Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Intergalactic Dust and Observations of Type Ia Supernovae   Estimates of the cosmic star formation rate and of cluster metallicities
independently imply that at z < 0.5 the gas in the universe has substantial
average metallicity: 1/10 < Z/Z_solar < 1/3 for Omega_gas = 0.05. This metal
density probably cannot be contained in known solar-metallicity galaxies of
density parameter Omega_star ~ 0.004, implying significant enrichment of the
intergalactic medium (IGM) by ejection of metals and dust from galaxies via
winds, in mergers or in dust efflux driven by radiation pressure. Galaxies have
a dust/metal ratio of ~ 0.5 in their interstellar media, but some fraction
(1-f) > 0 of this must be destroyed in the IGM or during the ejection process.
Assuming the Draine & Lee dust model and preferential destruction of small
grains, I calculate the reddening and extinction of a uniform cosmological dust
component in terms of (f) and the minimum grain size a_min. Very small grains
provide most of the reddening but less than half of the opacity for optical
extinction. For f > 0.3 and a_min > 0.1 microns, the intergalactic dust would
be too grey to have been detected by its reddening, yet dense enough to be
cosmologically important: it could account for the recently observed type Ia
supernova dimming at z ~ 0.5 without cosmic acceleration. The importance of
grey intergalactic dust of the described type can be tested by observations of
z=0.5 supernovae in (rest) R-band or longer wavelengths and by the fluxes of a
large sample of supernovae at z > 1. (Abridged)

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The categories of this paper are: quant-ph
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The categories of this paper are: mtrl-th
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The categories of this paper are: solv-int
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The categories of this paper are: math-ph
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The categories of this paper are: stat
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The categories of this paper are: dg-ga
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The categories of this paper are: hep-th
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The categories of this paper are: q-alg
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The categories of this paper are: cond-mat
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The categories of this paper are: atom-ph
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The categories of this paper are: physics
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The categories of this paper are: adap-org
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The categories of this paper are: q-bio
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The categories of this paper are: chao-dyn
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The categories of this paper are: funct-an
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The categories of this paper are: math