Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: The bright 175um knots of the Andromeda Galaxy   Discrete far-infrared (FIR) sources of M31 are identified in the ISO 175um
map and characterized via their FIR colours, luminosities and masses. With a
mean size of 800pc, they probably represent several clouds in chance projection
or giant cloud complexes. The 175um data point provides crucial information in
addition to the IRAS 60 and 100um data: At least two modified Planck curves
with temperatures of about 40K and 15-21K are necessary to fit the SEDs of the
knots. We distinguish between three types of knots - cold, medium, warm - in
order to recognize trends. Comparisons with radio and optical tracers show that
- statistically - the cold knots can be identified well with CO and HI radio
sources and thus might represent mainly molecular cloud complexes. The warm
knots coincide with known HII regions and supernova remnants. The medium knots
might contain a balanced mixture of molecular clouds and HII regions. The cold
knots have a considerable luminosity and their discovery raises the question of
hidden star formation. Though the optically dark dust lanes in M31 generally
match the FIR ring, surprisingly we do not find a convincing coincidence of our
knots with individual dark clouds which might therefore show mainly foreground
dust features. The ratio of FIR luminosity to dust mass, L/M, is used to
measure the energy content of the dust. The knots have a clear L/M excess over
the rest of M31, providing evidence that they are powered by star formation in
addition to the interstellar radiation field. The L/M ratio of the warm knots
is comparable to that of Galactic HII regions like M42 or NGC2024, while that
of the cold knots still reaches values like in the average Orion complex. Thus
both the warm and the cold knots are interpreted as containing large cloud
complexes with considerable ongoing star formation.

29
The categories of this paper are: funct-an
21
The categories of this paper are: adap-org
8
The categories of this paper are: hep-ex
12
The categories of this paper are: nucl-th
28
The categories of this paper are: alg-geom
20
The categories of this paper are: acc-phys
11
The categories of this paper are: hep-lat
19
The categories of this paper are: eess
35
The categories of this paper are: mtrl-th
25
The categories of this paper are: patt-sol
34
The categories of this paper are: chem-ph
31
The categories of this paper are: ao-sci
13
The categories of this paper are: quant-ph
30
The categories of this paper are: q-alg
17
The categories of this paper are: q-fin
16
The categories of this paper are: stat