how to find a group of galaxies.ii the sloan survey case erik tago (and j.einasto,e.saar,e.tempel,...
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![Page 1: How to find a group of galaxies.II The Sloan Survey case Erik Tago (and J.Einasto,E.Saar,E.Tempel, M.Einasto,J.Vennik,V.Müller Tartu Observatory,Potsdam](https://reader035.vdocuments.us/reader035/viewer/2022062407/56649d805503460f94a647cc/html5/thumbnails/1.jpg)
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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Contents0) Introduction1) 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 simulations3) How to find a group • Groupfinders : from pairs to superclusters4) What kind of problems arise and how to overcome them5) How to enjoy results
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How to find a group of galaxies.A new 2dF GRS group catalogue
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
Intro: historical reference-------------------------------------------------
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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 N=3…X
Local group N=3 + 40
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Galaxies interact in pairs & groups
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Local Group of galaxies
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Clusters
Clusters N=X… 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) : 10^6 galaxies
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Groupfinders and catalogues: a few reacent of them
AUTHOR+etal sample no. of gr. (N>=2) (N>=4)
• 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 2D+redshift• 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 subgroups4) 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 r=14.5) 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!