Astronomy and Astrophysics – Astrophysics
Scientific paper
2007-05-28
Astronomy and Astrophysics
Astrophysics
4 pages 5 figures 1 table, accepted in ApJ, july issue
Scientific paper
10.1086/519377
We present spectroscopic observations of the AndXII dwarf spheroidal galaxy using DEIMOS/Keck-II, showing it to be moving rapidly through the Local Group (-556 km/s heliocentric velocity, -281 km/s relative to Andromeda from the MW), falling into the Local Group from ~115 kpc beyond Andromeda's nucleus. AndXII therefore represents a dwarf galaxy plausibly falling into the Local Group for the first time, and never having experienced a dense galactic environment. From Green Bank Telescope observations, a limit on the H{I} gas mass of <3000 Msun suggests that AndXII's gas could have been removed prior to experiencing the tides of the Local Group galaxies. Orbit models suggest the dwarf is close to the escape velocity of M31 for published mass models. AndXII is our best direct evidence for the late infall of satellite galaxies, a prediction of cosmological simulations.
Blain Andrew
Chapman Sandra C.
Ibata Rodrigo
Irwin Mike
Letarte Bruno
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