Jaan Einasto and ICRANet 16 December 2012

Saturday, December 15, 12 1. Dark matter timeline Local Dark Matter: invisible matter in the Galaxy in Solar vicinity Global Dark Matter: invisible matter surrounding galaxies Global dark matter Local dark matter Zwicky (1933) Öpik (1915) Kahn & Woltjer (1959) Kapteyn, Jeans (1922) Cluster Stability Symposium (1961) Oort (1932, 1960) Flat rotation of M31: Roberts (1965) Kuzmin (1952, 1955) Cluster X-ray data (1972 - ) Eelsalu (1959) DM non-stellar corona: Einasto et al (1974) Jõeveer (1972, 1974) DM stellar halo: Ostriker et al (1974) Bahcall (1985) DM conferences in , Tbilisi (1975) Gilmore et al (1989) Low M/L of galaxies: Faber et al (1977) Extended flat rotation: Rubin, Bosma (1978) Gravitational lensing (1979 - ) Non-baryonic neutrino HDM (1981) Non-baryonic CDM: Blumenthal et al (1984) LambdaCDM (1986- ) Fermi CDM annihilation detection (2012)

Saturday, December 15, 12 Local dark matter

Jan Hendrik Oort Grigory Kuzmin

Oort (1932, 1960) - there is some local matter not in visible stars Öpik, Kuzmin - amount of local DM is small, if anything Bahcall (1985) - dynamical density exceeds the density of visible stars 2 times Discussion continued until 1990; low amount of local DM confirmed

Saturday, December 15, 12 Global dark matter: two paths

1. From velocity dispersion in clusters & groups M/L ≈ 30 – 300 M/Lsun versus Galactic populations M/L ≈ 1 – 10 M/Lsun (Faber 1977)

2. Galaxy models Sandra Faber If galaxies consist of known stellar populations, then in outskirts of galaxies the rotational speed should decrease (A) Observed rotation curves are flat on galaxy outskirts (B)

Saturday, December 15, 12 Velocity dispersion

Coma cluster Zwicky (1933)

M/L ≈ 30 – 300 M/Lsun Groups and pairs of galaxies M/L ≈ 30 – 60 M/Lsun Galactic populations

M/L ≈ 1 – 10 M/Lsun

Local group Kahn & Woltjer (1959) (M31 + Galaxy are approaching) ⇒

12 Mtot ≈ 2-4 x 10 Msun Fritz Zwicky M/L ≈ 100 M/Lsun Problems: dispersion uncertain - cluster may consists of subclusters, number of galaxies in groups small, problems with membership

Saturday, December 15, 12 Rotation curves of galaxies

Vera Rubin

Rotation curves (Rubin & Ford 1970, Roberts 1974), (Bosma 1978) flat - suggest increasing cumulative mass

Saturday, December 15, 12 Models for Galaxy, M31, dwarfs in Local Group, M87

Galaxy M31

It is impossible to bring photometric and rotation data into agreement with known stellar populations. Way out of difficulty - the presence of a new population - corona of large mass and radius.

Models with massive corona (Mcorona ≫ Mopt) (Einasto 1972) However: rotation curves too short to determine the size and mass of the dark corona

Saturday, December 15, 12 Companions of giant galaxies measure the internal mass inside their orbit V2(r) = G M(r)/r

Einasto, Kaasik & Saar (1974) massive corona

Ostriker, Peebles & Yahil (1974) massive halo

Total mass in galaxies including massive corona/ halo is 0.2 of critical density Enn Saar Jim Peebles Saturday, December 15, 12 Tallinn, Tbilisi DM conferences (1975) Nature of DM Objections to Dark Matter Concept

Classical cosmological paradigm Groups of galaxies are bound with conventional masses M/LS = 4, M/LE = 30 Big Bang nucleosynthesis & smoothness of the Hubble flow suggests an Ω = 0.05 Materne & Tammann (1975)

If DM exists these data must be explained

Saturday, December 15, 12 The nature of Dark Matter

The nature of DM was a subject of intensive discussions for long time.

Kahn & Woltjer (1959) - hot gas Ostriker, Peebles & Yahil (1974) - faint stars

Dark matter conference Tallinn (1975) - stars and gas contradict observations & nucleosynthesis constraints, neutrinos can form supercluster-sized halos, but not galaxy halos

No good DM candidate found

Saturday, December 15, 12 New evidence for DM X-ray Observations of Clusters

Coma cluster in optical and X-rays. From X-ray data temperature and mass distribution can be calculated. Masses found from velocity dispersions confirmed

Saturday, December 15, 12 Gravitational Lensing

Cluster mass from lensing support high M/L, as found by X-ray and velocity dispersion data (Ellis et al. 1995)

Saturday, December 15, 12 Density of baryonic matter

Observed abundances of light elements and nucleosynthesis theory allow to determine the density of baryonic matter within rather small interval about 0.04 of critical density. Total matter density from dynamical arguments is 0.2 - 0.3 of critical density.

DM must be non-baryonic

Saturday, December 15, 12 Acceptance of Dark Matter Astro-Particle If DM is non-baryonic, then this helps to explain the paradox of small temperature fluctuations of cosmic microwave background radiation.

The role of dark matter: Dark matter is needed to start early enough gravitational clustering to form structure. This solves the Big-Bang Nucleosynthesis controversy

Now the presence of dark matter was accepted by leading theorists.

Conferences in Tallinn and Vatican on astro-particle physics (1981)

Saturday, December 15, 12 Growth of temperature & density fluctuations

To build up observed structures the amplitude of initial density fluctuations at the epoch of recombination must be ~10-3. WMAP data show that amplitude of baryonic matter is ~ 10-5. Density perturbations of non-baryonic dark matter start growing already during the radiation-dominated era, and have an amplitude needed to form structures.

Saturday, December 15, 12 CMB spectrum

WMAP satellite data yield CMB spectrum which has 1st maximum at wavelength l=200. This wavelength depends on the total matter/ energy density: Omega = 1, i.e. the density is equal to critical. Baryonic matter has density Omega = 0.04 (direct measurements and nucleosynthesis constraints). Most matter/energy is dark.

Saturday, December 15, 12 The composition of Universe From combined CMB, supernova explosion & LSS data it follows the composition of the Universe

1.0 age=1.00/Ho

0.90/H 0.8 o

!o=1 0.80/Ho " 0.6 ! 0.75/H Baryonic Matter 0.04 o 0.4 SN1a CMB 0.70/H Dark Matter 0.23 o

Dark Energy 0.72 0.2

0.67/Ho 185 < lpeak < 209 0.0 0.0 0.2 0.4 0.6 0.8 1.0

!m Saturday, December 15, 12 Neutrinos as DM

The only known in 1981 non-baryonic particle was neutrino. However, numerical simulation of neutrino dominated universe (Melott 1983) has no fine structure as the real Universe (Joeveer, JE 1978).

Saturday, December 15, 12 Hot, Warm & Cold Dark Matter

Primack and Blumenthal (1984) suggested to classify elementary particles as dark matter candidates: hot, if free streaming erases all but supercluster-scale fluctuations (neutrinos); warm, if free streaming erases fluctuations smaller than galaxies; cold, if free streaming is unimportant.

Cold dark matter candidates are either very heavy particles that become non-relativistic very early (gravitinos, photinos), or are particles that have almost zero peculiar velocity (axions).

Saturday, December 15, 12 Left: LCDM simulation in box L=512 Mpc/h Right: SDSS slice, 10 Mpc/h thick at distance R=240 Mpc/h: rich superclusters in lower part form the Sloan Great Wall CDM model analyzed by Melott et al (1983) & Blumenthal et al (1984) LCDM simulation was performed by Gramann et al (1986) CDM & LCDM simulations represent observations well

Saturday, December 15, 12 Properties of DM halos

Central surface density of galaxies is constant over very wide range of galaxy luminosities. Some feedback between luminous baryonic matter and dark matter is needed to keep the surface density constant (the fraction of DM in galaxies of different luminosity is very different).

Saturday, December 15, 12 Rotation curves of galaxies

Salucci+07 mag

Rotation due to galactic populations, M31

Coadded from 3200 individual RCs 6 RD The fraction of dark matter halos/coronas in galaxies of different luminosity varies, however total rotation curves are similar (universal rotation curves). Some feedback between luminous and dark matter is needed.

Saturday, December 15, 12 Density of populations

This density function (Einasto profile) fits well visible galactic populations and DM halos, index alpha =1/N varies.

Saturday, December 15, 12 Modified Newton Dynamics Searches of DM particles have so far failed. Thus Newton gravitation law was modified which allows to explain flat rotation curves of galaxies.

However, there exists direct evidence for non-baryonic dark matter. Left: direct image of the 'bullet' cluster. Right: X-ray image of the cluster. Gravitational potential (green lines) coincide with the location of visible galaxies, but not with the location of the X-ray gas (red) the dominant baryonic component of the cluster. This separation is possible if the mass is in the collision-less non- baryonic dark matter halo, not in the baryonic X-ray gas (Clowe et at. 2004).

Saturday, December 15, 12 Further evidence for non-baryonic DM

•Smallness of CMB fluctuations ~ 10-5 To form galaxies & clusters, the amplitude of density fluctuations must be ~10-3 otherwise there is no time for the growth of the density perturbations

•From CMB observations we know that the total matter/energy density is equal to the critical density, from direct measurements & nucleosynthesis arguments the density of baryonic matter is 0.04 of the critical density, the rest is in the dark sector: dark matter & dark energy

Saturday, December 15, 12 Searches of DM particles

Fermi Large Area Telescope has detected DM annihilation to monochromatic gamma ray photons of energy 130 GeV from a small region in the Galactic centre (Weniger 2012, Tempel etal 2012a).

Saturday, December 15, 12 Searches of DM particles

Double peak at 110 & 130 GeV is observed in Galactic center and in 6 near clusters, corresponding to two annihilation patterns to gamma-gamma and gammaZ final states (Tempel et al. 2012b).

Saturday, December 15, 12 Conclusions

The discovery of Dark Matter was the result of combined study of galaxies and their populations There are 2 dark matter problems – dark matter in the Galaxy disk, and dark matter around galaxies and clusters.  Dark matter in the disk is baryonic (faint stars). The amount is small.  Dark matter around galaxies is non-baryonic Cold Dark Matter. It constitutes about 0.23 of the critical cosmological density. Dark matter is needed to start early enough gravitational clustering to form structure. Fermi LAT has detected DM annihilation into gamma ray photons of energy 110 & 130 GeV at the Galactic center and in 6 clusters. If confirmed by independent observations this is the 1st DM detection!

Saturday, December 15, 12 T e x t