431 research outputs found
Maxwell--Chern-Simons gauged non-relativistic O(3) model with self-dual vortices
A non-relativistic version of the 2+1 dimensional gauged Chern-Simons O(3)
sigma model, augmented by a Maxwell term, is presented and shown to support
topologically stable static self-dual vortices. Exactly like their counterparts
of the ungauged model, these vortices are shown to exhibit Hall behaviour in
their dynamics.Comment: 12 pages, LateX, to appear in Mod. Phys. Lett. 199
Exact Self-dual Soliton Solutions in a Gauged O(3) Sigma Model with Anomalous Magnetic Moment Interaction
It is shown that a gauged nonlinear sigma model with anomalous
magnetic moment interaction in dimensions is exactly integrable for
static, self-dual field configurations. The matter fields are exactly
equivalent to those of the usual ungauged nonlinear sigma model. These
static soliton solutions can be mapped into an Abelian purely magnetic vortex
solutions through a suitable reduction of the non-Abelian gauge group. A
relativistic Abelian model in dimensions is also presented where these
purely magnetic vortices can be realized.Comment: A discussion on case has been made. New references have been
added. To appear in Physics Letters B. RevTeX, 13 pages, no figur
The energy and dynamics of trapped radiative feedback with stellar winds
In this paper, we explore the significant, non-linear impact that stellar winds have on HâII regions. We perform a parameter study using three-dimensional radiative magnetohydrodynamic simulations of wind and ultraviolet radiation feedback from a 35 Mâ star formed self-consistently in a turbulent, self-gravitating cloud, similar to the Orion Nebula (M42) and its main ionizing source Ξ1 Ori C. Stellar winds suppress early radiative feedback by trapping ionizing radiation in the shell around the wind bubble. Rapid breakouts of warm photoionized gas (âchampagne flowsâ) still occur if the star forms close to the edge of the cloud. The impact of wind bubbles can be enhanced if we detect and remove numerical overcooling caused by shocks crossing grid cells. However, the majority of the energy in the wind bubble is still lost to turbulent mixing between the wind bubble and the gas around it. These results begin to converge if the spatial resolution at the wind bubble interface is increased by refining the grid on pressure gradients. Wind bubbles form a thin chimney close to the star, which then expands outwards as an extended plume once the wind bubble breaks out of the dense core the star formed in, allowing them to expand faster than a spherical wind bubble. We also find wind bubbles mixing completely with the photoionized gas when the HâII region breaks out of the cloud as a champagne flow, a process we term âhot champagneâ
Understanding the escape of LyC and Lyα photons from turbulent clouds
Understanding the escape of Lyman continuum (LyC) and Lyman alpha (Lya)
photons from molecular clouds is one of the keys to constraining the
reionization history of the Universe and the evolution of galaxies at high
redshift. Using a set of radiation-hydrodynamic simulations with adaptive mesh
refinement, we investigate how photons propagate and escape from turbulent
clouds with different masses, star formation efficiencies (SFEs), and
metallicities, as well as with different models of stellar spectra and
supernova feedback. We find that the escape fractions in both LyC and Lya are
generally increasing with time if the cloud is efficiently dispersed by
radiation and supernova feedback. When the total SFE is low (1% of the cloud
mass), 0.1-5% of LyC photons leave the metal-poor cloud, whereas the fractions
increase to 20-70% in clouds with a 10% SFE. LyC photons escape more
efficiently if gas metallicity is lower, if the upper mass limit in the stellar
initial mass function is higher, if binary interactions are allowed in the
evolution of stars, or if additional strong radiation pressure, such as Lya
pressure, is present. As a result, the number of escaping LyC photons can
easily vary by a factor of on cloud scales. The escape fractions of Lya
photons are systemically higher (60-80%) than those of LyC photons despite
large optical depths at line centre (). Scattering of Lya
photons is already significant on cloud scales, leading to double-peaked
profiles with peak separations of during
the initial stage of the cloud evolution, while it becomes narrower than
in the LyC bright phase. Comparisons
with observations of low-redshift galaxies suggest that Lya photons require
further interactions with neutral hydrogen to reproduce their velocity offset
for a given LyC escape fraction
The SPHINX cosmological simulations of the first billion years: The impact of binary stars on reionization
We present the SPHINX suite of cosmological adaptive mesh refinement
simulations, the first radiation-hydrodynamical simulations to simultaneously
capture large-scale reionization and the escape of ionizing radiation from
thousands of resolved galaxies. Our and co-moving Mpc volumes resolve
haloes down to the atomic cooling limit and model the inter-stellar medium with
better than pc resolution. The project has numerous goals in
improving our understanding of reionization and making predictions for future
observations. In this first paper we study how the inclusion of binary stars in
computing stellar luminosities impacts reionization, compared to a model that
includes only single stars. Owing to the suppression of galaxy growth via
strong feedback, our galaxies are in good agreement with observational
estimates of the galaxy luminosity function. We find that binaries have a
significant impact on the timing of reionization: with binaries, our boxes are
percent ionized by volume at , while without them our
volumes fail to reionize by . These results are robust to changes in
volume size, resolution, and feedback efficiency. The escape of ionizing
radiation from individual galaxies varies strongly and frequently. On average,
binaries lead to escape fractions of percent, about times
higher than with single stars only. The higher escape fraction is a result of a
shallower decline in ionizing luminosity with age, and is the primary reason
for earlier reionization, although the higher integrated luminosity with
binaries also plays a sub-dominant role
Anyonic Bogomol'nyi Solitons in a Gauged O(3) Sigma Model
We introduce the self-dual abelian gauged sigma models where the
Maxwell and Chern-Simons terms constitute the kinetic terms for the gauge
field. These models have quite rich structures and various limits. Our models
are found to exhibit both symmetric and broken phases of the gauge group. We
discuss the pure Chern-Simons limit in some detail and study rotationally
symmetric solitons.Comment: 14 pages, 6 Postscript figures uuencoded, written in REVTe
Constraining stellar assembly and AGN feedback at the peak epoch of star formation
We study stellar assembly and feedback from active galactic nuclei (AGN)
around the epoch of peak star formation (1<z<2), by comparing hydrodynamic
simulations to rest-frame UV-optical galaxy colours from the Wide Field Camera
3 (WFC3) Early-Release Science (ERS) Programme. Our Adaptive Mesh Refinement
simulations include metal-dependent radiative cooling, star formation, kinetic
outflows due to supernova explosions, and feedback from supermassive black
holes. Our model assumes that when gas accretes onto black holes, a fraction of
the energy is used to form either thermal winds or sub-relativistic
momentum-imparting collimated jets, depending on the accretion rate. We find
that the predicted rest-frame UV-optical colours of galaxies in the model that
includes AGN feedback is in broad agreement with the observed colours of the
WFC3 ERS sample at 1<z<2. The predicted number of massive galaxies also matches
well with observations in this redshift range. However, the massive galaxies
are predicted to show higher levels of residual star formation activity than
the observational estimates, suggesting the need for further suppression of
star formation without significantly altering the stellar mass function. We
discuss possible improvements, involving faster stellar assembly through
enhanced star formation during galaxy mergers while star formation at the peak
epoch is still modulated by the AGN feedback.Comment: 6 pages, 4 figures, accepted for publication in MNRAS Letter
Probing cosmic dawn with emission lines: predicting infrared and nebular line emission for ALMA and JWST
Infrared and nebular lines provide some of our best probes of the physics
regulating the properties of the interstellar medium (ISM) at high-redshift.
However, interpreting the physical conditions of high-redshift galaxies
directly from emission lines remains complicated due to inhomogeneities in
temperature, density, metallicity, ionisation parameter, and spectral hardness.
We present a new suite of cosmological, radiation-hydrodynamics simulations,
each centred on a massive Lyman-break galaxy that resolves such properties in
an inhomogeneous ISM. Many of the simulated systems exhibit transient but well
defined gaseous disks that appear as velocity gradients in [CII]~158.6m
emission. Spatial and spectral offsets between [CII]~158.6m and
[OIII]~88.33m are common, but not ubiquitous, as each line probes a
different phase of the ISM. These systems fall on the local [CII]-SFR relation,
consistent with newer observations that question previously observed
[CII]~158.6m deficits. Our galaxies are consistent with the nebular line
properties of observed galaxies and reproduce offsets on the BPT and
mass-excitation diagrams compared to local galaxies due to higher star
formation rate (SFR), excitation, and specific-SFR, as well as harder spectra
from young, metal-poor binaries. We predict that local calibrations between
H and [OII]~3727 luminosity and galaxy SFR apply up to , as
do the local relations between certain strong line diagnostics (R23 and
[OIII]~5007/H) and galaxy metallicity. Our new simulations are well
suited to interpret the observations of line emission from current (ALMA and
HST) and upcoming facilities (JWST and ngVLA)
New Methods for Identifying Lyman Continuum Leakers and Reionization-Epoch Analogues
Identifying low-redshift galaxies that emit Lyman continuum radiation (LyC leakers) is one of the primary, indirect methods of studying galaxy formation in the epoch of reionization. However, not only has it proved challenging to identify such systems, it also remains uncertain whether the low-redshift LyC leakers are truly âanaloguesâ of the sources that reionized the Universe. Here, we use high-resolution cosmological radiation hydrodynamics simulations to examine whether simulated galaxies in the epoch of reionization share similar emission line properties to observed LyC leakers at z ⌠3 and z ⌠0. We find that the simulated galaxies with high LyC escape fractions (fesc) often exhibit high O32 and populate the same regions of the R23âO32 plane as z ⌠3 LyC leakers. However, we show that viewing angle, metallicity, and ionization parameter can all impact where a galaxy resides on the O32âfesc plane. Based on emission line diagnostics and how they correlate with fesc, lower metallicity LyC leakers at z ⌠3 appear to be good analogues of reionization-era galaxies. In contrast, local [SâII]-deficient galaxies do not overlap with the simulated high-redshift LyC leakers on the SâII BaldwinâPhillipsâTerlevich (BPT) diagram; however, this diagnostic may still be useful for identifying leakers. We use our simulated galaxies to develop multiple new diagnostics to identify LyC leakers using infrared and nebular emission lines. We show that our model using only [CâII]158 ÎŒm and [OâIII]88 ÎŒm can identify potential leakers from non-leakers from the local Dwarf Galaxy Survey. Finally, we apply this diagnostic to known high-redshift galaxies and find that MACS 1149_JD1 at z = 9.1 is the most likely galaxy to be actively contributing to the reionization of the Universe
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