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Our Peculiar Motion Away from the Local Void

Abstract

The peculiar velocity of the Local Group of galaxies manifested in the cosmic microwave background dipole is found to decompose into three dominant components. The three components are clearly separated because they arise on distinct spatial scales and are fortuitously almost orthogonal in their influences. The nearest, which is distinguished by a velocity discontinuity at ~7 Mpc, arises from the evacuation of the Local Void. We lie in the Local Sheet that bounds the void. Random motions within the Local Sheet are small, and we advocate a reference frame with respect to the Local Sheet in preference to the Local Group. Our Galaxy participates in the bulk motion of the Local Sheet away from the Local Void. The component of our motion on an intermediate scale is attributed to the Virgo Cluster and its surroundings, 17 Mpc away. The third and largest component is an attraction on scales larger than 3000 km.s-1 and centered near the direction of the Centaurus Cluster. The amplitudes of the three components are 259, 185, and 455 km.s-1, respectively, adding collectively to 631 km.s-1 in the reference frame of the Local Sheet. Taking the nearby influences into account, particularly that of the Local Void, causes the residual attributed to large scales to align with observed concentrations of distant galaxies and reduces somewhat the amplitude of motion attributed to their pull. Concerning the motion of ~260 km.s-1 away from the Local Void, given the velocities expected from gravitational instability theory in the standard cosmological paradigm, the distance to the center of the Local Void must be at least 23 Mpc from our position. The Local Void is extremely large.

Figure 10 : The region of the Local Void. The ellipses outline the 3 apparent sectors of the Local Void. The solid dark blue ellipses show two projections of the Inner Local Void bounded on one edge by the Local Sheet. The North and South extensions of the Local Void are identified by the light blue short-dashed ellipses and the green long-dashed ellipses, respectively. These separate sectors are separated by bridges of wispy filaments. The red vector indicates the direction and amplitude of our motion away from the void

The full article can be found at Tully et al. 2008ApJ,676,184

For more information on this article email to : tully at ifa.hawaii.edu

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