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CONDITIONS IN DENSE INTERSTELLAR CLOUDS

Explore the tools and parameters used by astronomers to determine the conditions in dense interstellar clouds, including temperature, density, and molecule abundances. Discover the importance of understanding these conditions for star formation and the cycling of material in the interstellar medium.

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CONDITIONS IN DENSE INTERSTELLAR CLOUDS

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  1. CONDITIONS IN DENSE INTERSTELLAR CLOUDS Paul F. Goldsmith Jet Propulsion Laboratory with thanks to Ted Bergin, Di Li, the SWAS team, and the Taurus Mapping Project

  2. CONDITIONS IN DENSE CLOUDS • Let us take a broad view and include • intensive and extensive parameters • chemical and physical quantities • various cloud components • Rather than review numerous results which are probably largely well-known, I would like to describe the TOOL KIT which astronomers have developed to determine these conditions THE HUNT FOR MOLECULES

  3. OVERVIEW I will devote most of my time to this task, but cannot resist including some new observations that while undigested indicate that the list of parameters needs to be expanded, and that at least some of the tools to determine them are becoming available THE HUNT FOR MOLECULES

  4. IMPORTANCE OF KNOWING CONDITIONS IN THE DENSE ISM • We wish to understand dense (molecular) clouds for their own sake, but perhaps more importantly as part of cycling of material through different phases of the ISM • Molecular clouds are the starting point for star formation • Conditions in dense clouds may (!) have major effect on formation of new stars THE HUNT FOR MOLECULES

  5. PARAMETER TOOL(S) COMMENTS THE HUNT FOR MOLECULES

  6. MULTIPLE TRANSITIONS ALLOW DETERMINATION OF CONDITIONS • Temperature • H2 density • CO column density EXTRAGALACTIC GALACTIC 2 Components THE HUNT FOR MOLECULES

  7. SOURCES WITH HINSA FEATURES HI Narrow Self-Absorption Dark Clouds in Taurus Emission from Galactic HI Background HI is Very Cold & Produces Very Narrow Lines OH Emission THE HUNT FOR MOLECULES

  8. PARAMETER TOOL(S) COMMENTS THE HUNT FOR MOLECULES

  9. TAURUS MOLECULAR CLOUD IN 13CO FCRAO 14m 50” resolution Nyquist sampled map with 1.5 Mpixels; 98 o2 coverage THE HUNT FOR MOLECULES

  10. PARAMETER TOOL(S) COMMENTS THE HUNT FOR MOLECULES

  11. TAURUS MOL. CLOUD IN 12CO30’ beam (Ungerechts & Thaddeus 1987) THE HUNT FOR MOLECULES

  12. TAURUS MOLECULAR CLOUD IN 12CO FCRAO 14m 50” resolution Nyquist sampled map with 1.5 Mpixels; 98 o2 coverage THE HUNT FOR MOLECULES

  13. TEMPERATURE IN CENTRAL PORTION OF ORION USING CH3OH Beuther et al. 2005 SMA 0.9” resolution THE HUNT FOR MOLECULES

  14. CONDITIONS IN CEPH A DISK(Patel et al. 2005) SOURCE HW2 D = 720 pc Blue: 3.6cm (C) Red: 1.3cm (C) Green: CH3CN Color: Dust (C) THE HUNT FOR MOLECULES

  15. Methyl Cyanide Probes Temperature of Gas in Disk => T = 25 – 75 K THE HUNT FOR MOLECULES

  16. PARAMETER TOOL(S) COMMENTS THE HUNT FOR MOLECULES

  17. THE HUNT FOR MOLECULES

  18. PARAMETER TOOL(S) COMMENTS THE HUNT FOR MOLECULES

  19. ISSUES re. CHEMICAL ABUNDANCES • Accuracy of Column Densities • Averaging Along Line of Sight • Appropriate Normalization to use, e.g. N(H2) Considering that all clouds have less well-shielded “outsides” and better shielded “insides” there is possible confusion between SURFACE and VOLUME species THE HUNT FOR MOLECULES

  20. H2O ABUNDANCE IN VARIOUS CLOUDS SWAS Dedicated ApJ issue (Aug 2000); Odin Dedicated A&A Issue (May 2003) THE HUNT FOR MOLECULES

  21. SWAS: VERY EXTENDED H2O EMISSION Melnick et al. 2005 (in prep.) THE HUNT FOR MOLECULES

  22. IS WATER A SURFACE TRACER? Does the water vapor intensity correlate better with (believed) surface tracers than with (believed) volume tracers? Orion molecular cloud: surface: CN N=1-0 113.14 GHz volume: C18O J=1-0 THE HUNT FOR MOLECULES

  23. WATER ABUNDANCE WITHIN MOLECULAR CLOUDS 10-4 Photo-dissociation= Photo-desorption Photo-dissociation Freeze-out 10-7 H2O Abundance Rel. to H2 n/G0 Rate  n(t) peak abun. at 2 - 4 mag AV THE HUNT FOR MOLECULES

  24. CLOUD AGEA “New” Parameter & One Way to Determine It Cold HI in a dense, well-shielded clouds is residual of past history in predominantly atomic form due to lower n and N accompanying larger size As such, N(HI)/N(H2) allows determination of CLOUD AGE “age” = 2x106 – 3x107 yr THE HUNT FOR MOLECULES

  25. TIMESCALES • Of great importance for understanding cloud evolution • Relative values of chemical and physical timescales are particularly significant • A variety of timescales are critical in the process of star formation THE HUNT FOR MOLECULES

  26. Integrated Intensity K-km s-1 THE HUNT FOR MOLECULES

  27. CONDITIONS IN DENSE CLOUDS - CONCLUSIONS • Astronomers have a versatile tool kit for determining key physical and chemical parameters • But new and better tools are always needed! • The validity of tools will have to be checked carefully as research moves into new areas such as very dense, evolved regions (cores,…disks) and very distant regions (other galaxies) • Grain surface chemistry has to be dealt with along with gas phase, and it may be making things very complicated! • High spatial dynamic range studies are essential to unravel the processes that govern molecular cloud structure and evolution THE HUNT FOR MOLECULES

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