This may be the paper Gordon Richards’ referred to in the presentation Spaceman Spiff linked to. (Richards said another explanation may be required for increasing quasar luminosity with redshift from z=.12 to z=2.5 rather than increasing quasar super BH mass.)
The authors of this paper use a different analytical technique to estimate quasar super massive black hole mass. The finding presented in this paper questions the reduction of quasar super massive black hole mass with decreasing z. The increase in quasar super black hole mass with increasing redshift (z) has the hypothesized reason why quasar luminosity increases with redshift up until around z=2.5.
Apparently further papers concerning this subject are forthcoming.
http://arxiv.org/PS_cache/arxiv/pdf/...801.0243v2.pdf
Mass Functions of the Active Black Holes in Distant Quasars from the Sloan Digital Sky Survey
M. Vestergaard, X. Fan, C. Tremonti, Patrick Osmer, Gordon Richards
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Our tests suggest that the down-turn toward lower mass values is due to incompleteness of the quasar sample with respect to black hole mass. Further details and analysis of these mass functions will be presented in forthcoming papers.
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The subject of quasar metallicity evolution with increasing redshift (lack of) and quasar dust was discussed at recent quasar symposiums. This is only one of a number of papers concerning this subject.
It is interesting that quasar spectrum show a lack of metallicity evolution with redshift. Also interesting is finding of a large amount of dust in high redshift quasars. The explanation for this finding is that the conditions in the vicinity of a quasar are ideal for SNe supernova and the formation of dust. Some of the very high redshift quasars have supersolar metallicity of 1 to 10 times.
http://arxiv.org/abs/astro-ph/0603261v1
Metals and dust in high redshift AGNs by R. Maiolino et al.
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The lack of metallicity evolution is observed even in the spectra of the most distant QSOs known (z~6). This result is particularly surprising for elements such as Fe, C and Si, which are subject to a delayed enrichment, and requires that the hosts of these QSOs formed in short bursts and at very high redshift (z>10). The properties of dust in high-z QSOs are discussed within the context of the dust production mechanisms in the early universe. The dust extinction curve is observed to evolve beyond z>4, and by z~6 it is well described by the properties expected for dust produced by SNe, suggesting that the latter is the main mechanism of dust production in the early universe. We also show that the huge dust masses observed in distant QSOs can be accounted for by SN dust within the observational constraints currently available.
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