Discovery of a possibly single blue supergiant star in the intra-cluster region of Virgo cluster of galaxies

TL;DR

This paper reports the potential discovery of the farthest known blue supergiant star formed in situ within a ram pressure stripped trail of a dwarf galaxy in the Virgo cluster, highlighting star formation in extreme intra-cluster environments.

Contribution

It presents the first spectroscopic evidence of a blue supergiant star in a galaxy cluster trail, suggesting in situ star formation in intra-cluster medium.

Findings

Spectroscopic identification of a blue supergiant star in the Virgo cluster trail.

Indication of in situ star formation in intra-cluster medium.

Potential record for the farthest star observed spectroscopically.

Abstract

IC 3418 is a dwarf irregular galaxy falling into the Virgo cluster, and a 17 kpc long trail is seen behind the galaxy, which is considered to have formed due to ram pressure stripping. The trail contains compact knots and diffuse blobs of ultraviolet and blue optical emission and, thus, it is a clear site of recent star formation but in an unusual environment, surrounded by a million degree intra-cluster medium. We report on our optical spectroscopy of a compact source in the trail, SDSS J122952.66+112227.8, and show that the optical spectrum is dominated by emission from a massive blue supergiant star. If confirmed, our report would mark the farthest star with spectroscopic observation. We interpret that a massive O-type star formed in situ in the trail has evolved recently out of the main sequence into this blue supergiant phase, and now lacks any detectable spectral sign of its associated HII region. We argue that turbulence within the ram pressure striped gaseous trail may play a dominant role for the star formation within such trails.