The onset of secular evolution in the universe

Sá Freitas, Camila da (2023): The onset of secular evolution in the universe: determining the cosmic epoch of bar formation with integral field spectroscopy. Dissertation, LMU München: Fakultät für Physik

Abstract

Disc galaxies build up their mass in a two-phase scenario. At higher redshifts, external processes dominate the evolution of the galaxy. With the expansion of the Universe and the decrease in the frequency of interactions, these external processes give place to the internal development of the galaxy, including disc formation and settling. However, it is unclear when this transition occurs in the Universe. Once the disc settles, at least partially, it is often prone to developing a non-axisymmetric structure, namely the bar. One of the immediate effects due to the presence of the bar is the gas inflow towards central parts of the galaxy, leading to central star formation and the building of a new rotationally-supported stellar structure, i.e., the nuclear disc. Therefore, we can estimate the cosmic epoch of bar formation (and thus the transition time in the two-phase scenario) by deriving the star formation history of the nuclear disc. In this thesis, we present the first generally applicable methodology to derive the time of bar formation for a sizeable sample of galaxies and, additionally, we share the first results from applying this methodology to 19 galaxies observed with the MUSE integral field spectrograph on the VLT (mostly from the TIMER survey). Our methodology consists in carefully isolating the contribution of the nuclear disc to the observed spectra, in order to derive its star formation history free of contamination from other co-spatial stellar structures. To ascertain the uncertainties involved, particularly of a systematic nature, we run a thorough series of tests, leading to realistic error estimates. Among our main results, we find a wide range of values of disc-settling epochs (0 ≤ z ≤ 6), which indicates this is an ongoing process in the Universe that has commenced substantially earlier than previously thought. Analysing the current stellar mass of the bar-hosting galaxy, we find no correlation with the bar age. This contradicts the downsizing scenario that predicts that the more massive galaxies assembled their mass first, forming their bars first. Regarding secular evolution, we find evidence that bars can grow over time (relative to the host galaxy). In addition, by analysing the evolution of the light fraction enclosed in the bar over time, we find evidence of angular momentum exchange across the galaxy, with the trapping by the bar of stars from the galaxy disc, which can e plain the bar growth. This methodology allows us, for the first time, to test theoretical predictions regarding bar-driven evolution from an observational perspective, opening new lines of research in the near future.

• Dokumententyp: Dissertationen (Dissertation, LMU München)
• Themengebiete: 500 Naturwissenschaften und Mathematik ; 500 Naturwissenschaften und Mathematik > 530 Physik
• Fakultäten: Fakultät für Physik
• Sprache der Hochschulschrift: Englisch
• Datum der mündlichen Prüfung: 25. Oktober 2023
• 1. Bericht­erstatter:in: Dolag, Klaus