IQ_SYSTEM_MAIN is a special dbspace that contains structures necessary for the database to open: the checkpoint log, rollforward/rollback data for each committed transaction and each active checkpointed transaction, the incremental backup metadata, and database space and identity metadata.
The IQ_SYSTEM_MAIN dbspace is created at database creation or when you upgrade an older database to SAP Sybase IQ 16.0. IQ_SYSTEM_MAIN is always online when the database is open.