Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Formation of an extended stellar halo around an ultra-faint dwarf galaxy
  following one of the earliest mergers from galactic building blocks   Ultra-faint dwarf galaxies (UFDs) are promising observable proxies to
building blocks of galaxies formed in the early Universe. We study the
formation and evolution of UFDs using cosmological hydrodynamic simulations. In
particular, we show that a major merger of two building block galaxies with
3,900 Msun and 7,500 Msun at the cosmic age of 510 Myr results in a system with
an extended stellar distribution consistent with the de Vaucouleurs profile.
The simulated galaxy has an average stellar metallicity of [Fe/H]=-2.7 and
features a metallicity gradient. These results closely resemble the properties
of a recently discovered UFD, Tucana II, which is extremely metal-poor and has
a spatially extended stellar halo with the more distant stars being more
metal-poor. Our simulation suggests that the extended stellar halo of Tucana II
may have been formed through a past major merger. Future observational searches
for spatially extended structures around other UFDs, combined with further
theoretical studies, will provide tangible measures of the evolutionary history
of the ancient, surviving satellite galaxies.

22
The categories of this paper are: chao-dyn
23
The categories of this paper are: solv-int
20
The categories of this paper are: acc-phys
25
The categories of this paper are: patt-sol
5
The categories of this paper are: gr-qc
36
The categories of this paper are: cmp-lg
27
The categories of this paper are: comp-gas
21
The categories of this paper are: adap-org
3
The categories of this paper are: physics
32
The categories of this paper are: atom-ph
28
The categories of this paper are: alg-geom
13
The categories of this paper are: quant-ph
34
The categories of this paper are: chem-ph
4
The categories of this paper are: cond-mat
37
The categories of this paper are: supr-con
24
The categories of this paper are: dg-ga