A Test of Biased Galaxy Formation from PSS-II Dwarf Galaxies
Session 115 -- Cosmology and Dark Matter
Oral presentation, Saturday, January 15, 10:15-11:45, Salon III Room (Crystal Gateway)

## [115.05] A Test of Biased Galaxy Formation from PSS-II Dwarf Galaxies

J. Schombert (IPAC/Caltech), R. Pildis (UMich), J. Eder (Arecibo Obs), A. Oemler (Yale)

HI measurements and optical photometry have been obtained for new dwarfs off the Second Palomar Sky Survey. This sample is based on visual inspection of 35 PSS-II plates (1400 square degrees) using morphological criteria to identify dwarfs and with special emphasis on objects of low mean surface brightnesses. Over 310 candidates are identified with 134 detected in HI out to 10,000 km/s. The sample was imaged at V and I on the 2.4m telescope at MDM Observatory and has absolute mags ranging from $-$17 to $-$12 ($H_o = 85$), central surface brightness ranging from 22 to 24.5 $B$ mags arcsec$^{-2}$, scale lengths ranging from 0.5 to 2 kpc and HI masses from 10$^7$ to $3\times10^9$ $M_{\sun}$. The mean V-I color of the sample is quite blue at 0.75, over 0.2 mags bluer than a sample of higher surface brightness late-type galaxies. Very blue V-I colors have indicated young age in other surveys of LSB galaxies (see McGaugh 1992, Ph.D. Thesis, UMich). The spatial distribution of the sample is identical to the distribution of galaxies from the CfA survey, when selected by either absolute luminosity, HI mass or size, disputing any form of biasing at the time of galaxy formation.