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(abridged) We perform a reconstruction of the cosmological large scale flows in the nearby Universe using two complementary observational sets. The first, the SFI++ sample of Tully-Fisher (TF) measurements of galaxies, provides a direct probe of the flows. The second, the whole sky distribution of galaxies in the 2MASS redshift survey (2MRS), yields a prediction of the flows given the cosmological density parameter, $\Omega$, and a biasing relation between mass and galaxies. We aim at an unbiased comparison between the peculiar velocity fields extracted from the two data sets and its implication on the cosmological parameters and the biasing relation. We expand the fields in a set of orthonormal basis functions, each representing a plausible realization of a cosmological velocity field. Our analysis completely avoids the strong error covariance in the smoothed TF velocities by the use of orthonormal basis functions and employs elaborate realistic mock data sets to extensively calibrate the errors in 2MRS predicted velocities. We relate the 2MRS galaxy distribution to the mass density field by a linear bias factor, $b$, and include a luminosity dependent, $\propto L^\alpha$, galaxy weighting. We assess the agreement between the fields as a function of $\alpha$ and $\beta=f(\Omega)/b$, where $f$ is the growth factor of linear perturbations. The agreement is excellent with a reasonable $\chi^2$ per degree of freedom. For $\alpha=0$, we derive $0.28

We present a low-flux extension of the X-ray selected ROSAT Brightest Cluster Sample (BCS) published in Paper I of this series. Like the original BCS and employing an identical selection procedure, the BCS extension is compiled from ROSAT All-Sky Survey (RASS) data in the northern hemisphere (dec > 0 deg) and at high Galactic latitudes (|b| > 20 deg). It comprises 100 X-ray selected clusters of galaxies with measured redshifts z < 0.3 (as well as seven more at z > 0.3) and total fluxes between 2.8 x 10-12 erg cm-2 s-1 and 4.4 x 10-12 erg cm-2 s-1 in the 0.1-2.4 keV band (the latter value being the flux limit of the original BCS). The extension can be combined with the main sample published in 1998 to form the homogeneously selected extended BCS (eBCS), the largest and statistically best understood cluster sample to emerge from the ROSAT All-Sky Survey to date. The nominal completeness of the combined sample (defined with respect to a power law fit to the bright end of the BCS log N-log S distribution) is relatively low at 75 per cent (compared to 90 per cent for the high-flux sample of Paper I). However, just as for the original BCS, this incompleteness can be accurately quantified, and thus statistically corrected for, as a function of X-ray luminosity and redshift. In addition to its importance for improved statistical studies of the properties of clusters in the local Universe, the low-flux extension of the BCS is also intended to serve as a finding list for X-ray bright clusters in the northern hemisphere which we hope will prove useful in the preparation of cluster observations with the next generation of X-ray telescopes such as Chandra or XMM-Newton., 4 pages + 1 table, 4 figures, accepted for publication in MNRAS. An electronic version of the table will shortly be available from http://www.ifa.hawaii.edu/~ebeling/clusters/BCS.html

We re-examine the existence and extent of the planar structure in the local galaxy density field, the so-called supergalactic plane (SGP). This structure is studied here in three dimensions using both the new Optical Redshift Survey (ORS) and the IRAS 1.2-Jy redshift survey. The density contrast in a slab of thickness 20 h(-1) Mpc and diameter 80 Mpc aligned with the standard de Vaucouleurs supergalactic coordinates is delta(sgp)similar to 0.5 for both ORS and IRAS. The structure of the SGP is not well described by a homogeneous ellipsoid, although it does appear to be a flattened structure, which we quantify by calculating the moment of inertia tensor of the density field. The directions of the principal axes vary with radius, but the minor axis remains within theta(z)similar to 30 degrees of the standard SGP Z-axis, out to a radius of 80 h(-1) Mpc, for both ORS and IRAS. However, the structure changes shape with radius, varying between a flattened pancake and a dumbbell, the latter at a radius of similar to 50 h(-1) Mpc, where the Great Attractor and Perseus-Pisces superclusters dominate the distribution. This calls to question the connectivity of the 'plane' beyond similar to 40 h(-1) Mpc. The configuration found here can be viewed as part of a web of filaments and sheets, rather than as an isolated pancake-like structure. An optimal minimum variance reconstruction of the density field using Wiener filtering, which corrects for both redshift distortion and shot noise, yields a similar misalignment angle and behaviour of axes. The background-independent statistic of axes proposed here can be best used for testing cosmological models by comparison with N-body simulations.

We present a 90 per cent flux-complete sample of the 201 X-ray brightest clusters of galaxies in the northern hemisphere (dec > 0 deg), at high Galactic latitudes (|b| > 20 deg), with measured redshifts z < 0.3 and fluxes higher than 4.4 x 10^(-12) erg cm^(-2) s^{-1) in the 0.1-2.4 keV band. The sample, called the ROSAT Brightest Cluster Sample (BCS), is selected from ROSAT All-Sky Survey data and is the largest X-ray selected cluster sample compiled to date. In addition to Abell clusters, which form the bulk of the sample, the BCS also contains the X-ray brightest Zwicky clusters and other clusters selected from their X-ray properties alone. Effort has been made to ensure the highest possible completeness of the sample and the smallest possible contamination by non-cluster X-ray sources. X-ray fluxes are computed using an algorithm tailored for the detection and characterization of X-ray emission from galaxy clusters. These fluxes are accurate to better than 15 per cent (mean 1 sigma error). We find the cumulative log N-log S distribution of clusters to follow a power law k S^(-alpha) with alpha=1.31 (+0.06)(-0.03) (errors are the 10th and 90th percentiles) down to fluxes of 2 x 10^(-12) erg cm^(-2) s^(-1), i.e. considerably below the BCS flux limit. Although our best-fitting slope disagrees formally with the canonical value of -1.5 for a Euclidean distribution, the BCS log N-log S distribution is consistent with a non-evolving cluster population if cosmological effects are taken into account., Table 3, listing the sample, is supplied as a separate PS file. An electronic version of this table can be obtained from the first author's WWW pages: http://www.ifa.hawaii.edu/~ebeling/clusters/BCS.html