We discuss the results of a VLA2 [Napier et al., Proc. IEEE 71, 1295 (1983)] H I survey of the Boötes void and compare the distribution and H I properties of the void galaxies to those of galaxies found in a survey of regions of mean cosmic density. The Boötes survey covers 1100 Mpc3, or ∼1% of the volume of the void and consists of 24 cubes of typically 2 Mpc×2 Mpc×1280 km s-1, centered on optically known galaxies. Sixteen targets were detected in H I; 18 previously uncataloged objects were discovered directly in H I. The control samples consists of 12 cubes centered on IRAS-selected galaxies with FIR luminosities similar to those of the Boötes targets and located in regions of one to two times the cosmic mean density. In addition to the 12 targets 29 companions were detected in H I. We find that the number of galaxies within 1 Mpc of the targets is the same to within a factor of 2 for void and control samples, and thus that the small scale clustering of galaxies is the same in regions that differ by a factor of ∼6 in density on larger scales. A dynamical analysis of the galaxies in the void suggests that on scales of a few Mpc the galaxies are gravitationally bound, forming interacting galaxy pairs, loose pairs, and loose groups. One group is compact enough to qualify as a Hickson compact group (hereafter referred to as HCG [Hickson, APJ, 255 , 382 (1982)]. The galaxies found in the void are mostly late-type, gas-rich systems. A careful scrutiny of their H I and optical properties shows them to be very similar to field galaxies of the same morphological type. This, combined with our finding that the small scale clustering of the galaxies in the voids is the same as in the field, suggests that it is the near environment that mostly affects the evolution of galaxies.
All Science Journal Classification (ASJC) codes
- Astronomy and Astrophysics
- Space and Planetary Science