The Most Luminous Quasars Amy Kimball NRAO Charlottesville (NAASC)
Harvey LisztLondon, January 2006 Harvey Liszt NRAO, CHARLOTTESVILLE.
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Transcript of Harvey LisztLondon, January 2006 Harvey Liszt NRAO, CHARLOTTESVILLE.
Harvey Liszt London, January 2006
What do we learn from studyingWhat do we learn from studyingH3
+ in the diffuse ISM
Harvey Liszt
NRAO, CHARLOTTESVILLE
Harvey Liszt London, January 2006
Hydrogen-bearing molecules in diffuse ISM
• H2, HD & H3+ (hydrogen/H ratios?)(hydrogen/H ratios?)
• All explained by embarrassingly-simple notions of static equilibrium at low n(H)
• But why?– Such equilibrium is VERY slow to occur– The chemistry of trace species cannot be
understood in these terms
• Not to be ungrateful, but we mustn’t become complacent.
Harvey Liszt London, January 2006
H2 turns us us on …
Harvey Liszt London, January 2006
H2 turns us us on …
EBV =0.07 mag, N(H)~4x1020 cm-2
Harvey Liszt London, January 2006
H2 turns us us on …
EBV =0.07 mag, N(H)~4x1020 cm-2
Harvey Liszt London, January 2006
H2 turns us us on …
EBV =0.07 mag, N(H)~4x1020 cm-2
Harvey Liszt London, January 2006
H2 turns us us on …
EBV =0.07 mag, N(H)~4x1020 cm-2
Harvey Liszt London, January 2006
Protonate, diffuselydiffusely protonate
Harvey Liszt London, January 2006
Protonate, diffuselydiffusely protonate
•C
opernicus
Harvey Liszt London, January 2006
Protonate, diffuselydiffusely protonate
Harvey Liszt London, January 2006
Protonate, diffuselydiffusely protonate
•C
opernicus
• N(CH) ~ 2-4x1013 cm-2
• => N(H2) < 1021 cm-2
• But N(H)~7-10x1021 cm-2
Harvey Liszt London, January 2006
Protonate, diffuselydiffusely protonate
•C
opernicus
• N(CO)/N(H) < 1-5x10-6
• N(CH) ~ 2-4x1013 cm-2
• => N(H2) < 1021 cm-2
• But N(H)~7-10x1021 cm-2
Harvey Liszt London, January 2006
Protonate, diffuselydiffusely protonate
Harvey Liszt London, January 2006
But what about CO emission?
Harvey Liszt London, January 2006
But what about CO emission?
Harvey Liszt London, January 2006
“Getting it”• Previously (1974, actually) we learned that
H I clouds are full of H2
• In the mid-1990’s we found out that they are full of trace polyatomics (more later)
• Ca. 1999 - now we learn that diffuse gas has a relatively high abundance of H3
+
• DEAL WITH IT!
• Let’s move on and talk in these terms
Harvey Liszt London, January 2006
Nature makes H2 … can we?
Harvey Liszt London, January 2006
Nature makes H2 … can we?
Harvey Liszt London, January 2006
Nature makes H2 … can we?
Harvey Liszt London, January 2006
Nature makes H2 … can we?
• <TK> = 70-80K• <nTK> = 1-3,000=> n ~ 12-40/cc
Harvey Liszt London, January 2006
Nature makes H2 … can we?
• <TK> = 70-80K• <nTK> = 2-3,000=> n ~ 25-40/cc
Harvey Liszt London, January 2006
Nature makes H2 … can we?
• <TK> = 70-80K• <nTK> = 2-3,000=> n ~ 25-40/cc
Harvey Liszt London, January 2006
Nature makes H2 … can we?
Harvey Liszt London, January 2006
Nature makes H2 … can we?
Harvey Liszt London, January 2006
What did that take?• Wolfire et al. (1995) heating/cooling
– Small grains/PAH heat gas, neutralize atomic ions
• Spitzer’s (1978) H2 - formation rate
– H2 forms as H atoms land on large grains
– 3x10-18 n(H) n(H I) TK1/2 cm-3 s-1
– Slights details of grain conditions!
• Lee et al. (1996) H2 - shielding factors
• EQUILIBRIUM with ambient radiation
• In other words, an exercise in model-building
Harvey Liszt London, January 2006
Chemistry of H3+ in partly-atomic gas
Harvey Liszt London, January 2006
Chemistry of H3+ in partly-atomic gas
• Every primary ionization creates an electron (duh)(duh)
• Every e gets two chances at knocking off an H3+
<= Chain stops if < 10% of H is H2, n(H3+) ~ n(e)-2
Harvey Liszt London, January 2006
Chemistry of H3+ in partly-atomic gas
• Every primary ionization creates an electron (duh)(duh)
• Every e gets two chances at knocking off an H3+
<= Chain stops if < 10% of H is H2, n(H3+) ~ n(e)-2
Harvey Liszt London, January 2006
H2, H3+, HD & H
Harvey Liszt London, January 2006
H2, H3+, HD & H
Harvey Liszt London, January 2006
H2, H3+, HD & H
Harvey Liszt London, January 2006
H2, H3+, HD & H
Harvey Liszt London, January 2006
H2, H3+, HD & H
Harvey Liszt London, January 2006
H2, H3+, HD & H
Harvey Liszt London, January 2006
H2, H3+, HD & H
Harvey Liszt London, January 2006
Taking a breather …• H2, H3
+ & HD can be understood in the very simplest terms– Late-time equilibrium of optically transparent, low
density, quiescent gas clots– Atomic-ion neutralization by PAH very important– One twist, enhanced low-level ionization of H, H2
• HD needs the kick every bit as much as H3+
• Dense dark molecular gas ain’t needed – or wanted for that matter
• So what’s the rub?
Harvey Liszt London, January 2006
Taking a breather …• H2, H3
+ & HD can be understood in the very simplest terms– Late-time equilibrium of optically transparent, low
density, quiescent gas clots– Atomic-ion eutralization by PAH very important– One twist, enhanced low-level ionization of H, H2
• HD needs the kick every bit as much as H3+
• Dense dark molecular gas ain’t needed – or wanted for that matter
• So what’s the rub?
Harvey Liszt London, January 2006
H3+ is no silver bullet
• Abundances of trace molecules which were unexplained before H3
+ remain unexplained
Harvey Liszt London, January 2006
H3+ is no silver bullet
• Abundances of trace molecules which were unexplained before H3
+ remain unexplained
N(HCO+)=2.4x1012
N(H2) ~1x1021
Harvey Liszt London, January 2006
H3+ is no silver bullet
• Abundances of trace molecules which were unexplained before H3
+ remain unexplained
• CO + H3+ will not explain HCO+
– Instead, HCO+ + e CO
• O + H3+ competes with O+ + H2
only for n(H) > few hundred/cc N(HCO+)=2.4x1012
N(H2) ~1x1021
Harvey Liszt London, January 2006
How quickly does H2 form?
Harvey Liszt London, January 2006
How quickly does H2 form?
Harvey Liszt London, January 2006
How quickly does H2 form?
Harvey Liszt London, January 2006
How quickly does H2 form?
Harvey Liszt London, January 2006
How quickly does H2 form?
Harvey Liszt London, January 2006
How quickly does H2 form?
Harvey Liszt London, January 2006
How quickly does H2 form?
Harvey Liszt London, January 2006
How quickly does H2 form?
Harvey Liszt London, January 2006
How quickly does H2 form?
Harvey Liszt London, January 2006
How quickly does H2 form?
Harvey Liszt London, January 2006
Time evolution of H3+
Harvey Liszt London, January 2006
Time evolution of H3+
Harvey Liszt London, January 2006
Time evolution of H3+
• High abundances of H3+ and
effects of varying H do not appear until the last minute
Harvey Liszt London, January 2006
Time evolution of H3+
Harvey Liszt London, January 2006
Summing up: H2, H3+ & HD
• They are trying as hard as they can to convince us they’re in a profoundly simple state of equilibrium with the ambient radiation field at low density and extinction
• But we’re wise to them!!!!– HOW DID THEY GET TO EQUILIBRIUMHOW DID THEY GET TO EQUILIBRIUM
• Diffuse clouds have tricks up their sleeves– ALL THOSE TRACE MOLECULESALL THOSE TRACE MOLECULES
Harvey Liszt London, January 2006
Summing up: H2, H, H33++ & HD & HD
• Locally H2 seems easy, but lacks context
• What is a diffuse (or “H I”)(or “H I”) ‘cloud’?• Size &/or column density spectra, volume filling factor,
total amount of gas in diffuse ISM?
• Duration?
• External dynamics?– Mechanisms which carry material between ISM phases?
• Internal dynamics?– ‘Turbulence’?
» Disappointingly few clues in absorption profiles
» Trace molecule chemistry speaking to us in loud grunts
Harvey Liszt London, January 2006
Summing up: HH22,, H3+ & HD
• Both HD and H3+ want the same change
– Gratifying to see that ionization balance works• In diffuse gas ionization balance is EVERYTHING
– Confirming contribution of PAH
• Isn’t this paradoxical, wanting more ionizing radiation?
– Is the enhanced low-level H-ionization really H?• If not, what then?
• Whatever it is, does it extend beyond diffuse ISM?– 35 year history of dense cloud chemistry with low H
» Is it even possible to invert the chemistry to check H?
Harvey Liszt London, January 2006
Summing up: epistemology• We are left with TWO puzzles
– How to understand the trace molecules?• H3
+ per se doesn’t help
– Why doesn’t the study of hydrogen (which is after all the dominant gas constituent) in its so many forms – H I, D I, H+, H2, HD, H3
+ – provide more insight?
• Observation of neutral diffuse gas alone is a closed system, lacking needed information– Answers must come from outside
Harvey Liszt London, January 2006
The end, thanks for having me
Harvey Liszt London, January 2006
H2, H3+, HD & H