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

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 $⟨{\mu }_V⟩\sim 31.8_{-1.9}^{+1.3}$ mag arcsec${}^{-2}$, it is one of the most diffuse extragalactic streams currently known. The mean photometric metallicity of the stream is $⟨[M/H]⟩=-1.23\pm 0.02$ dex with a standard deviation of $0.28\pm 0.01$ dex, and we estimate the stellar mass to be $(8.5_{-2.8}^{+4.2})\times 10^6{\mathrm{M}}_{\odot }$ 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.

14 pages, 4 figures, Submitted to ApJ