- The MS slope depends on the SFR indicator used.
- The MS shows a bending at high stellar masses.
- Scatter increases with stellar mass, reaching ~0.45 dex at 10^{11} M_{\odot}.

## Abstract

By using a set of different SFR indicators, including WISE mid-infrared and Halpha emission, we study the slope of the Main Sequence (MS) of local star forming galaxies at stellar masses larger than 10^{10} M_{\odot}. The slope of the relation strongly depends on the SFR indicator used. In all cases, the local MS shows a bending at high stellar masses with respect to the slope obtained in the low mass regime. While the distribution of galaxies in the upper envelope of the MS is consistent with a log-normal distribution, the lower envelope shows an excess of galaxies, which increases as a function of the stellar mass but varies as a function of the SFR indicator used. The scatter of the best log-normal distribution increases with stellar mass from ~0.3 dex at 10^{10} M_{\odot} to ~0.45 at 10^{11} M_{\odot}. The MS high-mass end is dominated by central galaxies of group sized halos with a red bulge and a disk redder than the lower mass counterparts. We argue that the MS bending in this region is due to two processes: i) the formation of a bulge component as a consequence of the increased merger activity in groups, and ii) the cold gas starvation induced by the hot halo environment, which cuts off the gas inflow onto the disk. Similarly, the increase of the MS scatter at high stellar masses would be explained by the larger spread of star formation histories of central group and cluster galaxies with respect to lower mass systems.