Hauyu Baobab Liu

MILKY WAY SUPERMASSIVE BLACK HOLE: DYNAMICAL FEEDING FROM THE CIRCUMNUCLEAR ENVIRONMENT

The supermassive black hole (SMBH), Sgr A*, at the Galactic center is surrounded by a molecular circumnuclear disk (CND) lying between 1.5 and 4 pc radii. The irregular and clumpy structures of the CND suggest dynamical evolution and episodic feeding of gas toward the central SMBH. New sensitive data from the Submillimeter Array and Green Bank Telescope reveal several >5-10 pc scale molecular arms, which either directly connect to the CND or may penetrate inside the CND. The CND appears to be the convergence of the innermost parts of large-scale gas streamers, which are responding to the central gravitational potential well. Rather than being a quasi-stationary structure, the CND may be dynamically evolving, incorporating inflow via streamers, and feeding gas toward the center.

FRAGMENTATION AND OB STAR FORMATION IN HIGH-MASS MOLECULAR HUB-FILAMENT SYSTEMS

Filamentary structures are ubiquitously seen in the interstellar medium. The concentrated molecular mass in the filaments allows fragmentation to occur in a shorter timescale than the timescale of the global collapse. Such hierarchical fragmentation may further assist the dissipation of excessive angular momentum. It is crucial to resolve the morphology and the internal velocity structures of the molecular filaments observationally. We perform 05-25 angular resolution interferometric observations toward the nearly face-on OB cluster-forming region G33.92+0.11. Observations of various spectral lines, as well as the millimeter dust continuum emission, consistently trace several ~1?pc scale, clumpy molecular arms. Some of the molecular arms geometrically merge to an inner 3.0 + 2.8 ? 1.4 ? 103 M ?, 0.6?pc scale central molecular clump, and may directly channel the molecular gas to the warm (~50?K) molecular gas immediately surrounding the centrally embedded OB stars. The NH3 spectra suggest a medium turbulence line width of FWHM 2?km?s?1 in the central molecular clump, implying a 10?times larger molecular mass than the virial mass. Feedbacks from shocks and the centrally embedded OB stars and localized (proto)stellar clusters likely play a key role in the heating of molecular gas and could lead to the observed chemical stratification. Although (proto)stellar feedbacks are already present, G33.92+0.11 chemically appears to be at an early evolutionary stage given by the low abundance limit of SO2 observed in this region.

THE ORIGIN OF OB CLUSTERS: FROM 10 pc TO 0.1 pc

We observe the 1.2 mm continuum emission around the OB cluster-forming region G10.6-0.4, using the MAMBO-2 bolometer array of the IRAM 30 m telescope and the Submillimeter Array (SMA). Comparison of the Spitzer 24 μm and 8 μm images with our 1.2 mm continuum maps reveal an ionization front of an H II region, the photon-dominated layer, and several 5 pc scale filaments that follow the outer edge of the photon-dominated layer. The filaments, which are resolved in the MAMBO-2 observations, show regularly spaced parsec-scale molecular clumps, embedded with a cluster of dense molecular cores as shown in the SMA 0.87 mm observations. Toward the center of the G10.6-0.4 region, the combined SMA+IRAM 30 m continuum image reveals several parsec-scale protrusions. They may continue down to within 0.1 pc of the geometric center of a dense 3 pc scale structure, where a 200 M ☉ OB cluster resides. The observed filaments may facilitate mass accretion onto the central cluster-forming region in the presence of strong radiative and mechanical stellar feedback. Their filamentary geometry may also facilitate fragmentation. We did not detect any significant polarized emission at 0.87 mm in the inner 1 pc region with SMA.

THE HIGH-VELOCITY MOLECULAR OUTFLOWS IN MASSIVE CLUSTER-FORMING REGION G10.6-0.4

We report the arcsecond resolution Submillimeter Array observations of the {sup 12}CO (2-1) transition in the massive cluster-forming region G10.6-0.4. In these observations, the high-velocity {sup 12}CO emission is resolved into individual outflow systems, which have a typical size scale of a few arcseconds. These molecular outflows are energetic and are interacting with the ambient molecular gas. By inspecting the shock signatures traced by CH{sub 3}OH, SiO, and HCN emissions, we suggest that abundant star formation activities are distributed over the entire 0.5 pc scale dense molecular envelope. The star formation efficiency over one global free-fall timescale (of the 0.5 pc molecular envelope, {approx}10{sup 5} years) is about a few percent. The total energy feedback of these high-velocity outflows is higher than 10{sup 47} erg, which is comparable to the total kinetic energy in the rotational motion of the dense molecular envelope. From order-of-magnitude estimations, we suggest that the energy injected from the protostellar outflows is capable of balancing the turbulent energy dissipation. No high-velocity bipolar molecular outflow associated with the central OB cluster is directly detected, which can be due to the photoionization.

AN OVERALL PICTURE OF THE GAS FLOW IN A MASSIVE CLUSTER-FORMING REGION: THE CASE OF G10.6–0.4

The massive clump G10.6-0.4 is an OB cluster forming region, in which multiple UC HII regions have been identified. In the present study, we report arcsecond resolution observations of the CS (1-0) transition, the NH

ALMA Resolves the Spiraling Accretion Flow in the Luminous OB Cluster-forming Region G33.92+0.11

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Signatures of Gravitational Instability in Resolved Images of Protostellar Disks

(3,3) main hyperfine inversion transition, the CH

Comparing Young Massive Clusters and their Progenitor Clouds in the Milky Way

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Circumstellar disks of the most vigorously accreting young stars

OH J=5 transitions, and the centimeter free-free continuum emissions in this region. The comparisons of the molecular line emissions with the free--free continuum emissions reveal a 0.5 pc scale massive molecular envelope which is being partially dispersed by the dynamically-expanding bipolar ionized cavity. The massive envelope is rotationally flattened and has an enhanced molecular density in the mid-plane. In the center of this massive clump lies a compact (

WHAT IS CONTROLLING THE FRAGMENTATION IN THE INFRARED DARK CLOUD G14.225–0.506?: DIFFERENT LEVELS OF FRAGMENTATION IN TWIN HUBS

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