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Astron. Astrophys. 326, 477-488 (1997)

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The ESO Slice Project (ESP) galaxy redshift survey *

II. The luminosity function and mean galaxy density

E. Zucca 1, 2, G. Zamorani 1, 2, G. Vettolani 2, A. Cappi 1, R. Merighi 1, M. Mignoli 1, G.M. Stirpe 1, H. MacGillivray 3, C. Collins 4, C. Balkowski 5, V. Cayatte 5, S. Maurogordato 5, D. Proust 5, G. Chincarini 6, 7, L. Guzzo 6, D. Maccagni 8, R. Scaramella 9, A. Blanchard 10 and M. Ramella 11

1 Osservatorio Astronomico di Bologna, via Zamboni 33, I-40126 Bologna, Italy
2 Istituto di Radioastronomia del CNR, via Gobetti 101, I-40129 Bologna, Italy
3 Royal Observatory Edinburgh, Blackford Hill, Edinburgh EH9 3HJ, UK
4 School of EEEP, Liverpool John-Moores University, Byrom Street, Liverpool L3 3AF, UK
5 Observatoire de Paris, DAEC, Unité associée au CNRS, D0173 et à l'Université Paris 7, 5 Place J.Janssen, F-92195 Meudon, France
6 Osservatorio Astronomico di Brera, via Bianchi 46, I-22055 Merate (LC), Italy
7 Università degli Studi di Milano, via Celoria 16, I-20133 Milano, Italy
8 Istituto di Fisica Cosmica e Tecnologie Relative, via Bassini 15, I-20133 Milano, Italy
9 Osservatorio Astronomico di Roma, via Osservatorio 2, I-00040 Monteporzio Catone (RM), Italy
10 Université L. Pasteur, Observatoire Astronomique, 11 rue de l'Université, F-67000 Strasbourg, France
11 Osservatorio Astronomico di Trieste, via Tiepolo 11, I-34131 Trieste, Italy

Received 31 October 1996 / Accepted 30 April 1997

Abstract

The ESO Slice Project (ESP) is a galaxy redshift survey we have recently completed as an ESO Key-Project over about 23 square degrees, in a region near the South Galactic Pole. The survey is nearly complete to the limiting magnitude [FORMULA] and consists of 3342 galaxies with reliable redshift determination.

The ESP survey is intermediate between shallow, wide angle samples and very deep, one-dimensional pencil beams: spanning a volume of [FORMULA]   [FORMULA] Mpc3   at the sensitivity peak ( [FORMULA] ), it provides an accurate determination of the "local" luminosity function and the mean galaxy density.

We find that, although a Schechter function (with [FORMULA], [FORMULA] [FORMULA]   and [FORMULA]   [FORMULA] Mpc-3  ) is an acceptable representation of the luminosity function over the entire range of magnitudes ( [FORMULA] [FORMULA]  ), our data suggest the presence of a steepening of the luminosity function for [FORMULA] [FORMULA]  . Such a steepening at the faint end of the luminosity function, well fitted by a power law with slope [FORMULA], 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 fainter [FORMULA].

The amplitude and the [FORMULA] and [FORMULA] 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 [FORMULA] at [FORMULA], 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 [FORMULA] [FORMULA]   is well determined ( [FORMULA]   [FORMULA] Mpc-3  ). Its estimate for [FORMULA] [FORMULA]   is more uncertain, ranging from [FORMULA]   [FORMULA] Mpc-3  , in the case of a fit with a single Schechter function, to [FORMULA]   [FORMULA] 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 [FORMULA]  L [FORMULA]   Mpc-3, respectively.

Large over- and under- densities are clearly seen in our data. In particular, we find evidence for a "local" under-density ( [FORMULA] for [FORMULA]   [FORMULA] Mpc ) and a significant overdensity ( [FORMULA] ) at [FORMULA]. When these radial density variations are taken into account, our derived luminosity function reproduces very well the observed counts for [FORMULA], including the steeper than Euclidean slope for [FORMULA].

Key words: galaxies: distances and redshifts — luminosity function — surveys

* based on observations collected at the European Southern Observatory, La Silla, Chile.

Send offprint requests to: Elena Zucca (zucca@astbo1.bo.cnr.it)

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© European Southern Observatory (ESO) 1997

Online publication: October 15, 1997
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