The Hα Luminosity Function and Star Formation Rate at Z ≈ 0.24 in the Cosmos 2 Square-degree Field

To derive a new Hα luminosity function and to understand the clustering properties of star-forming galaxies at z ≈ 0.24, we have made a narrow-band imaging survey for Hα emitting galaxies in the HST COSMOS 2 square degree field. We used the narrow-band filter NB816 (λc = 8150 Å, ∆λ = 120 Å) and sampled Hα emitters with EWobs(Hα + [Nii]) > 12 Å in a redshift range between z = 0.233 and z = 0.251 corresponding to a depth of 70 Mpc. We obtained 980 Hα emitting galaxies in a sky area of 5540 arcmin, corresponding to a survey volume of 3.1×10 Mpc. We derive a Hα luminosity function with a best-fit Schechter function parameter set of α = −1.35 −0.13, logφ∗ = −2.65 +0.27 −0.38, and logL∗(erg s ) = 41.94 −0.23. The Hα luminosity density is 2.7 +0.7 −0.6 × 10 39 ergs s Mpc. After subtracting the AGN contribution (15 %) to the Hα luminosity density, the star formation rate density is evaluated as 1.8 −0.4 × 10 −2 M⊙ yr −1 Mpc. The angular two-point correlation function of Hα emitting galaxies of logL(Hα) > 39.8 is well fit by a power law form of w(θ) = 0.013 −0.001θ , corresponding to the correlation function of ξ(r) = (r/1.9Mpc). We also find that the Hα emitters with higher Hα luminosity are more strongly clustered than those with lower luminosity. Subject headings: galaxies: distances and redshifts — galaxies: evolution — galaxies: luminosity function, mass function