492 research outputs found
A simple prescription for simulating and characterizing gravitational arcs
Simple models of gravitational arcs are crucial to simulate large samples of
these objects with full control of the input parameters. These models also
provide crude and automated estimates of the shape and structure of the arcs,
which are necessary when trying to detect and characterize these objects on
massive wide area imaging surveys. We here present and explore the ArcEllipse,
a simple prescription to create objects with shape similar to gravitational
arcs. We also present PaintArcs, which is a code that couples this geometrical
form with a brightness distribution and adds the resulting object to images.
Finally, we introduce ArcFitting, which is a tool that fits ArcEllipses to
images of real gravitational arcs. We validate this fitting technique using
simulated arcs and apply it to CFHTLS and HST images of tangential arcs around
clusters of galaxies. Our simple ArcEllipse model for the arc, associated to a
S\'ersic profile for the source, recovers the total signal in real images
typically within 10%-30%. The ArcEllipse+S\'ersic models also automatically
recover visual estimates of length-to-width ratios of real arcs. Residual maps
between data and model images reveal the incidence of arc substructure. They
may thus be used as a diagnostic for arcs formed by the merging of multiple
images. The incidence of these substructures is the main factor preventing
ArcEllipse models from accurately describing real lensed systems.Comment: 12 pages, 11 figures, accepted for publication in A&
The first 62 AGN observed with SDSS-IV MaNGA - IV: gas excitation and star-formation rate distributions
We present maps of the ionized gas flux distributions, excitation,
star-formation rate SFR, surface mass density , and obtain total
values of SFR and ionized gas masses {\it M} for 62 Active Galactic Nuclei
(AGN) observed with SDSS-IV MaNGA and compare them with those of a control
sample of 112 non-active galaxies. The most luminous AGN -- with
L(\rm{[OIII]}\lambda 5007) \ge 3.8\times 10^{40}\,\mbox{erg}\,\mbox{s}^{-1},
and those hosted by earlier-type galaxies are dominated by Seyfert excitation
within 0.2 effective radius from the nucleus, surrounded by LINER
excitation or transition regions, while the less luminous and hosted by
later-type galaxies show equally frequent LINER and Seyfert excitation within
. The extent of the region ionized by the AGN follows the
relation -- as in the case of the Broad-Line
Region. The SFR distribution over the region ionized by hot stars is similar
for AGN and controls, while the integrated SFR -- in the range
\,M\,yr is also similar for the late-type
sub-sample, but higher in the AGN for 75\% of the early-type sub-sample. We
thus conclude that there is no signature of AGN quenching star formation in the
body of the galaxy in our sample. We also find that 66\% of the AGN have higher
ionized gas masses than the controls -- in the range
10\,M -- while 75\% of the AGN have higher
within than the control galaxies
Low energy elastic and electronically inelastic electron scattering from biomolecules.
Reactions initiated by collisions with low-energy secondary electrons has been found to be the prominent\ud
mechanism toward the radiation damage on living tissues through DNA strand breaks. Now it is widely accepted\ud
that during the interaction with these secondary species the selective breaking of chemical bonds is triggered\ud
by dissociative electron attachment (DEA), that is, the capture of the incident electron and the formation\ud
of temporary negative ion states [1,2,3]. One of the approaches largely used toward a deeper understanding\ud
of the radiation damage to DNA is through modeling of DEA with its basic constituents (nucleotide bases,\ud
sugar and other subunits). We have tried to simplify this approach and attempt to make it comprehensible\ud
at a more fundamental level by looking at even simple molecules. Studies involving organic systems such as\ud
carboxylic acids, alcohols and simple ¯ve-membered heterocyclic compounds are taken as starting points for\ud
these understanding. In the present study we investigate the role played by elastic scattering and electronic\ud
excitation of molecules on electron-driven chemical processes. Special attention is focused on the analysis of\ud
the in°uence of polarization and multichannel coupling e®ects on the magnitude of elastic and electronically\ud
inelastic cross-sections. Our aim is also to investigate the existence of resonances in the elastic and electronically\ud
inelastic channels as well as to characterize them with respect to its type (shape, core-excited or Feshbach),\ud
symmetry and position. The relevance of these issues is evaluated within the context of possible applications\ud
for the modeling of discharge environments and implications in the understanding of mutagenic rupture of DNA\ud
chains. The scattering calculations were carried out with the Schwinger multichannel method (SMC) [4] and\ud
its implementation with pseudopotentials (SMCPP) [5] at di®erent levels of approximation for impact energies\ud
ranging from 0.5 eV to 30 eV.\ud
References\ud
[1] B. Boudai®a, P. Cloutier, D. Hunting, M. A. Huels and L. Sanche, Science 287, 1658 (2000). [2] X. Pan, P.\ud
Cloutier, D. Hunting and L. Sanche, Phys. Rev. Lett. 90, 208102 (2003). [3] F. Martin, P. D. Burrow, Z. Cai,\ud
P. Cloutier, D. Hunting and L. Sanche, Phys. Rev. Lett. 93, 068101 (2004). [4] K. Takatsuka and V. McKoy,\ud
Phys. Rev. A 24, 2437 (1981); ibid. Phys. Rev. A 30, 1734 (1984). [5] M. H. F. Bettega, L. G. Ferreira and\ud
M. A. P. Lima, Phys. Rev. A 47, 1111 (1993)
Line strengths of early-type galaxies
In this paper we present measurements of velocity dispersions and Lick
indices for 509 galaxies in the local Universe, based on high signal-to-noise,
long slit spectra obtained with the 1.52 m ESO telescope at La Silla. The
conversion of our measurements into the Lick/IDS system was carried out
following the general prescription of Worthey and Ottaviani 1997. Comparisons
of our measurements with those of other authors show, in general, good
agreement. We also examine the dependence between these indices (e.g., Hbeta,
Mg_2, Fe5270 and NaD) and the central velocity dispersion (sigma), and we find
that they are consistent with those previously reported in the literature.
Benefiting from the relatively large size of the sample, we are able to
investigate the dependence of these relations on morphology and environment,
here represented by the local galaxy density. We find that for metallic lines
these relations show no significant dependence on environment or morphology,
except in the case of NaD, which shows distinct behavior for E and S0. On the
other hand, the Hbeta-logsigma shows a significant difference as a function of
the local density of galaxies, which we interpret as being caused by the
truncation of star formation in high density environments. Comparing our
results with those obtained by other authors we find a few discrepancies,
adding to the ongoing debate about the nature of these relations. Finally, we
report that the scatter of the Mg indices versus sigma relations correlate with
Hbeta, suggesting that age may contribute to the scatter. Furthermore, this
scatter shows no significant dependence on morphology or environment. Our
results are consistent with the current downsizing model, where low mass
galaxies have an extended star formation history (abridged).Comment: 88 pages, 24 figures, to be published in AJ, for further information
see http://staff.on.br/ogand
The electron-furfural scattering dynamics for 63 energetically open electronic states
We report on integral-, momentum transfer-and differential cross sections for elastic and electronically inelastic electron collisions with furfural (C5H4O2). The calculations were performed with two different theoretical methodologies, the Schwinger multichannel method with pseudopotentials (SMCPP) and the independent atom method with screening corrected additivity rule (IAM-SCAR) that now incorporates a further interference (I) term. The SMCPP with N energetically open electronic states (N-open) at either the static-exchange (N-open ch-SE) or the static-exchange-plus-polarisation (N-open ch-SEP) approximation was employed to calculate the scattering amplitudes at impact energies lying between 5 eV and 50 eV, using a channel coupling scheme that ranges from the 1ch-SEP up to the 63ch-SE level of approximation depending on the energy considered. For elastic scattering, we found very good overall agreement at higher energies among our SMCPP cross sections, our IAM-SCAR+I cross sections and the experimental data for furan (a molecule that differs from furfural only by the substitution of a hydrogen atom in furan with an aldehyde functional group). This is a good indication that our elastic cross sections are converged with respect to the multichannel coupling effect for most of the investigated intermediate energies. However, although the present application represents the most sophisticated calculation performed with the SMCPP method thus far, the inelastic cross sections, even for the low lying energy states, are still not completely converged for intermediate and higher energies. We discuss possible reasons leading to this discrepancy and point out what further steps need to be undertaken in order to improve the agreement between the calculated and measured cross sections. (C) 2016 AIP Publishing LLC
The first 62 AGN observed with SDSS-IV MaNGA -- III: stellar and gas kinematics
We investigate the effects of Active Galactic Nuclei (AGN) on the gas
kinematics of their host galaxies, using MaNGA data for a sample of 62 AGN
hosts and 109 control galaxies (inactive galaxies). We compare orientation of
the line of nodes (kinematic Position Angle - PA) measured from the gas and
stellar velocity fields for the two samples. We found that AGN hosts and
control galaxies display similar kinematic PA offsets between gas and stars.
However, we note that AGN have larger fractional velocity dispersion
differences between gas and stars [] when compared to their controls, as
obtained from the velocity dispersion values of the central (nuclear) pixel
(2.5" diameter). The AGN have a median value of of
, while the the median value for the control
galaxies is . 75% of the AGN show
, while 75% of the normal galaxies show , thus we suggest that the parameter can be
used as an indicative of AGN activity. We find a correlation between the
[OIII]5007 luminosity and for our sample. Our main
conclusion is that the AGN already observed with MaNGA are not powerful enough
to produce important outflows at galactic scales, but at 1-2 kpc scales, AGN
feedback signatures are always present on their host galaxies.Comment: 19 pages, 8 figures, published in MNRA
StarHorse: A Bayesian tool for determining stellar masses, ages, distances, and extinctions for field stars
Understanding the formation and evolution of our Galaxy requires accurate
distances, ages and chemistry for large populations of field stars. Here we
present several updates to our spectro-photometric distance code, that can now
also be used to estimate ages, masses, and extinctions for individual stars.
Given a set of measured spectro-photometric parameters, we calculate the
posterior probability distribution over a given grid of stellar evolutionary
models, using flexible Galactic stellar-population priors. The code (called
{\tt StarHorse}) can acommodate different observational datasets, prior
options, partially missing data, and the inclusion of parallax information into
the estimated probabilities. We validate the code using a variety of simulated
stars as well as real stars with parameters determined from asteroseismology,
eclipsing binaries, and isochrone fits to star clusters. Our main goal in this
validation process is to test the applicability of the code to field stars with
known {\it Gaia}-like parallaxes. The typical internal precision (obtained from
realistic simulations of an APOGEE+Gaia-like sample) are in
distance, in age, in mass, and mag in
. The median external precision (derived from comparisons with earlier
work for real stars) varies with the sample used, but lies in the range of
for distances, for ages,
for masses, and mag for . We provide StarHorse distances and
extinctions for the APOGEE DR14, RAVE DR5, GES DR3 and GALAH DR1 catalogues.Comment: 21 pages, 12 figures, accepte
Prevalence and molecular characterization of Clostridium difficile isolated from feedlot beef cattle upon arrival and mid-feeding period
<p>Abstract</p> <p>Background</p> <p>The presence of indistinguishable strains of <it>Clostridium difficile </it>in humans, food animals and food, as well as the apparent emergence of the food-animal-associated ribotype 078/toxinotype V as a cause of community-associated <it>C. difficile </it>infection have created concerns about the potential for foodborne infection. While studies have reported <it>C. difficile </it>in calves, studies of cattle closer to the age of harvest are required. Four commercial feedlots in Alberta (Canada) were enrolled for this study. Fecal samples were collected at the time of arrival and after acclimation (< 62, 62-71 or > 71 days on feed). Selective culture for <it>Clostridium difficile </it>was performed, and isolates were characterized by ribotyping and pulsed-field gel electrophoresis. A logistic regression model was built to investigate the effect of exposure to antimicrobial drugs on the presence of <it>C. difficile</it>.</p> <p>Results</p> <p><it>Clostridium difficile </it>was isolated from 18 of 539 animals at the time of feedlot arrival (CI = 2.3-6.1) and from 18 of 335 cattle at mid-feeding period (CI = 2.9-13.1). Overall, there was no significant difference in the prevalence of <it>C. difficile </it>shedding on arrival versus mid-feeding period (<it>P </it>= 0.47). No association between shedding of the bacterium and antimicrobial administration was found (<it>P </it>= 0.33). All the isolates recovered were ribotype 078, a toxinotype V strain with genes encoding toxins A, B and CDT. In addition, all strains were classified as NAP7 by pulsed field gel electrophoresis (PFGE) and had the characteristic 39 base pairs deletion and upstream truncating mutation on the <it>tcd</it>C gene.</p> <p>Conclusions</p> <p>It is apparent that <it>C. difficile </it>is carried in the intestinal tracts of a small percentage of feedlot cattle arriving and later in the feeding period and that ribotype 078/NAP7 is the dominant strain in these animals. Herd management practices associated with <it>C. difficile </it>shedding were not identified, however further studies of the potential role of antimicrobials on <it>C. difficile </it>acquisition and shedding are required.</p
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