Birds of a Feather? Magellan/IMACS Spectroscopy of the Ultra-Faint Satellites Grus II, Tucana IV, and Tucana V

Abstract

We present Magellan/IMACS spectroscopy of three recently discovered ultra-faint Milky Way satellites, Grus II, Tucana IV, and Tucana V. We measure systemic velocities of v hel = −110.0±0.5 km s −1 , v hel = 15.9 +1.8 −1.7 km s −1 , and v hel = −36.2 +2.5 −2.2 km s −1 for the three objects, respectively. Their large relative velocity differences demonstrate that the satellites are unrelated despite their close physical proximity to one another. We determine a velocity dispersion for Tuc IV of σ = 4.3 +1.7 −1.0 km s −1 , but are unable to resolve the velocity dispersions of the other two systems. For Gru II we place an upper

Gaia RR Lyrae Stars in Nearby Ultra-faint Dwarf Satellite Galaxies

“…Their stars are old and very metal-poor, with little chemical enrichment. For a recent review of this type of galaxy see Simon (2019); following his definition of a UFD as being those having M V < −7.7, we count 41 currently known UFDs which are satellites of the Milky Way. More than half of these were discovered in the last four years.…”

“…For Bootes III (Boo III) and Sagittarius II (Sgr II), members were taken from and Longeard et al (2020), respectively. Spectroscopic members of Grus II and Tucana V (Tuc V) come from the recent work by Simon et al (2019).…”