Author ORCID Identifier

Date Available


Year of Publication


Degree Name

Doctor of Philosophy (PhD)

Document Type

Doctoral Dissertation


Arts and Sciences


Physics and Astronomy

First Advisor

Renbin Yan


The baryonic cycle, being a fundamental process that shapes the cosmic ecosystem, describes the transformation and migration of baryonic matter in different phases. The warm ionized interstellar medium (ISM), defined as low-density gas that has temperature of the order of 10,000 K, represents an important link of the baryonic cycle and can be produced by a variety of energetic activities in galaxies, such as star formations, active galactic nuclei, and so forth. More importantly, the formation and evolution of the warm ionized gas not only traces the ongoing activities of the galaxies, but also reveals the past evolution of galaxies through its chemical imprint.

Observationally, since the warm ionized gas produces a series of detectable emission lines in the optical that traces the abundances and ionization states of different elements, it has been the main subject of the chemical evolution studies of galaxies. By decoding the emission-line spectra from the ionized gas, we can learn about how different elements are released into the ISM from generations of stars and how they in turn regulate the star-formation activities. Meanwhile, the ionization states of the elements reflect the ionizing energies and feedback mechanisms in galaxies.

However, converting the observed spectra to the properties of the ionized gas is a notoriously difficult task and has a lot of uncertainties. To obtain a better understanding of the physical properties of the warm ionized gas, I studied the emission-line spectra from a large sample of galaxies in Sloan Digital Sky Survey-IV Mapping Nearby Galaxies at Apache Point Observatory (SDSS-IV MaNGA) and computed a large grid of photoionization models to describe the observations. With these data and models, I established a novel multidimensional analysis method of emission-line ratios from the ionized gas. Using this method, I made new discoveries on the ionization mechanisms, spatial distribution, and dynamical evolution of the warm ionized gas. Moreover, I show that the current modeling approach for the warm ionized gas needs to be improved and more realistic treatment of the small-scale structures are vital for correctly interpreting the emission-line spectra. The multidimensional view on the emission-line diagnostics has great potential for future studies on the high-redshift galaxies as well as local interstellar medium.

Digital Object Identifier (DOI)

Funding Information

This study was partially supported by NSF AST-1715898 and NASA grant 80NSSC20K0436 subaward S000353. The work described in this dissertation was partially supported by a grant from the Research Grants Council of the Hong Kong Special Administrative Region, China [Project No: CUHK 14302522].

Funding for the Sloan Digital Sky Survey IV has been provided by the Alfred P. Sloan Foundation, the U.S. Department of Energy Office of Science, and the Participating Institutions. SDSS acknowledges support and resources from the Center for High-Performance Computing at the University of Utah. The SDSS web site is SDSS is managed by the Astrophysical Research Consortium for the Participating Institutions of the SDSS Collaboration including the Brazilian Participation Group, the Carnegie Institution for Science, Carnegie Mellon University, the Chilean Participation Group, the French Participation Group, Harvard-Smithsonian Center for Astrophysics, Instituto de Astrofísica de Canarias, The Johns Hopkins University, Kavli Institute for the Physics and Mathematics of the Universe (IPMU) / University of Tokyo, the Korean Participation Group, Lawrence Berkeley National Laboratory, Leibniz Institut für Astrophysik Potsdam (AIP), Max-Planck-Institut für Astronomie (MPIA Heidelberg), Max-Planck-Institut für Astrophysik (MPA Garching), Max-Planck-Institut für Extraterrestrische Physik (MPE), National Astronomical Observatories of China, New Mexico State University, New York University, University of Notre Dame, Observatório Nacional / MCTI, The Ohio State University, Pennsylvania State University, Shanghai Astronomical Observatory, United Kingdom Participation Group, Universidad Nacional Autónoma de México, University of Arizona, University of Colorado Boulder, University of Oxford, University of Portsmouth, University of Utah, University of Virginia, University of Washington, University of Wisconsin, Vanderbilt University, and Yale University.