A simple spectroscopic technique to identify rejuvenating galaxies by Junyu Zhang et al. on Monday 21 November
Rejuvenating galaxies are unusual galaxies that fully quench and then
subsequently experience a "rejuvenation" event to become star-forming once
more. Rejuvenation rates vary substantially in models of galaxy formation:
10%-70% of massive galaxies are expected to experience rejuvenation by z = 0.
Measuring the rate of rejuvenation is therefore important for calibrating the
strength of star formation feedback mechanisms. However, these observations are
challenging because rejuvenating systems blend in with normal star-forming
galaxies in broadband photometry. In this paper, we use the galaxy spectral
energy distribution (SED)-fitting code Prospector to search for observational
markers that distinguish normal star-forming galaxies from rejuvenating
galaxies. We find that rejuvenating galaxies have smaller Balmer absorption
line equivalent widths (EWs) than star-forming galaxies. This is analogous to
the well-known "K + A" or post-starburst galaxies, which have strong Balmer
absorption due to A-stars dominating the light: in this case, rejuvenating
systems have a lack of A-stars, instead resembling "O - A" systems. We find
star-forming galaxies that have H$\beta$, H$\gamma$, and/or H$\delta$
absorption EWs $\lesssim 3${\AA} corresponds to a highly pure selection of
rejuvenating systems. Interestingly, while this technique is highly effective
at identifying mild rejuvenation, "strongly" rejuvenating systems remain nearly
indistinguishable from star-forming galaxies due to the well-known stellar
outshining effect. We conclude that measuring Balmer absorption line EWs in
star-forming galaxy populations is an efficient method to identify rejuvenating
populations, and discuss several techniques to either remove or resolve the
nebular emission which typically lies on top of these absorption lines.
arXiv: http://arxiv.org/abs/http://arxiv.org/abs/2211.10450v1
