A pair of leading spiral arms in a luminous infrared galaxy?

TL;DR

This paper reports the discovery of a rare leading spiral arm in a luminous infrared galaxy, using near-infrared imaging and spectroscopy, which could provide new insights into spiral arm formation and galaxy interactions.

Contribution

It presents one of the few convincing cases of leading spiral arms in a galaxy, based on high-quality NIR observations, and discusses implications for galaxy dynamics and dark matter halo relationships.

Findings

Detection of a leading spiral arm in IRAS 18293-3134

Galaxy is strongly star-forming with a minor companion

Suggests larger NIR surveys could find more such cases

Abstract

Leading spiral arms are a rare phenomenon. We present here one of the very few convincing candidates of spiral arms opening counter-intuitively in the same direction as the galaxy disk is rotating. This detection in a luminous IR galaxy (LIRG) IRAS 18293-3134 is based on near infrared (NIR) adaptive optics imaging with the Very Large Telescope and long-slit NIR spectroscopy with the Anglo-Australian Telescope. We discuss the orientation of the galaxy based on imaging and derive rotation curves from both emission and absorption features in the spectrum. The galaxy is strongly star-forming and has a minor companion in a high-velocity encounter. The fact that the arms of IRAS 18293-3134 are not easily traceable from optical images suggests that larger samples of high-quality NIR imaging of interacting systems and LIRGs might uncover further cases of leading arms, placing constraints on spiral arm theories and retrograde encounters, and especially on the relationship between disk masses and dark matter halo masses.