Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Galactoseismology: Discovery of Vertical Waves in the Galactic Disk   We present evidence for a Galactic North-South asymmetry in the number
density and bulk velocity of solar neighborhood stars. The number density
profile, which is derived from main-sequence stars in the Sloan Digital Sky
Survey, shows a (North - South)/(North + South) deficit at |z| ~ 400 pc and an
excess at |z| ~ 800 pc. The bulk velocity profile, which is derived from the
Sloan Extension for Galactic Understanding and Exploration, shows a gradual
trend across the Galactic midplane as well as smaller-scale features. We
speculate that the North-South asymmetry, which has the appearance of a
wavelike perturbation, is intrinsic to the disk. We explore the physics of this
phenomenon through an analysis of the linearized Boltzmann and Poisson
equations and through one-dimensional simulations. The perturbation may be
excited by the passage of a satellite galaxy or dark matter subhalo through the
Galactic disk, in which case we are witnessing a recent disk-heating event.

37
The categories of this paper are: supr-con
36
The categories of this paper are: cmp-lg
0
The categories of this paper are: hep-ph
4
The categories of this paper are: cond-mat
32
The categories of this paper are: atom-ph
1
The categories of this paper are: cs
26
The categories of this paper are: bayes-an
3
The categories of this paper are: physics
2
The categories of this paper are: math
28
The categories of this paper are: alg-geom
21
The categories of this paper are: adap-org
23
The categories of this paper are: solv-int
34
The categories of this paper are: chem-ph
17
The categories of this paper are: q-fin
20
The categories of this paper are: acc-phys
33
The categories of this paper are: plasm-ph