The evolution of the dust temperatures of galaxies in the SFR–M_∗ plane up to z ~ 2^⋆,⋆⋆

¹ Max-Planck-Institut für extraterrestrische Physik, Postfach 1312, Giessenbachstraße 1, 85741 Garching, Germany
e-mail: magnelli@astro.uni-bonn.de
² Argelander-Institut für Astronomie, University of Bonn, auf dem Hügel 71, 53121 Bonn, Germany
³ Department of Physics and Astronomy, University College London, Gower Street, London WC1E 6BT, UK
⁴ INAF – Osservatorio Astronomico di Roma, via di Frascati 33, 00040 Monte Porzio Catone, Italy
⁵ Astronomy Centre, Dept. of Physics & Astronomy, University of Sussex, Brighton BN1 9QH, UK
⁶ Mullard Space Science Laboratory, University College London, Holmbury St Mary, Dorking RH5 6NT, UK
⁷ Herschel Science Centre, ESAC, Villanueva de la Cañada, 28691 Madrid, Spain
⁸ ESO, Karl-Schwarzschild-Straße 2, 85748 Garching, Germany
⁹ INAF – Osservatorio Astronomico di Trieste, via Tiepolo 11, 34143 Trieste, Italy
¹⁰ Laboratoire AIM, CEA/DSM-CNRS-Université Paris Diderot, IRFU/Service d’Astrophysique, Bât.709, CEA-Saclay, 91191 Gif-sur-Yvette Cedex, France
¹¹ California Institute of Technology, 1200 E. California Blvd., Pasadena CA 91125, USA
¹² Jet Propulsion Laboratory, 4800 Oak Grove Drive, Pasadena CA 91109, USA
¹³ Instituto de Astrofísica de Canarias (IAC), C/vía Láctea s/n, 38200 La Laguna, Spain
¹⁴ Departamento de Astrofísica, Universidad de La Laguna, 38206 La Laguna, Spain
¹⁵ Dipartimento di Astronomia, Università di Bologna, via Ranzani 1, 40127 Bologna, Italy
¹⁶ Center for Astrophysics and Space Astronomy, 389 UCB, University of Colorado, Boulder CO 80309, USA
¹⁷ Institute for Astronomy, University of Edinburgh, Royal Observatory, Blackford Hill, Edinburgh EH9 3HJ, UK
¹⁸ Department of Physics, University of Oxford, Keble Road, Oxford OX1 3RH, UK
¹⁹ School of Physics and Astronomy, The Raymond and Beverly Sackler Faculty of Exact Sciences, Tel Aviv University, 69978 Tel Aviv, Israel
²⁰ NASA Ames, Moffett Field, CA 94035, USA
²¹ Dipartimento di Astronomia, Universita di Padova, Vicolo dell’Osservatorio 3, 35122 Padova, Italy
²² Department of Physics & Astronomy, University of British Columbia, 6224 Agricultural Road, Vancouver BC V6T 1Z1, Canada

Received: 5 July 2013
Accepted: 11 November 2013

Abstract

We study the evolution of the dust temperature of galaxies in the SFR− M_∗ plane up to z ~ 2 using far-infrared and submillimetre observations from the Herschel Space Observatory taken as part of the PACS Evolutionary Probe (PEP) and Herschel Multi-tiered Extragalactic Survey (HerMES) guaranteed time key programmes. Starting from a sample of galaxies with reliable star-formation rates (SFRs), stellar masses (M_∗) and redshift estimates, we grid the SFR− M_∗parameter space in several redshift ranges and estimate the mean dust temperature (T_dust) of each SFR–M_∗ − z bin. Dust temperatures are inferred using the stacked far-infrared flux densities (100–500  μm) of our SFR–M_∗ − z bins. At all redshifts, the dust temperature of galaxies smoothly increases with rest-frame infrared luminosities (L_IR), specific SFRs (SSFR; i.e., SFR/M_∗), and distances with respect to the main sequence (MS) of the SFR− M_∗ plane (i.e., Δlog (SSFR)_MS = log [SSFR(galaxy)/SSFR_MS(M_∗,z)]). The T_dust − SSFR and T_dust − Δlog (SSFR)_MS correlations are statistically much more significant than the T_dust − L_IR one. While the slopes of these three correlations are redshift-independent, their normalisations evolve smoothly from z = 0 and z ~ 2. We convert these results into a recipe to derive T_dust from SFR, M_∗ and z, valid out to z ~ 2 and for the stellar mass and SFR range covered by our stacking analysis. The existence of a strong T_dust − Δlog (SSFR)_MS correlation provides us with several pieces of information on the dust and gas content of galaxies. Firstly, the slope of the T_dust − Δlog (SSFR)_MS correlation can be explained by the increase in the star-formation efficiency (SFE; SFR/M_gas) with Δlog (SSFR)_MS as found locally by molecular gas studies. Secondly, at fixed Δlog (SSFR)_MS, the constant dust temperature observed in galaxies probing wide ranges in SFR and M_∗ can be explained by an increase or decrease in the number of star-forming regions with comparable SFE enclosed in them. And thirdly, at high redshift, the normalisation towards hotter dust temperature of the T_dust − Δlog (SSFR)_MS correlation can be explained by the decrease in the metallicities of galaxies or by the increase in the SFE of MS galaxies. All these results support the hypothesis that the conditions prevailing in the star-forming regions of MS and far-above-MS galaxies are different. MS galaxies have star-forming regions with low SFEs and thus cold dust, while galaxies situated far above the MS seem to be in a starbursting phase characterised by star-forming regions with high SFEs and thus hot dust.