A dipole anisotropy of galaxy distribution: Does the CMB rest-frame exist in the local universe?

TL;DR

This study develops a method to detect dipole anisotropy in galaxy distribution caused by Earth's motion, applying it to SDSS data, and finds no significant anisotropy, consistent with standard cosmological models.

Contribution

The paper introduces a new statistical method to analyze dipole anisotropy in galaxy data, accounting for covariances and systematics, and applies it to SDSS data to test the CMB rest-frame hypothesis.

Findings

No significant dipole anisotropy detected in SDSS galaxy data.

Method can potentially detect aberration effects with future surveys like LSST.

Results support the CMB rest-frame being consistent with local galaxy distribution.

Abstract

The peculiar motion of the Earth causes a dipole anisotropy modulation in the distant galaxy distribution due to the aberration effect. However, the amplitude and angular direction of the effect is not necessarily the same as those of the cosmic microwave background (CMB) dipole anisotropy due to the growth of cosmic structures. In other words exploring the aberration effect may give us a clue to the horizon-scale physics perhaps related to the cosmic acceleration. In this paper we develop a method to explore the dipole angular modulation from the pixelized galaxy data on the sky properly taking into account the covariances due to the shot noise and the intrinsic galaxy clustering contamination as well as the partial sky coverage. We applied the method to the galaxy catalogs constructed from the Sloan Digital Sky Survey (SDSS) Data Release 6 data. After constructing the four galaxy catalogs that are different in the ranges of magnitudes and photometric redshifts to study possible systematics, we found that the most robust sample against systematics indicates no dipole anisotropy in the galaxy distribution. This finding is consistent with the expectation from the concordance Lambda-dominated cold dark matter model. Finally we argue that an almost full-sky galaxy survey such as LSST may allow for a significant detection of the aberration effect of the CMB dipole having the precision of constraining the angular direction to ~ 20 degrees in radius. Assuming a hypothetical LSST galaxy survey, we find that this method can confirm or reject the result implied from a stacked analysis of the kinetic Sunyaev-Zel'dovich effect of X-ray luminous clusters in Kashlinsky et al. (2008,2009) if the implied cosmic bulk flow is not extended out to the horizon.