DWARF SPIRALS

We report the discovery of a new class of galaxies, dwarf spirals, that serve as a morphological extension to the Hubble sequence for dwarf galaxies. Although they have a similar morphology to their giant counterparts, the dwarf spirals (dS) are characterized by faint total luminosities (M(B)>-17), small diameters (R(26)<5 kpc), low central surface brightnesses mu(0)>24 B mag arcsec(-2)), and low HI masses (M(HI)less than or equal to 10(9) M.) Most of these dwarf spirals have flocculent or multiple arm spiral patterns, but some have smooth disks, similar in appearance to a dwarf SO's, yet are rich in neutral gas. The combination of small angular size and low surface brightness explains why this class of galaxies was missed in previous cluster catalogs and field surveys. Since cluster catalogs are complete to much fainter surface brightness and smaller angular limits than most galaxy catalogs, yet contain no dS galaxies, we conclude that dwarf spirals are only found in the held. (C) 1995 American Astronomical Society.