Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: A dust component 2 kpc above the plane in NGC 891   The halo of NGC 891 has been the subject of studies for more than a decade.
One of its most striking features is the large asymmetry in H$\alpha$ emission.
In this letter, we will take a quantitative look at this asymmetry at different
wavelengths for the first time. We suggest that NGC 891 is intrinsically almost
symmetric and the large asymmetry in H$\alpha$ emission is mostly due to dust
attenuation. We will quantify the additional optical depth needed to cause the
observed asymmetry in this model. By comparing large strips on the North East
side of the galaxy with strips covering the same area in the South West we can
quantify and analyze the asymmetry in the different wavelengths. From the 24
$\mu$m emission we find that the intrinsic asymmetry in star formation in NGC
891 is small i.e., $\sim 30%$. The additional asymmetry in H$\alpha$ is modeled
as additional symmetric dust attenuation which extends up to $\sim$ 40\arcsec
(1.9 kpc) above the plane of the galaxy with a mid-plane value of $\tau$=0.8
and a scale height of 0.5 kpc

7
The categories of this paper are: hep-th
37
The categories of this paper are: supr-con
11
The categories of this paper are: hep-lat
10
The categories of this paper are: q-bio
9
The categories of this paper are: nlin
28
The categories of this paper are: alg-geom
26
The categories of this paper are: bayes-an
32
The categories of this paper are: atom-ph
33
The categories of this paper are: plasm-ph
17
The categories of this paper are: q-fin
36
The categories of this paper are: cmp-lg
29
The categories of this paper are: funct-an
15
The categories of this paper are: nucl-ex
23
The categories of this paper are: solv-int
25
The categories of this paper are: patt-sol
3
The categories of this paper are: physics