Journal Article

Lyα absorbers in motion: consequences of gravitational lensing for the cosmological redshift drift experiment*

Madhura Killedar and Geraint F. Lewis

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 402, issue 1, pages 650-656
Published in print February 2010 | ISSN: 0035-8711
Published online February 2010 | e-ISSN: 1365-2966 | DOI:
Lyα absorbers in motion: consequences of gravitational lensing for the cosmological redshift drift experiment*

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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 α (Lyα) 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 ultrastable high-resolution spectrographs to reach the cm s−1 resolution required. One source of noise that has not yet been assessed is the transverse motion of Lyα 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 Lyα clouds, particularly the collapsed structures associated with Lyman limit systems and damped Lyα systems. 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 Lyα absorbers will not pose a threat to the detection of the signal.

Keywords: gravitational lensing; methods: analytical; intergalactic medium; quasars: absorption lines; cosmology: theory

Journal Article.  5156 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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