The GALEX view of the Herschel Reference Survey

Ultraviolet structural properties of nearby galaxies^⋆

¹ European Southern Observatory, Karl Schwarzschild Str. 2, 85748 Garching bei München, Germany
e-mail: lcortese@eso.org
² Laboratoire d’Astrophysique de Marseille – LAM, Université d’Aix-Marseille & CNRS, UMR 7326, 38 rue F. Joliot-Curie, 13388 Marseille Cedex 13, France
³ UK ALMA Regional Centre Node, Jodrell Bank Centre for Astrophysics, School of Physics and Astronomy, University of Manchester, Oxford Road, Manchester M13 9PL, UK
⁴ School of Physics and Astronomy, Cardiff University, The Parade, Cardiff, CF24 3AA, UK
⁵ European Space & Technology Centre (ESTEC), PO Box 299, 2200 AG Noordwijk, The Netherlands
⁶ Institut d’Astrophysique Spatiale (IAS), Bâtiment 121, Université Paris-Sud 11 and CNRS, 91405 Orsay, France

Received: 30 March 2012
Accepted: 30 May 2012

Abstract

We present GALEX far-ultraviolet (FUV) and near-ultraviolet (NUV) as well as SDSS g, r, i photometry and structural parameters for the Herschel Reference Survey, a magnitude-, volume-limited sample of nearby galaxies in different environments. We use this unique dataset to investigate the ultraviolet (UV) structural scaling relations of nearby galaxies and to determine how the properties of the UV disk vary with atomic hydrogen content and environment. We find a clear change of slope in the stellar mass vs. effective surface brightness relation when moving from the optical to the UV, with more massive galaxies having brighter optical but fainter UV surface brightnesses than smaller systems. A similar change of slope is also seen in the radius vs. surface brightness relation. By comparing our observations with the predictions of a simple multi-zone chemical model of galaxy evolution, we show that these findings are a natural consequence of a much more efficient inside-out growth of the stellar disk in massive galaxies.

We confirm that isophotal radii are always a better proxy for the size of the stellar/star-forming disk than effective quantities and we show that the extent of the UV disk (normalized to the optical size) is strongly correlated to the integrated Hi gas fraction. This relation still holds even when cluster spirals are considered, with Hi-deficient systems having less extended star-forming disks than Hi-normal galaxies. Interestingly, the star formation in the inner part of Hi-deficient galaxies is significantly less affected by the removal of the atomic hydrogen, as expected in a simple ram-pressure stripping scenario. These results suggest that it is the amount of Hi that regulates the growth of the star-forming disk in the outskirts of galaxies.