A UV study of nearby luminous infrared galaxies: star formation histories and the role of AGN

TL;DR

This study uses UV and optical data to analyze star formation histories and AGN roles in 561 nearby luminous infrared galaxies, revealing diverse morphologies, star formation timescales, and the timing of AGN activity.

Contribution

It provides a comprehensive analysis of star formation and AGN activity in LIRGs using UV and optical photometry, highlighting the timing and impact of AGN on star formation.

Findings

Most LIRGs have old stellar populations (~6.8 Gyrs).

60% of LIRGs began recent star formation within the last Gyr.

14% of LIRGs host Type 2 AGN with no clear negative feedback evidence.

Abstract

We employ UV and optical photometry, from the GALEX and SDSS surveys respectively, to study the star formation histories of 561 luminous infrared galaxies (LIRGs) in the nearby Universe. A small fraction (~4%) of these galaxies have spheroidal or near-spheroidal morphologies and could be progenitors of elliptical galaxies. The remaining galaxies are morphologically late-type or ongoing mergers. 61% of the LIRGs do not show signs of interactions, while the remaining objects are either interacting (~18%) or show post-merger morphologies (~19%). The (SSP-weighted) average age of the underlying stellar populations in these objects is typically 5-9 Gyrs, with a mean value of ~6.8 Gyrs. ~60% of the LIRG population began their recent star formation (RSF) episode within the last Gyr, while the remaining objects began their RSF episodes 1 to 3 Gyrs in the past. Up to 35% of the stellar mass in the remnant forms in these episodes - the mean value is ~15%. The (decay) timescales of the star formation are typically a few Gyrs, indicating that the star formation rate does not decline significantly during the course of the burst. 14% of the LIRG population host (Type 2) AGN. The AGN hosts exhibit UV and optical colours that are redder than those of the normal (non-AGN) population. However, there is no evidence for a systematically higher dust content in the AGN hosts. AGN typically appear ~0.5-0.7 Gyrs after the onset of star formation and the redder colours are a result of older RSF episodes, with no measurable evidence of negative feedback from the AGN on the star formation in their host galaxies. (abridged)