493 research outputs found
Photo-induced two-body loss of ultracold molecules
The lifetime of nonreactive ultracold bialkali gases was conjectured to be
limited by sticky collisions amplifying three-body loss. We show that the
sticking times were previously overestimated and do not support this
hypothesis. We find that electronic excitation of NaK+NaK collision complexes
by the trapping laser leads to the experimentally observed two-body loss. We
calculate the excitation rate with a quasiclassical, statistical model
employing ab initio potentials and transition dipole moments. Using longer
laser wavelengths or repulsive box potentials may suppress the losses
Rest-frame ultra-violet spectra of massive galaxies at z=3: evidence of high-velocity outflows
Galaxy formation models invoke the presence of strong feedback mechanisms
that regulate the growth of massive galaxies at high redshifts. In this paper
we aim to: (1) confirm spectroscopically the redshifts of a sample of massive
galaxies selected with photometric redshifts z > 2.5; (2) investigate the
properties of their stellar and interstellar media; (3) detect the presence of
outflows, and measure their velocities. To achieve this, we analysed deep,
high-resolution (R~2000) FORS2 rest-frame UV spectra for 11 targets. We
confirmed that 9 out of 11 have spectroscopic redshifts z > 2.5. We also
serendipitously found two mask fillers at redshift z > 2.5, which originally
were assigned photometric redshifts 2.0 < z < 2.5. In the four highest-quality
spectra we derived outflow velocities by fitting the absorption line profiles
with models including multiple dynamical components. We found strongly
asymmetric, high-ionisation lines, from which we derived outflow velocities
ranging from 480 to 1518 km/s. The two galaxies with highest velocity show
signs of AGN. We revised the spectral energy distribution fitting U-band
through 8 micron photometry, including the analysis of a power-law component
subtraction to identify the possible presence of active galactic nuclei (AGN).
The revised stellar masses of all but one of our targets are >1e10 Msun, with
four having stellar masses > 5e10 Msun. Three galaxies have a significant
power-law component in their spectral energy distributions, which indicates
that they host AGN. We conclude that massive galaxies are characterised by
significantly higher velocity outflows than the typical Lyman break galaxies at
z ~ 3. The incidence of high-velocity outflows (~40% within our sample) is also
much higher than among massive galaxies at z < 1, which is consistent with the
powerful star formation and nuclear activity that most massive galaxies display
at z > 2.Comment: 17 pages, 14 figures, Accepted for publication in A&
Stabilized Finite Elements in FUN3D
A Streamlined Upwind Petrov-Galerkin (SUPG) stabilized finite-element discretization has been implemented as a library into the FUN3D unstructured-grid flow solver. Motivation for the selection of this methodology is given, details of the implementation are provided, and the discretization for the interior scheme is verified for linear and quadratic elements by using the method of manufactured solutions. A methodology is also described for capturing shocks, and simulation results are compared to the finite-volume formulation that is currently the primary method employed for routine engineering applications. The finite-element methodology is demonstrated to be more accurate than the finite-volume technology, particularly on tetrahedral meshes where the solutions obtained using the finite-volume scheme can suffer from adverse effects caused by bias in the grid. Although no effort has been made to date to optimize computational efficiency, the finite-element scheme is competitive with the finite-volume scheme in terms of computer time to reach convergence
Discovery of a faint, star-forming, multiply lensed, Lyman-alpha blob
We report the discovery of a multiply lensed Lyman- blob (LAB) behind
the galaxy cluster AS1063 using the Multi Unit Spectroscopic Explorer (MUSE) on
the Very Large Telescope (VLT). The background source is at 3.117 and is
intrinsically faint compared to almost all previously reported LABs. We used
our highly precise strong lensing model to reconstruct the source properties,
and we find an intrinsic luminosity of =
erg s, extending to 33 kpc. We find that the LAB is associated with a
group of galaxies, and possibly a protocluster, in agreement with previous
studies that find LABs in overdensities. In addition to Lyman-
(Ly) emission, we find \ion{C}{IV}, \ion{He}{II}, and \ion{O}{III}]
ultraviolet (UV) emission lines arising from the centre of the nebula. We used
the compactness of these lines in combination with the line ratios to conclude
that the \Lya nebula is likely powered by embedded star formation. Resonant
scattering of the \Lya photons then produces the extended shape of the
emission. Thanks to the combined power of MUSE and strong gravitational
lensing, we are now able to probe the circumgalatic medium of sub-
galaxies at .Comment: 7 pages, 7 figures; moderate changes to match the accepted A&A
versoi
Gravitationally Collapsing Shells in (2+1) Dimensions
We study gravitationally collapsing models of pressureless dust, fluids with
pressure, and the generalized Chaplygin gas (GCG) shell in (2+1)-dimensional
spacetimes. Various collapse scenarios are investigated under a variety of the
background configurations such as anti-de Sitter(AdS) black hole, de Sitter
(dS) space, flat and AdS space with a conical deficit. As with the case of a
disk of dust, we find that the collapse of a dust shell coincides with the
Oppenheimer-Snyder type collapse to a black hole provided the initial density
is sufficiently large. We also find -- for all types of shell -- that collapse
to a naked singularity is possible under a broad variety of initial conditions.
For shells with pressure this singularity can occur for a finite radius of the
shell. We also find that GCG shells exhibit diverse collapse scenarios, which
can be easily demonstrated by an effective potential analysis.Comment: 27 pages, Latex, 11 figures, typos corrected, references added, minor
amendments in introduction and conclusion introd
Stability of Chaplygin gas thin-shell wormholes
In this paper we construct spherical thin-shell wormholes supported by a
Chaplygin gas. For a rather general class of geometries we introduce a new
approach for the stability analysis of static solutions under perturbations
preserving the symmetry. We apply this to wormholes constructed from
Schwarzschild, Schwarzschild-de Sitter, Schwarzschild-anti de Sitter and
Reissner-Nordstrom metrics. In the last two cases, we find that there are
values of the parameters for which stable static solutions exist.Comment: 14 pages, 5 figures; v2: minor changes and new references added.
Accepted for publication in Physical Review
A highly-ionized region surrounding SN Refsdal revealed by MUSE
Supernova (SN) Refsdal is the first multiply-imaged, highly-magnified, and
spatially-resolved SN ever observed. The SN exploded in a highly-magnified
spiral galaxy at z=1.49 behind the Frontier Fields Cluster MACS1149, and
provides a unique opportunity to study the environment of SNe at high z. We
exploit the time delay between multiple images to determine the properties of
the SN and its environment, before, during, and after the SN exploded. We use
the integral-field spectrograph MUSE on the VLT to simultaneously target all
observed and model-predicted positions of SN Refsdal. We find MgII emission at
all positions of SN Refsdal, accompanied by weak FeII* emission at two
positions. The measured ratios of [OII] to MgII emission of 10-20 indicate a
high degree of ionization with low metallicity. Because the same high degree of
ionization is found in all images, and our spatial resolution is too coarse to
resolve the region of influence of SN Refsdal, we conclude that this high
degree of ionization has been produced by previous SNe or a young and hot
stellar population. We find no variability of the [OII] line over a period of
57 days. This suggests that there is no variation in the [OII] luminosity of
the SN over this period, or that the SN has a small contribution to the
integrated [OII] emission over the scale resolved by our observations.Comment: 5 pages, 4 figures, accepted for publication in A&
Stress condensation in crushed elastic manifolds
We discuss an M-dimensional phantom elastic manifold of linear size L crushed
into a small sphere of radius R << L in N-dimensional space. We investigate the
low elastic energy states of 2-sheets (M=2) and 3-sheets (M=3) using analytic
methods and lattice simulations. When N \geq 2M the curvature energy is
uniformly distributed in the sheet and the strain energy is negligible. But
when N=M+1 and M>1, both energies appear to be condensed into a network of
narrow M-1 dimensional ridges. The ridges appear straight over distances
comparable to the confining radius R.Comment: 4 pages, RevTeX + epsf, 4 figures, Submitted to Phys. Rev. Let
The story of supernova 'Refsdal' told by MUSE
We present MUSE observations in the core of the HFF galaxy cluster MACS
J1149.5+2223, where the first magnified and spatially-resolved multiple images
of SN 'Refsdal' at redshift 1.489 were detected. Thanks to a DDT program with
the VLT and the extraordinary efficiency of MUSE, we measure 117 secure
redshifts with just 4.8 hours of total integration time on a single target
pointing. We spectroscopically confirm 68 galaxy cluster members, with redshift
values ranging from 0.5272 to 0.5660, and 18 multiple images belonging to 7
background, lensed sources distributed in redshifts between 1.240 and 3.703.
Starting from the combination of our catalog with those obtained from extensive
spectroscopic and photometric campaigns using the HST, we select a sample of
300 (164 spectroscopic and 136 photometric) cluster members, within
approximately 500 kpc from the BCG, and a set of 88 reliable multiple images
associated to 10 different background source galaxies and 18 distinct knots in
the spiral galaxy hosting SN 'Refsdal'. We exploit this valuable information to
build 6 detailed strong lensing models, the best of which reproduces the
observed positions of the multiple images with a rms offset of only 0.26". We
use these models to quantify the statistical and systematic errors on the
predicted values of magnification and time delay of the next emerging image of
SN 'Refsdal'. We find that its peak luminosity should should occur between
March and June 2016, and should be approximately 20% fainter than the dimmest
(S4) of the previously detected images but above the detection limit of the
planned HST/WFC3 follow-up. We present our two-dimensional reconstruction of
the cluster mass density distribution and of the SN 'Refsdal' host galaxy
surface brightness distribution. We outline the roadmap towards even better
strong lensing models with a synergetic MUSE and HST effort.Comment: 21 pages, 9 figures, 6 tables; accepted for publication in the
Astrophysical Journal - extra information on data analysis added, all model
predictions and results unchange
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