UV/Optical/IR Color Sequences Along the Tidal Ring/Arm of Arp 107

TL;DR

This study analyzes UV, optical, and IR spectral energy distributions of star-forming regions in Arp 107, revealing color sequences that indicate variations in stellar ages and populations along the tidal arm.

Contribution

It demonstrates a correlation between UV/optical and mid-infrared colors, and suggests a gradient in stellar ages and populations along the tidal arm of Arp 107.

Findings

Color sequences mirror between UV/optical and mid-infrared.

Younger stars are located further out in the tidal arm.

Regions in Arp 107 are less actively star-forming than in other systems.

Abstract

We construct UV/optical/IR spectral energy distributions for 29 star forming regions in the interacting galaxy Arp 107, using GALEX UV, Sloan Digitized Sky Survey optical, and Spitzer infrared images. In an earlier study utilizing only the Spitzer data, we found a sequence in the mid-infrared colors of star-forming knots along the strong tidal arm in this system. In the current study, we find sequences in the UV/optical colors along the tidal arm that mirror those in the mid-infrared, with blue UV/optical colors found for regions that are red in the mid-infrared, and vice versa. With single-burst stellar population synthesis models, we find a sequence in the average stellar age along this arm, with younger stars preferentially located further out in the arm. Models that allow two populations of different ages and dust attenuations suggest that there may be both a young component and an older population present in these regions. Thus the observed color sequences may be better interpreted as a sequence in the relative proportion of young and old stars along the arm, with a larger fraction of young stars near the end. Comparison with star forming regions in other interacting galaxies shows that the Arp 107 regions are relatively quiescent, with less intense star formation than in many other systems.