Revealing Gas Inflows towards the Galactic Central Molecular Zone

TL;DR

This study investigates gas inflows into the Galactic Central Molecular Zone, revealing a large-scale CO structure driven by the Galactic bar, with detailed kinematic features and an estimated inflow rate comparable to nuclear wind outflows.

Contribution

It provides new insights into the morphology, kinematics, and mass inflow rate of gas structures feeding the Galactic Center, emphasizing the role of the Galactic bar in driving these inflows.

Findings

Identification of a ~3.1-3.6 kpc long CO structure linked to the Galactic bar.

Estimated gas inflow rate of 0.8-1.4 Msun/yr towards the CMZ.

Determination of the bar's inclination angle and pattern speed.

Abstract

We study the gas inflows towards the Galactic Central Molecular Zone (CMZ) based on the gas morphological and kinematic features from the MWISP in the region of l=1.2 deg--19.0 deg and |b|<3.0 deg. We find that the near dust lane extends to l~15 deg, in which the end of the large-scale gas structure intersects with the 3 kpc-ring at a distance of ~5 kpc. Intriguingly, many filamentary MCs, together with the bow-like/ballistic-like clouds and continuous CO features with notable velocity gradient, are finely outlined along the long structure. These MCs also have relatively large velocity dispersions, indicating the shocked gas generated by local continuous accretion and thus the enhanced turbulence along the entire gas structure. We suggest that the ~3.1--3.6 kpc long CO structure originates from the accretion molecular gas driven by the Galactic bar. The gas near the bar end at the 3 kpc-ring becomes an important reservoir for the large-scale accreting flows inwards to the CMZ through the bar channel. The inclination angle of the bar is estimated to be 20--26 deg, while the pattern speed of the bar is 30--35 km/s. The total mass of the whole gas lane is about (0.9-1.7)x10^7 Msun according to the calculated X_CO=(0.6-1.4)x10^20 cm^-2 (Kkm/s)^-1 from the large-scale CO data and the complementary HI data. The mean gas inflow rate is about 0.8-1.4 Msun/yr, which seems to be comparable to the outflow's rate of the Galactic nuclear winds after applying the updated lower X-factor value above.