CO Emission Delineating the Interface between the Milky Way Nuclear Wind Cavity and the Gaseous Disk

Based on the MWISP survey, we study high-z CO emission toward the tangent points, in which the distances of the molecular clouds (MCs) are well determined. In the region of l = 12 degrees-26 degrees and divide b divide less than or similar to 5.degrees 1, a total of 321 MCs with divide z divide greater than or similar to 110 pc are identified, of which nearly 30 extreme high-z MCs (EHMCs at divide z divide greater than or similar to 260 pc) are concentrated in a narrow region of R (GC) similar to 2.6-3.1 kpc. The EHMC concentrations, together with other high-z MCs at R (GC) less than or similar to 2.3-2.6 kpc, constitute molecular crater-wall structures surrounding the edges of the H i voids that are physically associated with the Fermi bubbles. Intriguingly, some large high-z MCs, which lie in the crater walls above and below the Galactic plane, show cometary structures with the head toward the plane, favoring the scenario that the entrained molecular gas moves with the multiphase flows from the plane to the high-z regions. We suggest that the Milky Way nuclear wind has a significant impact on the Galactic gaseous disk. The powerful nuclear wind at similar to 3-6 Myr ago is likely responsible for the observational features: (1) the enhanced CO gas lying in the edges of the H i voids, (2) the deficiency of atomic and molecular gas within R (GC) less than or similar to 3 kpc, (3) the possible connection between the EHMC concentrations and the 3 kpc arm, and (4) the elongated high-z MCs with the tail pointing away from the Galactic plane.