Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Are Galaxies Optically Thin to Their Own Lyman Continuum Radiation? II.
  NGC 6822   Halpha and UBV photometry of NGC 6822 are used to study the distribution of
OB stars and HII regions in the galaxy and to determine whether individual
regions of the galaxy are in a state of ionization balance. Four distinct
components of the Halpha emission (bright, halo, diffuse and field)
differentiated by their surface brightnesses are identified. We find that
approximately 1/2 of all OB stars in NGC 6822 are located in the field while
only 1/4 are found in the combined bright and halo regions, suggesting that OB
stars spend roughly 3/4 of their lifetimes outside ``classical'' H II regions.
Comparing the observed Halpha emission with that predicted from stellar
ionizing flux models, we find that although the bright, halo and diffuse
regions are probably in ionization balance, the field region is producing at
least 6 times as much ionizing flux as is observed. The ionization balance
results in NGC 6822 suggest that star formation rates obtained from Halpha
luminosities must underestimate the true star formation rate in this galaxy by
about 50%. Comparing our results for NGC 6822 with previous results for the
spiral galaxy M33, we find that the inner kiloparsec of M33 is in a more
serious state of ionization imbalance, perhaps due to its higher surface
density of blue stars.

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The categories of this paper are: mtrl-th
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The categories of this paper are: hep-ph
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The categories of this paper are: q-fin
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The categories of this paper are: hep-th
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The categories of this paper are: econ
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The categories of this paper are: bayes-an
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The categories of this paper are: comp-gas
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The categories of this paper are: nlin
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The categories of this paper are: cond-mat
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The categories of this paper are: nucl-ex
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The categories of this paper are: chem-ph
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The categories of this paper are: q-bio
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The categories of this paper are: physics
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The categories of this paper are: solv-int
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The categories of this paper are: funct-an
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The categories of this paper are: plasm-ph