Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: The nucleus of the Sagittarius dSph galaxy and M54: a window on the
  process of galaxy nucleation   We present the results of a thorough study of the nucleus of the Sgr dwarf
spheroidal galaxy and of the bright globular cluster M54 that resides within
the same nucleus (Sgr,N). We have obtained accurate radial velocities and
metallicity estimates for 1152 candidate Red Giant Branch stars of Sgr and M54
lying within ~ 9 arcmin from the center of the galaxy, from Keck/DEIMOS and
VLT/FLAMES spectra of the infrared Calcium II triplet. Using both velocity and
metallicity information we selected two samples of 425 and 321 very-likely
members of M54 and of Sgr,N, respectively. The two considered systems display
significantly different velocity dispersion profiles: M54 has a steeply
decreasing profile from r=0, where sigma= 14.2 km/s, to r=3.5 arcmin where it
reaches sigma=5.3 km/s, then it appears to rise again to sigma= 10 km/s at r=7
arcmin. In contrast Sgr,N has a uniformly flat profile at sigma=9.6 km/s over
the whole 0 < r < 9 arcmin range. Using data from the literature we show that
the velocity dispersion of Sgr remains constant at least out to r ~ 100 arcmin
and there is no sign of the transition between the outer
flat-luminosity-profile core and the inner nucleus in the velocity profile.
These results - together with a re-analysis of the surface brightness profile
of Sgr,N and a suite of dedicated N-body simulations - provide very strong
support for the hypothesis that the nucleus of Sgr formed independently of M54,
which probably plunged to its present position, coincident with Sgr,N, because
of significant decay of the original orbit due to dynamical friction.

14
The categories of this paper are: math-ph
35
The categories of this paper are: mtrl-th
0
The categories of this paper are: hep-ph
21
The categories of this paper are: adap-org
30
The categories of this paper are: q-alg
22
The categories of this paper are: chao-dyn
32
The categories of this paper are: atom-ph
37
The categories of this paper are: supr-con
7
The categories of this paper are: hep-th
36
The categories of this paper are: cmp-lg
20
The categories of this paper are: acc-phys
25
The categories of this paper are: patt-sol
2
The categories of this paper are: math
18
The categories of this paper are: econ
34
The categories of this paper are: chem-ph
33
The categories of this paper are: plasm-ph