¹²CO-to-¹³CO integrated intensity line ratio (ℛ₁₀) map (left) and overlay of the same in contours on top of an HST ACS F435W filter gray-scale image (right). The ratio decreases from about 40−45 at the northwestern edge down to ~30 along the nuclear dust lane, and ~10–20 at the northeastern, eastern, and western edges. ℛ₁₀ seems to be quite constant along the nuclear dust lane until the ratio steeply increases toward the dust lane in the west. North is up, east to the left, and the beam is shown in the lower right corner of each map. The cross marks the position of the phase center.