Star Formation in Extreme Environments

Abstract

This thesis investigates the gas content and star formation in a sample of 12 luminous and 4 ultra-luminous infrared galaxies (U/LIRGs). The primary aim is to analyze the relationship between those two properties to illuminate the physics driving star formation in these extreme environments. This is done through archival band 3 (84-116 GHz) Atacama Large Millimeter/submillimeter Array (ALMA) data. The tracers applied in this work are free-free radio continuum emission at 110 GHz for star formation rate surface density, CO (J=1-0) for bulk molecular gas surface density, and CN (N=1-0) for dense molecular gas surface density. Radio continuum images for each galaxy were created using Common Astronomy Software Applications (CASA) software package with the PHANGS-ALMA pipeline. Peaks in star formation efficiency for both bulk and dense gas align well with each other and with peaks in radio continuum emission. The galaxy NGC 3256 is highlighted as the main exception, where the locations of the peaks differ. The gas content displays a continuous distribution from spiral to U/LIRG data for both bulk and dense molecular gas surface density, and the dense gas fraction is significantly higher in the U/LIRGs. A Kennicutt-Schmidt (KS) plot reveals a fairly shallow slope, nearly the same as what is seen in spirals, and a dense gas KS relation appears to have a tighter correlation than the bulk gas. This work finds gas depletion times as short as 10-100 Myr, compared to 0.3-3 Gyr for spiral data. This thesis also discusses potential sources of error such as using a single pair of conversion factors from molecular line intensities to gas surface density or contamination from an active galactic nucleus. These results from a substantial sample of 16 extreme galaxies offer valuable insights into the mechanisms driving star formation and potential for future research.