Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Strangers in the night: Discovery of a dwarf spheroidal galaxy on its
  first Local Group infall   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.

18
The categories of this paper are: econ
22
The categories of this paper are: chao-dyn
26
The categories of this paper are: bayes-an
12
The categories of this paper are: nucl-th
2
The categories of this paper are: math
28
The categories of this paper are: alg-geom
15
The categories of this paper are: nucl-ex
33
The categories of this paper are: plasm-ph
21
The categories of this paper are: adap-org
30
The categories of this paper are: q-alg
19
The categories of this paper are: eess
0
The categories of this paper are: hep-ph
32
The categories of this paper are: atom-ph
1
The categories of this paper are: cs
20
The categories of this paper are: acc-phys
29
The categories of this paper are: funct-an