The Herschel Virgo Cluster Survey

XVIII. Star-forming dwarf galaxies in a cluster environment^⋆

¹ Centro de Astronomia e Astrofísica da Universidade de Lisboa, OAL, Tapada da Ajuda, 1349-018 Lisbon, Portugal
e-mail: grossi@oal.ul.pt
² Instituto de Astrofísica e Ciências do Espaço, Universidade de Lisboa, OAL, Tapada da Ajuda, 1349-018 Lisbon, Portugal
³ Departamento de Física, Faculdade de Ciências, Universidade de Lisboa, Edifício C8, Campo Grande, 1749-016 Lisbon, Portugal
⁴ INAF – Osservatorio Astrofisico di Arcetri, Largo Enrico Fermi 5, 50125 Firenze, Italy
⁵ Laboratoire AIM, CEA/DSM – CNRS – Université Paris Diderot, Irfu/Service d’Astrophysique, CEA Saclay, 91191 Gif-sur-Yvette, France
⁶ Sterrenkundig Observatorium, Universiteit Gent, Krijgslaan 281, 9000 Gent, Belgium
⁷ School of Physics and Astronomy, Cardiff University, Queens Buildings, The Parade, Cardiff CF24 3AA, UK
⁸ UK ALMA Regional Centre Node, Jodrell Bank Centre for Astrophysics, School of Physics and Astronomy, University of Manchester, Oxford Road, Manchester M13 9PL, UK
⁹ Center for Astrochemical Studies, Max-Planck-Institut für extraterrestrische Physik (MPE), Giessenbachstraße, 85748 Garching, Germany
¹⁰ Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA, UK
¹¹ Laboratoire d’Astrophysique de Marseille, UMR 6110 CNRS, 38 rue F. Joliot-Curie, 13388 Marseille, France
¹² INAF – Osservatorio Astronomico di Padova, Vicolo dell’Osservatorio 5, 35122 Padova, Italy
¹³ Centre for Astrophysics and Supercomputing, Swinburne University of Technology, Mail H30 – PO Box 218, Hawthorn, VIC 3122, Australia
¹⁴ Max-Planck-Institut für extraterrestrische Physik (MPE), Postfach 1312, Giessenbachstraße, 85748 Garching, Germany
¹⁵ Joint ALMA Observatory/European Southern Observatory, 3107 Alonso de Cordova, Vitacura, Santiago, Chile

Received: 27 August 2014
Accepted: 11 November 2014

Abstract

To assess the effects of the cluster environment on the different components of the interstellar medium, we analyse the far-infrared (FIR) and submillimetre (submm) properties of a sample of star-forming dwarf galaxies detected by the Herschel Virgo Cluster Survey (HeViCS). We determine dust masses and dust temperatures by fitting a modified black body function to the spectral energy distributions (SEDs). Stellar and gas masses, star formation rates (SFRs), and metallicities are obtained from the analysis of a set of ancillary data. Dust is detected in 49 out of a total 140 optically identified dwarfs covered by the HeViCS field; considering only dwarfs brighter than m_B = 18 mag, this gives a detection rate of 43%. After evaluating different emissivity indices, we find that the FIR-submm SEDs are best-fit by β = 1.5, with a median dust temperature T_d = 22.4 K. Assuming β = 1.5, 67% of the 23 galaxies detected in all five Herschel bands show emission at 500 μm in excess of the modified black-body model. The fraction of galaxies with a submillimetre excess decreases for lower values of β, while a similarly high fraction (54%) is found if a β-free SED modelling is applied. The excess is inversely correlated with SFR and stellar masses. To study the variations in the global properties of our sample that come from environmental effects, we compare the Virgo dwarfs to other Herschel surveys,such as the Key Insights into Nearby Galaxies: Far-Infrared Survey with Herschel (KINGFISH), the Dwarf Galaxy Survey (DGS), and the HeViCS Bright Galaxy Catalogue (BGC). We explore the relations between stellar mass and Hi fraction, specific star formation rate, dust fraction, gas-to-dust ratio over a wide range of stellar masses (from 10⁷ to 10¹¹ M_⊙) for both dwarfs and spirals. Highly Hi-deficient Virgo dwarf galaxies are mostly characterised by quenched star formation activity and lower dust fractions giving hints for dust stripping in cluster dwarfs. However, to explain the large dust-to-gas mass ratios observed in these systems, we find that the fraction of dust removed has to be less than that of the Hi component. The cluster environment seems to mostly affect the gas component and star formation activity of the dwarfs. Since the Virgo star-forming dwarfs are likely to be crossing the cluster for the first time, a longer timescale might be necessary to strip the more centrally concentrated dust distribution.