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