WALLABY SWG1 Gas‐rich dwarfs in the Local Group Emma Ryan‐Weber Bouchard, Jerjen, Koribalski, Meurer, Oosterloo, Wakker, Wilcots, Zucker WALLABY: Local Group Emma Ryan‐Weber (Swinburne) The Local Group A test bed for galaxy formation and evolution Credit: Mario Mateo WALLABY: Local Group Emma Ryan‐Weber (Swinburne) The missing satellite problem Credit Diemand Credit Johnston & Bullock WALLABY: Local Group Emma Ryan‐Weber (Swinburne) SDSS field of streams & 20 new dwarfs Credit Vasily Belokurov WALLABY: Local Group Emma Ryan‐Weber (Swinburne) Mass function of MW satellites Simon & Geha (2007) WALLABY: Local Group Emma Ryan‐Weber (Swinburne) Mass function of MW satellites Effect of Reionization? Simon & Geha (2007) WALLABY: Local Group Emma Ryan‐Weber (Swinburne) HI mass vs. distance to MW/M31 Tidal stripping may provide a more plausible explanaon of this relaonship Grcevich & Putman (2009) WALLABY: Local Group Emma Ryan‐Weber (Swinburne) A minimum dark matter halo mass? Detect HI to greater radii Strigari et al. (2009) Belokurov et al. (2007) WALLABY: Local Group Emma Ryan‐Weber (Swinburne) Phoenix dwarf Gas stripping as a trigger for star formation Gas has survived galacc winds and supernova explosions and triggers further star formaon. Young et al. (2007) WALLABY: Local Group Emma Ryan‐Weber (Swinburne) Leo T in HIPASS ERW et al. 2008 WALLABY: Local Group Emma Ryan‐Weber (Swinburne) Leo T WALLABY will be first blind survey of HI in the Local Group to be conducted with an interferometer. NOT having zero‐spacing data provides a significant advantage. GMRT observaons of Leo T Sensivity 5.2mJy/beam/channel Channel width 1.65 km/s 30” beam ERW et al. 2008 WALLABY: Local Group Emma Ryan‐Weber (Swinburne) Predictions for WALLABY Expect to detect 60 galaxies with 4 MHI>1.5x10 M⊙ at 300<d<1500 kpc with WALLABY Based on the HIPASS HIMF and a measured 3x overdensity of HI galaxies in the Local Group. WALLABY: Local Group Emma Ryan‐Weber (Swinburne) SWG1 plan •Three ways of finding HI in dwarf galaxies in the local group ‐ cross match HI data with known dwarfs ‐ cross match HI data with newly discovered stellar overdensies (SkyMapper, Pan‐STARRS) ‐ search for HI detecon without considering opcal data • How do you find galaxies in Galacc fluff, especially those that contains no stars? ‐ Use reprocessed Galacc All Sky Survey (GASS, McClure‐Griffiths 2009) data to determine a detecon method for LG dwarfs. WALLABY: Local Group Emma Ryan‐Weber (Swinburne) GASS Velocity res 0.82 km/s ‐400<V(LSR)<500 km/s rms sensivity 57 mK Credit S. Janowiecki WALLABY: Local Group Emma Ryan‐Weber (Swinburne) Science questions to be addressed • How do galaxies retain/gain gas and form stars ? (we will be able to compile physical evidence of gas stripping and galaxy ‘harassment’) • As we move further from the ‘zone of destrucon’ — beyond 250–350 kpc from the Milky Way/M 31 (see Tolstoy et al. 2009) — do we find more gas‐rich dwarfs with 7 Mhalo ∼ 10 M⊙ ? • Is there a common minimum halo mass for star formaon (see, e.g., Warren et al. 2007) ? • Is a galaxy’s star formaon history and HI mass‐to‐light rao dominated by inial condions (total mass, baryon fracon), or distance to the nearest spiral ? • Are there any gas‐rich galaxies without stars ? (the Local Volume would be the best place to find them as low mass galaxies have the lowest detected star formaon efficiencies) WALLABY: Local Group Emma Ryan‐Weber (Swinburne) .