Dwarf Spirals

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Session 51 -- Dwarf Galaxies
Display presentation, Tuesday, 10, 1995, 9:20am - 6:30pm

[51.10] Dwarf Spirals

J. Schombert (NASA HQ), R. Pildis (UMichigan), J. Eder (Arecibo Obs.), A. Oemler (Yale Univ.)

We report the discovery of a new class of galaxies, dwarf spirals, that completes the Hubble sequence for dwarf galaxies. Although they have similar morphology to their giant counterparts, the dwarf spirals (dS) are characterized by faint total luminosities ($M_B > -16.5$), small diameters ($R_26 < 4$ kpc), low central surface brightnesses ($\mu_o < 24 B$ mag arcsecs$^{-2}$ and low dynamical masses ($M_{dyn} < 10^9 M_{\sun}$). Most of these dwarf spirals have flocculent or multiple arm spiral patterns, but others have smooth disks similar in appearance to an S0. However, unlike S0's, they 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 galaxy catalogs and field surveys. Since cluster catalogs are complete to much fainter surface brightness and smaller angular limits than most galaxy catalogs, we conclude that dwarf spirals are only found in the field.

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