T. P. Robitaille

Max Planck Institute for Astronomy, Heidelburg, Baden-Württemberg, Germany

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Publications (129)379.16 Total impact

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    ABSTRACT: The Magellanic Bridge is the nearest low-metallicity, tidally stripped environment, offering a unique high-resolution view of physical conditions in merging and forming galaxies. In this paper we present analysis of candidate massive young stellar objects (YSOs), i.e., {\it in situ, current} massive star formation (MSF) in the Bridge using {\it Spitzer} mid-IR and complementary optical and near-IR photometry. While we definitely find YSOs in the Bridge, the most massive are $\sim10 M_\odot$, $\ll45 M_\odot$ found in the Large Magellanic Cloud (LMC). The intensity of MSF in the Bridge also appears decreasing, as the most massive YSOs are less massive than those formed in the past. To investigate environmental effects on MSF, we have compared properties of massive YSOs in the Bridge to those in the LMC. First, YSOs in the Bridge are apparently less embedded than in the LMC: 81% of Bridge YSOs show optical counterparts, compared to only 56% of LMC sources with the same range of mass, circumstellar dust mass, and line-of-sight extinction. Circumstellar envelopes are evidently more porous or clumpy in the Bridge's low-metallicity environment. Second, we have used whole samples of YSOs in the LMC and the Bridge to estimate the probability of finding YSOs at a given \hi\ column density, N(HI). We found that the LMC has $\sim3\times$ higher probability than the Bridge for N(HI) $>10\times10^{20}$ cm$^{-2}$, but the trend reverses at lower N(HI). Investigating whether this lower efficiency relative to HI is due to less efficient molecular cloud formation, or less efficient cloud collapse, or both, will require sensitive molecular gas observations.
    03/2014; 785(2).
  • Chris Beaumont, Thomas Robitaille, Michelle Borkin
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    ABSTRACT: Glue, written in Python, links visualizations of scientific datasets across many files, allowing for interactive, linked statistical graphics of multiple files. It supports many file formats including common image formats (jpg, tiff, png), ASCII tables, astronomical image and table formats (FITS, VOT, IPAC), and HDF5. Custom data loaders can also be easily added. Glue is highly scriptable and extendable.
    01/2014;
  • Thomas P. Robitaille, Barbara A. Whitney
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    ABSTRACT: In 2006, we made available a set of model spectral energy distributions (SEDs) for young stellar objects (YSOs) that has since been used by the community to model thousands of sources in nearby and more distant star forming regions in the Milky-Way and Magellanic clouds. We describe a new and much larger set of model SEDs that addresses many issues with the original models, such as the coverage of parameter space, the dependence on stellar evolutionary tracks, and is well suited to modelling long-wavelength observations such as those from Herschel. The new models were computed with Hyperion, a new Monte-Carlo radiative transfer code. We present the design of the new set of models and discuss improvements compared to the original models.
    11/2013;
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    ABSTRACT: In order to investigate whether the feedback produced by photo-ionisation has an important effect on the geometry of the circumstellar dust and gas around forming massive stars, we have observed the luminous southern embedded star AFGL 4176 in transitions of NH3 and the hydrogen recombination line H68α. We present our preliminary results, which show a compact H ii region embedded in a parsec-scale (radius ̃ 0.7 pc) rotating envelope/torus. In addition, the H ii region is found to be offset from the centre of the envelope, and the velocity gradient in the ionised gas is not aligned with the rotation axis of the envelope, suggesting complex dynamics and multiplicity.
    11/2013;
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    ABSTRACT: The Spitzer Space Telescope Legacy Program SAGE-SMC allows global studies of resolved stellar populations in the SMC in a different environment than our Galaxy. Using the SAGE-SMC IRAC (3.6-8.0 μm) and MIPS (24 and 70 μm) catalogs and images combined with near-infrared (JHK s ) and optical (UBVI) data, we identified a population of ~1000 intermediate- to high-mass young stellar objects (YSOs) in the SMC (three times more than previously known). Our method of identifying YSO candidates builds on the method developed for the Large Magellanic Cloud by Whitney et al. with improvements based on what we learned from our subsequent studies and techniques described in the literature. We perform (1) color-magnitude cuts based on five color-magnitude diagrams (CMDs), (2) visual inspection of multi-wavelength images, and (3) spectral energy distribution (SED) fitting with YSO models. For each YSO candidate, we use its photometry to calculate a measure of our confidence that the source is not a non-YSO contaminant, but rather a true YSO, based on the source's location in the color-magnitude space with respect to non-YSOs. We use this CMD score and the SED fitting results to define two classes of sources: high-reliability YSO candidates and possible YSO candidates. We found that, due to polycyclic aromatic hydrocarbon emission, about half of our sources have [3.6]-[4.5] and [4.5]-[5.8] colors not predicted by previous YSO models. The YSO candidates are spatially correlated with gas tracers.
    The Astrophysical Journal 11/2013; 778(1):15-. · 6.73 Impact Factor
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    ABSTRACT: We present an overview of the HERschel Inventory of The Agents of Galaxy Evolution (HERITAGE) in the Magellanic Clouds project, which is a Herschel Space Observatory open time key program. We mapped the Large Magellanic Cloud (LMC) and Small Magellanic Cloud (SMC) at 100, 160, 250, 350, and 500 μm with the Spectral and Photometric Imaging Receiver (SPIRE) and Photodetector Array Camera and Spectrometer (PACS) instruments on board Herschel using the SPIRE/PACS parallel mode. The overriding science goal of HERITAGE is to study the life cycle of matter as traced by dust in the LMC and SMC. The far-infrared and submillimeter emission is an effective tracer of the interstellar medium (ISM) dust, the most deeply embedded young stellar objects (YSOs), and the dust ejected by the most massive stars. We describe in detail the data processing, particularly for the PACS data, which required some custom steps because of the large angular extent of a single observational unit and overall the large amount of data to be processed as an ensemble. We report total global fluxes for the LMC and SMC and demonstrate their agreement with measurements by prior missions. The HERITAGE maps of the LMC and SMC are dominated by the ISM dust emission and bear most resemblance to the tracers of ISM gas rather than the stellar content of the galaxies. We describe the point source extraction processing and the criteria used to establish a catalog for each waveband for the HERITAGE program. The 250 μm band is the most sensitive and the source catalogs for this band have ~25,000 objects for the LMC and ~5500 objects for the SMC. These data enable studies of ISM dust properties, submillimeter excess dust emission, dust-to-gas ratio, Class 0 YSO candidates, dusty massive evolved stars, supernova remnants (including SN1987A), H II regions, and dust evolution in the LMC and SMC. All images and catalogs are delivered to the Herschel Science Center as part of the community support aspects of the project. These HERITAGE images and catalogs provide an excellent basis for future research and follow up with other facilities.
    The Astronomical Journal 08/2013; 146(3):62. · 4.97 Impact Factor
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    ABSTRACT: We have updated our publicly available dust radiative transfer code (HOCHUNK3D) to include new emission processes and various 3-D geometries appropriate for forming stars. The 3-D geometries include warps and spirals in disks, accretion hotspots on the central star, fractal clumping density enhancements, and misaligned inner disks. Additional axisymmetric (2-D) features include gaps in disks and envelopes, "puffed-up inner rims" in disks, multiple bipolar cavity walls, and iteration of disk vertical structure assuming hydrostatic equilibrium. We include the option for simple power-law envelope geometry, which combined with fractal clumping, and bipolar cavities, can be used to model evolved stars as well as protostars. We include non-thermal emission from PAHs and very small grains, and external illumination from the interstellar radiation field. The grid structure was modified to allow multiple dust species in each cell; based on this, a simple prescription is implemented to model dust stratification. We describe these features in detail, and show example calculations of each. Some of the more interesting results include the following: 1) Outflow cavities may be more clumpy than infalling envelopes. 2) PAH emission in high-mass stars may be a better indicator of evolutionary stage than the broadband SED slope; and related to this, 3) externally illuminated clumps and high-mass stars in optically thin clouds can masquerade as YSOs. 4) Our hydrostatic equilibrium models suggest that dust settling is likely ubiquitous in T Tauri disks, in agreement with previous observations.
    The Astrophysical Journal Supplement Series 07/2013; 207(2). · 16.24 Impact Factor
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    ABSTRACT: Spitzer surveys of the inner Galactic Plane (GLIMPSE I & II) revealed a promising new diagnostic for identifying actively accreting (proto)stars: extended excess emission in the IRAC 4.5 micron band, believed to trace shocked molecular gas in active protostellar outflows. We will present initial results from our search for extended excess 4.5 micron sources in the outer Galaxy GLIMPSE360 survey, focusing on the area of the survey associated with the Perseus arm.
    06/2013;
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    ABSTRACT: The Spitzer SAGE 8-micron image of the LMC is strongly dominated by interstellar emission from PAH molecules, and offers spatial and brightness dynamic range which far exceeds what is available from spectral-line radio observations. We examine the correlation of this emission with other gas tracers, including the radio lines of CO, HI, and HCO+ as observed by the ATCA and Mopra telescopes, and archival UV absorption spectra of HI and H2 from the HST and FUSE. We show preliminary results of radiative transfer simulations using the HYPERION code aimed at identifying regimes and techniques for using 8-micron emission as a high resolution (sub-pc) tracer of gas density.
    06/2013;
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    K. G. Johnston, D. S. Shepherd, T. P. Robitaille, K. Wood
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    ABSTRACT: This paper aims to investigate the hypothesis that the embedded luminous star AFGL2591-VLA3 (2.3E5Lsun at 3.33kpc) is forming according to a scaled-up version of a low-mass star formation scenario. We present multi-configuration VLA 3.6cm and 7mm, as well as CARMA C18O and 3mm continuum observations to investigate the morphology and kinematics of the ionized gas, dust, and molecular gas around AFGL2591. We also compare our results to ancillary near-IR images, and model the SED and 2MASS image profiles of AFGL2591 using a dust continuum radiative transfer code. The observed 3.6cm images uncover for the first time that the central powering source AFGL2591-VLA3 has a compact core plus collimated jet morphology, extending 4000AU eastward from the central source with an opening angle of <10deg at this radius. However, at 7mm VLA3 does not show a jet morphology, but instead compact (<500AU) emission, some of which (<0.57 mJy of 2.9mJy) is estimated to be from dust. We determine that the momentum rate of the jet is not sufficient to ionize itself via only shocks, and thus a significant portion of the emission is instead likely created in a photoionized wind. The C18O emission uncovers dense entrained material in the outflow(s) from the young stars in the region. The main features of the SED and 2MASS images of AFGL2591-VLA3 are also reproduced by our model dust geometry of a rotationally flattened envelope with and without a disk. The above results are consistent with a picture of massive star formation similar to that seen for low-mass protostars. However, within its envelope, AFGL2591-VLA3 contains at least four other young stars, constituting a small cluster. Therefore it appears that AFGL2591-VLA3 may be able to source its accreting material from a shared gas reservoir while still exhibiting the phenomena expected during the formation of low-mass stars. (Abridged)
    Astronomy and Astrophysics 03/2013; 551(43). · 5.08 Impact Factor
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    ABSTRACT: We present the results of a Nobeyama 45 m H2O maser and NH3 survey of all 94 northern GLIMPSE extended green objects (EGOs), a sample of massive young stellar objects (MYSOs) identified based on their extended 4.5 μm emission. We observed the NH3(1,1), (2,2), and (3,3) inversion lines, and detected emission toward 97%, 63%, and 46% of our sample, respectively (median rms ~ 50 mK). The H2O maser detection rate is 68% (median rms ~ 0.11 Jy). The derived H2O maser and clump-scale gas properties are consistent with the identification of EGOs as young MYSOs. To explore the degree of variation among EGOs, we analyze subsamples defined based on mid-infrared (MIR) properties or maser associations. H2O masers and warm dense gas, as indicated by emission in the higher-excitation NH3 transitions, are most frequently detected toward EGOs also associated with both Class I and II CH3OH masers. Ninety-five percent (81%) of such EGOs are detected in H2O (NH3(3,3)), compared to only 33% (7%) of EGOs without either CH3OH maser type. As populations, EGOs associated with Class I and/or II CH3OH masers have significantly higher NH3 line widths, column densities, and kinetic temperatures than EGOs undetected in CH3OH maser surveys. However, we find no evidence for statistically significant differences in H2O maser properties (such as maser luminosity) among any EGO subsamples. Combining our data with the 1.1 mm continuum Bolocam Galactic Plane Survey, we find no correlation between isotropic H2O maser luminosity and clump number density. H2O maser luminosity is weakly correlated with clump (gas) temperature and clump mass.
    The Astrophysical Journal 01/2013; 764(1):61. · 6.73 Impact Factor
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    ABSTRACT: The goal of the .Astronomy conference series is to bring together astronomers, educators, developers and others interested in using the Internet as a medium for astronomy. Attendance at the event is limited to approximately 50 participants, and days are split into mornings of scheduled talks, followed by 'unconference' afternoons, where sessions are defined by participants during the course of the event. Participants in unconference sessions are discouraged from formal presentations, with discussion, workshop-style formats or informal practical tutorials encouraged. The conference also designates one day as a 'hack day', in which attendees collaborate in groups on day-long projects for presentation the following morning. These hacks are often a way of concentrating effort, learning new skills, and exploring ideas in a practical fashion. The emphasis on informal, focused interaction makes recording proceedings more difficult than for a normal meeting. While the first .Astronomy conference is preserved formally in a book, more recent iterations are not documented. We therefore, in the spirit of .Astronomy, report 'unproceedings' from .Astronomy 4, which was held in Heidelberg in July 2012.
    01/2013;
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    ABSTRACT: The Milky Way is typically thought of as a spiral galaxy, but our understanding of its detailed structure remains vague thanks to our observational vantage point within its disk. Most of what we do know about the Milky Way's three-dimensional geometry comes from velocity-resolved observations of gas and stars. But, recently, it has become possible to combine exquisitely sensitive observations of dust with more traditional kinematically-resolved observations of gas to reveal totally new structures within the Milky Way. In this talk, I will explain why we now believe that some extraordinarily long so-called "infrared dark clouds" are in fact the "bones" of the Galaxy, marking out the true mid-plane of its disk to within less than a few parsecs. We call the long features "bones" thanks to recent numerical simulations of spiral galaxies that show a network of over-dense filaments within and between the arms that resemble an endoskeleton for a galaxy. The talk will highlight how both large surveys and new visualization tools have been critical in this investigation. By way of example, I will argue that the "Nessie" Infrared Dark Cloud is a nearly-continuous, many-hundreds-of-pc-long, ~pc-thick, structure, lying within a few pc of the mid-plane of the MIlky Way.
    01/2013;
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    ABSTRACT: Dust grains in the circumstellar disk, envelope, and outflow regions of Young Stellar Objects (YSOs) evolve from submicron size dust grains that permeate the interstellar medium to kilometer size protoplanets while the protostars they surround progress from collapsing prestellar cores to main sequence stars. We currently model high-resolution Hubble Space Telescope Near Infrared Camera and Multi-Object Spectrometer imaging and polarimetry for a group of four (IRAS04302+2247, IRAS04016+2610, CoKu Tau/1, DG Tau B) Taurus-Auriga YSOs known to span the earliest stellar evolutionary phases (Class I - Class I/II). We use both well-developed 3-D radiative transfer codes and variable dust grain models to sensitively constrain not only the geometry and optical depth of the scattering medium, but also the grain size distribution. We simultaneously fit multi-wavelength (submicron to millimeter) spectral energy distributions (SEDs) for our objects to further constrain the model results. We present data and model YSO polarization, image morphology, and SEDs for varying dust grain models.
    01/2013;
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    ABSTRACT: The star formation characteristics of dense massive clusters are the subject of several observational and theoretical efforts, given their importance in unveiling fundamental aspects such as the slope and upper cutoff of the Initial Mass Function (IMF),and the nature of massive star formation. The degree of success of such methods is limited by the fact that most of the studied clusters are spatially blended or unresolved by current facilities at mid- and far-infrared wavelengths. We present a Bayesian method to study these unresolved clusters using a SED fitting approach that uses a library of pre-computed SED models and archival data from multi-wavelength surveys, making special emphasis on the different beam sizes of the observations. We apply the method to the star-forming complex W43, located in the inner spiral arm of the galaxy and analyze the results in terms of the Luminosity Function (LF), and census of massive stars in this region. We then compare our results to theoretical predictions on the shape of the IMF, and its relation with the young stellar objects LM.
    01/2013;
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    ABSTRACT: We present the first near-IR scattered light detection of the transitional disk associated with the Herbig Ae star MWC 758 using data obtained as part of the Strategic Exploration of Exoplanets and Disks with Subaru, and 1.1 micron HST/NICMOS data. While sub-millimeter studies suggested there is a dust-depleted cavity with r=0.35, we find scattered light as close as 0.1 (20-28 AU) from the star, with no visible cavity at H, K', or Ks. We find two small-scaled spiral structures which asymmetrically shadow the outer disk. We model one of the spirals using spiral density wave theory, and derive a disk aspect ratio of h ~ 0.18, indicating a dynamically warm disk. If the spiral pattern is excited by a perturber, we estimate its mass to be 5+3,-4 Mj, in the range where planet filtration models predict accretion continuing onto the star. Using a combination of non-redundant aperture masking data at L' and angular differential imaging with Locally Optimized Combination of Images at K' and Ks, we exclude stellar or massive brown dwarf companions within 300 mas of the Herbig Ae star, and all but planetary mass companions exterior to 0.5. We reach 5-sigma contrasts limiting companions to planetary masses, 3-4 MJ at 1.0 and 2 MJ at 1.55 using the COND models. Collectively, these data strengthen the case for MWC 758 already being a young planetary system.
    The Astrophysical Journal 12/2012; 762(1). · 6.73 Impact Factor
  • K. G. Johnston, D. S. Shepherd, T. P. Robitaille, K. Wood
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    ABSTRACT: FITS images corresponding to Figs. 5, 6, 9, 11, 12 and 13 in the above paper. Figs. 5 and 6 are, respectively, 3.6 cm and 7mm continuum images taken with the Very Large Array (VLA). Fig. 9 contains ~2.8 and 2.7 mm continuum Combined Array for Research in Millimeter Astronomy (CARMA) images. Figs. 11 and 12 display a CARMA {13}CO image cube, and Fig. 13 presents a CARMA C{18}O image cube. Further details of the observations which produced these images are given in Section 2 of the paper. Note that the {13}CO observations are missing significant flux on extended scales, and are therefore difficult to interpret. (2 data files).
    VizieR Online Data Catalog. 11/2012;
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    ABSTRACT: We present the results of a Nobeyama 45-m water maser and ammonia survey of all 94 northern GLIMPSE Extended Green Objects (EGOs), a sample of massive young stellar objects (MYSOs) identified based on their extended 4.5 micron emission. We observed the ammonia (1,1), (2,2), and (3,3) inversion lines, and detect emission towards 97%, 63%, and 46% of our sample, respectively (median rms ~50 mK). The water maser detection rate is 68% (median rms ~0.11 Jy). The derived water maser and clump-scale gas properties are consistent with the identification of EGOs as young MYSOs. To explore the degree of variation among EGOs, we analyze subsamples defined based on MIR properties or maser associations. Water masers and warm dense gas, as indicated by emission in the higher-excitation ammonia transitions, are most frequently detected towards EGOs also associated with both Class I and II methanol masers. 95% (81%) of such EGOs are detected in water (ammonia(3,3)), compared to only 33% (7%) of EGOs without either methanol maser type. As populations, EGOs associated with Class I and/or II methanol masers have significantly higher ammonia linewidths, column densities, and kinetic temperatures than EGOs undetected in methanol maser surveys. However, we find no evidence for statistically significant differences in water maser properties (such as maser luminosity) among any EGO subsamples. Combining our data with the 1.1 mm continuum Bolocam Galactic Plane Survey, we find no correlation between isotropic water maser luminosity and clump number density. Water maser luminosity is weakly correlated with clump (gas) temperature and clump mass.
    10/2012;
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    ABSTRACT: We present new observations of 34 YSO candidates in the SMC. The anchor of the analysis is a set of Spitzer-IRS spectra, supplemented by groundbased 3-5 micron spectra, Spitzer and NIR photometry, optical spectroscopy and radio data. The sources' SEDs and spectral indices are consistent with embedded YSOs; prominent silicate absorption is observed in the spectra of at least ten sources, silicate emission is observed towards four sources. PAH emission is detected towards all but two sources. Based on band ratios (in particular the strength of the 11.3 micron and the weakness of the 8.6 micron bands) PAH emission towards SMC YSOs is dominated by predominantly small neutral grains. Ice absorption is observed towards fourteen sources in the SMC. The comparison of H2O and CO2 ice column densities for SMC, LMC and Galactic samples suggests that there is a significant H2O column density threshold for the detection of CO2 ice. This supports the scenario proposed by Oliveira et al. (2011), where the reduced shielding in metal-poor environments depletes the H2O column density in the outer regions of the YSO envelopes. No CO ice is detected towards the SMC sources. Emission due to pure-rotational 0-0 transitions of H2 is detected towards the majority of SMC sources, allowing us to estimate rotational temperatures and column densities. All but one source are spectroscopically confirmed as SMC YSOs. Of the 33 YSOs identified in the SMC, 30 sources populate different stages of massive stellar evolution. The remaining three sources are classified as intermediate-mass YSOs with a thick dusty disc and a tenuous envelope still present. We propose one of the sources is a D-type symbiotic system, based on the presence of Raman, H and He emission lines in the optical spectrum, and silicate emission in the IRS-spectrum. This would be the first dust-rich symbiotic system identified in the SMC. (abridged)
    Monthly Notices of the Royal Astronomical Society 10/2012; 428(4). · 5.52 Impact Factor
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    ABSTRACT: We present a self-consistent three-dimensional Monte-Carlo radiative transfer model of the stellar and dust emission in the Milky-Way, and have computed synthetic observations of the 3.6 to 100 microns emission in the Galactic mid-plane. In order to compare the model to observations, we use the GLIMPSE, MIPSGAL, and IRAS surveys to construct total emission spectra, as well as longitude and latitude profiles for the emission. The distribution of stars and dust is taken from the SKY model, and the dust emissivities includes an approximation of the emission from polycyclic aromatic hydrocarbons in addition to thermal emission. The model emission is in broad agreement with the observations, but a few modifications are needed to obtain a good fit. Firstly, by adjusting the model to include two major and two minor spiral arms rather than four equal spiral arms, the fit to the longitude profiles for |l|>30 degrees can be improved. Secondly, introducing a deficit in the dust distribution in the inner Galaxy results in a better fit to the shape of the IRAS longitude profiles at 60 and 100 microns. With these modifications, the model fits the observed profiles well, although it systematically under-estimates the 5.8 and 8.0 microns fluxes. One way to resolve this discrepancy is to increase the abundance of PAH molecules by 50% compared to the original model, although we note that changes to the dust distribution or radiation field may provide alternative solutions. Finally, we use the model to quantify which stellar populations contribute the most to the heating of different dust types, and which stellar populations and dust types contribute the most to the emission at different wavelengths.
    Astronomy and Astrophysics 08/2012; · 5.08 Impact Factor

Publication Stats

1k Citations
379.16 Total Impact Points

Institutions

  • 2011–2014
    • Max Planck Institute for Astronomy
      Heidelburg, Baden-Württemberg, Germany
    • The University of Arizona
      • Department of Astronomy
      Tucson, Arizona, United States
    • Keele University
      • Department of Physics and Astrophysics
      Newcastle-under-Lyme, England, United Kingdom
    • University of Texas at Austin
      • Department of Astronomy
      Austin, Texas, United States
  • 2013
    • Japan Aerospace Exploration Agency
      • Institute of Space and Astronautical Science (ISAS)
      Chōfu, Tōkyō, Japan
    • University College London
      • Department of Physics and Astronomy
      Londinium, England, United Kingdom
  • 2012
    • Leiden University
      • Leiden Observartory
      Leyden, South Holland, Netherlands
  • 2009–2012
    • Harvard-Smithsonian Center for Astrophysics
      • Smithsonian Astrophysical Observatory
      Cambridge, Massachusetts, United States
  • 2004–2009
    • University of St Andrews
      • School of Physics and Astronomy
      Saint Andrews, SCT, United Kingdom
  • 2008
    • University of Wisconsin, Madison
      • Department of Astronomy
      Mississippi, United States
  • 2007–2008
    • Scottish Universities Physics Alliance
      Glasgow, Scotland, United Kingdom