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The galaxy cluster Fornax, Unveiled in CO: how dense environments drive galaxy evolution

Zabel, Nikki 2020. The galaxy cluster Fornax, Unveiled in CO: how dense environments drive galaxy evolution. PhD Thesis, Cardiff University.
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This thesis investigates the effects of dense environments on galaxy evolution by studying the cold molecular gas in Fornax cluster galaxies. Cold molecular gas is the direct fuel for star formation. Therefore, understanding the way it is affected by the cluster is key to understanding galaxy evolution in such dense environments, and, with a large fraction of galaxies residing in groups and clusters, galaxy evolution as a whole. I will show that dense environments can directly affect the cold molecular gas reservoirs of galaxies, which in turn impacts related properties such as their star formation relations and gas-to-dust ratios. This thesis starts by presenting data from the ALMA Fornax Cluster Survey (AlFoCS). This includes moment maps, position-velocity diagrams, and spectra, as well as several integrated properties. All low-mass galaxies in Fornax, comprising roughly half the sample, have disturbed molecular gas reservoirs. With the exception of the massive spiral NGC1365, galaxies in the Fornax cluster have systematically lower molecular gas fractions than field galaxies at fixed stellar mass. Therefore, the Fornax cluster is (still) an active environment, that directly impacts even the tightly bound molecular gas in its galaxies. Using H_alpha observations from MUSE, the star formation relation in the Fornax cluster is calculated, and compared to those found by Kennicutt98 and Bigiel+08. The star formation relation in Fornax is close to these "classic" relations, albeit closer to their low-depletion time sides. There is, however, large scatter both between different galaxies and within them. The slightly decreased depletion times could be due to the compression of the molecular gas as a result of environmental effects as galaxies enter the cluster for the first time (e.g. ram pressure stripping). Finally, I study gas-to-dust (H_2-to-dust, HI-to-dust, and total gas-to-dust) ratios in the Fornax cluster, using additional observations from Herschel and ATCA. These ratios are studied both as a function of stellar mass, and of metallicity, estimated from the MUSE data. Gas-to-dust ratios in the Fornax cluster are systematically suppressed. This is both driven by decreased HI-to-dust ratios as well as decreased H_2-to-dust ratios. H_2-to-dust ratios in the Virgo cluster, on the other hand, are found to be increased. The low H_2-to-dust ratios in Fornax could be due to the accumulated production of dust during the star formation process, while H_2 is slowly depleted and not replenished as efficiently. Alternatively, H_2 could be stripped from these galaxies more efficiently than dust, or the ISM in Fornax galaxies could be different in such a way that we are not probing the gas and/or dust reservoirs accurately. The surprising difference with the more massive and dynamically active Virgo cluster suggests that different kinds of dense environments affect galaxies differently. In summary, in this thesis I will show some of the ways in which molecular gas is affected by environment, as well as the implications for related properties. I will conclude with some remaining puzzles, and how these can be solved with next-generation instruments.

Item Type: Thesis (PhD)
Date Type: Completion
Status: Unpublished
Schools: Physics and Astronomy
Subjects: Q Science > QB Astronomy
Uncontrolled Keywords: astronomy, galaxies, galaxy clusters, molecular gas, submillimeter, galaxy evolution, interstellar medium, cosmic dust
Funders: European Research Council, Cardiff University, School of Physics and Astronomy
Date of First Compliant Deposit: 16 February 2021
Last Modified: 27 Sep 2022 01:27

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