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Published March 2008 | Published
Journal Article Open

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 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.

Additional Information

© 2008. The American Astronomical Society. Received 2006 September 10; accepted 2007 September 5. The HST COSMOS Treasury program was supported through NASA grant HST-GO-09822.We greatly acknowledge the contributions of the entire COSMOS collaboration consisting of more than 70 scientists. The COSMOS science meeting in 2005 May was supported by in part by the NSF through grant OISE-0456439.We would also like to thank the Subaru Telescope staff for their invaluable help. This work was financially supported in part by the JSPS (nos. 15340059 and 17253001). S. S. S. and T. N. are JSPS fellows.

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