76 research outputs found
Inhomogeneous metal enrichment at z \sim 1.9: the Lyman limit systems in the spectrum of the HDF-S quasar
We present a detailed analysis of three metal absorption systems observed in
the spectrum of the HDF-South quasar J2233-606 (z_em = 2.238), taking advantage
of new VLT-UVES high resolution data (R=45000, S/N = 40-60, \lambda\lambda
3050-10000 \AA). Three main components, spanning about 300 km/s, can be
individuated in the Lyman limit system at z~1.92. They show a surprisingly
large variation in metallicities, respectively ~1/500, 1/8 and 1/100 solar. The
large value found for the second component at z=1.9259, suggests that the line
of sight crosses a star-forming region. In addition, there is a definite
correlation between velocity position and ionisation state in this component,
which we interpret as a possible signature of an expanding H II region. The
systems at z~1.94 and z~1.87 have also high metallicity, ~1/4 and 1/3 solar. We
find that photoionisation and collisional ionisation are equal alternatives to
explain the high excitation phase revealed by O VI absorption, seen in these
two systems. From the width of the Si IV, C IV, Si III and C III lines in the
system at z~1.87, we can estimate the temperature of the gas to be log T ~ 4.7,
excluding collisional ionisation. Finally, we compute the Si IV/C IV ratio for
all Voigt profile components in a sample of log N(C IV) > 14 systems at z < 2.
The values show a dispersion of more than an order of magnitude and most of
them are much larger than what is observed for weaker systems. This is probably
an indication that high column density systems preferably originate in galactic
halos and are mostly influenced by local ionising sources.Comment: 11 pages, 11 figures, accepted by A&A main journa
Model-independent evidence in favor of an end to reionization by z~6
We present new upper limits on the volume-weighted neutral hydrogen fraction,
, at z~5-6 derived from spectroscopy of bright quasars. The fraction of
the Lyman-alpha and Lyman-beta forests that is "dark" (with zero flux) provides
the only model-independent upper limit on , requiring no assumptions about
the physical conditions in the intergalactic medium or the quasar's unabsorbed
UV continuum. In this work we update our previous results using a larger sample
(22 objects) of medium-depth (~ few hours) spectra of high-redshift quasars
obtained with the Magellan, MMT, and VLT. This significantly improves the upper
bound on derived from dark pixel analysis to <= 0.06 + 0.05
(1{\sigma}) at z=5.9, and <= 0.04 + 0.05 (1{\sigma}) at z=5.6. These
results provide robust constraints for theoretical models of reionization, and
provide the strongest available evidence that reionization has completed (or is
very nearly complete) by z~6.Comment: 8 pages, 4 figures, accepted for publication by MNRA
Field tests for the ESPRESSO data analysis software
The data analysis software (DAS) for VLT ESPRESSO is aimed to set a new
benchmark in the treatment of spectroscopic data towards the
extremely-large-telescope era, providing carefully designed, fully interactive
recipes to take care of complex analysis operations (e.g. radial velocity
estimation in stellar spectra, interpretation of the absorption features in
quasar spectra). A few months away from the instrument's first light, the DAS
is now mature for science validation, with most algorithms already implemented
and operational. In this paper, I will showcase the DAS features which are
currently employed on high-resolution HARPS and UVES spectra to assess the
scientific reliability of the recipes and their range of application. I will
give a glimpse on the science that will be possible when ESPRESSO data become
available, with a particular focus on the novel approach that has been adopted
to simultaneously fit the emission continuum and the absorption lines in the
Lyman-alpha forest of quasar spectra.Comment: 4 pages, 1 figure; proceedings of ADASS XXVI, accepted by ASP
Conference Serie
Data Analysis Software for the ESPRESSO Science Machine
ESPRESSO is an extremely stable high-resolution spectrograph which is
currently being developed for the ESO VLT. With its groundbreaking
characteristics it is aimed to be a "science machine", i.e., a fully-integrated
instrument to directly extract science information from the observations. In
particular, ESPRESSO will be the first ESO instrument to be equipped with a
dedicated tool for the analysis of data, the Data Analysis Software (DAS),
consisting in a number of recipes to analyze both stellar and quasar spectra.
Through the new ESO Reflex GUI, the DAS (which will implement new algorithms to
analyze quasar spectra) is aimed to get over the shortcomings of the existing
software providing multiple iteration modes and full interactivity with the
data.Comment: 5 pages, 2 figures; proceedings of ADASS XXI
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