Radial distribution of dust, stars, gas, and star-formation rate in DustPedia^⋆ face-on galaxies

¹ INAF–Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, 50125 Florence, Italy
e-mail: casasola@arcetri.astro.it
² National Observatory of Athens, Institute for Astronomy, Astrophysics, Space Applications and Remote Sensing, Ioannou Metaxa and Vasileos Pavlou, 15236 Athens, Greece
³ Sterrenkundig Observatorium, Department of Physics and Astronomy, Universiteit Gent Krijgslaan 281 S9, 9000 Gent, Belgium
⁴ School of Physics and Astronomy, Cardiff University, The Parade, Cardiff CF24 3AA, UK
⁵ Department of Physics and Astronomy, University College London, Gower Street, London WC1E 6BT, UK
⁶ Laboratoire AIM, CEA/DSM – CNRS – Université Paris Diderot, IRFU/Service d’Astrophysique, CEA Saclay, 91191 Gif-sur-Yvette, France
⁷ Institut d’Astrophysique Spatiale, CNRS, Univ. Paris-Sud, Université Paris-Saclay, Bât. 121, 91405, Orsay Cedex, France
⁸ Instituto de Radioastronomía y Astrofísica, UNAM, Campus Morelia, A.P. 3-72, C.P. 58089, Mexico
⁹ Centre for Astrophysics Research, University of Hertfordshire, College Lane, Hatfield AL10 9AB, UK

Received: 22 April 2017
Accepted: 14 June 2017

Abstract

Aims. The purpose of this work is the characterization of the radial distribution of dust, stars, gas, and star-formation rate (SFR) in a sub-sample of 18 face-on spiral galaxies extracted from the DustPedia sample.

Methods. This study is performed by exploiting the multi-wavelength DustPedia database, from ultraviolet (UV) to sub-millimeter bands, in addition to molecular (¹²CO) and atomic (Hi) gas maps and metallicity abundance information available in the 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 profiles with an exponential curve and derived their scale-lengths. We also developed a method to solve for the CO-to-H₂ conversion factor (α_CO) per galaxy by using dust- and gas-mass profiles.

Results. Although each galaxy has its own peculiar behavior, we identified a common trend of the exponential scale-lengths versus wavelength. On average, the scale-lengths normalized to the B-band 25 mag/arcsec² radius decrease from UV to 70 μm, from 0.4 to 0.2, and then increase back up to ~0.3 at 500 microns. The main result is that, on average, the dust-mass surface-density scale-length is about 1.8 times the stellar one derived from IRAC data and the 3.6 μm surface brightness, and close to that in the UV. We found a mild dependence of the scale-lengths on the Hubble stage T: the scale-lengths of the Herschel bands and the 3.6 μm scale-length tend to increase from earlier to later types, the scale-length at 70 μm tends to be smaller than that at longer sub-mm wavelength with ratios between longer sub-mm wavelengths and 70 μm that decrease with increasing T. The scale-length ratio of SFR and stars shows a weak increasing trend towards later types. Our α_CO determinations are in the range (0.3−9) M_⊙ pc^-2 (K km s^-1)^-1, almost invariant by using a fixed dust-to-gas ratio mass (DGR) or a DGR depending on metallicity gradient.