The Herschel Exploitation of Local Galaxy Andromeda (HELGA)^{⋆,⋆⋆,⋆⋆⋆}

IV. Dust scaling relations at sub-kpc resolution

¹ Sterrenkundig Observatorium, Universiteit Gent, Krijgslaan 281, 9000 Gent, Belgium
e-mail: sebastien.viaene@ugent.be
² Jodrell Bank Centre for Astrophysics, School of Physics and Astronomy, University of Manchester, Oxford Road, Manchester M13 9PL, UK
³ Instituut voor Sterrenkunde, Katholieke Universiteit Leuven, Celestijnenlaan 200D, 3001 Leuven, Belgium
⁴ Department of Physics and Astrophysics, Vrije Universiteit Brussel, Pleinlaan 2, 1050 Brussels, Belgium
⁵ Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge, CB3 0HA, UK
⁶ Laboratoire d’Astrophysique de Marseille, UMR 6110 CNRS, 38 rue F. Joliot-Curie, 13388 Marseille, France
⁷ University of Crete, Department of Physics, Heraklion 71003, Greece
⁸ Centre for Astrophysics & Supercomputing, Swinburne University of Technology, Mail H30, PO Box 218, Hawthorn, VIC 3122, Australia
⁹ School of Physics and Astronomy, Cardiff University, Queens Buildings, The Parade, Cardiff CF24 3AA, UK
¹⁰ Infrared Processing and Analysis Center, California Institute of Technology, Pasadena CA 91125, USA
¹¹ Astronomy Department, University of Cape Town, 7701 Rondebosch, South Africa
¹² Department of Physics and Astronomy, University of Sussex, Brighton, BN1 9QH, UK
¹³ Istituto di Astrofisica e Planetologia Spaziali, INAF-IAPS, via Fosso del Cavaliere 100, 00133 Roma, Italy
¹⁴ Tartu Observatory, Observatooriumi 1, 61602 Tõravere, Estonia
¹⁵ National Institute of Chemical Physics and Biophysics, Rävala pst 10, 10143 Tallinn, Estonia
¹⁶ Department of Physics and Astronomy, Johns Hopkins University, 3701 San Martin Drive, Baltimore MD 21218, USA

Received: 29 January 2014
Accepted: 11 March 2014

Abstract

Context. Dust and stars play a complex game of interactions in the interstellar medium and around young stars. The imprints of these processes are visible in scaling relations between stellar characteristics, star formation parameters, and dust properties.

Aims. In the present work, we aim to examine dust scaling relations on a sub-kpc resolution in the Andromeda galaxy (M 31). The goal is to investigate the properties of M 31 on both a global and local scale and compare them to other galaxies of the local universe.

Methods. New Herschel observations are combined with available data from GALEX, SDSS, WISE, and Spitzer to construct a dataset covering UV to submm wavelengths. All images were brought to the beam size and pixel grid of the SPIRE 500 μm frame. This divides M 31 in 22 437 pixels of 36 arcseconds in size on the sky, corresponding to physical regions of 137 × 608 pc in the galaxy’s disk. A panchromatic spectral energy distribution was modelled for each pixel and maps of the physical quantities were constructed. Several scaling relations were investigated, focussing on the interactions of dust with starlight.

Results. We find, on a sub-kpc scale, strong correlations between M_dust/M_⋆ and NUV-r, and between M_dust/M_⋆ and μ_⋆ (the stellar mass surface density). Striking similarities with corresponding relations based on integrated galaxies are found. We decompose M 31 in four macro-regions based on their far-infrared morphology; the bulge, inner disk, star forming ring, and the outer disk region. In the scaling relations, all regions closely follow the galaxy-scale average trends and behave like galaxies of different morphological types. The specific star formation characteristics we derive for these macro-regions give strong hints of an inside-out formation of the bulge-disk geometry, as well as an internal downsizing process. Within each macro-region, however, a great diversity in individual micro-regions is found, regardless of the properties of the macro-regions. Furthermore, we confirm that dust in the bulge of M 31 is heated only by the old stellar populations.

Conclusions. In general, the local dust scaling relations indicate that the dust content in M 31 is maintained by a subtle interplay of past and present star formation. The similarity with galaxy-based relations strongly suggests that they are in situ correlations, with underlying processes that must be local in nature.