Hα emitting galaxies and the star formation rate density at 0.24

¹ Departamento de Astrofísica, Facultad de C.C Físicas, Universidad Complutense de Madrid, 28040 Madrid, Spain
² School of Physics and Astronomy, University of Nottingham, University Park, Nottingham NG7 2RD, UK

Corresponding author: S. Pascual, spr@astrax.fis.ucm.es

Received: 9 August 2001
Accepted: 20 September 2001

Abstract

We have carried out a survey searching for Hα emitting galaxies at using a narrow band filter tuned with the redshifted line. The total sky area covered was 0.19 square degrees within the redshift range 0.228 to 0.255 in a set of four fields in the ELAIS-N1 zone. This corresponds to a volume of Mpc³ and a look-back time of 3.6 Gyr when km s^-1 Mpc^-1 and are assumed. A total of 52 objects are selected as candidates for a broad band limiting magnitude of , plus 16 detected only in the narrow band image for a narrow band limiting magnitude for object detection of 21.0. The threshold detection corresponds to about 20 Å equivalent width with an uncertainty of ~±10 Å. Point-like objects (15) were excluded from our analysis using CLASS_STAR parameter from SExtractor. The contamination from other emission lines such as , and at redshifts 1.2, 0.66 and 0.61 respectively is estimated, and found to be negligible at the flux limits of our sample. We find an extinction-corrected Hα luminosity density of erg s^-1 Mpc^-3. This uncertainty takes into account the photometric and Poissonian errors only. Assuming a constant relation between the Hα luminosity and star formation rate, the SFR density in the covered volume is () yr^-1 Mpc^-3. This translates to () yr^-1 Mpc^-3 when the total density is corrected for the AGN contribution as estimated in the local Universe. This value is a factor ~4 higher than the local SFR density. This result needs to be confirmed by future spectroscopic follow-up observations.