The Clustering Dipole of the Local Universe from the Two Micron All Sky Survey

Abstract

The unprecedented sky coverage and photometric uniformity of the Two Micron All Sky Survey (2MASS) provides a rich resource for investigating the galaxies populating the local universe. A full characterization of the large-scale clustering distribution is important for theoretical studies of structure formation. 2MASS offers an all-sky view of the local galaxy population at 2.15 μm, unbiased by young stellar light and minimally affected by dust. We use 2MASS to map the local distribution of galaxies, identifying the largest structures in the nearby universe. The inhomogeneity of these structures causes an acceleration on the Local Group of galaxies, which can be seen in the dipole of the cosmic microwave background (CMB). We find that the direction of the 2MASS clustering dipole is 16° from the CMB dipole, confirming that the local galaxy distribution accelerates the Local Group. From the magnitude of the dipole, we find a value of the linear bias parameter b = 1.06 ± 0.17 in the Ks band. Thus, the linear bias parameter of Ks-selected galaxies is similar to the bias parameter found in other wave bands.