A pilot study using deep infrared imaging to constrain the star formation history of the XUV stellar populations in NGC 4625

TL;DR

This study uses deep infrared and ultraviolet imaging to analyze the star formation history in the outer regions of NGC 4625, revealing recent star formation likely triggered by galaxy interactions.

Contribution

It provides new deep infrared observations combined with UV data to constrain the stellar populations and star formation history in the galaxy's outer disk, highlighting the role of interactions.

Findings

Outer disk star formation is recent and ongoing.

Interactions with nearby galaxies likely triggered outer disk star formation.

Deep infrared imaging effectively constrains stellar populations in low surface brightness regions.

Abstract

In a LCDM universe, disk galaxies' outer regions are the last to form. Characterizing their contents is critical for understanding the ongoing process of disk formation, but observing outer disk stellar populations is challenging due to their low surface brightness. We present extremely deep 3.6 micron observations (Spitzer IRAC) of NGC 4625, a galaxy known for its radially extended ultraviolet emitting stellar population. We combine the new imaging with archival UV imaging from the GALEX mission to derive multiwavelength radial profiles for NGC 4625 and compare them to stellar populations models. The colors can be explained by the young stellar population that is responsible for the UV emission and indicate that the current star formation rates in the outermost disk are recent. Extended star formation in NGC 4625 may have been initiated by an interaction with neighboring galaxies NGC 4618 and NGC 4625a, supporting speculation that minor interactions are a common trigger for outer disk star formation and late stage disk growth.