Galaxy mergers up to z<2.5 I : The star formation properties of merging galaxies at separations 3-15 kpc

TL;DR

This study investigates how galaxy mergers at 0.3<z<2.5 affect star formation, finding minimal enhancement at separations of 3-15 kpc and highlighting mass-dependent impacts on star formation activity.

Contribution

It provides the first detailed analysis of star formation in galaxy mergers at intermediate redshifts with separations of 3-15 kpc, revealing low starburst fractions and mass-dependent effects.

Findings

Only 12% of major mergers are starbursting.

Higher starburst fraction (20%) in lower-mass merging galaxies.

Star formation enhancement is limited at 3-15 kpc separations.

Abstract

We present a study of the influence of galaxy mergers on star formation at 0.3<z<2.5. Major mergers are selected from the CANDELS/3D-HST catalog using a peak-finding algorithm. Mergers have projected galaxy nuclei separation of their members between 3-15 kpc. We compare the star formation activity in merging and non-merging galaxies and find no significant differences. We find that only 12% of the galaxies in major mergers (in which both galaxies have log(M/Msun)>10) are star-bursting (i.e., with SFR above the main sequence of star-forming galaxies by >0.5 dex). Merging galaxies which include galaxies with lower masses show a higher fraction of star-bursting galaxies (20%). The low fraction of star-bursting merging galaxies in this sample suggests that at galaxy nuclei separations of 3-15 kpc merging galaxies are still in a early stage and are yet to reach the maximum level of star formation activity. Furthermore, the level of star formation enhancement and its duration could be arguably reduced compared to local mergers, as shown by simulations of high-z mergers, and might also depend on the physical properties (such as stellar mass and gas fraction) of the merging galaxies. Finally, we compare the specific SFR between merging galaxies. Our results suggest that, as the mass of the merging galaxies increases, the star formation activity in the less massive member in the merger suffers a more dramatic impact than its companion galaxy.