The Nature of Galactic Spiral Arms

TL;DR

This paper discusses the importance of measuring spiral arm pattern speeds in disc galaxies to understand their nature and influence on galaxy evolution, highlighting the need for advanced observational techniques.

Contribution

It emphasizes the necessity of systematic observations of stellar kinematics and metallicities around spiral arms to test theoretical models.

Findings

Limited observational data on spiral arm pattern speeds.

Theoretical predictions from cosmological simulations are increasingly detailed.

A call for wide-area spectroscopic surveys with large telescopes.

Abstract

Spiral arms are the defining features of broad morphological classes of disc galaxies, but their nature and influence on galaxy evolution is still under debate. A key diagnostic for their nature is the spiral arm pattern speed: the radial profile of the angular rotation rate of spiral features. This profile determines the location and number of dynamical resonances where peculiar motions and azimuthal metallicity fluctuations in stars and gas can manifest; their precise patterns have the potential to support or reject theories of spiral structure. However, limited observations of this type have been carried out so far, despite an increasing number of theoretical predictions emerging from realistic and detailed cosmological simulations. A systematic observational programme focussed on the resolved kinematics and metallicities of stellar populations around galaxy spiral arms is required to confront these predictions. This calls for wide-area multi-object spectrographs on 12m-class telescopes capable of accurately capturing such data across the full coverage of spiral arms in nearby galaxies.