1,326 research outputs found
An Integral Field Study of Abundance Gradients in Nearby LIRGs
We present for the first time metallicity maps generated using data from the
Wide Field Spectrograph (WiFeS) on the ANU 2.3m of 9 Luminous Infrared Galaxies
(LIRGs) and discuss the abundance gradients and distribution of metals in these
systems. We have carried out optical integral field spectroscopy (IFS) of
several several LIRGs in various merger phases to investigate the merger
process. In a major merger of two spiral galaxies with preexisting disk
abundance gradients, the changing distribution of metals can be used as a
tracer of gas flows in the merging system as low metallicity gas is transported
from the outskirts of each galaxy to their nuclei. We employ this fact to probe
merger properties by using the emission lines in our IFS data to calculate the
gas-phase metallicity in each system. We create abundance maps and subsequently
derive a metallicity gradient from each map. We compare our measured gradients
to merger stage as well as several possible tracers of merger progress and
observed nuclear abundances. We discuss our work in the context of previous
abundance gradient observations and compare our results to new galaxy merger
models which trace metallicity gradient. Our results agree with the observed
flattening of metallicity gradients as a merger progresses. We compare our
results with new theoretical predictions that include chemical enrichment. Our
data show remarkable agreement with these simulations.Comment: Accepted for publication in ApJ. 26 pages, 18 figure
Damped lyman α absorbers as a probe of stellar feedback
We examine the abundance, clustering and metallicity of Damped Lyman-alpha
Absorbers (DLAs) in a suite of hydrodynamic cosmological simulations using the
moving mesh code AREPO. We incorporate models of supernova and AGN feedback, as
well as molecular hydrogen formation. We compare our simulations to the column
density distribution function at , the total DLA abundance at , the
measured DLA bias at and the DLA metallicity distribution at .
Our preferred models produce populations of DLAs in good agreement with most of
these observations. The exception is the DLA abundance at , which we
show requires stronger feedback in mass halos.
While the DLA population probes a wide range of halo masses, we find the
cross-section is dominated by halos of mass and virial velocities . The simulated DLA
population has a linear theory bias of , whereas the observations require
. We show that non-linear growth increases the bias in our
simulations to at , the smallest scale observed.
The scale-dependence of the bias is, however, very different in the simulations
compared against the observations. We show that, of the observations we
consider, the DLA abundance and column density function provide the strongest
constraints on the feedback model
Ex. 277-US-415
The 2004 annual report on riverine movements of adult Lost River, shortnose, and Klamath largescale suckers in the Williamson and Sprague rivers, Orego
Ex. 277-US-415
The 2004 annual report on riverine movements of adult Lost River, shortnose, and Klamath largescale suckers in the Williamson and Sprague rivers, Orego
Photograph of Abraham Lincoln Walks at Midnight Statue
The black and white photograph depicts the statue Abraham Lincoln Walks at Midnight, located in front of the West Virginia State Capitol.https://scholarsjunction.msstate.edu/fvw-photographs/1588/thumbnail.jp
Photograph of Abraham Lincoln Walks at Midnight Statue
The black and white photograph depicts the statue Abraham Lincoln Walks at Midnight, located in front of the West Virginia State Capitol.https://scholarsjunction.msstate.edu/fvw-artifacts/2214/thumbnail.jp
Chemical pre-processing of cluster galaxies over the past 10 billion years in the IllustrisTNG simulations
We use the IllustrisTNG simulations to investigate the evolution of the
mass-metallicity relation (MZR) for star-forming cluster galaxies as a function
of the formation history of their cluster host. The simulations predict an
enhancement in the gas-phase metallicities of star-forming cluster galaxies
(10^9< M_star<10^10 M_sun) at z<1.0 in comparisons to field galaxies. This is
qualitatively consistent with observations. We find that the metallicity
enhancement of cluster galaxies appears prior to their infall into the central
cluster potential, indicating for the first time a systematic "chemical
pre-processing" signature for {\it infalling} cluster galaxies. Namely,
galaxies which will fall into a cluster by z=0 show a ~0.05 dex enhancement in
the MZR compared to field galaxies at z<0.5. Based on the inflow rate of gas
into cluster galaxies and its metallicity, we identify that the accretion of
pre-enriched gas is the key driver of the chemical evolution of such galaxies,
particularly in the stellar mass range (10^9< M_star<10^10 M_sun). We see
signatures of an environmental dependence of the ambient/inflowing gas
metallicity which extends well outside the nominal virial radius of clusters.
Our results motivate future observations looking for pre-enrichment signatures
in dense environments.Comment: 5 pages, 4 figures, accepted for publication in MNRAS Letter
Hydrogen reionization in the illustris universe
Hydrodynamical simulations of galaxy formation such as the Illustris
simulations have progressed to a state where they approximately reproduce the
observed stellar mass function from high to low redshift. This in principle
allows self-consistent models of reionization that exploit the accurate
representation of the diffuse gas distribution together with the realistic
growth of galaxies provided by these simulations, within a representative
cosmological volume. In this work, we apply and compare two radiative transfer
algorithms implemented in a GPU-accelerated code to the wide
volume of Illustris in postprocessing in order to investigate the reionization
transition predicted by this model. We find that the first generation of
galaxies formed by Illustris is just about able to reionize the universe by
redshift , provided quite optimistic assumptions about the escape
fraction and the resolution limitations are made. Our most optimistic model
finds an optical depth of , which is in very good agreement
with recent Planck 2015 determinations. Furthermore, we show that moment-based
approaches for radiative transfer with the M1 closure give broadly consistent
results with our angular-resolved radiative transfer scheme. In our favoured
fiducial model, 20\% of the hydrogen is reionized by redshift , and
this rapidly climbs to 80\% by redshift . It then takes until
before 99\% of the hydrogen is ionized. On average, reionization proceeds
`inside-out' in our models, with a size distribution of reionized bubbles that
progressively features regions of ever larger size while the abundance of small
bubbles stays fairly constant
Multiphoton Transitions in a Spin System Driven by Strong Bichromatic Field
EPR transient nutation spectroscopy is used to measure the effective field
(Rabi frequency) for multiphoton transitions in a two-level spin system
bichromatically driven by a transverse microwave (MW) field and a longitudinal
radio-frequency (RF) field. The behavior of the effective field amplitude is
examined in the case of a relatively strong MW field, when the derivation of
the effective Hamiltonian cannot be reduced to first-order perturbation theory
in w_{1} / w_{rf} (w_{1} is the microwave Rabi frequency, w_{rf} is the RF
frequency). Experimental results are consistently interpreted by taking into
account the contributions of second and third order in w_{1} / w_{rf} evaluated
by Krylov-Bogolyubov-Mitropolsky averaging. In the case of inhomogeneously
broadened EPR line, the third-order correction modifies the nutation frequency,
while the second-order correction gives rise to a change in the nutation
amplitude due to a Bloch-Siegert shift.Comment: 7 pages, 6 figure
Introducing the illustris project: Simulating the coevolution of dark and visible matter in the universe
We introduce the Illustris Project, a series of large-scale hydrodynamical simulations of galaxy formation. The highest resolution simulation, Illustris-1, covers a volume of (106.5 Mpc)3, has a dark mass resolution of 6.26 × 106M⊙, and an initial baryonic matter mass resolution of 1.26 × 106M⊙. At z = 0 gravitational forces are softened on scales of 710 pc, and the smallest hydrodynamical gas cells have an extent of 48 pc. We follow the dynamical evolution of 2 × 18203 resolution elements and in addition passively evolve 18203 Monte Carlo tracer particles reaching a total particle count of more than 18 billion. The galaxy formation model includes: Primordial and metal-line cooling with self-shielding corrections, stellar evolution, stellar feedback, gas recycling, chemical enrichment, supermassive black hole growth, and feedback from active galactic nuclei. Here we describe the simulation suite, and contrast basic predictions of our model for the present-day galaxy population with observations of the local universe. At z = 0 our simulation volume contains about 40 000 well-resolved galaxies covering a diverse range of morphologies and colours including early-type, late-type and irregular galaxies. The simulation reproduces reasonably well the cosmic star formation rate density, the galaxy luminosity function, and baryon conversion efficiency at z = 0. It also qualitatively captures the impact of galaxy environment on the red fractions of galaxies. The internal velocity structure of selected well-resolved disc galaxies obeys the stellar and baryonic Tully-Fisher relation together with flat circular velocity curves. In the well-resolved regime, the simulation reproduces the observed mix of early-type and late-type galaxies. Our model predicts a halo mass dependent impact of baryonic effects on the halo mass function and the masses of haloes caused by feedback from supernova and active galactic nuclei
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