Baryonic Dark Matter and Galaxy Formation

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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 Fluctuations Cosmological
background Filamentary Structures Cosmological
simulations Baryonic Galaxies Seen with HST
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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?

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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 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)
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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)
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Hot Gas in filaments
Detection of OVI in X-ray?
WHIM
ICM
DM
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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)
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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 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)
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Predictions LCDM cusp versus core
Power law of density profile a 1-1.5,
observations a 0
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Hoekstra et al (2001)
sDM/sHI
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 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
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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
zgt1
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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?
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Too many small structures
Today, CDM simulations predict 100 times too
many small haloes around galaxies like the Milky
Way
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Cold Gas AccretionBars 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)
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Statistics on bar strength (OSU) Quantification
of the accretion rate Block, Bournaud, Combes,
Puerari, Buta 2002
Observed
Doubles the mass in 10 Gyr
No accretion
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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
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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 AccretionLopsided Galaxies
Peculiar galaxies without any companion Richter
Sancisi (1994) 1700 galaxies, 50 asymmetric
Late-types 77 Matthews et al 98 Stellar disk
also Zaritsky Rix 97 About 20 of
galaxies have A1 gt 0.2 In NIR distribution
(OSUB sample) 2/3 have A1 required by an
external mechanism
ltA1gt 1.5rd lt r lt2.5rd
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Frequency of m1 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 m1 of isolated
galaxies, the correlation with type and with
m2 ? a large number of m1 by accretion

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Simulations m1 accretion
Only gas accretion (here with 4 Mo/yr) can
explain the observed frequency of m1 and the
long life-time of the perturbation
NGC 1637 simulation observations NIR
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Avoidance of dynamical friction
GAS
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 Same process as feedback, but can be
more efficient (Gnedin Zhao 02)
The gas, stripped, does not experience friction
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Disruption of small structures
More cold gas in dwarf haloes Much less
concentration 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
LSB (Mayer et al 01)
HSB
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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
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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)
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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)
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Baryonic dark matter? Cold H2 Clouds
Mass 10-3 Mo density 1010 cm-3 size 20
AU 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)
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
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D1.8
Formation by Jeans recursive fragmentation ? ?a
hierarchical fractal ML N ML-1 rLD NrL-1D a
rL-1/rL N-1/D cf Pfenniger Combes 1994
D2.2
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Projected mass log scale (15 mag) N10,
L9 The surface filling factor depends strongly
on D lt 1 for D1.7
Pfenniger Combes 1994
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Turbulence?
Simulation of 2D turbulence 800x800, with star
formation 70 Myr Ratio 1000 between
densities max and min (Vazquez-Semadeni et al 97)
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Simulations of self-gravitating gas Klessen et
al (98)
Gas clouds (____) Proto-stellar cores
(------) vertical limit with N5105 dN/ dm
m?, with ? -1.5 At the end, 60 of the mass
is in the cores
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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
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Simulations of the galactic plane Huber
Pfenniger (01)
D smaller with more dissipation
Middle Dissipation
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Cooling flows in galaxy clusters
Cooling time lt 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...
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Perseus Ha (WIYN) and optical (HST)
Ha, 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 lt 200kpc (Ettori et al 02) oscillation
dynamical time
60kpc filament Ha (Cowie et al 85) at
V(amas) ?Cooling wake The cD galaxy at V374km/s
w/o cluster
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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)
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Polar Ring Galaxies (PRG)
PRG are composed of an early-type host surrounded
by a gasstars 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
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Formation of Polar Rings
By accretion? Schweizer et al 83 Reshetnikov et
al 97
By collision? Bekki 97, 98
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Tully-Fisher for PRGs
UGC4261
AM2020-504
TF in I band
Iodice et al 2002
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TF in K band for PRGs with simulations
15peak
Ex Simulations
Circles massless triangles massive
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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
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Model of E3 halo flattened in the equatorial
plane xy
Massless ring
Massive ring (as massive as the host)
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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 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
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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

• 4 lines
• 1000 x more sensitive ISO-SWS
• L2
• Soyuz
• 99 Meuro

Survey integration 5s 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
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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