Funny Thing Happened on the way to convergence: Large-scale Cosmic Flows
Hume Feldman (University of Kansas)
September 05, 2014
Abstract: Modeling the cosmic velocity field, and especially estimating its lowest order moment, the bulk flow, has been a popular pursuit among aficionados in the cosmological community for three decades now. Other than estimating the magnitude and direction of the flow, one of the main difficulties has been defining the scale of flow detected. Currently, it seems that the main contentious issue is exactly that, what is the scale of the flow. There is a nearly universal agreement as to the direction of the flow, however, there is a great disagreement as to the magnitude as a function of scale of the flow. The way various groups define the scale, and thus compare to theoretical expectations varies greatly which lead to disagreements and thus lack of consensus among practitioners. We developed and applied the Minimal Variance (MV) formalism to optimize and clearly define the scale of a particular analysis, using the width of the survey window function as a proxy for scale. Comparing the MV ideal window function to any analysis window function provides an unbiased estimate to the survey width (or scale) and thus provides a method to directly compare various results. I will discuss the method and compare various recent analyses and show that the disagreements are not as significant as they appear.