ALMA View of the High-velocity-dispersion Compact Cloud CO 0.02–0.02 at the Galactic Center

Abstract

We report the results of observations toward the center of the molecular cloud CO 0.02–0.02 made using the Atacama Large Millimeter/Submillimeter Array. The successfully obtained 1″ resolution images of CO J = 3–2, H13CN J = 4–3, H13CO+ J = 4–3, SiO J = 8–7, CH3OH J K a , K c = 71,7–61,6 A+ lines, and 900 μm continuum show several new features, which have not been identified in previous observations. The dense gas probe (H13CN, SiO, CH3OH) images are dominated by a pair of northeast-southwest elongated filaments, which may be the main body of CO 0.02–0.02. Two striped patterns perpendicular to each other (F1 and F2) and a high-velocity feature (HV), which appear in different velocity ranges, were prominent in the CO image. An emission hole that may represent an expanding feature was found in the F1 velocity range. F2 appeared to align along the western edge of a 20 pc × 13 pc ellipse (the Large Shell) identified in the single-dish CO map. The HV contains eight compact clumps at the positive high-velocity end of the CO emissions. Based on these results, we propose a formation scenario for CO 0.02–0.02; internal explosions of supernovae, external perturbations by the Large Shell, and gravitational acceleration by a less-luminous star cluster have formed CO 0.02–0.02 in its current state.

A Broad Line-width, Compact, Millimeter-bright Molecular Emission Line Source near the Galactic Center

“…These are peculiar clouds characterized by their compact sizes (d  5 pc) and broad velocity widths (ΔV  50 km s −1 ). These have been explained as either material accelerated by supernova explosions, a connecting bridge between colliding clouds, or gas orbiting around invisible massive objects (Oka et al 2014(Oka et al , 2016(Oka et al , 2022Iwata et al 2023). The MUBLO shares some properties with HVCCs, specifically the broad line width, but it is much smaller than the known HVCCs.…”

“…All reported HVCCs have been found with single-dish telescopes and thus are extended over parsec scales, while the MUBLO has a radius smaller than r < 5000 au (r < 0.02 pc). Recent ALMA observations toward two HVCCs detected several unresolved ultracompact clumps with broad velocity width (ΔV ∼ 50 km s −1 ; Takekawa et al 2019;Iwata et al 2023). These differ from the MUBLO in a few observational respects: their line widths are somewhat narrower, they are detected in different lines (CO, CH 3 OH, SiO, HCN), they do not contain compact millimeter continuum sources, and they are surrounded by and connected to extended high-velocity-dispersion gas.…”