The RASS-SDSSGalaxy 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 globalproperties of the systems (total mass, velocity dispersion, LX, Lop)
●understanding the selection effects introduced by different cluster detection andselection methods
The method & dataset
● multiwavelenght approach:
✔RASS data for the X-ray properties (LX)
✔SDSS data for optical (Lop) and dynamical (mass, V) clusterproperties, 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) AbellClusters
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 (AXUClusters) and their nature
The Composite Cluster Luminosity Function
The 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 goodrepresentation for more than 90% of the clusters, as confirmed by the 2test.
When measured within thephysical size of the systems(given by r200), the Cluster LF isuniversal
(Popesso et al. 2005)
...at the bright end
●Composite cluster LF is ableto locate the BCGs.
...at the bright end
Composite cluster LF is able tolocate the BCGs (Popesso et al.2005, A&A submitted).
Solid line LBCG
Lin & Mohr (2004) , Yang et al. (2005)
...at the faint end
DGR=N(-18.5rr
●When measured within r200
●or r500, the DGR is constant
...at the faint end
DGR=N(-18.5rr
●When measured within r200
●or r500, the DGR is constant
When the LFs is measured withina fixed metric aperture of 1 Mpc,it varies from cluster to cluster.
●the overall disagreement aboutthe faint-end slope of the clusterLF in the literature is due toaperture effects
The Cluster LF by Galaxy Morphological type
We use the color cut at u-r=2.22 of Strateva et al. (2001) todistinguish 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 thefaint end)
●the cluster LF is universal when measured with the virialradius
●DGR increasing with the clustercentric distance
●LF steepening due to dwarf early type galaxies whichdominate the cluster core (< 0.6 r200)
●are the dwarf early type galaxies the spheroidalremnants of stripped and faded spirals as predicted byharassment scenario (Moore et al. 1996, 1998)?
The Abell X-ray Underluminous Clusters
● Do different clusterdetection and selectionmethods select the samecluster population?
Lx M2002.04 0.04
scatter ~60%
(Popesso et al. 2005, A&A, 433,431)
137 optically selected Abell clusters(3D overdensity spectroscopicallyconfirmed):
●88 clusters have clear RASS X-raycounterpart
●27 marginally significant ( < 3)detection
●24 no X-ray detection
(Popesso et al. 2005, A&A submitted)
RASS is too shallow to detect suchfaint X-ray sources (see also Basilakoset 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 confirmreliable 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-rayunderluminous (AXU) systems
●AXU clusters do not follow the LX-M200 relation (meandeviation -1.0 dex)
●AXU clusters do follow the Lop-M200 relation
●AXU systems show leptokurtic velocity distribution in theouter regions (systems in accretion?)
●systems in formation also at low z?
●multi-wavelength approach is needed for optimizingcompleteness ans reliability of cluster samples.