POTENT Reconstruction from Mark III Velocities

Abstract

We present an improved POTENT method for reconstructing the velocity and mass density fields from radial peculiar velocities, test it with mock catalogs, and apply it to the Mark III Catalog. Method improvments: (a) inhomogeneous Malmquist bias is reduced by grouping and corrected in forward or inverse analyses of inferred distances, (b) the smoothing into a radial velocity field is optimized to reduce window and sampling biases, (c) the density is derived from the velocity using an improved nonlinear approximation, and (d) the computational errors are made negligible. The method is tested and optimized using mock catalogs based on an N-body simulation that mimics our cosmological neighborhood, and the remaining errors are evaluated quantitatively. The Mark III catalog, with ~3300 grouped galaxies, allows a reliable reconstruction with fixed Gaussian smoothing of 10-12 Mpc/h out to ~60 Mpc/h. We present maps of the 3D velocity and mass-density fields and the corresponding errors. The typical systematic and random errors in the density fluctuations inside 40 Mpc/h are \pm 0.13 and \pm 0.18. The recovered mass distribution resembles in its gross features the galaxy distribution in redshift surveys and the mass distribution in a similar POTENT analysis of a complementary velocity catalog (SFI), including the Great Attractor, Perseus-Pisces, and the void in between. The reconstruction inside ~40 Mpc/h is not affected much by a revised calibration of the distance indicators (VM2, tailored to match the velocities from the IRAS 1.2Jy redshift survey). The bulk velocity within the sphere of radius 50 Mpc/h about the Local Group is V_50=370 \pm 110 km/s (including systematic errors), and is shown to be mostly generated by external mass fluctuations. With the VM2 calibration, V_50 is reduced to 305 \pm 110 km/s.Comment: 60 pages, LaTeX, 3 tables and 27 figures incorporated (may print the most crucial figures only, by commenting out one line in the LaTex source

The Laniakea supercluster of galaxies

“…Hercules separates from Shapley and Perseus-Pisces separates from Lepus. 03: 16 Here we see contours of the cosmic web as defined by the Velocity-web. Local eigenvalues of the shear tensor are evaluated giving the red, blue, and white contours enclosing knots, filaments, and sheets.…”

“…Voids are usually the demarcations between attraction basins but divergences can occur along filaments and sheets. We give particular attention to the very nearby case between our home basin of attraction and the Perseus-Pisces complex 15,16 . There is a particularly impressive example of an apparent bridge between attractors that is diverging given by the feature called the "arch" in a supplemental figure.…”

Bayesian 3D velocity field reconstruction with virbius

“…Several attempts have been made at reconstructing the density field directly from distance data. For example one can note the POTENT method (Bertschinger & Dekel 1989;Dekel et al 1990Dekel et al , 1999, the Wiener filter approach (Zaroubi et al 1995), or the Unbiased Minimum Variance algorithm (Zaroubi 2002). Additionally, the procedure to derive the power spectrum of the velocity field is relatively complex and prone to the same aforementioned systematics, though there have been some early attempts at measuring it (Jaffe & Kaiser 1995;Zaroubi et al 1997;Macaulay et al 2011Macaulay et al , 2012.…”

The Global Cosmological Parameters

“…The value of Ω 0.6 /b derived from many analyses varies from 0.3 to 1.1, though we see a general trend to favour a high value. Notably, the most recent POTENT analysis using the Mark III compilation of velocities (Willick et al 1997) indicates a high density universe Ω = 0.5 − 0.7, and Ω > 0.3 only at a 99% confidence level (Dekel et al 1999). …”