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Galactic ageing and quenching

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posted on 2025-01-24, 03:55 authored by Pablo Corcho Caballero

This thesis investigates the present and past star formation activity of galaxies, and the physical mechanisms that govern the conversion of gas into stars in the local Universe. Utilizing extensive data from large spectroscopic surveys, the first part focuses on studying the distribution of nearby galaxies in terms of specific star formation rate (sSFR), and total stellar mass (M*). We find that the distribution features a single mode, corresponding to the Main Sequence of star-forming galaxies, and extended asymptotic power-law tails at both ends, consistent with a single population of galaxies with different levels of star formation activity. Theoretical predictions from cosmological simulations are in agreement with observations down to the so-called Green Valley, where galaxies display intermediate to low levels of star formation. Below this limit, most quiescent galaxies in cosmological simulations completely ceased forming stars a few Gyr ago, after undergoing some quenching episode, while observations indicate that these galaxies still retain residual levels of star formation. This facts lead to the second part of the thesis, devoted to study the star formation history of galaxies and determine the role of quenching episodes in shaping their evolution. We developed a diagnostic tool, referred to as the Ageing Diagram, designed to discriminate between galaxies dominated by secular evolution (Ageing), and systems that recently stopped forming stars (Quenched). This technique is applied to several integral field spectroscopic galaxy samples, on resolved and integrated scales, in combination with synthetic data from simulations. The results reveal the existence of two parallel and narrow galaxy sequences – representing the Ageing and Quenching scenarios – indicating that, rather than two stages of galaxy evolution intrinsic to all galaxies (i.e., bimodal interpretation), there are two main evolutionary pathways with a common end. Galaxies might become red either due to the influence of some quenching mechanism(s), or simply by continuous star formation, eventually leading to the depletion of the gas reservoir. We show that more than 70% of nearby galaxies evolve secularly, while a small fraction of systems, 5-10%, has been quenched in the last ~Gyr. The remaining fraction of galaxies corresponds to an old population, whose former star forming is difficult to infer. We conclude by exploring the physical causes of galaxy quenching, and find that environment is the most likely candidate, especially regarding low-mass satellite galaxies, although we also detected a small fraction of isolated intermediate-mass systems whose quenching could be related to internal processes.

History

Table of Contents

1 General introduction -- 2 Observing galaxies -- 3 A single galaxy population -- 4 Simulating galaxies -- 5 Do galaxies die? -- 6 The Ageing Diagram: do galaxies quench? -- 7 Ageing and quenching on resolved scales -- 8 Ageing and quenching through the Ageing Diagram -- 9 Ageing and quenching through the Ageing Diagram II -- 10 Discussion -- A Appendix -- B Appendix -- C Appendix -- D List of abbreviations

Notes

Cotutelle thesis in conjunction with Universidad Autónoma de Madrid Thesis by publication

Awarding Institution

Macquarie University Universidad Autónoma de Madrid

Degree Type

Thesis PhD

Degree

Doctor of Philosophy

Department, Centre or School

Australian Astronomical Optics

Year of Award

2023

Principal Supervisor

Ángel Rafael López Sánchez

Additional Supervisor 1

Andrew Hopkins

Additional Supervisor 2

Yago Ascasibar

Rights

Copyright: The Author Copyright disclaimer: https://www.mq.edu.au/copyright-disclaimer

Language

English

Extent

339 pages

Former Identifiers

AMIS ID: 277387

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