ISAAC spectroscopy of emission line galaxies at z = 2.2

Abstract

The IR Spectrometer and Array Camera (ISAAC) at the VLT has ben used for follow-up spectroscopy of 11 candidate H(alpha) emitting galaxies at z approximately equals 2.2 detected in a preparatory, IR narrow band filter imaging survey. This survey was conducted with Son of ISAAC at the ESO NTT and covered an area of 100 sq. arcmin including the WFPC2 and STIS fields in the HDFS. Line emission within the wavelength range of the 2.1 micrometers narrow band filters is confirmed in 6 of the candidates and in all but one of the 6 detected at &gt;= 4 (sigma) in the survey. Although only a single emission line is observed its identification with H(alpha) is relatively secure and the absence of (NII) (6548,6584 Angstrom) is consistent with high ionization and/or low metallicity systems. Velocity dispersions and one H(alpha) rotation curve imply masses of up to approximately 10<SUP>10</SUP>M. Star formation rates of the individual galaxies derived from the H(alpha) fluxes are 20-35 M yr<SUP>-1</SUP> and the total star formation rate density is 0.12 M Mpc<SUP>-3</SUP>. This is the same as found at z approximately equals 1.3 from H(alpha) observations with NICMOS on HST$_1) and close to that at z equals 3-4.5 derived from the extinction corrected UV continuum fluxes of Lyman Break galaxies<SUP>2</SUP>.