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H2 in external galaxies and baryonic dark matter
London March 2007
Françoise COMBES
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Hypothesis for dark baryons
b ~ 5% 90% of baryons are dark
Baryons in compact objects (brown dwarfs, white dwarfs,
black holes) are either not favored by micro-lensing experimentsor suffer major problems(Alcock et al 2001, Lasserre et al 2000, Tisserand et al 2004)
Best hypothesis is gas, Either hot gas in the intergalactic and inter-cluster medium(Nicastro et al 2005)
Or cold gas in the vicinity of galaxies and cosmicfilaments (Pfenniger & Combes 94)
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Dark gas in the solar neighborhood
By a factor 2 (or more)Grenier et al (2005)
Dust detected in B-V(by extinction)and in emission at 3mm
Emission Gamma associatedTo the dark gas
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Arnault et al 1988
LCO/M(HI) α (O/H)2.2
Confirmed by Taylor & Kobulnicky (98)But see Walter et al (2003) Leroy et al (2005)
Dwarfs and low
metallicity environments
N6946
CO as a tracer of H2
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HI as a tracer of DMHI gas is the interface with the extragalactic radiation fieldBeyond the HI disk, truncature due to ionisation the interface is ionized
Explains the correlation DM/HI
(Bosma 1981, Freeman 1994, Carignan 1997)
The observed ratio DM/HI ~10 for spiral galaxies, varies slightlywith morphological type, decreases for dwarfs and LSB
Mass profiles for dwarf Irr galaxies dominated by DM stringent test that constrain CDM (Burkert & Silk 1997)
even collisional (Spergel & Steinhardt 99)
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Extension in UV (GALEX) XUV disks, M83 and others
M83, Galex, +HI contours (red)Thilker et al 2005Yellow line RHII, 10Mo/pc2 in HI
Bluer regions outsideYounger SF + scattered light
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Extension of galaxies in HI
HI
M83: optical
NGC 5055 Sbc Milky Way-like spiral (109 M of HI): M83
Dark halo exploration
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Hoekstra et al (2001)
DM/HI
In average ~10
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Rotation Curves of dwarfs
DM has a radial distribution identical to that of HI gas
The ratio DM/HI depends slightly on type(larger for early-types)
NGC1560
HI x 6.2
From Combes 2000
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Combination with MONDNGC 1560 Tiret & Combes 2007, variation of a0 ~ 1/(gas/HI)
V4 = a0 GM
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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)
Baryonic dark matter incold H2 clouds
Around galaxies, the baryonicmatter may dominate
The stability of cold H2 gas is dueto its fractal structure
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First structures
After recombinaison, GMCs of 105-6 Mo collapse and fragmentdown to 10-3 Mo, H2 cooling efficient
The bulk of the gas does not form stars but a fractal structure, in statistical equilibrium with TCMBSporadic star formation
after the first stars, Re-ionisation
The cold gas survives and will be assembled in more large scale structures to form galaxies
A way to solve the « cooling catastrophy »
Regulates the consumption of gas into stars (reservoir)
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Where are the baryons?
6% in galaxies ; 3% in galaxy clusters (X-ray gas)
<18% in Lyman-alpha forest of cosmic filaments
5-10% in the Warm-Hot WHIM 105-106K
65% are not yet identified!
The majority of baryons are not in galaxies
WHIM
ICM
DM
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Ly-alpha forest
(Ly) = 0.008[N14J-23 R100 4.8/(+3)]1/2 h70
= 18% of baryons
N14 = typical Lycolumn densityJ = J-23 Extragalactic background radiation fieldR100 = assumed radius of absorber
Could be lower by a factor 3, if R100 = 0.1
Broad to narrow Ly ratio is 3 times larger at low redshift
Lehner et al (2006)
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WHIM from OVI absorptions
Stocke et al (2006) FUSEThe WHIM is observed at 350kpc from large galaxiesAt 100 kpc from dwarf galaxies
Certainly due to SN and superbubbles outflowAGN feedback, or Intergalactic accretion schocks(Shull 2006)
Multiphase gasHI and OVI not correlated
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WHIM 105-6K (OVI) 5-10%
Danforth & Shull 2005b(OVI) = 0.002-0.004 (0.2/f)(0.1/Z) = 5-10%
f(OVI) assumed ionisation fraction 20%Z metallicity, assumed 0.1 solar
Ionisation (photo) and metallicity quite uncertain
NeVIII more difficult to find, but photoionisation less uncertainF(NeVIII) < 15%
b(NeVIII) < b(OVI)
Assuming IGM, but if only around galaxies?
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>106K WHIM observations?OVII, OVIII
Detection of 2 filaments at z=0.011 and z=0.027 with ChandraIn front of the los of Mk421 blazar, during an outburst (ToO)n = 10-6 cm-3, N ~10 15cm-2 (~5-100)
X-ray absorption lines OVII, NVII +FUSE OVIOVII, and individual lines at 2-4 (Nicastro et al 2005)Not confirmed by XMM summary of observations of Mk421Williams et al (2006)
May be 40% of the missing baryons, as predictedby CDM simulations (Cen et al 1999)
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Nicastro et al 2005
3 lines fittedat the same timez=0z=0.011z=0.027v=3300km/sv=8090km/s
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UV Lines of H2
• Absorption lines with FUSE (Av < 1.5)• Ubiquitous H2 in our Galaxy (Shull et al 2000, Rachford
et al 2001) translucent or diffuse clouds, from 1014cm-2
• Absorption in LMC/SMC reduced H2 abundances, high UV field (Tumlinson et al 2002)
• High Velocity Clouds detected (Richter et al 2001) in H2
(not in CO)
• 16/35 IVCs detected, while 1/19 HVC detected in H2
Wakker et al 2006
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FUSE Spectrum of the LMC star Sk-67-166 (Tumlinson et al 2002) NH2 = 5.5 1015cm-2
Ly 4-0
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Infrared Lines of H2
• Ground state, with ISO & Spitzer (28, 17, 12, 9μ) • From the ground, 2.2 μ, v=1-0 S(1)• excitation by shocks, SN, outflows, UV pumping, X
• require T > 2000K, nH2 > 104cm-3
• exceptional merger N6240: 0.01% of L in the 2.2 μ line (all vib lines 0.1%?)
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H2 distribution in NGC891 (Valentijn, van der Werf 1999)S(0) filled; S(1) open – CO profile (full line)
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NGC 891, Pure rotational H2 lines S(0) & S(1)S(0) wider: more extendedDerived N(H2)/N(HI) = 20 ; Dark Matter?
Large quantitiesof H2 revealed by ISO
N(H2) = 1023 cm-2
T = 80 – 90 K
5-15 X HI
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Spitzer H2 results
H2 line survey for 77 ULIRGs z=0.02-0.93 (Higdon S. et al 2006)
H2 mass (warm)= 107 to 109 MoWarm H2 is 1% of all H2 (CO)
H2 in Tidal Dwarf Galaxies :NGC5291 N/S: 460, 400 KMH2 (warm) =1-1.5105 Mo; if colder (150 K): 106 Mo
H2 in Stephan’s quintet: large-scale shock (Appleton et al 06)
H2 in the nascent starburst N1377 (Roussel et al 2006)
H2 in Cooling flows filaments (Egami et al 2006)
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Spitzer and
IRAS Images
+HI spectra (GBT)
High Velocity Clouds (HVC) infalling onto the Galaxy
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First detection of dust emission in the HVC– HVC Emissivity at 100
m ~ 10 times smaller than local gas, but only a factor 2 smaller at 160 m
Colder dust
Infrared-HI correlation
I (x,y) = ii NHI
i (x,y) + C(x,y)
Miville-Deschênes et al 2005
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H2 in Stephan’s quintetAppleton et al 2006broad (870 km/s) bright H2
group-wide shock wave
typical H2 excitation diagram: T01=185K at 51018T35=675K
No PAH features, very low excitation ionized gas
Shocks when the high-V intrudercollides with gas filaments in the group
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Perseus Cluster
Fabian et al 2003
Salome, Combes, Edge et al 06
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H2 in cooling flow clusters
Egami et al 2006
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ConclusionsDark baryons should in the form of gasA significant part could be cold molecular gas
The best tracer: pure rotational lines:Observations of excited warm H2 as a tracer
H2 in the outer parts of galaxies: H2* is a tracer of the bulk ofmolecular gas, which is invisible; In the main disk CO is a tracer, but it fails in the outer parts
Goals of the H2EX mission:Distribution of the warm H2 with respect to the underlying SF
Relation between the HI and H2 in galaxies; the detailed kinematicswill help to associate the various gas phases
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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 Cosmic Vision ESA
• 4 lines
• 1000 x more sensitive ISO-SWS
• L2
• Soyuz
• 100-200 Meuro