Synthetic HI observations of spiral structure in the outer disk in galaxies

TL;DR

This paper creates synthetic 21cm velocity maps from hydrodynamical simulations to study spiral structures in the outer regions of galaxy disks, aiding comparison with observations.

Contribution

It introduces a method to generate synthetic velocity maps from simulations focusing on spiral patterns in galaxy outskirts, including complex structures.

Findings

Synthetic maps reveal spiral wave propagation beyond corotation.

Outer disk spiral patterns can be modeled and compared with observations.

Simulations show the presence of complex spiral structures in the gaseous periphery.

Abstract

By means of 3D hydrodynamical simulations, in a separate paper we have discussed the properties of non-axisymmetric density wave trains in the outermost regions of galaxy disks, based on the picture that self-excited global spiral modes in the bright optical stellar disk are accompanied by low-amplitude short trailing wave signals outside corotation; in the gas, such wave trains can penetrate through the outer Lindblad resonance and propagate outwards, forming prominent spiral patterns. In this paper we present the synthetic 21~cm velocity maps expected from simulated models of the outer gaseous disk, focusing on the case when the disk is dominated by a two-armed spiral pattern, but considering also other more complex situations. We discuss some aspects of the spiral pattern in the gaseous periphery of galaxy disks noted in our simulations that might be interesting to compare with specific observed cases.