Optical observations of clusters of galaxies

Coma Cluster

A larger image of the Coma Cluster

The Virgo Cluster

The Virgo Supercluster

Optical Catalogs The Abell Catalog (1958)

The Abell Cluster Catalog Use the Palomar Sky Survey, complete photographic all sky survey made at Mount Palomar observatory in the 1950's. clusters have to satisfy four criteria: –Richness: A cluster must have a minimum population of 50 members within a magnitude range of m3 to m3+2 (where m3 is the magnitude of the third brightest member of the cluster) Group 0: galaxies Group 1: galaxies Group 2: galaxies Group 3: galaxies Group 4: galaxies Group 5: more than 299 galaxies –Compactness: the “Abell radius,” is defined as 1.72/z arcminutes, (or 1.5H -1 Mpc) –Distance: A cluster should have a nominal redshift of between 0.02 and 0.2 –Galactic-Latitude: Areas ouside the Milky Way (even if some clusters where incleded)

The Abell Cluster Catalog The Abell catalog of rich clusters of galaxies contains 4,073 rich galaxy clusters: 2,712 from the" Northern Survey” and 1,361 in the Southern Survey Clusters are identified as: Abell X, where X = 1 to 4076 –A426, the Perseus Cluster –A1656, the Coma Cluster –A3526, the Centaurus Cluster The selection criteria are rather arbitrary The catalogue is highly contaminated

Optical Catalogs The Abell Catalog (1958) The Zwicky Catalog ( )

The Zwicky Catalog Uses a subset of the Palomar Sky Survey: Zwicky identified clusters in 560 of the POSS fields. To determine cluster diameters, Zwicky drew isopleths at the level where the cluster density was twice that of the background density of galaxies. The number of cluster members was determined by: – counting all galaxies within the isopleth – within three magnitudes of the brightest member, –subtracting the background count. All Zwicky clusters are rich clusters, having at least 50 members within 3 magnitudes of the brightest member. Same clusters are classified larger and more populous by Zwicky than it is by Abell. Zwicky clusters may contain two or three Abell clusters. E.g. Zwicky Hercules contains Abell clusters 2147, 2151 and 2152.

Recent Cluster catalogues To avoid projection problems we should know the galaxy cluster member redshift This is expensive in terms of time

The 2dF survey

APM and 2dF sky coverage

2dF

Show movie

Recent Cluster catalogues To avoid projection problems we should know the galaxy cluster member redshift This is expensive in terms of time Photometric survey

Red Sequence

The Red Sequence Cluster Survey The Red-Sequence Cluster Survey is the largest area, moderately deep imaging survey ever undertaken on 4m class telescopes. The survey comprises 100 square degrees of imaging in 2 filters (R and z), to a depth sufficient to find galaxy clusters to z~1.4 (2 mags past M* at z=1)

Table Characteristics of Regular and Irregular Clusters PropertyRegular ClustersIrregular Clusters SymmetryMarked spherical symmetryLittle or no symmetry Concentration High concentration of members toward cluster center No marked concentration to a unique cluster center; often two or more nuclei of concentration are present Collisions Numerous collisions and close encounters Collisions and close encounters are relatively rare Types of galaxies All or nearly all galaxies in the first 3 or 4 magnitude intervals are elliptical and/or S0 galaxies All types of galaxies are usually present except in the poor groups, which may not contain giant ellipticals. Late-type spirals and/or irregular galaxies present Number of galaxiesOrder of 10 3 or moreOrder of 10 to 10 3 Diameter (Mpc)Order of SubclusteringProbably absent or unimportant Often present. Double and multiple systems of galaxies common Radial velocities dispersionOrder of 10 3 km/secOrder of km/sec Mass (from Virial Theorem)Virial TheoremOrder of M sun Order of M sun Other characteristics Cluster often centered about one or two giant elliptical galaxies Examples Coma cluster (A1656); Corona Borealis cluster (A2065) Virgo cluster, Hercules cluster (A2151)

Optical Classification of clusters of galaxies cD - single dominant cD (elliptical) galaxy (A2029, A2199) B - dominant binary, like Coma L - linear array of galaxies (Perseus) C - single core of galaxies F - flattened (IRAS ) I - irregular distribution (Hercules)

Emission Processes of Clusters of Galaxies in the X-ray Band

Cluster Gas Density

Observables Relations T-M Virial Equilibrium Kinetic Energy for the gas Thermodynamic T-M relation

Status of The IGM Age of Clusters ~ few Gyr; R ~ 1-2 Mpc T ~ 1-10 keV; Gas highly ionized Electrons free mean path Gas may be treated as a fluid Timescale for Coulomb Collisions Electrons are in kinetic equilibrium Maxwellian velocity distribution Timescale for soundwave propagation Gas is in hydrostatic equilibrium

Intracluster Medium Hydrostatic equilibrium (spherical symmetry) We can measure the Cluster mass Dynamical Properties of the Galaxies Isothermal Cluster King profile Beta Profile

Emission Processes of Clusters of Galaxies in the X-ray Band The IGM is a PlasmaThe IGM is a Plasma Electrons are accelerated by the ionsElectrons are accelerated by the ions They emit for BremsstrahlungThey emit for Bremsstrahlung Electrons are in kinetic equilibrium (Maxwellian V distr. ) Cluster emission is mainly thermal Bremsstrahlung

Emission Processes of Clusters of Galaxies in the X-ray Band Beside IGM contains some metals (0.3 Solar) They produce line emission

X-ray Observations Gas densityGas density Gas TemperatureGas Temperature Gas chemical compositionGas chemical composition If assume hydrostatic equilibriumIf assume hydrostatic equilibrium Cluster Mass

Clusters –Cosmology connection Clusters are useful cosmological tools

Rosati, Borgani & Norman 03 Evolution of N(M,z) to constrain cosmological parameters

Instead of M we can either use L X  n gas 2  (T) Volume or T gas But: matter is dark & we need light to see/count/measure galaxy clusters…

Observables Relations T-M Virial Equilibrium Kinetic Energy for the gas Thermodynamic T-M relation

X-ray scaling laws: M  T 3/2 Evrard, Metzler & Navarro (1996) use gasdynamic simulations to assess the accuracy of X-ray mass estimations & conclude that within an overdensity between 500 and 2500, the masses from  -model are good. The scatter can be reduced if M is estimated from the tight M-T relation observed in simulations: M 500 = 2.22e15 (T/10 keV) 3/2 h Msun law  -model

X-ray scaling laws: M  T 3/2 Nevalainen et al. (2000) using a ASCA (clusters: 6) & ROSAT (groups: 3) T profiles: (i) in the 1-10 keV range, M 1000  T 1.8 [preheating due to SN?], but (ii) at T>4 keV, M 1000  T 3/2 [they claim, but measure 1.8  0.5 at 90%…] & norm 50% [!!!] lower than EMN : EMN96

X-ray scaling laws: M  T 3/2 Finoguenov et al. (2001) use a flux-limited sample of 63 RASS clusters (T mainly from ASCA) & 39 systems btw keV with ASCA T profile. (i) Steeper profile than 3/2, high scatter in groups (ii) deviations from simulations due to pre-heating [makes flat n gas ] & z_formation (iii) M from  -model:  depends on T EMN96

X-ray scaling laws: M  T 3/2 Allen et al. (2001): 7 massive clusters observed with Chandra, M T 2500 relation. ME01 slope of 1.52  0.36 & normalization lower than 40%.

Observables Relations L-M X-ray Luminosity

Observables Relations L-T Theoretically However from an observation point of view

X-ray scaling laws: self-similar? We have a consistent picture at T>3 keV, but also evidence that cool clusters/groups may be not just a scaled version of high-T clusters [ review in Mulchaey 2000 ] T5T5 T3T3

X-ray scaling laws: evolution

Luminosity Function Local (left) & high-z (right) XLF: no evolution evident below 3e44 erg/s, but present at 3  level above it (i.e. more massive systems are rare at z>0.5) Rosati et al. 03

Temperature Function & cosmological constraints Henry 00Markevitch 98

Cosmology in the WMAP era 1-st year results of the temperature anisotropies in the CMB from MAP (Bennett et al., Spergel et al 03) put alone constraints on  tot,  b h 2,  m h 2.

Cosmology in the WMAP era However, the final answer to the cosmology quest is not given: the cosmological parameters in CMB are degenerate… complementary the equation of state of Dark Energy & its evolution with redshift is not known given that, we can play the reverse game: fix the cosmology & see what your cosmology-dependent data require

Cosmology in the WMAP era In non-flat cosmologies, there is degeneracy in  m -   space (e.g.   =0 is consistent with MAP results, but requires H 0 =32 and  tot =1.28…). To get tighter & non-degenerated constraints, one needs to add something else, like, P(k) from 2dF & Lyman-  forest, Hubble KP, SN Ia, clusters survey…: complementarity Allen etal 02

Cosmology in the WMAP era The equation of state of the Dark Energy & its evolution with time: only post-MAP CMB surveys (i.e. Planck in 2007), SN Ia, X- ray/SZ clusters can answer in the next future

Cosmology in the WMAP era The equation of state of the Dark Energy & its evolution with time: only post-MAP CMB surveys (i.e. Planck in 2007), SN Ia, X- ray/SZ clusters can answer in the next future Mohr et al.