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

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

3. 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: T ex >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 Motivations

4. H atom UV Visible IR Paschen Series

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

6. 21 cm line  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 Spins

7. o Associated with hyperfine transition of HI o Population of the states is described by the Boltzmann equation o Used in emission or absorption o Doppler shift gives information on velocity o Ideal probe of the evolution of HI: 21 cm line T [Myr] Z em/abs ν 47010130 MHz 2701590 MHz 1802070 MHz

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

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

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

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

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

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

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

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

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

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

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

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

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

21. Marchesini et al. 2002

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

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

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

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

26. Intermediate and high velocity clouds o Gas clouds with velocities incompatible with differential galactic rotation o IVC: 50-100 km/s o HVC: >100 km/s o 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 Miller 2004 M51M83

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

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

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

31. o 4315 HI 21cm emission line from HI Parkes All Sky Survey (HIPASS) HI mass function of galaxies at z=0 Ω HI = ρ HI / ρ crit AHISS

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

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

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

35. absorption features at ν>ν Lyα HIQSO Damped Lyalpha systems

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

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

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

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

40. Damped Lyalpha systems Kanekar & Chengalur 2003 spiral galaxies

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

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

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

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

45. Fundamental constants Michael Murphy

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

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