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GC-1 and GC-2 are two globular clusters (GCs) in the remote halo of M81 andM82 in the M81 group discovered by Jang et al. using the {\it Hubble SpaceTelescope} ({\it HST}) images. These two GCs were observed as part of theBeijing--Arizona--Taiwan--Connecticut (BATC) Multicolor Sky Survey, using 14intermediate-band filters covering a wavelength range of 4000--10000 \AA. Weaccurately determine these two clusters' ages and masses by comparing theirspectral energy distributions (from 2267 to 20000~{\AA}, comprising photometricdata in the near-ultraviolet of the {\it Galaxy Evolution Explorer}, 14 BATCintermediate-band, and Two Micron All Sky Survey near-infrared $JHK_{\rm s}$filters) with theoretical stellar population-synthesis models, resulting inages of $15.50\pm3.20$ for GC-1 and $15.10\pm2.70$ Gyr for GC-2. The masses ofGC-1 and GC-2 obtained here are $1.77-2.04\times 10^6$ and $5.20-7.11\times10^6 \rm~M_\odot$, respectively. In addition, the deep observations with theAdvanced Camera for Surveys and Wide Field Camera 3 on the {\it HST} are usedto provide the surface brightness profiles of GC-1 and GC-2. The structural anddynamical parameters are derived from fitting the profiles to three differentmodels; in particular, the internal velocity dispersions of GC-1 and GC-2 arederived, which can be compared with ones obtained based on spectralobservations in the future. For the first time, in this paper, the $r_h$ versus$M_V$ diagram shows that GC-2 is an ultra-compact dwarf in the M81 group.

Ages and structural and dynamical parameters of two globular clusters in the M81 group