standard background job is running after deleting a user also

Hi Gurus,

in my production system environment i observed below thing.

1)Default standard background jobs were scheduled by earlier basis admin after some days he left and his id also deleted but still some jobs are running with his id and finishing also, how is it possible without having his ID in system?

2) what is the standard procedure to schedule default standard bg jobs in SAP? either from sap* or DDIC or basis admin?

one more question regarding Audit logs:

1)can we activate audit log for selective ids and selective period?

2)if we activate audit log is there any performance issues will come?

Thanks in advance

Venkat