The Autofib Survey



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The Autofib Survey

  The Autofib Survey [\protect\astronciteEllis et al.1996] has used the Autofib fibre positioner on the Anglo-Australian Telescope to collect large numbers of redshifts. The collaboration has collected over 1700 redshifts for galaxies with apparent magnitude in the range 11.5 < b < 24.0 to determine the rest-frame B-band galaxy luminosity function (LF) as a function of redshift and star-formation activity from z = 0 to z 0.75. The range of apparent magnitudes makes it possible to study the shape of the LF as a function of redshift. (The CFRS could only provide information on ``Schechter segments'' due to its narrower range of apparent magnitudes.) The Autofib survey used the [OII] emission line as a star-formation activity indicator, and the dividing line between quiescent and active galaxies was set at a rest-frame equivalent width W of 20 Å.

Locally (z 0.1), the Autofib luminosity function is fitted with a Schechter faint end slope of 1.1 and Schechter normalization of 0.026 h Mpc, which argues for a high normalization of the local LF. The luminosity function as a function of redshift shows strong evolution, especially for galaxies with luminosities fainter than L. In the redshift ranges 0.150.35 and 0.350.75, the faint end steepens to = 1.41 and = 1.45. The picture is particularly revealing when the luminosity functions of quiescent and active galaxies are constructed separately. Although the faint end of both LF's is flat locally, the LF of galaxies with W > 20 Åsteepens to = 1.44 beyond z = 0.25 whereas the LF of quiescent galaxies remains flat. The space density of star-forming galaxies decreased at all luminosities by almost a factor of 2 from z 0.4 to z 0.15. This decline corresponds to an overall fading of the star-forming population of 0.5 mag over this redshift range. As other redshift surveys, the Autofib survey cannot constrain the luminosity evolution of individual galaxies. The steepening of the overall LF with lookback time is of the form orginally postulated by Broadhurst et al. broad88.



next up previous contents
Next: Hubble Space Telescope Up: Evolution of the Previous: The Canada-France Redshift



Luc Simard
Mon Sep 2 12:37:40 PDT 1996