Transcript Diapositiva 1 - Universidad de Guanajuato

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
Depto. de Astronomía (UGto)
Astronomía Extragaláctica y Cosmología Observacional
 Definition: Richness
Pair
Group
Poor Cluster
Rich Cluster
Supercluster
→
2 galaxies
→
~ 10 galaxies
→
~ 100 galaxies
→ ~ 1 000 galaxies
→ ~ 10 000 galaxies
(~ 1012 M)
(~ 1012-1013 M)
(~ 1013-1014 M)
(~ 1014-1015 M)
(~ 1015-1016 M)
Hercules/A2151 (Cl)
Stephan Quintet (CGr)
M51 (GPair)
 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]
 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)
 Catalogs: Abell-ACO
[ACO 1989, ApJS 70, 1]
Field LF
Zone of Avoidance
z = f(m10)
 Catalogs: Abell-ACO
Richness Classes (R )
Distance Classes (D)
0
1
2
3
4
5
30 – 49
50 – 79
80 – 129
130 – 199
200 – 300
300 or more
1
2
3
4
5
6
13.3 – 14.0
14.1 – 14.8
14.9 – 15.6
15.7 – 16.4
16.5 – 17.2
17.3 – 18.0
R
(Ngal)
D
(range of m10)
0.0283
0.0400
0.0577
0.0787
0.1310
0.1980
(mean zest)
Limitations: - projection effects [incompleteness (?) and contamination (about 10%)]
- Scott (1957) effect: R increases with zest
 Catalogs: Abell-ACO
Abell
ACO
Ncl = 4073
Complete to z ~ 0.2 (zmax ~ 0.4)
n(R  1) = 10-5 h3 Mpc-3  <r> ~ 50 h-1 Mpc
 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
 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
 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
 Catalogs: other classical cluster catalogs
NoSOCS
AqrCC
EDCC
APMCC
ACO Supl.
 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)
 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)
 Catalogs: Groups (and clusters), representative ones
Catalog
▪ Hickson
▪ SCG
Ngr
zlim
mlim
100
59
Area
POSSI
Ref.
COSMOS
Hickson et al. 1989
Prandoni et al. 1994
P-P
POSSI
4.7 sr
0.01 sr
0.21 sr
0.61 sr
1.01 sr
all-sky
Trasarti-Battistoni et al. 1998
White et al. 1999
Ramella et al. 2002
Ramella et al. 1999
Tucker et al. 2000
Eke et al. 2004
Miller et al. 2005
Crook et al. 2007
▪ P-PS
188
▪ WBL
732
▪ UZC-SSRS
1 168
▪ ESP
231
▪ LCRS
1 495
▪ 2PIGG (2dFGRS) 12 566
▪ C4CC (SDSS-DR2)
748
▪ 2MGrC (2MASS) ~ 1 500
0.05
0.03
0.04
0.16
0.15
0.20
0.17
0.05
B ≤ 15.5
mph ≤ 15.7
B ≤ 15.5
bJ ≤ 19.4
R ≤ 17.5
bJ ≤ 19.5
r ≤ 17.7
Ks ≤ 11.3
▪ Abell/ACO
▪ EDCC
▪ APMCC
▪ NoSOCs
0.20
0.19
0.13
0.25
mph ≤ 20.0 ~8.2 sr Abell 1958, ACO 1989
bJ ≤ 20.5 0.5 sr Lumsden et al. 1992
bJ ≤ 20.5 1.31 sr Dalton et al. 1997
rF ≤ 19.5 3.35 sr Gal et al. 2008
4 073
737
937
16 546
 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...
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
Bautz & Morgan:
 I → central cD galaxy
 II → intermediate E/cD
 III → no dominant galaxy
 also intermediate types
I-II and II-III
 Morphology and Classification
Abell type
Regular (Early)
Intermediate
Irregular (Late)
Zwicky type
Compact
Medium-Compact
Open
Bautz-Morgan type
I, I-II, II
(II), II-III
(II-III), III
Rood-Sastry type
cD, B, (LsC)
(L),(F),(C)
(F), I
Content
Elliptical-rich
Spiral-poor
Spiral-rich
35%
45%
20%
20%
50%
30%
15%
35%
50%
Symmetry
spherical
intermediate
irregular shape
Central concentration
high
moderate
very little
Central profile
steep
intermediate
flat
Radio emission?
50%
50%
20%
X-ray luminosity
high
intermediate
low
Examples
A2199, Coma
A194, A539
Virgo, A1228
E
L
S
(field 10%)
(field 20%)
(field 70%)
 Morphology and Classification
[Geller & Beers 1982, PASP 94, 421]
 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)
 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]
 Substructures & Radial Profiles
A2521
gals w/ z (in the cluster)
isoplets
radial profile
A2595
 Substructures & Radial Profiles
A3985
A2565-B
gals w/ z
(foreground)
(background)
 Environmental effects and segregation
Effects from clusters to galaxies
Effects from galaxies to clusters
dominant galaxy
morphological segregation
gas loss (by ram pressure)
Butcher-Oemler effect
merging (by dynamical friction)
ICM metal enrichment
ICM warming
relativistic particles injection
 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
 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?
Hydra Cluster cD
Perseus Cluster cD
A496 Cluster cD
 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]
 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]
 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
 Environmental effects and segregation
Recent evolution:
fraction of clusters of 1015 M formed
 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]
 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]
 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