Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Hubble Space Telescope Imaging of the Ultracompact Blue Dwarf Galaxy HS
  0822+3542: An Assembling Galaxy in a Local Void?   We present deep U, narrow-V, and I-band images of the ultracompact blue dwarf
galaxy HS 0822+3542, obtained with the Advanced Camera for Surveys / High
Resolution Channel of the Hubble Space Telescope. This object is extremely
metal-poor (12 + log(O/H) = 7.45) and resides in a nearby void. The images
resolve it into two physically separate components that were previously
described as star clusters in a single galaxy. The primary component is only
\~100 pc in maximum extent, and consists of starburst region surrounded by a
ring-like structure of relatively redder stars. The secondary component is ~50
pc in size and lies at a projected distance of ~80 pc away from the primary,
and is also actively star-forming. We estimate masses ~10^7 M(sol) and ~10^6
M(sol) for the two components, based on their luminosities, with an associated
dynamical timescale for the system of a few Myr. This timescale and the
structure of the components suggests that a collision between them triggered
their starbursts. The spectral energy distributions of both components can be
fitted by the combination of recent (few Myr old) starburst and an evolved
(several Gyr old) underlying stellar population, similar to larger blue compact
dwarf galaxies. This indicates that despite its metal deficiency the object is
not forming its first generation of stars. However, the small sizes and masses
of the two components suggests that HS 0822+3542 represents a dwarf galaxy in
the process of assembling from clumps of stars intermediate in size between
globular clusters and objects previously classified as galaxies. Its relatively
high ratio of neutral gas mass to stellar mass (~1) and high specific star
formation rate, log(SFR/M(sol) = -9.2, suggests that it is still converting
much of its gas to stars.

18
The categories of this paper are: econ
34
The categories of this paper are: chem-ph
16
The categories of this paper are: stat
10
The categories of this paper are: q-bio
29
The categories of this paper are: funct-an
31
The categories of this paper are: ao-sci
27
The categories of this paper are: comp-gas
2
The categories of this paper are: math
1
The categories of this paper are: cs
0
The categories of this paper are: hep-ph
26
The categories of this paper are: bayes-an
19
The categories of this paper are: eess
21
The categories of this paper are: adap-org
8
The categories of this paper are: hep-ex
9
The categories of this paper are: nlin
22
The categories of this paper are: chao-dyn