Abstract
Low-mass stars form in dense regions of molecular clouds, where gas and dust collapse under gravity to produce deeply embedded protostars. The properties of these young systems are shaped by the environments in which they form: infalling envelopes, compact warm inner regions, disks, jets, and molecular outflows all influence how material is accreted, redistributed, and processed. These components are closely connected, and their interaction determines how mass, momentum, and energy move through the protostellar system. The complexity of embedded protostars makes it challenging to identify which physical structures are being traced by a given observation. This dissertation aims to deepen our understanding of early low-mass star formation by using molecular line emission to study the physical and chemical structure of embedded protostellar environments.
Molecules are central to this effort because they respond to the conditions of the gas in which they reside. Their emission depends on density, temperature, excitation, opacity, abundance, and dynamical processes such as shocks and outflows. Some molecules are associated with warm or shocked gas, while others trace dense envelope material or chemically distinct cold regions. Isotopologues provide an additional way to separate optical depth effects from the underlying gas structure. By observing molecular emission with radio telescopes such as the Atacama Large Millimeter/submillimeter Array (ALMA), it is possible to connect the spatial and kinematic distribution of molecular tracers to the environments that shape young protostars.
In this dissertation, I employ ALMA molecular line observations to study embedded low-mass protostars across multiple spatial scales, from compact inner-source regions to envelope-scale structures and survey-scale samples. In Chapter 1, I review the process of low-mass star formation and the role of molecular tracers in studying embedded protostellar systems. In Chapter 2, I investigate the Class 0 protostar CARMA-7 using ALMA Band 8 observations of SO2. By comparing SO2 with SiO and CH3CN, I show that SO2 traces warm, kinematically broadened gas near the base of the outflow, distinct from both the high-velocity jet/outflow material traced by SiO and the compact warm dense gas traced by CH3CN. In Chapter 3, I present an analyis of the SMORES survey, using HCO+ and its isotopologues to study envelope-scale molecular emission in five embedded protostellar systems. This work shows how optical depth, isotopologue selection, and deuterium chemistry influence the observed structure of dense gas. In Chapter 4, I place these source-specific studies in the broader context of the COMPASS Large Program, connecting them to survey-scale studies of line-rich spectra, isotopologues, deuteration, and chemical complexity in embedded Class 0/I protostars. Finally, in Chapter 5, I summarize the findings presented in this dissertation and discuss future directions for using molecular tracers to study the physical and chemical evolution of embedded protostellar systems.
