The 2dF Galaxy Redshift Survey: Galaxy luminosity functions per spectral type
Abstract
We calculate the optical bj luminosity function of the 2dF Galaxy Redshift Survey (2dFGRS) for different subsets defined by their spectral properties. These spectrally selected subsets are defined using a new parameter, eta, which is a linear combination of the first two projections derived from a Principal Component Analysis. This parameter eta identifies the average emission and absorption line strength in the galaxy rest-frame spectrum and hence is a useful indicator of the present star formation. We use a total of 75,000 galaxies in our calculations, chosen from a sample of high signal-to-noise, low redshift galaxies observed before January 2001. We find that there is a systematic steepening of the faint end slope (alpha) as one moves from passive (alpha = -0.54) to active (alpha = -1.50) star-forming galaxies, and that there is also a corresponding faintening of the characteristic magnitude M*-5log_10(h) (from -19.6 to -19.1). We also show that the Schechter function provides a poor fit to the quiescent (Type 1) LF for very faint galaxies (M-5log_10(h) fainter than -16.0), perhaps suggesting the presence of a significant dwarf population. The luminosity functions presented here agree well with those calculated previously from a much smaller sample of 2dF galaxies and display similar trends to those calculated from other surveys. We also present a new procedure for determining self-consistent K-corrections and investigate possible fibre-aperture biases.Keywords
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