The Hα luminosity function and star formation rate at z ≈ 0.24 in the COSMOS 2 square degree field

Abstract

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, Δ λ = 120 Å) and sampled Hα emitters with EW_(obs)(H α + [N II]) > 12Å 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 arcmin^2, corresponding to a survey volume of 3.1 × 10^4 Mpc^3. We derive a Hα luminosity function with a best-fit Schechter function parameter set of α = − 1.35_(−0.13)^(+0.11), log ф_* = − 2.65_(−0.38)^(+0.27), and log L_*(ergs s^(−1)) = 41.94_(−0.23)^(+0.38). The Hα luminosity density is 2.7_(−0.6)^(+0.7) × 10^(39) ergs s^(−1) Mpc^(−3). After subtracting the AGN contribution (15%) to the Hα luminosity density, the star formation rate density is evaluated as 1.8_(−0.4)^(+0.7) × 10^(−2) M_סּ yr^(−1) Mpc^(−3). The angular two-point correlation function of Hα-emitting galaxies of log L(H α) > 39.8 is well fit by a power-law form of w(θ) = 0.013−_(0.001)^(+0.002)θ^(−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.