Towards unveiling the Cosmic Reionization: the ionizing photon production efficiency (ξ_ion) of Low-mass Hα emitters at z ∼ 2.3
The Astrophysical Journal(2024)
Abstract
We investigate the galaxy properties of ∼400 low-mass
(<10^9 M_⊙) Hα emitters (HAEs) at z ∼ 2.3 in the ZFOURGE
survey. The selection of these HAEs is based on the excess in the observed
K_s broad-band flux compared to the stellar continuum estimated from the
best-fit SED. These low-mass HAEs have elevated SFR(Hα) above the star
formation main sequence (SFMS), making them potential analogs of the galaxies
that reionized the universe during the epoch of reionization. The ionizing
photon production efficiencies (ξ_ion) of the low-mass HAEs have a median
value of log(ξ_ion/erg^-1 Hz)=25.24^+0.10_-0.13(25.35^+0.12_-0.15), assuming the Calzetti (SMC) curve for the stellar
continuum dust correction. This value is higher than that of main sequence
galaxies by ∼0.2 dex at similar redshift, indicating that the low-mass
HAEs are more efficient in producing ionizing photons. Our results also
consolidate the trend of increasing ξ_ion with redshift, but reveal a
"downsizing" relationship between ξ_ion and stellar mass (M_⊙)
with increasing redshift. We further explore the dependence of ξ_ion on
other galaxy properties, such as the UV spectral slope (β_UV),
the UV magnitude (M_UV), the equivalent widths (EWs) of
Hα and [Oiii] emission lines. Galaxies with the bluer UV slopes,
fainter UV luminosities and higher equivalent widths exhibit elevated
ξ_ion by a factor of ∼2 compared to the median ξ_ion of our
sample. JWST data will provide an opportunity to extend our method and further
investigate the properties of low-mass galaxies at high redshifts.
MoreTranslated text
Key words
High-redshift galaxies,Emission line galaxies,Reionization,Galaxy evolution
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