1,124 research outputs found
The power spectrum of the flux distribution in the Lyman-alpha forest of a Large sample of UVES QSO Absorption Spectra (LUQAS)
The flux power spectra of the Lyman-alpha forest from a sample of 27 QSOs
taken with the high resolution echelle spectrograph UVES on VLT are presented.
We find a similar fluctuation amplitude at the peak of the ``3D'' flux power
spectrum at k ~ 0.03 (km/sec)^(-1) as the study by Croft et al. (2002), in the
same redshift range. The amplitude of the flux power spectrum increases with
decreasing redshift if corrected for the increase in the mean flux level as
expected if the evolution of the flux power spectrum is sensitive to the
gravitational growth of matter density fluctuations. This is in agreement with
the findings of McDonald et al. (2000) at larger redshift. The logarithmic
slope of the "3D" flux power spectrum, P_F(k), at large scales k < 0.03
(km/sec)^(-1), is 1.4 +- 0.3, i.e. 0.3 shallower than that found by Croft et
al. (2002) but consistent within the errors.Comment: 18 pages, 9 PS figures, 6 tables. Note that the k-values of the 1D
flux power spectrum had been erroneously shifted by half a bin size (in log
k) in the previous version. All the other results are unaffected. New tables
can be found at http://www.ast.cam.ac.uk/~rtnigm/luqas.ht
The effect of (strong) discrete absorption systems on the Lyman α forest flux power spectrum
We demonstrate that the Lyman alpha forest flux power spectrum of 'randomized' quasi-stellar object (QSO) absorption spectra is comparable in shape and amplitude to the flux power spectrum of the original observed spectra. In the randomized spectra a random shift in wave-length has been added to the observed absorption lines as identified and fitted with VPFIT. At 0.03 s km(-1) 15 contribute at large scales, k < 0.03 s km(-1). We further show that a fraction of &GSIM; 15 per cent of the mean flux decrement is contributed by strong absorbers at z &GSIM; 2.1. Analysis of the flux power spectrum which use numerical simulations with too few strong absorption systems calibrated with the observed mean flux may underestimate the inferred rms fluctuation amplitude and the slope of the initial dark matter power spectrum
Spatial fluctuations in the spectral shape of the UV background at 2<z<3 and the reionization of helium
The low density hydrogen and helium in the IGM probed by QSO absorption lines
is sensitive to the amplitude and spectral shape of the metagalactic UV
background. We use realistic HI and HeII Ly-alpha forest spectra, constructed
from state-of-the-art hydrodynamical simulations of a Lambda-CDM Universe, to
confirm the reliability of using line profile fitting techniques to infer the
ratio of the metagalactic HI and HeII ionization rates. We further show that
the large spatial variations and the anti-correlation with HI absorber density
observed in the ratio of the measured HeII to HI column densities can be
explained in a model where the HI ionization rate is dominated by the combined
UV emission from young star forming galaxies and QSOs and the HeII ionization
rate is dominated by emission from QSOs only. In such a model the large
fluctuations in the column density ratio are due to the small number of QSOs
expected to contribute at any given point to the HeII ionization rate. A
significant contribution to UV emission at the HeII photoelectric edge from hot
gas in galaxies and galaxy groups would decrease the expected fluctuations in
the column density ratio. Consequently, this model appears difficult to
reconcile with the large increase in HeII opacity fluctuations towards higher
redshift. Our results further strengthen previous suggestions that observed
HeII Ly-alpha forest spectra at z~2-3.5 probe the tail end of the reionization
of HeII by QSOs.Comment: 14 pages, 7 figures, accepted for publication in MNRAS. Minor changes
to submitted version, most notably an extra section (5.2) and figure (fig.6
Deuteronomy and Numbers
Four light isotopes - D, ^3He, ^4He and ^7Li - were produced by nuclear
reactions a few seconds after the big bang. New measurements of ^3He in the ISM
by Gloeckler and Geiss and of deuterium in high redshift hydrogen clouds by
Tytler and his collaborators provide further confirmation of big-bang
nucleosynthesis and new insight about the density of ordinary matter (baryons).Comment: 6 pages LaTeX with 1 eps Figur
Geometrical Effects of Baryon Density Inhomogeneities on Primordial Nucleosynthesis
We discuss effects of fluctuation geometry on primordial nucleosynthesis. For
the first time we consider condensed cylinder and cylindrical-shell fluctuation
geometries in addition to condensed spheres and spherical shells. We find that
a cylindrical shell geometry allows for an appreciably higher baryonic
contribution to be the closure density (\Omega_b h_{50}^2 \la 0.2) than that
allowed in spherical inhomogeneous or standard homogeneous big bang models.
This result, which is contrary to some other recent studies, is due to both
geometry and recently revised estimates of the uncertainties in the
observationally inferred primordial light-element abundances. We also find that
inhomogeneous primordial nucleosynthesis in the cylindrical shell geometry can
lead to significant Be and B production. In particular, a primordial beryllium
abundance as high as [Be] = 12 + log(Be/H) is possible while still
satisfying all of the light-element abundance constraints.Comment: Latex, 20 pages + 11 figures(not included). Entire ps file with
embedded figures available via anonymous ftp at
ftp://genova.mtk.nao.ac.jp/pub/prepri/bbgeomet.ps.g
The UVES Spectral Quasar Absorption Database (SQUAD) Data Release 1: The first 10 million seconds
We present the first data release (DR1) of the UVES Spectral Quasar
Absorption Database (SQUAD), comprising 467 fully reduced, continuum-fitted
high-resolution quasar spectra from the Ultraviolet and Visual Echelle
Spectrograph (UVES) on the European Southern Observatory's Very Large
Telescope. The quasars have redshifts -5, and a total exposure time of 10
million seconds provides continuum-to-noise ratios of 4-342 (median 20) per
2.5-km/s pixel at 5500 \AA. The SQUAD spectra are fully reproducible from the
raw, archival UVES exposures with open-source software, including our
UVES_popler tool for combining multiple extracted echelle exposures which we
document here. All processing steps are completely transparent and can be
improved upon or modified for specific applications. A primary goal of SQUAD is
to enable statistical studies of large quasar and absorber samples, and we
provide tools and basic information to assist three broad scientific uses:
studies of damped Lyman- systems (DLAs), absorption-line surveys and
time-variable absorption lines. For example, we provide a catalogue of 155 DLAs
whose Lyman- lines are covered by the DR1 spectra, 18 of which are
reported for the first time. The HI column densities of these new DLAs are
measured from the DR1 spectra. DR1 is publicly available and includes all
reduced data and information to reproduce the final spectra.Comment: 21 pages, 18 figures. Accepted by MNRAS. All final quasar spectra,
reduced contributing exposures, and supplementary material available via
https://github.com/MTMurphy77/UVES_SQUAD_DR
A z = 3.045 Lyα emitting halo hosting a QSO and a possible candidate for AGN-triggered star formation
In this third paper in a series on the nature of extended, asymmetric Lyα emitters at z ∼ 3 we report the discovery, in an ultra-deep, blind, spectroscopic long-slit survey, of a Lyα emitting halo around a QSO at redshift 3.045. The QSO is a previously known, obscured active galactic nucleus (AGN). The Lyα emitting halo appears extended along the direction of the slit and exhibits two faint patches separated by 17 proper kpc in projection from the QSO. Comparison of the two-dimensional spectrum with archival Hubble Space Telescope ACS images shows that these patches coincide spatially with emission from a peculiar, dumbbell-shaped, faint galaxy. The assumptions that the Lyα emission patches are originating in the galaxy and that the galaxy is physically related to the QSO are at variance with photometric estimates of the galaxy redshift. We show, however, that a population of very young stars at the redshift of the QSO may fit the existing rest-frame broad-band UV photometry of the galaxy. If this scenario is correct, then the symmetry of the galaxy in continuum and Lyα emission, the extension of the QSO’s Lyα emission in its direction, and the likely presence of a young stellar population in close proximity to a (short-lived) AGN suggest that this may be an example of AGN feedback triggering external star formation in high-redshift galaxies
The kinetic temperature in a damped Lyman-alpha absorption system in Q2206-199 - an example of the warm neutral medium
By comparing the widths of absorption lines from OI, SiII and FeII in the
redshift z=2.076 single-component damped Lyman alpha absorption system in the
spectrum of Q2206-199 we establish that these absorption lines arise in Warm
Neutral Medium gas at ~12000 +/- 3000K. This is consistent with thermal
equilibrium model estimates of ~ 8000K for the Warm Neutral Medium in galaxies,
but not with the presence of a significant cold component. It is also
consistent with, but not required by, the absence of CII* fine structure
absorption in this system. Some possible implications concerning abundance
estimates in narrow-line WNM absorbers are discussed.Comment: 9 pages, 3 figures. MNRAS accepte
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