The multiphase ISM

The multiphase ISM

Brief review of multiphase ISM topic presented at ISM* Group Meeting

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Claire Murray

July 20, 2020
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  1. The multiphase ISM* Claire Murray ISM* Group Meeting 07/20/20

  2. The multiphase ISM* * extremely broad topic for which I

    will not do justice or cover completely Claire Murray ISM* Group Meeting 07/20/20
  3. The interstellar medium: there’s stuff out there Extinction Absorption Polarization

    Barnard et al. 1905 Hartmann et al. 1904; Beals 1936 Hiltner et al. 1949 Ferriere 2001
  4. And it’s everywhere! Trumpler 1930 Ferriere 2001

  5. “Phase” = population with distinct T, n Hot Ionized Medium

    (HIM) 6 4 2 1 -3 -1 3 -1 4 2 + Dust Warm Ionized Medium (WIM) Warm Neutral Medium (WNM) Cold Neutral Medium (CNM) Molecular medium Log (T) ~ Log (n) ~
  6. “Galactic Science with the SKA” (Lorentz Center, 2014) The ISM

    is “multiphase”
  7. “Galactic Science with the SKA” (Lorentz Center, 2014) The ISM

    is “multiphase”
  8. Neutral hydrogen (HI) is multiphase GASS: McClure-Griffiths et al. 2009;

    McClure-Griffiths et al. 2015 p e p e 21 cm Parkes Radio Telescope
  9. Interferometric 21cm reveals cold and warm HI Hughes et al.

    1971 Clark 1965 Owens Valley Radio Observatory Background continuum source
  10. “Two-phase” equilibrium model Adapted from FGH69 Cold Warm Unstable Pressure

  11. “Two-phase” equilibrium model Cold Warm Unstable Pressure Adapted from FGH69

  12. A third, hot, diffuse component needs to be included OVI

    absorption Jenkins & Meloy 1974 Soft X-ray emission Burstein 1977 log(T) ~5.6-6.4 log(T)>6.3
  13. “Three phase” equilibrium model

  14. “Three phase” equilibrium model

  15. Ok, great, but is this what we see?

  16. Wolfire et al. 2003 ‣ Depends on metallicity, dust-to-gas ratio,

    radiation field… Heating •Photoelectric dust emission •Cosmic rays •Soft X-rays •Photoionization (C I, Si I, Fe I) •Collisional ionization of H, He Cooling •Radiative line emission (e.g., C II, O I, Lya) •e- recombination onto dust Phases = complex balance on vast range of scales
  17. Microphysics Macrophysics • Diffusion of ionizing photons from HII regions

    • Low-energy cosmic ray propagation • X-rays from soft gamma ray repeaters • Magnetic / hydrodynamic waves • MHD turbulence • Magnetic reconnection • Shocks from: SF, HII regions, cloud collisions, Galactic dynamics, spiral arms, etc… … requiring global understanding of many different energy sources! NASA/CXC/UCSC/ L. Lopez et al. WHAM/UW-Madison NASA/Goddard Conceptual Image Lab ESA/Planck Collaboration Nature; Gaensler et al. 2011 ESA/NASA/Hubble/ AURA/NSF Heiles & Troland 2003b Amount, temperature and ionization state depend on… ``The Warm Neutral Medium is the key to the Universe.”
  18. Morphology is a powerful tool Heiles 1967 • HI lives

    in “blobby sheets”? NRAO 300 ft
  19. Morphology is a powerful tool Heiles 1967 • HI lives

    in “blobby sheets”? NRAO 300 ft Nov 15 1988
  20. Peek et al. 2018 GALFA-HI, Arecibo Observatory; ~4’ angular resolution

    Morphology is a powerful tool
  21. Morphology is a powerful tool • HI fibers aligned with

    the magnetic field are real, cold structures Clark, Peek et al. 2014
  22. Morphology is a powerful tool Clark, Peek et al. 2014,

    2019 • HI fibers aligned with the magnetic field are real, cold structures
  23. Morphology is a powerful tool • HI fibers aligned with

    the magnetic field are real, cold structures • Large-scale bubbles and “chimney” breakouts illustrate past dynamics McClure-Griffiths et al. 2010
  24. Morphology is a powerful tool • HI fibers aligned with

    the magnetic field are real, cold structures • Large-scale bubbles and “chimney” breakouts illustrate Galaxy dynamics • Structure of intermed.-velocity clouds reveal role of colliding flows in phase transitions Miville-Deschenes et al. 2018
  25. Thermally-unstable gas is prevalent Cold Warm Unstable Adapted from Field,

    Goldsmith & Habing 1969
  26. Thermally-unstable gas is prevalent Optical depth TB [K] • Sensitive

    21cm observations detect gas with T~20-7000 K 52% 20% 28% WNM UNM CNM Heiles & Troland 2003; Murray et al. 2018b
  27. Thermally-unstable gas is prevalent • Sensitive 21cm observations detect gas

    with T~20-7000 K • Turbulence, supernovae populate “unstable” regime Audit & Hennebelle 2005 Weak turbulence Pressure CNM WNM Unstable Density Density Weak turbulence Strong turbulence Density SNe driven in density peaks SNe driven randomly Gatto et al. 2015
  28. We haven’t hunted down all phases yet ``Dark” gas? “Total

    gas” = HI + CO ‣ Optically-thick HI? ‣ H2 untraced by CO? ‣ Variations in dust grain emissivitiy? • ``Dark gas”: what is it? Planck Collaboration et al. 2011 Grenier et al. 2005 Dust rays
  29. We haven’t hunted down all phases yet ``Dark” gas? “Total

    gas” = HI + CO ‣ Optically-thick HI? ‣ H2 untraced by CO? ‣ Variations in dust grain emissivitiy? • ``Dark gas”: what is it? Planck Collaboration et al. 2011 Murray et al. 2018a Mostly not Grenier et al. 2005 Dust rays
  30. We don’t know where the diffuse gas is Murray et

    al. 2020; in prep WNM + CNM, |b|>30° GALFA-HI + HI4Pi; Peek et al. 2018, HI4Pi Collaboration et al. 2016
  31. We don’t know where the diffuse gas is Murray et

    al. 2020; in prep CNM, |b|>30° GALFA-HI + HI4Pi; Peek et al. 2018, HI4Pi Collaboration et al. 2016 Murray, Peek & Kim 2020
  32. The ISM is multiphase … and complicated

  33. Nope. Cox 2005 McKee & Ostriker 1977 The ISM is

    multiphase … and complicated “…the ideas are useful, the geometry is wrong, and the details trouble me."
  34. SRG/eROSITA 2020 HIM

  35. WIM Haffner et al. 2019

  36. HI4Pi et al. 2016 WNM

  37. Murray et al. in prep CNM

  38. ESA/Planck; Dame et al. 2001 Molecular gas

  39. “fin”