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 ${\langle μ_{\it V} \rangle} \sim 31.8_{-1.9}^{+1.3}$ 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.

Figures (1)

• Figure 1: Left: The spatial distribution of RGB stars around M83. These stars are extracted from the CMD box defined by the solid red polygon in Figure \ref{['fig:CMD']}. The known substructure and satellite galaxies are outlined in orange. Middle: The same as in the left panel, but with the solid red polygon indicating the recently-detected S-stream. The dashed red polygon shows the off-stream field, defined by rotating the solid red polygon 90 degrees clockwise around the center of M83. The cyan solid (dashed) circle indicates a region at 0.25 (0.20) degree from the center of M83. Right: the signal-to-noise ratio (S/N) map smoothed using a Gaussian kernel with a bandwidth of 1.2 arcmin. The red contour shows where the S/N reaches a value of 15. The yellow dashed and dotted lines represent the ridge lines of S-stream and N-stream, respectively. The cyan 'x'-mark ('+'-mark) corresponds to the densest parts of the S-stream (N-stream).