108 research outputs found
The star formation history of damped Lyman alpha absorbers
The local power law relationship between the surface densities of neutral
hydrogen gas and star formation rate (SFR) can be used to explore the SFR
properties of damped Lyman alpha (DLA) systems at higher redshift. We find that
while the SFR densities for DLA systems are consistent with luminous star
forming galaxies at redshifts below z~0.6, at higher redshifts their SFR
density is too low for them to provide a significant contribution to the cosmic
star formation history (SFH). This suggests that the majority of DLAs may be a
distinct population from the Lyman break galaxies (LBGs) or submillimeter
star-forming galaxies that together dominate the SFR density at high redshift.
It is also possible that the DLAs do not trace the bulk of the neutral gas at
high redshift. The metallicity properties of DLAs are consistent with this
interpretation. The DLAs show a metal mass density lower by two orders of
magnitude at all redshifts than that inferred from the SFH of the universe.
These results are consistent with DLAs being dominated by low mass systems
having low SFRs or a late onset of star formation, similar to the star
formation histories of dwarf galaxies in the local universe.Comment: 9 pages, 5 figures, accepted for publication in Ap
The ESO UVES Advanced Data Products Quasar Sample - VI. Sub-Damped Lyman- Metallicity Measurements and the Circum-Galactic Medium
The Circum-Galactic Medium (CGM) can be probed through the analysis of
absorbing systems in the line-of-sight to bright background quasars. We present
measurements of the metallicity of a new sample of 15 sub-damped Lyman-
absorbers (sub-DLAs, defined as absorbers with 19.0 < log N(H I) < 20.3) with
redshift 0.584 < < 3.104 from the ESO Ultra-Violet Echelle
Spectrograph (UVES) Advanced Data Products Quasar Sample (EUADP). We combine
these results with other measurements from the literature to produce a
compilation of metallicity measurements for 92 sub-DLAs as well as a sample of
362 DLAs. We apply a multi-element analysis to quantify the amount of dust in
these two classes of systems. We find that either the element depletion
patterns in these systems differ from the Galactic depletion patterns or they
have a different nucleosynthetic history than our own Galaxy. We propose a new
method to derive the velocity width of absorption profiles, using the modeled
Voigt profile features. The correlation between the velocity width delta_V90 of
the absorption profile and the metallicity is found to be tighter for DLAs than
for sub-DLAs. We report hints of a bimodal distribution in the [Fe/H]
metallicity of low redshift (z < 1.25) sub-DLAs, which is unseen at higher
redshifts. This feature can be interpreted as a signature from the metal-poor,
accreting gas and the metal-rich, outflowing gas, both being traced by sub-DLAs
at low redshifts.Comment: 64 pages, 31 figures, 27 tables. Submitted to MNRA
HST Observations of the Gravitationally Lensed Cloverleaf Broad Absorption Line QSO H1413+1143: Modeling the Lens
We investigate gravitational lens models for the quadruply-lensed Cloverleaf
BAL QSO H1413+1143 based on the HST WFPC/WFPC2 astrometric and photometric data
of the system by Turnshek et al. and the HST NICMOS-2 data by Falco et al. The
accurate image positions and the dust-extinction-corrected relative
amplifications, along with a possible detection of the lensing galaxy in the
infrared, permit more accurate lens models than were previously possible. While
more recent models are qualitatively consistent with the HST data, none of the
previous models considered the dust-extinction-corrected relative
amplifications of the image components. We use the power-law elliptical mass
model to fit the HST data. We find that a single elliptical galaxy perturbed by
an external shear can fit the image positions within the observational
uncertainties; however, the predicted relative magnifications are only roughly
consistent with the observational relative amplifications. We find that a
primary galaxy combined with a secondary galaxy in the vicinity of the
Cloverleaf or a cluster centered (south-)west of the Cloverleaf can fit both
the image positions and relative amplifications within the observational
uncertainties. We discuss future observations which could be used to test
and/or further constrain lens models of the Cloverleaf.Comment: 23 pages (in aaspp.sty) including 5 tables and 3 figures, Accepted
for publication in the Astrophysical Journa
On the Steady Nature of Line-Driven Disk Winds
We perform an analytic investigation of the stability of line-driven disk
winds, independent of hydrodynamic simulations. Our motive is to determine
whether or not line-driven disk winds can account for the wide/broad UV
resonance absorption lines seen in cataclysmic variables (CVs) and
quasi-stellar objects (QSOs). In both CVs and QSOs observations generally
indicate that the absorption arising in the outflowing winds has a steady
velocity structure on time scales exceeding years (for CVs) and decades (for
QSOs). However, published results from hydrodynamic simulations of line-driven
disk winds are mixed, with some researchers claiming that the models are
inherently unsteady, while other models produce steady winds. The analytic
investigation presented here shows that if the accretion disk is steady, then
the line-driven disk wind emanating from it can also be steady. In particular,
we show that a gravitational force initially increasing along the wind
streamline, which is characteristic of disk winds, does not imply an unsteady
wind. The steady nature of line-driven disk winds is consistent with the 1D
streamline disk-wind models of Murray and collaborators and the 2.5D
time-dependent models of Pereyra and collaborators. This paper emphasizes the
underlying physics behind the steady nature of line-driven disk winds using
mathematically simple models that mimic the disk environmen
On the Steady Nature of Line-Driven Disk Winds: Application to Cataclysmic Variables
We apply the semi-analytical analysis of the steady nature of line-driven
winds presented in two earlier papers to disk winds driven by the flux
distribution of a standard Shakura & Sunyaev (1973) disk for typical
cataclysmic variable (CV) parameters. We find that the wind critical point
tends to be closer to the disk surface towards the inner disk regions. Our main
conclusion, however, is that a line-driven wind, arising from a steady disk
flux distribution of a standard Shakura-Sunyaev disk capable of locally
supplying the corresponding mass flow, is steady. These results confirm the
findings of an earlier paper that studied "simple" flux distributions that are
more readily analyzable than those presented here. These results are consistent
with the steady velocity nature of outflows observationally inferred for both
CVs and quasi-stellar objects (QSOs). We find good agreement with the 2.5D CV
disk wind models of Pereyra and collaborators. These results suggest that the
likely scenario to account for the wind outflows commonly observed in CVs is
the line-driven accretion disk wind scenario, as suggested early-on by Cordova
& Mason (1982). For QSOs, these results show that the line-driven accretion
disk wind continues to be a promising scenario to account for the outflows
detected in broad absorption line (BAL) QSOs, as suggested early-on by Turnshek
(1984), and analyzed in detail by Murray et al. (1995).Comment: 35 pages, 20 figure
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