  The gas response to a proposed spiral stellar pattern for our Galaxy is
presented here as calculated via 2D hydrodynamic calculations utilizing the
ZEUS code in the disk plane. The locus is that found by Drimmel (2000) from
emission profiles in the K band and at 240 $\mu m$. The self-consistency of the
stellar spiral pattern was studied in previous work (see Martos et al. 2004).
It is a sensitive function of the pattern rotation speed, $\Omega_p$, among
other parameters which include the mass in the spiral and its pitch angle. Here
we further discuss the complex gaseous response found there for plausible
values of $\Omega_p$ in our Galaxy, and argue that its value must be close to
$20 km s^{-1} kpc^{-1}$ from the strong self-consistency criterion and other
recent, independent studies which depend on such parameter. However, other
values of $\Omega_p$ that have been used in the literature are explored to
study the gas response to the stellar (K band) 2-armed pattern. For our best
fit values, the gaseous response to the 2-armed pattern displayed in the K band
is a four-armed pattern with complex features in the interarm regions. This
response resembles the optical arms observed in the Milky Way and other
galaxies with the smooth underlying two-armed pattern of the old stellar disk
populations in our interpretation.
