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
- Institute for Cosmic Ray Research, The University of Tokyo, Kashiwa-no-ha, Kashiwa 277-8582 (Japan)
- Observatoire de Genève, Universitè de Genève, 51 Ch. des Maillettes, 1290 Versoix (Switzerland)
- Department of Astronomy, Graduate School of Science, The University of Tokyo, Hongo, Bunkyo-ku, Tokyo, 113-0033 (Japan)
We present the Lyα luminosity functions (LFs) derived by our deep Subaru narrowband survey that identifies a total of 3137 Lyα 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 Lyα luminosity range of logL{sub Lyα}=41.7--44.4 erg s{sup −1}. We determine the Lyα LF at z = 2.2 with unprecedented accuracy and obtain the best-fit Schechter parameters of L{sub Lyα}{sup ∗}=5.29{sub −1.13}{sup +1.67}×10{sup 42} erg s{sup −1}, ϕ{sub Lyα}{sup ∗}=6.32{sub −2.31}{sup +3.08}×10{sup −4} Mpc{sup −3}, and α=−1.75{sub −0.09}{sup +0.10}, showing a steep faint-end slope. We identify a significant hump at the LF bright end (logL{sub Lyα}>43.4 erg s{sup −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 ∼ 2 down to the faint magnitude limit of M {sub UV} ≃ −22.5 and to constrain the faint-end slope of the AGN UV LF, α {sub AGN} = −1.2 ± 0.1, which is flatter than those at z > 4. Based on the Lyα and UV LFs from our and previous studies, we find an increase of Lyα escape fraction f{sub esc}{sup Lyα} from z ∼ 0 to 6 by two orders of magnitude. This large f{sub esc}{sup Lyα} 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 Lyα by resonance scattering. Our uniform expanding shell models suggest that the typical H i column density decreases from N{sub HI}∼7×10{sup 19} (z ∼ 0) to ∼1 × 10{sup 18} cm{sup −2} (z ∼ 6) to explain the large f{sub esc}{sup Lyα} increase.
- OSTI ID:
- 22869071
- Journal Information:
- Astrophysical Journal, Vol. 823, Issue 1; Other Information: Country of input: International Atomic Energy Agency (IAEA); ISSN 0004-637X
- Country of Publication:
- United States
- Language:
- English
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