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We have carried out a survey searching for H alpha emitting galaxies atz~0.24 using a narrow band filter tuned with the redshifted line. The total skyarea covered was 0.19 square degrees within the redshift range 0.228 to 0.255in a set of four fields in the ELAIS-N1 zone. This corresponds to a volume of9.8 10^3 Mpc^3 and a look-back time of 3.6 Gyr when H0=50 km s^{-1} Mpc^{-1}and q=0.5 are assumed. A total of 52 objects are selected as candidates for abroad band limiting magnitude of I~22.9, plus 16 detected only in the narrowband image for a narrow band limiting magnitude for object detection of 21.0.The threshold detection corresponds to about 20 A equivalent width with anuncertainty of ~ 10 AA. Point-like objects (15) were excluded from our analysisusing CLASS_STAR parameter from SExtractor}. The contamination from otheremission lines such as O[II] 3727, H beta and [OIII] 4959,5007 at redshifts1.2, 0.66 and 0.61 respectively is estimated, and found to be negligible at theflux limits of our sample. We find an extinction-corrected H alpha luminositydensity of 5.4 10^39 erg s^{-1} Mpc^{-3}. This uncertainty takes into accountthe photometric and Poissonian errors only. Assuming a constant relationbetween the H alpha luminosity and star formation rate, the SFR density in thecovered volume is 0.043 M_sun yr^{-1} Mpc^{-3}. This translates to 0.037 M_sunyr^{-1} Mpc^{-3} when the total density is corrected for the AGN contributionas estimated in the local Universe. This value is a factor ~4 higher than thelocal SFR density. This result needs to be confirmed by future spectroscopicfollow-up observations.Comment: 10 pages, 7 figures. To be published in Astronomy & Astrophysics.  Corrected astrometry in Table 2, field b4. Corrected luminosity funcion from  Tresse & Maddox on figure 6. Corrected mismatched logL axis on figure

Hαemitting galaxies and the star formation rate density at $\vec{z}$ $\simeq$ 0.24