Resolved stellar structures around NGC4631 from a Subaru/Hyper Suprime-Cam survey

Mikito Tanaka

We report on resolved stellar structures of nearby on-going interacting galaxy group mainly consisting of NGC4631 and NGC4656. We have observed the galaxy system using the Hyper Suprime-Cam (HSC) on the Subaru telescope and performed reduction for our data with HSC pipeline 3.8.5. However, the sky-subtraction process of the pipeline didn't work well in case that bulk of CCD chip were suffered from an apparently large object such as nearby galaxies. Therefore, we performed our own sky-subtraction procedure in order to estimate a large-scale sky-gradient. Furthermore, we have conducted photometry based on PyRAF/DAOphot. Eventually, we have newly detected 8 candidates of dwarf galaxies in the outer region of NGC4631 and confirmed the three candidates and the two tidal streams around NGC4631. The 3 or 4 candidates detected in this study could be a star-forming dwarf irregular galaxy because these dwarfs have massive blue main-sequence stars. On the other hand, the other 7 candidates could be an old dwarf spheroidal galaxy because these dwarf galaxies are dominated by old stellar populations such as red giant branch stars. Apparently, these dwarf galaxies are isotropically distributed around NGC4631 (not NGC4656) in contrast to dwarf galaxies of MW and M31 distributed in a thin plane. Furthermore, the effective radius to absolute magnitude relation of the dwarf galaxies in this galaxy group is similar to that of the Local Group and the other galaxy systems, implying that the dwarf galaxy system of the NGC4631 group may have formed through similar processes as the Local Group. In this conference, we would like to show spatial distributions and fundamental properties such as distance and metallicity of these dwarf galaxies and tidal streams based on resolved stellar populations.