Globular Cluster Candidates in NGC 891

TL;DR

This study identifies and characterizes 43 globular cluster candidates in NGC 891 using deep Hubble Space Telescope images, suggesting its globular cluster system is comparable in size to that of the Milky Way.

Contribution

First detailed survey of globular cluster candidates in NGC 891 using HST imaging, providing photometry and structural parameters for these objects.

Findings

43 globular cluster candidates identified

16 high-rank candidates similar to Milky Way clusters

NGC 891's globular cluster system may be nearly as large as the Milky Way's

Abstract

We use deep images taken with the Advanced Camera for Surveys on board the Hubble Space Telescope of the disk galaxy NGC 891, to search for globular cluster candidates. This galaxy has long been considered to be a close analog in size and structure to the Milky Way and is nearly edge-on, facilitating studies of its halo population. These extraplanar ACS images, originally intended to study the halo field-star populations, reach deep enough to reveal even the faintest globular clusters that would be similar to those in the Milky Way. From the three pointings we have identified a total of 43 candidates after culling by object morphology, magnitude, and colour. We present (V,I) photometry for all of these, along with measurements of their effective radius and ellipticity. The 16 highest-rank candidates within the whole sample are found to fall in very much the same regions of parameter space occupied by the classic Milky Way globular clusters. Our provisional conclusion from this survey is that the total globular cluster population in NGC 891 as a whole may be almost as large as that of the Milky Way.