Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: SCORPIO-II: Spectral indices of weak Galactic radio sources   In the next few years the classification of radio sources observed by the
large surveys will be a challenging problem, and spectral index is a powerful
tool for addressing it. Here we present an algorithm to estimate the spectral
index of sources from multiwavelength radio images. We have applied our
algorithm to SCORPIO (Umana et al. 2015), a Galactic Plane survey centred
around 2.1 GHz carried out with ATCA, and found we can measure reliable
spectral indices only for sources stronger than 40 times the rms noise. Above a
threshold of 1 mJy, the source density in SCORPIO is 20 percent greater than in
a typical extra-galactic field, like ATLAS (Norris et al. 2006), because of the
presence of Galactic sources. Among this excess population, 16 sources per
square degree have a spectral index of about zero, suggesting optically thin
thermal emission such as Hii regions and planetary nebulae, while 12 per square
degree present a rising spectrum, suggesting optically thick thermal emission
such as stars and UCHii regions.

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The categories of this paper are: physics
32
The categories of this paper are: atom-ph
23
The categories of this paper are: solv-int
29
The categories of this paper are: funct-an
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The categories of this paper are: econ
11
The categories of this paper are: hep-lat
35
The categories of this paper are: mtrl-th
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The categories of this paper are: hep-ex
24
The categories of this paper are: dg-ga
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The categories of this paper are: q-bio
37
The categories of this paper are: supr-con
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The categories of this paper are: comp-gas
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The categories of this paper are: adap-org
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The categories of this paper are: cmp-lg
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The categories of this paper are: hep-ph
12
The categories of this paper are: nucl-th