MIDIS: The Relation between Strong (Hb+[OIII]) Emission, Star Formation and Burstiness Around the Epoch of Reionization

TL;DR

This study explores the properties of strong (Hb+[OIII]) emission line galaxies from redshift 8 to 5.5 using JWST data, revealing their star formation characteristics and relation to galaxy evolution during reionization.

Contribution

It presents new observations of (Hb+[OIII]) emitters at high redshift with JWST, analyzing their star formation and metallicity, and compares them to non-emitters for a comprehensive view.

Findings

Strong (Hb+[OIII]) emitters show anti-correlation with stellar mass and age.

Emitters are found on both the main sequence and starburst regions.

High EW_0(Hb+[OIII]) may be linked to low metallicity at low SFRs.

Abstract

We investigate the properties of strong (Hb+[OIII]) emitters before and after the end of the Epoch of Reionization from z=8 to z=5.5. We make use of ultra-deep JWST/NIRCam imaging in the Parallel Field of the MIRI Deep Imaging Survey (MIDIS) in the Hubble eXtreme Deep Field (P2-XDF), in order to select prominent (Hb+[OIII]) emitters (with rest EW_0 > 100 Angstroms) at z=5.5-7, based on their flux density enhancement in the F356W band with respect to the spectral energy distribution continuum. We complement our selection with other (Hb+[OIII]) emitters from the literature at similar and higher (z=7-8) redshifts. We find (non-independent) anti-correlations between EW_0(Hb+[OIII]) and both galaxy stellar mass and age, in agreement with previous studies, and a positive correlation with specific star formation rate (sSFR). On the SFR-M* plane, the (Hb+[OIII]) emitters populate both the star-formation main sequence and the starburst region, which become indistinguishable at low stellar masses (log10(M*) < 7.5). We find tentative evidence for a non-monotonic relation between EW_0(Hb+[OIII]) and SFR, such that both parameters correlate with each other at SFR > 1 Msun/yr, while the correlation flattens out at lower SFRs. This suggests that low metallicities producing high EW_0(Hb+[OIII]) could be important at low SFR values. Interestingly, the properties of the strong emitters and other galaxies (33% and 67% of our z=5.5-7 sample, respectively) are similar, including, in many cases, high sSFR. Therefore, it is crucial to consider both emitters and non-emitters to obtain a complete picture of the cosmic star formation activity around the Epoch of Reionization.