H i intensity mapping: a single dish approach

We discuss the detection of large-scale H i 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 S-3 simulated H i 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 T-sys = 50 K, 50 feedhorns and 1 year of observations, we find that at low redshift (z approximate to 0.3), a resolution of similar to 40 arcmin and a survey of similar to 5000 deg(2) is close to optimal, whereas at higher redshift (z approximate to 0.9) a resolution of similar to 10 arcmin and similar to 500 deg(2) 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 similar to 40 m dish and a similar to 60 element receiver array held similar to 90 m 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 approximate to 0.3 with an accuracy similar to 2.4 per cent and that w can be measured to an accuracy of 16 per cent.