Molecular component in the Milky Way IRAM Summer School Lecture 2 Françoise COMBES.
Baryonic Dark Matter and Galaxy Formation Françoise Combes, Observatoire de Paris 29 Avril 2005.
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Transcript of Baryonic Dark Matter and Galaxy Formation Françoise Combes, Observatoire de Paris 29 Avril 2005.
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Baryonic Dark Matter and Galaxy Formation
Françoise Combes, Observatoire de Paris
29 Avril 2005
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Scenario of structure formation
Primordial FluctuationsCosmological background
Filamentary StructuresCosmological simulations
Baryonic GalaxiesSeen with HST
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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?
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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)
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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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Hot Gas in filaments
WHIM
ICM
DM
Detection of OVI in X-ray?
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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)
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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)
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Predictions CDM: cusp versus core
Power law of density profile ~1-1.5, observations ~0
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Hoekstra et al (2001)
DM/HI
In average ~10
Cf Baryonic TF relation (McGaugh et al 00)
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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
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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
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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
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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
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Too many small structures
Today, CDM simulations predict 100 times too manysmall haloes around galaxieslike the Milky Way
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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)
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Statistics on bar strength (OSU)
Quantification of the accretion rate Block, Bournaud, Combes,
Puerari, Buta 2002
Observed
No accretionDoubles the massin 10 Gyr
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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
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History of star formation
Isolated galaxy Galaxy with accretion and mergers
Accretion is compatible with doubling the mass in 10 Gyr
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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
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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
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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
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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
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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
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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
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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)
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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)
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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?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
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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
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Projected mass log scale (15 mag)
N=10, L=9
The surface fillingfactordepends strongly on D
< 1% for D=1.7
Pfenniger & Combes 1994
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Simulation of 2D turbulence800x800, with star formation 70 MyrRatio 1000 between densitiesmax and min(Vazquez-Semadeni et al 97)
Turbulence?
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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
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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
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Simulations of the galactic plane Huber & Pfenniger (01)
MiddleDissipation
D smaller with more dissipation
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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...
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Perseus H (WIYN) and optical (HST)
H, Conselice 01
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Acoustic waves in Perseus with
Chandra
Fabian et al 2003
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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
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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)
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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
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Formation of Polar Rings
By collision?Bekki 97, 98
By accretion?Schweizer et al 83Reshetnikov et al 97
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Tully-Fisher for PRGs
TF in I bandIodice et al 2002
AM2020-504
UGC4261
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TF in K band for PRGs with simulations15%peak
Ex Simulations
Circles: masslesstriangles: massive
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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
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Model of E3 halo flattened in the equatorial plane xy
Massive ring(as massive as the host)
Massless ring
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TF of the host vs Polar Ring
Spiral galaxies
hosts
PRs
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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
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H2 pure rotational lines
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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
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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 Spitzer Milky Way, NGC 1560
• 4 lines
• 1000 x more sensitive ISO-SWS
• L2
• Soyuz
• 99 Meuro
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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