Baryonic Dark Matter and Galaxy Formation

Françoise Combes, Observatoire de Paris

29 Avril 2005

Scenario of structure formation

Primordial FluctuationsCosmological background

Filamentary StructuresCosmological simulations

Baryonic GalaxiesSeen with HST

Main problems of the -CDM paradigm

Dark matter cusps in galaxy centers, in particular absent in dwarf Irr, dominated by dark matter

Low angular momentum of baryons, and consequent smallradius of disks

High predicted number of small haloes

Can the hypothesis that dark baryons are in the form of coldgas help to solve the problems?

Hypothesis for dark baryons

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 (Pfenniger & Combes 94)

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

Hot Gas in filaments

WHIM

ICM

DM

Detection of OVI in X-ray?

First gas structures

After recombinaison, GMCs of 10 5-6 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 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)

Cusps in galaxy centers

Dwarf Irr galaxies are dominated by dark matter, but also the gas mass is dominating the stellar mass

Obey the DM/HI = cste relation

All rotation curves can be explained, when the observed surfacedensity of gas is multiplied by a constant factor

CDM would not be dominating in the center, as is already the casein more evolved early-type galaxies, dominated by the stars

Simulated CCGS (cold collapsed gas and stars) is a function of b

(Gardner et al 03), and of resolution of simulations(physics below the resolution)

Predictions CDM: cusp versus core

Power law of density profile ~1-1.5, observations ~0

Hoekstra et al (2001)

DM/HI

In average ~10

Cf Baryonic TF relation (McGaugh et al 00)

Rotation curves of dwarfs

DM radial distribution identical to that in HI gas

The DM/HI ratio depends slightly on type(larger for early-types)

NGC1560

HI x 6.2

Angular momentum and disk formation

Baryons lose their angular momentum on the CDM

Usual paradigm: baryons at the start same specific AM than DMThe gas is hot and shock heated to the Virial temperature of the halo

But another way to accrete mass is cold gas mass accretion

Gas is channeled through filaments, moderately heated by weak shocks, and radiating quickly

Accretion is not spherical, gas keeps angular momentumRotation near the Galaxies, more easy to form disks

External gas accretion

Katz et al 2002:

shock heating to the dark halovirial temperature, before coolingto the neutral ISM temperature?Spherical

Cold mode accretion is the mostefficient: weak shocks, weakheating and efficient radiation

gas channeled along filamentsstrongly dominates at z>1

Influence of Feedback

Thacker & Couchman (2001) Conclusion: does not solve the problem not enough resolution?

5 1015erg/gadiabaticduring 30 Myr

Preventing starformation

Gas above thecurve cannot cool

Too many small structures

Today, CDM simulations predict 100 times too manysmall haloes around galaxieslike the Milky Way

Cold Gas Accretion:Bars and secular evolution

Dynamical instabilities are responsible for evolutionWith self-regulation

Bars form in a cold unstable diskBars produce gas inflow, and Gas inflow destroys the bar +gas accretion

Recent debate about this cycle-- is bar destruction efficient?-- can bars reform?Central Mass Concentration (CMC)

Statistics on bar strength (OSU)

Quantification of the accretion rate Block, Bournaud, Combes,

Puerari, Buta 2002

Observed

No accretionDoubles the massin 10 Gyr

Merging of companion and gas accretion

To have bars, cold gas is requiredto increase self-gravity of the disk

Dwarf companions: not more than 10% of accretion(interaction between galaxies heat the disk, Toth & Ostriker 92)

Massive interactions: develop the spheroids

Required: a source of continuous cold gas accretionfrom the filaments in the near environment of galaxies

Cosmological accretion can explain bar reformation

History of star formation

Isolated galaxy Galaxy with accretion and mergers

Accretion is compatible with doubling the mass in 10 Gyr

Cold Gas Accretion:Lopsided Galaxies

Peculiar galaxies without any companionRichter & Sancisi (1994) 1700 galaxies, 50% asymmetric

Late-types 77%Matthews et al 98Stellar disk alsoZaritsky & Rix 97

About 20% of galaxieshave A1 > 0.2In NIR distribution (OSUB sample) 2/3 have A1 required byan external mechanism

<A1> 1.5rd < r <2.5rd

Frequency of m=1 perturbationBaldwin et al 80: kinematic waves have long life-time, but not sufficient to explain the A1 frequencyMergers Gas accretion Bournaud, Combes, Jog, Puerari, 2005

The parameter A1 (density) does not correlate with the tidal index Tp ~ M/m r3/D3

Most galaxies are isolated (Wilcots & Prescott 04)A1 and A2 are correlated, for each type

Interactions and mergers cannot explain The m=1 of isolated galaxies, the correlation with type and with m=2 a large number of m=1 by accretion

Simulations m=1 : accretion

NGC 1637: simulation observations NIR

Only gas accretion (here with 4 Mo/yr)can explain the observed frequency of m=1and the long life-time of the perturbation

Avoidance of dynamical friction

CDM

GAS

If the gas flows slowlyin a cold phase on galaxies,the hierarchical merging willlose less angular momentumthrough dynamical friction

Late (instead of early) accretion

Same process as feedback, but can be more efficient(Gnedin & Zhao 02)

The gas, stripped, does notexperience friction

Disruption of small structures

More cold gas in dwarf haloesMuch less concentration

Baryonic clumps heat DM throughdynamical friction and smooth any cuspin dwarf galaxies

The material is more dissipative, more resonant, andmore prone to disruption and merging

May change the mass function for low-mass galaxies

LSB (Mayer et al 01)

HSB

Dark Matter in Galaxy Clusters

In clusters, the hot gas dominates the visible massMost baryons have become visible

fb = b / m ~ 0.15

The radial distribution dark/visible is reversedThe mass becomes more and more visible with radius

(David et al 95, Ettori & Fabian 99, Sadat & Blanchard 01)

The gas mass fraction varies from 10 to 25% according to clusters

Radial distribution of the hot gas fraction fg in clustersThe abscissa is the mean density in radius r, normalisedto the critical density (Sadat & Blanchard 2001)

Metallicity in clusters and galaxies

MFeICM = 2.2 MFe gal

Metals are ejected via winds, not rampressure, since no dependance on richness, or , but Renzini 03)

Same MFe/LB in clusters and galaxies

Clusters have not lost iron,nor accreted pristine materialFe ~cste

Same processing in the field(Renzini 1997, 2003)

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?Cold H2 Clouds

90% of baryons are not visible(primordial nucleosynthesis)

Around galaxies, the baryonicmatter dominates

The stability of cold H2 gas is dueto its fractal structure

Formation by Jeans recursivefragmentation ?

a hierarchical fractal

ML = N ML-1

rLD = NrL-1

D

α = rL-1/rL= N-1/D

cf Pfenniger & Combes 1994

D=2.2

D=1.8

Projected mass log scale (15 mag)

N=10, L=9

The surface fillingfactordepends strongly on D

< 1% for D=1.7

Pfenniger & Combes 1994

Simulation of 2D turbulence800x800, with star formation 70 MyrRatio 1000 between densitiesmax and min(Vazquez-Semadeni et al 97)

Turbulence?

Simulations ofself-gravitating gas

Klessen et al (98)

Gas clouds (____)Proto-stellar cores (------)

vertical: limit with N=5105

dN/ dm ~ mγ, with γ ~ -1.5

At the end, 60% of the mass is in the cores

Stabilisation by galactic shearSemelin & Combes 2000

The only way to maintain the fractalis to re-inject energy at largescale

The natural process is galactic rotation

The structures at small and large scalesthen subsist statistically

The shear continuously breaks the condensations, which reform

Filaments form in permanenceat large scale

Simulations of the galactic plane Huber & Pfenniger (01)

MiddleDissipation

D smaller with more dissipation

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 ampkitude 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 optical (HST)

H, Conselice 01

Acoustic waves in Perseus with

Chandra

Fabian et al 2003

Abell 1795: cooling wake

T(cool) 300 Myr (Fabian et al 01)

200 Mo/yr for R < 200kpc (Ettori et al 02)

= oscillation dynamical time

60kpc filament H (Cowie et al 85)at V(amas)Cooling wakeThe cD galaxy at V=374km/s w/o cluster

A1795: CO(2-1) integrated map

Tight correspondance between CO(2-1) emission and the lines H +[NII] (grey scale)Radio Jets: contours 6cm van Breugel et al 1984The AGN creates cavités in the hot gaz cooling on the boaderof cavités, where CO and H are observed(Salomé & Combes 2004)

Polar Ring Galaxies (PRG)

PRG are composed of an early-type hostsurrounded by a gas+stars perpendicular ring

The polar ring is akin to late-type galaxieslarge amount of HI, young stars, blue colors

Unique opportunity to check the shape ofdark matter halo

But how to relate DM of PRG to DM ofspiral progenitors?

Formation scenarios

Formation of Polar Rings

By collision?Bekki 97, 98

By accretion?Schweizer et al 83Reshetnikov et al 97

Tully-Fisher for PRGs

TF in I bandIodice et al 2002

AM2020-504

UGC4261

TF in K band for PRGs with simulations15%peak

Ex Simulations

Circles: masslesstriangles: massive

Non-circular polar ringsBoth components are seen nearly edge-on (selection effect)

Observed V for PR is the smallest, when DM isflattened in the host

the more DM, the more PR are excentric

Model of E3 halo flattened in the equatorial plane xy

Massive ring(as massive as the host)

Massless ring

TF of the host vs Polar Ring

Spiral galaxies

hosts

PRs

Implications of TF of PRGs

Most of PRGs require dark matter, aligned along the polar disk

Only 2 cases, where the ring is light, can be explained withonly the visible baryonic mass flattened along the host

With collisionless DM, both merging and accretion scenariosproduce either spherical haloes, or flattened along the host

If a large fraction of the DM around galaxies is dissipativeit is possible to account for the flattening along the polar disk

A large fraction must be gas

H2 pure rotational lines

ISO -Signal of dark matter

N(H2) = 1023 cm-2

T = 80 – 90 K

5-15 X HI

NGC 891

Grey matter

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 physics of the baryonic gas is a crucial clue to theformation of galaxies

The usual assumption that gas is shock heated to the virial temperatureof the dark haloes might not be true

Cold gas accretion instead, with the consequence of more baryonsaccreted at a given time dominance in the center of galaxies masking the cusps large gas extent around galaxies, less angular momentum lostby dynamical friction more disruption and merging of the small masses