Post on 26-Dec-2015
A hot topic:
the 21cm line
I
Benedetta CiardiMPA
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 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
H atom
UV
Visible
IRPaschenSeries
Atmospheric visibility
T. Wilson
Spitzer
Hubble
ChandraCompton 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] Zem/abs ν
470 10 130 MHz
270 15 90 MHz
180 20 70 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 2006 Atlas 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 2006 Atlas 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
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
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: 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
Intermediate and high velocity clouds
Miller 2004
M51 M83
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
ΩHI=ρHI/ρcrit
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
220102 cmNHI
absorption features at ν>νLyα
HI QSO
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 ΩHI
Damped Lyalpha systems
220102 cmNHI
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
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
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
Damped Lyalpha systems
Kan
eka
r & C
hen
galu
r 20
03
spiral galaxies
Damped Lyalpha systems
York e
t al. 2
00
7
DLA at z=2.289
Ly-alpha
21cm
Damped Lyalpha systems DLA at z=0.0912
Ly-alpha
21cm
Rao & Turnshek 2000 Lane 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
Mich
ael M
urp
hy
hc
e22
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
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?