TY - JOUR

T1 - A Simple Spectroscopic Technique to Identify Rejuvenating Galaxies

AU - Zhang, Junyu

AU - Li, Yijia

AU - Leja, Joel

AU - Whitaker, Katherine E.

AU - Nersesian, Angelos

AU - Bezanson, Rachel

AU - van der Wel, Arjen

N1 - Publisher Copyright: © 2023. The Author(s). Published by the American Astronomical Society.

PY - 2023/7/13

Y1 - 2023/7/13

N2 - 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-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 normal 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 Hβ, Hγ, and/or Hδ absorption EWs ≲3 Å 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.

AB - 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-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 normal 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 Hβ, Hγ, and/or Hδ absorption EWs ≲3 Å 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.

U2 - 10.3847/1538-4357/acd84a

DO - 10.3847/1538-4357/acd84a

M3 - Journal article

AN - SCOPUS:85165346212

VL - 952

JO - Astrophysical Journal

JF - Astrophysical Journal

SN - 0004-637X

IS - 1

M1 - 6

ER -