Published in the Minnesota Lectures on Extragalactic HI,
A.S.P. Conference Series Vol. 106, ed. Evan Skillman, 1996.
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Abstract. Many factors shape our view of the extragalactic universe. Chief among these are selection effects introduced by the sensitivity of astronomical instruments, competition with background noise and confusing sources of emission, and preconceptions about the nature of galaxies. In this chapter I examine selection effects from a general standpoint, mainly considering their influence on optical and HI observations, and conclude with presentation of results from a new Arecibo survey of a slice of the extragalactic sky at 21 cm. This new survey represents the most sensitive survey to date, covering about 50 square degrees at high Galactic latitudes, and uncovering a large population of previously uncataloged objects. I derive an HI luminosity function and conclude with an estimate of the total mass function of galaxies based on these data.
Key Words: selection effects, HI surveys, galaxies, luminosity function, Omega
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