2013MNRAS.434.1239B

We discuss the detection of large-scale Hi intensity fluctuations using a single dish approach with the ultimate objective of measuring the baryonic acoustic oscillations (BAO) and constraining the properties of dark energy. To characterize the signal we present 3D power spectra, 2D angular power spectra for individual redshift slices and also individual line-of-sight spectra computed using the S3 simulated Hi catalogue which is based on the Millennium Simulation. We consider optimal instrument design and survey strategies for a single dish observation at low and high redshift for a fixed sensitivity. For a survey corresponding to an instrument with Tsys = 50K, 50 feedhorns and 1 year of observations, we find that at low redshift (z ~ 0.3), a resolution of ∼ 40arcmin and a survey of ∼ 5000deg2 is close to optimal, whereas at higher redshift (z ~ 0.9) a resolution of ∼ 10arcmin and ∼ 500deg2 would be necessary - something which would be difficult to achieve cheaply using a single dish. Continuum foreground emission from the Galaxy and extragalactic radio sources are potentially a problem. In particular, we suggest that it could be that the dominant extragalactic foreground comes from the clustering of very weak sources. We assess its amplitude and discuss ways by which it might be mitigated. We then introduce our concept for a dedicated single dish telescope designed to detect BAO at low redshifts. It involves an underillumintated static ∼ 40m dish and a ∼ 60 element receiver array held ∼ 90m above the underilluminated dish. Correlation receivers will be used with each main science beam referenced against an antenna pointing at one of the celestial poles for stability and control of systematics. We make sensitivity estimates for our proposed system and projections for the uncertainties on the power spectrum after 1 year of observations. We find that it is possible to measure the acoustic scale at z ~ 0.3 with an accuracy ∼ 2.4 percent and that w can be measured to an accuracy of 16 percent.