RT Journal Article T1 Hα emitting galaxies and the star formation rate density at z ≃ 0.24 A1 Pascual, S. A1 Gallego Maestro, Jesús A1 Aragón Salamanca, A. A1 Zamorano Calvo, Jaime AB 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 9.8 x 10^3 Mpc^3 and a look-back time of 3.6 Gyr when H_0 = 50 km s^-1 Mpc^-1 and q_0 = 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 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 [O II] λ 3727, H _ β and [O III] λ λ 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 H_ α luminosity density of (5.4 ± 1.1) x 10^39 erg s^-1 Mpc^-3. This uncertainty takes into account the photometric and Poissonian errors only. Assuming a constant relation between the H_α luminosity and star formation rate, the SFR density in the covered volume is (0.043 ± 0.009) M_⨀ yr^-1 Mpc^-3. 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. PB EDP Sciencies SN 0004-6361 YR 2001 FD 2001-12 LK https://hdl.handle.net/20.500.14352/59800 UL https://hdl.handle.net/20.500.14352/59800 LA eng NO Baugh, C. M., Cole, S., Frenk, C. S., & Lacey, C. G. 1998, ApJ, 498, 504Bertin, E., & Arnouts, S. 1996, A&AS, 117, 393Castelli, F., & Kurucz, R. L. 1994, AAP, 281, 817Charlot, S. 1998, in The Next Generation Space Telescope: Science Drivers and Technological Challenges, 135Cole, S., Aragón Salamanca, A., Frenk, C. S., Navarro, J. F., & Zepf, S. E. 1994, MNRAS, 271, 781Ellis, R. S., Colless, M., Broadhurst, T., Heyl, J., & Glazebrook, K. 1996, MNRAS, 280, 235Gallagher, J. S., Hunter, D. A., & Bushouse, H. 1989, AJ, 97, 700Gallego, J., Zamorano, J., Aragón Salamanca, A., & Rego, M. 1995, ApJ, 455, L1Gallego, J., Zamorano, J., Rego, M., & Vitores, A. G. 1997, ApJ, 475, 502Glazebrook, K., Blake, C., Economou, F., Lilly, S., & Colless, M. 1999, MNRAS, 306, 843Gronwall, C. 1999, in After the Dark Ages: When Galaxies were Young (the Universe at 2