Ubiquitous [OII] Emission in Quiescent Galaxies at z ~ 0.85

Abstract

Using deep rest-frame optical spectroscopy from the Large Early Galaxy Astrophysical Census (LEGA-C) survey, conducted using VIMOS on the ESO Very Large Telescope, we systematically search for low-ionization [O II] λλ3726,3729 emission in the spectra of a mass-complete sample of z ≈ 0.85 galaxies. Intriguingly, we find that 59 percent of UVJ-quiescent (i.e. non star-forming) galaxies in the sample have ionized gas, as traced by [O II] emission, detected above our completeness limit of 1.5 Å. The median stacked spectrum of the lowest equivalent width quiescent galaxies also shows [O II] emission. The overall fraction of sources with [O II] above our equivalent width limit is comparable to what we find in the low-redshift Universe from GAMA and MASSIVE, except perhaps at the highest stellar masses (> 10 11.5 M ). However, stacked spectra for the individual low-equivalent width systems uniquely indicates ubiquitous [O II] emission in the higher-z LEGA-C sample, with typical [O II] luminosities per unit stellar mass that are a factor of ×3 larger than the lower-z GAMA sample. Star formation in these otherwise quiescent galaxies could play a role in producing the [O II] emission at higher-z, although it is unlikely to provide the bulk of the ionizing photons. More work is required to fully quantify the contributions of evolved stellar populations or active galactic nuclei to the observed spectra.

Different higher-order kinematics between star-forming and quiescent galaxies based on the SAMI, MAGPI and LEGA-C surveys

“…Even though this introduces a bias in the resulting second moment of the LOSVD, the MILES SSP library provides consistently the best fits to the galaxy continuum (surpassed only by the MILES stellar template library, in agreement with e.g. van de Sande et al 2017b;Maseda et al 2021). There are three reasons why a biased measurement of the second moment is not important in this article.…”