scholarly journals Astrometric observations of water maser sources toward the Galactic Center with VLBI

2021 ◽  
Vol 2145 (1) ◽  
pp. 012011
Author(s):  
D Sakai ◽  
T Oyama ◽  
T Nagayama ◽  
H Kobayashi ◽  
M Honma
Keyword(s):  
Molecular Clouds ◽  
Galactic Center ◽  
Galactic Disk ◽  
Kinematic Model ◽  
Three Dimensional ◽  
Circular Motion ◽  
Proper Motions ◽  
Center Region ◽  
Maser Sources ◽  
Water Maser

Abstract The Central Molecular Zone (CMZ) in the Galactic Center region shows outstanding non-circular motion unlike the Galactic disk. Although several models describing this non-circular motion are proposed, an uniform kinematic model of the CMZ orbit is not appeared. Three dimensional velocity information including proper motions will be critical to constrain the orbital models of the CMZ because most of models proposed are devised to reproduce the line-of-sight velocity pro les of the molecular clouds in this region. To reveal the dynamics of the Galactic center region, we conducted VLBI astrometric observations of 22 GHz water maser sources toward the Galactic center with VERA. By measuring parallaxes and proper motions, we can identify whether each source is actually located in the CMZ or not, and identify the three dimensional positions and velocities in the non-circular orbit if the source is located in the CMZ. We show the results of astrometric study for several maser sources associated with molecular clouds toward the Galactic center including Sgr B2 complex and Sgr D HII region. The parallax measurement toward Sgr B2 obtained the parallax of 0.133 0:038 mas, and its proper motions indicated that Sgr B2 complex is moving toward the positive Galactic longitude with V = 100 km s−1 relative to Sgr A*.

scholarly journals Proper Motions and Distances of Water Maser Complexes

1984 ◽  
Vol 110 ◽  
pp. 335-338
Author(s):  
M. H. Schneps ◽  
M. J. Reid ◽  
J. M. Moran ◽  
R. Genzel ◽  
D. Downes ◽  
...  
Keyword(s):  
Spectral Line ◽  
Galactic Center ◽  
Three Dimensional ◽  
Proper Motions ◽  
Preliminary Results ◽  
First Results ◽  
Maser Sources ◽  
Water Maser

We report preliminary results of a long term spectral line VLBI experiment to observe internal proper motions of water maser sources in the vicinity of newly formed stars. This technique yields a picture of the three-dimensional kinematics of the region and a measure of the distance to the source. First results from the galactic center source SGR B2 are presented.

scholarly journals Molecular Line Observations of the Galactic Center Region

1989 ◽  
Vol 136 ◽  
pp. 129-133 ◽  
Author(s):  
A. A. Stark ◽  
J. Bally ◽  
R. W. Wilson ◽  
M. W. Pound
Keyword(s):  
Molecular Clouds ◽  
Virial Theorem ◽  
Galactic Center ◽  
Galactic Disk ◽  
High Mass ◽  
Molecular Gas ◽  
Molecular Line ◽  
Center Region ◽  
The Galaxy ◽  
Cloud Medium

A decade of galactic center observations at the Crawford Hill 7 m antenna is summarized. The galactic center region contains several hundred high-mass, high-density molecular clouds with physical properties very different from clouds in the outer galactic disk. There is also a considerable amount of molecular gas not bound into clouds, but sheared by differential rotation into a molecular inter-cloud medium not seen elsewhere in the Galaxy. These observations can be explained by a combination of the tidal density limit and the virial theorem. The distribution of emission on the sky and in velocity suggests that most of the dense gas is confined to a 500 pc long ridge of emission which may be a dust lane along the central bar.

scholarly journals CO and OH in the Galactic Center Region

1980 ◽  
Vol 87 ◽  
pp. 111-112
Author(s):  
Junji Inatani ◽  
Nobuharu Ukita
Keyword(s):  
Emission Line ◽  
Intensity Ratio ◽  
Molecular Clouds ◽  
Galactic Center ◽  
Point Of View ◽  
The Other ◽  
Kinetic Temperature ◽  
Two Dimensional ◽  
Center Region ◽  
Dimensional Distribution

The two-dimensional distribution of molecular clouds in the galactic center region has been investigated in the CO 115 GHz line and in the OH 1665 and 1667 MHz lines. As the former is an emission line, we can find molecular clouds without the unavoidable bias to continuum sources which is inherent in a survey of OH absorption lines. Because the CO line is usually optically thick, the brightness temperature of the line is directly related to the kinetic temperature of the cloud. On the other hand, the real optical depth of the OH line can be obtained from the intensity ratio between 1665 and 1667 MHz lines (assuming LTE). From this point of view we have compared the CO and OH observational results.

scholarly journals The geometry of the magnetic field in the central molecular zone measured by PILOT

2019 ◽  
Vol 630 ◽  
pp. A74 ◽  
Author(s):  
A. Mangilli ◽  
J. Aumont ◽  
J.-Ph. Bernard ◽  
A. Buzzelli ◽  
G. de Gasperis ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Molecular Clouds ◽  
Angular Resolution ◽  
Galactic Center ◽  
Galactic Plane ◽  
Mean Field ◽  
Field Orientation ◽  
Center Region ◽  
The Mean ◽  
The Magnetic Field

We present the first far infrared (FIR) dust emission polarization map covering the full extent of Milky Way’s central molecular zone (CMZ). The data, obtained with the PILOT balloon-borne experiment, covers the Galactic center region − 2° < ℓ < 2°, − 4° < b < 3° at a wavelength of 240 μm and an angular resolution of 2.2′. From our measured dust polarization angles, we infer a magnetic field orientation projected onto the plane of the sky (POS) that is remarkably ordered over the full extent of the CMZ, with an average tilt angle of ≃22° clockwise with respect to the Galactic plane. Our results confirm previous claims that the field traced by dust polarized emission is oriented nearly orthogonally to the field traced by GHz radio synchrotron emission in the Galactic center region. The observed field structure is globally compatible with the latest Planck polarization data at 353 and 217 GHz. Upon subtraction of the extended emission in our data, the mean field orientation that we obtain shows good agreement with the mean field orientation measured at higher angular resolution by the JCMT within the 20 and 50 km s−1 molecular clouds. We find no evidence that the magnetic field orientation is related to the 100 pc twisted ring structure within the CMZ. The low polarization fraction in the Galactic center region measured with Planck at 353 GHz combined with a highly ordered projected field orientation is unusual. This feature actually extends to the whole inner Galactic plane. We propose that it could be caused by the increased number of turbulent cells for the long lines of sight towards the inner Galactic plane or to dust properties specific to the inner regions of the Galaxy. Assuming equipartition between magnetic pressure and ram pressure, we obtain magnetic field strength estimates of the order of 1 mG for several CMZ molecular clouds.

scholarly journals Protostellar Outflows at the EarliesT Stages (POETS)

2020 ◽  
Vol 635 ◽  
pp. A118
Author(s):  
L. Moscadelli ◽  
A. Sanna ◽  
C. Goddi ◽  
V. Krishnan ◽  
F. Massi ◽  
...  
Keyword(s):  
Thermal Emission ◽  
Three Dimensional ◽  
Radio Continuum ◽  
Young Stellar Objects ◽  
High Mass ◽  
Proper Motions ◽  
Long Baseline ◽  
Protostellar Outflows ◽  
Water Masers ◽  
Water Maser

Context. 22 GHz water masers are the most intense and widespread masers in star-forming regions. They are commonly associated with protostellar winds and jets emerging from low- and high-mass young stellar objects (YSO). Aims. We wish to perform for the first time a statistical study of the location and motion of individual water maser cloudlets, characterized by typical sizes that are within a few au, with respect to the weak radio thermal emission from YSOs. Methods. For this purpose, we have been carrying out the Protostellar Outflows at the EarliesT Stages survey of a sample (38) of high-mass YSOs. The 22 GHz water maser positions and three-dimensional (3D) velocities were determined through multi-epoch Very Long Baseline Array observations with accuracies of a few milliarcsec (mas) and a few km s−1, respectively. The position of the ionized core of the protostellar wind, marking the YSO, was determined through sensitive radio continuum, multi-frequency Jansky Very Large Array observations with a typical error of ≈20 mas. Results. The statistic of the separation of the water masers from the radio continuum shows that 84% of the masers are found within 1000 au from the YSO and 45% of them are within 200 au. Therefore, we can conclude that the 22 GHz water masers are a reliable proxy for locating the position of the YSO. The distribution of maser luminosity is strongly peaked towards low values, indicating that about half of the maser population is still undetected with the current Very Long Baseline Interferometry detection thresholds of 50–100 mJy beam−1. Next-generation, sensitive (at the nJy level) radio interferometers will have the capability to exploit these weak masers for an improved sampling of the velocity and magnetic fields around the YSOs. The average direction of the water maser proper motions provides a statistically-significant estimate for the orientation of the jet emitted by the YSO: 55% of the maser proper motions are directed on the sky within an angle of 30° from the jet axis. Finally, we show that our measurements of 3D maser velocities statistically support models in which water maser emission arises from planar shocks with propagation direction close to the plane of the sky.

scholarly journals Disk-Halo interaction: The molecular clouds in the Galactic center region

2012 ◽  
Vol 372 ◽  
pp. 012027 ◽  
Author(s):  
D Riquelme ◽  
J Martín-Pintado ◽  
R Mauersberger ◽  
M A Amo-Baladrón ◽  
S Martín ◽  
...  
Keyword(s):  
Molecular Clouds ◽  
Galactic Center ◽  
Center Region

scholarly journals Supernova OH (1720 MHz) masers in Sgr A East, W28 and G359.1-0.5

2002 ◽  
Vol 206 ◽  
pp. 212-216
Author(s):  
F. Yusef-Zadeh ◽  
D.A. Roberts ◽  
Geoff Bower ◽  
M. Wardle ◽  
W.M. Goss
Keyword(s):  
Linear Polarization ◽  
Molecular Clouds ◽  
Supernova Remnants ◽  
Galactic Center ◽  
Main Line ◽  
Maser Emission ◽  
New Class ◽  
Sgr A ◽  
Maser Sources

A new class of OH (1720 MHz) masers unaccompanied by main-line transitions have recently been discovered (Frail, Goss and Slysh 1994). These masers lie at the interface between supernova remnants (SNRs) interacting with molecular clouds. We discuss three new aspects of SN masers found in the direction toward the Galactic center: (i) the detection of a new −130 kms−1 OH (1720 MHz) maser in the southern lobe of the molecular ring at the Galactic center: (ii) the detection of extended OH (1720 MHz) maser emission from W28 accompanying the compact maser sources and (iii) the detection of linear polarization of the brightest OH (1720 MHz) maser in SNR G359.1-0.5.

scholarly journals Molecular Clouds in the Central 100-pc of the Galactic Center

1989 ◽  
Vol 136 ◽  
pp. 135-140 ◽  
Author(s):  
M. Tsuboi ◽  
T. Handa ◽  
M. Inoue ◽  
J. Inatani ◽  
N. Ukita
Keyword(s):  
Molecular Clouds ◽  
Large Scale ◽  
Galactic Center ◽  
Galactic Latitude ◽  
Center Region ◽  
Elliptical Shape ◽  
Latitude Region ◽  
Galactic Longitude

We have observed CS (J=1–0/2–1) lines in a 60′×30′(1×b) area of the Galactic center region. There are two large-scale features with elliptical shape in the position–velocity maps, which suggest shell–like structures in the region. One is the ring with a radius of ~40 pc in the positive galactic latitude region and another is the shell with a radius of ~20 pc in the negative galactic longitude region. These could be due to suggest star bursts occurred in the Galactic center region.

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