  The Nobeyama Millimeter Array (NMA) has been used to make aperture synthesis
CO(1-0) observations of the post-starburst galaxy NGC 5195. CO(1-0) and
HCN(1-0) observations of NGC 5195 using the Nobeyama 45 m telescope are also
presented. High-resolution (1".9 x 1".8 or 86 pc x 81 pc at D = 9.3 Mpc) NMA
maps show a strong concentration of CO emission toward the central a few 100 pc
region of NGC 5195, despite the fact that the current massive star formation is
suppressed there. The HCN-to-CO integrated intensity ratio on the brightness
temperature scale, R_{HCN/CO}, is about 0.02 within the central r < 400 pc
region. This R_{HCN/CO} is smaller than those in starburst regions by a factor
of 5 - 15. These molecular gas properties would explain why NGC 5195 is in a
post-starburst phase; most of the dense molecular cores (i.e., the very sites
of massive star formation) have been consumed away by a past starburst event,
and therefore a burst of massive star formation can no longer last, although a
large amount of low density gas still exists. We propose that dense molecular
gas can not be formed from remaining diffuse molecular gas because the
molecular gas in the center of NGC 5195 is too stable to form dense cores via
gravitational instabilities of diffuse molecular gas.
