Survey Motivation

One of the current problems of observational cosmology is the inability to reconcile the large numbers of blue galaxies seen at faint magnitudes (see Koo & Kron 1992 for a review, and more recent work by Lilly et al. 1991, Metcalfe et al. 1995) with the results of recent spectroscopic redshift surveys (Ellis et al. 1996, and references therein). These surveys () indicate the majority of these objects lie at modest redshift () rather than the high redshifts originally expected. While simple no evolution (NE) models of the universe are able to account for the slope of the observed redshift distribution, the number counts of these faint blue galaxies (FBGs) to faint limits () are well in excess of that predicted by NE models. Furthermore, it appears that the number count data are more easily modelled with the use of a non-zero cosmological constant and , both of which are disfavoured options from a theoretical standpoint (Schade & Ferguson 1994).

Ellis et al. (1996) claim that the excess population of galaxies at is primarily due to a separate population of star-forming galaxies characterised by broad [OII] equivalent widths, a suggestion first made by Broadhurst et al. (1988) and later confirmed by Broadhurst et al. (1992) as the spectroscopic studies increased in depth. No such equivalent population has yet been detected locally (). This is a crucial issue in the interpretation of the excess FBG counts, for if local galaxy samples are incomplete (e.g. surface brightness selection effects) then an artificial excess in the galaxy counts will appear at higher redshift (Schade & Ferguson 1994). The TTF Field Galaxy Survey aims to place stronger constraints on galaxy SFRs and luminosities both at where the FBG excess is observed, and at where an equivalent local population has long been suspected but not observed.

б© Copyright Astronomical Society of Australia 1997