1,464 research outputs found
On the Cosmic Evolution of Fe/Mg in QSO Absorption Line Systems
We investigate the variation of the ratio of the equivalent widths of the
FeII2600 line to the MgII2796,2803 doublet as a
function of redshift in a large sample of absorption lines drawn from the
JHU-SDSS Absorption Line Catalog. We find that despite large scatter, the
observed ratio shows a trend where the equivalent width ratio
decreases monotonically with
increasing redshift over the range . Selecting the
subset of absorbers where the signal-to-noise ratio of the MgII equivalent
width is 3 and modeling the equivalent width ratio
distribution as a gaussian, we find that the mean of the gaussian distribution
varies as . We discuss various possible
reasons for the trend. A monotonic trend in the Fe/Mg abundance ratio is
predicted by a simple model where the abundances of Mg and Fe in the absorbing
clouds are assumed to be the result of supernova ejecta and where the cosmic
evolution in the SNIa and core-collapse supernova rates is related to the
cosmic star-formation rate. If the trend in reflects the
evolution in the abundances, then it is consistent with the predictions of the
simple model.Comment: 10 pages, 4 figures, final version published in MNRA
Galaxy mergers moulding the circum-galactic medium - I. The impact of a major merger
Galaxies are surrounded by sizeable gas reservoirs which host a significant
amount of metals: the circum-galactic medium (CGM). The CGM acts as a mediator
between the galaxy and the extra-galactic medium. However, our understanding of
how galaxy mergers, a major evolutionary transformation, impact the CGM remains
deficient. We present a theoretical study of the effect of galaxy mergers on
the CGM. We use hydrodynamical cosmological zoom-in simulations of a major
merger selected from the Illustris project such that the z=0 descendant has a
halo mass and stellar mass comparable to the Milky Way. To study the CGM we
then re-simulated this system at a 40 times better mass resolution, and
included detailed post-processing ionization modelling. Our work demonstrates
the effect the merger has on the characteristic size of the CGM, its
metallicity, and the predicted covering fraction of various commonly observed
gas-phase species, such as H I, C IV, and O VI. We show that merger-induced
outflows can increase the CGM metallicity by 0.2-0.3 dex within 0.5 Gyr
post-merger. These effects last up to 6 Gyr post-merger. While the merger
increases the total metal covering fractions by factors of 2-3, the covering
fractions of commonly observed UV ions decrease due to the hard ionizing
radiation from the active galactic nucleus, which we model explicitly. Our
study of the single simulated major merger presented in this work demonstrates
the significant impact that a galaxy interaction can have on the size,
metallicity, and observed column densities of the CGM
The slow flow model of dust eflux in local star-forming galaxies
We develop a dust efflux model of radiation pressure acting on dust grains which
successfully reproduces the relation between stellar mass, dust opacity and star forma-
tion rate observed in local star-forming galaxies. The dust content of local star-forming
galaxies is set by the competition between the physical processes of dust production
and dust loss in our model. The dust loss rate is proportional to the dust opacity
and star formation rate. Observations of the relation between stellar mass and star
formation rate at several epochs imply that the majority of local star-forming galax-
ies are best characterized as having continuous star formation histories. Dust loss is
a consequence of sustained interaction of dust with the radiation field generated by
continuous star formation. Dust efflux driven by radiation pressure rather than dust
destruction offers a more consistent physical interpretation of the dust loss mechanism.
By comparing our model results with the observed relation between stellar mass, dust
extinction and star formation rate in local star-forming galaxies we are able to con-
strain the timescale and magnitude of dust loss. The timescale of dust loss is long and
therefore dust is effluxed in a “Slow Flow". Dust loss is modest in low mass galaxies
but massive galaxies may lose up to 70 80% of their dust over their lifetime. Our
Slow Flow model shows that mass loss driven by dust opacity and star formation
may be an important physical process for understanding normal star-forming galaxy
evolution.Department of HE and Training approved lis
Coherent manipulation of charge qubits in double quantum dots
The coherent time evolution of electrons in double quantum dots induced by
fast bias-voltage switches is studied theoretically. As it was shown
experimentally, such driven double quantum dots are potential devices for
controlled manipulation of charge qubits. By numerically solving a quantum
master equation we obtain the energy- and time-resolved electron transfer
through the device which resembles the measured data. The observed oscillations
are found to depend on the level offset of the two dots during the manipulation
and, most surprisingly, also the on initialization stage. By means of an
analytical expression, obtained from a large-bias model, we can understand the
prominent features of these oscillations seen in both the experimental data and
the numerical results. These findings strengthen the common interpretation in
terms of a coherent transfer of electrons between the dots.Comment: 18 pages, 4 figure
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