Probing the star-formation modes in merging galaxies

TL;DR

This study investigates star formation in merging galaxies using high-resolution HI and UV data, revealing increased star formation efficiency in merger regions and supporting simulation predictions about gas behavior during mergers.

Contribution

It provides detailed observational evidence of turbulent-driven star formation in nearby mergers, aligning with and testing theoretical models and simulations.

Findings

Higher SFR/HI ratios in merger outskirts compared to isolated spirals.

SFR/HI increases towards the centers of mergers.

Results support the link between gas turbulence and star formation efficiency.

Abstract

Merging systems at low redshift provide the unique opportunity to study the processes related to star formation in a variety of environments that presumably resemble those seen at higher redshifts. Previous studies of distant starbursting galaxies suggest that stars are born in turbulent gas, with a higher efficiency than in MW-like spirals. We have investigated in detail the turbulent-driven regime of star-formation in nearby colliding galaxies combining high resolution VLA B array HI maps and UV GALEX observations. With these data, we could check predictions of our state-of-the-art simulations of mergers, such as the global sharp increase of the fraction of dense gas, as traced by the SFR, with respect to the diffuse gas traced by HI during the merging stage, following the increased velocity dispersion of the gas. We present here initial results obtained studying the SFR-HI relation at 4.5 kpc resolution. We determined SFR/HI mass ratios that are higher in the external regions of mergers than in the outskirts of isolated spirals, though both environments are HI dominated. SFR/HI increases towards the central regions following the decrease of the atomic gas fraction and possibly the increased star-formation efficiency. These results need to be checked with a larger sample of systems and on smaller spatial scales. This is the goal of the on-going Chaotic THINGS project that ultimately will allow us to determine why starbursting galaxies deviate from the Kennicutt-Schmidt relation between SFR density and gas surface density.