The Fossil Nuclear Outflow in the Central 30 pc of the Galactic Center

We report a new 1 pc (30″) resolution CS(J=2-1) line map of the central 30 pc of the Galactic center (GC), made with the Nobeyama 45 m telescope. We revisit our previous study of an extraplanar feature called the polar arc (PA), which is a molecular cloud located above SgrA*, with a velocity gradient perpendicular to the galactic plane. We find that the PA can be traced back to the galactic disk. This provides clues to the launching point of the PA, roughly 6 × 10⁶ years ago. Implications of the dynamical timescale of the PA might be related to the Galactic center lobe at parsec scale. Our results suggest that, in the central 30 pc of the GC, the feedback from past explosions could alter the orbital path of molecular gas down to the central tenth of a parsec. In the follow-up work of our new CS(J=2-1) map, we also find that, near systemic velocity, the molecular gas shows an extraplanar hourglass-shaped feature (HG-feature) with a size of ∼13 pc. The latitude-velocity diagrams show that the eastern edge of the HG-feature is associated with an expanding bubble B1, ∼7 pc away from SgrA*. The dynamical timescale of this bubble is ∼3 × 10⁵ years. This bubble is interacting with the 50 km s^-1 cloud. Part of the molecular gas from the 50 km s^-1 cloud was swept away by the bubble to b=-0\buildrel{\circ}\over{.} 2. The western edge of the HG-feature seems to be molecular gas entrained from the 20 km s^-1 cloud toward the north of the galactic disk. Our results suggest a fossil explosion in the central 30 pc of the GC, a few 10⁵ years ago.