Multiple emission lines of H$\alpha$ emitters at $z \sim 2.3$ from the broad and medium-band photometry in the ZFOURGE Survey

TL;DR

This study analyzes emission lines of approximately 1300 H-alpha emitters at redshift 2.3 using broad and medium-band photometry from ZFOURGE, revealing galaxy evolution trends and potential contributors to cosmic reionization.

Contribution

It introduces a photometric method to extract multiple emission lines from H-alpha emitters at z~2.3, providing insights into their properties without spectroscopic data.

Findings

Discrepancy in metallicity and ionization compared to local galaxies.

High equivalent width [OIII] in low-mass galaxies suggests potential LyC leakage.

Properties of some galaxies resemble extreme emitters and Lyα emitters at similar redshifts.

Abstract

We present a multiple emission lines study of $\sim$1300 H$\alpha$ emitters (HAEs) at $z \sim 2.3$ in the ZFOURGE survey. In contrast to the traditional spectroscopic method, our sample is selected based on the flux excess in the ZFOURGE-$K_s$ broad-band data relative to the best-fit stellar continuum. Using the same method, we also extract the strong diagnostic emission lines for these individual HAEs: [OIII]$\lambda\lambda4959,5007$, [OII]$\lambda\lambda3726,3729$. Our measurements exhibit good consistency with those obtained from spectroscopic surveys. We investigate the relationship between the equivalent widths (EWs) of these emission lines and various galaxy properties, including stellar mass, stellar age, star formation rate (SFR), specific SFR (sSFR), ionization states (O32). We have identified a discrepancy between between HAEs at $z\sim2.3$ and typical local star-forming galaxy observed in the SDSS, suggesting the evolution of lower gas-phase metallicity ($Z$) and higher ionization parameters ($U$) with redshift. Notably, we have observed a significant number of low-mass HAEs exhibiting exceptionally high $EW_{\mathrm{[OIII]}}$. Their galaxy properties are comparable to those of extreme objects, such as extreme O3 emitters (O3Es) and Ly$\alpha$ emitters (LAEs) at $z\simeq2-3$. Considering that these characteristics may indicate potential strong Lyman continuum (LyC) leakage, higher redshift anaglogs of the low-mass HAEs could be significant contributors to the cosmic reionization. Further investigations on this particular population are required to gain a clearer understanding of galaxy evolution and cosmic reionization.