2020ApJ...893...26S

The physics regulating star formation (SF) in Hickson Compact Groups (HCG) has thus far been difficult to describe, due to their unique kinematic properties. In this study, we expand upon previous works to devise a more physically meaningful SF relation able to better encompass the physics of these unique systems. We combine CO(1-0) data from the Combined Array from Research in Millimeter Astronomy to trace the column density of molecular gas Σ_gas and deep Hα imaging taken on the Southern Astrophysical Research Telescope tracing Σ_SFR to investigate SF efficiency across face-on HCG, NGC 7674. We find a lack of universality in SF, with two distinct sequences present in the Σ_gas-Σ_SFR plane; one for inside and one for outside the nucleus. We devise an SF relation based on the multi-freefall nature of gas and the critical density, which itself is dependent on the virial parameter α_vir, the ratio of turbulent to gravitational energy. We find that our modified SF relation fits the data and describes the physics of this system well with the introduction of a virial parameter of about 5-10 across the galaxy. This α_vir leads to an order-of-magnitude reduction in SFR compared to α_vir~1 systems.