Free-Floating HI Clouds in the M 81 Group

TL;DR

This study uncovers a population of extremely low-mass, free-floating HI clouds in the M 81 group, primarily located southeast of the central triplet, suggesting they may be tidal debris from galaxy interactions.

Contribution

First detection and mapping of low-mass HI clouds in the M 81 group, proposing a tidal debris origin for these clouds based on observational evidence.

Findings

Low-mass HI clouds are concentrated southeast of M 81

The clouds lack optical counterparts, indicating they are gaseous

Tidal interactions are the most plausible origin for these clouds

Abstract

Recent VLA observations pointed at dwarf spheroidal (dSph) galaxies in the M 81 group reveal a hitherto hidden population of extremely low mass (~1e5 Msol) HI clouds with no obvious optical counterparts. We have searched 10 fields in the M81 group totalling 2.2 square degree, both targeting known dwarf spheroidal galaxies and blank fields around the central triplet. Our observations show that the new population of low-mass HI clouds appears to be confined to a region toward the South-East of the central triplet (at distances of ~100 kpc from M 81). Possible explanations for these free-floating HI clouds are that they are related to the dSphs found to the South-East of M 81, that they belong to the galaxies of the M 81 triplet (equivalent to HVCs), that they are of primordial nature and provide fresh, unenriched material falling into the M 81 group, or that they are tidal debris from the 3-body interaction involving M 81-M 82-NGC 3077. Based on circumstantial evidence, we currently favour the latter explanation.