BRIGHT AND FAINT ENDS OF Lyα LUMINOSITY FUNCTIONS AT z=2 DETERMINED BY THE SUBARU SURVEY: IMPLICATIONS FOR AGNs, MAGNIFICATION BIAS, AND ISM H I EVOLUTION

We present the Ly alpha luminosity functions (LFs) derived by our deep Subaru narrowband survey that identifies a total of 3137 Ly alpha emitters (LAEs) at z = 2.2 in five independent blank fields. This sample of LAEs is the largest to date and covers a very wide Ly alpha luminosity range of log L-Ly alpha = 41.7-44.4 erg s(-1). We determine the Ly alpha LF at z = 2.2 with unprecedented accuracy and obtain the best-fit Schechter parameters of L-Ly alpha* = 5.29(-1.13)(+1.67) x 10(42) erg s(-1), phi(Ly alpha)* = 6.32(2.31)(+3.08) x 10(-4) Mpc(-3), and alpha = -1.75(-0.09)(+0.10), showing a steep faint-end slope. We identify a significant hump at the LF bright end (log L-Ly alpha > 43.4 erg s(-1)). Because all of the LAEs in the bright-end hump have a bright counterpart(s) in either the X-ray, UV, or radio data, this bright-end hump is not made by gravitational lensing magnification bias but by active galactic nuclei (AGNs). These AGNs allow us to derive the AGN UV LF at z similar to 2 down to the faint magnitude limit of M-UV similar or equal to -22.5 and to constrain the faint-end slope of the AGN UV LF, alpha(AGN) = -1.2 +/- 0.1, which is flatter than those at z > 4. Based on the Ly alpha and UV LFs from our and previous studies, we find an increase of Ly alpha escape fraction f(esc)(Ly alpha) from z similar to 0 to 6 by two orders of magnitude. This large f(esc)(Ly alpha) increase can be explained neither by the evolution of stellar population nor by outflow alone, but by the evolution of neutral hydrogen H I density in the interstellar medium that enhances dust attenuation for Ly alpha by resonance scattering. Our uniform expanding shell models suggest that the typical H I column density decreases from N-H I similar to 7 x 10(19) (z similar to 0) to similar to 1 x 10(18) cm(-2) (z similar to 6) to explain the large f(esc)(Ly alpha) increase.