NGC 2782: a merger remnant with young stars in its gaseous tidal tail

TL;DR

This study identifies and characterizes young star-forming regions in the gaseous tidal tail of the merger remnant NGC 2782, revealing their ages, masses, and high metallicities, suggesting formation from enriched gas expelled during galaxy collision.

Contribution

First detailed analysis of young star-forming regions in NGC 2782's tidal tail, including age, mass, and metallicity measurements confirming their origin from enriched galactic gas.

Findings

Seven UV sources found in the tidal tail with ages 1-11 Myr.

High metallicities similar to the galaxy's nucleus, indicating enriched gas origin.

Regions are resolved into smaller systems in optical imaging.

Abstract

We have searched for young star-forming regions around the merger remnant NGC 2782. By using GALEX FUV and NUV imaging and HI data we found seven UV sources, located at distances greater than 26 kpc from the center of NGC 2782, and coinciding with its western HI tidal tail. These regions were resolved in several smaller systems when Gemini/GMOS r-band images were used. We compared the observed colors to stellar population synthesis models and we found that these objects have ages of ~1 to 11 Myr and masses ranging from 10^3.9 to 10^4.6 Msun. By using Gemini/GMOS spectroscopic data we confirm memberships and derive high metallicities for three of the young regions in the tail (12+log(O/H)=8.74\pm0.20, 8.81\pm0.20 and 8.78\pm0.20). These metallicities are similar to the value presented by the nuclear region of NGC 2782 and also similar to the value presented for an object located close to the main body of NGC 2782. The high metallicities measured for the star-forming regions in the gaseous tidal tail of NGC 2782 could be explained if they were formed out of highly enriched gas which was once expelled from the center of the merging galaxies when the system collided. An additional possibility is that the tail has been a nursery of a few generations of young stellar systems which ultimately polluted this medium with metals, further enriching the already pre-enriched gas ejected to the tail when the galaxies collided.