The H alpha luminosity function and star formation rate at z approximate to 0.24 in the COSMOS 2 square degree field

To derive a new H alpha luminosity function and to understand the clustering properties of star-forming galaxies at z approximate to 0.24, we have made a narrowband imaging survey for H alpha-emitting galaxies in the Hubble Space Telescope (HST) COSMOS 2 square degree field. We used the narrowband filter NB816 (lambda(c) = 8150 angstrom, Delta lambda = 120 angstrom) and sampled H alpha emitters with EW(obs)(H alpha + [N II]) > 12 angstrom in a redshift range between z = 0.233 and 0.251 corresponding to a depth of 70 Mpc. We obtained 980 H alpha-emitting galaxies in a sky area of 5540 arcmin(2), corresponding to a survey volume of 3.1 x 10(4) Mpc(3). We derive a H alpha luminosity function with a best-fit Schechter function parameter set of alpha=-1.35(-0.13)(+0.11), log phi* = -2.65(-0.38)(+0.27), and L*(ergs s(-1)) = 41.94(-0.23)(+0.38). The H alpha luminosity density is 2.7(-0.6)(+0.7) x 10(39) ergs s(-1) Mpc(-3). After subtracting the AGN contribution ( 15%) to the H alpha luminosity density, the star formation rate density is evaluated as 1.8(-0.4)(+0.7) x 10(-2) M(circle dot) yr(-1) Mpc(-3). The angular two-point correlation function of H alpha-emitting galaxies of log L(H alpha) > 39.8 is well fit by a power-law form of w(theta) = 0.013(-0.001)(+0.002)theta(-0.88 +/- 0.03) , corresponding to the correlation function of xi(r) = (r/1.9 Mpc)(-1.88). We also find that the H alpha emitters with higher H alpha luminosity are more strongly clustered than those with lower luminosity.