How to find a group of galaxies'II The Sloan Survey case

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How to find a group of galaxies.IIThe Sloan
Survey case

• Erik Tago
• (and J.Einasto,E.Saar,E.Tempel,
• M.Einasto,J.Vennik,V.Müller
• Tartu Observatory,Potsdam Observatory)
• Tuorla-Tartu meeting
• Tuorla Observatory , Oct 4-5 , 2007

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Contents

• 0) Introduction
• 1) What is a group of galaxies theoretical and
  operational points of view
• Hierarchy from a single galaxy to supercluster
  and beyond
  
• The non-island Universe interacting galaxies
  2) Where from to search for groups ?
• Observations galaxy and redshift surveys
• Numerical simulations
• 3) How to find a group
• Groupfinders from pairs to superclusters
• 4) What kind of problems arise and how to
  overcome them
• 5) How to enjoy results

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How to find a group of galaxies.A new 2dF GRS
group catalogue
Intro historical reference ----------------------
---------------------------

• Erik Tago,Jaan Einasto, Enn Saar, Maret Einasto,
  Ivan Suhhonenko, Mihkel Jõeveer, Jaan Vennik,
  Pekka Heinämäki, Douglas Tucker
• Tartu Observatory, Tuorla Observatory,
• Fermilab
• Tartu-Tuorla seminar
• June 20-21 2005 Tõravere

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Hierarchy in the world of galaxies

• What is a group isn't a trivial question
• Hierarchy from single galaxy through
  pair, group, cluster, supercluster -- to
  supercluster-void network
• Is there a really single galaxy ? May-be
  among giant galaxies. In general I prefer an
  answer NO
• Pairs of galaxies some examples
• Milky Way /Andromeda
• Interacting pairs M51 , the Antennae,
  the Mice
• Groups N3X
• Local group N3 40

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Galaxies interact in pairs groups
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Local Group of galaxies
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Clusters

• Clusters NX 10 000 galaxies
• Shapley supercluster includes 33 Abell clusters
• Has this classification some physical
  meaning? - in particular for groups and
  clusters (YES?)
  

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Rich cluster of galaxies Abell 1689
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Shapley supercluster of galaxies
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Multi-nucleus cluster of galaxies an evidence
for group merging
CL0958-4702 Spitzer
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Bullet cluster of galaxies encounting clusters
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APM and 2dFGRS sky coveridge
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SDSS DR6
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GROUPFINDER METHODS

• Cell count
• Cluster analysis, FoF method, percolation
• Minimal spanning tree
• Matched filter method
• Adaptive filter method
• Kernel based methods
• Voronoi tesselation
• Wavelet transform
• Maximum brightest cluster galaxies
• etc

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Redshift surveys we have used

• Abell (ACO) 4072 1300 clusters
• 2dF GRS 250 000 galaxies
• Sloan Survey (SDSS) 106 galaxies

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Groupfinders and catalogues a few reacent of
them

• AUTHORetal sample no. of gr. (Ngt2)
  (Ngt4)
• Eke 2005 2dFGRS 28877
  7020
• Merchan 2002
  2209
• Yang 2004
  12096 2502
• Tago 2005
  25215 4852
• Merchan 2005 SDSS DR3
  10864
• Goto 2005 DR2
  335
• Weinmann 2006 DR2 16012
  3720
• Berlind 2007 DR3
  4119
• Tago 2007 DR5 50362
  9454
• 
  
  

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A groupfinder and a catalogue our case

• We use Friends of Friends (FoF) groupfinder
  (cluster analysis)
• applying linking length (LL) scaling
• a) using simulated clusters
• b) calibrating observed groups by shifting
• to higher distances

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The LL scaling recipe

• Perform preliminary FoF
• Select of initial nearby groups
• Shift the groups step by step to larger distances
  and recalculatate their properties
• reject the group members which do not satisfy
  visibility conditions for the catalogue
  luminosity window
• using Minimal Spanning Tree method determine new
  LL which is needed to link reduced group at
  new distance
• Find LL law, and using this perform final FoF

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Number density of groups
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Number density of galaxies in the 2dFGRS and
SDSS DR5
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Multiplicity function
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The scaling of membershipfor individual groups
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Scaling law of linking length for the SDSS DR5
North sample
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What kind of problems ?

• Not a 3D space but 2Dredshift
• Distorsions in redshift space
• In redshift space we can see
• 1) fingers of God due to dynamical
  dispersion in
• groups and clusters ( 10 1500 km/s) ?
• 2) substructures multimodal velocity
  distribution
• 3) contamination by fore and background
• groups and galaxies , merging of
  subgroups
• 4) Selection effects depending on distance due to
  flux limited samples
• a) number density decrease
• b) richness decrease
• c) volume effect distant clusters are
  larger
• Evolutionary effect
• Luminosity-density relation in groups and
  clusters
• 
  

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How to ovecome the problems ?

• Do not study groups (in this paper not applied)
• Restrict samples from low (SDSS incomplete
  r14.5) and high redshift (17.7)
• Luminosity corrected by weight
• Perform FoF in two direction radial and
  transversal - assuming some ratio of them (6
  12)
• Linking Length scaling
  
  

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Distribution of velocity dispersion as a function
of distance
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Distribution of maximum projected size as a
function of distance
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Sky distribution of groups by Berlind(), Tago
(O - group,o- pair)
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FoF result for 2dF GRS at A933 cluster
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Clusters of galaxies

• In redshift space we see
• 1) fingers of God due to dynamical dispersion
  among member galaxies
• ( Abell clusters sigma_V 100 1500 km/s)
• 2) substructures multimodal velocity
• distribution
• 3) contamination by fore and background
• groups and galaxies

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Numerical simulation

• Pioneers Alar and Jury Toomre 1970ies
• modelling of interacting galaxies
• John Dubinsky models of cluster formation

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To enjoy your own results

• You have to compare with other results and find
  that your results being better
• This is the case.
• You have to share your results with others
• NEXT SLIDE

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Welcome to our web site for groups and clusters

• http//www.aai.ee/erik/sdss
• sdss dr5 group catalogue
• Thank You!