Troy Porter
Stanford University
Geometry, Not Calorimetry, Drives the Radio-Infrared-Gamma-ray Correlation
I will talk about our recent results on the radio-infrared-γ-ray correlation observed in star-forming galaxies. This well-established correlation is a tracer of the production of cosmic rays within galaxies, but its persistence across different galaxy types (spirals, irregulars) and spatial scales remains an open question. Scenarios where various factors, including cosmic ray injection and transport, magnetic field amplification, and gas density are coupled in a self-regulating manner to maintain the correlation across diverse environments. We test an alternative, that it is instead driven mainly by viewing geometry rather than local cosmic-ray calorimetry. Using synthetic observations of Milky Way-like models, I will show that a tight, near-linear relation can arise from line-of-sight integration through a structured disc, but can weaken for edge-on views. Our conclusion is that the correlation is largely geometric in origin, and that its scatter may diagnose galaxy structure and viewing angle.