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Astron. Astrophys. 362, 9-18 (2000)


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H[FORMULA] emitting galaxies and the cosmic star formation rate at z [FORMULA] 2.2 *

A.F.M. Moorwood 1, P.P. van der Werf 2, J.G. Cuby 3 and E. Oliva 4

1 European Southern Observatory, Karl-Schwarzschild-Strasse 2, 85748 Garching, Germany (amoor@eso.org)
2 Leiden Observatory, P.O Box 9513, 2300 RA Leiden, The Netherlands
3 European Southern Observatory, Alonso de Cordova 3107, Santiago, Chile
4 Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, 50125 Firenze, Italy

Received 3 July 2000 / Accepted 9 August 2000

Abstract

An infrared imaging survey in narrow band filters around 2.1 µm has yielded [FORMULA] 10 candidate H[FORMULA] emitting galaxies at z [FORMULA] 2.2 of which 6 have been subsequently confirmed spectroscopically with ISAAC at the ESO VLT. The survey reached a limiting line flux of [FORMULA] 5x10-17 erg cm- 2 s-1 and covered 100 arcmin2 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][FORMULA]6548,6584 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[FORMULA] and a rotation curve obtained for one galaxy yields an inclination corrected rotational velocity of [FORMULA] 140 km s-1 at 3 kpc 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 H[FORMULA] fluxes are 20-35 M[FORMULA] yr-1 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 H[FORMULA]. Comparison with the HST NICMOS grism H[FORMULA] survey of Yan et al. (1999) reveals little or no evolution in the H[FORMULA] luminosity function between z [FORMULA] 1.3 and 2.2. The inferred star formation rate density of 0.12 M[FORMULA] Mpc-3 yr-1 is also equal to that most recently estimated from the UV continuum fluxes of galaxies at z [FORMULA] 3-4.5 by Steidel et al. (1999). Spectroscopy covering H[FORMULA] and [OIII][FORMULA]4959,5007 is planned to gain further insight into the extinction and metal abundance in these galaxies.

Key words: galaxies: evolution – galaxies: distances and redshifts – galaxies: formation – galaxies: starburst – cosmology: early Universe

* Based on observations collected at the European Southern Observatories on La Silla and Paranal, Chile. Also based on data from the ESO Imaging Survey and HST archives.

Send offprint requests to: A. Moorwood

© European Southern Observatory (ESO) 2000

Online publication: October 30, 19100

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