Discovery of Massive, Mostly Star-formation Quenched Galaxies with Extremely Large Lyman-alpha Equivalent Widths at z ~ 3

TL;DR

This paper reports the discovery of six massive galaxies at z ~ 3 with extremely large Lyman-alpha equivalent widths and evolved stellar populations, providing insights into galaxy evolution during peak cosmic star formation.

Contribution

The study introduces a new class of galaxies, MAESTLOs, characterized by large Lyman-alpha emission and evolved stars, filling a gap in understanding galaxy transition phases.

Findings

Six MAESTLOs with large Lya EW and massive stellar content.

Extended Lya emission likely caused by star formation and superwinds.

These galaxies serve as a link between star-forming and passive galaxies.

Abstract

We report a discovery of 6 massive galaxies with both extremely large Lya equivalent width and evolved stellar population at z ~ 3. These MAssive Extremely STrong Lya emitting Objects (MAESTLOs) have been discovered in our large-volume systematic survey for strong Lya emitters (LAEs) with twelve optical intermediate-band data taken with Subaru/Suprime-Cam in the COSMOS field. Based on the SED fitting analysis for these LAEs, it is found that these MAESTLOs have (1) large rest-frame equivalent width of EW_0(Lya) ~ 100--300 A, (2) M_star ~ 10^10.5--10^11.1 M_sun, and (3) relatively low specific star formation rates of SFR/M_star ~ 0.03--1 Gyr^-1. Three of the 6 MAESTLOs have extended Ly$\alpha$ emission with a radius of several kpc although they show very compact morphology in the HST/ACS images, which correspond to the rest-frame UV continuum. Since the MAESTLOs do not show any evidence for AGNs, the observed extended Lya emission is likely to be caused by star formation process including the superwind activity. We suggest that this new class of LAEs, MAESTLOs, provides a missing link from star-forming to passively evolving galaxies at the peak era of the cosmic star-formation history.