Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Discovery of a Giant Stellar Tidal Stream Around the Disk Galaxy NGC
  4013   We report the discovery of a giant, loop-like stellar structure around the
edge-on spiral galaxy NGC 4013. This arcing feature extends 6 arcmin (~26 kpc
in projected distance) northeast from the center and 3 arcmin (~=12 kpc) from
the disk plane; likely related features are also apparent on the southwest side
of the disk, extending to 4 arcmin (~17 kpc). The detection of this low
surface-brightness muR= 27.0+0.3-0.2 mag/sqarcsec) structure is independently
confirmed in three separate datasets from three different telescopes.
  Although its true three dimensional geometry is unknown, the sky- projected
morphology of this structure displays a match with the theoretical predictions
for the edge-on, projected view of a stellar tidal streams of a dwarf satellite
moving in a low inclined (~25deg), nearly circular orbit. Using the recent
model of the Monoceros tidal stream in the Milky Way by Penarrubia et al. as
template, we find that the progenitor system may have been a galaxy with an
initial mass 6*10^8 Msun, of which current position and final fate is unknown.
According to this simulation, the tidal stream may be approximately ~2.8 Gyr of
age.
  Our results demonstrate that NGC 4013, previously considered a prototypical
isolated disk galaxy in spite of having one of the most prominent HI warps
detected thus far, may have in fact suffered a recent minor merger. This
discovery highlights that undisturbed disks at high surface brightness levels
in the optical but warped in HI maps may in fact reveal complex signatures of
recent accretion events in deep photometric surveys.

1
The categories of this paper are: cs
11
The categories of this paper are: hep-lat
10
The categories of this paper are: q-bio
31
The categories of this paper are: ao-sci
32
The categories of this paper are: atom-ph
2
The categories of this paper are: math
21
The categories of this paper are: adap-org
27
The categories of this paper are: comp-gas
25
The categories of this paper are: patt-sol
4
The categories of this paper are: cond-mat
35
The categories of this paper are: mtrl-th
17
The categories of this paper are: q-fin
13
The categories of this paper are: quant-ph
0
The categories of this paper are: hep-ph
8
The categories of this paper are: hep-ex
22
The categories of this paper are: chao-dyn