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A hot topic: the 21cm line I

A hot topic: the 21cm line I. Benedetta Ciardi. MPA. Outline. I: Introduction on 21cm line & its present use II: IGM reionization process III: Other future applications IV: Radio telescopes. Motivations. Hydrogen is the dominant atom in the Universe: 93% of the atoms produced

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A hot topic: the 21cm line I

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  1. A hot topic: the 21cm line I Benedetta Ciardi MPA

  2. Outline • I: Introduction on 21cm line & its present use • II: IGM reionization process • III: Other future applications • IV: Radio telescopes

  3. Motivations Hydrogen is the dominant atom in the Universe: 93% of the atoms produced in the Big Bang were H. How can we observe it? H2: Tex>500 K  very hard to observe cold H2 HII: free-free emission (Bremsstrahlung) free-bound emission (recombination) HI: bound-bound emission  excitation needed hyperfine transition at 21cm  cold HI can be probed

  4. H atom Paschen Series IR Visible UV

  5. Atmospheric visibility Hubble Spitzer Chandra Compton GRO T. Wilson

  6. 21 cm line Spins • Electron and proton are oppositely charged  • Magnetic poles aligned oppositely with respect to the spin • Spin parallel  energy a bit higher • Spin anti-parallel  energy a bit lower

  7. 21 cm line • Associated with hyperfine transition of HI • Population of the states is described by the Boltzmann equation • Used in emission or absorption • Doppler shift gives information on velocity • Ideal probe of the evolution of HI:

  8. History • Prediction of 21cm line in 1944 by Oort & van de Hulst • 1st detection on March 25th 1951 by Harold Ewen & Edward Purcell • Total cost: 500$ • Time from receipt of money to detection of line: 1yr (3.5 months actual work)

  9. What have we observed with 21 cm line? • Distribution of HI in the Milky Way and other galaxies

  10. HI distribution in galaxies • 21cm is not absorbed by dust  easily used to map HI • Doppler shift gives information on the velocity of the HI along the l.o.s.

  11. HI distribution in galaxies • 21cm is not absorbed by dust  easily used to map HI • Doppler shift gives information on the velocity of the HI along the l.o.s. Oort, Kerr & Wersterhout 1958

  12. HI distribution in galaxies • 21cm is not absorbed by dust  easily used to map HI • Doppler shift gives information on the velocity of the HI along the l.o.s. Levine, Blitz & Heiles 2006 Atlas of the universe

  13. HI distribution in galaxies • 21cm is not absorbed by dust  easily used to map HI • Doppler shift gives information on the velocity of the HI along the l.o.s. Levine, Blitz & Heiles 2006 Atlas of the universe

  14. HI distribution in galaxies • 21cm is not absorbed by dust  easily used to map HI • Doppler shift gives information on the velocity of the HI along the l.o.s. Andromeda HI density Velocity Braun, Corbelli et al. (in prep.)

  15. HI distribution in galaxies • 21cm is not absorbed by dust  easily used to map HI • Doppler shift gives information on the velocity of the HI along the l.o.s. • HI more extended than e.g. optical  study outer parts of galaxies

  16. Radio @ 0.4 GHz: cosmic rays 21cm: HI Radio @ 2.7 GHz: synchrotron emission from eˉ CO @ 115 GHz: molecular clouds FIR-MID @ 3-25 x 10³ GHz: thermal emission from dust NASA

  17. HI distribution in galaxies • 21cm is not absorbed by dust  easily used to map HI • Doppler shift gives information on the velocity of the HI along the l.o.s. • HI more extended than e.g. optical  study outer parts of galaxies NGC 2782 Optical 21cm Smith 1994; Jogee, Kenney & Smith 1998

  18. HI distribution in galaxies • 21cm is not absorbed by dust  easily used to map HI • Doppler shift gives information on the velocity of the HI along the l.o.s. • HI more extended than e.g. optical  study outer parts of galaxies Verheijen et al. 2001; Bottema et al. 1995 Mundell et al.

  19. HI distribution in galaxies • 21cm is not absorbed by dust  easily used to map HI • Doppler shift gives information on the velocity of the HI along the l.o.s. • HI more extended than e.g. optical  study outer parts of galaxies M81 Group Stellar light distribution 21cm distribution NRAO/AUI

  20. HI distribution in galaxies • 21cm is not absorbed by dust  easily used to map HI • Doppler shift gives information on the velocity of the HI along the l.o.s. • HI more extended than e.g. optical  study outer parts of galaxies • Rotation curves of galaxies

  21. Marchesini et al. 2002

  22. HI distribution in galaxies • 21cm is not absorbed by dust  easily used to map HI • Doppler shift gives information on the velocity of the HI along the l.o.s. • HI more extended than e.g. optical  study outer parts of galaxies • Rotation curves of galaxies

  23. HI distribution in galaxies • 21cm is not absorbed by dust  easily used to map HI • Doppler shift gives information on the velocity of the HI along the l.o.s. • HI more extended than e.g. optical  study outer parts of galaxies • Rotation curves of galaxies  dark matter Light curves HI rotation curves Rotation curves from light curves van Albada & Sancisi 1986

  24. What have we observed with 21 cm line? • Distribution of HI in the Milky Way and other galaxies

  25. What have we observed with 21 cm line? • Distribution of HI in the Milky Way and other galaxies • Intermediate and high velocity clouds

  26. Intermediate and high velocity clouds • Gas clouds with velocities incompatible with differential galactic rotation • IVC: 50-100 km/s • HVC: >100 km/s • Various origin: • - Galactic fountain • - gas stripped during interactions between galaxies • - infalling IG gas • - remnants from Local Group formation Binney & Marrifield Wakker et al. 2007

  27. Intermediate and high velocity clouds M51 M83 Miller 2004

  28. Intermediate and high velocity clouds Wakker et al. 2007

  29. What have we observed with 21 cm line? • Distribution of HI in the Milky Way and other galaxies • Intermediate and high velocity clouds

  30. What have we observed with 21 cm line? • Distribution of HI in the Milky Way and other galaxies • Intermediate and high velocity clouds • HI emission from galaxies  HI mass function of galaxies

  31. AHISS ΩHI=ρHI/ρcrit HI mass function of galaxies at z=0 • 4315 HI 21cm emission line from HI Parkes All Sky Survey (HIPASS)

  32. What have we observed with 21 cm line? • Distribution of HI in the Milky Way and other galaxies • Intermediate and high velocity clouds • HI emission from galaxies  HI mass function of galaxies

  33. What have we observed with 21 cm line? • Distribution of HI in the Milky Way and other galaxies • Intermediate and high velocity clouds • HI emission from galaxies  HI mass function of galaxies • Damped Lyalpha systems

  34. Damped Lyalpha systems • Highest column density HI absorption lines seen in QSOs spectra:

  35. HI QSO absorption features at ν>νLyα Damped Lyalpha systems

  36. Damped Lyalpha systems • Highest column density HI absorption lines seen in QSOs spectra: • Low SF and metallicity • Precursors of today's galaxies and the primary gas reservoir • Account for most neutral gas at z<5 (highest z=4.46)  used to estimate ΩHI

  37. Damped Lyalpha systems • Highest column density HI absorption lines seen in QSOs spectra: • Low SF and metallicity • Precursors of today's galaxies and the primary gas reservoir • Account for most neutral gas at z<5 (highest z=4.46)  used to estimate ΩHI

  38. Wolfe, Gawiser & Prochaska 2005 Damped Lyalpha systems • Highest column density HI absorption lines seen in QSOs spectra: • Low SF and metallicity • Precursors of today's galaxies and the primary gas reservoir • Account for most neutral gas at z<5 (highest z=4.46)  used to estimate ΩHI • Observations in the optical (QSOs absorption spectra)

  39. Damped Lyalpha systems • Highest column density HI absorption lines seen in QSOs spectra: • Low SF and metallicity • Precursors of today's galaxies and the primary gas reservoir • Account for most neutral gas at z<5 (highest z=4.46)  used to estimate ΩHI • Observations in the optical (QSOs absorption spectra) • Observations in the radio (radio sources absorption spectra) Kanekar & Chengular 2003 Rao 2005 Wolfe, Gawiser, Prochaska 2005 York et al. 2007

  40. Damped Lyalpha systems Kanekar & Chengalur 2003 spiral galaxies

  41. DLA at z=2.289 Damped Lyalpha systems Ly-alpha York et al. 2007 21cm

  42. DLA at z=0.0912 Damped Lyalpha systems Rao & Turnshek 2000 Lane et al. 2000 Ly-alpha 21cm

  43. What have we observed with 21 cm line? • Distribution of HI in the Milky Way and other galaxies • Intermediate and high velocity clouds • HI emission from galaxies  HI mass function of galaxies • Damped Lyalpha systems

  44. What have we observed with 21 cm line? • Distribution of HI in the Milky Way and other galaxies • Intermediate and high velocity clouds • HI emission from galaxies  HI mass function of galaxies • Damped Lyalpha systems • Fundamental constants

  45. Michael Murphy Fundamental constants

  46. Fundamental constants Murphy at al. 2001 Curran, Kanekar & Darling 2004 • Redshifted spectral lines provide a probe for variations in constants

  47. What have we observed with 21 cm line? • Distribution of HI in the Milky Way and other galaxies • Intermediate and high velocity clouds • HI emission from galaxies  HI mass function of galaxies • Damped Lyalpha systems • Fundamental constants

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