Similarities and uniqueness of Ly$\alpha$ emitters among star-forming galaxies at z=2.5

TL;DR

This study uses deep narrow-band imaging to compare Ly$ ext{alpha}$ emitters (LAEs) and H$ ext{alpha}$ emitters (HAEs) at z=2.5, revealing LAEs are low-mass, actively star-forming galaxies with distinct properties from most HAEs.

Contribution

It provides the first detailed comparison of LAEs and HAEs at z=2.5, highlighting the physical differences and similarities, especially in mass, size, and Ly$ ext{alpha}$$ emission characteristics.

Findings

LAEs are located along the same mass-SFR sequence as HAEs but in lower mass regime.

Massive LAEs tend to have more compact sizes.

Most HAEs do not show Ly$ ext{alpha}$ emission, often showing absorption instead.

Abstract

We conducted a deep narrow-band imaging survey with the Subaru Prime Focus Camera on the Subaru Telescope and constructed a sample of Ly$\alpha$ emitters (LAEs) at z=2.53 in the UDS-CANDELS field where a sample of H$\alpha$ emitters (HAEs) at the same redshift is already obtained from our previous narrow-band observation at NIR. The deep narrow-band and multi broadband data allow us to find LAEs of stellar masses and star-formation rates (SFRs) down to $\gtrsim$$10^8$ M$_\odot$ and $\gtrsim$0.2 M$_\odot$/yr, respectively. We show that the LAEs are located along the same mass-SFR sequence traced by normal star-forming galaxies such as HAEs, but towards a significantly lower mass regime. Likewise, LAEs seem to share the same mass--size relation with typical star-forming galaxies, except for the massive LAEs, which tend to show significantly compact sizes. We identify a vigorous mass growth in the central part of LAEs: the stellar mass density in the central region of LAEs increases as their total galaxy mass grows. On the other hand, we see no Ly$\alpha$ line in emission for most of the HAEs. Rather, we find that the Ly$\alpha$ feature is either absent or in absorption (Ly$\alpha$ absorbers; LAAs), and its absorption strength may increase with reddening of the UV continuum slope. We demonstrate that a deep Ly$\alpha$ narrow-band imaging like this study is able to search for not only LAEs but also LAAs in a certain redshift slice. This work suggests that LAEs trace normal star-forming galaxies in the low-mass regime, while they remain as a unique population because the majority of HAEs are not LAEs.