Abstract. This paper presents 2112 new 21-cm neutral hydrogen line measurements carried out with the meridian transit Nançay radiotelescope. Among these data we give also 213 new radial velocities which complement those listed in three previous papers of this series. These new measurements, together with the HI data collected in LEDA, put to 6 700 the number of galaxies with 21-cm line width, radial velocity, and apparent diameter in the so-called KLUN sample.

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Abstract. The Local Group environment at 1-10 Mpc expands linearly and smoothly, as if ruled by uniform matter, while observations show on the same scales the very lumpy local galaxy universe. This enigma in cosmology has also been demonstrated by high-resolution N-body CDM simulations. We suggest that the homogeneous dark energy component, revealed by SNIa observations, may resolve the problem of the local cold Hubble flow within the highly non-uniform environment. Linear density perturbations on a homogeneous background with the equation of state pQ = wρQc 2 are decaying for w < −1/3. Exact non-linear Einstein's equations for a spherically symmetric matter concentration, show that there is a zero-mass surface where the positive mass of the local cloud is compensated by the negative dark energy mass, and beyond this surface dark energy dominates dynamically. In such regions the velocity dispersion is adiabatically cooling, and this may explain why the Hubble law starts on the outskirts of the Local Group, with the same H0 as globally and with a remarkably small velocity dispersion.

The influence of Malmquist bias on the studies of extragalactic distances is reviewed, with brief glimpses of the history from Kapteyn to Scott. Special attention is paid to two kinds of biases, for which the names Malmquist biases of the first and second kind are proposed. The essence of these biases and the situations where they occur are discussed. The bias of the first kind is related to the classical Malmquist bias (involving the "volume effect"), while the bias of the second kind appears when standard candles are observed at different (true) distances, whereby magnitude limit cuts away a part of the luminosity function. In particular, study of the latter bias in distance indicators such as Tully Fisher, available for large fundamental samples of galaxies, allows construction of an unbiased absolute distance scale in the local galaxy universe where approximate kinematic relative distances can be derived. Such investigations, using the method of normalized distances or of the Spaenhauer diagram, support the linearity of the Hubble law and make it possible to derive an unbiased value of the Hubble constant.

Aims. Interstellar polarization of starlight at high galactic latitudes gives information on the direction of the local Galactic magnetic field and the distribution of cosmic dust in wide "windows" perpendicular to the Galactic plane. Polarization data allow us to construct for the first time high-latitude polarization maps with resolution and sky coverage high enough to examine in detail the distribution of the interstellar polarization and the direction of the Galactic magnetic field around Galactic poles. Methods. We measured the polarization for more than 2400 new stars at distances of up to 600 pc and within 60• and 30• from the north and south Galactic poles. Here we describe the measurements and properties of the resulting total sample of about 3600 stars (completeness, radial distribution), and present polarization maps of the regions around the north (b > 30• ) and south (b > 60 • ) poles. Results. The new interstellar polarization maps give wider and higher resolution views around the Galactic poles than previous maps. The major patterns in the maps are significant asymmetries in the polarization, one in the northern sky directly across the local spiral and the second between the northern and southern Galactic hemispheres. We confirm that there is significantly more interstellar polarization at high southern latitudes than at high northern latitudes within the local spiral. A comparison of our optical polarization map with the proposed models using local dust-and gas shells, (i.e., Weaver's Loop I superbubble, Wolleben's two-bubble model, the interaction between the Local Bubble and the Loop I superbubble) reveals interesting features. 1) The optical and radio polarizations are lower in the eastern than in the western branch of Loop I, which may be caused by a weaker effective magnetic field in the eastern part where the diffuse IRAS emission is bright; this illustrates that low optical polarization does not always imply little dust. 2) We can see a clear signature of the western side of Wolleben's S2 shell (at 35 < l < 55), while there is no alignment of the polarization directions along the suggested wall of S2 in the eastern part, though the alignment along S1 is visible. 3) In the upper parts of the suggested interaction zone between the Local Bubble and the Loop I superbubble our data show polarizations aligned along the zone contour. The week and rather randomly directed polarizations measured previously in the eastern part of this region may reflect the shorter distances (<250 pc) in the investigated sample of stars.

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The cosmological vacuum, which is perfectly uniform, dominates by density over all the forms of cosmic matter. It makes the Universe be actually more uniform than it could be seen from the visible picture of the highly non-uniform matter distribution, especially inside the observed cell of uniformity (100 − 150 Mpc). This uniformity reveals itself in the structure of the Hubble matter flow which extends over a giant range of cosmic space scales -from few Mpc to a thousand Mpc,preserving its kinematical identity. According to Sandage (1999), this flow is mysteriously regular and quiet even deep inside the cell of uniformity. An answer we propose to the question in the title above is as follows: This is most probably because the flow is dynamically controlled by the cosmological vacuum. An additional conjecture of cosmological intermittency, that addresses a complex statistical structure of initial chaotic perturbations, is also suggested in this context.