Lyman Alpha Emitters in Hierarchical Galaxy Formation II. UV Continuum Luminosity Function and Equivalent Width Distribution

TL;DR

This paper presents a theoretical model predicting UV luminosity functions and Lyman alpha equivalent width distributions of LAEs, successfully matching observations from redshift 3 to 6 without extra free parameters, highlighting the role of clumpy dust and young stellar populations.

Contribution

The study introduces a dust extinction model with clumpy distribution that explains large EW LAEs and reproduces observed trends without invoking Pop III stars or top-heavy IMFs.

Findings

Model accurately reproduces observed UV LFs and EW distributions.

Clumpy dust and young stellar populations are key to large EW LAEs.

Agreement with observed EW-extinction correlation and UV brightness trends.

Abstract

We present theoretical predictions of UV continuum luminosity function (UV LF) and Lya equivalent width (EW) distribution of Lyman alpha emitters (LAEs) in the framework of the hierarchical clustering model of galaxy formation. The model parameters about LAEs were determined by fitting to the observed Lya LF at z=5.7 in our previous study, and the fit indicates that extinction of Lya photons by dust is significantly less effective than that of UV continuum photons, implying clumpy dust distribution in interstellar medium. We then compare the predictions about UV LFs and EW distributions with a variety of observations at z ~ 3-6, allowing no more free parameters and paying careful attention to the selection conditions of LAEs in each survey. We find that the predicted UV LFs and EW distributions are in nice agreement with observed data, and especially, our model naturally reproduces the existence of large EW LAEs (> 240 A) without introducing Pop III stars or top-heavy initial mass function. We show that both the stellar population (young age and low metallicity) and extinction by clumpy dust are the keys to reproduce large EW LAEs. The evidence of EW enhancement by clumpy dust is further strengthened by the quantitative agreement between our model and recent observations about a positive correlation between EW and extinction. The observed trend that brighter LAEs in UV continuum tend to have smaller mean EW is also reproduced, and the clumpy dust is playing an important role again for this trend. We suggested in our previous study that the transmission of intergalactic medium for Lya emission rapidly decreases from z ~ 6 to 7 by the fitting to Lya LFs, and this evidence is quantitatively strengthened by the comparison with the UV LF and EW distribution at z ~ 6.6.