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Cosmic Rays: Gas Phase Astrophysics and Astrochemistry

Cosmic Rays: Gas Phase Astrophysics and Astrochemistry. Marco Spaans (Groningen) Rowin Meijerink (Leiden), Edo Loenen (Leiden), Paul van der Werf (Leiden), Padelis Papadopoulos (Bonn). CRDRs (CRs/SNe) MDRs (shocks) PDRs (UV/SBs) XDRs (X-ray/AGN).

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Cosmic Rays: Gas Phase Astrophysics and Astrochemistry

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  1. Cosmic Rays:Gas Phase Astrophysics and Astrochemistry Marco Spaans (Groningen) Rowin Meijerink (Leiden), Edo Loenen (Leiden), Paul van der Werf (Leiden), Padelis Papadopoulos (Bonn)

  2. CRDRs (CRs/SNe) • MDRs (shocks) • PDRs (UV/SBs) • XDRs (X-ray/AGN)

  3. Multi-Phase Medium; heating by CRs or dust(Wolfire et al. 2003; Spaans & Norman 1997; Field et al. 1969)

  4. Metallicity & Multi-Phase ISM: Lower metallicity yields smaller molecular clouds X-factor: CO/H2 Mihos et al. (1999), Bolatto et al. (1999), Roellig et al. (2006)

  5. CR protons upto 100 MeV listed: H2 ionization, while 1-20 GeV CRs responsible for bulk of π0 mesons → 2γ and, e.g., pp→pnπ+

  6. Effects of CRs? • One often has a UV irradiated cloud edge • PDR model with CR rate = 5x10-15 s-1; so SN rate for ~100 M0/yr • Note small changes in C, OH and H2O

  7. CR ionization acts deep in molecular clouds (similar to XDRs)

  8. PDRs: 6 < E < 13.6 eV • Heating: Photo-electric emission from grains and cosmic rays • Cooling: Fine-structure lines like [OI] 63, 145; [CII] 158 μm and emission by H2, CO, H2O • 10 eV photon penetrates 0.5 mag of dust • Heating efficiency ~ 0.1 – 1.0 %

  9. XDRs: E > 1 keV • Heating: X-ray photo-ionization --> fast electrons - Coulomb heating H and H2vibexcitation - UV • Cooling: [FeII] 1.26, 1.64; [OI] 63; [CII] 158; [SiII] 35 μm; thermal H2vib; gas-dust • 1 keV photon penetrates 1022 cm-2 of NH • Heating efficiency ~ 10 – 50 %

  10. PDR (left) with n=105 cm-3 and G=103.5 • XDR with n=105 cm-3 and FX = 5.1 erg s-1 cm-3 • Note NH dependence H2, C+, C, CO, OH, etc.

  11. ------------------------------------------------------- CR heating: ~8 eV per H2 ionization (H, He slightly different Cravens & Dalgarno 1978)

  12. CRs can dominate gas heating for SFR > 100 Mo/yr; think of Arp220 and IMF through MJeans(Papadopoulos 2010)

  13. CRs drive ionization and shift C+-C-CO transition

  14. CRs drive ionization, form molecular ions

  15. Particularly oxygen bearing ones!

  16. BUT: CRs ≠ X-rays; only very high CR rates boost OH+ and H2O+ (fine-structure lines little affected by CRs)

  17. Mrk 231 SPIRE data van der Werf et al. (2010)

  18. How about shocks? M82, shock tracer SiO 2-1 + 4.8 GHz radio (García-Burillo et al. 2001, IRAM PdB)

  19. M82, CO 6-5 (116K; Ward et al. 2003, CSO)

  20. Jump Conditions

  21. J-Shocks of > 50 km/s lead to high compression, molecule dissociation and reformation in the shock wake

  22. J-shock structure

  23. J-shock chemistry

  24. Summary • CRs (strongly) affect cloud chemistry (in SBs) and can be distinguished from XDRs and shocks through OH, H2O, OH+, H2O+, H3O+ and high-J CO; not through fine-structure and low-J CO lines if UV irradiation acts • For the future, ALMA will be crucial to provide spatial information on CR exposed molecular clouds

  25. Maloney et al. (1996)

  26. Energetics G0 =1.6x10-3 erg cm-2 s-1is the Habing flux over 6-13.6 eV Orion Bar has 105 G0 FX= 84 L44 r2-2erg cm-2 s-1 is the X-ray flux over 1-100 keV with a power law E-0.9 Think of Seyfert nucleus at 100 pc or TTauri star with 1032 erg/s at 20 AU

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