1. Philip J. Humphrey (UCI) Tracing the Gas to the Virial Radius (R 100 ) in a Fossil Group arXiv:1106.3322 David A. Buote (UC Irvine), Fabrizio Brighenti (Bologna), H élène M. L. G. Flohic (U Chile), Fabio Gastaldello (Milan), William G. Mathews (UCSC)

2. Introduction Cluster outskirts… Well-behaved? (eg. Reiprich et al, 2009) Non-relaxed? (eg. Bautz et al, 2009; Kawaharada et al 2010) Clumpy? (eg. Simionescu et al 2011; Urban et al. 2011)

3. Fossil group (Vikhlinin 99) => relaxed R 500 XIS 0 RXJ1159+5531 Chandra Residuals plot 1.2 Mpc = R vir 90 kpc = 0.08 R vir Vikhlinin et al (2006) Chandra

4. Spectral analysis XIS 0 Chandra Suzaku Hot gas X-ray background Instrumental background

5. Spectral analysis Chandra Galactic/ local CXB Detected + undetected Chandra Suzaku Agreement!

6. Results (Vikhlinin et al 2006) Chandra Suzaku Fit projected kT, density Project 3D gas model onto sky Agrees with deprojection analysis R 500 No flattening at large radii

7. Results Construct hydrostatic model (Buote talk) R vir = 1120±40 kpc, consistent with past work Add in central galaxy Add in other galaxies (Vikhlinin 99) Add in IntraCluster Light (Purcell 07) Cosmological f b Baryonic closure within R vir

8. Robustness of results Solar wind Charge Exchange? CXB model shape?

9. Robustness of results Results appear robust!

10. Conclusions Trace the gas to R vir RXJ1159 in single Suzaku pointing Robust results Well-behaved at large radii Fossil groups optimal? Efficient observing strategy