AMiBA計畫之發展與初期運作

Abstract

CBI and ACBAR reported in the CMB power spectrum ${it l}>2000$, they detected power excess to the primary signal. Secondary signal, mainly unresolved SZ effect of fainter objects, has been proposed to explain the result. AMiBA intends to measure this band power to higher accuracy, and put a tighter constraint on $sigma_{8}$, which is directly related to the amplitude of primordial density fluctuation. A second goal of AMiBA is to measure the number count of high redshift galaxy clusters, thereby probing the evolution of structure formation history using the most massive bound objects. To conduct numerical simulation on the expected science output, we report an instantaneous heating scheme, for which gases in dense regions receive a temperature increment of several keV at $z=2$ whereas those in rarefied regions remain intact, that can produce bound objects obeying the observed mass-temperature and luminosity-temperature relations. Based on these simulations and AMiBA sensitivity, we expect to measure the $it{l}sim3000$ band to $5-sigma$ in one month with 60cm dish. Upgrading to 1.2m dish, and we may measure the SZ power in $it{l}=4000--6000$ band in 1.5 months. And for blind surveys, we expect to find $sim$10 clusters/$deg^2$ with deep exposures ($sim$0.8 $deg^2$/month). Detailed testing of AMiBA a two-element prototype has been conducted on site. The 7-element system was recently installed and is being commissioned. Initial test shows a promising white spectrum of noise. The important tasks of ground pickup and delay measurement has been performed or planned. And a sweeping CW source is being designed and tested to be the main calibrator of AMiBA.