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Cold dust in the Galactic halo: first detection of dust emission in a high-velocity cloud :

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. High Velocity Clouds. Observed on 20% of the sky. XFLS.

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Cold dust in the Galactic halo: first detection of dust emission in a high-velocity cloud :

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  1. 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.

  2. High Velocity Clouds • Observed on 20% of the sky XFLS

  3. 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

  4. … 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

  5. 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?

  6. High Velocity Clouds • Observed on 20% of the sky XFLS

  7. Spitzer Extragalactic First-Look Survey XFLS

  8. Infrared-HI comparison of theSpitzer Extragalactic First-Look Survey Draco nebula IRAS 100 micron and GBT-HI overlay

  9. HI Spectra HI Maps Lockman and Condon 2005 GBT Observations

  10. 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

  11. Spitzer and IRAS Images

  12. Infrared-HI correlation In (x,y) = Si ani NHIi (x,y) + Cn (x,y) • Multivariate regression to estimate the infrared emissivity of each HI component. • First detection of dust emission in the HVC • HVC Emissivity at 100 mm ~ 10 times smaller than local gas, but only a factor 2 smaller at 160mm • Colder dust

  13. Infrared-HI Correlation

  14. Dust in Complex C • Dust Temperatures and emissivities per HI atom

  15. Gas column densities • Dust emissivity per H a 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 s) • NH(HVC) > 1.6/0.3 * NHI (HVC) • NHII/NH ~ 0.2 (Wakker et al. 1999) • Most of the HVC gas is in molecules

  16. FUSE search for H2 in absorption Richter et al. 2001

  17. 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? • HVCscould 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 ?

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