# Presentation: 801911

## Wide Field Imagers in Space and the Cluster Forbidden Zone

- Megan Donahue
- Space Telescope Science Institute
- Acknowledgements to: Greg Aldering  (LBL) and
- Marc Postman (STScI)

## Why Study High-Redshift Massive Clusters?

- Clusters are the largest sites where we can “see” nearly all of the baryons that are there.
- Clusters are thought to be “fair samples” of the universe.
- Cluster evolution: predictable, hierarchical, and gravitationally-driven
- Cluster evolution: sensitive to the overall density of the universe and the spectrum of initial density fluctuations (~8 Mpc)

## Survey Questions

- Are our fundamental assumptions about cluster formation and galaxy evolution valid?
- What do the first clusters in the universe look like?
- Is cluster formation related to the formation of quasars and radio galaxies?
- When did galaxies and stars pollute the intracluster medium?
- When did clusters acquire dense, hot atmospheres?

## The Cluster Forbidden Zone z=1.5 and beyond

- Old galaxies are difficult to detect in the optical at z>1.0
- X-ray surface brightness fades
- Ground-based infrared observations have high sky background.

- Weak-lensing techniques require numerous background sources
- SZ follow-up requires spectroscopy or photometry of spectral features prominent in the infrared (H-K break).

## Go Wide

- The most massive clusters have a space density of ~1 per cubic Gpc between z=0-1.
- Cluster evolution makes rare clusters rarer at high redshift.

## Evrard, et al. 2001, astro-ph/0110246

- Triangles -CDM
- Circles -CDM

- 5x1013 h-1 Msolar

- 3x1014

- 1015

## Go Red: Space-based infrared

- Lower sky background (no OH emission)
- Lower absorption (no H2O bands)
- Wide-field, diffraction-limited image quality

## Go Deep

- Cluster evolution has been relatively modest since z~1 (constraining m).
- Cluster formation models predict that cluster assembly was likely more rapid at earlier times.
- Metal injection into cluster gas must have occurred at z>0.8.

## Cluster Discovery in the Forbidden Zone

- Wide-field: at least 1000 square degrees (see figure from Evrard)
- Near-IR: HAB ~ 24 mag arcsec-2 enables detection of clusters out to z=2-2.5, 50% yield  (matched filter experience).
- X-ray: 3 10-15 sensitivity for a 6 keV cluster at z=2.
- texp = 600 ksec for Chandra
-          60 ksec for XMM

## Plan

- Cluster discovery in the near-IR
- PRIME  (near-IR Discovery mission, Zheng JHU): PI science 2006-2009
- Possible SNAP GO program (perhaps to follow up S-Z cluster candidates)
- Cluster properties: velocity dispersions, temps
- Multi-spec observations (R=100) with NGST (not possible with Keck)
- Constellation-X (at 100x XMM collecting area, z=2 cluster temps could be obtained in about 25,000 seconds); iron abundances in ~100,000 seconds

## Preparatory Theory Needed

- Projection effects through full N-body simulations for weak-lensing surveys.
- Intracluster medium evolution with feedback and entropy considerations for realistic X-ray and S-Z predictions.
- Galaxy evolution in crowded environments: will all clusters at all redshifts have an old galaxy population?

## Conclusions

- Finding and studying high-redshift clusters are critical to understanding structure formation and the history of star and galaxy formation.
- High-redshift clusters are rare: wide-area space-based surveys in the near IR are the best way to find them.
- Coordinated multi-wavelength observations, SZ, near-IR, and X-ray, are required to reveal the properties of the clusters: mass, metallicity, galaxy content.