1,160 research outputs found
The AGN dusty torus as a clumpy two-phase medium: radiative transfer modeling with SKIRT
We modeled the AGN dusty torus as a clumpy two-phase medium, with
high-density clumps embedded in a low-density interclump dust. To obtain
spectral energy distributions and images of the torus at different wavelengths,
we employed the 3D Monte Carlo radiative transfer code SKIRT. Apart from the
grid of two-phase models, we calculated the corresponding sets of clumps-only
models and models with a smooth dust distribution for comparison. We found that
the most striking feature of the two-phase model is that it might offer a
natural solution to the common issue reported in a number of papers -- the
observed excess of the near-infrared emission.Comment: Proceedings of the Torus Workshop 2012 held at the University of
Texas at San Antonio, 5-7 December 2012. C. Packham, R. Mason, and A.
Alonso-Herrero (eds.). 8 pages, 5 figures. A grid of model SEDs available at
https://sites.google.com/site/skirtorus
AGN Dusty Tori as a Clumpy Two-Phase Medium: The 10 Micron Silicate Feature
We investigated the emission of active galactic nuclei dusty tori in the
infrared domain, with a focus on the 10 micron silicate feature. We modeled the
dusty torus as a clumpy two-phase medium with high-density clumps and a
low-density medium filling the space between the clumps. We employed a
three-dimensional radiative transfer code to obtain spectral energy
distributions and images of tori at different wavelengths. We calculated a grid
of models for different parameters and analyzed the influence of these
parameters on the shape of the mid-infrared emission. A corresponding set of
clumps-only models and models with a smooth dust distribution is calculated for
comparison. We found that the dust distribution, the optical depth and a random
arrangement of clumps in the innermost region, all have an impact on the shape
and strength of the silicate feature. The 10 micron silicate feature can be
suppressed for some parameters, but models with smooth dust distribution are
also able to produce a wide range of the silicate feature strength.Comment: 5 pages, 2 figures. Proceedings of the "8th Serbian Conference on
Spectral Line Shapes in Astrophysics", Divcibare, Serbia, June 6-10 2011.
Model SEDs available for download at https://sites.google.com/site/skirtorus
A new view on the ISM of galaxies: far-infrared and submillimetre spectroscopy with Herschel
The FIR/submm window is amongst the least explored spectral regions of the
electromagnetic spectrum. It is, however, a key to study the general properties
of the interstellar medium of galaxies, as it contains important spectral line
diagnostics from the neutral, ionized and molecular ISM. The Herschel Space
Observatory, successfully launched on 14 May 2009, is the first observatory to
cover the entire FIR/submm range between 57 and 672 mum. We discuss the main
results from the ISO era on FIR spectroscopy of galaxies and the enormous
science potential of the Herschel mission through a presentation of its
spectroscopic extragalactic key programs.Comment: 10 pages, 4 figures, accepted for publication in New Astronomy
Review
A low-frequency study of recently identified double-double radio galaxies
In order to understand the possible mechanisms of recurrent jet activity in
radio galaxies and quasars, which are still unclear, we have identified such
sources with a large range of linear sizes (220 917 kpc), and hence time
scales of episodic activity. Here we present high-sensitivity 607-MHz Giant
Metrewave Radio Telescope (GMRT) images of 21 possible double-double radio
galaxies (DDRGs) identified from the FIRST survey to confirm their episodic
nature. These GMRT observations show that none of the inner compact components
suspected to be hot-spots of the inner doubles are cores having a flat radio
spectrum, confirming the episodic nature of these radio sources. We have
indentified a new DDRG with a candidate quasar, and have estimated the upper
spectral age limits for eight sources which showed marginal evidence of
steepening at higher frequencies. The estimated age limits (11 52 Myr) are
smaller than those of the large-sized ( 1 Mpc) DDRGs.Comment: Accepted for publication in MNRAS. 14 pages, 7 figure
Discovery of a red quasar with recurrent activity
We report a new double-double radio quasar, DDRQ, J07464526 which exhibits
two cycles of episodic activity. From radio continuum observations at 607 MHz
using the GMRT and 1400 MHz from the FIRST survey we confirm its episodic
nature. We examine the SDSS optical spectrum and estimate the black hole mass
to be (8.20.3)10M from its observed MgII emission
line, and the Eddington ratio to be 0.03. The black hole mass is significantly
smaller than for the other reported DDRQ, J0935+0204, while the Eddington
ratios are comparable. The SDSS spectrum is significantly red continuum
dominated suggesting that it is highly obscured with
mag. This high obscuration further indicates the
existence of a large quantity of dust and gas along the line of sight, which
may have a key role in triggering the recurrent jet activity in such objects.Comment: 5 pages, 3 figures, 1 table. Accepted for publication in Ap
The Herschel exploitation of local galaxy Andromeda (HELGA) V: Strengthening the case for substantial interstellar grain growth
In this paper we consider the implications of the distributions of dust and
metals in the disc of M31. We derive mean radial dust distributions using a
dust map created from Herschel images of M31 sampling the entire far-infrared
(FIR) peak. Modified blackbodies are fit to approximately 4000 pixels with a
varying, as well as a fixed, dust emissivity index (beta). An overall metal
distribution is also derived using data collected from the literature. We use a
simple analytical model of the evolution of the dust in a galaxy with dust
contributed by stellar sources and interstellar grain growth, and fit this
model to the radial dust-to-metals distribution across the galaxy. Our analysis
shows that the dust-to-gas gradient in M31 is steeper than the metallicity
gradient, suggesting interstellar dust growth is (or has been) important in
M31. We argue that M31 helps build a case for cosmic dust in galaxies being the
result of substantial interstellar grain growth, while the net dust production
from stars may be limited. We note, however, that the efficiency of dust
production in stars, e.g., in supernovae (SNe) ejecta and/or stellar
atmospheres, and grain destruction in the interstellar medium (ISM) may be
degenerate in our simple model. We can conclude that interstellar grain growth
by accretion is likely at least as important as stellar dust production
channels in building the cosmic dust component in M31.Comment: 12 pages, 7 figures. Published in MNRAS 444, 797. This version is
updated to match the published versio
A novel panel of mouse models to evaluate the role of human pregnane X receptor and constitutive androstane receptor in drug response
The pregnane X receptor (PXR) and the constitutive androstane receptor (CAR) are closely related orphan nuclear hormone receptors that play a critical role as xenobiotic sensors in mammals. Both receptors regulate the expression of genes involved in the biotransformation of chemicals in a ligand-dependent manner. As the ligand specificity of PXR and CAR have diverged between species, the prediction of in vivo PXR and CAR interactions with a drug are difficult to extrapolate from animals to humans. We report the development of what we believe are novel PXR- and CAR-humanized mice, generated using a knockin strategy, and Pxr- and Car-KO mice as well as a panel of mice including all possible combinations of these genetic alterations. The expression of human CAR and PXR was in the predicted tissues at physiological levels, and splice variants of both human receptors were expressed. The panel of mice will allow the dissection of the crosstalk between PXR and CAR in the response to different drugs. To demonstrate the utility of this panel of mice, we used the mice to show that the in vivo induction of Cyp3a11 and Cyp2b10 by phenobarbital was only mediated by CAR, although this compound is described as a PXR and CAR activator in vitro. This panel of mouse models is a useful tool to evaluate the roles of CAR and PXR in drug bioavailability, toxicity, and efficacy in humans
Investigating the potential for genetic selection of dairy calf disease traits using management data.
Genetic selection could be a tool to help improve the health and welfare of calves, however, to date, there is limited research on the genetics of calfhood diseases. This study aimed to understand the current impact of calf diseases, by investigating incidence rates, estimating genetic parameters, and providing industry recommendations to improve calf disease recording practices on farms. Available calf disease data comprised of 69,695 Holstein calf disease records for respiratory problems (RESP) and diarrhea (DIAR), from 62,361 calves collected on 1,617 Canadian dairy herds from 2006 to 2021. Single and multiple trait analysis using both a threshold and linear animal model for each trait were evaluated. Furthermore, each trait was analyzed using 2 scenarios with respect to minimum disease incidence threshold criterion (herd-year incidence of at least 1% and 5%) to highlight the impact of different filtering thresholds on selection potential. Observed scale heritability estimates for RESP and DIAR ranged from 0.02 to 0.07 across analyses, while estimated genetic correlations between the traits ranged from 0.50 to 0.62. Sires were compared based on their estimated breeding value and their diseased daughter incidence rates. On average, calves born to the bottom 10% of sires were 1.8 times more likely to develop RESP and 1.9 times to develop DIAR compared with daughters born to the top 10% of sires. Results from the current study are promising for the inclusion of both DIAR and RESP in Canadian genetic evaluations. However, for effective genetic evaluation we require standardized approaches on data collection and industry outreach to highlight the importance of collecting and uploading this information to herd management software. In particular, it is important that the herd management software is accessible to the national milk recording system to allow for use in national genetic evaluation
Review: Opportunities and challenges for the genetic selection of dairy calf disease traits.
Interest in dairy cow health continues to grow as we better understand health's relationship with production potential and animal welfare. Over the past decade, efforts have been made to incorporate health traits into national genetic evaluations. However, they have focused on the mature cow, with calf health largely being neglected. Diarrhoea and respiratory disease comprise the main illnesses with regard to calf health. Conventional methods to control calf disease involve early separation of calves from the dam and housing calves individually. However, public concern regarding these methods, and growing evidence that these methods may negatively impact calf development, mean the dairy industry may move away from these practices. Genetic selection may be a promising tool to address these major disease issues. In this review, we examined current literature for enhancing calf health through genetics and discussed alternative approaches to improve calf health via the use of epidemiological modelling approaches, and the potential of indirectly selecting for improved calf health through improving colostrum quality. Heritability estimates on the observed scale for diarrhoea ranged from 0.03 to 0.20, while for respiratory disease, estimates ranged from 0.02 to 0.24. The breadth in these ranges is due, at least in part, to differences in disease prevalence, population structure, data editing and models, as well as data collection practices, which should be all considered when comparing literature values. Incorporation of epidemiological theory into quantitative genetics provides an opportunity to better determine the level of genetic variation in disease traits, as it accounts for disease transmission among contemporaries. Colostrum intake is a major determinant of whether a calf develops either respiratory disease or diarrhoea. Colostrum traits have the advantage of being measured and reported on a continuous scale, which removes the issues classically associated with binary disease traits. Overall, genetic selection for improved calf health is feasible. However, to ensure the maximum response, first steps by any industry members should focus efforts on standardising recording practices and encouragement of uploading information to genetic evaluation centres through herd management software, as high-quality phenotypes are the backbone of any successful breeding programme
The Herschel Virgo Cluster Survey XVI: a cluster inventory
Herschel FIR observations are used to construct Virgo cluster galaxy
luminosity functions and to show that the cluster lacks the very bright and the
numerous faint sources detected in field galaxy surveys. The far-infrared SEDs
are fitted to obtain dust masses and temperatures and the dust mass function.
The cluster is over dense in dust by about a factor of 100 compared to the
field. The same emissivity (beta) temperature relation applies for different
galaxies as that found for different regions of M31. We use optical and HI data
to show that Virgo is over dense in stars and atomic gas by about a factor of
100 and 20 respectively. Metallicity values are used to measure the mass of
metals in the gas phase. The mean metallicity is about 0.7 solar and 50% of the
metals are in the dust. For the cluster as a whole the mass density of stars in
galaxies is 8 times that of the gas and the gas mass density is 130 times that
of the metals. We use our data to consider the chemical evolution of the
individual galaxies, inferring that the measured variations in effective yield
are due to galaxies having different ages, being affected to varying degrees by
gas loss. Four galaxy scaling relations are considered: mass-metallicity,
mass-velocity, mass-star formation rate and mass-radius - we suggest that
initial galaxy mass is the prime driver of a galaxy's ultimate destiny.
Finally, we use X-ray observations and galaxy dynamics to assess the dark and
baryonic matter content compared to the cosmological model
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