unknown files found in ASM

I have one ASM instance on 11.2.0.3, it has 4 disk groups, each allocated same size, and created same amount data files with same size, but 2 disk groups use 32 GB more space compare to other 2. Checking ASM directory, found following files existing in ASM directory. Do not know how those files have been created. How to find out?

<disk group name>/ASM/DATAFILE
Type      Redund  Striped  Time             Sys  Name
DATAFILE  UNPROT  COARSE   AUG 18 17:00:00  Y    POOL_IX_1.dbf.275.785156109
DATAFILE  UNPROT  COARSE   JUL 09 17:00:00  Y    USG_DATA_LARGE.267.785093697.wakwau.280.788204801
DATAFILE  UNPROT  COARSE   JUL 25 17:00:00  Y    usg_data_rated_event_01crash.dbf.282.789585537

Thanks,

George