HI in Local Group Dwarf Galaxies

HI in Local Group Dwarf Galaxies

HI in Local Group Dwarf Galaxies

Jana GrcevichAdvisor: Mary Putman

Jana GrcevichAdvisor: Mary Putman

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

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

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

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

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


Leo TLeo T

(Ryan-Weber et al. 2007 in prep)

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.

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


• HI Cloud Vel. = ~40 km/s

SculptorSculptor


• Two clouds discovered by Carignan et al. 1998 with Parkes/ATCA



• Two clouds discovered by Carignan et al. 1998 with Parkes/ATCA



SculptorSculptor


• 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

SculptorSculptor

(Putman 2003)

Sculptor Dwarf l = 287.5 b = -83.2

TucanaTucana


• HI cloud first detected by Oosterloo et al. (1996) who claimed it was associated with the Magellanic Stream


• 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


• HI Vel. = 130 km/s• ~54 km/s Velocity

Difference

TucanaTucana

(Putman 2003)

Tucana l = 322.9 b = -47.4

HI vs GC DistanceHI vs GC Distance

QuickTime™ and aTIFF (LZW) decompressor

are needed to see this picture.

HI vs GC DistanceHI vs GC Distance

QuickTime™ and aTIFF (LZW) decompressor

are needed to see this picture.

All Non-Detections

Non-DetectionsAndAmbiguousDetections

MajorityConfidentDetectionsAt > 105

Solar Masses

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)

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


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)


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?

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

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

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

Documents

HI in Local Group Dwarf Galaxies