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NEUTRAL HYDROGEN

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Tot. 0. 1/3300. looks like HI is an endangered species !!! Where are the missing baryons ? ... but, only a tiny fraction of total baryons are neutral ... – PowerPoint PPT presentation

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Title: NEUTRAL HYDROGEN


1
NEUTRAL HYDROGEN
Frank Briggs RSAA and ATNF
z 8
z 0
2
Neutral gas in nearby GALAXIES
Optical Radio
3
Neutral gas in nearby GALAXIES
Radio only
4
Neutral gas in nearby GALAXIES
Velocity field from 21cm Line
5
Neutral gas in nearby GALAXIES
first strong evidence for Dark Matter in
galaxies
Velocity field from 21cm Line
Important Kinematic Tracer
6
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7
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8
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9
The Mice
10
our view of the Milky Way in the 21cm line
11
HI
12
  • HI fuel for star formation
  • . galaxies
  • HI kinematic tracer
  • . deduce galaxy mass
    distributions

13

14
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15
looks like HI is an endangered species !!!
16
Where are the missing baryons ???
17
??? How do you find H clouds ???
??? How do you find HI clouds ???
18
Energy Levels in Hydrogen
E 0
Energy
Ground State
19
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20
Energy Levels in Hydrogen
E 0
Energy
Ground State
21
Energy Levels in Hydrogen
E 0
Energy
Ground State
22
Energy Levels in Hydrogen
E 0
To excite optical UV lines need at least
10.2 eV
Energy
Ground State
23
Energy Levels in Hydrogen
E 0
Hyperfine splitting of H ground state
Energy
21 cm line
Ground State
24
Recombination competes with
Re-ionization
25
Time scales for Recombination
t n /R
recomb
e
26
Time scales for Recombination in IGM
t n /R
recomb
e
27
Time scales for Recombination
t n /R
recomb
e
28
Cartoon for Z 0
Sea of ionized baryons
F
?? Just HI ??
Stars HI gas
29
Is there an invisible population of LSB but
HI rich clouds ???
How could it escape notice ???
30
Radio spectroscopy
31
Optical Luminosity Function
(2df Madgwick etal)
info on HI Content of galaxies
Absolute Magnitude
32
HI Mass Function (dashed curve)
33
HI Content according to galaxy mass
34
Blind surveys for HI clouds
Arecibo Telescope
35
Feed Systems
36
Arecibo Telescope
very good for looking straight up !
37
Frequency
Time
38
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39
Arecibo Survey results
Log( M /M )
HI
solar
(Zwaan et al 1997)
40
Arecibo HI content according to galaxy mass
(Zwaan et al 1997)
41
where are HI selected galaxies located ???
Follow the same Large Scale Structure as
optically selected
except in rich clusters, which are HI
deficient
42
Latest (and greatest) survey HIPASS
Consortium ATNF, Melbourne, Cardiff, RSAA
43
Latest (and greatest) survey HIPASS
Results detected 1000s of galaxies no clear
IG HI Clouds
44
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45
Summary of HI in nearby (z0) Universe
  • good tracer of galaxies
  • but, only a tiny fraction of total baryons are
    neutral
  • looks like hydrogen must be confined, so that
    it can
  • shield itself against the ionizing background
  • if confined to sufficient density to remain
    neutral,
  • the gas is unstable to collapse and star
    formation
  • gt at z0, HI is inevitably associated
    with stars
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