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http://hdl.handle.net/11375/29267
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DC Field | Value | Language |
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dc.contributor.advisor | Wilson, Christine | - |
dc.contributor.author | He, Hao | - |
dc.date.accessioned | 2023-12-08T20:27:47Z | - |
dc.date.available | 2023-12-08T20:27:47Z | - |
dc.date.issued | 2023 | - |
dc.identifier.uri | http://hdl.handle.net/11375/29267 | - |
dc.description.abstract | In this thesis, I aim to understand the interplay between giant molecular clouds (GMCs) and star formation in nearby starburst galaxy mergers. I start with a case study on the unique star formation products, young massive clusters (YMCs), in a typical starburst galaxy merger, the Antennae. Based on the Atacama Large Millimeter/submillimeter Array (ALMA) radio continuum data, I identify 6 potential YMCs in the Antennae overlap region. I further perform virial analyses on these YMCs combining the radio continuum data and archival CO 2-1 data and confirm these radio sources are bound structures that are likely to be future star clusters. I also cross match our detected YMCs with optical clusters identified using Hubble Space Telescope (HST) data and find a good correspondence in the number of produced total ionizing photon, but a significant position offsets between these two types of objects, which suggests these radio detected YMCs are going through an emerging stage out of GMCs. I further compare the YMC stellar mass and gas mass with GMC-scale properties and find more than 50% of GMC star formation happens in these YMCs, with more massive GMCs tending to produce more massive YMCs. Overall, my study provides a rare sample of embedded YMCs and points out the close connection between GMC properties and YMC formation. I then approach the open question of the interplay between GMCs and star formation from the molecular gas side by quantifying GMC dynamical states and correlating these GMC quantities with star formation rate (SFR). In this study I perform a comparison between the observed galaxy mergers from the ALMA telescope and the simulated mergers from the idealized Feedback In Realistic Environment (FIRE) simulation. I find that GMCs in the simulated mergers before the merging event are similar to the observed GMCs in normal spiral galaxies, which suggests the success in the simulation to reproduce realistic GMCs. After the merging, GMCs become denser, more turbulent and less gravitationally bound. I measure the virial parameter of the simulated GMCs and find that the virial parameter variation is similar to the star formation rate (SFR) variation, which suggests that starburst events are responsible for dispersing GMCs and making them less gravitationally bound. I also correlate GMC virial parameter with gas depletion time, which indicates how fast the star formation activity is using up all the available gas, and find no correlation between these two quantities. Our results suggest that star formation activities are more complicated than what we thought and large-scale environmental factors might be responsible for regulating star formation activities in starburst mergers. I then constrain GMC physical properties from the observational side by applying RADEX modeling to multiple CO and 13CO observational data. Specifically, I aim to constrain the CO-to-H2 conversion factor (αCO) that is crucial for measuring GMC surface density and virial parameter. I find that αCO values in the Antennae are ~4 times smaller than that of the Milky Way, and hence GMCs in the Antennae are less gravitationally bound than normal spiral galaxies, which is consistent with the prediction of my previous simulation project. I further correlate αCO with multiple physical quantities and observables and find strong correlations between αCO and CO 1-0 intensity, optical depth, 13CO/CO ratio, velocity dispersion and virial parameter. Compared with literature studies, I confirm that the low αCO in starburst systems is caused by low optical depth due to GMCs out of virial equilibrium. My study also provides potential calibration tools to measure αCO spatial variation within individual galaxies. These projects provide a starting point for us to understand the molecular gas and star formation in the most extreme starburst environments. It is crucial to expand analyses of individual galaxies in these projects to a broader, more statistically significant sample to understand the universal physics that regulates star formation activities in these systems. | en_US |
dc.language.iso | en | en_US |
dc.title | Molecular Gas and Star Formation in Nearby Starburst Galaxy Mergers | en_US |
dc.type | Thesis | en_US |
dc.contributor.department | Physics and Astronomy | en_US |
dc.description.degreetype | Dissertation | en_US |
dc.description.degree | Doctor of Science (PhD) | en_US |
Appears in Collections: | Open Access Dissertations and Theses |
Files in This Item:
File | Description | Size | Format | |
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thesis_PhD.pdf | 9.75 MB | Adobe PDF | View/Open |
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