The systabstats and sysstatistics tables store statistics for all tables, indexes, and any unindexed columns for which you have explicitly created statistics:
systabstats stores information about the table or index as an object, and is updated by query processing, data definition language, and update statistics commands
sysstatistics stores information about the values in a specific column, and is updated by data definition language and update statistics commands
See “Effects of SQL commands on statistics”. For complete information about all system tables, including these, see the Reference Manual: Tables