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Multiscale Structure in Cold H I

Multiscale Structure in Cold H I. Steven J. Gibson. National Astronomy and Ionosphere Center. Collaborators. Ken Nordsieck – UW-Madison Mark Holdaway – NRAO-Tucson Russ Taylor, Jeroen Stil – U. Calgary Chris Brunt - U. Exeter Peter Dewdney, Lloyd Higgs - DRAO. Big Bang. Molecular

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Multiscale Structure in Cold H I

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  1. Multiscale Structure in Cold H I Steven J. Gibson National Astronomy and Ionosphere Center

  2. Collaborators • Ken Nordsieck – UW-Madison • Mark Holdaway – NRAO-Tucson • Russ Taylor, Jeroen Stil – U. Calgary • Chris Brunt - U. Exeter • Peter Dewdney, Lloyd Higgs - DRAO

  3. Big Bang Molecular Clouds Stars Diffuse ISM Area of Interest Stellar Remnants Planets People Cell Phones The History of the Universe (condensed) Galactic Infall Stellar Mass Loss Disruption Star Condensation Formation Stellar Evolution

  4. Why Study Cold H I? • Abundant ISM phase • Traces quiescent gas(needed for star formation) • Exhibits intricate small-scale structure • Relationship with molecular hydrogen • Radiative transfer probes Galactic structure

  5. The Utility of Dust • Challenge – observed power spectra are red, so very small stuff hard to see, especially in HI • Approach -- try other CNM tracers, like dust! HI and dust should be well mixed in the CNM, and dust is traced by continuum (absorbed, scattered, or thermally radiated), so more detectable. Still, should compare the two where possible to check their agreement. • In the Galactic plane this may not work, and we must try other things like HISA. But first consider HI emission and dust structure in a nearby cloud.

  6. The Pleiades Cluster – Optical Image by Robert Gendler

  7. Pleiades Reflection Nebula Relatively unconfused sightline (IRAS, E(B-V), Na I absorption, polarimetry) • Nearby (130 pc), well-lit nebula (good view of small-scale structure • Abundant structure is already known in many ISM tracers, including optical filaments • Additional evidence for structure implied by derived dust scattering properties in the UV (a ~ 0.4, g ~ 0.8), which are at odds with most models unless the dust is clumpy • Chance cloud/cluster collision – opportunity to see random CNM sample lit by passing stars (perhaps shaped in part by the interaction, but only in part)

  8. Extended Pleiades Nebulosity - Image by Russell

  9. Burrell Schmidt 0.6m Mosaic (log intensity scale) Gibson & Nordsieck (2003)

  10. IRAS 100 um, Log Scale

  11. Larger IRAS View

  12. Burrell-Schmidt 0.6m Mosaic (log intensity scale)

  13. Burrell-Schmidt 0.6m Mosaic (log intensity scale)

  14. Single Burrell-Schmidt Field

  15. Single Burrell-Schmidt Field

  16. Close-up of nebulosity East of Merope - WIYN 3.5m Merope (23 Tau)

  17. Close-up of nebulosity East of Merope - WIYN 3.5m Merope (23 Tau)

  18. IC 349, Barnard’s Merope Nebula HST Planetary Camera (Herbig & Simon 2000)

  19. IRAS 100 um, Log Scale

  20. IRAS 100 um, Log Scale

  21. Burrell-Schmidt 0.6m Mosaic (log intensity scale)

  22. VLA D-array mosaic + Green Bank 43m H I 21cm emission V(LSR) = -1.3 km/s Gibson, Holdaway & Nordsieck (1995)

  23. VLA D-array mosaic + Green Bank 43m H I 21cm emission V(LSR) = +10 km/s Gibson, Holdaway & Nordsieck (1995)

  24. HI Filaments : Cylinders or Sheets? • VLA beam-scale = 60” ~ 0.035 pc • dT ~ 30 K, FWHM ~ 6 km/s • So NHI(tau<<1) ~ 3.5e+20 cm^-2 • If line-of-sight thickness = angular diameter, then n ~ 3000 cm^-3; for T=50 K, n*T = 150,000!

  25. HI Filaments : Cylinders or Sheets? • PCNM(therm)/k ~ 4000 (``standard’’) • PCNM(turbulence) /k ~ 20,000 (Heiles 1997) • PCNM(HSEQ)/k ~ 28,000 (Boulares & Cox 1990) • P(therm) => elongation factor of 38 or T=1.3 K • P(turb) => elongation factor of 7.5 or T=6.7 K • P(HSEQ) => elongation factor 5.4 or T=9.3 K

  26. VLA D-array mosaic + Green Bank 43m H I 21cm emission V(LSR) = +10 km/s

  27. How Else Can CNM Be Imaged? • Dust and Emission are both useful for targets away from the Galactic plane. • What about down in the disk, where most material is found? • Try absorption, using velocity to discriminate distance and to probe Galactic kinematics

  28. A Very Nearby Edge-On Spiral

  29. Galactic H I 21 cm Line Emission Leiden-Dwingeloo Northern Sky Survey (Hartmann & Burton 1997)

  30. A Closer View of Galactic H I(Small Single-Dish Radio Telescope; one velocity plane in the Perseus Arm) 25-m Radio Telescope, Dwingeloo (0.5 degree beam) Netherlands Foundation for Radio Astronomy

  31. A Closer View of Galactic H I(Radio Interferometer Synthesis Array; one velocity plane in the Perseus Arm) 7-element Interferometer, Penticton (1 arcminute beam) Dominion Radio Astrophysical Observatory equivalent diameter equals 600m Canadian Galactic Plane Survey (Taylor et al. 2003)

  32. H I Self-Absorption (HISA) Has both fine-scale angular and velocity structure.

  33. CGPS Sample HISA

  34. Dark Optical and Radio Clouds • Both HISA and classical optical dark clouds trace cold gas in the ISM. • Optical dark clouds can be found on many scales. • With synthesis imaging, we see that HISA also exists on a range of scales. • How small does it go?

  35. Coalsack Dust Cloud Perseus HISA Complex Distance ~ 600 pc Angular size ~ 7 x 4 deg2 Physical size ~ 75 x 45 pc2 Distance ~ 2000 pc Angular size ~ 3 x 2 deg2 Physical size ~ 105 x 70 pc2

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