DustPedia: Multiwavelength
Photometry & Imagery of 875
Nearby Galaxies in 42 Bands
Christopher Clark
Sam Verstocken, Simone Bianchi.
& the DustPedia team
[email protected]
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’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