Stellar populations and star formation histories of the most extreme [OIII] emitters at $z=1.3-3.7$

Abstract

As the James Webb Space Telescope approaches scientific operation, there is much interest in exploring the redshift range beyond that accessible with Hubble Space Telescope imaging. Currently, the only means to gauge the presence of such early galaxies is to age-date the stellar population of systems in the reionisation era. As a significant fraction of 𝑧 7 − 8 galaxies are inferred from Spitzer photometry to have extremely intense [O III] emission lines, it is commonly believed these are genuinely young systems that formed at redshifts 𝑧 < 10, consistent with a claimed rapid rise in the star formation density at that time. Here we study a spectroscopically-confirmed sample of extreme [O III] emitters at 𝑧 = 1.3 − 3.7, using both dynamical masses estimated from [O III] line widths and rest-frame UV to near-infrared photometry to illustrate the dangers of assuming such systems are genuinely young. For the most extreme of our intermediate redshift line emitters, we find dynamical masses 10 − 100 times that associated with a young stellar population mass, which are difficult to explain solely by the presence of additional dark matter or gaseous reservoirs. Adopting nonparametric star formation histories, we show how the near-infrared photometry of a subset of our sample reveals an underlying old (> 100 Myr) population whose stellar mass is 40 times that associated with the starburst responsible for the extreme line emission. Without adequate rest-frame near-infrared photometry we argue it may be premature to conclude that extreme line emitters in the reionisation era are low mass systems that formed at redshifts below 𝑧 10.

Strong C IV emission from star-forming galaxies: a case for high Lyman continuum photon escape

“…Roberts-Borsani et al 2020;Laporte et al 2021). Recently, Tang et al (2022) also reported the presence of evolved stellar populations in extreme [O ] 𝜆5007 emitting galaxies at redshifts 1.3−3.7, where this evolved population can be up to ∼ 40 times more massive than the young starburst associated with the extreme line emission.…”

The Physical Properties of Star-Forming Galaxies with Strong [O III] Lines at z=3.25

“…The strong [O III] emission lines may reveal the extreme conditions of the interstellar medium in a galaxy, and likely associate with low metallicity and high ionizing parameters (McLinden et al 2011;Nakajima et al 2014;Onodera et al 2020;Tang et al 2021b). The extreme [O III] ELGs are often seen as analogs of galaxies in the reionization era (Tang et al 2019;Du et al 2020;Tang et al 2021aTang et al , 2022. And galaxies with large [O III] equivalent widths (EWs; from 200 Å to 800 Å) are widely used to address the Lyα continuum escape fraction in the high-z universe (Fletcher et al 2019;Katz et al 2020;Barrow et al 2020).…”