Browsing by Author "Remy-Ruyer, A."

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    An overview of the Dwarf Galaxy Survey
    (The Astronomical Society of the Pacific, 2013) Remy-Ruyer, A.; Galametz, M.; Vaccari, Mattia; Madden, S.C.
    The Dwarf Galaxy Survey (DGS) program is studying low-metallicity galax- ies using 230h of far-infrared (FIR) and submillimetre (submm) photometric and spectroscopic observations of the Herschel Space Observatory and draws to this a rich database of a wide range of wavelengths tracing the dust, gas and stars. This sample of 50 galaxies includes the largest metallicity range achievable in the local Universe including the lowest metallicity (Z) galaxies, 1/50 Z⊙, and spans 4 orders of magnitude in star formation rates. The survey is designed to get a handle on the physics of the interstellar medium (ISM) of low metallicity dwarf galaxies, especially on their dust and gas properties and the ISM heating and cooling processes. The DGS produces PACS and SPIRE maps of low-metallicity galaxies observed at 70, 100, 160, 250, 350, and 500 μm with the highest sensi- tivity achievable to date in the FIR and submm. The FIR fine-structure lines, [CII] 158μm, [OI] 63μm, [OI] 145μm, [OIII] 88μm, [NIII] 57μm and [NII] 122 and 205 μm have also been observed with the aim of studying the gas cooling in the neutral and ionized phases. The SPIRE FTS observations include many CO lines (J=4-3 to J=13-12), [NII] 205 μm and [CI] lines at 370 and 609 μm. This paper describes the sample selection and global properties of the galaxies, the observing strategy as well as the vast ancillary database available to comple- ment the Herschel observations. The scientific potential of the full DGS survey is described with some example results included.
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    Revealing the cold dust in low-metallicity environments: I. Photometry analysis of the Dwarf Galaxy Survey with Herschel
    (EDP Sciences, 2013) Remy-Ruyer, A.; Madden, S.C.; Galliano, F.; Hony, S.; Sauvage, M.; Bendo, G.J.; Roussel, H.; Pohlen, M.; Smith, M.W.L.; Galametz, M.; Cormier, D.; Lebouteiller, V.; Wu, R.; Baes, M.; Barlow, M.J.; Boquien, M.; Boselli, A.; Ciesla, L.; De Looze, I.; Karczewski, O.L.; Panuzzo, P.; Spinoglio, L.; Vaccari, M.; Wilson, C.D.
    Context. We present new photometric data from our Herschel Guaranteed Time Key Programme, the Dwarf Galaxy Survey (DGS), dedicated to the observation of the gas and dust in low-metallicity environments. A total of 48 dwarf galaxies were observed with the PACS and SPIRE instruments onboard the Herschel Space Observatory at 70, 100, 160, 250, 350, and 500 µm. Aims. The goal of this paper is to provide reliable far infrared (FIR) photometry for the DGS sample and to analyse the FIR/submillimetre (submm) behaviour of the DGS galaxies. We focus on a systematic comparison of the derived FIR properties (FIR luminosity, LFIR, dust mass, Mdust , dust temperature, T, emissivity index, β) with more metal-rich galaxies and investigate the detection of a potential submm excess. Methods. The data reduction method is adapted for each galaxy in order to derive the most reliable photometry from the final maps. The derived PACS flux densities are compared with the Spitzer MIPS 70 and 160 µm bands. We use colour-colour diagrams to analyse the FIR/submm behaviour of the DGS galaxies and modified blackbody fitting procedures to determine their dust properties. To study the variation in these dust properties with metallicity, we also include galaxies from the Herschel KINGFISH sample, which contains more metal-rich environments, totalling 109 galaxies. Results. The location of the DGS galaxies on Herschel colour-colour diagrams highlights the differences in dust grain properties and/or global environments of low-metallicity dwarf galaxies. The dust in DGS galaxies is generally warmer than in KINGFISH galaxies (TDGS ∼ 32 K and TKINGFIS H ∼ 23 K). The emissivity index, β, is ∼ 1.7 in the DGS, however metallicity does not make a strong effect on β. The proportion of dust mass relative to stellar mass is lower in low-metallicity galaxies: Mdust /Mstar ∼ 0.02% for the DGS versus 0.1% for KINGFISH. However, per unit dust mass, dwarf galaxies emit about six times more in the FIR/submm than higher metallicity galaxies. Out of the 22 DGS galaxies detected at 500 µm, about 41% present an excess in the submm beyond the explanation of our dust SED model, and this excess can go up to 150% above the prediction from the model. The excess mainly appears in lower metallicity galaxies (12+log(O/H) ;S 8.3), and the strongest excesses are detected in the most metal-poor galaxies. However, we so stress the need for observations longwards of the Herschel wavelengths to detect any submm excess appearing beyond 500 .