The ACCELERATION programme: I. Cosmology with the redshift drift

TL;DR

This paper discusses the ACCELERATION programme's efforts to prepare for measuring the cosmological redshift drift, analyzing peculiar accelerations in different gas regions via simulations, and proposing a new technique to improve detection prospects.

Contribution

It introduces the 'Lya cell' method to enhance redshift drift detection and provides simulation-based estimates of peculiar accelerations affecting measurements.

Findings

Star-forming gas shows large peculiar acceleration, hindering drift detection.

Lya forest absorbers have much lower peculiar accelerations, suitable for measurements.

Current data constrains the redshift drift to less than 65 m/s/year.

Abstract

Detecting the change of a cosmological object's redshift due to the time evolution of the Universal expansion rate is an ambitious experiment that will be attempted with future telescope facilities. In this paper, we describe the ACCELERATION programme, which aims to study the properties of the most underdense regions of the Universe. One of the highlight goals of this programme is to prepare for the redshift drift measurement. Using the EAGLE cosmological hydrodynamic simulations, we estimate the peculiar acceleration of gas in galaxies and in the Lya forest. We find that star-forming 'cold neutral gas' exhibits large peculiar acceleration due to the high local density of baryons near star-forming regions. We conclude that absorption by cold neutral gas is unlikely to yield a detection of the cosmological redshift drift. On the other hand, we find that the peculiar accelerations of Lya forest absorbers are more than an order of magnitude below the expected cosmological signal. We also highlight that the numerous low H I column density systems display lower peculiar acceleration. Finally, we propose a new 'Lya cell' technique that applies a small correction to the wavelength calibration to secure a relative measurement of the cosmic drift between two unrelated cosmological sources at different redshifts. For suitable combinations of absorption lines, the cosmological signal can be more than doubled, while the affect of the observer peculiar acceleration is mitigated. Using current data of four suitable Lya cells, we infer a limit on the cosmological redshift drift to be dv/dt_obs < 65 m/s/year (2 sigma).