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INTERSTELLAR MEDIUM PROCESSING IN THE INNER 20 pc IN GALACTIC CENTER
Liu, Hauyu Baobab,Ho, Paul T. P.,Wright, Melvyn C. H.,Su, Yu-Nung,Hsieh, Pei-Ying,Sun, Ai-Lei,Kim, Sungsoo S.,Minh, Young Chol IOP Publishing 2013 The Astrophysical journal Vol.770 No.1
<P>We present the Submillimeter Array 157 pointing mosaic in 0.86 mm dust continuum emission with 5 ''.1 x 4 ''.2 angular resolution, and the National Radio Astronomy Observatory Green Bank 100 m Telescope (GBT) observations of the CS/(CS)-S-34/(CS)-C-13 1-0 and SiO 1-0 emission with <= 20 '' x 18 '' angular resolution. The dust continuum image marginally resolves at least several tens of 10-10(2) M-circle dot dense clumps in the 5' field including the circumnuclear disk (CND) and the exterior gas streamers. There is very good agreement between the high resolution dust continuum map of the CND and all previous molecular line observations. As the dust emission is the most reliable optically thin tracer of the mass, free from most chemical and excitation effects, we demonstrate the reality of the abundant localized structures within the CND, and their connection to external gas structures. From the spectral line data, the velocity dispersions of the dense clumps and their parent molecular clouds are similar to 10-20 times higher than their virial velocity dispersions. This supports the idea that the CND and its immediate environment may not be stationary or stable structures. Some of the dense gas clumps are associated with 22 GHz water masers and 36.2 GHz and 44.1 GHz CH3OH masers. However, we do not find clumps that are bound by the gravity of the enclosed molecular gas. Hence, the CH3OH or H2O maser emission may be due to strong (proto) stellar feedback, which may be dispersing some of the gas clumps.</P>
MILKY WAY SUPERMASSIVE BLACK HOLE: DYNAMICAL FEEDING FROM THE CIRCUMNUCLEAR ENVIRONMENT
Liu, Hauyu Baobab,Hsieh, Pei-Ying,Ho, Paul T. P.,Su, Yu-Nung,Wright, Melvyn,Sun, Ai-Lei,Minh, Young Chol IOP Publishing 2012 The Astrophysical journal Vol.756 No.2
<P>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.</P>
Minh, Young Chol,Liu, Hauyu Baobab,Ho, Paul T. P.,Hsieh, Pei-Ying,Su, Yu-Nung,Kim, Sungsoo S.,Wright, Melvyn IOP Publishing 2013 The Astrophysical journal Vol.773 No.1
<P>Ammonia (3, 3) and (6, 6) transitions have been observed using the Green Bank Telescope toward the Sgr A region. The gas is mainly concentrated in 50 km s(-1) and 20 km s(-1) clouds located in a plane inclined to the galactic plane. These 'main' clouds appear to be virialized and influenced by the expansion of the supernova remnant Sgr A East. The observed emission shows very complicated features in the morphology and velocity structure. Gaussian multi-component fittings of the observed spectra revealed that various 'streaming' gas components exist all over the observed region. These components include those previously known as 'streamers' and 'ridges,' but most of these components appear not to be directly connected to the major gas condensations (the 50 km s(-1) and 20 km s(-1) clouds). They are apparently located out of the galactic plane, and they may have a different origin than the major gas condensations. Some of the streaming components are expected to be sources that feed the circumnuclear disk of our Galactic center directly and episodically. They may also evolve differently than major gas condensations under the influence of the activities of the Galactic center.</P>
Molecular Gas Feeding the Circumnuclear Disk of the Galactic Center
Hsieh, Pei-Ying,Koch, Patrick M.,Ho, Paul T. P.,Kim, Woong-Tae,Tang, Ya-Wen,Wang, Hsiang-Hsu,Yen, Hsi-Wei,Hwang, Chorng-Yuan American Astronomical Society 2017 The Astrophysical journal Vol.847 No.1
<P>The interaction between a supermassive black hole (SMBH) and the surrounding material is of primary importance in modern astrophysics. The detection of the molecular 2 pc circumnuclear disk (CND) immediately around the Milky Way SMBH, SgrA*, provides a unique opportunity to study SMBH accretion at subparsec scales. Our new wide-field CS(J = 2 - 1) map toward the Galactic center (GC) reveals multiple dense molecular streamers that originated from the ambient clouds 20 pc further out, and that are connected to the central 2 pc of the CND. These dense gas streamers appear to carry gas directly toward the nuclear region and might be captured by the central potential. Our phase-plot analysis indicates that these streamers show a signature of rotation and inward radial motion with progressively higher velocities as the gas approaches the CND and finally ends up corotating with the CND. Our results might suggest a possible mechanism of gas feeding the CND from 20 pc around 2 pc in the GC. In this paper, we discuss the morphology and the kinematics of these streamers. As the nearest observable Galactic nucleus, this feeding process may have implications for understanding the processes in extragalactic nuclei.</P>
VLA AMMONIA LINE OBSERVATIONS OF THE YOUNG STELLAR OBJECT IRAS 19550+3248
LEE Ho-GYU,KOO BON-CHUL,PARK YONG-SUN,HO PAUL T. P. The Korean Astronomical Society 2002 Journal of The Korean Astronomical Society Vol.35 No.2
We present the results of VLA $NH_3$ (1,1) and (2,2) line observations of the young-stellar object (YSO) IRAS 19550+3248. The integrated intensity map of the $NH_3$ (1,1) line shows that there are two ammonia cores in this region; core A which is associated with the YSO, and core B which is diffuse and located at the northeast of core A. Core A is compact and elongated along the east-west direction (0.07 pc$\times$0.05 pc) roughly perpendicular to the molecular outflow axis. Core B is diffuse and extended (0.18 pc$\times$0.07 pc). $NH_3$ (2,2) line is detected only toward core A, which indicates that it is hotter (~ 15 K), presumably due to the heating by the YSO. The $NH_3$ (1,1) line toward core A is wide (${\Delta}v{\ge} 3 km s^{-l}$) and appears to have an anomalous intensity ratio of the inner satellite hyperfine lines. The large line width may be attributed to the embedded YSO, but the hyperfine anomaly is difficult to explain. We compare the results of $NH_3$ observations with those of previous CS observations and find that the CS emission is detected only toward core A and is much more extended than the $NH_3$ emission.
MOLECULAR OUTFLOWS AND THE FORMATION PROCESS OF VERY LOW-MASS OBJECTS
PHAN-BAO, NGOC,DANG-DUC, CUONG,LEE, CHIN-FEI,HO, PAUL T.P. The Korean Astronomical Society 2015 天文學論叢 Vol.30 No.2
We present observational results characterizing molecular outflows from very low-mass objects in ${\rho}$ Ophiuchi and Taurus. Our results provide us with important implications that clarify the formation process of very low-mass objects.