  The Gemini Infrared Multi-Object Spectrograph (GIRMOS) will be a
near-infrared, multi-object, medium spectral resolution, integral field
spectrograph (IFS) for Gemini North Telescope, designed to operate behind the
future Gemini North Adaptive Optics system (GNAO). In addition to a first
ground layer Adaptive Optics (AO) correction in closed loop carried out by
GNAO, each of the four GIRMOS IFSs will independently perform additional
multi-object AO correction in open loop, resulting in an improved image quality
that is critical to achieve top level science requirements. We present the
baseline parameters and simulated performance of GIRMOS obtained by modeling
both the GNAO and GIRMOS AO systems. The image quality requirement for GIRMOS
is that 57% of the energy of an unresolved point-spread function ensquared
within a 0.1 x 0.1 arcsecond at 2.0 {\mu} m. It was established that GIRMOS
will be an order 16 x 16 adaptive optics (AO) system after examining the
tradeoffs between performance, risks and costs. The ensquared energy
requirement will be met in median atmospheric conditions at Maunakea at
30{\deg} from zenith.
