Large-scale stellar age-velocity spiral pattern in NGC 4030

Abstract

The processes driving the formation and evolution of late-type galaxies continue to be a debated subject in extragalactic astronomy. Investigating stellar kinematics, especially when combined with age estimates, provides crucial insights into the formation and subsequent development of galactic discs. Post-processing of exceptionally high-quality integral field spectroscopy data of NGC 4030 acquired with the Multi Unit Spectroscopic Explorer (MUSE) has revealed a striking grand design spiral pattern in the velocity dispersion map, that has not been detected in other galaxies. This pattern spatially correlates with HII regions, suggesting that stars currently being born exhibit lower velocity dispersion as compared to surrounding areas where star-formation is less active. We examined the age-velocity relation (AVR) and propose that its configuration might be shaped by a combination of heating mechanisms, seemingly consistent with findings from recent high-resolution cosmological zoom-in simulations. The complex structure of the uncovered AVR of NGC 4030 supports the hypothesis that stellar populations initially inherit the velocity dispersion σ of the progenitor cold molecular gas, which depends on formation time and galactocentric distance, subsequently experiencing kinematic heating due to cumulative gravitational interactions during their lifetime. While advancing our understanding of the AVR, these findings also offer a new framework for investigating disc heating mechanisms and their role in the evolution of galactic discs.