1,552 research outputs found
A high-redshift quasar absorber without CIV - a galactic outflow caught in the act?
We present a detailed analysis of a very unusual sub-damped Lyman alpha
(sub-DLA) system at redshift z=2.304 towards the quasar Q0453-423, based on
high signal-to-noise (S/N), high-resolution spectral data obtained with
VLT/UVES. With a neutral hydrogen column density of log N(HI)=19.23 and a
metallicity of -1.61 as indicated by [OI/HI] the sub-DLA mimics the properties
of many other optically thick absorbers at this redshift. A very unusual
feature of this system is, however, the lack of any CIV absorption at the
redshift of the neutral hydrogen absorption, although the relevant spectral
region is free of line blends and has very high S/N. Instead, we find high-ion
absorption from CIV and OVI in another metal absorber at a velocity more than
220km/s redwards of the neutral gas component. We explore the physical
conditions in the two different absorption systems using Cloudy photoionisation
models. We find that the weakly ionised absorber is dense and metal-poor while
the highly ionised system is thin and more metal-rich. The absorber pair
towards Q0453-423 mimics the expected features of a galactic outflow with
highly ionised material that moves away with high radial velocities from a
(proto)galactic gas disk in which star-formation takes place. We discuss our
findings in the context of CIV absorption line statistics at high redshift and
compare our results to recent galactic-wind and outflow models.Comment: 11 pages, 7 figures, accepted by A&
VLT/UVES observations of peculiar alpha abundances in a sub-DLA at z ~ 1.8 towards the quasar B1101-26
We present a detailed analysis of chemical abundances in a sub-damped Lyman
alpha absorber at z=1.839 towards the quasar B1101-26, based on a
very-high-resolution (R ~ 75,000) and high-signal-to-noise (S/N >100) spectrum
observed with the UV Visual Echelle spectrograph (UVES) installed on the ESO
Very Large Telescope (VLT). The absorption line profiles are resolved into a
maximum of eleven velocity components spanning a rest-frame velocity range of
200 km/s. Detected ions include CII, CIV, NII, OI, MgI, MgII, AlII, AlIII,
SiII, SiIII, SiIV, FeII, and possibly SII. The total neutral hydrogen column
density is log N(HI) = 19.48 +/- 0.01. From measurements of column densities
and Doppler parameters we estimate element abundances of the above-given
elements. The overall metallicity, as traced by [OI/HI], is -1.56 +/- 0.01. For
the nitrogen-to-oxygen ratio we derive an upper limit of [NI/OI] < -0.65, which
suggests a chemically young absorption line system. This is supported by a
supersolar alpha/Fe ratio of [SiII/FeII] ~ 0.5. The most striking feature in
the observed abundance pattern is an unusually high sulphur-to-oxygen ratio of
0.69 < [SII/OI] < 1.26. We calculate detailed photoionisation models for two
subcomponents with Cloudy, and can rule out that ionisation effects alone are
responsible for the high S/O ratio. We instead speculate that the high S/O
ratio is caused by the combination of several effects, such as specific
ionisation conditions in multi-phase gas, unusual relative abundances of heavy
elements, and/or dust depletion in a local gas environment that is not well
mixed and/or that might be related to star-formation activity in the host
galaxy. We discuss the implications of our findings for the interpretation of
alpha-element abundances in metal absorbers at high redshift.Comment: 16 pages, 10 figures, to be published in A&
Multiple origins for the DLA at toward PKS 1127145 indicated by a complex dust depletion pattern of Ca, Ti, and Mn
We investigate the dust depletion properties of optically thick gas in and
around galaxies and its origin we study in detail the dust depletion patterns
of Ti, Mn, and Ca in the multi-component damped Lyman- (DLA) absorber
at toward the quasar PKS 1127145.} We performed a
detailed spectral analysis of the absorption profiles of CaII, MnII, TiII, and
NaI associated with the DLA toward PKS 1127145, based on optical
high-resolution data obtained with the UVES instrument at the Very Large
Telescope (VLT). We obtained column densities and Doppler-parameters for the
ions listed above and determine their gas-phase abundances, from which we
conclude on their dust depletion properties. We compared the Ca and Ti
depletion properties of this DLA with that of other DLAs. One of the six
analyzed absorption components shows a striking underabundance of Ti and Mn in
the gas-phase, indicating the effect of dust depletion for these elements and a
locally enhanced dust-to-gas ratio. In this DLA and in other similar absorbers,
the MnII abundance follows that of TiII very closely, implying that both ions
are equally sensitive to the dust depletion effects. Our analysis indicates
that the DLA toward PKS 1127145 has multiple origins. With its narrow line
width and its strong dust depletion, component 3 points toward the presence of
a neutral gas disk from a faint LSB galaxy in front of PKS 1127145, while
the other, more diffuse and dust-poor, absorption components possibly are
related to tidal gas features from the interaction between the various,
optically confirmed galaxy-group members. In general, the Mn/CaII ratio in
sub-DLAs and DLAs possibly serves as an important indicator to discriminate
between dust-rich and dust-poor in neutral gas in and around galaxies.Comment: 10 pages, 8 figures, accepted for A&
Modeling specific action potentials in the human atria based on a minimal reaction-diffusion model
We present an effective method to model empirical action potentials of
specific patients in the human atria based on the minimal model of
Bueno-Orovio, Cherry and Fenton adapted to atrial electrophysiology. In this
model, three ionic are currents introduced, where each of it is governed by a
characteristic time scale. By applying a nonlinear optimization procedure, a
best combination of the respective time scales is determined, which allows one
to reproduce specific action potentials with a given amplitude, width and
shape. Possible applications for supporting clinical diagnosis are pointed out.Comment: 16 pages, 8 figure
Absorption signatures of warm-hot gas at low redshift: NeVIII
At z<1 a large fraction of the baryons is thought to reside in diffuse gas
that has been shock-heated to high temperatures (log T=5-6). Absorption by the
770.41, 780.32 {\AA} doublet of NeVIII in quasar spectra represents a unique
tool to study this elusive warm-hot phase. We have developed an analytic model
for the properties of NeVIII absorbers that allows for an inhomogeneous metal
distribution. Our model agrees with the predictions of a simulation from the
OWLS project indicating that the average line-of-sight metal-filling fraction
within the absorbing gas is low (c_L~0.1). Most of the NeVIII in our model is
produced in low-density, collisionally ionized gas (log n=-6 to -4 cm^-3, log
T=5-6). Strong NeVIII absorbers (log N(NeVIII)>14), like those recently
detected by HST/COS, are found to arise in higher density gas (log n>-4, log
T=5.75). NeVIII cloudlets harbour only 1 per cent of the cosmic baryon budget.
The baryon content of the surrounding gas (which has similar densities and
temperatures as the NeVIII cloudlets) is a factor 1/c_L higher. We conclude
that NeVIII absorbers are robust probes of shock-heated diffuse gas, but that
spectra with signal-to-noise ratios S/N>100 would be required to detect the
bulk of the baryons in warm-hot gas.Comment: 19 pages, 10 figures; MNRAS in press; minor changes with respect to
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