Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: On the nature of the ring-like structure in the outer Galactic disk   We examine the tidal disruption of satellite galaxies in a cosmological
simulation of the formation of a disk galaxy in the $\Lambda$CDM scenario. We
find that the disruption of satellite galaxies in orbits roughly coplanar with
the disk leads naturally to the formation of ring-like stellar structures
similar to that recently discovered in the outer disk of the Milky Way. Two
interpretations appear plausible in this context. One is that the ring is a
transitory, localized radial density enhancement reflecting the apocenter of
particles stripped from a satellite during a recent pericentric passage (a
``tidal arc'' reminiscent of the tidal arms seen in disk galaxy mergers). In
the second scenario, the ring is analogous to the ``shells'' found around some
elliptical galaxies, and would result from a minor merger that took place
several Gyr ago. The two interpretations differ in several ways. Tidal arcs are
expected to span a limited longitude range; may carry a substantial fraction of
the original mass of the satellite; should exhibit a significant velocity
gradient with Galactic longitude; and are in all likelihood asymmetric above
and below the plane of the disk. Shells, on the other hand, may comprise at
most a small fraction of the original mass of the satellite and, due to their
more relaxed state, ought to be symmetric above and below the plane, with no
discernible velocity gradients across the structure. If confirmed as a tidal
feature, the ring discovered by SDSS in the outer Galactic disk would
strengthen the view--supported by numerical simulations--that minor mergers
have played a significant role building up not only the stellar halo, but also
the disk components of the Galaxy.

1
The categories of this paper are: cs
13
The categories of this paper are: quant-ph
26
The categories of this paper are: bayes-an
31
The categories of this paper are: ao-sci
37
The categories of this paper are: supr-con
3
The categories of this paper are: physics
9
The categories of this paper are: nlin
36
The categories of this paper are: cmp-lg
11
The categories of this paper are: hep-lat
20
The categories of this paper are: acc-phys
33
The categories of this paper are: plasm-ph
8
The categories of this paper are: hep-ex
2
The categories of this paper are: math
12
The categories of this paper are: nucl-th
29
The categories of this paper are: funct-an
0
The categories of this paper are: hep-ph