The H$\hat{I}\pm$ Luminosity Function and Star Formation Rate at $z\approx 0.24$ in the Cosmos 2 Square-Degree Field

Abstract

To derive a new H$\hat{I}\pm$ luminosity function and to understand the clustering properties of star-forming galaxies at $z\approx 0.24$, we have made a narrow-band imaging survey for H$\hat{I}\pm$ emitting galaxies in the HST COSMOS 2 square degree field. We used the narrow-band filter NB816 ($\hat{I}{»}_c=8150$ à , $\hat{I}”\hat{I}»=120$ à ) and sampled H$\hat{I}\pm$ emitters with $EW_{\rm obs}(\rm Hα+ [N\textsc{ii}]) > 12$ à in a redshift range between $z=0.233$ and $z=0.251$ corresponding to a depth of 70 Mpc. We obtained 980 H$\hat{I}\pm$ emitting galaxies in a sky area of 5540 arcmin${}^2$, corresponding to a survey volume of $3.1\times 10^4\mathrm{Mp}{\mathrm{c}}^3$. We derive a H$\hat{I}\pm$ luminosity function with a best-fit Schechter function parameter set of $\hat{I}\pm =-1.35_{-0.13}^{+0.11}$, $\log \ddot{I}{•}_{\ast }=-2.65_{-0.38}^{+0.27}$, and $\log L_{\ast }(\mathrm{erg}{\mathrm{s}}^{-1})=41.94_{-0.23}^{+0.38}$. The H$\hat{I}\pm$ luminosity density is $2.7_{-0.6}^{+0.7}\times 10^{39}$ ergs s${}^{-1}$ Mpc${}^{-3}$. After subtracting the AGN contribution (15 %) to the H$\hat{I}\pm$ luminosity density, the star formation rate density is evaluated as $1.8_{-0.4}^{+0.7}\times 10^{-2}$ $M_{\sun}$ yr${}^{-1}$ Mpc${}^{-3}$. The angular two-point correlation function of H$\hat{I}\pm$ emitting galaxies of $\log L(\mathrm{H}\hat{\mathrm{I}}\pm )>39.8$ is well fit by a power law form of $w(\hat{I}¸)=0.013_{-0.001}^{+0.002}\hat{I}{¸}^{-0.88\pm 0.03}$, corresponding to the correlation function of $\hat{I}¾(r)=(r/1.9\mathrm{Mpc}{)}^{-1.88}$. We also find that the H$\hat{I}\pm$ emitters with higher H$\hat{I}\pm$ luminosity are more strongly clustered than those with lower luminosity.

13 pages, 9 fifgure, to apper in ApJS