UV (2000Å) observations of nearby well resolved spiral galaxies

Abstract UV (2000A) images of nearby well resolved galaxies (M31, M33, M51, M81, M101 and NGC4258) have been obtained during repetitive flights of a balloon-borne 40-cm, 12 – 20 arcsec resolution telescope. In the case of M51, the ultraviolet flux was derived for 36 circular regions where published gas contents exist. After corrections for dust extinction, the UV luminosity per unit area is found to correlate the HI+H2 surface density and thus confirms that the total gas density is a driving parameter for large scale star formation processes.