In this paper , we present photometry of 53 globular clusters ( GCs ) in the M31 outer halo , including the GALEX FUV and NUV , SDSS ugriz , 15 intermediate-band filters of BATC , and 2MASS JHK _ { s } bands .
By comparing the multicolour photometry with stellar population synthesis models , we determine the metallicities , ages , and masses for these GCs , aiming to probe the merging/accretion history of M31 .
We find no clear trend of metallicity and mass with the de-projected radius .
The halo GCs with age younger than \approx 8 Gyr are mostly located at the de-projected radii around 100 kpc , but this may be due to a selection effect .
We also find that the halo GCs have consistent metallicities with their spatially-associated substructures , which provides further evidence of the physical association between them .
Both the disk and halo GCs in M31 show a bimodal luminosity distribution .
However , we should emphasize that there are more faint halo GCs which are not being seen in the disk .
The bimodal luminosity function of the halo GCs may reflect different origin or evolution environment in their original hosts .
The M31 halo GCs includes one intermediate metallicity group ( -1.5 < [ Fe/H ] < -0.4 ) and one metal-poor group ( [ Fe/H ] < -1.5 ) , while the disk GCs have one metal-rich group more .
There are considerable differences between the halo GCs in M31 and the Milky Way ( MW ) .
The total number of M31 GCs is approximately three times more numerous than that of the MW , however , M31 has about six times the number of halo GCs in the MW .
Compared to M31 halo GCs , the Galactic halo ones are mostly metal-poor .
Both the numerous halo GCs and the higher-metallicity component are suggestive of an active merger history of M31 .