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Comparing Simulations and Observations of the Lyman-Alpha Forest I. Methodology
We describe techniques for comparing spectra extracted from cosmological
simulations and observational data, using the same methodology to link
Lyman-alpha properties derived from the simulations with properties derived
from observational data. The eventual goal is to measure the coherence or
clustering properties of Lyman-alpha absorbers using observations of quasar
pairs and groups. We quantify the systematic underestimate in opacity that is
inherent in the continuum fitting process of observed spectra over a range of
resolution and signal-to-noise ratio. We present an automated process for
detecting and selecting absorption features over the range of resolution and
signal-to-noise of typical observational data on the Lyman-alpha "forest".
Using these techniques, we detect coherence over transverse scales out to 500
h^{-1}_{50} kpc in spectra extracted from a cosmological simulation at z = 2.Comment: 52 pages, includes 14 figures, to appear in ApJ v566 Feb 200
The ultraviolet spectra of radio-loud and radio-quiet quasars
The rest-frame ultraviolet spectral properties of matched samples of radio-loud, radio-moderate, and
radio-quiet quasars are investigated, using quasars drawn from the Large Bright QSO Survey. We
confirm the absence of spectral differences between radio-loud and radio-quiet quasars at rest-frame
wavelengths longward of 1600 Ă, as reported by previous authors. However, at shorter wavelengths we
find a significant difference: radio-loud quasars have narrower (96% confidence), higher
equivalent-width (97% confidence) Lyman-a and C IV emission lines. We further investigate quasars
which are radio quiet, but have radio-to-optical flux ratios at the upper extreme of the radio-quiet
population. Broad absorption line quasars are overabundant by a factor of â10 in this radio-moderate
population; the overabundance is significant at a 99.99% confidence level.The LBQS is supported by National Science Foundation
Grant No. AST 90-01181, for which we are grateful. Peter
Strittmatter kindly made funds available for publication.
We also wish to thank Craig Foltz and Paul Hewett for
many helpful discussions. P.J.F. is supported by a SERC/
NATO advanced fellowship
Lensed Quasar Hosts
Gravitational lensing assists in the detection of quasar hosts by amplifying
and distorting the host light away from the unresolved quasar core images. We
present the results of HST observations of 30 quasar hosts at redshifts 1 < z <
4.5. The hosts are small in size (r_e <~ 6 kpc), and span a range of
morphologies consistent with early-types (though smaller in mass) to
disky/late-type. The ratio of the black hole mass (MBH, from the virial
technique) to the bulge mass (M_bulge, from the stellar luminosity) at 1<z<1.7
is broadly consistent with the local value; while MBH/M_bulge at z>1.7 is a
factor of 3--6 higher than the local value. But, depending on the stellar
content the ratio may decline at z>4 (if E/S0-like), flatten off to 6--10 times
the local value (if Sbc-like), or continue to rise (if Im-like). We infer that
galaxy bulge masses must have grown by a factor of 3--6 over the redshift range
3>z>1, and then changed little since z~1. This suggests that the peak epoch of
galaxy formation for massive galaxies is above z~1. We also estimate the duty
cycle of luminous AGNs at z>1 to be ~1%, or 10^7 yrs, with sizable scatter.Comment: 8 pages, 6 figures, review article with C. Impey at the conference on
"QSO Host Galaxies: Evolution and Environment", Aug. 29-Sep. 2, 2005, Lorentz
Center, Leiden, The Netherland
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