A&A 582, A121 (2015) Astronomy DOI: 10.1051/0004-6361/201526067 & c ESO 2015 Astrophysics Linking dust emission to fundamental properties in galaxies: the low-metallicity picture? A. Rémy-Ruyer1;2, S. C. Madden2, F. Galliano2, V. Lebouteiller2, M. Baes3, G. J. Bendo4, A. Boselli5, L. Ciesla6, D. Cormier7, A. Cooray8, L. Cortese9, I. De Looze3;10, V. Doublier-Pritchard11, M. Galametz12, A. P. Jones1, O. Ł. Karczewski13, N. Lu14, and L. Spinoglio15 1 Institut d’Astrophysique Spatiale, CNRS, UMR 8617, 91405 Orsay, France e-mail: [email protected]; [email protected] 2 Laboratoire AIM, CEA/IRFU/Service d’Astrophysique, Université Paris Diderot, Bât. 709, 91191 Gif-sur-Yvette, France 3 Sterrenkundig Observatorium, Universiteit Gent, Krijgslaan 281 S9, 9000 Gent, Belgium 4 UK ALMA Regional Centre Node, Jodrell Bank Centre for Astrophysics, School of Physics & Astronomy, University of Manchester, Oxford Road, Manchester M13 9PL, UK 5 Laboratoire d’Astrophysique de Marseille – LAM, Université d’Aix-Marseille & CNRS, UMR 7326, 38 rue F. Joliot-Curie, 13388 Marseille Cedex 13, France 6 Department of Physics, University of Crete, 71003 Heraklion, Greece 7 Zentrum für Astronomie der Universität Heidelberg, Institut für Theoretische Astrophysik, Albert-Ueberle-Str. 2, 69120 Heidelberg, Germany 8 Center for Cosmology, Department of Physics and Astronomy, University of California, Irvine, CA 92697, USA 9 Centre for Astrophysics & Supercomputing, Swinburne University of Technology, Mail H30, PO Box 218, Hawthorn VIC 3122, Australia 10 Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA, UK 11 Max-Planck für Extraterrestrische Physik, Giessenbachstr. 1, 85748 Garching-bei-München, Germany 12 European Southern Observatory, Karl-Schwarzschild-Str. 2, 85748 Garching-bei-München, Germany 13 Department of Physics and Astronomy, University of Sussex, Brighton, BN1 9QH, UK 14 NASA Herschel Science Center, MS 100-22, California Institute of Technology, Pasadena, CA 91125, USA 15 Instituto di Astrofisica e Planetologia Spaziali, INAF-IAPS, Via Fosso del Cavaliere 100, 00133 Roma, Italy Received 10 March 2015 / Accepted 14 July 2015 ABSTRACT Aims. In this work, we aim to provide a consistent analysis of the dust properties from metal-poor to metal-rich environments by linking them to fundamental galactic parameters. Methods. We consider two samples of galaxies: the Dwarf Galaxy Survey (DGS) and the Key Insights on Nearby Galaxies: a Far- Infrared Survey with Herschel (KINGFISH), totalling 109 galaxies, spanning almost 2 dex in metallicity. We collect infrared (IR) to submillimetre (submm) data for both samples and present the complete data set for the DGS sample. We model the observed spectral energy distributions (SED) with a physically-motivated dust model to access the dust properties: dust mass, total-IR luminosity, polycyclic aromatic hydrocarbon (PAH) mass fraction, dust temperature distribution, and dust-to-stellar mass ratio. Results. Using a different SED model (modified black body), different dust composition (amorphous carbon in lieu of graphite), or a different wavelength coverage at submm wavelengths results in differences in the dust mass estimate of a factor two to three, showing that this parameter is subject to non-negligible systematic modelling uncertainties. We find half as much dust with the amorphous carbon dust composition. For eight galaxies in our sample, we find a rather small excess at 500 µm (≤1.5σ). We find that the dust SED of low-metallicity galaxies is broader and peaks at shorter wavelengths compared to more metal-rich systems, a sign of a clumpier medium in dwarf galaxies. The PAH mass fraction and dust temperature distribution are found to be driven mostly by the specific star formation rate, sSFR, with secondary effects from metallicity. The correlations between metallicity and dust mass or total-IR luminosity are direct consequences of the stellar mass-metallicity relation. The dust-to-stellar mass ratios of metal-rich sources follow the well-studied trend of decreasing ratio for decreasing sSFR. The relation is more complex for low-metallicity galaxies with high sSFR, and depends on the chemical evolutionary stage of the source (i.e. gas-to-dust mass ratio). Dust growth processes in the ISM play a key role in the dust mass build-up with respect to the stellar content at high sSFR and low metallicity. Conclusions. We conclude that the evolution of the dust properties from metal-poor to metal-rich galaxies derives from a complex interplay between star formation activity, stellar mass, and metallicity. Key words. dust, extinction – evolution – galaxies: dwarf – galaxies: evolution – infrared: ISM – infrared: galaxies 1. Introduction seeds of this evolution lie in the star formation histories of the galaxies, and in their interaction with their environment through The processes by which galaxies evolve from primordial envi- gas infall, outflows, or mergers. The interstellar medium (ISM) ronments to present-day galaxies are still widely debated, but the plays a key role in this evolution since it is the site of stellar birth ? Figures 12 and 13, Tables 4–9, and Appendices are available in and the repository of stellar ejecta. electronic form at http://www.aanda.org Article published by EDP Sciences A121, page 1 of 42 A&A 582, A121 (2015) Although interstellar dust represents only ∼1% of the to- among which more than half are dwarf galaxies and ∼35% have tal mass of the ISM, it is an important agent in star formation. Z ≤ 1=5 Z . We confirmed with this significant sample of low- Dust absorbs the stellar radiation that would otherwise dissoci- metallicity sources that the dust is warmer at low metallicities ate molecules and thus actively participates in the cooling of the and identified several galaxies with submm excess. This study ISM. It is also a catalyser for molecular gas formation by provid- was conducted using only Herschel data and a modified black ing a surface where atoms can react (Hasegawa & Herbst 1993; body to model the dust emission. In Rémy-Ruyer et al.(2014), Vidali et al. 2004; Le Bourlot et al. 2012; Bron et al. 2014). The we confirmed the higher gas-to-dust mass ratios (G/D) at low presence of dust can increase the H2 formation rate by about two metallicities using the sample of Rémy-Ruyer et al.(2013), and orders of magnitudes compared to H2 formation without dust a semi-empirical spectral energy distribution (SED) model over (Tielens 2005), thus facilitating star formation. the whole IR range. We showed that the G/D is actually higher at Dust forms from the available heavy elements in the explo- low metallicities than that expected from a simple description of sively ejected material from core-collapse supernovæ (SN) and the dust evolution in the ISM. The large scatter in the observed in the quiescent outflows from low-mass stars (Todini & Ferrara G/D is intrinsic to the galaxies and reflects a non-universal dust- 2001; Gomez et al. 2012a,b; Indebetouw et al. 2014; Rowlands to-metal mass ratio (see also Dwek 1998; De Cia et al. 2013; et al. 2014; Matsuura et al. 2015). The refractory dust grains Zafar & Watson 2013; Mattsson et al. 2014a). We showed that may, after their injection into the ISM, grow by accretion or the metallicity was the main driver of the G/D but that the scat- coagulation in dense molecular clouds (Bazell & Dwek 1990; ter was controlled by the different SFHs of the sources. Thus Stepnik et al. 2001, 2003; Köhler et al. 2012, 2015), locking metallicity is not the only parameter shaping the dust properties. even more heavy elements in the solid phase of the ISM (Savage As a follow-up of Rémy-Ruyer et al.(2013, 2014), we aim & Sembach 1996; Whittet 2003). Through destructive processes to provide a consistent picture of the evolution of the dust prop- (such as erosion or sputtering; see Jones et al. 1994, 1996; Serra erties from metal-poor to metal-rich galaxies. On the observa- Díaz-Cano & Jones 2008; Bocchio et al. 2012, 2014), elements tional side, we present the complete catalogue of IR-to-submm are released again into the gas phase. Metallicity, defined as the flux densities for the Dwarf Galaxy Survey (DGS). We use a mass fraction of heavy elements, or “metals”, in the ISM, is thus semi-empirical dust SED model, which accounts for starlight in- a key parameter in studying the evolution of galaxies. tensity mixing in the ISM, to interpret the whole IR-to-submm Understanding how dust properties evolve as a function of observed SEDs. In this work, we extend the range of dust proper- metal enrichment can provide important constraints for galaxy ties and look at the dust mass, the total IR (TIR) luminosity, the evolution studies. Dwarf galaxies in the local Universe are ideal PAH mass fraction, and the dust temperature distribution. The targets for such a study as many of them have low metallicity and dust temperature distribution is directly linked to the SED shape high star formation activity. As such, they present star formation and provides valuable insight into the average dust temperature properties and ISM conditions that are the closest analogues to and the broadness of the FIR peak of the SED. We also discuss those thought to be present in the primordial environments of the the evolution of dust-to-stellar mass ratios and link it to the evo- early Universe (Madau et al. 1998). lution of the G/D observed in Rémy-Ruyer et al.(2014). For the Previous studies already demonstrated that the dust proper- analysis we do not only consider metallicity as our main param- ties in low-metallicity galaxies were notably different from that eter, but also include the specific star formation rate (SFR) and of metal-rich sources. Low-metallicity galaxies harbour warmer the stellar mass.