The main sequence of star-forming galaxies at z~0.6: reinstating major mergers

TL;DR

This study re-evaluates the role of major mergers in star formation at z~0.6, showing they contribute significantly to the total star formation rate, contrary to previous beliefs that they are not the main driver.

Contribution

It demonstrates that when considering all merger phases, major mergers account for over half of the star formation activity at z~0.6, challenging earlier conclusions.

Findings

Major mergers contribute 53-88% of the total SFR at z~0.6.

The fraction of LIRGs in the fusion phase aligns with observed merger rates.

No tension exists between the main sequence scatter and merger-driven SFR peaks.

Abstract

The relation between the star formation rate and the stellar mass of star-forming galaxies has been used to argue that major mergers cannot be the main driver of star formation. Here, we re-examine these arguments using the representative IMAGES-CDFS sample of star-forming galaxies at z=0.4-0.75, taking advantage of their previously established classification into pre-fusion, fusion, and relaxing galaxy mergers. Contrary to previous claims, we show there is no tension between the main sequence scatter and the average duration of the fusion star formation rate SFR peak. We confirm previous estimates of the fraction of SFR due to morphologically-selected galaxies (~23%) or the SFR enhancement due to major merger during the fusion phase (~10%). However, galaxy mergers are not instantaneous processes, which implies that the total fraction of the SFR associated to galaxies undergoing major mergers must account for the three merger phases. When doing so, galaxies involved in major mergers are found to represent 53-88% of the total SFR at z~0.6. The fraction of LIRGs in the fusion phase is found to be in agreement with the observed morphological fraction of LIRGs without disks and with the observed and expected major merger rates at z<1.5.