Cold dust in the Galactic halo: first detection of dust emission in a high-velocity cloud : Francois...
Transcript of Cold dust in the Galactic halo: first detection of dust emission in a high-velocity cloud : Francois...
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Cold dust in the Galactic halo: first detection of dust emission in
a high-velocity cloud :
Francois Boulanger et
Marc-Antoine Miville-Deschênes
Miville Deschenes, Boulanger, Reach and Noriega-Crespo 2005, Ap. J. 631 L57.
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XFLS
High Velocity Clouds
• Observed on 20% of the sky
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Widespread interest in HVCs is due to their mystery ...
> Debatted origin
• Galactic fountain
• Tidal debris of local group dwarf galaxies
• Dark matter halos in the Local Group
Physical description, spatial distribution, masses and dynamics
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… and their potential for being important
> Formation and evolution of galaxies
• Potential tracers of small dark matter halos
• Source of gas to fuel star formation
• Accretion of low metallicity gas for chemical evolution
• Energy, mass and angular momentum flows within galaxies
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Multiphase systems
> First detection : Muller, Oort and Raimond 1963 C. R. Acad. Sc. Paris (21cm line, Dwingeloo 25 m dish)
> Today:
• Cold neutral gas (HI)
• Warm neutral and ionized gas (HI, Halpha)
• Conductive interfaces (OVI, CIV, NV)
• Embedded in a Galactic halo of coronal gas (X-rays)
Dust and Molecules?
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XFLS
High Velocity Clouds
• Observed on 20% of the sky
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XFLS
Spitzer Extragalactic First-Look Survey
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Infrared-HI comparison of theSpitzer Extragalactic First-Look Survey
IRAS 100 micron and GBT-HI overlay
Draco nebula
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HI SpectraHI Maps
Lockman and Condon 2005
GBT Observations
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IRIS: a new generation of IRAS maps
• Comparison with Schlegel et al.– Better photometry (scale and brightness correction)– Better angular resolution 4 IRAS bands (Schlegel et al. is only 100 micron)
Miville-Deschenes & Lagache, 2005
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Spitzer and IRAS Images
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• Multivariate regression to estimate the infrared emissivity of each HI component.
First detection of dust emission in the HVC– HVC Emissivity at 100 m ~
10 times smaller than local gas, but only a factor 2 smaller at 160 m
Colder dust
Infrared-HI correlation
I (x,y) = ii NHI
i (x,y) + C(x,y)
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Infrared-HI Correlation
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Dust in Complex C
• Dust Temperatures and emissivities per HI atom
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Gas column densities
• Dust emissivity per H gas metallicity for a fixed fraction of heavy elements in dust (fixed depletion)
• ZHVC /ZSun = 0.2 +/- 0.1 (Tripp et al. 2003)
• Dust emissivity per HI, HVC over Local ISM value > 1.6 (3 )
NH(HVC) > 1.6/0.3 * NHI (HVC)
• NHII/NH ~ 0.2 (Wakker et al. 1999)
Most of the HVC gas is in molecules
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FUSE search for H2 in absorption
Richter et al. 2001
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Conclusions and Perspectives• Confirmation of dust detection result on other fields
HVC in Spitzer extra-galactic fields: dedicated GBT+DRAO observations scheduled Dedicated Spitzer observing program?
HVCs could make part of the sub-mm extra-galactic background!
• Search for CO emission from molecular clumps
IRAM 30m proposal Clumps origin: self gravitating long lived structures or signatures of the dynamical interaction with the Galactic corona
New perspective on HVCs and the Galaxy evolution
New hunting grounds for molecules ?