Predicting the Merger Fraction of Lyman alpha Emitters from Redshift z~3 to z~7

TL;DR

This study predicts the evolution of merger fractions in high-redshift Lyman-alpha emitters from z~3 to z~7 using simulations and a model linking star formation to mass accretion, highlighting mergers' role in star formation.

Contribution

It introduces a model where star formation in Lyman-alpha emitters is proportional to mass accretion rate, and predicts merger fractions over a wide redshift range, aligning with observations.

Findings

Major merger fraction increases from 35% at z~3 to 50% at z~7.

Predicted merger fractions suggest mergers significantly drive star formation in high-redshift Lya emitters.

Future observations with a 3:1 merger definition will find >30% major merger fraction at z>3.

Abstract

Rapid mass assembly, likely from mergers or smooth accretion, has been predicted to play a vital role in star-formation in high-redshift Lyman-alpha (Lya) emitters. Here we predict the major merger, minor merger, and smooth accreting Lya emitter fraction from z~3 to z~7 using a large dark matter simulation, and a simple physical model that is successful in reproducing many observations over this large redshift range. The central tenet of this model, different from many of the earlier models, is that the star-formation in Lya emitters is proportional to the mass accretion rate rather than the total halo mass. We find that at z~3, nearly 35% of the Lya emitters accrete their mass through major (3:1) mergers, and this fraction increases to about 50% at z~7. This imply that the star-formation in a large fraction of high-redshift Lya emitters is driven by mergers. While there is discrepancy between the model predictions and observed merger fractions, some of this difference (~15%) can be attributed to the mass-ratio used to define a merger in the simulation. We predict that future, deeper observations which use a 3:1 definition of major mergers will find >30% major merger fraction of Lya emitters at redshifts >3.