The Void in the Sculptor Group Spiral Galaxy NGC 247

TL;DR

This study investigates a mysterious void in the stellar disk of the dwarf galaxy NGC 247, suggesting it may result from a recent collision with a dark matter sub-halo, based on Hubble data analysis.

Contribution

It provides the first detailed analysis of the void in NGC 247's disk, proposing a novel interaction with a dark sub-halo as its cause.

Findings

Stars inside the void are older than those outside.

The void's long-lived nature suggests a recent dark matter interaction.

Age variation supports the collision hypothesis.

Abstract

The dwarf galaxy NGC 247, located in the Sculptor Filament, displays an apparent void on the north side of its spiral disk. The existence of the void in the disk of this dwarf galaxy has been known for some time, but the exact nature and cause of this strange feature has remained unclear. We investigate the properties of the void in the disk of NGC 247 using photometry of archival Hubble Space Telescope data to analyze the stars in and around this region. Based on a grid of isochrones from log(t)=6.8 to log(t)=10.0, we assign ages using nearest-neighbor interpolation. Examination of the spatial variation of these ages across the galaxy reveals an age difference between stars located inside the void region and stars located outside this region. We speculate that the void in NGC 247's stellar disk may be due to a recent interaction with a nearly dark sub-halo that collided with the disk and could account for the long-lived nature of the void.