arXiv: Cosmology and Nongalactic Astrophysics | 2019
The Hubble constant tension with next generation galaxy surveys
Abstract
The rate at which the universe is expanding today is a fundamental parameter in cosmology which governs our understanding of structure formation and dark energy. However, current measurements of the Hubble constant, $H_0$, show a significant tension ($\\sim 4-6\\sigma$) between early- and late-Universe observations. There are ongoing efforts to check the diverse observational results and also to investigate possible theoretical ways to resolve the tension~-- which could point to radical extensions of the standard model. Here we demonstrate the potential of next-generation spectroscopic galaxy surveys to shed light on the Hubble constant tension. Surveys such as those with Euclid and the Square Kilometre Array (SKA) are expected to reach sub-percent precision on Baryon Acoustic Oscillation (BAO) measurements of the Hubble parameter, with a combined redshift coverage of $0.1<z<3$. This wide redshift range, together with the high precision and low level of systematics in BAO measurements, mean that these surveys will provide independent and tight constraints on $H(z)$. These $H(z)$ measurements can be extrapolated to $z = 0$ to provide constraints on $H_0$, which can be model independent if we use non-parametric regression. To this end we use Gaussian processes and we find that Euclid-like surveys can reach $\\sim$3\\% precision on $H_0$, with SKA-like intensity mapping surveys reaching $\\sim$2\\%. When we combine the low-redshift SKA-like Band 2 survey with either its high-redshift Band 1 counterpart, or with the non-overlapping Euclid-like survey, the precision is predicted to be close to 1\\% with 40 $H(z)$ data points. This would be sufficient to rule out the current early- or late-Universe measurements at a $\\sim$5$\\sigma$ level.