Grand Design vs. Multi-Armed Spiral Galaxies: Dependence on Galaxy Structure

TL;DR

This study uses citizen science data to classify spiral galaxies and explores how their structural properties relate to spiral arm types, revealing correlations with galaxy mass, bulge type, and morphology.

Contribution

Developed a semi-automatic classification algorithm for spiral arms using Galaxy Zoo 3D data, linking galaxy structure to spiral arm morphology.

Findings

Grand design galaxies have smaller stellar masses than multi-armed galaxies.

Grand design galaxies tend to have larger concentrations and classical bulges.

Star formation rates are similar across arm types when controlling for mass and concentration.

Abstract

We developed an algorithm to use Galaxy Zoo 3D spiral arm masks produced by citizen scientist volunteers to semi-automatically classify spiral galaxies as either multi-armed or grand design spirals. Our final sample consists of 299 multi-armed and 245 grand design galaxies. On average, the grand design galaxies have smaller stellar masses than the multi-armed galaxies. For a given stellar mass, the grand design galaxies have larger concentrations, earlier Hubble types, smaller half-light radii, and larger central surface mass densities than the multi-armed galaxies. Lower mass galaxies of both arm classes have later Hubble types and lower concentrations than higher mass galaxies. In our sample, a higher fraction of grand design galaxies have classical bulges rather than pseudo-bulges, compared to multi-armed galaxies. These results are consistent with theoretical models and simulations which suggest that dense classical bulges support the development and/or longevity of 2-armed spiral patterns. Similar specific star formation rates are found in multi-armed and grand design galaxies with similar stellar masses and concentrations. This implies that the specific star formation rates in spiral galaxies is a function of concentration and stellar mass, but independent of the number of spiral arms. Our classifications are consistent with arm counts from the Galaxy Zoo 2 project and published m=3 Fourier amplitudes.