Bo”otes IV: A New Milky Way Satellite Discovered in the Subaru Hyper Suprime-Cam Survey and Implications for the Missing Satellite Problem. (arXiv:1906.07332v1 [astro-ph.GA])

Bo”otes IV: A New Milky Way Satellite Discovered in the Subaru Hyper Suprime-Cam Survey and Implications for the Missing Satellite Problem. (arXiv:1906.07332v1 [astro-ph.GA])
<a href="http://arxiv.org/find/astro-ph/1/au:+Homma_D/0/1/0/all/0/1">Daisuke Homma</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Chiba_M/0/1/0/all/0/1">Masashi Chiba</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Komiyama_Y/0/1/0/all/0/1">Yutaka Komiyama</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Tanaka_M/0/1/0/all/0/1">Masayuki Tanaka</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Okamoto_S/0/1/0/all/0/1">Sakurako Okamoto</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Tanaka_M/0/1/0/all/0/1">Mikito Tanaka</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Ishigaki_M/0/1/0/all/0/1">Miho N. Ishigaki</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Hayashi_K/0/1/0/all/0/1">Kohei Hayashi</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Arimoto_N/0/1/0/all/0/1">Nobuo Arimoto</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Carlsten_S/0/1/0/all/0/1">Scott G. Carlsten</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Lupton_R/0/1/0/all/0/1">Robert H. Lupton</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Strauss_M/0/1/0/all/0/1">Michael A. Strauss</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Miyazaki_S/0/1/0/all/0/1">Satoshi Miyazaki</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Torrealba_G/0/1/0/all/0/1">Gabriel Torrealba</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Wang_S/0/1/0/all/0/1">Shiang-Yu Wang</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Murayama_H/0/1/0/all/0/1">Hitoshi Murayama</a>

We report on the discovery of a new Milky Way (MW) satellite in Bo”otes
based on data from the on-going Hyper Suprime-Cam (HSC) Subaru Strategic
Program (SSP). This satellite, named Bo”otes IV, is the third ultra-faint
dwarf that we have discovered in the HSC-SSP. We have identified a
statistically significant (32.3$sigma$) overdensity of stars having
characteristics of a metal-poor, old stellar population. The distance to this
stellar system is $D_{odot}=209^{+20}_{-18}$ kpc with a $V$-band absolute
magnitude of $M_V=-4.53^{+0.23}_{-0.21}$ mag. Bo”otes IV has a half-light
radius of $r_h=462^{+98}_{-84}$ pc and an ellipticity of
$0.64^{+0.05}_{-0.05}$, which clearly suggests that this is a dwarf satellite
galaxy. We also found another overdensity that appears to be a faint globular
cluster with $M_V=-0.20^{+0.59}_{-0.83}$ mag and $r_h=5.9^{+1.5}_{-1.3}$ pc
located at $D_{odot}=46^{+4}_{-4}$ kpc. Adopting the recent prediction for the
total population of satellites in a MW-sized halo by Newton et al. (2018),
which combined the characteristics of the observed satellites by SDSS and DES
with the subhalos obtained in $Lambda$CDM models, we estimate that there
should be about two MW satellites at $M_Vle0$ in the $sim676$ deg$^2$ covered
by HSC-SSP, whereas that area includes six satellites. Thus, the observed
number of satellites is larger than the theoretical prediction. On the face of
it, we have a problem of too many satellites, instead of the well-known missing
satellites problem whereby the $Lambda$CDM theory overpredicts the number of
satellites in a MW-sized halo. This may imply that the models need more
refinements for the assignment of subhalos to satellites such as considering
those found by the current deeper survey. [abridged]

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