  We present ultraviolet (UV) photometry of M31 globular clusters (GCs) found
in 23 Galaxy Evolution Explorer (GALEX) images covering the entirety of M31. We
detect 485 and 273 GCs (and GC candidates) in the near-ultraviolet (NUV; 2267
A) and far-ultraviolet (FUV; 1516 A), respectively. Comparing M31 data with
those of Galactic GCs in the UV with the aid of population models, we find that
the age ranges of old GCs in M31 and the Galactic halo are similar. Three
metal-rich ([Fe/H]>-1) GCs in M31 produce significant FUV flux making their
FUV-V colors unusually blue for their metallicities. These are thought to be
analogs of the two peculiar Galactic GCs NGC 6388 and NGC 6441 with extended
blue HB stars. Based on the models incorporating helium enriched subpopulations
in addition to the majority of the population that have a normal helium
abundance, we suggest that even small fraction of super-helium-rich
subpopulations in GCs can reproduce the observed UV bright metal-rich GCs.
Young clusters in M31 show distinct UV and optical properties from GCs in Milky
Way. Population models indicate that their typical age is less than ~ 2 Gyrs. A
large fraction of young GCs have the kinematics of the thin, rapidly rotating
disk component. However, a subset of the old GCs also shares the thin-disk
kinematics of the younger clusters. The existence of young GCs on the outskirts
of M31 disk suggests the occurrence of a significant recent star formation in
the thin-disk of M31. Old thin-disk GCs may set constraints on the epoch of
early formation of the M31 thin-disk. We detect 12 (10) intermediate-age GC
candidates in NUV (FUV). We suggest that some of spectroscopically identified
intermediate-age GCs may not be truly intermediate in age, but rather older GCs
that possess developed HB.
