High-z galaxy clusters as cosmological probes:

1. High-z galaxy clusters as cosmological probes: Recent Results and Future prospects Mike Gladders Carnegie Observatories hubble fellow symposium, stsci, april20th, 2006

2. Cast of Characters OCIW:Alan Dressler, Edo Berger,Gus Oemler, Francois Schweizer, Luis Ho,Pat McCarthy, Nidia Morel,Kathleen Koviak U. Catolica:Felipe Barrientos, Leopoldo Infante U. Toronto:Kris Blindert, Dave Gilbank, Howard Yee U. Colorado:Erica Ellingson, Amelia Hicks MIT:Mark Bautz U. Victoria:Henk Hoekstra York U.:Pat Hall U. Chicago: John Carlstrom

3. The Plot The RCS Galaxy cluster Surveys Cosmology from N(M,z) Analysis of RCS-1 Strong Lensing Follow-up Challenges: New Instruments (Pushing the Redshift Envelope: High-z Clusters in Association with Short/Hard GRBs)

4. The Basics: galaxy clusters and cosmology • Galaxy cluster represent the large-scale bound endpoint of structure formation via gravitational collapse • Clusters sit at the intersections of filaments in the “cosmic web”, and are composed mostly of dark matter with a frosting of baryons in the form of hot gas and stars • Clusters evolve over time by accumulation of other galaxies, groups and clusters from their surrounding environment • this evolution is cosmology dependent

5. the surveys: RCS-1(complete) • 95 square degrees of R (6500Å) and z’ (9200Å) imaging to a depth sufficient to find clusters to z~1.4; best at 0.4<z<1.0 • Cluster finding using a refined version of the algorithm in Gladders & Yee (2000), first catalogs in Gladders & yee (2005). clusters found as concentrations in color, magnitude and position • Contamination and completeness tested extensively via simulations

6. the surveys: RCS-2 (Ongoing) • 830 square degrees of new grz imaging, shallower than RCS-1 but much deeper than SDSS. with CFHT Legacy deep/wide added is 1000 square degrees. • completion planned 2007a: first of the next-gen large cluster surveys designed to measure dark energy. • extensive follow-up, principally to calibrate mass-observables, is ongoing in parallel, using mostly rcs-1 clusters

7. RCS-1: Cosmological Analysis • Recently we have completed a first analysis of the entire RCS-1 catalog (Gladders et al. 2006) using the so-called “self-calibration” method (Majumdar & Mohr 2004). • The catalog is richness and significance limited, over the redshift interval 0.35<z<0.95; at the chosen limits incompleteness corrections are small (<20%, typically 10%) and well understood.

8. RCS-1: Cosmological Analysis We fit for Ωm and σ8 (presuming a flat w=-1 universe) and four parameters describing the mass-richness relation, namely the slope, α, and zeropoint, A, evolution in A in redshift as (1+z)γ, so that the relation between cluster mass, M200, and richness, R, is M200=10A Rα(1+z)γ We also account for scatter in this relation with a fixed fractional scatter in mass parameterised by fsc.

9. Blindert et al. 2006 RCS-1: Cosmological Analysis The following results are obtained: Ωm 0.31 +0.11 -0.10 σ8 0.67 +0.18 -0.13 A 10.55 +2.27 -1.71 α 1.64 +0.91 -0.90 γ 0.4 +2.11 -3.80 fsc 0.73 +0.18 -0.16 0.238-0.266 WMAP 3-year 0.722-0.772 WMAP 3-year 9.89 +-0.89 Yee & Ellingson 2003, CNOC-1 1.64 +-0.28 Yee & Ellingson 2003, CNOC-1 consistent with marginal evolution 0.6-0.7 Blindert et al. 2006 (RCS-1) Ωm 0.30 +0.12 -0.11 σ8 0.70 +0.27 -0.15

10. Strong Lensing 3 Samples: RCS-1 Primary: arcs detected in R in survey imaging (Gladders et al. 2001,2003) RCS-1 Secondary: arcs detected in I in follow-up imaging of high-z candidate clusters (Gladders et al. 2003) RCS-2 Primary (initial): arcs detected in g and/or r in survey imaging

11. 30 arcsec 1 arcmin RCS-1: Strong Lensing Samples

12. RCS-1: Strong Lensing Samples

13. RCS-1: Strong Lensing Samples

14. Z=3.86 RCS-1: Strong Lensing Samples Z=0.9

15. 9 hrs GMOS N&S Gilbank et al. 2006 RCS-1: Background Galaxies

16. 49” radius! (one of the most massive objects known) z=3.01 RCS-2: Strong Lensing Example Z=0.698 LDSS-3 imaging

17. RCS-2: Strong Lensing Example SZ Effect from the SZA, courtesy J. Carlstrom

18. RCS-2: Strong Lensing Samples 27 new clusters with giant arcs, ¼ of the survey

19. Strong Lensing Three surprises: • Large proportion of multiple arc clusters •  distribution of lensing cross sections includes a small population with large cross section which dominate the lensing statistics. Latest modeling papers give similar results - its due to triaxiality and orientation effects (e.g. Ho & White ‘04).

20. Strong Lensing Three surprises: • Redshift distribution of lenses skewed to high-z •  implies evolution in cluster properties? •  implies that mass alone is not responsible for promoting clusters as good lenses: something associated with cluster assembly enhances cross sections and/or an effect at low-z reduces cross sections…. • Clusters with arcs not obviously most massive •  expectation from modeling is for a strong preference for the most massive systems to form bulk of all arcs.

21. Strong Lensing: comparing to predictions Predictions, Realities (a little out of date…Dec05) Model estimated from Dalal, Holder and Hennawi (2004)

22. Strong Lensing: comparing to predictions Background point are the VIRGO Hubble volume cluster catalog for LCDM model

23. Strong Lensing: comparing to predictions Hennawi, et al. 2005 ? ? ? Hennawi, et al. 2005

24. Strong Lensing: Dark Matter Properties? • If dark matter has a (very!) small non-gravitational self-interaction (a la Spergel and Steinhardt 1999) then… • If the timescale for a particle in a cluster-like environment to have an interaction is of order a Hubble time, clusters at low-redshift will preferentially have isothermal (puffed up) cores – and hence be less efficient lenses… • And This effect should work faster for more massive systems which would tend to move the lensing cross sections toward lower mass systems as well…

25. The Follow-Up Challenge • Ultimately the grand cosmological tests envisioned with massive clusters samples, and the study of unique subsets such as cluster lenses requires detailed and extensive follow-up observations at many wavelengths. • Large amounts of large optical telescope time are required to get the necessary spectroscopy. • Redshifting and field crowding are significant problems : new instruments would be useful…

26. LDSS-3: Clusters at high redshift • “My first instrument” is the LDSS-3 spectrograph. It is a complete overhaul of the old LDSS-2 spectrograph from the WHT 4m. • New optics, dispersers, detector, electronics and filters all installed : Image quality now better than site delivers (<0”.2) and the throughput is the highest of any multi-object spectrograph…

27. LDSS-3: First Light – Feb 2005 Peak Throughput: 41% Peak Throughput: 42% 25% Edges: 4400Å-7800Å 25% Edges: 4400Å-9900Å 10% Edges: 3800Å-9200Å 10% Edges: 3900Å-10200Å

28. GISMO: Strong Lensing and Cluster Cores • GISMO (the Gladders Image-Slicing Multi-Slit Option for IMACS) is an addition to the IMACS ½ degree field MOS spectrograph at Magellan. • GISMO is a field-reformatter that allows the power of the large spectrograph to be brought to bear on a small (3.2’x3.5’: ACS!) field of view: 8x the normal spatial density of slits, with no spectral compromises!

29. GISMO

30. GISMO GISMO Optics (96 elements) collimator field lens

31. GISMO

32. GISMO

33. Clusters at z~2: GRBs as Signposts • Since high-z clusters are very rare, using easily visible signposts (this used to mean AGN!) is helpful. Short-hard gamma-ray bursts may be our new best window onto the highest redshift clusters… • We have recently discovered a short-hard grb which appears to be hosted in a galaxy in a z~1.8 cluster!

34. Clusters at z~2: Short-Hard GRBs GRB050813

35. Clusters at z~2: Short-Hard GRBs

36. Clusters at z~2: Short-Hard GRBs Excess over field is ~50x background data from Miyazaki et al. 2003

37. Clusters at z~2: Short-Hard GRBs z=0.72 known foreground z~1.8