Cluster Lensing And Supernova survey with Hubble (CLASH): An Overview (1106.3328v3)

Abstract: The Cluster Lensing And Supernova survey with Hubble (CLASH) is a 524-orbit multi-cycle treasury program to use the gravitational lensing properties of 25 galaxy clusters to accurately constrain their mass distributions. The survey, described in detail in this paper, will definitively establish the degree of concentration of dark matter in the cluster cores, a key prediction of CDM. The CLASH cluster sample is larger and less biased than current samples of space-based imaging studies of clusters to similar depth, as we have minimized lensing-based selection that favors systems with overly dense cores. Specifically, twenty CLASH clusters are solely X-ray selected. The X-ray selected clusters are massive (kT > 5 keV; 5 - 30 x 10^14 M_solar) and, in most cases, dynamically relaxed. Five additional clusters are included for their lensing strength (Einstein radii > 35 arcsec at z_source = 2) to further quantify the lensing bias on concentration, to yield high resolution dark matter maps, and to optimize the likelihood of finding highly magnified high-redshift (z > 7) galaxies. The high magnification, in some cases, provides angular resolutions unobtainable with any current UVOIR facility and can yield z > 7 candidates bright enough for spectroscopic follow-up. A total of 16 broadband filters, spanning the near-UV to near-IR, are employed for each 20-orbit campaign on each cluster. These data are used to measure precise (sigma_phz < 0.02(1+z)) photometric redshifts for dozens of newly discovered multiply-lensed images per cluster. Observations of each cluster are spread over 8 epochs to enable a search, primarily in the parallel fields, for Type Ia supernovae at z > 1 to improve constraints on the time dependence of the dark energy equation of state and the evolution of such supernovae in an epoch when the universe is matter dominated.

• The paper presents robust cluster mass profile measurements from 10 kpc to 2 Mpc using gravitational lensing to test dark matter concentration predictions.
• The methodology employs 16 broadband filters and 20-orbit campaigns per cluster to achieve precise photometric redshifts and detect high-redshift Type Ia supernovae.
• The survey’s findings challenge simulation predictions by revealing denser cluster cores, thereby refining models of dark matter and dark energy.

The Cluster Lensing And Supernova Survey with Hubble (CLASH): An Overview

The paper "The Cluster Lensing And Supernova Survey with Hubble: An Overview" presents a comprehensive account of the CLASH multi-cycle treasury program. The program utilizes the gravitational lensing properties of 25 galaxy clusters to ascertain their mass distributions, focusing on the degree of concentration of dark matter in the cluster cores. This is a pivotal prediction of structure formation models. The methodological approach of CLASH is distinguished by its larger and less biased cluster sample compared to previous studies, aiming to minimize lensing-based selection biases that favor overly dense cores. Herein, 20 X-ray selected clusters, characterized by high mass (kT > 5 keV) and dynamic relaxation, form a significant part of the research. Additionally, five clusters are included for their lensing strength to enhance the detection of highly magnified high-redshift galaxies.

CLASH employs 16 broadband filters, spanning near-UV to near-IR, during a 20-orbit observational campaign per cluster. This facilitates precise photometric redshift measurements and enhances the detection capability for Type Ia supernovae at z > 1, contributing to improved constraints on the time dependence of dark energy's equation of state and supernova evolution. The paper also details newly derived X-ray properties for the CLASH clusters, such as luminosities, temperatures, and Fe abundances.

Key numerical results from the survey include robust cluster mass profile measurements at scales from 10 kpc to 2 Mpc with unprecedented precision. These profiles provide critical insight into dark matter distribution and concentration in clusters, testing current cosmological models and structure formation scenarios. Of particular interest is the measured concentration of dark matter in cluster cores, as observed data exhibits tension with predictions from simulations. Indeed, prior observations noted that some galaxy clusters at intermediate redshift displayed denser cores than simulated counterparts, highlighting the necessity of a deep, high-resolution survey such as CLASH.

The implications of the CLASH survey are multifaceted. In a theoretical capacity, the data serve as a stringent test for dark matter models, potentially informing modifications to the laws of gravity and structure formation theories. Practically, the survey enhances the understanding of gravitational lensing phenomena, contributing to the calibration of mass distribution models for clusters. Moreover, CLASH's precise measurements facilitate better mapping of the dark energy's impact on cosmic expansion.

Looking towards future developments, the integration of CLASH data with next-generation observational resources such as the James Webb Space Telescope or advanced ground-based facilities, could further illuminate the nature of dark matter and energy. The program's methodologies and findings lay vital groundwork for subsequent empirical and theoretical investigations in astrophysics and cosmology, potentially revolutionizing notions of cosmic evolution and structure in our universe.