S19A0055

We propose to carry out spectroscopic follow-up observations of an ultra-faint dwarf galaxy in the Milky Way, Virgo I, which has recently been discovered by our group from the Hyper Suprime-Cam (HSC) survey data. This galaxy is one of the faintest dwarf satellites ever discovered, with a V-band absolute magnitude of only MV ≃ −0.33 mag, and is located at a heliocentric distance of 91 kpc, which is just at the limit that Subaru/HSC can reach for identifying a low-luminosity galaxy. Medium resolution spectroscopy of eleven candidate member stars in Virgo I, including red giant branch and asymptotic giant branch stars, as well as candidate field halo stars in the same direction, will allow us to assess the membership in Virgo I through the analysis of their radial velocities. Based on the obtained radial velocity dispersion of the confirmed member stars, we will estimate the dynamical state of this system, the basic chemo-dynamical properties and the mass-metallicity relation at the lowest mass end. Note that the proposed observations had been awarded 1.5 nights in S18A, but we did not gether any data due to bad weather conditions.


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