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Register a new userCosmology with the Square Kilometre Array
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Steve Rawlings
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We review how the Square Kilometre Array (SKA) will address fundamental questions in cosmology, focussing on its use for neutral Hydrogen (HI) surveys. A key enabler of its unique capabilities will be large (but smart) receptors in the form of aperture arrays. We outline the likely contributions of Phase-1 of the SKA (SKA1), Phase-2 SKA (SKA2) and pathfinding activities (SKA0). We emphasise the important role of cross-correlation between SKA HI results and those at other wavebands such as: surveys for objects in the EoR with VISTA and the SKA itself; and huge optical and near-infrared redshift surveys, such as those with HETDEX and Euclid. We note that the SKA will contribute in other ways to cosmology, e.g. through gravitational lensing and $H_{0}$ studies.
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Theoretical uncertainties on non-linear scales are among the main obstacles to exploit the sensitivity of forthcoming galaxy and hydrogen surveys like Euclid or the Square Kilometre Array (SKA). Here, we devise a new method to model the theoretical error that goes beyond the usual cut-off on small scales. The advantage of this more efficient implementation of the non-linear uncertainties is tested through a Markov-Chain-Monte-Carlo (MCMC) forecast of the sensitivity of Euclid and SKA to the parameters of the standard $Lambda$CDM model, including massive neutrinos with total mass $M_ u$, and to 3 extended scenarios, including 1) additional relativistic degrees of freedom ($Lambda$CDM + $M_ u$ + $N_mathrm{eff}$), 2) a deviation from the cosmological constant ($Lambda$CDM + $M_ u$ + $w_0$), and 3) a time-varying dark energy equation of state parameter ($Lambda$CDM + $M_ u$ + $left(w_0,w_a right)$). We compare the sensitivity of 14 different combinations of cosmological probes and experimental configurations. For Euclid combined with Planck, assuming a plain cosmological constant, our method gives robust predictions for a high sensitivity to the primordial spectral index $n_{rm s}$ ($sigma(n_s)=0.00085$), the Hubble constant $H_0$ ($sigma(H_0)=0.141 , {rm km/s/Mpc}$), the total neutrino mass $M_ u$ ($sigma(M_ u)=0.020 , {rm eV}$). Assuming dynamical dark energy we get $sigma(M_ u)=0.030 , {rm eV}$ for the mass and $(sigma(w_0), sigma(w_a)) = (0.0214, 0.071)$ for the equation of state parameters. The predicted sensitivity to $M_ u$ is mostly stable against the extensions of the cosmological model considered here. Interestingly, a significant improvement of the constraints on the extended model parameters is also obtained when combining Euclid with a low redshift HI intensity mapping survey by SKA1, demonstrating the importance of the synergy of Euclid and SKA.
The Square Kilometre Array (SKA) is a planned large radio interferometer designed to operate over a wide range of frequencies, and with an order of magnitude greater sensitivity and survey speed than any current radio telescope. The SKA will address many important topics in astronomy, ranging from planet formation to distant galaxies. However, in this work, we consider the perspective of the SKA as a facility for studying physics. We review four areas in which the SKA is expected to make major contributions to our understanding of fundamental physics: cosmic dawn and reionisation; gravity and gravitational radiation; cosmology and dark energy; and dark matter and astroparticle physics. These discussions demonstrate that the SKA will be a spectacular physics machine, which will provide many new breakthroughs and novel insights on matter, energy and spacetime.
The present-day Universe is seemingly dominated by dark energy and dark matter, but mapping the normal (baryonic) content remains vital for both astrophysics - understanding how galaxies form - and astro-particle physics - inferring properties of the dark components. The Square Kilometre Array (SKA) will provide the only means of studying the cosmic evolution of neutral Hydrogen (HI) which, alongside information on star formation from the radio continuum, is needed to understand how stars formed from gas within dark-matter over-densities and the roles of gas accretion and galaxy merging. `All hemisphere HI redshift surveys to redshift 1.5 are feasible with wide-field-of-view realizations of the SKA and, by measuring the galaxy power spectrum in exquisite detail, will allow the first precise studies of the equation-of-state of dark energy. The SKA will be capable of other uniquely powerful cosmological studies including the measurement of the dark-matter power spectrum using weak gravitational lensing, and the precise measurement of H0 using extragalactic water masers. The SKA is likely to become the premier dark-energy-measuring machine, bringing breakthroughs in cosmology beyond those likely to be made possible by combining CMB (e.g. Planck), optical (e.g. LSST, SNAP) and other early-21st-century datasets.
We investigate the capabilities of various stages of the SKA to perform world-leading weak gravitational lensing surveys. We outline a way forward to develop the tools needed for pursuing weak lensing in the radio band. We identify the key analysis challenges and the key pathfinder experiments that will allow us to address them in the run up to the SKA. We identify and summarize the unique and potentially very powerful aspects of radio weak lensing surveys, facilitated by the SKA, that can solve major challenges in the field of weak lensing. These include the use of polarization and rotational velocity information to control intrinsic alignments, and the new area of weak lensing using intensity mapping experiments. We show how the SKA lensing surveys will both complement and enhance corresponding efforts in the optical wavebands through cross-correlation techniques and by way of extending the reach of weak lensing to high redshift.
We review the current status of the Square Kilometre Array (SKA) by outlining the science drivers for its Phase-1 (SKA1) and setting out the timeline for the key decisions and milestones on the way to the planned start of its construction in 2016. We explain how Phase-2 SKA (SKA2) will transform the research scope of the SKA infrastructure, placing it amongst the great astronomical observatories and survey instruments of the future, and opening up new areas of discovery, many beyond the confines of conventional astronomy.
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