An Isolated HII Region near ESO 481-G017

TL;DR

This study uses VLA 21-cm observations to investigate a remote HII region near ESO 481-G017, revealing its possible origin from tidal interactions or a low-luminosity companion galaxy, and providing insights into isolated star formation.

Contribution

First detailed radio observation of a remote HII region near ESO 481-G017, exploring its environment and origin through velocity and HI data.

Findings

HII region has minimal continuum emission, indicating recent star formation.

Velocity difference suggests the HII region may originate from tidal interactions or a faint companion.

The HI mass of ESO 481-G017 is 1.1×10^9 solar masses.

Abstract

We obtained VLA 21-cm observations of the galaxy ESO 481-G017 to determine the environment and trigger of remote star formation traced by a HII region found 43 kpc from the galaxy (in projection). ESO 481-G017 is an early type spiral galaxy with a HI mass of 1.1*10^9 Msun and a distance of 55 Mpc. The isolated HII region has a H-alpha luminosity of 10^38.1 erg s^-1 and minimal continuum emission suggesting that new stars have formed where little or no stars previously existed. The difference in velocity between the HI disk of ESO 481-G017 (3840-4000 km s^-1) and the isolated HII region (4701 +/- 80 km s^-1) indicates the origin of the HII region may be stars forming in a tidal feature or newly triggered star formation in a very low luminosity companion galaxy. The VLA observations shed light on the nature of this young object.