2008ApJS..175..128S

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 narrowband imaging survey for Hα-emitting galaxies in the Hubble Space Telescope (HST) COSMOS 2 square degree field. We used the narrowband filter NB816 (λ_c=8150 Å, Δλ=120 Å) and sampled Hα emitters with EW_obs(Hα+[N II])>12 Å in a redshift range between z=0.233 and 0.251 corresponding to a depth of 70 Mpc. We obtained 980 Hα-emitting galaxies in a sky area of 5540 arcmin², corresponding to a survey volume of 3.1x10⁴ Mpc³. We derive a Hα luminosity function with a best-fit Schechter function parameter set of α=-1.35^+0.11_–0.13, logφ_*=-2.65^+0.27_–0.38, and logL_*(ergs/s)=41.94^+0.38_–0.23. The Hα luminosity density is 2.7^+0.7_–0.6x10³⁹ ergs/s/Mpc3. After subtracting the AGN contribution (15%) to the Hα luminosity density, the star formation rate density is evaluated as 1.8^+0.7_–0.4x10^–2 M_☉/yr/Mpc3. 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^+0.002_–0.001θ^{–0.88±0.03}, corresponding to the correlation function of ξ(r)=(r/1.9 Mpc)^–1.88. We also find that the Hα emitters with higher Hα luminosity are more strongly clustered than those with lower luminosity.