| Institution: | Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA,; Department of Physics and Astronomy, Johns Hopkins University, Baltimore, MD 21218-2686, USA,; Department of Physics, South Road, Durham DH1 3LE,; Anglo-Australian Observatory, PO Box 296, Epping, NSW 2121, Australia,; Research School of Astronomy and Astrophysics, The Australian National University, Weston Creek, ACT 2611, Australia,; Astrophysics Research Institute, Liverpool John Moores University, Twelve Quays House, Birkenhead L14 1LD,; Department of Astrophysics, University of New South Wales, Sydney, NSW 2052, Australia,; Department of Physics, Keble Road, Oxford OX1 3RH,; School of Physics and Astronomy, North Haugh, St Andrews, Fife KY6 9SS,; Department of Astronomy, Caltech, Pasadena, CA 91125, USA,; Department of Physics, University of Leeds, Woodhouse Lane, Leeds LS2 9JT,; School of Physics and Astronomy, University of Nottingham, Nottingham NG7 2RD and; Institute for Astronomy, University of Edinburgh, Royal Observatory, Blackford Hill, Edinburgh EH9 3HJ |
| Abstract: | We calculate the optical b J luminosity function (LF) 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, η , which is a linear combination of the first two projections derived from a Principal Component Analysis. This parameter η 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 2001 January. We find that there is a systematic steepening of the faint-end slope ( α ) as one moves from passive ( α =-0.54) to active ( α =-1.50) star-forming galaxies, and that there is also a corresponding faintening of the rest frame characteristic magnitude M *-5 log10( 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 J-5 log10( h ) fainter than ?16.0], perhaps suggesting the presence of a significant dwarf population. The LFs 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. |
