HI in Local Group Dwarf Galaxies
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HI in Local Group Dwarf Galaxies
HI in Local Group Dwarf Galaxies
Jana GrcevichAdvisor: Mary Putman
Jana GrcevichAdvisor: Mary Putman
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HI in Local Group DwarfsHI 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
• 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
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DataData
HIPASS LAB GALFA
Declination Range
-90 to +25 -90 to +90 -1 to +38
Spatial Resolution
15.5’ 35.7’ 3.4’
Velocity Resolution
26.4 km/s 1.3 km/s 0.2 km/s
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Mass Limit RelationsMass Limit Relations
HIPASS(26.4 km/s)
M=2.38 x 10-2 D2kpc
M0
LAB(10 km/s)
M=6.24 x 10-1 D2kpc
M0
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HI Mass Upper LimitsHI Mass Upper Limits
Bootes I 60 < 86
Bootes II 60 < 86
Coma Berenices
44 < 46
Hercules 140 < 466
Leo IV 160 < 609
Segue 23 < 13
Ursa Major I
100 < 6240
Ursa Major II
30 < 562
Willman I 38 < 901
Canis Venetici I
220 < 3.0 x 104
Canis Venetici II
150 < 1.4 x 104
Object Distance HI Mass
(kpc) (solar masses)
HIPASS LAB
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Leo T in GALFALeo 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
• 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
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Leo TLeo T
(Ryan-Weber et al. 2007 in prep)
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Non-detections & Confident DetectionsNon-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.
• 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.
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FornaxFornax
Contours at 3, 7, 11, and 15 sigma
• 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
• 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
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SculptorSculptor
Contours at 3, 5, 7, and 9 sigma
• Two clouds discovered by Carignan et al. 1998 with Parkes/ATCA
• Optical Vel. = 102 km/s
• HI Vel. = 105 km/s
• Two clouds discovered by Carignan et al. 1998 with Parkes/ATCA
• Optical Vel. = 102 km/s
• HI Vel. = 105 km/s
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SculptorSculptor
Contours at 3, 5, 7, and 9 sigma
• 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
• 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
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SculptorSculptor
(Putman 2003)
Sculptor Dwarf l = 287.5 b = -83.2
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TucanaTucana
Contours at 3, 5, 7, and 9 sigma
• 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
• 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
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TucanaTucana
(Putman 2003)
Tucana l = 322.9 b = -47.4
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HI vs GC DistanceHI vs GC Distance
QuickTime™ and aTIFF (LZW) decompressor
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HI vs GC DistanceHI vs GC Distance
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All Non-Detections
Non-DetectionsAndAmbiguousDetections
MajorityConfidentDetectionsAt > 105
Solar Masses
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Mass Loss MechanismMass 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)
• 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)
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Diffuse Halo MediumDiffuse 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):
IGMv2 > gas/3
• Assume dwarfs in the transition region are being actively stripped of gas
• Density of hot halo medium is given by (Gunn & Gott 1972):
IGMv2 > gas/3
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Diffuse Halo MediumDiffuse Halo Medium
IGM ~ gas/(3 v2) = 2.2 x 10-4 cm-3
Typical values for a Leo T-like progenitorkm s-1
gas ~ 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)
IGM ~ gas/(3 v2) = 2.2 x 10-4 cm-3
Typical values for a Leo T-like progenitorkm s-1
gas ~ 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)
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Diffuse Halo MediumDiffuse Halo Medium
IGM ~ 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
seenThe diffuse halo medium is or was “clumpy”Leo T doesn’t represent the progenitorOther mass lowering mechanisms - reionization?
IGM ~ 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
seenThe diffuse halo medium is or was “clumpy”Leo T doesn’t represent the progenitorOther mass lowering mechanisms - reionization?
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Gas AccretionGas 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
• 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
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ConclusionsConclusions• 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
• 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
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Future WorkFuture Work
QuickTime™ and aYUV420 codec decompressorare needed to see this picture.
HVC simulation by Fabian Heitsch
Rel. Velocity = 150 km s-1
Cloud:R = 25 pcT = 1 x 104 Kn = 0.5 cm-3
Ambient Gas:T = 5 x 106 Kn = 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
• 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