S22B0107

We propose a wide-field deep HSC photometry of the halo region of the Triangulum galaxy (M33). M33 is relatively well observed in the central region, but no deep observations have been conducted in the outer region. Therefore, the existence of the stellar halo in M33 is still under debate. The combination of the narrow-band filter NB515 and 3 broad-band filters g, r, i makes it possible to detect the faint structures of M33 without contaminations. Combining the NB515 with g and i bands efficiently separates red giant branch stars in M33 from foreground dwarf stars, while the combination of g, r, and i bands discriminates background unresolved galaxies. With the widest field-of-view among 8m-class telescopes, Subaru/HSC covers the outer region of M33 and can detect red clump stars at greater depths. We make use of the data to detect stellar halos, confirm stellar populations that are lower metallicity than large galaxies, and compare the surface brightness profile with those of other spiral galaxies, providing new insights into galactic halos. This observation unravels the M33 stellar halo and reveals the similarities and differences in the nature of the stellar halo compared to the Milky Way and the Andromeda galaxy for the first time.

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