Probing the Primordial Power Spectrum with Cluster Number Counts

TL;DR

This paper explores how galaxy cluster counts can extend constraints on the primordial power spectrum beyond CMB limitations, especially using lensing surveys to improve accuracy.

Contribution

It introduces a method to use cluster counts to probe the primordial power spectrum at higher wave numbers, surpassing CMB constraints, with potential improvements from lensing surveys.

Findings

Cluster counts can extend primordial spectrum constraints up to 0.45 h Mpc^{-1}.

Constraints are limited by uncertainties in mass scaling relations.

Lensing surveys may provide tighter constraints due to direct mass measurements.

Abstract

We investigate how well galaxy cluster number counts can constrain the primordial power spectrum. Measurements of the primary anisotropies in the cosmic microwave background (CMB) may be limited, by the presence of foregrounds from secondary sources, to probing the primordial power spectrum at wave numbers less than about 0.30 h Mpc^{-1}. We break up the primordial power spectrum into a number of nodes and interpolate linearly between each node. This allows us to show that cluster number counts could then extend the constraints on the form of the primordial power spectrum up to wave numbers of about 0.45 h Mpc^{-1}. We estimate combinations of constraints from PLANCK and SPT primary CMB and their respective SZ surveys. We find that their constraining ability is limited by uncertainties in the mass scaling relations. We also estimate the constraint from clusters detected from a SNAP like gravitational lensing survey. As there is an unambiguous and simple relationship between the filtered shear of the lensing survey and the cluster mass, it may be possible to obtain much tighter constraints on the primordial power spectrum in this case.