scholarly journals Hat Creek HCO+ and HCN Observations of Sgr A

1989 ◽  
Vol 136 ◽  
pp. 407-410
Author(s):  
M.C.H. Wright ◽  
J. M. Marr ◽  
D. C. Backer
Keyword(s):  
Surface Density ◽  
Filling Factor ◽  
Galactic Center ◽  
Radio Continuum ◽  
Line Of Sight ◽  
Excitation Temperature ◽  
The Galaxy ◽  
Molecular Lines ◽  
Sgr A ◽  
Absorption Features

We report aperture synthesis observations of the HCO+ and HCN J=1–0 molecular lines towards the Galactic center. These data complement existing HCN data and trace a dense molecular ring surrounding the ionized central 2 pc of the Galaxy. The new data are consistent with the model of a clumpy, almost complete ring which is inclined to the line of sight at 50 to 75 degrees. The same structure is seen in HCO+ and in HCN with the exception of an HCN feature at 60 to 100 km/s in the western part of the ring, which is not detected in HCO+ emission. The HCN and HCO+ are collisionally excited in clumps with densities around 10 cm and volume filling factor 1/3 to 1/30. H13 CN emission from the ring was detected at about 1/7 of the intensity of the HCN; the latter is optically thick and is mapping a combination of surface density and excitation temperature. The HCO+ emission shows deep absorption features associated with galactic structure along the line of sight. Absorption features corresponding to the 3 kpc arm, the inner disk and an expanding ring at −195 km/s can be seen in absorption against the Sgr A radio continuum.

scholarly journals Radio Continuum Emission from the Nuclei of Normal Galaxies

1980 ◽  
Vol 5 ◽  
pp. 177-184 ◽  
Author(s):  
J. M. van der Hulst
Keyword(s):  
Radio Emission ◽  
Galactic Center ◽  
Galactic Nuclei ◽  
Radio Continuum ◽  
Continuum Emission ◽  
Thermal Source ◽  
Very Large Array ◽  
Normal Galaxies ◽  
The Galaxy ◽  
Sgr A

During the last few years detailed and sensitive observations of the radio emission from the nuclei of many normal spiral galaxies has become available. Observations from the Very Large Array (VLA) of the National Radio Astronomy Observatory (NRAO1), in particular, enable us to distinguish details on a scale of ≤100 pc for galaxies at distances less than 21 Mpc. The best studied nucleus, however, still is the center of our own Galaxy (see Oort 1977 and references therein). Its radio structure is complex. It consists of an extended non-thermal component 200 × 70 pc in size, with embedded therein several giant HII regions and the central source Sgr A (˜9 pc in size). Sgr A itself consists of a thermal source, Sgr A West, located at the center of the Galaxy, and a weaker, non-thermal source, Sgr A East. Sgr A West moreover contains a weak, extremely compact (≤10 AU) source. The radio morphology of several other galactic nuclei is quite similar to that of the Galactic Center, as will be discussed in section 2. Recent reviews of the radio properties of the nuclei of normal galaxies have been given by Ekers (1978a,b) and De Bruyn (1978). The latter author, however, concentrates on galaxies with either active nuclei or an unusual radio morphology. In this paper I will describe recent results from the Westerbork Synthesis Radio Telescope (WSRT, Hummel 1979), the NRAO 3-element interferometer (Carlson, 1977; Condon and Dressel 1978), and the VLA (Heckman et al., 1979; Van der Hulst et al., 1979). I will discuss the nuclear radio morphology in section 2, the luminosities in section 3, and the spectra in section 4. In section 5 I will briefly comment upon the possible implications for the physical processes in the nuclei that are responsible for the radio emission.

scholarly journals SiO and H2O Masers in the Central Parsec of the Galaxy

1998 ◽  
Vol 164 ◽  
pp. 229-230 ◽  
Author(s):  
Karl M. Menten ◽  
Mark J. Reid
Keyword(s):  
Galactic Center ◽  
Radio Continuum ◽  
Continuum Emission ◽  
Proper Motions ◽  
Infrared Images ◽  
Evolved Stars ◽  
The Galaxy ◽  
Sgr A ◽  
Central Parsec ◽  
Infrared Sources

AbstractWe have discovered maser emission from SiO and H2O molecules toward a number of evolved stars within the central parsec of our Galaxy. The maser positions can be registered with milliarcsecond precision relative to the radio continuum emission of the nonthermal Galactic center source Sgr A*. Since the masing stars are prominent infrared sources, our data can be used to locate the position of Sgr A* on infrared images of the Galactic center region. Using VLBA observations it will be possible to measure proper motions of the maser stars, which can be used to put constraints on the mass distribution in the central parsec.

scholarly journals An Anisotropic Gas Jet from the Nucleus of the Galaxy

1980 ◽  
Vol 5 ◽  
pp. 171-171
Author(s):  
Yasuo Fukui
Keyword(s):  
Galactic Center ◽  
Central Line ◽  
Line Of Sight ◽  
Line Profiles ◽  
Large Velocity ◽  
The Galaxy ◽  
On Line ◽  
Sgr A ◽  
Inner Region ◽  
Large Velocity Gradient

Molecular hydrogen of ≥108M⊚ exists in the galactic center region as has been revealed by recent observations of molecular emission lines. In the inner region of , most of the dominant emission features are located at and 0 km s-1 ≤ v ≤ 100 km s-1 extremely unevenly with respect to the galactic center. As a model of the molecular complex we propose a fan of 360 pc radius whose pivot is at the nucleus. The vertical angle of the fan is about 50° and the central line of the fan makes an angle of about 60° to the line of sight. Molecules in the fan are radially outflowing from the center with the velocity of 110-140 km s-1l. The 1-v pattern of the fan model agrees very well with the observational data. As for Sgr A and Sgr B2 numerical calculation of molecular line profiles has been made by using the large velocity gradient approximation. The calculation shows that the broad and asymmetric line profiles in the complex are well reproduced in the fan model. Further, an isotope effect on line shape is predicted, which will be viable for an observational check of the model.

scholarly journals CO Along the Line of Sight to Galactic Center Infrared Sources

1989 ◽  
Vol 136 ◽  
pp. 469-471
Author(s):  
T. R. Geballe
Keyword(s):  
High Resolution ◽  
Millimeter Wave ◽  
Galactic Center ◽  
Line Of Sight ◽  
Wave Spectra ◽  
Molecular Lines ◽  
Sgr A ◽  
Western Side ◽  
Infrared Sources

High resolution spectra of the 4.64 micron 1–0 R2 line of CO toward infrared sources in the galactic center reveal absorption components identified with features in radio and millimeter wave spectra of molecular lines. They demonstrate that the +20 km/s cloud is situated in front of the Sgr A West and the +50 km/s cloud is behind it. The spectra of IRS 3 and IRS 7 have strong absorptions near +50 km/s, which may originate in the 2 pc radius circumnuclear ring; if so then the western side of the ring lies in front of the galactic center. A less likely interpretation is that these objects, which are only a few arc-seconds from IRS 16, are behind the +50 km/s cloud and, thus, well behind the galactic center.

scholarly journals How far actually is the Galactic Center IRS 13E3 from Sagittarius A*?

2020 ◽  
Vol 72 (3) ◽  
Author(s):  
Masato Tsuboi ◽  
Yoshimi Kitamura ◽  
Takahiro Tsutsumi ◽  
Ryosuke Miyawaki ◽  
Makoto Miyoshi ◽  
...  
Keyword(s):  
Galactic Center ◽  
Three Dimensional ◽  
Line Of Sight ◽  
Recombination Line ◽  
Intermediate Mass ◽  
Ionized Gas ◽  
Sagittarius A ◽  
Projection Distance ◽  
Spectroscopic Information ◽  
Sgr A

Abstract The Galactic Center IRS 13E cluster is a very intriguing infrared object located at ${\sim } 0.13$ pc from Sagittarius A$^\ast$ (Sgr A$^\ast$) in projection distance. There are arguments both for and against the hypothesis that a dark mass like an intermediate mass black hole (IMBH) exists in the cluster. We recently detected the rotating ionized gas ring around IRS 13E3, which belongs to the cluster, in the H30$\alpha$ recombination line using ALMA. The enclosed mass is derived to be $M_{\mathrm{encl.}}\simeq 2\times 10^{4}\, M_\odot$, which agrees with an IMBH and is barely less than the astrometric upper limit mass of an IMBH around Sgr A$^\ast$. Because the limit mass depends on the true three-dimensional (3D) distance from Sgr A$^\ast$, it is very important to determine it observationally. However, the 3D distance is indefinite because it is hard to determine the line-of-sight (LOS) distance by usual methods. We attempt here to estimate the LOS distance from spectroscopic information. The CH$_3$OH molecule is easily destroyed by the cosmic rays around Sgr A$^{\ast }$. However, we detected a highly excited CH$_3$OH emission line in the ionized gas stream associated with IRS 13E3. This indicates that IRS 13E3 is located at $r\gtrsim 0.4$ pc from Sgr A$^{\ast }$.

scholarly journals New Data on the Peculiar Galaxy MRK 273

1990 ◽  
Vol 124 ◽  
pp. 201-208 ◽  
Author(s):  
A. S. Asatrian ◽  
A. R. Petrosian ◽  
F. Börngen
Keyword(s):  
Radio Continuum ◽  
Main Body ◽  
Blue Color ◽  
Close System ◽  
Peculiar Galaxy ◽  
The Galaxy ◽  
Thermal Origin ◽  
Absorption Features

AbstractOn the basis of direct UBV and spectral observations at Tautenburg (DDR) 2m and Special Observatory (USSR) 6m telescopes respectively the colorimetric and spectral investigations of the megamaser galaxy MRK 273 are carried out. It is seen that: MRK 273 is in a physical group of galaxies, which contains at least five members. Two bright central condensations of MRK 273 are Seyfert nuclei. The area of the main body of MRK 273 which contains both Seyfert nuclei and from which comes out a straight tail, is redder than the remaining part of the galaxy. The tail has a pronounced blue color and most probably radiates in [OIII] λ5007 line. Observed radio continuum, OH and HI absorption features are related to bright “a” nucleus of galaxy. We come to the conclusion that MRK 273 which is the member of the group of the galaxies is itself a close system of two objects with AGNs. The tail, with radiation being of thermal origin, probably is the result of the interaction of these galaxies.

scholarly journals 10.2. High proper motions in the vicinity of Sgr A∗: unambiguous evidence for a massive central black hole

1998 ◽  
Vol 184 ◽  
pp. 433-434
Author(s):  
A. M. Ghez ◽  
B. L. Klein ◽  
C. McCabe ◽  
M. Morris ◽  
E. E. Becklin
Keyword(s):  
Black Hole ◽  
Milky Way ◽  
Galactic Center ◽  
Robust Method ◽  
Proper Motions ◽  
Central Black Hole ◽  
Milky Way Galaxy ◽  
The Galaxy ◽  
Sgr A

Although the notion that the Milky Way galaxy contains a supermassive central black hole has been around for more than two decades, it has been difficult to prove that one exists. The challenge is to assess the distribution of matter in the few central parsecs of the Galaxy. Assuming that gravity is the dominant force, the motion of the stars and gas in the vicinity of the putative black hole offers a robust method for accomplishing this task, by revealing the mass interior to the radius of the objects studied. Thus objects located closest to the Galactic Center provide the strongest constraints on the black hole hypothesis.

scholarly journals RADIO CONTINUUM OBSERVATIONS OF THE GALACTIC CENTER: PHOTOEVAPORATIVE PROPLYD-LIKE OBJECTS NEAR SGR A*

2015 ◽  
Vol 801 (2) ◽  
pp. L26 ◽  
Author(s):  
F. Yusef-Zadeh ◽  
D. A. Roberts ◽  
M. Wardle ◽  
W. Cotton ◽  
R. Schödel ◽  
...  
Keyword(s):  
Galactic Center ◽  
Radio Continuum ◽  
Sgr A

scholarly journals A Survey of Radio Recombination Line Emission From the Galactic Center Region

1989 ◽  
Vol 136 ◽  
pp. 159-166 ◽  
Author(s):  
K. R. Anantharamaiah ◽  
Farhad Yusef-Zadeh
Keyword(s):  
Galactic Center ◽  
Line Emission ◽  
Radio Continuum ◽  
Strong Line ◽  
Line Profiles ◽  
Ionized Gas ◽  
Center Region ◽  
Radio Recombination Line ◽  
Nonthermal Emission ◽  
Sgr A

Preliminary results of a systematic survey of H78α, H91α and H98β emission from the inner 40′ of the Galactic center region are presented. This region consists of two prominent continuum features, the Sgr A complex and the radio continuum Arc. In spite of much nonthermal emission arising from these two features, we detected strong line emission with large line widths in more than half of the observed 130 positions. Many of the detections are new, in particular −50 km s−1 ionized gas linking the Sgr A complex and the Arc, β line emission from GO.1+0.08 (the arched filaments), and α line emission from the loop-like structures which surround the non-thermal filaments near G0.2−0.05. We find that much of the detected lines are probably associated with the −50 km s−1 and the 20 km s−1 molecular clouds, known to lie near the Galactic center. We present line profiles of a number of Galactic center sources including Sgr B1, Sgr C and Sgr D.

scholarly journals The Compact Nonthermal Radio Source at the Galactic Center: an Update

1989 ◽  
Vol 136 ◽  
pp. 527-534
Author(s):  
K. Y. Lo
Keyword(s):  
Radio Source ◽  
Galactic Center ◽  
Central Star ◽  
Radio Sources ◽  
Stellar Objects ◽  
Nonthermal Radio ◽  
Compact Radio Source ◽  
The Galaxy ◽  
Observational Status ◽  
Sgr A

We review the current observational status of Sgr A∗, the compact nonthermal radio source at the galactic center. Sgr A∗ is a unique radio source at a unique location of the Galaxy. It is unlike any compact radio source associated with known stellar objects, but it is similar to extragalactic nuclear compact radio sources. The positional offset between Sgr A∗ and IRS16 places little constraint on the nature of the underlying energy source, since IRS16 need not be the core of the central star cluster. Sgr A∗ is still the best candidate for marking the location of a massive collapsed object.

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