Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: A universal angular momentum profile for galactic halos   [Abridged] We study the angular-momentum profiles of a statistical sample of
halos drawn from a high-resolution N-body simulation of the LCDM cosmology. We
find that the cumulative mass distribution of specific angular momentum, j, in
a halo of mass Mv is well fit by a universal function, M(<j) = Mv \mu
j/(j_0+j). This profile is defined by one shape parameter (\mu or j_0) in
addition to the global spin parameter \lambda. It follows a power-law over most
of the mass, and flattens at large j, with the flattening more pronounced for
small values of \mu. Compared to a uniform sphere in solid-body rotation, most
halos have a higher fraction of their mass in the low- and high-j tails of the
distribution. The spatial distribution of angular momentum in halos tends to be
cylindrical and is well-aligned within each halo for ~80% of the halos. We
investigate two ideas for the origin of this profile. The first is based on a
revised version of linear tidal-torque theory combined with extended
Press-Schechter mass accretion, and the second focuses on j transport in minor
mergers. Finally, we briefly explore implications of the M(<j) profile on the
formation of galactic disks assuming that j is conserved during an adiabatic
baryonic infall. The implied gas density profile deviates from an exponential
disk, with a higher density at small radii and a tail extending to large radii.
The steep central density profiles may imply disk scale lengths that are
smaller than observed. This is reminiscent of the "angular-momentum problem"
seen in hydrodynamic simulations, even though we have assumed perfect j
conservation. A possible solution is to associate the central excesses with
bulge components and the outer regions with extended gaseous disks.

15
The categories of this paper are: nucl-ex
28
The categories of this paper are: alg-geom
8
The categories of this paper are: hep-ex
2
The categories of this paper are: math
23
The categories of this paper are: solv-int
13
The categories of this paper are: quant-ph
37
The categories of this paper are: supr-con
7
The categories of this paper are: hep-th
0
The categories of this paper are: hep-ph
11
The categories of this paper are: hep-lat
3
The categories of this paper are: physics
16
The categories of this paper are: stat
26
The categories of this paper are: bayes-an
1
The categories of this paper are: cs
34
The categories of this paper are: chem-ph
10
The categories of this paper are: q-bio