Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: The emission line spectrum of the UV deficient quasar Ton 34: evidence
  of shock excitation?   Emission lines in quasars are believed to originate from a photoionized
plasma. There are, however, some emission features which appear to be
collisionally excited, such as the FeII multiplet bands. Shortward of Ly_alpha,
there also are a few permitted lines of species from low to intermediate
ionization. Ton 34 (z=1.928) exhibits the steepest far-UV continuum decline
known (Fnu propto nu^{-5.3}) shortward of 1050A. This object also emits
unusually strong low to intermediate excitation permitted lines shortward of
the Lyman limit. Using archive spectra of Ton 34 from HST, IUE and Palomar, we
measure the fluxes of all the lines present in the spectra and compare their
relative intensities with those observed in composite quasar spectra. Our
analysis reveals unusual strengths with respect to Ly_alpha of the following
low to intermediate excitation permitted lines: OII+OIII (835A), NIII+OIII
(686-703A) and NIII+NIV (765A). We compare the observed line spectrum with both
photoionization and shock models. Photoionization cannot reproduce the
strengths of these far-UV lines. Shocks with Vs ~ 100 km/s turn out to be
extremely efficient emitters of these lines and are favored as excitation
mechanism.

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The categories of this paper are: cmp-lg
7
The categories of this paper are: hep-th
3
The categories of this paper are: physics
20
The categories of this paper are: acc-phys
23
The categories of this paper are: solv-int
11
The categories of this paper are: hep-lat
25
The categories of this paper are: patt-sol
22
The categories of this paper are: chao-dyn
34
The categories of this paper are: chem-ph
9
The categories of this paper are: nlin
10
The categories of this paper are: q-bio
24
The categories of this paper are: dg-ga
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The categories of this paper are: supr-con
4
The categories of this paper are: cond-mat
5
The categories of this paper are: gr-qc
8
The categories of this paper are: hep-ex