Lyman alpha absorbers in motion: consequences of gravitational lensing for the cosmological redshift drift experiment

Abstract

The evolution of the expansion rate of the Universe results in a drift in the redshift of distant sources over time. A measurement of this drift would provide us with a direct probe of expansion history. The Lyman alpha forest has been recognized as the best candidate for this experiment, but the signal would be weak and it will take next generation large telescopes coupled with ultra-stable high resolution spectrographs to reach the cm/s resolution required. One source of noise that has not yet been assessed is the transverse motion of Lyman alpha absorbers, which varies the gravitational potential in the line of sight and subsequently shifts the positions of background absorption lines. We examine the relationship between the pure cosmic signal and the observed redshift drift in the presence of moving Lyman alpha clouds, particularly the collapsed structures associated with Lyman limit systems (LLSs) and damped Lyman alpha systems (DLAs). Surprisingly, the peculiar velocities and peculiar accelerations both enter the expression, although the acceleration term stands alone as an absolute error, whilst the velocity term appears as a fractional noise component. An estimate of the magnitude of the noise reassures us that the motion of the Lyman alpha absorbers will not pose a threat to the detection of the signal.

8 pages, 1 figure. Accepted by MNRAS

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Cited by in corpus (14)

• Real-time Cosmology
• Cosmographic analysis of redshift drift
• Chameleonic Generalized Brans--Dicke model and late-time acceleration
• Multipole decomposition of redshift drift -- model independent mapping of the expansion history of the Universe
• Redshift drift in an inhomogeneous universe: averaging and the backreaction conjecture
• Tangential Velocity of the Dark Matter in the Bullet Cluster from Precise Lensed Image Redshifts
• Forecast and analysis of the cosmological redshift drift
• The Instantaneous Redshift Difference of Gravitationally Lensed Images: Theory and Observational Prospects
• Direct detection of the cosmic expansion: the redshift drift and the flux drift
• Redshift drift in a universe with structure II: Light rays propagated through a Newtonian N-body simulation
• Null Gravitational Redshift by a Reissner-Nordström Black Hole in the Strong Field Limit
• Gravitational frequency shift of light in equatorial plane of a radially moving Schwarzschild black hole
• Dynamical analysis of the redshift drift in FLRW universes
• The Mattig Expression for a d-dimensional Gauss Bonnet FRWL Cosmology