The effect of our local motion on the Sandage–Loeb test of the cosmic expansion

Inoue, Takuya; Komatsu, Eiichiro; Aoki, Wako; Chiba, Takeshi; Misawa, Toru; Usuda, Tomonori

doi:10.1093/pasj/psz131

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The effect of our local motion on the Sandage–Loeb test of the cosmic expansion

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Inoue, Takuya
Physical Cosmology, MPI for Astrophysics, Max Planck Society;

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Komatsu, Eiichiro
Physical Cosmology, MPI for Astrophysics, Max Planck Society;

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Citation

Inoue, T., Komatsu, E., Aoki, W., Chiba, T., Misawa, T., & Usuda, T. (2019). The effect of our local motion on the Sandage–Loeb test of the cosmic expansion. Publications of the Astronomical Society of Japan, 72(1): L1. doi:10.1093/pasj/psz131.

Cite as: https://hdl.handle.net/21.11116/0000-0006-8566-1

Abstract

Redshifts of an astronomical body measured atmultiple epochs (e.g., separated by 10 yr)
are different due to the cosmic expansion. This so-called Sandage–Loeb test offers a
direct measurement of the expansion rate of the Universe. However, acceleration in
the motion of the Solar System with respect to the cosmic microwave background also
changes redshifts measured at multiple epochs. If not accounted for, it yields a biased
cosmological inference. To address this,we calculate the acceleration of the Solar System
with respect to the Local Group of galaxies to quantify the change in themeasured redshift
due to local motion. Our study is motivated by the recent determination of the mass of
the Large Magellanic Cloud (LMC), which indicates a significant fraction of the MilkyWay
mass. We find that the acceleration towards the Galactic Center dominates, which gives
a redshift change of 7 cms⁻¹ in 10 yr, while the accelerations due to the LMC and M31
cannot be ignored, depending on lines of sight. We create all-sky maps of the expected
change in redshift and the corresponding uncertainty, which can be used to correct for
this effect.