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The RASS-SDSS Galaxy Cluster Survey

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The RASS-SDSS Galaxy Cluster Survey P. Popesso (ESO), A. Biviano (Osservatorio di Trieste), H. B hringer (MPE), M. Romaniello (ESO). – PowerPoint PPT presentation

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Title: The RASS-SDSS Galaxy Cluster Survey


1
The RASS-SDSS Galaxy Cluster Survey
  • P. Popesso (ESO),
  • A. Biviano (Osservatorio di Trieste),
  • H. Böhringer (MPE),
  • M. Romaniello (ESO).

2
  • The Survey
  • following the variations of the properties of
    cluster galaxies with the global properties of
    the systems (total mass, velocity dispersion, LX,
    Lop)
  • 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

3
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

4
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 )

5
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 r200), the Cluster LF is
universal (Popesso et al. 2005)
6
...at the bright end
  • Composite cluster LF is able to locate the BCGs.

7
...at the bright end
  • Composite cluster LF is able to locate the BCGs
    (Popesso et al. 2005, AA submitted).
  • Solid line LBCG ???????
  • Lin Mohr (2004) , Yang et al. (2005)

8
  • ...at the faint end
  • DGRN(-18.5???r??????????????r ??????
  • When measured within r200
  • or r500, the DGR is constant

9
  • ...at the faint end
  • DGRN(-18.5???r??????????????r ??????
  • When measured within r200
  • or r500, the DGR is constant

10
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

11
The Cluster LF by Galaxy Morphological type
  • We use the color cut at u-r2.22 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

12
The dependence on the environment
13
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 (lt 0.6 r200)
  • are the dwarf early type galaxies the spheroidal
    remnants of stripped and faded spirals as
    predicted by harassment scenario (Moore et al.
    1996, 1998)?

14
The Abell X-ray Underluminous Clusters
  • Do different cluster detection
    and selection methods select the same
    cluster population?
  • Lx ? M2002.04 ?0.04
  • scatter 60
  • (Popesso et al. 2005, AA, 433, 431)

15
  • 137 optically selected Abell clusters (3D
    overdensity spectroscopically confirmed)
  • 88 clusters have clear RASS X-ray counterpart
  • 27 marginally significant ( lt 3?) detection
  • 24 no X-ray detection
  • (Popesso et al. 2005, AA submitted)
  • RASS is too shallow to detect such faint X-ray
    sources (see also Basilakos et al. 2004, Donahue
    et al. 2003)

16
  • normal X-ray emittting Abell clusters mean
    deviation -0.1?0.3 dex
  • AXU mean deviation -1.0?0.4 dex
  • Tail Index (Beers et al. 1991) and subclustering
    analysis confirm reliable estimate of the cluster
    mass

17
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18
The nature of the AXU clusters
19
The velocity dispersion distribution
  • AXU clusters leptokurtic distribution in the
    outer region,
  • typical of systems in accretion

20
Conclusions Part II
  • Optical selection reveals a population of X-ray
    underluminous (AXU) systems
  • AXU clusters do not follow the LX-M200 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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