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Astronomía Extragaláctica y Cosmología Observacional

Depto. de Astronomía (UGto). Astronomía Extragaláctica y Cosmología Observacional. Lecture 9 Groups and Clusters of Galaxies – I (Galaxies). Definition – Richness Catalogs rich clusters groups compact groups pairs Morphology and Classification Radial Profiles Substructuring

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Astronomía Extragaláctica y Cosmología Observacional

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  1. Depto. de Astronomía (UGto) Astronomía Extragaláctica y Cosmología Observacional Lecture 9 Groups and Clusters of Galaxies – I (Galaxies) • Definition – Richness • Catalogs • rich clusters • groups • compact groups • pairs Morphology and Classification Radial Profiles Substructuring Environmental Effects and Segregation • cDs • morphological segregation (morphology-density relation) • Red Sequence and Butcher-Oemler effect • ram pressure and galaxy harassment

  2. Definition: Richness Pair → 2 galaxies (~ 1012 M) Group → ~ 10 galaxies (~ 1012-1013 M) Poor Cluster → ~ 100 galaxies (~ 1013-1014 M) Rich Cluster → ~ 1 000 galaxies (~ 1014-1015 M) Supercluster→ ~ 10 000 galaxies (~ 1015-1016 M) Hercules/A2151 (Cl) Stephan Quintet (CGr) M51 (GPair)

  3. Pairs Interacting Galaxies [Arp & Madore 1982, JRASC 76, 315 Toomre & Toomre 1972, ApJ 178, 623 ] Dumbbell [Matthews et al. 1964, ApJ 140, 35 ] Wirth et al. 1982, AJ 87, 602, Gregory et al. 1994, A&A 106, 1] [Alonso et al. 2005, MNRAS 375, 1017]

  4. Catalogs: Abell-ACO • 1958 – G. Abell [ApJS 3, 211]: first systematic search (by visual inspection) for rich clusters • Palomar Observatory Sky Survey (POSS, Schmidt 1.2m, δ > 27°, |b|  30°, 879 pairs of plates) • blue band → 103a-O emulsion, mO,lim = 21.1 • red band →103a-E emulsion, mE,lim= 20.0 • criteria: • richness→Ngal  50 galaxies, between m3 and m3+2 mag (local sky subtraction) • compactness→ r < RA = 1.5 h-1 Mpc = (1.72/zest) arcmin zest = f(m10) • distance→0.02 (plate size limit) < z < 0.2 (mag limit  m3 ≤ 17.5) • Ncl = 2712 (statistical sample: Ncl= 1682) • 1989 – Abell, Corwin & Olowin [ACO, ApJS 70, 1]: extension to southern celestial hemisphere • ESO/SERC Southern Sky Survey [UK Schmidt 1.2m (AAO) + ESO Schmidt 1.0m (La Silla), δ < 17°, |b|  30°, 606 pairs of plates] • blue band → IIIa-J emulsion + GG395 filter, mJ,lim = 22.5 • red band → IIIa-F emulsion + RG610 filter, mF,lim= 21.5 • same criteria (except for a “universal” sky subtractions, based on a field LF) • Ncl = 1361 (rich) + 1174(supplementary – less rich, R = 0, or D > 6)

  5. Catalogs: Abell-ACO [ACO 1989, ApJS 70, 1] Field LF z = f(m10) Zone of Avoidance

  6. Catalogs: Abell-ACO Richness Classes (R ) 0 30 – 49 1 50 – 79 2 80 – 129 3 130 – 199 4 200 – 300 5 300 or more R (Ngal) Distance Classes (D) 1 13.3 – 14.0 0.0283 2 14.1 – 14.8 0.0400 3 14.9 – 15.6 0.0577 4 15.7 – 16.4 0.0787 5 16.5 – 17.2 0.1310 6 17.3 – 18.0 0.1980 D (range of m10) (mean zest) Limitations: - projection effects [incompleteness (?) and contamination (about 10%)] - Scott (1957) effect: R increases with zest

  7. Catalogs: Abell-ACO Abell ACO Ncl = 4073 Complete to z ~ 0.2 (zmax ~ 0.4) n(R  1) = 10-5h3 Mpc-3  <r> ~ 50 h-1 Mpc

  8. Catalogs: other classical cluster catalogs • 1961-1968 – Zwicky et al. [Catalogue of Galaxies and Clusters of Galaxies]: • POSS • criteria: • richness→Ngal  50 galaxies, between m1 and m1+3 mag • density → isopleth: ngal > 2 nfield • Ncl = 9134 • 1985 – Shectman [ApJS 57, 77]: based on • Shane & Wirtanen [1954] counts • Lick Galaxy Survey (b  40°, δ  -22.5°) • Ncl = 646

  9. Catalogs: other classical cluster catalogs • 1992 – Lumsden et al. [MNRAS 258, 1]: Edinburgh-Durham Cluster Catalog (EDCC) • COSMOS (Coordinates and Magnitudes Object Survey) machine • Ncl = 737 • 1997 – Dalton et al. [MNRAS 289, 263]: • APM Cluster Catalogue (APMCC) • APM (Automatic Plate Measuring) machine • Ncl = 937

  10. Catalogs: other cluster catalogs • 2003 – Gal et al. [AJ 125, 2064]: Northern Sky Optical Cluster Survey (NoSOCS) • POSS-2 (2nd Epoch) – DPOSS (digitized at STScI – PDS) • SExtractor, photometric redshifts • Ncl = 8155

  11. Catalogs: other classical cluster catalogs NoSOCS AqrCC EDCC APMCC ACO Supl.

  12. Catalogs: Groups Compact: • Loose: • usually detected by percolation analysis • Ngal 3 (or 5) • 1982 – Hickson [ApJ 255, 382]: the most • known catalog of compact groups (HCG) • criteria: • richness→ Ngal 4, in a magnitude range ≤ 3 mag • concentration → <Σgal> ≤ 26 μR • isolation → no galaxy with m < m1+3 inside 3Rcg • Ncg = 100 (1948) (1877)

  13. Catalogs: Groups • Are compact groups real bound systems? • they contain more spirals than expected from the usual morphology-density relation • they have very short predicted lifetimes against merging • the number of “members” with discordant redshifts is very high (~ 1/3) Stephan Quintet (CGr)

  14. Catalogs: Groups (and clusters), representative ones Catalog Ngr zlim mlim Area Ref. • Hickson 100 POSSI Hickson et al. 1989 • SCG 59 COSMOS Prandoni et al. 1994 • P-PS 188 0.05 B ≤ 15.5 P-P Trasarti-Battistoni et al. 1998 • WBL 732 0.03 mph≤ 15.7 POSSI White et al. 1999 • UZC-SSRS 1 168 0.04 B ≤ 15.5 4.7 sr Ramella et al. 2002 • ESP 231 0.16 bJ≤ 19.4 0.01 sr Ramella et al. 1999 • LCRS 1 495 0.15 R ≤ 17.5 0.21 sr Tucker et al. 2000 • 2PIGG (2dFGRS) 12 566 0.20 bJ≤ 19.5 0.61 sr Eke et al. 2004 • C4CC (SDSS-DR2) 748 0.17 r ≤ 17.7 1.01 sr Miller et al. 2005 • 2MGrC (2MASS) ~ 1 500 0.05 Ks ≤ 11.3 all-sky Crook et al. 2007 • Abell/ACO 4 073 0.20 mph≤ 20.0~8.2 sr Abell 1958, ACO 1989 • EDCC 737 0.19 bJ≤ 20.5 0.5 sr Lumsden et al. 1992 • APMCC 937 0.13 bJ≤ 20.5 1.31 sr Dalton et al. 1997 • NoSOCs 16 546 0.25 rF≤ 19.5 3.35 sr Gal et al. 2008

  15. Morphology and Classification • Criteria: • richness (Abell R ) • shape of the galaxy distribution (Abell) • concentration (Zwicky) • distribution of the brightest members (10, RS) • presence or absence of a cD galaxy (BM) • morphology of the dominant galaxy (BM) • subclustering • galaxy content... • Bautz & Morgan: • I → central cD galaxy • II → intermediate E/cD • III → no dominant galaxy • also intermediate types I-II and II-III Rood & Sastry: • Abell: • regular • irregular • Zwicky: • compact • semi-compact • open • cD → single dominant cD • B → dominant binary • L → linear array of galaxies • C → single core of galaxies • F → flattened distribution • I → irregular distribution

  16. Morphology and Classification

  17. Morphology and Classification [Geller & Beers 1982, PASP 94, 421]

  18. Radial Profiles • Many models have been proposed in order to describe the radial distribution of galaxies in a cluster, the classical ones been the Hubble profile and the de Vaucouleurs profile (originally proposed for ellipticals) 1962 – I. King [AJ 71, 64]: proposed a radial profile (for globular clusters) derived from • solutions of the Fokker-Planck equation (isothermal sphere), • that fits quite well the distribution of galaxies in a cluster: • Σ(r) = Σ0 [1 + (r/Rc)2]-γ(in 2D) • n(r) = n0 [1 + (r/Rc)2]-3γ/2 (in 3D) • where Σ0 and n0 are the central projected and spatial • densities, related by • Σ0 = 2 Rc n0 • Rc is the core radius (usually in the range • 0.1–0.25 h-1 Mpc), and γ is the slope for r > Rc, • originally γ = 1 (slightly smaller values are found • for galaxy clusters) • Other proposed models are models without a core, like the Hernquist [1990, ApJ 356, 359] and Navarro, Frenk & White [1997, ApJ 490, 493] (that fits well the distribution of DM, for which it was constructed)

  19. Substructures • There are many methods for detecting substructures (merging groups?) in a cluster • 1-D (redshift space) • deviations from Gaussianity (skewness and kurtosis) • 2-D (projection) • surface number density contour maps (isodensity) [Geller & Beers 1982, PASP 94, 421] • symmetry test (β) (and others) [West et al. 1988, ApJ 327, 1] • multiscale analysis (wavelets) [Girardi et al. 1997, ApJ 482, 41] • 3-D • δ-test (local  global kinematics) [Dressler & Shectman 1988, AJ 95, 985] • surface photometry test [West & Bothum 1990, ApJ 350, 36] • ε-statistics (mass) [Bird 1993, AJ 107, 1637] • κ-test (modified δ-test) [Colless & Dunn 1996, ApJ 458, 435] [Bravo-Alfaro et al. 2008]

  20. Substructures & Radial Profiles A2521 isoplets radial profile gals w/ z (in the cluster) A2595

  21. Substructures & Radial Profiles A3985 A2565-B gals w/ z (foreground) (background)

  22. Environmental effects and segregation Effects from clusters to galaxies Effects from galaxies to clusters dominant galaxy ICM metal enrichment morphological segregation ICM warming gas loss (by ram pressure) relativistic particles injection Butcher-Oemler effect merging (by dynamical friction)

  23. Environmental effects and segregation • Dominant galaxy: • galaxies brighter than normal galaxies (MV ≈ -24), with a narrow dispersion (0.3 – 0.35 mag) • rest at (or close to) the centre of rich clusters (there are no cDs where s ≤ 1 gal Mpc-3) • present an extended stellar envelope (is it part of the galaxy or of the cluster?) • most of them present double nucleus (25 – 50%) • are usually flat and aligned to the galaxy distribution in the cluster (or to neighbor clusters) • they do not follow the luminosity function of the other cluster galaxies

  24. Environmental effects and segregation • Proposed formation scenarios: • merger of bright galaxies or accretion of small ones by dynamical friction (galactic cannibalism) [Ostrike & Tremaine 1975, Dubinski 1998], but high   large times, also peculiar velocities • accumulation of loose stars that fall in the cluster potential, taken off galaxies by tidal effects[Merritt 1984], but colors and metallicities … • accumulation of gas in the cluster potential by cooling flows[Mushotzky et al. 1981], but not observed … • formation in groups [Merritt 1985, Coziol et al 2008] • primordial formation (before clusters), but how? A496 Cluster cD Hydra Cluster cD Perseus Cluster cD

  25. Environmental effects and segregation • Morphological segregation: • rich and regular clusters present a high fraction of early-type galaxies (E and S0), and a strong radial gradient of this fraction (higher in the centre) • poor and irregular clusters and groups present a high fraction of S, and have small or no gradient of morphological types Morphology-density relation with z: [Dressler 1980, ApJ 236, 351] [Dressler el al. 1997, ApJ 490, 577] [Smith et al. 2005, ApJ 620, 78]

  26. Environmental effects and segregation • Red Sequence: • Color-Magnitude Diagram (CMD): red galaxies form a well defined sequence (called “red sequence”) • mostly early type (E and S0) with more evolved/older stellar populations (limit for evolution) • the slope driven by the mass-metallicity relation [see López-Cruz et al. 2004, ApJ 614, 679]

  27. Environmental effects and segregation [Butcher & Oemler 1984, ApJ 285, 426] • Butcher-Oemler effect: • there is an excess of blue galaxies in clusters at high redshifts when compared to local clusters

  28. Environmental effects and segregation fraction of clusters of 1015M formed • Recent evolution: • rich clusters formed recently (z < 2) • there is considerable evolution of galaxies in clusters in the recent past (z < 0.5) • have galaxies evolved mostly in clusters/groups? [Richstone, Loeb & Turner 1992, ApJ 393, 477]

  29. Environmental effects and segregation • Ram pressure of gas: • the pressure of the IC hot gas is higher than the pressure of the HI in the S galaxies • so, S can loose HI by ram pressure of the IC gas [Bravo-Alfaro et al. 2000, AJ 119, 580]

  30. References • Papers: • Bautz & Morgan 1970, ApJ 162, L149 • Rood & Sastry 1971, PASP 83, 313 • Ostriker & Tremaine 1975, ApJ 202, L113 • Mushotzky et al. 1981, ApJ 244, L47 • Hickson 1982, ApJ 255, 382 • Merritt 1984, ApJ 276, 26 • Merritt 1985, ApJ 289, 18 • Prandoni, Iovino & MacGillivray 1994, AJ 107, 1235 • Trasarti-Battistoni 1998, A&AS 130, 341 • White et al. 1999, AJ 118, 2014 • Ramella et al. 1999, A&A 342, 1 • Tucker et al. 2000, ApJS 130, 237 • Ramella et al. 2002, AJ 123, 2976 • Eke et al. 2004, MNRAS 348, 866 • Miller et al. 2005, AJ 130, 968 • Crook et al. 2007, ApJ 655, 790 • Coziol et al. 2008, submitted to AJ • Bravo-Alfaro et al. 2008, in preparation

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