Astronomy and Astrophysics – Astrophysics
Scientific paper
2007-03-29
Astronomy and Astrophysics
Astrophysics
To appear in "Cosmology, Galaxy Formation and Astroparticle Physics on the Pathway to the SKA", Eds. Kloekner, Jarvis, Rawling
Scientific paper
In this short contribution we consider what types of surveys might be optimally pursued with path-finding instruments of 1%, 10% and finally 100% of the projected SKA sensitivity from the perspective of scientific applications that utilize the red-shifted 21 cm emission line. Achieving interesting HI galaxy sample sizes with 1% SKA surveys requires very substantial survey durations, of about 1000 days. Good sampling (log(N)~5) down to below M_HI* can then be achieved out to z=0.2 over 8000 deg^2 of survey area or even to z=0.5 over 800 deg^2. The same surveys will permit the resolved imaging of order 1000 galaxies in each of several red-shift bins as well as detection of faint neutral filaments in the vicinity of galaxies with a column density of about 10^18 cm^-2. Once 10% SKA sensitivities are achieved, then ground-breaking surveys are possible with only 100 day duration. Sample sizes of log(N)~6 extending below M_HI* are possible over 800 deg^2 out to z=0.5 and over 80 deg^2 out to z=1. Such surveys will permit very competitive measurement of acoustic oscillations in the galaxy power spectrum. One can then envision a series of 10% SKA surveys probing different depths. With the 100% SKA sensitivity the capabilities are truly phenomenal. Survey sample sizes in the range log(N)=7-8 are feasible over the red-shift range of 0.2 to about 5. Precise tracking of potential time evolution of dark energy (via the baryonic acoustic oscillation signature) should be possible out to z~3. The local cosmic web will be imaged down to N_HI=10^16 cm^-2. What exactly will be seen at z > 3 ? This will depend crucially on the SKA sensitivity in the critical frequency window of 350 to 200 MHz.
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