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Understanding the Milky Way's Interstellar Medium and Cosmic Rays

This presentation by Alberto Carramiñana from the National Institute of Astrophysics, Optics, and Electronics discusses the intricate components of the Milky Way's interstellar medium (ISM) and the nature of cosmic rays. Topics include the composition of the ISM, stellar evolution, and the physical processes that govern gas dynamics and star formation. Additionally, it addresses the origin and propagation of cosmic rays, their energy spectrum, and their interaction with the Galactic magnetic field. Essential for those interested in astrophysics and cosmic phenomena.

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Understanding the Milky Way's Interstellar Medium and Cosmic Rays

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  1. Astroparticle physics2. The Milky Way interstellar medium and cosmic-rays Alberto Carramiñana Instituto Nacional de Astrofísica, Óptica y Electrónica Tonantzintla, Puebla, México Xalapa, 3 August 2004

  2. These presentations • Available (soon!) as http://www.inaoep.mx/alberto/cursos/ap2004_1a.ppt http://www.inaoep.mx/alberto/cursos/ap2004_1b.ppt http://www.inaoep.mx/alberto/cursos/ap2004_2.ppt http://www.inaoep.mx/alberto/cursos/ap2004_3.ppt http://www.inaoep.mx/alberto/cursos/ap2004_4.ppt

  3. The interstellar medium of the Galaxy • ISM: gas, dust, magnetic field, cosmic-rays. • Feedack: {gas (SF) stars (Winds, Sne) gas} • Stars enrich (& steer) gas; gas forms new stars. • Pressure equilibrium. Halo 300 pc Disk GC 15 kpc

  4. A little note: Oort’s limit • Statistical study of motion of stars in the Solar neighborhood: first evidence of “missing mass”. • Can be baryonic (or it can be non-baryonic...).

  5. ISM clouds • Most of the ISM (70%) is HI, H2, HII: • diffuse HI clouds:30 to 80 K, 100 to 800 cm-3, 1 to 100 M. • translucent molecular clouds:15 to 50 K, 500 to 5000 cm-3, 3 to 100 M, several pc accross. • giants molecular clouds: 20 K, 100 to 300 cm-3, up to 106 M, 50 pc • GMC cores :100 to 200 K, 107 to 109 cm-3, 10 to 1000 M, 0.05 to 1 pc. • Bok globules :10 K, n>104 cm-3, 1 to 1000 M, 1pc, (all?) harbour young stars in their center. • HII regions: ionized by massive near star.

  6. Dark clouds Brighter cloud!

  7. Stars • About 1011 of them in the Milky Way (Mg > 1.5 1011M). • Form, live and die: • M<8 M: pufff... • M>8 M: bang! • M>30 M: bang!? pufff? bang!!? SN 1987A

  8. Stellar remnants • Planetary nebula + white dwarf: • Vexp  100 km/s • Supernova remnant (SNR) + neutron star: • Vexp > 1000 km/s

  9. CO@2.6mm

  10. E  1 keV

  11. At 408 MHz

  12. Cosmic-rays • Energetic particles in Earth’s environment • Basic questions: • Energy? • Composition? • Origin? • Isotropy?

  13. Cosmic-rays: measured abundances • Charged particles: 99% nuclei + 1% electrons. • Heavy nuclei more abundant in CRs than solar. • {Li, Be, B} and {Sc, V, Ti,...} high C/O and Fe spallation • Cross sections spallation  X = 5 to 10 g cm-2 L  1000 kpc

  14. Cosmic-rays: energy spectrum • Power-law: • Secondaries (B) have steeper spectra than primaries (C,O).

  15. Cosmic-rays: energy density • Local ISM Spectrum inferred ucr 1eV cm-3 (0.83 for p alone) • CR and Galactic energetics: • Are SN the sources of (Galactic) CR? • Shock acceleration models: Fermi mechanism ok! • Need the smoking gun...

  16. Cosmic-rays: propagation • Cosmic-rays do not propagate in straight lines: trapped by Galactic magnetic field (average 3G) • Transport equation: • Leaky box model: • CR travel path: • Proton injection spectrum: • 10Be (mean life 3.9 Myrs) analysis: (Garcia-Muñoz, Mason & Simpson 1977)

  17. Galactic radio emission • Galactic radio emission = e-synchrotron • Inferred electron spectrum: 1 eV cm-3 • n(E)  E-2.14 for 70 MeV to 1200 MeV • n(E)  E-3.0 above 1 GeV • Electrons 1% of Earth’sCR spectrum.

  18. Cosmic-ray nuclei and matter • Galactic -ray emission model: • e-bremssthralung • pion production (secondary e produced) • e-inverse compton • Model needs HI & CO data input. Hunter et al. 1997

  19. Galactic -ray spectrum • 0 production spectrum 68 MeV bump • Galactic emission fairly well modelled. • Evidence for electrons and nuclei. Strong, Moskalenko & Reimer 2004

  20. Nearby galaxies • Only LMC detected as (weak) -ray source. • Limits on SMC, M31, nearby starburst cosmic-rays (E<1015 eV) are Galactic (local).

  21. Cosmic-ray and -ray sources • High energy sources must accelerate particles to produce -rays.

  22. Galactic -ray sources • Solar flare • Pulsars (aside: bound on photon mass) • Unidentified Galactic sources: young & old • SNR positional coincidences (so, maybe....) • young & old radio quiet pulsars • wind nebulae • microquasars

  23. Photon mass • Crab pulsar pulse coherent from (at least) 100 MHz to 1 GeV. • Pulse period = 33 ms. • Pulse broadening < 5% • Distance = 2 kpc (1 pc = 31015 m) • What is the limit on the mass of to photon?

  24. Cerenkov observations • Certain detection of Crab nebula. • Probable PSR 1706-44, Vela, SN1006. • Results not fully consistent (Č to Č, Č to EG) Weekes (2000)

  25. Kuiper et al. (2001) Crab spectrum • Nebula: can fit synchrotron + inverse Compton. • Pulsar: syncrotron + curvature + inverse Compton.

  26. Pulsar energetics: the Crab • Rotating neutron star: R* =10 km, M* =1.44 M , I = 1045 g/cm2 

  27. Pulsars • >1000 radio pulsars know • Power: up to few 1038 erg/s (Crab) per pulsar vs 2  1040 erg/s (CRs)  Probably sufficient • Pulsar models: pure electron acceleration • in vacuum: 1016 eV available; • in e+e- magnetosphere: only a “fraction” Romani 1994

  28. What do we need? • The hadronic 0 smoking gun! • And GLAST

  29. Very high energy cosmic-rays • Pulsar and Sne models can only reach 1015 eV (the knee) • At 100 TeV gyro-radius  thickness of Galactic disc. • To continue...

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