A Long Stellar Stream in M83: Possible Connection Between XUV Disks and Minor Mergers?

TL;DR

This study confirms and characterizes a vast, diffuse stellar stream in M83, linking it to a minor merger event that may have influenced the galaxy's outer gas and star formation activity.

Contribution

First detailed mapping of the S-stream in M83 using deep photometry, revealing its properties and suggesting a connection to a past minor merger event affecting the galaxy's outer disk.

Findings

The S-stream is approximately 81 kpc long and 9 kpc wide.

It has a very low surface brightness of around 31.8 mag arcsec$^{-2}$.

The stream's metallicity and structure suggest a common origin with the northern counterpart.

Abstract

We present the confirmation and characterization of a long stream (S-stream) in the southern part of M83. This feature is revealed using deep wide-field photometric data obtained by the Hyper Suprime-Cam (HSC) mounted on the Subaru Telescope. Using individual red giant branch (RGB) stars, we successfully trace the stream over a large length of $\sim 81$~kpc and a considerable width of $\sim 9$ kpc. With a mean surface brightness of ${\langle \mu_{\it V} \rangle} \sim 31.8_{-1.9}^{+1.3}$ mag arcsec$^{-2}$, it is one of the most diffuse extragalactic streams currently known. The mean photometric metallicity of the stream is $\langle[{\rm M/H}]\rangle = -1.23\pm0.02$ dex with a standard deviation of $0.28\pm0.01$ dex, and we estimate the stellar mass to be $(8.5_{-2.8}^{+4.2}) \times 10^6~{\rm M_\odot}$ from the luminosity of RGB stars. Compared to its well-known northern counterpart, the S-stream is slightly more metal-poor, but our large-area RGB map shows compelling evidence that these two features are related, originating from a single low-mass merger event. We identify density variations along the S-stream, which more likely reflect intrinsic density structure within the progenitor rather than the interaction with dark matter subhalos. Similarities between the morphology of the S-stream and some features in the \HI distribution suggest that a minor merger event may have disturbed and redistributed M83's outer \HI gas, leading to triggered star formation and the formation of the XUV disk.