2 Field of the search

To outline the position of the Local Void on the sky, we reproduce in Fig. 1 the distribution of galaxies with known corrected radial velocities V₀ < 1500 km s^-1 in a region RA = [10.0, 23.5]$^{\rm h}$, D = [-20, +60]$\hbox{$^\circ$}$. The 19 nearest galaxies with V₀ < 750 km s^-1 are shown as larger open circles. The radial velocities were taken from the PGC catalogue (Paturel et al. 1992) and updated with data from recent publications. The curves correspond to the Milky Way avoidance zone within galactic latitudes +10 and $-10\hbox{$^\circ$}$. As it can be seen from Fig. 1, inside a circle of 60$\hbox{$^\circ$}$diameter around a point of {RA = 18$^{\rm h}38^{\rm m}$, $D = +18\hbox{$^\circ$}$} there is no galaxy having a radial velocity V₀ < 1500 km s^-1. Searches for new nearby galaxies in the most obscured part of this area undertaken by Nakanishi et al. (1997) among the IRAS sources, as well for HI-rich dwarf galaxies (Hoffman et al. 1992), added nothing within the drawn circle.

The distribution of more distant galaxies in the same sky region is shown in Fig. 2. The first galaxies inside the Local Void zone appear just beyond V₀ = 1500 km s^-1. Adopting for the Hubble parameter H = 75 km s^-1/Mpc, we find that the empty volume is $\gt 3\ 10^3$ Mpc³.

 

Figure 1: Distribution of galaxies from PGC with radial velocities V0 < 1500 km s-1 in the equatorial coordinates. The nearest galaxies with corrected radial velocities V0 < 750 km s-1 are marked by larger circles. Two curves outline the Milky Way region with $\mid b\mid < 10\hbox{$^\circ$}$. A circle of 60 degree diameter indicates the Hercules-Aquila void region

 

Figure 2: The same as Fig. 1 but for more distant galaxies with 1500 < V0 < 2250 km s-1

It should be emphasized that there is still no systematic search for nearby dwarf galaxies in the whole Local Void area. Therefore, the possibility for such a large volume to be completely devoided of galaxies remains unproved. In the next section we describe the results of a special survey for nearby dwarf galaxy candidates on almost the whole area of the Local Void.