Latest News from the Sites

The primary DustPedia data set now consists of 835 galaxies extracted from the Herschel database fully reduced and calibrated by us in a uniform way. In addition we have assembled ancillary data from other data bases that provides data from the ultra-violet to the sub-mm. The result is just over 25,000 multi-wavelength images of galaxies. We have also carried out fully aperture-matched photometry of all the galaxies in all bands so that each galaxy has an extensive SED that can now be used to explore our science objectives (Fig. 1).

All the data has been supplied to the DustPedia database (see below). We are also looking at the distribution of dust above the plane of edge-on galaxies by the stacking of numerous images and investigating the effect of the local environment on the properties of galaxies in the sample.

Fig. 1 – Normalised spectra of DustPedia galaxies colour coded by morphological type.

The DustPedia Database

Within the framework of the DustPedia project we are in the process of constructing the DustPedia database (a work in progress until the end of the DustPedia project - April 2018). The Database will consist of all of the derived quantities, for each of the galaxies, from our models as well as all the available multi-wavelength observations and photometry for each galaxy.

The Data

The link "Data" on the left side of the Database website re-directs to a search page where the user can look for available observations in the database. The user can search with Galaxy Name, Hubble Stage (T), Velocity (in km/s), Inclination Angle (in degrees), and size (D25 in arcmin). In each search parameter the user can define the range desired but also have the option to define only the lower or the higher limit. A "show all results in a single page" button allows the user to print all results on a single page. The data hosted in the archive, so far, are all the available maps for the DustPedia sample coming from the GALEX, SDSS, DSS, 2MASS, WISE, Spitzer, Herschel, and Planck surveys. Photometry cut-outs (in .png format) is available for every galaxy showing the exact aperture used for the photometry, per band, as well as the annulus used to calculate the background.

The Photometry

The link "Photometry" on the left side of the Database website provides the relevant tables (.csv format) with the photometry for each DustPedia galaxy. The relevant "Photometry Release Notes" document, describing the details of the photometric analysis is also given.

The SED Model

The link "SED Model" on the left side of the Database website re-directs to the page where the results from our hierarchical Bayesian dust SED model, called HerBIE (A LINK TO HERBIE IF AVAILABLE) (HiERarchical Bayesian Inference for dust Emission; Galliano 2017). This part is under construction.

The RT Model

The link "RT Model" on the left side of the Database website re-directs to the page where the results from our Monte Carlo Radiative Transfer code, called SKIRT (http://users.ugent.be/~mbaes/SKIRT.html) (Stellar Kinematics Including Radiative Transfer; Baes et al. 2003; Baes et al. 2011). This part is under construction. The Database can be accessed here.

The Ghent team continue to develop the SKIRT numerical radiative transfer model. SKIRT is a state-of-the-art software code for simulating continuum radiation transfer in dusty astrophysical systems, such as galaxies and accretion disks. SKIRT employs the Monte Carlo technique to emulate the relevant physical processes including scattering, absorption and emission by the dust. The code features a wealth of built-in geometries, light source spectra, dust characterizations, dust grids, and detectors, in addition to various mechanisms for importing models generated by hydrodynamical simulations. The configuration for a particular simulation is defined at either at runtime with a user-friendly command-line interface, or with a graphical interface called SkirtMakeUp. More details on SKIRT can be found at: http://www.skirt.ugent.be/website/index.html. Recent developments include our first attempts at modelling face-on galaxies (Fig. 2) and the interpretation of spectral energy distributions (Fig. 3).
Fig. 2. Left - images of M51 from the ultra-violet to the far-infrared. Centre – SKIRT radiative transfer models. Right – the residual after subtracting the model from the observation.
Fig. 3 A SKIRT fit to the spectral energy distribution of IC2531 – the black line is using our own THEMIS dust model (see below).

We continue our development of the THEMIS physical dust model (see: http://www.ias.u-psud.fr/themis/). Dust within the THEMIS model is principally comprised of large carbon-coated amorphous silicate grains and small hydro- carbonaceous grains (Fig. 4). The model was initially developed to investigate the nature of dust in the diffuse ISM and successfully explains the observed NIR-FUV extinction, IR- mm dust thermal emission and the shape of the IR emission bands. The model has also successfully confronted the latest available measures of the diffuse ISM dust extinction and emission in the Milky Way. The THEMIS model has now been fully incorporated within our radiative transfer modeling (see above) and within our Bayesian spectral energy fitting method (see below).

Fig. 4. Schematic view of the dust composition and stratification between diffuse ISM and dense molecular clouds in the THEMIS dust model. The major evolutionary processes acting on the dust in each region are indicated on the right, i.e., photo-processing, accretion, and coagulation with increasing density and extinction from top to bottom

In constructing the Spectral Energy Distribution (SED) fitting model, CEA has developed a Bayesian approach to the full SED modeling for DustPedia galaxies. Several relevant latest dust mixtures (Zubko et al., 2004, BARE-GR-S; Galliano et al., 2011, AC; Compiègne et al., 2011; Jones et al., 2013, THEMIS), have been incorporated into the CEA HerBIE SED model (HiERarchical Bayesian Inference for dust Emission). HerBIE is a numerically intensive code, requiring several billions of SED model calculations per run. It has therefore been optimized by interpolating a large grid of pre-computed SED models. These pre-computed grids are a collection of physically-characterized SED templates which are then built upon to describe complete galaxy SEDs. As part of the tasks surrounding this work package, we have built grids for numerous astrophysically relevant dust models: equilibrium grain emission for several solid compounds, modified black bodies, uniformly illuminated dust mixtures, non-uniformly illuminated dust mixtures, etc. These libraries of models give the spectral emission from UV to radio as well as the synthetic photometry in the mostly used broadband filters, for a given combination of physical parameters (Fig. 5).

Fig. 5. Comparison of the various dust models. The left panel shows the emission per dust mass and the right panel per H atom. The representation of the left panel is more relevant when using these models to fit other regions, while the representation of the right panel is more relevant in terms of calibration of the model.

As well as carrying out, in close collaboration with the Cardiff group, detailed quality checks on the DustPedia data we have also been exploring the varying radial distributions of dust, gas and star formation rate in a sub-sample (18) of face-on DustPedia galaxies. We have exploited the multi-wavelength, from ultraviolet (UV) to sub-millimeter bands, DustPedia database, in addition to millimeter and centimeter maps and metallicity abundance information available in literature. We fitted the surface brightness profiles of the tracers of dust and stars, the mass surface density profiles of dust, stars, molecular gas, and total gas, and the SFR surface density with an exponential curve and derived their exponential scale-lengths. How the normalized scale length varies with wavelength and different components of the ISM can be seen in Fig.6. We have also developed a method to solve for the CO-to-H2 conversion factor (αCO) per galaxy by using dust and gas mass profiles.

Fig. 6 Mean scale-length normalized with respect to r25 of all sample galaxies as a function of wavelength.

DustPedia data can be accessed at this LINK. View the acknowledgement page to correctly credit the project.

Post docs

The IAS has recently recruited two post docs. to the DustPedia dust modelling team:

Gururaj Wagle started a two-year post doc. on the 1st September (100% at the IAS) and will be working on PDR dust modelling using THEMIS coupled to the radiative transfer code CRT. He has already started modelling the Horsehead Nebula PDR. He could not be at the meeting because of a conflict with the interview for his work visa. He will be at the Athens meeting.

Marco Bocchio started a one-year post doc. on the 1st October (based at the Arcetri node but spending the month of October at the IAS and then one week per month thereafter). Weekly video-conferences with Marco have ben arranged. Marco will work on dust evolution in HII regions and PDRs and, in particular the effect of grain charge and hard photons on the evolution of carbonaceous nano-particles. He will also follow up on Aurelie’s work on the 2 or 3 phase ISM `toy’ model and spend some time on dust sources and sinks modelling. In the latter case on the as yet poorly determined ISM dust formation/growth aspects. He is also working on the Hershel PSF re-construction. 

Dissemination and publicising DustPedia

The IAS team has been active in promoting DustPedia at a number of conferences and workshops this year:

Aurelie (talk) - Gas, Dust, and Star-Formation in Galaxies. May 25-29, 2015, Crete

Ant, Aurelie, Melanie & Nathalie (each of us gave a talk & Ant gave a general seminar) - Two-day workshop at MPE Garching 

Ant - Two-day discussion meeting at Yerkes Observatory, USA. Wide-ranging discussions about all aspects of dust among the participants (Don York - organiser, Al Harper, Lew Hobbs, Aigen Li, Takeshi Oka, Steve Sibner - chemist, Greg Sloan, Dan Welty, Adolf Witt)

Ant (invited talk) - IAU, Focus Meeting 12 - Bridging Laboratory Astrophysics and Astronomy. August 3-5, 2015, Honolulu, Hawaii. 

Continuing projects

The dust modelling at the IAS is now being developed under the umbrella acronym THEMIS (The Heterogeneous dust Evolution Model at the IaS). 

Melanie, Nathalie and Ant are further developing the dust model in its application to dust in denser regions. This has led to two papers on cloud- and core-shone recently submitted to A&A on dust evolution in the outer regions of molecular clouds. The model results are consistent with the observations, which impose significant constraints on the nature of dust evolution as a function of the local density and radiation field. 

Melanie is also working on applying the dust model to circumstellar discs.  

Guru is taking the lead on modelling the Horsehead PDR using the appropriate radiation field and exploring dust evolution here within the framework of the earlier PhD thesis work by Mathieu Compiegne at the IAS. 

Marco is taking the lead in the study of carbonaceous nano-particle evolution in HII regions in collaboration, principally, with Laurent Verstraete, at the IAS, Nathalie and Ant. Guru will then use the derived physical constraints in his PDR dust modelling. 

  • The third DustPedia consortium meeting was organised in the Monasterium convention centre in Ghent on October 29-30.
  • All PACS data have been fully reduced.
  • Quality control has started. The dust grid structures that can be used in the SKIRT radiative transfer code have been restructured, which allows for a more flexible application.
  • A first version of AstroMagic, a new python package for semi-automated data reduction developed as part of the DustPedia project, has been released (beta-version). It is available on GitHub.
  • A preliminary version of a radiative transfer model for M81 has been constructed.

Essentially the Herschel data has now all been extracted from the database and reduced. The data has been made available (along with the PACS data from Ghent) to the rest of the consortium and will be quality tested at Arcetri. We are in the process of extracting the auxiliary data from the other various databases. We are also working on the development of an automated photometry package to carry out the multi-band photometry that the science projects will require. We have started work on an initial DustPedia paper that will describe the project.

On November 1st, Andreas Noutsopoulos, a software engineer, was hired at the National Observatory of Athens with a two month contract to develop the "DustPedia" archive. All the Herschel data will be combined in a database with other available data on each galaxy. Furthermore, the output of the models on each galaxy (radiative transfer models and SED fitting models) will be tabulated. A search tool will be developed to look for sources within the archive with specified parameter ranges.