[PGA2001] ELAIS a3 8661 , the SIMBAD biblio

We have carried out a survey searching for Hα emitting galaxies at z≃0.24 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 9.8x10³Mpc³ and a look-back time of 3.6Gyr when H₀=50km/s/Mpc and q₀=0.5 are assumed. A total of 52 objects are selected as candidates for a broad band limiting magnitude of I∼22.9, 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 20Å equivalent width with an uncertainty of ~±10Å. Point-like objects (15) were excluded from our analysis using CLASS_STAR parameter from SExtractor. The contamination from other emission lines such as [OII]λ3727, Hβ and [OIII]λλ 4959,5007 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 (5.4±1.1)x10³⁹erg/s/Mpc³. 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 (0.043±0.009)M_☉/yr/Mpc³. This translates to (0.037 ±0.009) M_☉ 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.