Deep optical imaging of star-forming blue early-type galaxies: Color map structures and faint features indicative of recent mergers

TL;DR

This study uses deep optical imaging to reveal faint merger features in blue early-type galaxies, suggesting they are post-merger systems with ongoing star formation, shedding light on their evolution into passive ellipticals.

Contribution

It provides the first detailed optical color maps showing faint merger signatures in blue early-type galaxies, supporting their role as transitional post-merger systems.

Findings

Faint merger features detected in 37 out of 55 galaxies.

All galaxies show structures indicative of recent mergers in color maps.

Features are not visible in shallower SDSS imaging.

Abstract

Blue early-type galaxies with galaxy-scale ongoing star formation are interesting targets in order to understand the stellar mass buildup in elliptical and S0 galaxies in the local Universe. We study the star-forming population of blue early-type galaxies to understand the origin of star formation in these otherwise red and dead stellar systems. The legacy survey imaging data taken with the dark energy camera in the $g$, $r$, and $z$ bands for 55 star-forming blue early-type galaxies were examined, and $g-r$ color maps were created. We identified low surface brightness features near 37 galaxies, faint-level interaction signatures near 15 galaxies, and structures indicative of recent merger activity in the optical color maps of all 55 galaxies. These features are not visible in the shallow Sloan Digital Sky Survey imaging data in which these galaxies were originally identified. Low surface brightness features found around galaxies could be remnants of recent merger events. The star-forming population of blue early-type galaxies could be post-merger systems that are expected to be the pathway for the formation of elliptical galaxies. We hypothesize that the star-forming population of blue early-type galaxies is a stage in the evolution of early-type galaxies. The merger features will eventually disappear, fuel for star formation will cease, and the galaxy will move to the passive population of normal early-type galaxies.