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 sourcesSZ follow-up requires spectroscopy or photometry of spectral features prominent in the infrared (H-K break).

Go WideThe 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 -CDMCircles -CDM

5x1013 h-1 Msolar

3x1014

1015

Go Red: Space-based infraredLower sky background (no OH

emission)Lower absorption (no H2O bands)

Wide-field, diffraction-limited image quality

Go DeepCluster 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.