2,135 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&
Perinatal tissue oxygenation and neurodevelopment in preterm and growth restricted infants
Preterm birth and fetal growth restriction present major risk factors for an inadequate oxygen supply of the developing brain and other organs. Doppler ultrasound and near-infrared spectroscopy help assess organ oxygen delivery in the fetus and newborn. Using these techniques, this thesis investigated how placental insufficiency and drug exposure before birth affect oxygenation of the brain, kidneys, and intestines in preterm and growth restricted infants. Additionally, this thesis assessed how fetal âbrain-sparingâ (redistribution of blood flow to the brain at the expense of other organs as a compensatory response to chronically low oxygen levels in placental insufficiency) and oxygenation of the brain after birth relate to neurodevelopmental outcome.Our data suggest that fetal brain-sparing and higher cerebral oxygen saturations after birth are related to less behavioral problems and better executive functions. On the other hand, fetal brain-sparing may cause cerebral oxygen levels being too high for preterm babies, which we associated with an increased risk of retinopathy of prematurity, a potentially blinding eye condition, and poorer long-term Performance IQ. Epigenetic changes seem to be involved. Moreover, fetal brain-sparing seems to impair autoregulatory mechanisms, with which the brain protects itself from harmful fluctuations in blood flow and oxygenation after birth. Fetal exposure to drugs with vasodilative properties, appeared to also affect organ oxygen delivery in the newborn. This needs to be taken into account when using these drugs in pregnant women or when investigating new treatments for placental insufficiency
Self-esteem moderates affective reactions to briefly presented emotional faces
According to the sociometer hypothesis individuals with low self-esteem experience increased negative affect in response to negative social stimuli, even when these stimuli are not perceived consciously. Using an affective priming paradigm, the present study examined whether trait self-esteem would moderate mood following briefly presented facial expressions. Results from 43 undergraduates revealed that, after controlling for baseline mood, anxiety and depression, the degree of negative affect experienced by the participants following exposure to expressions of anger and disgust varied as a function of their self-esteem. Implications for individuals with low-self esteem and our understanding of the link between self-esteem and negative affect are discussed
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