51,970 research outputs found
The ALPINE-ALMA [C II] survey: Star-formation-driven outflows and circumgalactic enrichment in the early Universe
We study the efficiency of galactic feedback in the early Universe by stacking the [C II] 158 μm emission in a large sample of normal star-forming galaxies at 4 4. From the stacking analysis of the datacubes, we find that the combined [C II] core emission (|v|< 200 km s⁻¹) of the higher-SFR galaxies is extended on physical sizes of ∼30 kpc (diameter scale), well beyond the analogous [C II] core emission of lower-SFR galaxies and the stacked far-infrared continuum. The detection of such extended metal-enriched gas, likely tracing circumgalactic gas enriched by past outflows, corroborates previous similar studies, confirming that baryon cycle and gas exchanges with the circumgalactic medium are at work in normal star-forming galaxies already at early epochs
On measuring the Tully-Fisher relation at
The evolution of the line width - luminosity relation for spiral galaxies,
the Tully-Fisher relation, strongly constrains galaxy formation and evolution
models. At this moment, the kinematics of z>1 spiral galaxies can only be
measured using rest frame optical emission lines associated with star
formation, such as Halpha and [OIII]5007/4959 and [OII]3727. This method has
intrinsic difficulties and uncertainties. Moreover, observations of these lines
are challenging for present day telescopes and techniques. Here, we present an
overview of the intrinsic and observational challenges and some ways way to
circumvent them. We illustrate our results with the HST/NICMOS grism sample
data of z ~ 1.5 starburst galaxies. The number of galaxies we can use in the
final Tully-Fisher analysis is only three. We find a ~2 mag offset from the
local rest frame B and R band Tully-Fisher relation for this sample. This
offset is partially explained by sample selection effects and sample specifics.
Uncertainties in inclination and extinction and the effects of star formation
on the luminosity can be accounted for. The largest remaining uncertainty is
the line width / rotation curve velocity measurement. We show that high
resolution, excellent seeing integral field spectroscopy will improve the
situation. However, we note that no flat rotation curves have been observed for
galaxies with z>1. This could be due to the described instrumental and
observational limitations, but it might also mean that galaxies at z>1 have not
reached the organised motions of the present day.Comment: 13 pages, 7 figures, A&A accepte
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Geochemistry and petrogenesis of volcanic rocks from Daimao Seamount (South China Sea) and their tectonic implications
The South China Sea (SCS) experienced three episodes of seafloor spreading and left three fossil spreading centers presently located at 18°N, 17°N and 15.5°N. Spreading ceased at these three locations during magnetic anomaly 10, 8, and 5c, respectively. Daimao Seamount (16.6. Ma) was formed 10. my after the cessation of the 17°N spreading center. Volcaniclastic rocks and shallow-water carbonate facies near the summit of Daimao Seamount provide key information on the seamount's geologic history. New major and trace element and Sr-Nd-Pb isotopic compositions of basaltic breccia clasts in the volcaniclastics suggest that Daimao and other SCS seamounts have typical ocean island basalt-like composition and possess a 'Dupal' isotopic signature. Our new analyses, combined with available data, indicate that the basaltic foundation of Daimao Seamount was formed through subaqueous explosive volcanic eruptions at 16.6. Ma. The seamount subsided rapidly (>. 0.12. mm/y) at first, allowing the deposition of shallow-water, coral-bearing carbonates around its summit and, then, at a slower rate (<. 0.12. mm/y). We propose that the parental magmas of SCS seamount lavas originated from the Hainan mantle plume. In contrast, lavas from contemporaneous seamounts in other marginal basins in the western Pacific are subduction-related
Mapping Global Star Formation in the Interacting Galaxy Pair Arp32
A multi-wavelength set of photometric data including UV (GALEX), optical, near-IR, infrared (Spitzer) and radio (VLA 20cm) images and spectroscopic observations are used to map the dust-obscured and unobscured star formation in the galaxy pair Arp 32. The system consists of an actively starforming galaxy and another one with depressed star formation. The most active galaxy has disrupted morphology and different sites of star formation. Spectroscopic data show hints of nuclear activity in its core, intense star formation in limited regions of the galaxy as well as an underlying population of stars witnessing a past episode of star formation. Current star formation rates are estimated from UV and bolometric IR luminosities
Electric Transport Theory of Dirac Fermions in Graphene
Using the self-consistent Born approximation to the Dirac fermions under
finite-range impurity scatterings, we show that the current-current correlation
function is determined by four-coupled integral equations. This is very
different from the case for impurities with short-range potentials. As a test
of the present approach, we calculate the electric conductivity in graphene for
charged impurities with screened Coulomb potentials. The obtained conductivity
at zero temperature varies linearly with the carrier concentration, and the
minimum conductivity at zero doping is larger than the existing theoretical
predictions, but still smaller than that of the experimental measurement. The
overall behavior of the conductivity obtained by the present calculation at
room temperature is similar to that at zero temperature except the minimum
conductivity is slightly larger.Comment: 6 pages, 3 figure
Non-LTE analysis of copper abundances for the two distinct halo populations in the solar neighborhood
Two distinct halo populations were found in the solar neighborhood by a
series of works. They can be clearly separated by [alpha\Fe] and several other
elemental abundance ratios including [Cu/Fe]. Very recently, a non-local
thermodynamic equilibrium (non-LTE) study revealed that relatively large
departures exist between LTE and non-LTE results in copper abundance analysis.
We aim to derive the copper abundances for the stars from the sample of Nissen
et al (2010) with both LTE and non-LTE calculations. Based on our results, we
study the non-LTE effects of copper and investigate whether the high-alpha
population can still be distinguished from the low-alpha population in the
non-LTE [Cu/Fe] results. Our differential abundance ratios are derived from the
high-resolution spectra collected from VLT/UVES and NOT/FIES spectrographs.
Applying the MAFAGS opacity sampling atmospheric models and spectrum synthesis
method, we derive the non-LTE copper abundances based on the new atomic model
with current atomic data obtained from both laboratory and theoretical
calculations. The copper abundances determined from non-LTE calculations are
increased by 0.01 to 0.2 dex depending on the stellar parameters compared with
the LTE results. The non-LTE [Cu/Fe] trend is much flatter than the LTE one in
the metallicity range -1.6<[Fe/H]<-0.8. Taking non-LTE effects into
consideration, the high- and low-alpha stars still show distinguishable copper
abundances, which appear even more clear in a diagram of non-LTE [Cu/Fe] versus
[Fe/H]. The non-LTE effects are strong for copper, especially in metal-poor
stars. Our results confirmed that there are two distinct halo populations in
the solar neighborhood. The dichotomy in copper abundance is a peculiar feature
of each population, suggesting that they formed in different environments and
evolved obeying diverse scenarios.Comment: 9 pages, 7 figures, 2 table
Approximation for discrete Fourier transform and application in study of three-dimensional interacting electron gas
The discrete Fourier transform is approximated by summing over part of the
terms with corresponding weights. The approximation reduces significantly the
requirement for computer memory storage and enhances the numerical computation
efficiency with several orders without loosing accuracy. As an example, we
apply the algorithm to study the three-dimensional interacting electron gas
under the renormalized-ring-diagram approximation where the Green's function
needs to be self-consistently solved. We present the results for the chemical
potential, compressibility, free energy, entropy, and specific heat of the
system. The ground-state energy obtained by the present calculation is compared
with the existing results of Monte Carlo simulation and random-phase
approximation.Comment: 11 pages, 13 figure
Averaging approximation to singularly perturbed nonlinear stochastic wave equations
An averaging method is applied to derive effective approximation to the
following singularly perturbed nonlinear stochastic damped wave equation \nu
u_{tt}+u_t=\D u+f(u)+\nu^\alpha\dot{W} on an open bounded domain
\,, \,. Here is a small parameter
characterising the singular perturbation, and \,, \,, parametrises the strength of the noise. Some scaling transformations
and the martingale representation theorem yield the following effective
approximation for small , u_t=\D u+f(u)+\nu^\alpha\dot{W} to an error of
\ord{\nu^\alpha}\,.Comment: 16 pages. Submitte
Exploring the quantum critical behaviour in a driven Tavis-Cummings circuit
Quantum phase transitions play an important role in many-body systems and
have been a research focus in conventional condensed matter physics over the
past few decades. Artificial atoms, such as superconducting qubits that can be
individually manipulated, provide a new paradigm of realising and exploring
quantum phase transitions by engineering an on-chip quantum simulator. Here we
demonstrate experimentally the quantum critical behaviour in a
highly-controllable superconducting circuit, consisting of four qubits coupled
to a common resonator mode. By off-resonantly driving the system to renormalise
the critical spin-field coupling strength, we have observed a four-qubit
non-equilibrium quantum phase transition in a dynamical manner, i.e., we sweep
the critical coupling strength over time and monitor the four-qubit scaled
moments for a signature of a structural change of the system's eigenstates. Our
observation of the non-equilibrium quantum phase transition, which is in good
agreement with the driven Tavis-Cummings theory under decoherence, offers new
experimental approaches towards exploring quantum phase transition related
science, such as scaling behaviours, parity breaking and long-range quantum
correlations.Comment: Main text with 3 figure
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