7 Conclusion

To study relations between global optical and HI parameters of galaxies we used a nearly complete sample of nearby galaxies with corrected radial velocities, V₀ < 500 kms^-1 (the KKT sample). Comparing with the previous investigation undertaken by [11, Huchtmeier & Richter (1988),] the initial KKT sample was updated by new nearby objects and also by new more homogeneous data on galaxy distances, apparent magnitudes and other observational parameters. A survey of basic relations between the global characteristics of nearby galaxies is presented in Table 1. We note the following properties among them:

1) In the whole range of diameters from 1 Kpc to 40 Kpc the LV galaxies follow the Tully-Fisher relation, ${\rm log}A_{25}\propto(0.99\pm0.06){\rm log}V_{\rm m}$,whose linear character may have a deep evolutionary sense.

2) The hydrogen mass-to-luminosity and hydrogen mass-to-"total" mass ratios increase systematically from giant galaxies to dwarfs. The median value of $M_{\rm HI}/M_{25}$ is 0.25, however, some very nearby dwarf galaxies, such as UGCA 292, having received no detailed study as yet, have $M_{\rm HI}/M_{25} = 1 - 3.$

3) For the LV galaxies their "total" mass (inside the standard optical diameter)-to-the total blue luminosity ratios are concentrated in the range of 0.2 to $16 \;M_{\hbox{$\odot$}}/L_{\hbox{$\odot$}}$ with the median $3.0 \;M_{\hbox{$\odot$}}/L_{\hbox{$\odot$}}$.This ratio tends to decrease slightly from giant galaxies to dwarfs, which needs an explanation within the common idea of presence of large amount of Dark Matter in dwarf irregular systems.

4) Our sample galaxies differ in their mean surface brightness almost by a factor of 100. The hydrogen mass-to-luminosity ratio for them shows a clear-cut increase towards the low surface brightness objects. A similar but less distinct relation is also seen for the total mass-to-luminosity ratios. Both correlations may be caused by star formation processes going on in the galaxies.

5) To quantitatively estimate the local mass density around each LV galaxy, produced by its neighbours, we used the so-called "tidal index". Despite the differences of about six orders in the local densities, the ratios $M_{\rm HI}/L$ and M₂₅/L do not show pronounced correlation with the tidal index similar to the HI-deficit or morphological segregation seen in rich galaxy clusters.

6) The amount of hydrogen mass in a galaxy and its angular momentum follow a nearly linear relation, ${\rm log}M_{\rm HI}\propto(0.99\pm0.04){\rm log}(V_{\rm m}\cdot A_{25})$ in the range of angular momentum which exceeds three orders. According to [29, Zasov (1974)] it means that the gaseous disks of giant, normal, and dwarf galaxies are situated near the threshould of gravitational instability favouring star formation in them.

Acknowledgements

This work is supported by INTAS-RFBR grant 95-IN-RU-1390 and DFG grant KS 9112.