NEUTRAL HYDROGEN

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NEUTRAL HYDROGEN
Frank Briggs RSAA and ATNF
z 8
z 0
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Quasar Absorption lines
Wavelength (Angstroms)
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Quasar
(all DLAs have metal lines)
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Photons DE gt 13.6 eV
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bathe HI cloud in photoionizing radiation
?? minimum thickness of skin before
becomes self-shielding ??
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bathe HI cloud in photoionizing radiation
optical depth t gt 1 for DE 13.6 eV
photons
note t lt 1 transparent hard to heat!
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Energy Levels in Hydrogen
Optically thick at the Lyman limit
Optically thick in the Lyman
continuum
E 0
Energy
Ground State
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Energy Levels in Hydrogen
Optically thick in the Lyman
continuum
E 0
BUT HI layer is transparent to all other
wavelengths shorter than the
Lyman limit
Energy
Ground State
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Ionization by ambient starlight with l gt 912
Angstrom
E 0
Energy
Ground State
H He C N O Na Mg Al Si Ca Ti Cr Mn Fe Zn
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Quasar Absorption lines
Wavelength (Angstroms)
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Quasar Absorption lines
Lyman a forest
DLA
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Quasar Absorption lines

• thoroughly developed statistics !!!
• for Lyman a and metal lines

(ordinary Galaxies
(whatever is common is most likely to intervene
by chance)
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Relative interception cross sections
Z3 Ly break galaxy
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HI Column density distribution function
Petijean etal 1993
-10
-15
Log f(NHI)
-20
12 14 18
20 22
Log NHI
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HI Column density distribution function
Petijean etal 1993
-10
-15
Log f(NHI)
-20
12 14 18
20 22
Log NHI
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Relative interception cross sections What are
these things???
Z3 Ly break galaxy
(tough to image)pin
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nearby Neutral gas disks analogs to high Z DLAs
???
Optical Radio
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Extended, low-column density gas analog of
LymanLimit/MgII
CIV is the lower density material ??
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Square Kilometre Array
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ARRAY
Simple antenna elements
Array
Station
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Sensivity depends on collecting area
Angular resolution l/D
D
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Sensivity depends on collecting area

Angular resolution l/D
D
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VLA
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6th ATNF Synthesis Imaging Workshop Synthesis
Imaging from Centimetre to Millimetre
Wavelengths 12-16 May 2003 at Narrabri
NSW www.atnf.csiro.au/synthesis
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ARRAY
Simple antenna elements
Array
Station
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SKA Design
Magic Carpet
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Eggs on Legs
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3C196-G1 z 0.437 HST image (Ridgway
Stockton)
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Radio spectrum at 988 MHz Westerbork (Briggs,
deBruyn, Vermeulen)
Double Lobed Radio Source
300 km/s
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map emission ?
map absorption ?
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new GMRT
Kanekar Chengalur 988 MHz
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high redshift radio galaxies
TNR J22541857
TNR J1402-1510
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Radio galaxy spectra
No DLA absorption lines
No UV continuum
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Molonglo Telescope SKAMP III

• frequency coverage
• sensitivity
• RFI rejection

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Cosmic Evolution Indicators
Redshift
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Cosmic Evolution Indicators
Redshift
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Gnedins simulation of Reionization
http//casa.colorado.edu/gnedin/GALLERY/
log(mean intensity of ionizing flux)
log(Neutral fraction)
log(density)
log T
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.. ionized
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MAP
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MAP Result
Z 17 4
???
Rules out WDM
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Global Signal
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The Z20 Expt
JR, FB, et al
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Passband filters (from load scan) and RFI (from
sky scan)
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LOFAR and SKA
distributed star formation
Quasar
10 arcmin
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SUMMARY still plenty to do !
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