A panoramic view of the Milky Way analogue NGC 891

TL;DR

This study provides the first detailed panoramic view of the stellar halo of NGC 891, revealing complex substructures and a previously undetected thick stellar cocoon, enhancing understanding of spiral galaxy outskirts beyond the Local Group.

Contribution

It offers the first ground-based panoramic imaging of a Milky Way analogue beyond the Local Group, uncovering new stellar structures and substructures in NGC 891.

Findings

Detection of a giant stellar stream looping around NGC 891.

Identification of a large, flat, thick cocoon-like stellar structure.

Revealed complex substructures in the galaxy's outskirts.

Abstract

Recent panoramic observations of the dominant spiral galaxies of the Local Group have revolutionized our view of how these galaxies assemble their mass. However, it remains completely unclear whether the properties of the outer regions of the Local Group large spirals are typical. Here, we present the first panoramic view of a spiral galaxy beyond the Local Group, based on the largest, contiguous, ground-based imaging survey to date resolving the stellar halo of the nearest prime analogue of the Milky Way, NGC 891 (D~10 Mpc). The low surface brightness outskirts of this galaxy are populated by multiple, coherent, and vast substructures over the 90kpc * 90kpc extent of the survey. These include a giant stream, the first to be resolved into stars beyond the Local Group using ground-based facilities, that loops around the parent galaxy up to distances of ~50kpc. The bulge and the disk of the galaxy are found to be surrounded by a previously undetected large, flat and thick cocoon-like stellar structure at vertical and radial distances of up to ~15kpc and ~40kpc respectively.