Signatures of long-lived spiral patterns

TL;DR

This study identifies multiple signatures of long-lived spiral patterns in galaxies by analyzing azimuthal age/color gradients, surface density maps, and phase angles across different wavebands, confirming their persistence in at least half of the sample.

Contribution

It introduces a method combining stellar mass maps and Fourier analysis to detect signatures of long-lived spiral modes in galaxies, advancing understanding of spiral structure longevity.

Findings

At least 50% of analyzed spirals show signatures of long-lived modes.

Mass maps from optical and near-infrared imaging effectively reveal spiral structure.

Fourier analysis confirms the presence of long-lived spiral signatures.

Abstract

Azimuthal age/color gradients across spiral arms are a signature of long-lived spirals. From a sample of 19 normal (or weakly barred) spirals where we have previously found azimuthal age/color gradient candidates, 13 objects were further selected if a two-armed grand-design pattern survived in a surface density stellar mass map. Mass maps were obtained from optical and near-infrared imaging, by comparing with a Monte Carlo library of stellar population synthesis models that allowed us to obtain the mass-to-light ratio in the J band, (M/L)_J, as a function of (g-i) versus (i-J) color. The selected spirals were analyzed with Fourier methods in search for other signatures of long-lived modes related to the gradients, such as the gradient divergence toward corotation, and the behavior of the phase angle of the two-armed spiral in different wavebands, as expected from theory. The results show additional signatures of long-lived spirals in at least 50% of the objects.