GAS-RICH DWARF GALAXIES FROM THE 2ND PALOMAR SKY SURVEY .2. OPTICAL-PROPERTIES

We describe the optical properties of a sample of 101 gas-rich field d warf galaxies found on Second Palomar Sky Survey plates, most newly di scovered as part of a survey to investigate the clustering properties of dwarf galaxies relative to giants. These galaxies have low surface brightnesses and are relatively distant, with recession velocities ran ging up to 10(4) km s(-1). They have bluer V-I colors (median value of 0.75) than either actively star-forming giant galaxies or low-metalli city globular clusters, implying that these dwarfs have both low metal licities and little past star formation. These galaxies are also extre mely gas-rich, with a median H I mass-to-V luminosity ratio of approxi mately 2 in solar units. We divide the sample into two groups: true dw arfs with diameters (at 25 I mag arcsec(-2)) less than 7.5 kpc and Mag ellanic dwarfs with diameters greater than that value. The true dwarfs have greater H I mass-to-V luminosity ratios and slightly bluer V-I c olors than the Magellanic dwarfs. Overall, the optical properties of o ur sample of dwarf galaxies point toward their being quiescent objects that have undergone little star formation over the age of the univers e. They are not faded objects but instead may be going through one of their first periods of weak star formation.