A hot topic: the 21cm line I Benedetta Ciardi MPA
I: Introduction on 21cm line & its present use II: IGM reionization process III: Other future applications IV: Radio telescopes Outline
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
H atom UV Visible IR Paschen Series
Atmospheric visibility T. Wilson Spitzer Hubble Chandra Compton GRO
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
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 MHz MHz MHz
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
o Distribution of HI in the Milky Way and other galaxies What have we observed with 21 cm line?
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.
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
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
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
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
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
x 10³ GHz: thermal emission from dust 21cm: HI NASA 0.4 GHz: cosmic rays 2.7 GHz: synchrotron emission from eˉ 115 GHz: molecular clouds
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
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
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
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
Marchesini et al. 2002
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
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
o Distribution of HI in the Milky Way and other galaxies What have we observed with 21 cm line?
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?
Intermediate and high velocity clouds o Gas clouds with velocities incompatible with differential galactic rotation o IVC: 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
Intermediate and high velocity clouds Miller 2004 M51M83
Intermediate and high velocity clouds Wakker et al. 2007
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?
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?
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
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?
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?
o Highest column density HI absorption lines seen in QSOs spectra: Damped Lyalpha systems
absorption features at ν>ν Lyα HIQSO Damped Lyalpha systems
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
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
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
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
Damped Lyalpha systems Kanekar & Chengalur 2003 spiral galaxies
Damped Lyalpha systems York et al DLA at z=2.289 Ly-alpha 21cm
Damped Lyalpha systems DLA at z= Ly-alpha 21cm Rao & Turnshek 2000Lane et al. 2000
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?
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?
Fundamental constants Michael Murphy
Fundamental constants o Redshifted spectral lines provide a probe for variations in constants Murphy at al Curran, Kanekar & Darling 2004
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?