HI & CO Velocity Dispersions

kat.ac.za

HI & CO Velocity Dispersions - Karoo Array Telescope

HI & CO Velocity Dispersions

Moses Mogotsi

Supervisor: W.J.G. de Blok

Masters

ACGC, UCT

SKA Africa Bursary Conference 2011


Radio Observations

Moses Mogotsi : HI & CO Velocity

Dispersions SKA Bursary Conference

2011


Radio Observations

DISPERSION

Moses Mogotsi : HI & CO Velocity

Dispersions SKA Bursary Conference

2011


Radio Observations

DISPERSION

Scale Height

Temperature

Turbulence

Opacity

Dynamics

Mass/Flux Distribution

Kinetic Energy

Star Formation?

Moses Mogotsi : HI & CO Velocity

Dispersions SKA Bursary Conference

2011


HI & CO

HI

• Atomic Hydrogen

• Everywhere

• Cold, Warm 50-100K, 8000K

• Low Density

CO

• Molecule

• Molecular Clouds, H 2 tracer

• Cold


THINGS

• Walter et al 2008

• The HI Nearby Galaxy

Survey

HI 21cm emission

• High Resolution

• High Sensitivity

• Very Large Array

Moses Mogotsi : HI & CO Velocity

Dispersions SKA Bursary Conference

2011


HERACLES

• Leroy et al 2009

• Hera CO Line Extragalactic

Survey

CO (J=2-1) survey of nearby

galaxies

• High Sensitivity

• Optical Disk Coverage

• IRAM 30m Telescope

Moses Mogotsi : HI & CO Velocity

Dispersions SKA Bursary Conference

2011


Moses Mogotsi : HI & CO Velocity

Dispersions SKA Bursary Conference

2011


Method

• 16 Galaxies

• Fitting Velocity Profiles : Gaussian, Hermite

• Determining Dispersions

• Pixel-by-Pixel HI, CO Comparisons

• Radial Analysis, Trends with other properties

Moses Mogotsi : HI & CO Velocity

Dispersions SKA Bursary Conference

2011


Limits of the Data

• 4σ Νoise Cut-off

Velocity Resolutions :

CO : 5.2km/s

HI : 2.6-5.2km/s

• Spatial Resolution : 13”

Moses Mogotsi : HI & CO Velocity

Dispersions SKA Bursary Conference

2011


Limits of the Data

• 4σ-noise Cut-off

Velocity Resolutions : 5.2km/s

• Spatial Resolution : 13”

• Beam Smearing

• Rotation

• Multiple LOS Components

• Interpretation of Profiles

• Selection Effects

Moses Mogotsi : HI & CO Velocity

Dispersions SKA Bursary Conference

2011


Scales

Peretto

2011

kpc

500pc

100pc


Scales

Peretto

2011

kpc

500pc

100pc


Scales

Peretto

2011

Cloud-Cloud dispersions

Internal Cloud dispersions

kpc

500pc

100pc


Results

Moses Mogotsi : HI & CO Velocity

Dispersions SKA Bursary Conference

2011

Mogotsi et al 2012 [in prep]


Moses Mogotsi : HI & CO Velocity

Dispersions SKA Bursary Conference

2011

Mogotsi et al 2012 [in prep]


Moses Mogotsi : HI & CO Velocity

Dispersions SKA Bursary Conference

2011

Mogotsi et al 2012 [in prep]


Moses Mogotsi : HI & CO Velocity

Dispersions SKA Bursary Conference

2011

Mogotsi et al 2012 [in prep]


Moses Mogotsi : HI & CO Velocity

Dispersions SKA Bursary Conference

2011

Mogotsi et al 2012 [in prep]


Moses Mogotsi : HI & CO Velocity

Dispersions SKA Bursary Conference

2011

Mogotsi et al 2012 [in prep]


Other work

• Consistent with :

– Wilson et al 2010

– Tamburro et al 2009

Moses Mogotsi : HI & CO Velocity

Dispersions SKA Bursary Conference

2011


What causes dispersion?

σ eff2 = υ thermal2 + σ non-thermal

2

σ eff2 = υ thermal2 + σ turbulence

2

Moses Mogotsi : HI & CO Velocity

Dispersions SKA Bursary Conference

2011


What causes dispersion?

HI

• Cold, Warm 50-100K, 8000K

• Low Density

CO

• Cold


What causes dispersion?

σ eff2 = υ thermal2 + σ turbulence

2

• SFR, MRI, Galactic rotation, Gaseous selfgravity,

Instabilities ... [????]

Moses Mogotsi : HI & CO Velocity

Dispersions SKA Bursary Conference

2011


σ HI , σ CO and Star Formation

Mogotsi et al 2012 [in prep]

Moses Mogotsi : HI & CO Velocity

Dispersions SKA Bursary Conference

2011


σ HICO and Star Formation

Mogotsi et al 2012 [in prep]

Moses Mogotsi : HI & CO Velocity

Dispersions SKA Bursary Conference

2011


σ HICO and Star Formation

Mogotsi et al 2012 [in prep]

Moses Mogotsi : HI & CO Velocity

Dispersions SKA Bursary Conference

2011


Preliminary Conclusions

• Dispersion Difference : 6.5 ± 1.1 km.s -1 σ HICO

(inclination-deprojected : 4.0 ± 1.4 km.s -1 )

• Dispersion Ratio : 1.6 ± 0.23 σ HICO

• σ HI & σ CO do not change uniformly in galaxies

• σ obs > υ thermal ....Turbulence domination?

• Radial σ decline

• σ increases with increasing ΣSFR (at high ΣSFR)

• σ HICO increases with increasing ΣSFR (at high ΣSFR)

Moses Mogotsi : HI & CO Velocity

Dispersions SKA Bursary Conference

2011


THINGS HERACLES HI & CO Velocity Dispersions Mogotsi et al 2012 [in prep]

Weirdo #2

Moses Mogotsi : HI & CO Velocity

Dispersions SKA Bursary Conference

2011


Weirdo #1

Mogotsi et al 2012 [in prep]

Moses Mogotsi : HI & CO Velocity

Dispersions SKA Bursary Conference

2011


Weirdo #2

Mogotsi et al 2012 [in prep]

Moses Mogotsi : HI & CO Velocity

Dispersions SKA Bursary Conference

2011


THINGS HERACLES HI & CO Velocity Dispersions Mogotsi et al 2012 [in prep]

Weirdo #2

Moses Mogotsi : HI & CO Velocity

Dispersions SKA Bursary Conference

2011


Ancillary Slides

Moses Mogotsi : HI & CO Velocity

Dispersions SKA Bursary Conference

2011


True Meaning...

• σ obs2 = σ cloud-cloud2 + σ internal

2

• σ obs2 = υ thermal2 + σ turbulence

2

• σ obs2 = σ z2 + σ xy

2

Moses Mogotsi : HI & CO Velocity

Dispersions SKA Bursary Conference

2011


HII

HI

HII

HI

HI

HII

HI

H 2

HI

H 2

HI

HI

HI

HII

HI

H 2

HI

H 2

H 2

H 2

H 2

H 2

H 2

H 2

HI

HII

HI

H 2

H 2

HI

H 2

H 2

HI

HII

HI

Moses Mogotsi : HI & CO Velocity

Dispersions SKA Bursary Conference

2011


Moses Mogotsi : HI & CO Velocity

Dispersions SKA Bursary Conference

2011


Moses Mogotsi : HI & CO Velocity

Dispersions SKA Bursary Conference

2011


PDR

G~G0 exp(-2 Av)

Moses Mogotsi : HI & CO Velocity

Dispersions SKA Bursary Conference

2011

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