832 research outputs found
High-Resolution Spectroscopy from 3050 to 10000 A of the HDF-S QSO J2233-606 with UVES at the ESO VLT
We report on high-resolution observations () of the Hubble
Deep Field South QSO J2233-606 obtained with the VLT UV-Visual Echelle
Spectrograph (UVES). We present spectral data for the wavelength region \AA. The ratio of the final spectrum is about 50 per
resolution element at 4000 \AA, 90 at 5000 \AA, 80 at 6000 \AA, 40 at 8000 \AA.
Redshifts, column densities and Doppler widths of the absorption features have
been determined with Voigt-profile fitting. A total of 621 lines have been
measured. In particular 270 Ly-alpha lines, 41 Ly-beta and 24 systems
containing metal lines have been identified. Together with other data in the
literature, the present spectrum confirms that the evolution of the number
density of Ly-alpha lines with \huno has an upturn at .Comment: 34 pages Latex, with 3 PostScript figures. Astronomical Journal, in
press. A few revised upper limit
Large-Scale Correlations in the Lyman-alpha Forest at z = 3-4
We present a study of the spatial coherence of the intergalactic medium
toward two pairs of high-redshift quasars with moderate angular separations
observed with Keck/ESI, Q1422+2309A/Q1424+2255 (z_em = 3.63, theta = 39") and
Q1439-0034A/B (z_em = 4.25, theta = 33"). The crosscorrelation of transmitted
flux in the Lyman-alpha forest shows a 5-7 sigma peak at zero velocity lag for
both pairs. This strongly suggests that at least some of the absorbing
structures span the 230-300/h_70 proper kpc transverse separation between
sightlines. We also statistically examine the similarity between paired spectra
as a function of transmitted flux, a measure which may be useful for comparison
with numerical simulations. In investigating the dependence of the correlation
functions on spectral characteristics, we find that photon noise has little
impact for S/N >~ 10 per resolution element. However, the agreement between the
autocorrelation along the line sight and the crosscorrelation between
sightlines, a potential test of cosmological geometry, depends significantly on
instrumental resolution. Finally, we present an inventory of metal lines. These
include a a pair of strong C IV systems at z ~ 3.4 appearing only toward
Q1439B, and a Mg II + Fe II system present toward Q1439 A and B at z = 1.68.Comment: 33 pages, 13 figures, submitted to Ap
Temperature and Kinematics of CIV Absorption Systems
We use Keck HIRES spectra of three intermediate redshift QSOs to study the
physical state and kinematics of the individual components of CIV selected
heavy element absorption systems. Fewer than 8 % of all CIV lines with column
densities greater than 10^{12.5} cm^{-2} have Doppler parameters b < 6 km/s. A
formal decomposition into thermal and non-thermal motion using the simultaneous
presence of SiIV gives a mean thermal Doppler parameter b_{therm}(CIV) = 7.2
km/s, corresponding to a temperature of 38,000 K although temperatures possibly
in excess of 300,000 K occur occasionally. We also find tentative evidence for
a mild increase of temperature with HI column density. Non-thermal motions
within components are typically small (< 10 km/s) for most systems, indicative
of a quiescent environment. The two-point correlation function (TPCF) of CIV
systems on scales up to 500 km/s suggests that there is more than one source of
velocity dispersion. The shape of the TPCF can be understood if the CIV systems
are caused by ensembles of objects with the kinematics of dwarf galaxies on a
small scale, while following the Hubble flow on a larger scale. Individual high
redshift CIV components may be the building blocks of future normal galaxies in
a hierarchical structure formation scenario.Comment: submitted to the ApJ Letters, March 16, 1996 (in press); (13 Latex
pages, 4 Postscript figures, and psfig.sty included
The Observability of Metal Lines Associated with the Lyman-alpha Forest
We develop a prescription for characterizing the strengths of metal lines
associated with Lyman-alpha forest absorbers (LYFAs) of a given neutral
hydrogen column density N_HI and metallicity [Fe/H]. This Line Observability
Index (LOX) is line-specific and translates, for weak lines, into a measure of
the equivalent width. It can be evaluated quickly for thousands of transitions
within the framework of a given model of the Lyman-alpha forest, providing a
ranking of the lines in terms of their strengths and enabling model builders to
select the lines that should be detectable in observed spectra of a given
resolution and signal-to-noise ratio. We compute the LOX for a large number of
elements and transitions in two cosmological models of the Lyman-alpha forest
at z=3 derived from a hydrodynamic simulation of structure formation, and we
discuss how the LOX depends on redshift and on model parameters such as the
mean baryonic density and radiation field. We find that the OVI (1032,1038)
doublet is the best probe of the metallicity in low column density LYFAs N_{HI}
\approx 10^{14.5} cm^{-2}). Metallicities down to [O/H] \sim -3 ([Fe/H] \sim
-3.5 with the assumed [O/Fe] ratio) yield OVI absorption features that should
be detectable in current high-quality spectra, provided that the expected
position of the OVI feature is not contaminated by HI absorption. The strongest
transitions in lower ionisation states of oxygen are OV(630), OIV(788), and
OIII(833), and are likely to be detected with next generation UV instruments.
Of the lines with rest wavelengths \lambda_r > 1216, which can potentially be
observed redwards of the \lya forest, the CIV(1548,1551) doublet is expected to
dominate in all LYFAs, regardless of the value of N_HI.Comment: Substantially revised version: larger line database, additional
cosmological model analyzed. Accepted for Ap
Hydrodynamical Simulations of the Lyman Alpha Forest: Model Comparisons
We investigate the properties of the Lyman alpha forest as predicted by
numerical simulations for a range of currently viable cosmological models. This
is done in order to understand the dependencies of the forest on cosmological
parameters. Focusing on the redshift range from two to four, we show that: (1)
most of the evolution in the distributions of optical depth, flux and column
density can be understood by simple scaling relations, (2) the shape of optical
depth distribution is a sensitive probe of the amplitude of density
fluctuations on scales of a few hundred kpc, (3) the mean of the b distribution
(a measure of the width of the absorption lines) is also very sensitive to
fluctuations on these scales, and decreases as they increase. We perform a
preliminary comparison to observations, where available. A number of other
properties are also examined, including the evolution in the number of lines,
the two-point flux distribution and the HeII opacity.Comment: 37 pages, 21 figures, submitted to Ap
Correlation between the Mean Matter Density and the Width of the Saturated Lyman Alpha Absorption
We report a scaling of the mean matter density with the width of the
saturated Lyman alpha absorptions. This property is established using the
``pseudo-hydro'' technique (Croft et al. 1998). It provides a constraint for
the inversion of the Lyman alpha forest, which encounters difficulty in the
saturated region. With a Gaussian density profile and the scaling relation, a
simple inversion of the simulated Lyman alpha forests shows that the
one-dimensional mass power spectrum is well recovered on scales above 2 Mpc/h,
or roughly k < 0.03 s/km, at z=3. The recovery underestimates the power on
small scales, but improvement is possible with a more sophisticated algorithm.Comment: 7 pages, 9 figures, accepted for publication in MNRAS, replaced by
the version after proo
The Form and Evolution of the Clustering of QSO Heavy-Element Absorption-Line Systems
We have analyzed the clustering of C IV and Mg II absorption-line systems on
comoving scales from 1 to 16 \hMpc, using an extensive catalog of heavy-element
QSO absorbers with mean redshift 2.2 (C IV) and 0.9 (Mg II). We find that, for
the C IV sample as a whole, the absorber line-of-sight correlation function is
well-fit by a power law with index and
comoving correlation length \hMpc (). The
clustering of absorbers at high redshift is thus of a form like that of
galaxies and clusters at low redshift, and of amplitude such that absorbers are
correlated on scales of galaxy clusters. We also trace the evolution of the
mean amplitude of the correlation function from to . We
find that, when parametrized as ,
the amplitude grows rapidly with decreasing redshift, with maximum-likelihood
value for the evolutionary parameter of ().
When extrapolated to zero redshift, the correlation length is \hMpc . This suggests that the strong C IV and Mg II absorbers,
on megaparsec scales, are biased tracers of the higher-density regions of
space, and that agglomerations of strong absorbers along a line of sight are
indicators of clusters and superclusters. This is supported by recent
observations of ``Lyman break'' galaxies. The rapid growth seen in the
clustering of absorbers mimics that expected in a a critical universe from
linear theory of gravitational instability, and is consistent with
gravitationally induced growth of perturbations.Comment: 26 pages (LaTex, uses aaspp4.sty), with 8 encapsulated PostScript
figures. Includes an augmented discussion of the close relationship between
strong absorbers, clusters, and ``Lyman break'' galaxies. To appear in The
Astrophysical Journal, vol. 500, June 10, 199
The Local Effects of Cosmological Variations in Physical 'Constants' and Scalar Fields I. Spherically Symmetric Spacetimes
We apply the method of matched asymptotic expansions to analyse whether
cosmological variations in physical `constants' and scalar fields are
detectable, locally, on the surface of local gravitationally bound systems such
as planets and stars, or inside virialised systems like galaxies and clusters.
We assume spherical symmetry and derive a sufficient condition for the local
time variation of the scalar fields that drive varying constants to track the
cosmological one. We calculate a number of specific examples in detail by
matching the Schwarzschild spacetime to spherically symmetric inhomogeneous
Tolman-Bondi metrics in an intermediate region by rigorously construction
matched asymptotic expansions on cosmological and local astronomical scales
which overlap in an intermediate domain. We conclude that, independent of the
details of the scalar-field theory describing the varying `constant', the
condition for cosmological variations to be measured locally is almost always
satisfied in physically realistic situations. The proof of this statement
provides a rigorous justification for using terrestrial experiments and solar
system observations to constrain or detect any cosmological time variations in
the traditional `constants' of Nature.Comment: 30 pages, 3 figures; corrected typo
Physical conditions in the ISM towards HD185418
We have developed a complete model of the hydrogen molecule as part of the
spectral simulation code Cloudy. Our goal is to apply this to spectra of
high-redshift star-forming regions where H2 absorption is seen, but where few
other details are known, to understand its implication for star formation. The
microphysics of H2 is intricate, and it is important to validate these
numerical simulations in better-understood environments. This paper studies a
well-defined line-of-sight through the Galactic interstellar medium (ISM) as a
test of the microphysics and methods we use. We present a self-consistent
calculation of the observed absorption-line spectrum to derive the physical
conditions in the ISM towards HD185418, a line-of-sight with many observables.
We deduce density, temperature, local radiation field, cosmic ray ionization
rate, chemical composition and compare these conclusions with conditions
deduced from analytical calculations. We find a higher density, similar
abundances, and require a cosmic ray flux enhanced over the Galactic background
value, consistent with enhancements predicted by MHD simulations.Comment: 31 pages, accepted for publication in Ap
The explanation of unexpected temperature dependence of the muon catalysis in solid deuterium
It is shown that due to the smallness of the inelastic cross-section of the
-atoms scattering in the crystal lattice at sufficiently low temperatures
the -mesomolecules formation from the upper state of the hyperfine
structure starts earlier than the mesoatoms thermolization. It
explains an approximate constancy of the -mesomolecule formation rate in
solid deuterium.Comment: 6 pages, 2 jpeg-figure
- âŠ