1. H 2 in external galaxies and baryonic dark matter London March 2007 Françoise COMBES

2. 2 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 experiments or 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 cosmic filaments (Pfenniger & Combes 94)

3. 3 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 associated To the dark gas

4. 4 Arnault et al 1988 L CO /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 H 2

5. 5 HI as a tracer of DM HI gas is the interface with the extragalactic radiation field Beyond 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 slightly with 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)

6. 6 Extension in UV (GALEX) XUV disks, M83 and others M83, Galex, +HI contours (red) Thilker et al 2005 Yellow line RH II, 10M o /pc 2 in HI Bluer regions outside Younger SF + scattered light

7. 7 Extension of galaxies in HI HIHI M83: optical NGC 5055 Sbc Milky Way-like spiral (10 9 M  of HI): M83 Dark halo exploration

8. 8 Hoekstra et al (2001)  DM /  HI In average ~10

9. 9 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

10. 10 Combination with MOND NGC 1560 Tiret & Combes 2007, variation of a 0 ~ 1/(gas/HI) V 4 = a 0 GM

11. 11 Mass ~ 10 -3 Mo density ~10 10 cm -3 size ~ 20 AU N(H 2 ) ~ 10 25 cm -2 t ff ~ 1000 yr Adiabatic regime: much longer life-time Fractal: collisions lead to coalescence, heating, and to a statistical equilibrium (Pfenniger & Combes 94) Baryonic dark matter in cold H 2 clouds Around galaxies, the baryonic matter may dominate The stability of cold H 2 gas is due to its fractal structure

12. 12 First structures After recombinaison, GMCs of 10 5-6 Mo collapse and fragment down to 10 -3 Mo, H 2 cooling efficient The bulk of the gas does not form stars but a fractal structure, in statistical equilibrium with TCMB Sporadic 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)

13. 13 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 10 5 -10 6 K  65% are not yet identified! The majority of baryons are not in galaxies WHIM ICM DM

14. 14 Ly-alpha forest  (Ly  ) = 0.008[N 14 J -23 R 100 4.8/(  +3)] 1/2 h 70 = 18% of baryons N 14 = typical Ly  column density J = J -23  Extragalactic background radiation field R 100 = assumed radius of absorber Could be lower by a factor 3, if R 100 = 0.1 Broad to narrow Ly  ratio is 3 times larger at low redshift Lehner et al (2006)

15. 15 WHIM from OVI absorptions Stocke et al (2006) FUSE The WHIM is observed at 350kpc from large galaxies At 100 kpc from dwarf galaxies Certainly due to SN and superbubbles outflow AGN feedback, or Intergalactic accretion schocks (Shull 2006) Multiphase gas HI and OVI not correlated

16. 16 WHIM 10 5-6 K (OVI) 5-10% Danforth & Shull 2005  b (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 uncertain F(NeVIII) < 15%  b (NeVIII) <  b (OVI) Assuming IGM, but if only around galaxies?

17. 17 >10 6 K WHIM observations? OVII, OVIII Detection of 2 filaments at z=0.011 and z=0.027 with Chandra In front of the los of Mk421 blazar, during an outburst (ToO) n = 10 -6 cm-3, N ~10 15 cm -2 (  ~5-100) X-ray absorption lines OVII, NVII +FUSE OVI OVII, and individual lines at 2-4  (Nicastro et al 2005) Not confirmed by XMM summary of observations of Mk421 Williams et al (2006) May be 40% of the missing baryons, as predicted by CDM simulations (Cen et al 1999)

18. 18 Nicastro et al 2005 3 lines fitted at the same time z=0 z=0.011 z=0.027 v=3300km/s v=8090km/s

19. 19 UV Lines of H 2 Absorption lines with FUSE (Av < 1.5) Ubiquitous H 2 in our Galaxy (Shull et al 2000, Rachford et al 2001) translucent or diffuse clouds, from 10 14 cm -2 Absorption in LMC/SMC reduced H 2 abundances, high UV field (Tumlinson et al 2002) High Velocity Clouds detected (Richter et al 2001) in H 2 (not in CO) 16/35 IVCs detected, while 1/19 HVC detected in H 2 Wakker et al 2006

20. 20 FUSE Spectrum of the LMC star Sk-67-166 (Tumlinson et al 2002) NH 2 = 5.5 10 15 cm -2 Ly 4-0

21. 21 Infrared Lines of H 2 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, nH 2 > 10 4 cm -3 exceptional merger N6240: 0.01% of L in the 2.2 μ line (all vib lines 0.1%?)

22. 22 H 2 distribution in NGC891 (Valentijn, van der Werf 1999) S(0) filled; S(1) open – CO profile (full line)

23. 23 NGC 891, Pure rotational H 2 lines S(0) & S(1) S(0) wider: more extended Derived N(H 2 )/N(HI) = 20 ; Dark Matter? Large quantities of H 2 revealed by ISO N(H 2 ) = 10 23 cm -2 T = 80 – 90 K 5-15 X HI

24. 24 Spitzer H 2 results  H 2 line survey for 77 ULIRGs z=0.02-0.93 (Higdon S. et al 2006) H 2 mass (warm)= 10 7 to 10 9 Mo Warm H 2 is 1% of all H 2 (CO)  H 2 in Tidal Dwarf Galaxies :NGC5291 N/S: 460, 400 K MH 2 (warm) =1-1.510 5 Mo; if colder (150 K): 10 6 Mo  H 2 in Stephan’s quintet: large-scale shock (Appleton et al 06)  H 2 in the nascent starburst N1377 (Roussel et al 2006)  H 2 in Cooling flows filaments (Egami et al 2006)

25. 25 Spitzer and IRAS Images +HI spectra (GBT) High Velocity Clouds (HVC) infalling onto the Galaxy

26. 26  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) =  i  i N HI i (x,y) + C  (x,y) Miville-Deschênes et al 2005

27. 27 H 2 in Stephan’s quintet Appleton et al 2006 broad (870 km/s) bright H 2 group-wide shock wave typical H 2 excitation diagram: T 01 =185K at 510 18 T 35 =675K No PAH features, very low excitation ionized gas Shocks when the high-V intruder collides with gas filaments in the group

28. 28 Perseus Cluster Fabian et al 2003 Salome, Combes, Edge et al 06

29. 29 H 2 in cooling flow clusters Egami et al 2006

30. 30 Conclusions Dark baryons should in the form of gas A significant part could be cold molecular gas The best tracer: pure rotational lines: Observations of excited warm H 2 as a tracer  H 2 in the outer parts of galaxies: H 2 * is a tracer of the bulk of molecular 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 H 2 with respect to the underlying SF  Relation between the HI and H 2 in galaxies; the detailed kinematics will help to associate the various gas phases

31. 31 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