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The Assembly of Galaxy Clusters

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  1. Karl Andersson – Astro Lunch April 11, 2008 The Assembly of Galaxy Clusters arXiv:0804.0426 Berrier et al.

  2. Question • ~60% of cluster galaxies are spheroidal (E, S0) • Only ~30% of field galaxies • How cluster galaxies transform to ‘’early-type’’? • ‘’pre-processing’’ in a group environment? • More frequent merging for cluster galaxies? • Internal cluster processes? • Ram pressure stripping • Cold gas ‘’strangulation’’ • Galaxy-galaxy ‘’harassment’’ Karl Andersson – Astro Lunch April 11, 2008

  3. Answer? • ~60% of cluster galaxies are spheroidal (E, S0) • Only ~30% of field galaxies • How cluster galaxies transform to ‘’early-type’’? • ‘’pre-processing’’ in a group enviroment? • More frequent merging for cluster galaxies? • Internal cluster processes! • Ram pressure stripping • Cold gas ‘’strangulation’’ • Galaxy-galaxy ‘’harassment’’ Karl Andersson – Astro Lunch April 11, 2008

  4. Setup • N-body simulation using Adaptive Refinement Tree (ART, Kravtsov et al. 1997) • 120 h-1 Mpc box with 5123 1.07 109 h-1 Msun particles • Sample of 53 clusters (1.0-5.8) 1014 h-1 Msun • with total 834 subhalos M>1011.5 h-1 Msun ==galaxies Karl Andersson – Astro Lunch April 11, 2008

  5. Origin • Most galaxy halos are accreted directly from the field Karl Andersson – Astro Lunch April 11, 2008

  6. Origin • Most galaxy halos are accreted directly from the field Makes group ‘’pre-processing’’ unlikely Karl Andersson – Astro Lunch April 11, 2008

  7. Timescales • Average cluster galaxies spend little time in a group environment, ~4 Gyr in cluster Karl Andersson – Astro Lunch April 11, 2008

  8. Merging • Field halos are more likely to have had a recent (< 6 Gyr) merger than cluster subhalos Merging is probably not the main cause of galaxy transformation Karl Andersson – Astro Lunch April 11, 2008

  9. Summary • Cluster galaxies are accreted mostly from the field – spend little time in group environment • Mergers are more common for field galaxies than for cluster galaxies • ~50% of cluster galaxies have spent 4 Gyr or more within cluster at z=0 • Internal cluster processes operate on ~4 Gyr (gravitational), ~1 Gyr (intra-cluster medium related) timescales Karl Andersson – Astro Lunch April 11, 2008