Star–Forming Galaxies and Large–Scale Structure (Poster paper)

Summary

ABSTRACT

From the preliminary analysis of a sample of ≃ 600 galaxies with b_j ≤ 19.4, and spanning a redshift interval up to z ≃ 0.3, we deduce that star formation per unit luminosity, as indicated by the OII 3727 line equivalent width, is a function of galaxy luminosity (decreasing at increasing luminosities), redshift (increasing at increasing redshift, or, physically, look–back time) and environment.

INTRODUCTION

At the ESO 3.6m telescope at La Silla, we are currently performing a redshift survey of galaxies with b_j ≤ 19.4, in a rectangular area ≃ 22° × 1° (plus a nearby area of ≃ 5° × 1°) in a region around the South Galactic Pole. Up to now we have acccumulated spectra for ≃ 2,000 galaxies over ≃ 70% of the area.

The distribution in distance of the survey galaxies exibits significative peaks above the expectation at D ≃ 180h^-1 Mpc and D ≃ 300h^-1 Mpc. These peaks correspond to large scale structures extending over a significant fraction of the strip.

A large fraction of galaxies (≃ 40%) shows the presence of one or more emission lines (OII λ3727, Hβ, OIII λλ4959,5007). These objects can be either spiral galaxies, where lines originate mostly from HII regions in the disks, or galaxies undergoing a significant burst of star formation. The observed peaks in the galaxy distribution are much less pronounced when only emission line galaxies are considered. This suggests that either spiral galaxies are less frequent in the densest regions, thus confirming a large scale validity of the well known morphology–density relation, or starburst phenomena in galaxies occur preferentially in low density environments, or both.