A Gaseous Group with Unusual Remote Star Formation

TL;DR

This study uses radio and UV observations to investigate a remote star-forming region in a spiral galaxy, revealing a likely dwarf galaxy undergoing ram pressure stripping as the source of the gas and star formation.

Contribution

It provides new evidence linking remote star formation to ram pressure stripping of a dwarf galaxy near ESO 481-G017.

Findings

A 120 kpc HI disk with 1.2x10^10 Msun mass around ESO 481-G017.

Detection of dwarf galaxies and an HI cloud near the galaxy.

The remote HII region is likely caused by ram pressure stripping of a dwarf galaxy.

Abstract

We present VLA 21-cm observations of the spiral galaxy ESO 481-G017 to determine the nature of remote star formation traced by an HII region found 43 kpc and ~800 km s^-1 from the galaxy center (in projection). ESO 481-G017 is found to have a 120 kpc HI disk with a mass of 1.2x10^10 Msun and UV GALEX images reveal spiral arms extending into the gaseous disk. Two dwarf galaxies with HI masses close to 10^8 Msun are detected at distances of ~200 kpc from ESO 481-G017 and a HI cloud with a mass of 6x10^7 Msun is found near the position and velocity of the remote HII region. The HII region is somewhat offset from the HI cloud spatially and there is no link to ESO 481-G017 or the dwarf galaxies. We consider several scenarios for the origin of the cloud and HII region and find the most likely is a dwarf galaxy that is undergoing ram pressure stripping. The HI mass of the cloud and Halpha luminosity of the HII region (10^38.1 erg s^-1) are consistent with dwarf galaxy properties, and the stripping can trigger the star formation as well as push the gas away from the stars.