Stellar streams around dwarf galaxies in the Local Universe

TL;DR

This study investigates stellar streams around dwarf galaxies in the Local Universe, providing initial observational data, classifying accretion features, and discussing detection challenges to inform low-mass galaxy evolution models.

Contribution

It presents the first release of accretion features around dwarf galaxies from the DES and DECaLS surveys, including new identifications and a classification metric for debris.

Findings

5.1% of dwarfs show accretion features in the DES footprint

Detection of streams around dwarfs is more challenging than around massive galaxies

Results highlight the need for better theoretical models of low-mass merger morphologies

Abstract

While mergers between massive galaxies and their dwarf satellites are well studied, the properties of dwarf - dwarf satellite mergers are not well constrained. Stellar streams trace satellite disruption and, in the dwarf galaxy regime, are predicted to provide novel constraints on low-mass galaxy evolution and dark matter. However, the mass ratios required to form these streams make them challenging to detect. We present a preview of the Stellar Stream Legacy Survey (SSLS) in the dwarf galaxy regime. The SSLS aims to produce a statistically large, homogeneous sample of stellar streams for comparison with galaxy evolution theory. We visually inspect dwarf galaxies using the DESI Legacy Imaging Survey (DES and DECaLS footprints, r-band 29 mag arcsec^-2 within 4 - 35 Mpc. We develop a classification metric to categorise accretion debris around dwarf galaxies, and measure the frequency of accretion features in the DES footprint only. We present the first release of accretion features around dwarf galaxies collected from the DES and DECaLS footprints, including 1 stream, 11 shells, and 8 asymmetric stellar halos, of which 17 constitute new identifications. In the DES footprint, we inspect 730 dwarfs and find that 5.1% (37/730) show accretion features. Although this frequency measurement is lower than the SSLS result for massive galaxies, we discuss the observational biases behind detecting streams in the dwarf galaxy regime. Our results highlight the difficulty of detecting streams around dwarfs, and identify the need for improved theoretical modelling of low-mass merger morphologies. Nevertheless, they place constraints on hierarchical mass assembly in this regime.