Download pres

Baryonic Dark Matter and Galaxy
Formation
Françoise Combes, Observatoire de Paris
29 Avril 2005
Scenario of structure formation
Primordial Fluctuations
Cosmological background
Filamentary Structures
Cosmological simulations
Baryonic Galaxies
Seen with HST
Main problems of the L-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 small
radius of disks
 High predicted number of small haloes
Can the hypothesis that dark baryons are in the form of cold
gas 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 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 (Pfenniger & Combes 94)
Dark gas in the solar neighborhood
Dust detected in B-V
(by extinction)
and in emission at 3mm
Emission Gamma associated
To the dark gas
By a factor 2 (or more)
Grenier et al (2005)
Hot Gas in filaments
Detection of OVI in X-ray?
WHIM
ICM
DM
First gas structures
After recombinaison, GMCs of 10 5-6 Mo collapse and fragment
down 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 sDM/sHI = cste relation
All rotation curves can be explained, when the observed surface
density of gas is multiplied by a constant factor
 CDM would not be dominating in the center, as is already the case
in more evolved early-type galaxies, dominated by the stars
Simulated CCGS (cold collapsed gas and stars) is a function of Wb
(Gardner et al 03), and of resolution of simulations
(physics below the resolution)
Predictions LCDM: cusp versus core
Power law of density profile a ~1-1.5, observations a ~0
Hoekstra et al (2001)
sDM/sHI
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 DM
The 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 momentum
Rotation near the Galaxies, more easy to form disks
External gas accretion
Katz et al 2002:
shock heating to the dark halo
virial temperature, before cooling
to the neutral ISM temperature?
Spherical
Cold mode accretion is the most
efficient: weak shocks, weak
heating and efficient radiation
gas channeled along filaments
strongly dominates at z>1
Influence of Feedback
5 1015erg/g
adiabatic
during 30 Myr
Preventing star
formation
Gas above the
curve cannot
cool
Thacker & Couchman (2001) Conclusion: does not solve the
problem not enough resolution?
Too many small
structures
Today, CDM simulations
predict 100 times too many
small haloes around galaxies
like the Milky Way
Cold Gas Accretion:
Bars and secular evolution
Dynamical instabilities are responsible for evolution
With self-regulation
Bars form in a cold unstable disk
Bars 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
Observed
Block, Bournaud, Combes,
Puerari, Buta 2002
Doubles the mass
in 10 Gyr
No accretion
Merging of companion and gas accretion
To have bars, cold gas is required
to 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 accretion
from 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 companion
Richter & Sancisi (1994) 1700 galaxies, 50% asymmetric
<A1> 1.5rd < r <2.5rd
Late-types 77%
Matthews et al 98
Stellar disk also
Zaritsky & Rix 97
About 20% of galaxies
have A1 > 0.2
In NIR distribution
(OSUB sample)
2/3 have A1 required by
an external mechanism
Frequency of m=1 perturbation
Baldwin et al 80: kinematic waves have long life-time,
but not sufficient to explain the A1 frequency
Mergers
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
Only gas accretion (here with 4 Mo/yr)
can explain the observed frequency of m=1
and the long life-time of the
perturbation
NGC 1637: simulation
observations NIR
Avoidance of dynamical friction
GAS
CDM
If the gas flows slowly
in a cold phase on galaxies,
the hierarchical merging will
lose less angular momentum
through dynamical friction
Late (instead of early) accretion
The gas, stripped, does not
experience friction
Same process as feedback,
but can be more efficient
(Gnedin & Zhao 02)
Disruption of small structures
More cold gas in dwarf haloes
Much less concentration
LSB (Mayer et al 01)
Baryonic clumps heat DM through
dynamical friction and smooth any cusp
in dwarf galaxies
The material is more dissipative,
more resonant, and
more prone to disruption and merging
May change the mass function for
low-mass galaxies
HSB
Dark Matter in Galaxy Clusters
In clusters, the hot gas dominates the visible mass
Most baryons have become visible
fb = Wb / Wm ~ 0.15
The radial distribution dark/visible is reversed
The 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 clusters
The abscissa is the mean density in radius r, normalised
to the critical density (Sadat & Blanchard 2001)
Metallicity in clusters and galaxies
MFeICM = 2.2 MFe gal
Metals are ejected via winds, not ram
pressure, since no dependance on
richness, or S, but s (Renzini 03)
Same MFe/LB in clusters and
galaxies
Clusters have not lost iron,
nor accreted pristine material
a/Fe ~cste
Same processing in the field
(Renzini 1997, 2003)
Baryonic dark matter?
Cold H2 Clouds
Mass ~ 10-3 Mo
density ~1010 cm-3
size ~ 20 AU
90% of baryons are not visible
(primordial nucleosynthesis)
Around galaxies, the baryonic
matter dominates
The stability of cold H2 gas is due
to its fractal structure
N(H2) ~ 1025 cm-2
tff ~ 1000 yr
Adiabatic regime:
much longer life-time
Fractal: collisions
lead to coalescence,
heating, and to a
statistical equilibrium
(Pfenniger & Combes 94)
Formation by Jeans recursive
fragmentation ?
D=1.8
a hierarchical fractal
ML = N ML-1
rLD = NrL-1D
α = rL-1/rL= N-1/D
cf Pfenniger & Combes 1994
D=2.2
Projected mass
log scale (15 mag)
N=10, L=9
The surface filling
factor
depends strongly on D
< 1% for D=1.7
Pfenniger & Combes 1994
Turbulence?
Simulation of 2D turbulence
800x800, with star formation
70 Myr
Ratio 1000 between densities
max and min
(Vazquez-Semadeni et al 97)
Simulations of
self-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 shear
Semelin & Combes 2000
The only way to maintain the fractal
is to re-inject energy at large
scale
The natural process is galactic
rotation
The structures at small and large scales
then subsist statistically
The shear continuously breaks the
condensations, which reform
Filaments form in permanence
at large scale
Simulations of the galactic plane
Huber & Pfenniger (01)
D smaller with more
dissipation
Middle
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 detected
Edge (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 black
Hole: schocks, jets, acoustic waves, bubles...
Perseus Ha (WIYN) and optical (HST)
Ha, 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 Ha (Cowie et al 85)
at V(amas)
Cooling wake
The 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
Ha +[NII] (grey scale)
Radio Jets: contours 6cm van Breugel et al 1984
The AGN creates cavités in the hot gaz  cooling on the boader
of cavités, where CO and Ha are observed
(Salomé & Combes 2004)
Polar Ring Galaxies (PRG)
PRG are composed of an early-type host
surrounded by a gas+stars perpendicular ring
The polar ring is akin to late-type galaxies
large amount of HI, young stars, blue colors
Unique opportunity to check the shape of
dark matter halo
But how to relate DM of PRG to DM of
spiral progenitors?
Formation scenarios
Formation of Polar Rings
By accretion?
Schweizer et al 83
Reshetnikov et al 97
By collision?
Bekki 97, 98
UGC4261
Tully-Fisher for PRGs
AM2020-504
Iodice et al 2002
TF in I band
TF in K band for PRGs with simulations
15%peak
Ex Simulations
Circles: massless
triangles: massive
Non-circular polar rings
Both components are seen
nearly edge-on (selection effect)
Observed V for PR is the
smallest, when DM is
flattened in the host
the more DM, the more PR are
excentric
Model of E3 halo flattened in the equatorial plane xy
Massless ring
Massive ring
(as massive as the host)
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 with
only the visible baryonic mass flattened along the host
With collisionless DM, both merging and accretion scenarios
produce either spherical haloes, or flattened along the host
If a large fraction of the DM around galaxies is dissipative
it 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
• 4 lines
• 1000 x more sensitive ISO-SWS
• L2
• Soyuz
• 99 Meuro
Survey
integration 5s limit
[sec] [erg s-1 cm-2 sr-1]
Milky Way
100
10-6
ISM SF
100
10-6
Nearby Galaxies
200
7 10-7
Deep Extra-Galactic 1000
3 10-7
total area
[degrees]
110
55
55
5
 CNES  Spitzer  Milky Way, NGC 1560
Conclusion
The physics of the baryonic gas is a crucial clue to the
formation of galaxies
The usual assumption that gas is shock heated to the virial temperature
of the dark haloes might not be true
Cold gas accretion instead, with the consequence of more baryons
accreted at a given time
 dominance in the center of galaxies masking the cusps
 large gas extent around galaxies, less angular momentum lost
by dynamical friction
 more disruption and merging of the small masses