The DEEP2 Galaxy Redshift Survey First Results on Groups and Clusters

1
The DEEP2 Galaxy Redshift Survey First Results
on Groups and Clusters

• Brian F. Gerke for the DEEP2 team
• AAS meeting, Atlanta
• 7 January 2004

Image NGC 7331, taken during DEIMOS commissioning
2
Why find groups?

• Study galaxy properties and formation
  historyespecially in extreme environments
• Study formation and evolution of groups and
  clusters (the most massive virialized objects)
• Improve simulations (how do galaxies populate DM
  halos?)
• Constrain cosmological parameters (abundance of
  groups with z and sv can constrain WM, WL and
  w)
• Etc

3
Difficulties

• The usual suspects redshift-space distortion and
  incomplete sampling
• DEIMOS slit collisions bias against clustered
  objects
• R-band selection (rest frame U at z1) misses
  reddest galaxies
• Evolution of LSS (groups smaller at z1)

4
The Voronoi-Delaunay Group-Finding Algorithm

• Uses Voronoi cell volume to find cluster seeds
• Uses Delaunay mesh information to estimate
  density of cluster core
• Searches adaptively for group members based on
  central density estimate

Figure from C. Marinoni, et al. (original
implementation)
5
Tests on Mock Catalogs

• Twelve independent mocks from Yan et al.Groups
  are galaxies in virialized DM halos
• Can gauge success at reconstructing individual
  groups
• Can also gauge success at reconstructing
  properties of the catalog.

6
First DEEP2 Group Catalog
7
First DEEP2 Group Catalog
8
Group catalog properties