Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: ISOCAM Observations of NGC 6946: Mid-IR Structure   The nearby spiral galaxy NGC 6946 was observed with ISO-CAM in the
mid-infrared, achieving 7 arcsec resolution and sub-MJy/steradian sensitivity.
Images taken with CAM filters LW2 (7 microns) and LW3 (15 microns) are analysed
to determine the morphology of this galaxy and understand better the emission
mechanisms. The mid-infrared emission follows an exponential disk with a scale
length 75 arcsec. This is 60% of the scale length in the optical R-band and
radio continuum. The nuclear starburst region is too bright for reliable
measurement in these images. Its surface brightness exceeds the inner disk by
at least a factor of 12. The arms and interarm regions are clearly detected,
with each of these components contributing about equally to the disk emission.
The arm-interarm contrast is 2-4 in the mid-IR, close to that measured in the
visible R band light and lower than the contrast in $H\alpha$, suggesting that
non-ionizing radiation contributes significantly to dust heating.

21
The categories of this paper are: adap-org
15
The categories of this paper are: nucl-ex
9
The categories of this paper are: nlin
12
The categories of this paper are: nucl-th
36
The categories of this paper are: cmp-lg
3
The categories of this paper are: physics
35
The categories of this paper are: mtrl-th
23
The categories of this paper are: solv-int
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The categories of this paper are: dg-ga
18
The categories of this paper are: econ
29
The categories of this paper are: funct-an
10
The categories of this paper are: q-bio
7
The categories of this paper are: hep-th
37
The categories of this paper are: supr-con
30
The categories of this paper are: q-alg
13
The categories of this paper are: quant-ph