Luke Leisman Calvin College. Photo Credit: SLOAN Digital Sky Survey. Great Lakes Cosmology Workshop June 15, 2010

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1 Luke Leisman Calvin College Photo Credit: SLOAN Digital Sky Survey Great Lakes Cosmology Workshop June 15, 2010

2 Acknowledgements Funding: Sid Jansma Calvin Summer Research Fellowship Co-workers: Deborah Haarsma, David Sebald Calvin College Megan Donahue, Mark Voit, Seth Bruch Michigan State University Hans Böhringer and Daniele Pierini Max-Planck Institute, Germany Judith Croston University of Southampton, United Kingdom Gabriel Pratt and Monique Arnaud University of Paris, France

3 Brightest Cluster Galaxies: Importance Most massive galaxies in the universe Central location in cluster Extended envelope (e.g. Vale & Ostriker 2008) Different properties from ellipticals of the same mass (von der Linden 2007)

4 BCGs unsolved mysteries Formation history (Rasmussen et al. 2010, Stott et al. 2010, others) Interplay with host cluster (e.g. Lin & Mohr 2004) Used as a standard candle (Postman and Lauer 1995) Yet, found in wide variety of cluster environments Cluster gas properties may give insight into these mysteries

5 Cluster Gas Gas in clusters emit X-rays via free-free emission Gas density is well determined by X-ray surface brightness In some clusters high density leads to significant energy loss which can turn on feedback mechanisms (McNamara & Nulsen 2007, many others) Our work is focusing on clusters with low core densities/ long cooling times

6 Data from the Representative XMM- Newton Cluster Structure Survey (REXCESS) (Bohringer et al. 2007) Sample of 33 clusters Selected based on X-ray luminosity Range of redshifts from 0.05 < z < 0.15 Data directly observed: Southern Observatory for Astrophysical Research (SOAR) and XMM- Newton Our Sample

7 Optical Reduction BCGs magnitudes are difficult to measure Crowded fields masks (Varella et al. 2009) Total magnitude confused by sky background and Intracluster light metric magnitudes Procedure: Mask light from non-bcg sources Fit the remaining light using elliptical isophotes Numerically integrate ellipses inside metric radius

8 Results from Haarsma et al ApJ 713, 1037 Blue star - cool core clusters Green X - BCG far from cluster center 90% of BCGs in REXCESS within R 500 Consistent with previous studies (Bildfell et al 2008, Rafferty et al. 2008, Sanderson et al. 2009, Hudson et al. 2009) Correlation of BCG mass with cluster mass: L BCG α M cl 0.18+/-0.07 Consistent with previous results (Schombert 1988, Whiley et al. 2007, Brough et al. 2008, etc.)

9 Results: Core Gas Density vs BCG Luminosity Unexpected correlation between core gas density and BCG metric luminosity Follows power law: n e α L 2.7+/-0.4 Possible Explanation: merger history Need follow up data to confirm trend

10 Our Samples Data from the Representative XMM- Newton Cluster Structure Survey (REXCESS) (Böhringer et al. 2007) Sample of 33 clusters Selected based on X-ray luminosity Range of redshifts from 0.05 < z < 0.15 Data directly observed: Southern Observatory for Astrophysical Research (SOAR) and XMM- Newton Data from the Archive of Chandra Cluster Entropy Profiles (ACCEPT) (Cavagnolo et al. 2009) Sample of 240 clusters, 98 with X-ray & optical Selected based on archival availability Range of redshifts from < z < 0.3 Data was mined from archived data: Sloan Digital Sky Survey (SDSS) and Chandra

11 We are using images from SDSS, but not their catalog magnitudes. Why? Means of comparison Better deblending/masking SDSS does not provide a metric radius We have the flexibility to measure BCG magnitudes in many different ways

12 Hot off the Press ACCEPT REXCESS

13 Hot off the Press ACCEPT REXCESS line is the fit from REXCESS results

14 Hot off the Press ACCEPT REXCESS

15 Hot off the Press ACCEPT REXCESS

16 Photo Credit: SLOAN Digital Sky Survey Photo Credit: SLOAN Digital Sky Survey Abell 2124 Abell 773 BCG Identification In most cases BCG is obvious Considerations: Brightness Proximity to cluster center Profile/diffuseness of emission Color/red sequence Number of neighbors In up to 40% of clusters the BCG is not located at the dynamical center (Skibba et al. 2009)

17 Summary Haarsma et al REXCESS sample of 33 clusters Confirmed weak cluster mass vs BCG mass correlation Found most BCGs (90%) located near cluster core Discovered trend between gas properties and BCG stellar properties Suggested a model to explain the trend via long term merger history Follow Up in Progress ACCEPT/SDSS sample of 98 clusters No clear trend in full sample Possible trend in sub-samples Investigating the issue of BCG identification