Presentation #310.06D in the session Evolution of Galaxies V.
Star-formation is regulated by the physical conditions of the interstellar medium (ISM), where gas cooling, heating, and feedback from stars and supermassive black holes all compete to drive the evolution of galaxies. In this dissertation talk, I study the nature of star-formation from a cold gas perspective using multi-wavelength observations of z=0-2 luminous, infrared (IR) galaxies and supporting simulations. With combined spectroscopy from ALMA, VLA, and Spitzer of far-IR cooling lines, CO(1-0), and Polycylic Aromatic Hydrocarbons (PAHs), I measure physical quantities of the ISM such as the gas heating efficiency at z=0 and z~2. Compact, IR-luminous galaxies at all redshifts exhibit low heating efficiencies and high star-formation efficiencies, linking parsec-scale ISM properties of star-forming regions to the global evolution of the galaxy. Dust grain diagnostics at mid-IR wavelengths reveal the important role played by the PAH size distribution in regulating radiative feedback of stars onto gas. Moreover, there is evidence for unusually low gas heating rates at z~2 which may contribute to the high star-formation rates at early times. Systematic changes in the physics of gas heating and cooling with redshift would support efficiency-driven star-formation in the past, a scenario favored by some high-z molecular gas surveys but not all. I will present ongoing archival research and upcoming programs to statistically test this link between the efficiency of star-formation and gas conditions, and discuss how JWST can be used to push diagnostics of the ISM out to higher redshifts. Finally, I will highlight key areas that simulations can help overcome limiting empirical challenges.