Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Detection of the 2175\AA~ extinction feature and 21-cm absorption in two
  MgII systems at z~1.3   We have discovered two dusty intervening MgII absorption systems at z~1.3 in
the Sloan Digital Sky Survey (SDSS) database. The overall spectra of both QSOs
are red (u-K>4.5 mag) and are well modelled by the composite QSO spectrum
reddened by the extinction curve from the Large Magellanic Cloud (LMC2)
Supershell redshifted to the rest-frame of the MgII systems. In particular, we
detect clearly the presence of the UV extinction bump at $\lambda_{\rm
rest}\sim 2175$~\AA. Absorption lines of weak transitions like
SiII$\lambda$1808, CrII$\lambda$2056, CrII+ZnII$\lambda$2062,
MnII$\lambda$2594, CaII$\lambda$3934 and TiII$\lambda$1910 from these systems
are detected even in the low signal-to-noise ratio and low resolution SDSS
spectra, suggesting high column densities of these species. The depletion
pattern inferred from these absorption lines is consistent with that seen in
the cold neutral medium of the LMC. Using the LMC A_V vs. N(HI) relationship we
derive N(HI)~$6\times 10^{21}$ cm$^{-2}$ in both systems. Metallicities are
close to solar. Giant Metrewave Radio Telescope (GMRT) observations of these
two relatively weak radio loud QSOs (f$_\nu$~50mJy) resulted in the detection
of 21-cm absorption in both cases. We show that the spin temperature of the gas
is of the order of or smaller than 500K. These systems provide a unique
opportunity to search for molecules and diffuse interstellar bands at z>1.

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The categories of this paper are: chao-dyn
37
The categories of this paper are: supr-con
16
The categories of this paper are: stat
12
The categories of this paper are: nucl-th
1
The categories of this paper are: cs
36
The categories of this paper are: cmp-lg
19
The categories of this paper are: eess
26
The categories of this paper are: bayes-an
15
The categories of this paper are: nucl-ex
31
The categories of this paper are: ao-sci
29
The categories of this paper are: funct-an
33
The categories of this paper are: plasm-ph
25
The categories of this paper are: patt-sol
8
The categories of this paper are: hep-ex
5
The categories of this paper are: gr-qc
32
The categories of this paper are: atom-ph