2000A&A...362....9M

An infrared imaging survey in narrow band filters around 2.1µm has yielded ∼10 candidate Hα emitting galaxies at z≃2.2 of which 6 have been subsequently confirmed spectroscopically with ISAAC at the ESO VLT. The survey reached a limiting line flux of ∼5x10^–17erg/cm²/s and covered 100arcmin² including the Hubble Deep Field South (HDFS) WFPC2 and STIS fields. This is the largest spectroscopically confirmed sample of high redshift galaxies selected by narrow band infrared imaging. None of the objects falls within the areas of the deep HST images but some are visible in the WFPC2 flanking fields and the ESO Imaging Survey (EIS) Deep images of HDFS. Only one of the objects observed by HST appears to be an interacting system. Absence of [NII]λλ6548,6584 line emission in the spectra is consistent with them being high ionization and/or low metallicity systems. The observed velocity dispersions imply masses of typically 10¹⁰M☉ and a rotation curve obtained for one galaxy yields an inclination corrected rotational velocity of ≃140km/s at 3kpc which is within the range of nearby disk galaxies.The absolute B magnitude of this galaxy lies 3 magnitudes above the local Tully-Fisher relationship. Star formation rates of the individual galaxies derived from the Hα fluxes are 20-35M☉/yr without any correction for extinction whereas SFRs derived from the rest frame UV continuum fluxes of the same galaxies are up to a factor of 4 lower - consistent with lower extinction to Hα. Comparison with the HST NICMOS grism Hα survey of Yan et al. (1999ApJ...519L..47Y) reveals little or no evolution in the Hα luminosity function between z∼1.3 and 2.2. The inferred star formation rate density of 0.12M☉/Mpc³/yr is also equal to that most recently estimated from the UV continuum fluxes of galaxies at z≃3-4.5 by Steidel et al. (1999ApJ...519....1S). Spectroscopy covering Hβ and [OIII]λλ4959,5007 is planned to gain further insight into the extinction and metal abundance in these galaxies.