We calculate the optical b _ { \scriptscriptstyle J } 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 ratio , 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 rest-frame characteristic magnitude M ^ { * } -5 \log _ { 10 } ( h ) ( from - 19.6 to - 19.2 ) .
We also show that the Schechter function provides a poor fit to the quiescent ( Type 1 ) LF for very faint galaxies ( M _ { b _ { \scriptscriptstyle J } } -5 \log _ { 10 } ( h ) fainter than - 16.0 ) , perhaps suggesting the presence of a significant dwarf population .
The luminosity functions presented here give a precise confirmation of the trends seen previously in a much smaller preliminary 2dFGRS sample , and in other surveys .
We also present a new procedure for determining self-consistent K -corrections and investigate possible fibre-aperture biases .