18 research outputs found
SKIRT: hybrid parallelization of radiative transfer simulations
We describe the design, implementation and performance of the new hybrid
parallelization scheme in our Monte Carlo radiative transfer code SKIRT, which
has been used extensively for modeling the continuum radiation of dusty
astrophysical systems including late-type galaxies and dusty tori. The hybrid
scheme combines distributed memory parallelization, using the standard Message
Passing Interface (MPI) to communicate between processes, and shared memory
parallelization, providing multiple execution threads within each process to
avoid duplication of data structures. The synchronization between multiple
threads is accomplished through atomic operations without high-level locking
(also called lock-free programming). This improves the scaling behavior of the
code and substantially simplifies the implementation of the hybrid scheme. The
result is an extremely flexible solution that adjusts to the number of
available nodes, processors and memory, and consequently performs well on a
wide variety of computing architectures.Comment: 21 pages, 20 figure
Radiative transfer in disc galaxies V. The accuracy of the KB approximation
We investigate the accuracy of an approximate radiative transfer technique
that was first proposed by Kylafis & Bahcall (hereafter the KB approximation)
and has been popular in modelling dusty late-type galaxies. We compare
realistic galaxy models calculated with the KB approximation with those of a
three-dimensional Monte Carlo radiative transfer code SKIRT. The SKIRT code
fully takes into account of the contribution of multiple scattering whereas the
KB approximation calculates only single scattered intensity and multiple
scattering components are approximated. We find that the KB approximation gives
fairly accurate results if optically thin, face-on galaxies are considered.
However, for highly inclined () and/or optically thick
(central face-on optical depth ) galaxy models, the approximation can
give rise to substantial errors, sometimes, up to . Moreover, it
is also found that the KB approximation is not always physical, sometimes
producing infinite intensities at lines of sight with high optical depth in
edge-on galaxy models. There is no "simple recipe" to correct the errors of the
KB approximation that is universally applicable to any galaxy models.
Therefore, it is recommended that the full radiative transfer calculation be
used, even though it's slower than the KB approximation.Comment: 10 pages, 6 figures, accepted for publication in MNRA
Measuring the dust content and formation in SN 1987A using detailed radiative transfer modelling
AbstractCore-collapse supernovae are expected to be efficient producers of dust, and recent Herschel and ALMA observations have revealed up to 1 M⊙ of cold dust in the inner ejecta of SN 1987A. The formation time scale, spatial distribution and clumpiness, and the importance of the different heating sources of the dust remain poorly understood. We have started a project to make detailed 3D dust radiative transfer models for SN 1987A, based on a combination of the latest observational constraints and input from 3D hydrodynamical models and dust formation models. Preliminary results seem to indicate the need for large, micron-sized dust grains, and a relatively large dust mass.</jats:p
High-resolution radiative transfer modelling of M33
The authors thank the anonymous reviewer, whose comments
have certainly improved the manuscript. The authors also thank
Peter Camps for valuable technical advice, along with all of
the participants at the recent SKIRT meeting for comments and
discussions. I.D.L. gratefully acknowledges the supports of the
Research Foundation – Flanders (FWO). M.W.L.S acknowledges
funding from the UK Science and Technology Facilities Council
consolidated grant ST/K000926/1. M.R. acknowledges support by
the research projects AYA2014-53506-P and AYA2017-84897P
from the Spanish Ministerio de Econom´ıa y Competitividad. This
research made use of MONTAGE (http://montage.ipac.caltech.edu/),
which is funded by the National Science Foundation under Grant
Number ACI-1440620, and was previously funded by the National
Aeronautics and Space Administration’s Earth Science Technology
Office, Computation Technologies Project, under Cooperative
Agreement Number NCC5-626 between NASA and the California
Institute of Technology. This research has made use of Astropy, a community-developed core PYTHON package for Astronomy (http:
//www.astropy.org/; Astropy Collaboration et al. 2013, 2018). This
research has made use of NumPy (http://www.numpy.org/; van der
Walt, Colbert & Varoquaux 2011), SciPy (http://www.scipy.org/),
andMatPlotLib (http://matplotlib.org/; Hunter 2007). This research
made use of APLpy, an open-source plotting package for PYTHON
(https://aplpy.github.io/; Robitaille & Bressert 2012).In this work, we characterize the contributions from both ongoing star formation and the
ambient radiation field in Local Group galaxy M33, as well as estimate the scale of the local
dust-energy balance (i.e. the scale at which the dust is re-emitting starlight generated in that
same region) in this galaxy through high-resolution radiative transfer (RT) modelling, with
defined stellar and dust geometries. We have characterized the spectral energy distribution
(SED) of M33 from UV to sub-mm wavelengths, at a spatial scale of 100 pc. We constructed
input maps of the various stellar and dust geometries for use in the RTmodelling. By modifying
our dust mix (fewer very small carbon grains and a lower silicate-to-carbon ratio as compared
to the Milky Way), we can much better fit the sub-mm dust continuum. Using this new dust
composition, we find that we are able to well reproduce the observed SED of M33 using our
adopted model. In terms of stellar attenuation by dust, we find a reasonably strong, broad
UV bump, as well as significant systematic differences in the amount of dust attenuation
when compared to standard SED modelling.We also find discrepancies in the residuals of the
spiral arms versus the diffuse interstellar medium (ISM), indicating a difference in properties
between these two regimes. The dust emission is dominated by heating due to the young stellar
populations at all wavelengths (∼80 per cent at 10 μm to ∼50 per cent at 1 mm). We find that
the local dust-energy balance is restored at spatial scales greater than around 1.5 kpc.Funding from the UK Science and Technology Facilities Council consolidated grant ST/K000926/1. M.R. acknowledges support by the research projects AYA2014-53506-P and AYA2017-84897P from the Spanish Ministerio de Economía y Competitividad. This research made use of MONTAGE (http://montage.ipac.caltech.edu/), which is funded by the National Science Foundation under Grant Number ACI-1440620, and was previously funded by the National Aeronautics and Space Administration’s Earth Science Technology Office, Computation Technologies Project, under Cooperative Agreement Number NCC5-626 between NASA and the California Institute of Technolog
The first maps of κd - the dust mass absorption coefficient - in nearby galaxies, with DustPedia
The dust mass absorption coefficient, κd is the conversion function used to infer physical dust masses from observations of dust emission. However, it is notoriously poorly constrained, and it is highly uncertain how it varies, either between or within galaxies. Here we present the results of a proof-of-concept study, using the DustPedia data for two nearby face-on spiral galaxies M 74 (NGC 628) and M 83 (NGC 5236), to create the first ever maps of κd in galaxies. We determine κd using an empirical method that exploits the fact that the dust-to-metals ratio of the interstellar medium is constrained by direct measurements of the depletion of gas-phase metals. We apply this method pixel-by-pixel within M 74 and M 83, to create maps of κd. We also demonstrate a novel method of producing metallicity maps for galaxies with irregularly sampled measurements, using the machine learning technique of Gaussian process regression. We find strong evidence for significant variation in κd. We find values of κd at 500 μm spanning the range 0.11-0.25 m^{2 kg^{-1}} in M 74, and 0.15-0.80 m^{2 kg^{-1}} in M 83. Surprisingly, we find that κd shows a distinct inverse correlation with the local density of the interstellar medium. This inverse correlation is the opposite of what is predicted by standard dust models. However, we find this relationship to be robust against a large range of changes to our method - only the adoption of unphysical or highly unusual assumptions would be able to suppress it
Herschel observations of edge-on spirals (Heroes) IV. Dust energy balance problem
We present results of the detailed dust energy balance study for the seven large edge-on galaxies in the HEROES sample using three-dimensional (3D) radiative transfer (RT) modelling. Based on available optical and near-infrared (NIR) observations of the HEROES galaxies, we derive the 3D distribution of stars and dust in these galaxies. For the sake of uniformity, we apply the same technique to retrieve galaxy properties for the entire sample: we use a stellar model consisting of a Sérsic bulge and three double-exponential discs (a superthin disc for a young stellar population and thin and thick discs for old populations). For the dust component, we adopt a double-exponential disc with the new THEMIS dust-grain model. We fit oligochromatic RT models to the optical and NIR images with the fitting algorithm fitskirt and run panchromatic simulations with the skirt code at wavelengths ranging from ultraviolet to submillimeter. We confirm the previously stated dust energy balance problem in galaxies: for the HEROES galaxies, the dust emission derived from our RT calculations underestimates the real observations by a factor 1.5-4 for all galaxies except NGC 973 and NGC 5907 (apparently, the latter galaxy has a more complex geometry than we used). The comparison between our RT simulations and the observations at mid-infrared-submillimetre wavelengths shows that most of our galaxies exhibit complex dust morphologies (possible spiral arms, star-forming regions, more extended dust structure in the radial and vertical directions). We suggest that, in agreement with results from the literature, the large- and small-scale structure is the most probable explanation for the dust energy balance problem
High-resolution, 3D radiative transfer modelling : IV. AGN-powered dust heating in NGC 1068
The star formation rate and the mass of interstellar medium (ISM) have a high predictive power for the future evolution of a galaxy. Nevertheless, deriving such properties is not straightforward. Dust emission, an important diagnostic of star formation and ISM mass throughout the Universe, can be powered by sources unrelated to ongoing star formation. In the framework of the DustPedia project we set out to disentangle the radiation of the ongoing star formation from that of the older stellar populations. This is done through detailed 3D radiative transfer simulations of face-on spiral galaxies. We take special care in modelling the morphological features present for each source of radiation. In this particular study, we focus on NGC 1068, which in addition contains an active galactic nucleus (AGN). The effect of diffuse dust heating by an AGN (beyond the torus) has so far only been investigated for quasars. This additional dust heating source further contaminates the broadband fluxes that are used by classic galaxy modelling tools to derive physical properties. We aim to fit a realistic model to the observations of NGC 1068 and quantify the contribution of the several dust-heating sources. Our model is able to reproduce the global spectral energy distribution of the galaxy. It matches the resolved optical and infrared images fairly well, but deviates in the UV and the submillimetre (submm). This is partly due to beam smearing effects, but also because the input dust distribution is not sufficiently peaked in the centre. We find that AGN contamination of the broadband fluxes has a strong dependency on wavelength. It peaks in the mid-infrared, drops in the far-infrared, and then rises again at submm wavelengths. We quantify the contribution of the dust-heating sources in each 3D dust cell and find a median value of 83% for the star formation component. The AGN contribution is measurable at the percentage level in the disc, but quickly increases in the inner few hundred parsecs, peaking above 90%. This is the first time the phenomenon of an AGN heating the diffuse dust beyond its torus is quantified in a nearby star-forming galaxy. NGC 1068 only contains a weak AGN, meaning this effect could be stronger in galaxies with a more luminous AGN. This could significantly impact the derived star formation rates and ISM masses for such systems
HERschel Observations of Edge-on Spirals (HEROES). IV. Dust energy balance problem
We present results of the detailed dust energy balance study for the seven
large edge-on galaxies in the HEROES sample using 3D radiative transfer (RT)
modelling. Based on available optical and near-infrared observations of the
HEROES galaxies, we derive the 3D distribution of stars and dust in these
galaxies. For the sake of uniformity, we apply the same technique to retrieve
galaxy properties for the entire sample: we use a stellar model consisting of a
S\'ersic bulge and three double-exponential discs (a superthin disc for a young
stellar population and thin and thick discs for old populations). For the dust
component, we adopt a double-exponential disc with the new THEMIS dust-grain
model. We fit oligochromatic radiative transfer (RT) models to the optical and
near-infrared images with the fitting algorithm FitSKIRT and do panchromatic
simulations with the SKIRT code at wavelengths ranging from ultraviolet to
submillimeter. We confirm the previously stated dust energy balance problem in
galaxies: for the HEROES galaxies, the dust emission derived from our RT
calculations underestimates the real observations by a factor 1.5-4 for all
galaxies except NGC 973 and NGC 5907 (apparently, the latter galaxy has a more
complex geometry than we used). The comparison between our RT simulations and
the observations at mid-infrared-submillimeter wavelengths shows that most of
our galaxies exhibit complex dust morphologies (possible spiral arms,
star-forming regions, more extended dust structure in the radial and vertical
directions). We suggest that, in agreement with the results from Saftly et al.
(2015), the large- and small-scale structure is the most probable explanation
for the dust energy balance problem.Comment: 53 pages, 31 figures, Accepted for publication in Astronomy &
Astrophysic