FORS spectroscopy of galaxies in the Hubble Deep Field-South

Abstract

We present low resolution multi-object spectroscopy of an I -band magnitude limited ($I_{{\rm AB}} \simeq$ 23–23.5) sample of galaxies located in an area centered on the Hubble Deep Field-South (HDFS). The observations were obtained using the Focal Reducer$/$low dispersion Spectrograph (FORS) on the ESO Very Large Telescope. Thirty-two primary spectroscopic targets in the HST-WFPC2 HDFS were supplemented with galaxies detected in the Infrared Space Observatory's survey of the HDFS and the ESO Imaging Deep Survey to comprise a sample of 100 galaxies for spectroscopic observations. Based on detections of several emission lines, such as [OII] λ 3727, H$_{\beta}$ and [OIII] λ 5007, or of other spectroscopic features, we measured accurate redshifts for 50 objects in the central HDFS and flanking fields. The redshift range of the current sample of galaxies is 0.6–1.2, with a median redshift of 1.13 (at I $\simeq$ 23.5 not corrected for completeness). The sample is dominated by starburst galaxies with only a small fraction of ellipticals (~10%). For the emission line objects, the extinction corrected [OII] λ 3727 line strengths yield estimates of star formation rates in the range 0.5–30 $M_{\odot}$ yr -1 . We used the present data to derive the [OII] λ 3727 luminosity function up to redshift of 1.2. When combined with [OII] λ 3727 luminosity densities for the local and high redshift Universe, our results confirm the steep rise in the star formation rate (SFR) to z $\simeq$ 1.3.