The ESO Slice Project ( ESP ) galaxy redshift survey ?

The ESO Slice Project (ESP) is a galaxy redshift survey we have recently completed as an ESOKey-Project over about 23 square degrees, in a region near the South Galactic Pole. The survey is nearly complete to the limiting magnitude bJ = 19.4 and consists of 3342 galaxies with reliable redshift determination. TheESP survey is intermediate between shallow,wide angle samples and very deep, one-dimensional pencil beams: spanning a volume of ∼ 5 × 104 h−3 Mpc3 at the sensitivity peak (z ∼ 0.1), it provides an accurate determination of the “local” luminosity function and the mean galaxy density. We find that, although a Schechter function (with α = −1.22,M∗ bJ = −19.61 +5 logh and φ∗ = 0.020 h3 Mpc−3 ) is an acceptable representation of the luminosity function over the entire range of magnitudes (MbJ ≤ −12.4 +5 logh ), our data suggest the presence of a steepening of the luminosity function forMbJ ≥ −17 +5 logh . Such a steepening at the faint end of the luminosity function, well fitted by a power law with slope β ∼ −1.6, is almost completely due to galaxies with emission lines: in fact, dividing our galaxies into two samples, i.e. galaxies with and without emission lines, we find significant differences in their luminosity functions. In particular, galaxies with emission lines show a significantly steeper slope and a fainterM∗. Send offprint requests to: Elena Zucca ([email protected]) ? based on observations collected at the European Southern Observatory, La Silla, Chile. The amplitude and theα andM∗ parameters of our luminosity function are in good agreement with those of the AUTOFIB redshift survey (Ellis et al. 1996). Viceversa, our amplitude is significantly higher, by a factor ∼ 1.6 at M ∼ M∗, than that found for both the Stromlo-APM (Loveday et al. 1992) and the Las Campanas (Lin et al. 1996) redshift surveys. Also the faint end slope of our luminosity function is significantly steeper than that found in these two surveys. The galaxy number density for MbJ ≤ −16 +5 logh is well determined (n̄ = 0.08 ± 0.015 h3 Mpc−3 ). Its estimate for MbJ ≤ −12.4 +5 logh is more uncertain, ranging from n̄ = 0.28 h3 Mpc−3 , in the case of a fit with a single Schechter function, to n̄ = 0.54 h3 Mpc−3 , in the case of a fit with a Schechter function and a power law. The corresponding blue luminosity densities in these three cases are ρLUM = (2.0, 2.2, 2.3)× 108 h L Mpc−3, respectively. Large overand underdensities are clearly seen in our data. In particular, we find evidence for a “local” under-density (n ∼ 0.5n̄ for Dcomoving ≤ 140 h−1 Mpc ) and a significant overdensity (n ∼ 2n̄) at z ∼ 0.1. When these radial density variations are taken into account, our derived luminosity function reproduces very well the observed counts for bJ ≤ 19.4, including the steeper than Euclidean slope for bJ ≤ 17.0.