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Is there a correlation between the presence of bent radio sources
and the X-ray environment ?
Oozeer NHartRAO
2010 South African SKA Postgraduate Bursary Conference
Content
Galaxy groups/cluster
Multi-wavelength view Methodology
Preliminary sample
Data mining
Statistical tool
Preliminary results
Conclusion
Galaxy groups/clusters
Groups: < 50 members, s ~ 150 km/s, M ~ 2 × 1013 M⊙
Clusters: > 50 members, s ~ 800 km/s, M ~ 1 × 1015 M⊙
Clusters
Rich Poor
LooseCompact
Galaxy clusters are
the largest gravitationally bound system
~ 50 to 1000's of galaxies,
diffuse hot gas
dark matter
Most galaxies exist in groups/clusters, Clusters are in super-clusters
Clusters and super-clusters of galaxies have been studied extensively both for
their intrinsic properties and
to investigate the dark matter in the universe, the baryon content of the universe, large-scale structure, evolution, and cosmology.
Galaxy clusters
Our views of clusters of galaxies have changed dramatically over the past decade.
Clusters are no longer seen as simple, spherical, isolated structures in virial or hydrostatic equilibrium.
Dynamic, evolving and young , strongly influenced by large scale strutctures , Chambers et al 2000.
The general process of galaxy cluster formation through hierarchical merging is well understood, but many details, such as the impact of feedback sources on the cluster environment and radiative cooling in the cluster core, are not.
How can we find clusters ?
X-ray surveys
Optical/IR surveys
Radio surveys
Sunyaev-Zel’dovich (SZ) effect
Gravitational lensing
X-ray view (direct detection) X-ray studies of groups of galaxies provides information about the
environment (hot gas of the ICM) and the process occurring therein.
Presence of diffuse X-ray emission in a group would indicate the group is likely to be gravitationally bound
temperature, luminosity and surface brightness profile provide information concerning the depth of the potential well and the distribution of mass in the system.
Bachall et al, 2008.
Optical view
Typical Properties of Clusters and Groups
Distribution of Clusters with Richness and Distance
Number Density of Clusters
Fraction of Galaxies in Clusters
Galaxy Overdensity in Rich Clusters
Density Profile
Central Density and Core Size
Galactic Content in Rich Clusters
Velocity Dispersion
Radio surveys (in-direct detection)
Importance of radio sources and radio surveys
Classes of objects - Bent radio sources !!!
The existence of bent radio sources implies close interactions between the radio structure and the surrounding environment of these sources.
Therefore it is by studying the characteristics and properties of a source and its medium that we can explain the shape of the radio source.
Bent radio sources show various morphologies, from Wide Angle Tail radio galaxies (WATs) to Head Tail sources (HTs) and Narrow Angle Tail radio galaxies (NATs).
Environment of bent radio sources !!! NATs
Bending due to ram pressure stripping
Relatively high sv
Exist in both poor (Venkatesan et al, 1994) and rich clusters (Sarazin, 1988 – for review)
WATs
C or V - radio morphology FRI/FRII break
Associated with cD or D optical host galaxy
cDs and Ds giant elliptical at rest in the potential well of the cluster (sv ~ 100 kms-1)
Poor cluster (Patnaik et al. 1986, Oozeer et al. 2010) and rich cluster (Pinkney et al. 2000 )
FIRST - Blanton et al, 2001.
• 384 sources visually selected from the VLA FIRST survey
• Optically followed up (imaging and spectroscopy)
• Low-z complete sample showed that 50% of BDs are found in clusters, as revealed in the optical and X-ray
COSMOS field
z ~ 0.220cm
Xray: rainbowOptical: RGBRadio: red
200kpc
CWAT-01 at z~0.2:Merging of 4+ sub-clusters of galaxies Individual sub-clusters = 5E13 MSOL
Smolcic et al., 2007, Oklopcic et al., 2010
MRC 1925-296 & MRC 1928-266
MRC B1925-296 – Note the similarity shape of the X-ray blob and the radio jets
MRC B1925-296 – ROSAT PSPC pointing
HST & Chandra image of MRC B1928-266
MRC B1928-266 – The cluster environment as revealed by the NAT south of the X-ray plasma
MRC B1928-266 – HST image with radio overlay. This new cluster is at z=0.352
Methodology - sample Popesso+, 2007 and Yoon+, 2008, Owen, 1997
Galaxy clusters in SDSS-DR5
137 spectroscopically confirmed Abell systems
924 records of BCG
– Our sample: 45 Abell clusters
0.04 < z <0.15
Median z = 0.08
WAT=17, NAT=11, Gal?=17
Vizier
NVSS (1.4 GHz radio survey) counterparts
Optical counterparts – Soan Digital sky survey (SDSS)
X-ray environment - Rosat All Sky Survey (RASS, X-ray clusters)
R-statistics tool
Correlation matrix
Linear – BCG to Radio peak
RadPow – radio luminosity at 1.4 GHz
Sigma – velocity dispersion
R_band – Rband Luminosity
XLinear – separation between BCG and X-ray peak
Lx - X-ray luminosity
Mass – Virial mass
Virial – virial size
NHI – neutral hydrogen density
Morphological Type – (WAT, NAT or G)
Correlation coefficients
Velocity dispersion
[km/s]
R band luminosity
[Lsol]
99.9Cluster
Virial Size [Mpc]
1.4 GHz Radio power
[Whz-1]
BCG/X-ray separation
[Mpc]
39 17 27 27 26 Xray Lumi [W]
26 27 17BCG/Radio separation
[Mpc]
Mpc)1(
1
km/s100073.1 1
30
200
h
zcl
vR
Lx- sv relation
The best fit is given by
log(Lx)=1.56 log(sv)
+32.24
(Mahdavi et al, 1997.)
Some authors have found that
Lx µ sv4
( Xue & Wu,2000; Ortiz-Gil et al., 2004)
However, Cava et al., 2009
log(Lx)=(4.0±0.3) log(sv)
+(32.6±1.7)
Lx v/s Lrad at 1.4 GHz
Zhao et al., 1989 found NO correlation between Lx and
P20cm from an X-ray selected
sample of 71 Abell clusters.
However, we know X-ray luminosity/ radio correlation exist for various classes of objects, e.g: for AGN, Seyferts, halos, etc ....
Conclusion Since the appearance of radio sources is affected by interaction with the
ICM (confinement, distortion), we can use bent radio sources to locate distant clusters of galaxies that would be difficult to find in optical (b.c. of projection effects) or X-ray (b.c. of flux limits) surveys.
Data mining – need to get a good platform to query maximum data (~ 55 000 new BCGs , Tago et al, 2010)
Demonstrate a statistical tool which can be used to analyse huge data set
Most of the physical parameters investigated here seems to correlate to X-ray luminosity