RSAA Colloquia / Seminars / Feast-of-Facts: Friday, 26 October 2018, 14:00-14:30; Duffield Lecture Theatre

Diane Salim

"Turbulence in Hickson Compact Group NGC7674"

Hickson compact group (HCG) galaxies are a prime experimental ground for learning about star formation (SF) due to their unique kinematic properties. No previously devised SF relations have been able to accurately describe the physics of the observed star formation rate in these HCG systems. In this study we extend on previous works to devise a more physically meaningful SF relation to better encompass the physics of these unique systems. We combine CO(1--0) data from the Combined Array from Research in Millimeter Astronomy (CARMA) to trace the column density of molecular gas Dgas and deep Ha imaging taken on the Southern Astrophysical Research (SOAR) Telescope tracing D_SFR to investigate star formation efficiency across face-on HCG, NGC7674. We find a lack of universality in star formation, with two distinct sequences present in the D_gas-D_SFR plane (also known as the Kennicutt-Schmidt (KS) plane); one for inside and one for outside the nucleus. We devise a SF relation based on the multi-freefall prescription of gas and the critical density, which itself is dependant on the virial parameter a_vir, the ratio of turbulent to gravitational energy. We find that our modified SF relation describes the physics of this system well for a virial parameter of about 5--10 across the galaxy, leading to an order-of-magnitude reduction in SFR compared to a_vir~1 systems.