KDG 218, a Nearby Ultra-Diffuse Galaxy

Abstract

We present properties of the low-surface-brightness galaxy KDG 218 observed with the HST/ACS. The galaxy has a half-light (effective) diameter of $a_e=47^{\prime \prime }$ and a central surface brightness of $S{B}_V(0)=24.4^m/s{q}^{\prime \prime }$. The galaxy remains unresolved with the HST/ACS, which implies its distance of {$D>13.1$ Mpc} and linear effective diameter of $A_e>3.0$ kpc. We notice that KDG 218 is most likely associated with a galaxy group around the massive lenticular NGC 4958 galaxy at approximately $22$ Mpc, or with the Virgo Southern Extension filament at approximately $16.5$ Mpc. At these distances, the galaxy is classified as an ultra-diffuse galaxy (UDG) similar to those found in the Virgo, Fornax, and Coma clusters. We also present a sample of 15 UDG candidates in the Local Volume. These sample galaxies have the following mean parameters: $⟨D⟩=5.1$ Mpc, $⟨A_e⟩=4.8$ kpc, and $⟨S{B}_B(e)⟩=27.4^m/s{q}^{\prime \prime }$. All the local UDG candidates reside near massive galaxies located in the regions with the mean stellar mass density (within 1 Mpc) about 50 times greater than the average cosmic density. The local fraction of UDGs does not exceed 1.5% of the Local Volume population. We notice that the presented sample of local UDGs is a heterogeneous one containing irregular, transition, and tidal types, as well as objects consisting of an old stellar population.

14 pages, 4 figures, 3 tables, published in the Astrophysical Bulletin

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Cited by in corpus (1)

• Keck Spectroscopy of the Coma Cluster Ultra-Diffuse Galaxy Y358: Dynamical Mass in a Wider Context