DustPedia: Multiwavelength Photometry and Imagery of 876 Nearby Galaxies in 42 Ultraviolet–Microwave Bands

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1. DustPedia: Multiwavelength Photometry & Imagery of 875 Nearby Galaxies in

   42 Bands Christopher Clark Sam Verstocken, Simone Bianchi. & the DustPedia team cclark@stsci.edu We present multiwavelength imagery and photometry across 42 UV–microwave bands for 875 nearby galaxies. This database contains custom Herschel reductions, plus standardised GALEX, SDSS, DSS, 2MASS, WISE, Spitzer, and Planck data. We also present CAAPR, the pipeline we use to conduct aperture-matched photometry of our data; CAAPR is designed to produce consistent photometry for the enormous range of galaxy and observation types we employ. The 27-band aperture-matched photometry, in combination with ancillary catalogue data from IRAS and Planck, represents 21857 photometric measurements. This rich database of imagery & photometry will be invaluable for SPICA follow-up, and is publicly available at: dustpedia.astro.noa.gr Initiate pipeline for current target Most stages can be enabled / disabled The DustPedia sample contains every extended (1’<D25<1°) galaxy within 3000 km s-1 (~40 Mpc) that was observed by the Herschel Space Observatory, excluding only the most extended Local Group galaxies. The DustPedia imagery database is centred around our custom Herschel reductions, produced using the most up-to date calibrations, combining all available Herschel data for each galaxy in the sample. Our multiwavelength ancillary imagery was assembled from the archives of GALEX, SDSS, DSS, 2MASS, WISE, Spitzer, and Planck. We combine all available data in each band, and the resulting FITS files are standardised to use consistent orientations, map sizes, header formats, and pixel units of Jy pix-1. This database is now publicly available, and is continuing to expand as more data is added, such as metallicity and gas measurements. CAAPR Comprehensive & Adaptable Aperture Photometry Routine We developed the CAAPR pipeline to perform our aperture-matched photometry. In particular, CAAPR features a novel method for extrapolating aperture noise in maps too small to allow placement of random sky apertures. This ensures that all of our uncertainties are cross-comparable, vital for SED fitting. CAAPR is freely available on GitHub. Perform data preparation & aperture fitting for all bands in parallel Fit and subtract large- scale sky structure Cutout / reproject input image Query web catalogues to find and remove foreground stars Example shown to left Fit elliptical aperture to source emission Example shown above Deconvolve aperture with PSF of current band Combine apertures from all bands to generate final aperture Perform photometry for all bands in parallel Alternatively, user may provide pre-defined apertures Convolve aperture with band PSF Perform photometry using elliptical source aperture and annular background aperture Model source emission in 2D to calculate aperture correction, using band PSF Correct flux for foreground Galactic extinction Attempt to estimate aperture noise using full-size randomly- placed sky apertures If insufficient map area for full-size sky apertures, switch to noise extrapolation Extrapolate what aperture noise would be at full aperture size Place large numbers of smaller sky apertures across map, spanning a range of sizes Example of star-removal, for WISE 3.4 µm data of IC 342 Overview illustration of our elliptical aperture fitting process, for SPIRE 250 µm data of NGC 5364 Model trend between sky aperture area and corresponding aperture noise Output final results, and make image grid showing apertures See example below-left Single threaded Multi-threaded Multiple threads spawned Multiple threads collected The source apertures (solid green lines) and background annuli (dashed green lines) produced by CAAPR for our aperture-matched multiwavelength photometry of NGC 3686. The DustPedia photometry database contains the outputs of the 27-band aperture-matched photometry performed by CAAPR. We also provide supplementary photometry for IRAS and Planck, taken from existing datasets. All outputs have undergone manual inspection and flagging for a range of potential issues. In total, we present 21857 photometric measurements for our 875 galaxies. A typical DustPedia galaxy has multiwavelength photometry spanning 25 bands. An example SED is shown above. Multiwavelength SED of NGC 3686, illustrating the rich photometric coverage possible in DustPedia. Solid circles show our aperture- matched CAAPR fluxes; hollow circles show supplementary fluxes. For complete details of our imagery and photometry data products, along with a full description of the operation of CAAPR, please refer to C J R Clark et al (2018). dustpedia.com