Forecasts of redshift drift constraints on cosmological parameters

Abstract

Cosmological observations usually map our present-day past light cone. However, it is also possible to compare different past light cones. This is the concept behind the redshift drift, a model-independent probe of fundamental cosmology. In simple physical terms, this effectively allows us to watch the Universe expand in real time. While current facilities only allow sensitivities several orders of magnitude worse than the expected signal, it should be possible to detect it with forthcoming ones. Here we discuss the potential impact of measurements by three such facilities: the Extremely Large Telescope (the subject of most existing redshift drift forecasts), but also the Square Kilometre Array and intensity mapping experiments. For each of these we assume the measurement sensitivities estimated respectively in Liske et al. (2008), Klockner et al. (2015 and Yu et al. (2014). We focus on the role of these measurements in constraining dark energy scenarios, highlighting the fact that although on their own they yield comparatively weak constraints, they do probe regions of parameter space that are typically different from those probed by other experiments, as well as being redshift-dependent. Specifically, we quantify how combinations of several redshift drift measurements at different redshifts, or combinations of redshift drift measurements with those from other canonical cosmological probes, can constrain some representative dark energy models. Our conclusion is that a model-independent mapping of the expansion of the universe from redshift z = 0 to z = 4-a challenging but feasible goal for the next generation of astrophysical facilities-can have a significant impact on fundamental cosmology.

Cosmological impact of redshift drift measurements

“…Our primary goal is to forecast the uncertainties on cosmological parameters from redshift drift measurements, using Fisher Matrix techniques detailed in Alves et al (2019).…”

“…Importantly, cosmological parameter sensitivities of the redshift are redshift-dependent-see Alves et al (2019) for a through discussion. This needs to be convolved with the spectroscopic velocity uncertainty of each experiment, bearing in mind that the ELT one is redshift dependent (cf.…”

“…Nevertheless, these measurements also constrain specific cosmological models. An overview can be found in Quercellini et al (2012), and more recent explorations include Kim et al (2015); Martins et al (2016); Alves et al (2019). These show that although ELT redshift drift measurements, on their own, lead to constraints that are not tighter than those E-mail: joshua.esteves.mail@gmail.com (JE) † E-mail: Carlos.Martins@astro.up.pt (CJAPM) ‡ E-mail: up201705220@edu.fc.up.pt (BGP) § E-mail: catarina.alves.18@ucl.ac.uk (CSA) achievable from other data, they do probe different regions of parameter space, enabling the breaking of key degeneracies upon combination.…”

Black Hole Shadow Drift and Photon Ring Frequency Drift

“…Optimistic estimates show that these facilities could reach a precision of 10 −10 , for example with monitoring programs of 1000 hours of exposure with a 40-meter telescope [7]. For this reason, cosmology with redshift drifts is an active field of research [8][9][10][11][12][13][14][15][16][17][18][19][20], which we advance further with this work, in which we investigate how the cosmological drift would affect the image from black hole shadows and interferometric signatures from black holes' photon rings.…”

“…Optimistic estimates show that these facilities could reach a precision of 10 −10 , for example with monitoring programs of 1000 hours of exposure with a 40-meter telescope [7]. For this reason, cosmology with redshift drifts is an active field of research [8][9][10][11][12][13][14][15][16][17][18][19][20], which we advance further with this work, in which we investigate how the cosmological drift would affect the image from black hole shadows and interferometric signatures from black holes' photon rings.Black holes were first predicted over a century ago, yet the first direct image of a black hole was reconstructed only very recently by the Event Horizon Telescope (EHT) collaboration [21][22][23][24][25][26][27]. The direct detection of the shadow of M87 , the supermassive black hole at the centre of the galaxy Messier 87, suggests we will soon be able to obtain black hole parameters such as their mass, spin and charge in a systematic way.…”