We present the detection of a large population of ultra diffuse galaxies ( UDGs ) in two massive galaxy clusters , Abell S1063 at z = 0.348 and Abell 2744 at z = 0.308 , based on F814W and F105W images in the Hubble Frontier Fields Program .
We find 47 and 40 UDGs in Abell S1063 and Abell 2744 , respectively .
Color-magnitude diagrams of the UDGs show that they are mostly located at the faint end of the red sequence .
From the comparison with simple stellar population models , we estimate their stellar mass to range from 10 ^ { 8 } to 10 ^ { 9 } M _ { \odot } .
Radial number density profiles of the UDGs show a turnover or a flattening in the central region at r < 100 kpc .
We estimate the total masses of the UDGs using the galaxy scaling relations .
A majority of the UDGs have total masses , M _ { 200 } = 10 ^ { 10 } to 10 ^ { 11 } ~ { } M _ { \odot } , and only a few of them have total masses , M _ { 200 } = 10 ^ { 11 } to 10 ^ { 12 } ~ { } M _ { \odot } .
The total number of UDGs within the virial radius is estimated to be N ( UDG ) = 770 \pm 114 for Abell S1063 , and N ( UDG ) = 814 \pm 122 for Abell 2744 .
Combining these results with data in the literature , we fit the relation between the total numbers of UDGs and the masses of their host systems for M _ { 200 } > 10 ^ { 13 } M _ { \odot } with a power law , N ( UDG ) = M _ { 200 } ^ { 1.05 \pm 0.09 } .
These results suggest that a majority of the UDGs have a dwarf galaxy origin , while only a small number of the UDGs are massive L _ { * } galaxies that failed to form a normal population of stars .