Bar ages derived for the first time in nearby galaxies — Insights on secular evolution from the TIMER sample – Camila de Sá Freitas

Once galaxies settle their discs and become self-gravitating, stellar bars can form, driving the subsequent evolution of their host galaxy. Determining the ages of bars can therefore shed light on the epoch of the onset of secular evolution. In my talk, I will present the first broadly applicable methodology to derive bar ages and its application to a sample of 20 nearby galaxies. The method is based on the co-eval build-up of nuclear structures and bars, and involves using IFS data from the MUSE to disentangle the star formation history of the nuclear disc from the background population. This allows us to derive the formation epoch of the nuclear disc and, thus, of the bar. We estimate the bar formation epoch of nearby galaxies – mostly from the TIMER survey–, creating the largest sample of galaxies with known bar ages to date. We find bar formation epochs varying between 1 and 13 Gyr ago, illustrating how disc-settling and bar formation are processes that first took place in the early Universe and are still taking place in some galaxies. We infer the bar fraction over cosmological time with our sample, finding remarkable agreement with that obtained from direct studies of galaxies at high redshifts. Additionally, for the first time we are able to investigate secular evolution processes taking into account the ages of bars. Our results agree with the scenario in which bars aid the quenching of the host galaxy, with galaxies hosting older bars tending to be more “quenched”. We also find that older bars tend to be longer, stronger and host larger nuclear discs. Furthermore, we find evidence of the nuclear disc stellar mass build-up over time. On the other hand, we find no evidence of downsizing playing a role on bar formation, since we find that bar age is independent of galaxy stellar mass. With the means to estimate bar ages, we can begin to understand better when and how bars shape the observed properties of disc galaxies.