COLD FRONTS IN GROUPS AND
CLUSTERS AND THEIR
DYNAMICAL STATE IN THE
OPTICAL
FABIO GASTALDELLO
INAF-IASF MILAN & UC IRVINE
M. MESSA, L. DI GESU
S. GHIZZARDI, M. ROSSETTI, D. BUOTE, S. ETTORI,
F. BRIGHENTI, W. MATHEWS
OUTLINE
• INTRO: SLOSHING COLD FRONTS AND OBSERVABLE
EFFECTS
• SLOSHING COLD FRONTS IN THE RELAXED GROUPS
NGC 5044 AND IC 1860
• PECULIAR VELOCITY OF BCGs AND X-RAY
THERMODYNAMICAL STATE / PRESENCE OF CFs
COLD FRONTS IN CLUSTERS
IN MERGING CLUSTERS
IN RELAXED CLUSTERS
Markevitch & Vikhlinin 07
SLOSHING CFs IN CLUSTERS
Ascasibar & Markevitch 06
SLOSHING CFs IN CLUSTERS
•
SB DISCONTUINITIES, SPIRAL FEATURES IN T
• STEEP ENTROPY GRADIENT
• cD PECULIAR VELOCITY
• ABUNDANCE DISCONTUINITIES
Ascasibar & Markevitch 06
HOW ABOUT GROUPS ?
EXAMPLES IN MERGING
SYSTEMS, e.g. NGC 1404
IN FORNAX
(Machacek+05)
SLOSHING CFs IN NGC 5044
z=0.009 kT=1.2 keV
Gastaldello+09
SLOSHING CFs IN NGC 5044
MENDEL+08 STUDY
OF 111 MEMBERS:
PECULIAR VELOCITY
OF 150 km/s WRT
THE MEAN VELOCITY
SLOSHING CFs IN NGC 5044
DETECTION OF A SUBSTRUCTURE (99.9 %) AT 1.4 Mpc
MENDEL+08. OR NGC 5054 (DAVID+09).
SLOSHING CFs IN IC 1860
z=0.022 kT=1.4 keV
Di Gesu, FG, et al. in prep
SLOSHING CFs IN IC 1860
Di Gesu, FG, et al. in prep
SLOSHING CFs IN IC 1860
PRELIMINARY MODELING CONSISTENT WITH DENSITY JUMP OF 1.4.
SLOSHING CFs IN IC 1860
STUDY OF 81 MEMBERS AVAILABLE IN NED:
PECULIAR VELOCITY OF 100 km/s WRT THE MEAN VELOCITY
SLOSHING CFs IN IC 1860
SUBSTRUCTURE PRESENT AT THE 98.2 % LEVEL
PECULIAR VELOCITIES OF
BCGs AND X-RAY STATE
CAVAGNOLO+09
COZIOL+09
241 CLUSTERS
452 ABELL CLUSTERS W/ MORE
THAN 10 MEMBERS
K0 AS INDICATOR OF
THERMODYNAMICAL STATE
VP OF BCG
CROSS-MATCH OF X-RAY PEAK
AND BCG POSITION. ONLY IN
EXTREME MERGERS (A754,
A3376) LARGE SEPARATION.
RESULTING SAMPLE OF 54
OBJECTS
FG, Messa, et al. in prep
PECULIAR VELOCITIES OF
BCGs AND X-RAY STATE
CC
NCC
VPEC OF BCGs AND X-RAY STATE
With CF
NO CF
A133
176
A478
340
A1644
29
A1068
127
A1795
238
A2107
187
A496
55
A2556
85
A2029
61
A2626
802
A2052
185
A2717
107
A2199
156
A3112
215
CENTAURUS
125
A4059
27
A85
43
A3581
ESO 3060170
MKW3S
A1361
A2667
31
20
27
204
382
CAVEAT: SUBSTRUCTURES !
ABELL 2626
82 MEMBERS
PEAK 1
CLEAR DETECTION OF
SUBSTRUCTURES ALREADY
IN MOHR+96
PEAK 2
IT HOSTS A MINI RADIO
HALO (GITTI+04)
vcl: 17307 km/s  16533 km/s
Vp: 802 km/s  27 km/s
σv: 1057 km/s  658 km/s
kT=2.9 keV
VPEC OF BCGs: SOME PEOPLE SAY ...
COZIOL+09: “A large fractions of BCGs have significant peculiar velocity. This
has one immediate consequence, which is that most clusters harboring a dominant
galaxy are not dynamically relaxed”
VAN DEN BOSCH+05: “The brightest galaxy in a dark matter halo is expected to
reside at rest at the centre of the halo. In this paper, we test this `Central
Galaxy Paradigm' (CGP) using group catalogues extracted from the Two-Degree
Field Galaxy Redshift Survey (2dFGRS) and the Sloan Digital Sky Survey (SDSS).
We show that the CGP is only consistent with the data in haloes with M < 1013
Msun, while in more massive haloes the data indicate a non-zero offset between
the brightest galaxy and the satellites. This indicates that either central
galaxies reside at the minimum of the dark matter potential, but that the halo
itself is not yet fully relaxed, or, that the halo is relaxed, but that the central
galaxy oscillates in its potential well.
VPEC OF BCGs: SOME PEOPLE SAY ...
MIRALDA-ESCUDE’+95: “The fact that cD galaxies often have large peculiar
velocities relative to the average of the cluster galaxies has been used as an
argument against their identification as cluster centers: however, clusters are
continuously merging, and their density peaks do not need to coincide with their
centers of mass. Substructure will cause the density peaks to move, in response
to the gravitational forces of the infalling material”
SUMMARY
• SLOSHING COLD FRONTS ARE STARTING TO BE
DETECTED IN AN INCREASING NUMBER OF GROUPS:
FEATURE PRESENT AT ALL SCALES (see also NGC 5098:
Randall+09, NGC 5846: Machaceck poster)
• OFF-AXIS MERGERS INDUCING COLD FRONTS CAN
EXPLAIN SPEEDING BCGs ALSO IN RELAXED
CLUSTERS: NEEDS FURTHER INVESTIGATION
TAKING CARE OF POSSIBLE SUBSTRUCTURES