An H$\alpha$ Cloud in the HI Tail: Recent Star Formation in the Outskirts of NGC 4258 Revealed by Nanshan 1-m Telescope

TL;DR

This study uses deep Hα imaging and archival data to reveal ongoing star formation in the outskirts of NGC 4258, including an HI cloud in its tail, suggesting extended star formation regions outside the main galaxy.

Contribution

First-light deep Hα imaging combined with archival data uncovers star formation in the HI tail of NGC 4258, highlighting the importance of wide-field Hα imaging for studying galaxy outskirts.

Findings

Star formation detected in an HI cloud 16 kpc from NGC 4258

Presence of ultra-blue compact objects indicating young star clusters

Star formation in galaxy halos may influence galaxy evolution

Abstract

We present first-light deep H$\alpha$ imaging taken with the Nanshan 1-meter wide-field telescope on the local galaxy NGC 4258, alongside archival data from Hubble Space telescope (HST), Westerbork Synthesis Radio Telescope, and The Dark Energy Camera Legacy Survey. The H$\alpha$ image shows ongoing star formation not only inside the galaxy but also in an HI cloud in the eastern HI tail, which is roughly 16 kpc away from the main galaxy. The HST images reveal several ultra-blue compact objects ($\rm F555W - F814W <-0.5 mag,\, FWHM\sim 0.2''$) in the H$\alpha$ bright region, aligned with the HI tail, suggesting the presence of young open cluster candidate in the HI tail. Our results suggest that wide field H$\alpha$ imaging is a valuable tool for investigating recent star formation in the extended regions of NGC 4258. Furthermore, the star formation in diffuse HI tails could highlight an potential aspect of galaxy stellar halo formation, warranting further investigation of the impact of star formation in halos on galaxy evolution.