Letter to the Editor

New search strategy for high z intervening absorbers: GRB 021004, a pilot study^*

¹ European Southern Observatory, Alonso de Cordova 3107, Casilla 19001, Santiago 19, Chile
² European Southern Observatory, Karl-Schwarzschild-Strasse 2, 85748, Garching bei München, Germany
³ Department of Physics and Astronomy, Århus University, Ny Munkegade, 8000 Århus C, Denmark
⁴ Astronomical Observatory, Copenhagen University, Juliane Mariesvej 30, 2100 København K, Denmark

Corresponding author: P. M. Vreeswijk, pvreeswi@eso.org

Received: 25 April 2003
Accepted: 6 August 2003

Abstract

We present near-infrared narrow- and broad-band imaging of the field of GRB 021004, performed with ISAAC on the UT1 of the ESO Very Large Telescope. The narrow-band filters were chosen to match prominent emission lines at the redshift of the absorption-line systems found against the early-time afterglow of GRB 021004: [] at and Hα at , respectively. For the system we find an emission-line source at an impact parameter of 16″, which is somewhat larger than the typical impact parameters of a sample of absorbers at redshifts around unity. Assuming that this tentative redshift-identification is correct, the star formation rate of the galaxy is  yr^-1. Our study reaches star-formation rate limits (5σ) of 5.7 M yr^-1 at , and 7.7 M yr^-1 at . These limits correspond to a depth of roughly 0.13 L^*. Any galaxy counterpart of the absorbers nearer to the line of sight either has to be fainter than this limit or not be an emission-line source.