1 / 23

HI in Local Group Dwarf Galaxies

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.

doctor
Download Presentation

HI in Local Group Dwarf Galaxies

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. HI in Local Group Dwarf Galaxies Jana Grcevich Advisor: Mary Putman

  2. 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

  3. Data HIPASS LAB GALFA

  4. Mass Limit Relations

  5. HI Mass Upper Limits Object Distance HI Mass (kpc) (solar masses) HIPASS LAB

  6. 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

  7. Leo T (Ryan-Weber et al. 2007 in prep)

  8. 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.

  9. 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

  10. 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

  11. Sculptor • Sculptor Dwarf is in the same direction as the Magellanic Stream and Sculptor Group • Sky is crowded at this velocity • Cloud could be a filament extending toward the sculptor group or a chance superposition Contours at 3, 5, 7, and 9 sigma

  12. Sculptor (Putman 2003) Sculptor Dwarf l = 287.5 b = -83.2

  13. 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

  14. Tucana (Putman 2003) Tucana l = 322.9 b = -47.4

  15. HI vs GC Distance

  16. HI vs GC Distance Non- Detections And Ambiguous Detections Majority Confident Detections At > 105 Solar Masses All Non- Detections

  17. 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)

  18. 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): rIGMv2 >s2 rgas/3

  19. Diffuse Halo Medium rIGM~s2 rgas/(3 v2) = 2.2 x 10-4 cm-3 Typical values for a Leo T-like progenitor skm 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)

  20. 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?

  21. 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

  22. 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

  23. Future Work Rel. Velocity = 150 km s-1 Cloud: R = 25 pc T = 1 x 104 K n = 0.5 cm-3 Ambient Gas: T = 5 x 106 K n = 1 x 10-3 cm-3 • Analysis of the star formation histories of the dwarfs and how this 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 HVC simulation by Fabian Heitsch

More Related