Star Formation Histories Across the Interacting Galaxy NGC 6872, the Largest-Known Spiral

TL;DR

This study investigates the star formation history and current activity across the large interacting galaxy NGC 6872, revealing extended star formation in the arms and regional variations in star formation rate conversion factors.

Contribution

It provides detailed spatial analysis of star formation and stellar populations in NGC 6872, highlighting differences from previous simulations and regional variations in SFR conversion.

Findings

Most star formation occurs in the galaxy's extended arms.

Little star formation is observed in the central 5 kpc.

No recent increase in star formation due to interaction.

Abstract

NGC 6872, hereafter the Condor, is a large spiral galaxy that is interacting with its closest companion, the S0 galaxy IC 4970. The extent of the Condor provides an opportunity for detailed investigation of the impact of the interaction on the current star formation rate and its history across the galaxy, on the age and spatial distribution of its stellar population, and on the mechanism that drive the star formation activity. To address these issues we analyzed the far-ultraviolet (FUV) to near-infrared (near-IR) spectral energy distribution (SED) of 17, 10 kpc diameter, regions across the galaxy, and derived their star formation history, current star formation rate, and stellar population and mass. We find that most of the star formation takes place in the extended arms, with very little star formation in the central 5 kpc of the galaxy, in contrast to what was predicted from previous numerical simulations. There is a trend of increasing star formation activity with distance from the nucleus of the galaxy, and no evidence for a recent increase in the current star formation rate (SFR) due to the interaction. The nucleus itself shows no significant current star formation activity. The extent of the Condor also provides an opportunity to test the applicability of a single standard prescription for conversion of the FUV + IR (22 micron) intensities to a star formation rate for all regions. We find that the conversion factor differs from region to region, arising from regional differences in the stellar populations.