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HI in Local Group Dwarf Galaxies Jana Grcevich Advisor: Mary Putman HI in Local Group Dwarfs • Limits on HI content of the newly discovered dwarfs • HI in Leo T • HI in other low-mass local group dwarfs • Galactocentric Distance vs. HI content • Halo Density Estimation • Gas Accretion Data HIPASS Declination -90 to +25 Range Spatial 15.5’ Resolution Velocity 26.4 km/s Resolution LAB GALFA -90 to +90 -1 to +38 35.7’ 3.4’ 1.3 km/s 0.2 km/s Mass Limit Relations HIPASS (26.4 km/s) LAB (10 km/s) M=2.38 x 10-2 D2kpc M0 M=6.24 x 10-1 D2kpc M0 HI Mass Upper Limits Object Distance HI Mass (kpc) (solar masses) Bootes I 60 < 86 Bootes II 60 < 86 Coma 44 Berenices < 46 Hercules < 466 140 Ursa Major I 100 < 6240 Ursa Major II 30 < 562 Willman I 38 < 901 220 < 3.0 x 104 < 1.4 x 104 Leo IV 160 < 609 Canis Venetici I Segue 23 < 13 Canis 150 Venetici II HIPASS LAB Leo T in GALFA • Lowest luminosity galaxy discovered which has current star formation (Irwin et al. 2007 • T - “transition” • Optical Vel. = 38.1 km/s • HI Vel. = 35 km/s Leo T (Ryan-Weber et al. 2007 in prep) Non-detections & Confident Detections • Additional galaxies not detected: Cetus, Sextans, Leo I, And III, And V, And VI, Leo II, Leo IV, Ursa Minor, Draco, and Sagittarius. • Confident Detections: Antlia, Phoenix, Pegasus, Aquarius, and LGS3. Fornax • Moment Map 32.87 to 59.26 km/s • Unclear if cloud is part of typical MW emission, an HVC of separate origin, or the Fornax Dwarf • Optical Vel. = 53 km/s • HI Cloud Vel. = ~40 km/s Contours at 3, 7, 11, and 15 sigma Sculptor • Two clouds discovered by Carignan et al. 1998 with Parkes/ATCA • Optical Vel. = 102 km/s • HI Vel. = 105 km/s Contours at 3, 5, 7, and 9 sigma Sculptor • Sculptor Dwarf is in the same direction as the Magellanic Stream and Sculptor Group • Sky is crowded at this velocity Contours at 3, 5, 7, and 9 sigma • Cloud could be a filament extending toward the sculptor group or a chance superposition Sculptor (Putman 2003) Sculptor Dwarf l = 287.5 b = -83.2 Tucana • HI cloud first detected by Oosterloo et al. (1996) who claimed it was associated with the Magellanic Stream • Optical Vel. = 184 km/s • HI Vel. = 130 km/s • ~54 km/s Velocity Difference Contours at 3, 5, 7, and 9 sigma Tucana (Putman 2003) Tucana l = 322.9 b = -47.4 HI vs GC Distance QuickTime™ and a TIFF (LZW) decompressor are needed to see this picture. HI vs GC Distance NonDetections And All NonAmbiguous Detections Detections QuickTime™ and a TIFF (LZW) decompressor are needed to see this picture. Majority Confident Detections At > 105 Solar Masses Mass Loss Mechanism • Simulations suggest that ram pressure is the primary mass loss mechanism, assisted by tidal and possibly internal effects (Mayer et al 06; Mori & Burkert 01; Quilis & Moore 2001) Diffuse Halo Medium • Assume dwarfs in the transition region are being actively stripped of gas • Density of hot halo medium is given by (Gunn & Gott 1972): rIGM v2 > s2 rgas/3 Diffuse Halo Medium rIGM ~ s2 rgas/(3 v2) = 2.2 x 10-4 cm-3 Typical values for a Leo T-like progenitor skm s-1 rgas ~ NHI,core/R ~ 1 x 1020 cm-2/600 pc = 5.4 x10-2 cm-3 v ~ 60 km s-1 (1D velocity dispersion for Local Group dwarf galaxies from Van den Bergh 1999a) Diffuse Halo Medium rIGM ~ 2.2 x 10-4 cm-3 Observations suggest a hot gaseous corona with a mean density of 2 x 10-5 cm-3 within 150 kpc (Sembach et al. 2003) Explanations: Orbits take them further in than they are now seen The diffuse halo medium is or was “clumpy” Leo T doesn’t represent the progenitor Other mass lowering mechanisms - reionization? Gas Accretion • Average HI mass of galaxies 300 kpc out or more: 4 x 106 M0 • Galaxies within 300 kpc would contribute about 8 x 107 M0 to the MW Conclusions • All of the SDSS dwarfs except Leo T are devoid of gas to our detection limits, and these upper limits are lower than the HI mass of any known dwarf which has HI. • Dwarf galaxies at smaller galactocentric distances have less HI on average than those at larger distances. • The HI -distance trend supports data from simulations which suggest ram-pressure stripping/tidal effects are responsible for the low HI content of dSphs • The diffuse halo density can be estimated, but yields densities higher than expected • Accretion from the dwarfs provides insufficient fuel to support long term star formation in the MW at the observed rate Future Work Rel. Velocity = 150 km s-1 Cloud: • Analysis of the star R = 25 pc formation histories of the T = 1 x 104 K dwarfs and how this n = 0.5 cm-3 correlates with HI content • Galfa observations of HI in the vicinity of local group dwarfs • Simulations of gas clouds being stripped and study of head tail clouds Ambient Gas: T = 5 x 106 K n = 1 x 10-3 cm-3 HVC simulation by Fabian Heitsch Quic kTime™ and a YUV420 c odec dec ompres sor are needed to see this picture.