Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: What controls the [O III] 5007 line strength in AGN?   AGN display an extreme range in the narrow emission line equivalent widths.
Specifically, in the PG quasar sample the equivalent width of the narrow [O
III] 5007 line has a range of >300, while the broad Hb line, for example, has a
range of 10 only. The strength of [O III] 5007 is modulated by the covering
factor, CF, of the narrow line region (NLR) gas, its density n_e, and
ionization parameter U. To explore which of these factors produces the observed
large range in [O III] 5007 strength, we measure the strength of the matching
narrow Hb and [O III] 4363 lines, detected in 40 out of the 87 z<0.5 PG quasars
in the Boroson & Green sample. The photoionization code CLOUDY is then used to
infer CF, n_e, and U in each object, assuming a single uniform emitting zone.
We find that the range of CF (~0.02-0.2) contributes about twice as much as the
range in both n_e and U towards modulating the strength of the [O III] 5007
line. The CF is inversely correlated with luminosity, but it is not correlated
with L_Edd as previously speculated. The single zone [O III] 5007 emitting
region is rather compact, having R=40L_44^0.45 pc. These emission lines can
also be fit with an extreme two zone model, where [O III] 4363 is mostly
emitted by a dense (n_e=10^7) inner zone at R=L_44^0.5 pc, and [O III] 5007 by
a low density (n_e=10^3) extended outer zone at R=750L_44^0.34 pc. Such an
extended [O III] 5007 emission should be well resolved by HST imaging of
luminous AGN. Further constraints on the radial gas distribution in the NLR can
be obtained from the spectral shape of the IR continuum emitted by the
associated dust.

25
The categories of this paper are: patt-sol
7
The categories of this paper are: hep-th
23
The categories of this paper are: solv-int
28
The categories of this paper are: alg-geom
0
The categories of this paper are: hep-ph
34
The categories of this paper are: chem-ph
13
The categories of this paper are: quant-ph
12
The categories of this paper are: nucl-th
15
The categories of this paper are: nucl-ex
2
The categories of this paper are: math
31
The categories of this paper are: ao-sci
22
The categories of this paper are: chao-dyn
16
The categories of this paper are: stat
18
The categories of this paper are: econ
19
The categories of this paper are: eess
26
The categories of this paper are: bayes-an