# d1005+68: A New Faint Dwarf Galaxy in the M81 Group

## TL;DR

The paper reports the discovery of d1005+68, a faint dwarf galaxy in the M81 Group, characterized by its size, luminosity, and potential satellite-of-a-satellite status, expanding knowledge of satellite galaxy populations.

## Contribution

This is the first identification of a faint dwarf galaxy that may be a satellite of a satellite outside the Local Group, using Subaru Hyper Suprime-Cam observations.

## Key findings

- d1005+68 is among the faintest confirmed satellites outside the Local Group.
- It has a half-light radius of approximately 188 pc and an absolute magnitude of about -7.94.
- d1005+68 may be a satellite of the nearby M81 satellite BK5N.

## Abstract

We present the discovery of d1005+68, a new faint dwarf galaxy in the M81 Group, using observations taken with the Subaru Hyper Suprime-Cam. d1005+68's color-magnitude diagram is consistent with a distance of $3.98_{-0.43}^{+0.39}$ Mpc, establishing group membership. We derive an absolute $V$-band magnitude, from stellar isochrone fitting, of $M_{V} = -7.94_{-0.50}^{+0.38}$, with a half-light radius of $r_{h} = 188_{-41}^{+39}$ pc. These place d1005+68 within the radius-luminosity locus of Local Group and M81 satellites and among the faintest confirmed satellites outside the Local Group. Assuming an age of 12 Gyr, d1005+68's red giant branch is best fit by an isochrone of [Fe/H] $= -1.90 \pm 0.24$. It has a projected separation from nearby M81 satellite BK5N of only 5 kpc. As this is well within BK5N's virial radius, we speculate that d1005+68 may be a satellite of BK5N. If confirmed, this would make d1005+68 one of the first detected satellites-of-a-satellite.