Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: The Formation History of the Ultra-Faint Dwarf Galaxies   We present early results from a Hubble Space Telescope survey of the
ultra-faint dwarf galaxies. These Milky Way satellites were discovered in the
Sloan Digital Sky Survey, and appear to be an extension of the classical dwarf
spheroidals to low luminosities, offering a new front in the efforts to
understand the missing satellite problem. Because they are the least luminous,
most dark matter dominated, and least chemically evolved galaxies known, the
ultra-faint dwarfs are the best candidate fossils from the early universe. The
primary goal of the survey is to measure the star-formation histories of these
galaxies and discern any synchronization due to the reionization of the
universe. We find that the six galaxies of our survey have very similar
star-formation histories, and that each is dominated by stars older than 12
Gyr.

20
The categories of this paper are: acc-phys
4
The categories of this paper are: cond-mat
27
The categories of this paper are: comp-gas
22
The categories of this paper are: chao-dyn
23
The categories of this paper are: solv-int
0
The categories of this paper are: hep-ph
37
The categories of this paper are: supr-con
29
The categories of this paper are: funct-an
3
The categories of this paper are: physics
16
The categories of this paper are: stat
7
The categories of this paper are: hep-th
5
The categories of this paper are: gr-qc
26
The categories of this paper are: bayes-an
13
The categories of this paper are: quant-ph
25
The categories of this paper are: patt-sol
12
The categories of this paper are: nucl-th