Download - A hot topic: the 21cm line I
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A hot topic:
the 21cm line
I
Benedetta CiardiMPA
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I: Introduction on 21cm line & its present use
II: IGM reionization process
III: Other future applications
IV: Radio telescopes
Outline
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Hydrogen is the dominant atom in the Universe: 93% of the atoms producedin 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
Motivations
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H atom
UV
Visible
IRPaschenSeries
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Atmospheric visibility
T. Wilson
Spitzer
Hubble
ChandraCompton GRO
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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
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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] Zem/abs ν
470 10 130 MHz
270 15 90 MHz
180 20 70 MHz
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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
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o Distribution of HI in the Milky Way and other galaxies
What have we observed with 21 cm line?
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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.
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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
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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 2006 Atlas of the universe
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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 2006 Atlas of the universe
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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
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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
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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
cloudsgasinmoleculescomplex:GHz10x4.42.8@MIR 4
dust and starsgiant:GHz10x248.6@NIR 4
stars:GHz10x4.6@Optical 5
gas shocked hot,:GHz10x36-6@rays-X 7
H and CR collisions:GHz10x7.2@rays- 13
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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
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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
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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
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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
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Marchesini et al. 2002
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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
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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
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o Distribution of HI in the Milky Way and other galaxies
What have we observed with 21 cm line?
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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?
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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 & MarrifieldWakker et al. 2007
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Intermediate and high velocity clouds
Miller 2004
M51 M83
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Intermediate and high velocity clouds
Wakker et al. 2007
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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?
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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?
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o 4315 HI 21cm emission line from HI Parkes All Sky Survey (HIPASS)
HI mass function of galaxies at z=0
ΩHI=ρHI/ρcrit
AHISS
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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?
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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?
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o Highest column density HI absorption lines seen in QSOs spectra:
Damped Lyalpha systems
220102 cmNHI
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absorption features at ν>νLyα
HI QSO
Damped Lyalpha systems
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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 ΩHI
Damped Lyalpha systems
220102 cmNHI
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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 ΩHI
Damped Lyalpha systems
220102 cmNHI
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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 ΩHI
o Observations in the optical (QSOs absorption spectra)
Damped Lyalpha systems
220102 cmNHIW
olfe
, Gaw
iser &
Pro
chaska
20
05
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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 ΩHI
o Observations in the optical (QSOs absorption spectra)
o Observations in the radio (radio sources absorption spectra)
Damped Lyalpha systems
220102 cmNHI
Kanekar & Chengular 2003Rao 2005
Wolfe, Gawiser, Prochaska 2005York et al. 2007
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Damped Lyalpha systems
Kan
eka
r & C
hen
galu
r 20
03
spiral galaxies
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Damped Lyalpha systems
York e
t al. 2
00
7
DLA at z=2.289
Ly-alpha
21cm
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Damped Lyalpha systems DLA at z=0.0912
Ly-alpha
21cm
Rao & Turnshek 2000 Lane et al. 2000
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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?
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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?
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Fundamental constants
Mich
ael M
urp
hy
hc
e22
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Fundamental constants
o Redshifted spectral lines provide a probe for variations in constants
Murphy at al. 2001Curran, Kanekar & Darling 2004
)(1)0(
)0(...),,(
)(
2
1
12
2
1
1
zz
zz
y
yyemy
z
p
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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?