Kavli Affiliate: Hitoshi Murayama
| First 5 Authors: Daisuke Homma, Masashi Chiba, Yutaka Komiyama, Masayuki Tanaka, Sakurako Okamoto
| Summary:
We present the final results of our search for new Milky Way (MW) satellites
using the data from the Hyper Suprime-Cam (HSC) Subaru Strategic Program (SSP)
survey over $sim 1,140$ deg$^2$. In addition to three candidates that we
already reported, we have identified two new MW satellite candidates in the
constellation of Sextans at a heliocentric distance of $D_{odot} simeq
126$kpc, and Virgo at $D_{odot} simeq 151$kpc, named Sextans II and Virgo
III, respectively. Their luminosities (Sext II:$M_Vsimeq-3.9$mag; Vir
III:$M_Vsimeq-2.7$mag) and half-light radii (Sext II:$r_hsimeq154$ pc; Vir
III:$r_hsimeq 44$ pc) place them in the region of size-luminosity space of
ultra-faint dwarf galaxies (UFDs). Including four previously known satellites,
there are a total of nine satellites in the HSC-SSP footprint. This discovery
rate of UFDs is much higher than that predicted from the recent models for the
expected population of MW satellites in the framework of cold dark matter
models, thereby suggesting that we encounter a too many satellites problem.
Possible solutions to settle this tension are also discussed.
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