The ASCS contains the Message Server and also the Enqueue Server.
There is no specific requirement for the hardware resources provided or suggested for ASCS. That doesn't mean the ASCS should be setup with the least possible configuration as the Enqueue is part of the ASCS you need a significant amount of memory. Have a look at this SAP note and the attached PDF about what it ssys about the ASCS.
1612283 - Hardware Configuration Standards and Guidance
Regards
RB