hunt for cold h 2 molecules
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Hunt for cold H 2 molecules. Françoise Combes, Observatoire de Paris 20 Septembre 2005. H 2 pure rotational lines. Uncertainties in X= H 2 /CO. Metallicity gradients (factor 10) Density structure (factor 10, across the mass spectrum) - PowerPoint PPT PresentationTRANSCRIPT
Hunt for cold H2 molecules
Françoise Combes, Observatoire de Paris
20 Septembre 2005
H2 pure rotational lines
Uncertainties in X= H2/CO
Metallicity gradients (factor 10)Density structure (factor 10, across the mass spectrum)Excitation conditions: High-z SB galaxies, X divided by 5
In spiral and dwarf galaxies, rotation curves could be explainedthrough HI-scaling by a factor 7-10Quite easy to explain rotation curves with dark H2 gas
Only 10-20% of the dark baryons in galaxiesThe rest in cosmic filaments
Dark baryons (90% of them) are not in compact objects (microlensing)
and should be in gas: either hot or cold
Perspectives of detectionH2 is a furtive molecule at low T: symmetric, no dipole
Hyperfine structure? (or ultrafine)Para-H2: I=0, J even -- Ortho-H2: I=1, Jodd
F=I+J F = 0, 1 and 2Interaction between nuclear spin, and B generated by rotationF=1-0: 546.4 kHz ( =0.5km)F=2-1 54.8 kHz (= 5.5km)
Line intensities extremely weak (nuclear magnetic dipole, A = 10-32s-1)
Require 106x surface for HI detection, i.e. 300x300km (beam 5’)Grid at 4, 8 per km (2400x2400 grid on the Moon?)
At the limit of T=0, H2 should be all paraO/P = 9 exp(-170/T)
But out of equilibrium, at low densityProton exchange H+ + H2(J=1) H+ +H2(J=0)
Significant amount of ortho-H2 at 3K
At 3K, the pressure of H2 clumps is 100 times the saturatedvapor pressure (Combes & Pfenniger 1997)
Latent heat = 110K/H2, no time to form much snowBut conditions for dimerisation
Continuum emission of dimers (dipole induced by collisions)Schaefer (1996, 1998)
Primordial molecules
HD: weak dipole moment(proton more mobile than deuteron)= 5.8 10-4 Debye (Trefler & Gush 1968)
J=1-0, 130 K above ground state, = 112Only from excited regions not a good tracer
LiH: = 5.9 Debye (Laurence et al 1963)
J=1-0, 21 K above ground state, = 0.67mm (450GHz)Impossible from the ground, H2O absorptionLiH/H2 ~ 10-10
~1 N(LiH) = 1012cm-2 or N(H2) =1022cm-2
H2+:Abundance 10-11-10-10
Hyperfine structure, but not in N=0 state, only N=1, I=1, S=1/2Eu=110K, the more likely at 1343 MHz
Traces of C and O in « primordial » gas
A residual 10-3 solar abundance in Ly clouds
CO emission very sensitive to Z (=1 cloud size varies)Threshold of photo-dissociation (Av=0.25mag?)
Problem of heating sources, T ~ Tbg
Absorption, bias towards diffuse cloudsSurface filling factor < 1%
Mass ~ 10-3 Modensity ~1010 cm-3
size ~ 20 AU
N(H2) ~ 1025 cm-2
tff ~ 1000 yr
Adiabatic regime:much longer life-time
Fractal: collisionslead to coalescence, heating, and to astatistical equilibrium(Pfenniger & Combes 94)
Hardly visible cold H2 Clouds
Around galaxies, the baryonicmatter dominates
Connection with the filaments
The stability of cold H2 gas is dueto its fractal structure
Fractal M ~ rD
Recursive Jeansfragmentation
Projected mass log scale (15 mag)
The surface fillingfactordepends strongly on D
< 1% for D=1.7
Pfenniger & Combes 1994
-rays: Dark gas in the solar neighborhood
H2 x a factor 2 (or more)Grenier et al (2005)
Dust detected in B-V(by extinction)and in emission at 3mm
-Emission associatedto the dark gas
Cooling flows in galaxy clusters
Cooling time < Hubble time at the center of clusters Gas Flow, 100 to 1000 Mo/yr
Mystery: cold gas or stars formed are not detected?
Today, the amplitude of the flow has been reduced by 10 and the cold gas is detectedEdge (2001) Salomé & Combes (2003) 23 detected galaxies in CO
Results from Chandra & XMM: cooling flow self-regulated
Re-heating process, feedback due to the active nucleus or blackHole: schocks, jets, acoustic waves, bubles...
Perseus H (WIYN) and CO (IRAM)
H, Conselice 01 Salome, Combes, Edge et al 05
Perseus ClusterFabian et al 2003
OSER: Optical Scintillation by Extraterrestrial Refractors
Moniez, 2005
ISO –Pure
H2 rotational lines
N(H2)= 1023 cm-2
T = 80 – 90 K
5-15 X N(HI)
NGC 891
Valentijn &
Van der Werf 99
H2EXplorer
Survey integration 5 limit total area [sec] [erg s-1 cm-2 sr-1] [degrees]Milky Way 100 10-6 110 ISM SF 100 10-6 55 Nearby Galaxies 200 7 10-7 55 Deep Extra-Galactic 1000 3 10-7 5
CNES Spitzer Milky Way, NGC 1560
• 4 lines
• 1000 x more sensitive ISO-SWS
• L2
• Soyuz
• 99 Meuro
ConclusionThe H2/CO conversion ratio is still a big question in many « non-standard » circumstances: high-redshift galaxies, externalregions of galaxies, etc..
There could be large quantities of cold H2 not yet detected
Best future tracers pure rotational H2 lines, with H2* excited as tracer (H2EX) gamma rays (but cosmic rays?) primordial molecules, HD, LiH (high z, ALMA) absorption lines (UV, mm..) continuum dust emission (e.g. Miville-Deschênes et al 2005)