A hot topic:

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A hot topic the 21cm line I
Benedetta Ciardi
MPA
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Outline

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

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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 Texgt500 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
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H atom
Paschen Series
IR
Visible

UV
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Atmospheric visibility
Hubble
Spitzer
Chandra
Compton GRO

T. Wilson
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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

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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

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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)

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What have we observed with 21 cm line?

• Distribution of HI in the Milky Way and other
  galaxies

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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.

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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
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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
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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
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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.)
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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

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

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Marchesini et al. 2002
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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

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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
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What have we observed with 21 cm line?

• Distribution of HI in the Milky Way and other
  galaxies

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What have we observed with 21 cm line?

• Distribution of HI in the Milky Way and other
  galaxies
• Intermediate and high velocity clouds

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Intermediate and high velocity clouds

• Gas clouds with velocities incompatible with
  differential galactic rotation
• IVC 50-100 km/s
• HVC gt100 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
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Intermediate and high velocity clouds
M51
M83
Miller 2004
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Intermediate and high velocity clouds
Wakker et al. 2007
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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

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HI mass function of galaxies at z0

• 4315 HI 21cm emission line from HI Parkes All
  Sky Survey (HIPASS)

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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

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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

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Damped Lyalpha systems

• Highest column density HI absorption lines seen
  in QSOs spectra

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Damped Lyalpha systems
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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 zlt5 (highest
  z4.46) ? used to estimate OHI

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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 zlt5 (highest
  z4.46) ? used to estimate OHI

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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 zlt5 (highest
  z4.46) ? used to estimate OHI
• Observations in the optical (QSOs absorption
  spectra)

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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 zlt5 (highest
  z4.46) ? used to estimate OHI
• 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
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Damped Lyalpha systems
Kanekar Chengalur 2003
spiral galaxies
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Damped Lyalpha systems
DLA at z2.289
Ly-alpha
York et al. 2007
21cm
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Damped Lyalpha systems
DLA at z0.0912
Rao Turnshek 2000
Lane et al. 2000
Ly-alpha
21cm
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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

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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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Fundamental constants
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Fundamental constants
Murphy at al. 2001 Curran, Kanekar Darling 2004

• Redshifted spectral lines provide a probe for
  variations in constants

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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