Connecting Faint End Slopes of the Lyman-$\hat{I}\pm$ emitter and Lyman-break Galaxy Luminosity Functions

Abstract

We predict Lyman-$\hat{I}\pm$ (Ly$\hat{I}\pm$) luminosity functions (LFs) of Ly$\hat{I}\pm$-selected galaxies (Ly$\hat{I}\pm$ emitters, or LAEs) at $z=3-6$ using the phenomenological model of Dijkstra & Wyithe (2012). This model combines observed UV-LFs of Lyman-break galaxies (LBGs, or drop out galaxies), with constraints on their distribution of Ly$\hat{I}\pm$ line strengths as a function of UV-luminosity and redshift. Our analysis shows that while Ly$\hat{I}\pm$ LFs of LAEs are generally not Schechter functions, these provide a good description over the luminosity range of ${\log }_{10}(L_{\hat{I}}\pm /\mathrm{erg}{\mathrm{s}}^{-1})=41-44$. Motivated by this result, we predict Schechter function parameters at $z=3-6$. Our analysis further shows that (i) the faint end slope of the Ly$\hat{I}\pm$ LF is steeper than that of the UV-LF of Lyman-break galaxies, (with a median $\hat{I}{\pm }_{Ly\hat{I}\pm }<-2.0$ at $z\gtrsim 4$), and (ii) a turn-over in the Ly$\hat{I}\pm$ LF of LAEs at Ly$\hat{I}\pm$ luminosities $10^{40}$ erg s${}^{-1}<L_{\hat{I}}\pm \lesssim 10^{41}$ erg s${}^{-1}$ may signal a flattening of UV-LF of Lyman-break galaxies at $-12>M_{\mathrm{UV}}>-14$. We discuss the implications of these results - which can be tested directly with upcoming surveys - for the Epoch of Reionization.

8 pages, 6 figures, submitted to MNRAS (after revision following referee's report)