S18A0017abst
S18A0017
This is re-submission of previously accepted proposal (S16B-QN014). We collected only 5% of the requested data and here we propose to carry out the observation again. We propose to observe 20 nearby (<∼20 Mpc) galaxies to their virial radii with HSC for the first observational test of the missing satellite problem beyond the Local Group (LG). The problem has been a big challenge to the widely accepted ΛCDM paradigm, and by its nature, the problem must be addressed with a statistical rigor as proposed here; however, it has been tested only within the LG so far. In fact, both our pilot observation and recent hydro-dynamical simulations have revealed a large diversity of Milky Way-sized halos in terms of the abundance of dwarf satellite galaxies. Building upon the pilot observation, we now propose to carry out a larger survey of galaxies outside of the LG with HSC and perform a statistical test of the missing satellite problem for the very first time. As a secondary goal, we also aim to probe the spatial alignment of dwarf galaxies, which could also be another potential challenge to ΛCDM. With a small investment of 20 hours, we will make a significant impact in the field.
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