The RASS-SDSS Galaxy Cluster Survey
P. Popesso (ESO),
A. Biviano (Osservatorio di Trieste),
H. Böhringer (MPE),
M. Romaniello (ESO).
The Survey:
●following the variations of the properties of cluster galaxies with the global
properties of the systems (total mass, velocity dispersion, LX, L
op)
●understanding the selection effects introduced by different cluster detection and
selection methods
The method & dataset
● multiwavelenght approach:
✔RASS data for the X-ray properties (LX)
✔SDSS data for optical (Lop
) and dynamical (mass, V) cluster
properties, spectrophotometric properties of cluster galaxies
The cluster samples
● 130 X-ray selected clusters (the RASS-SDSS Cluster Sample)
● 137 optically selected (3D overdensity spectroscopically confirmed) Abell
Clusters
Outlines:
● Part I
– universality of the cluster Luminosity Function (LF)
– the cluster dwarf galaxy population
– morphology-density relation of the dwarf systems● Part II
– the Abell X-ray Underluminous Clusters (AXU
Clusters) and their nature
The Composite Cluster Luminosity FunctionThe cluster composite LF is obtained by stacking the individual LFs (background subtracted) within the virial radius.
●Best fit: double Schechter Function
● at the bright end:
● at the faint end:
in the r band
km/s/Mpc )
Is the cluster LF universal?The composite cluster LF, calculated within the virial radius, is a good representation for more than 90% of the clusters, as confirmed by the 2 test.
When measured within the physical size of the systems (given by r
200), the Cluster LF is
universal (Popesso et al. 2005)
...at the bright end
● Composite cluster LF is able
to locate the BCGs.
...at the bright end
Composite cluster LF is able to locate the BCGs (Popesso et al. 2005, A&A submitted).
Solid line LBCG
Lin & Mohr (2004) , Yang et al. (2005)
...at the faint endDGR=N(-18.5rr
●When measured within r
200
●or r500
, the DGR is constant
...at the faint endDGR=N(-18.5rr
●When measured within r
200
●or r500
, the DGR is constant
When the LFs is measured within
a fixed metric aperture of 1 Mpc,
it varies from cluster to cluster.
●the overall disagreement about the faint-end slope of the cluster LF in the literature is due to aperture effects
The Cluster LF by Galaxy Morphological type
We use the color cut at u-r=2.22 of Strateva et al. (2001) to distinguish red early type galaxies from blue late type galaxies.
Early type galaxies Late type galaxies
Popesso et al. 2005c, astro-ph/0506201
The dependence on the environment
Conclusions Part I
● bimodal behaviour of the cluster LF (steepening at the faint end)
● the cluster LF is universal when measured with the virial radius
● DGR increasing with the clustercentric distance
● LF steepening due to dwarf early type galaxies which dominate the cluster core (< 0.6 r
200)
● are the dwarf early type galaxies the spheroidal remnants of stripped and faded spirals as predicted by harassment scenario (Moore et al. 1996, 1998)?
The Abell X-ray Underluminous Clusters● Do different cluster
detection and selection methods select the same cluster population?
Lx M200
2.04 0.04
scatter ~60%
(Popesso et al. 2005, A&A, 433, 431)
137 optically selected Abell clusters (3D overdensity spectroscopically confirmed):●88 clusters have clear RASS X-ray
counterpart●27 marginally significant ( < 3)
detection●24 no X-ray detection (Popesso et al. 2005, A&A submitted)
RASS is too shallow to detect such
faint X-ray sources (see also Basilakos
et al. 2004, Donahue et al. 2003)
● normal X-ray emittting Abell clusters: mean deviation -0.10.3 dex
● AXU: mean deviation -1.00.4 dex
● Tail Index (Beers et al. 1991) and subclustering analysis confirm
reliable estimate of the cluster mass
The nature of the AXU clusters
The velocity dispersion distribution
AXU clusters: leptokurtic distribution in the outer region,
typical of systems in accretion
Conclusions Part II● Optical selection reveals a population of X-ray
underluminous (AXU) systems
● AXU clusters do not follow the LX-M
200 relation (mean
deviation -1.0 dex)
● AXU clusters do follow the Lop
-M200
relation
● AXU systems show leptokurtic velocity distribution in the outer regions (systems in accretion?)
● systems in formation also at low z?
● multi-wavelength approach is needed for optimizing completeness ans reliability of cluster samples.
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