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 Molecular Fan of 360-pc Radius in the Galactic Center Region

1980 ◽  
Vol 87 ◽  
pp. 209-211
Author(s):  
Yasuo Fukui
Keyword(s):  
Molecular Complex ◽  
Galactic Center ◽  
Carbon Isotope Ratio ◽  
Central Line ◽  
Line Profiles ◽  
Center Region ◽  
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 (see e.g. Oort 1977). In the inner region of most of the dominant emission features concentrate at and 0 km s-1 ≲v ≲100 km s-1 extremely unevenly with respect to the galactic center (see Fig. 1). As a model of the molecular complex we propose a fan of 360-pc radius whose pivot is at the center. 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 flowing out radially from the center with a velocity of 110-140 km s-1. The ℓ-v pattern of the fan model is superposed on the CO map in Fig. 1. The model can explain the whole structure of the molecular complex as well as several fine details such as asymmetry in emission line profiles (Fukui et al. 1979). As for Sgr A and Sgr B2, numerical calculations of molecular line profiles have been made by using the large velocity gradient approximation. The calculations show that the broad and asymmetric line profiles in the complex are well reproduced by the fan model. Further, an isotope effect on line shape is predicted, which will be useful as an observational check of the fan model. Additionally, the carbon isotope ratio 12C/13C in HCN and CO was estimated to be 10-20 in the Sgr A +50-km s-1 cloud.

scholarly journals Mapping the Galactic Center

1996 ◽  
Vol 171 ◽  
pp. 369-369
Author(s):  
W.J. Duschl ◽  
S. von Linden ◽  
T. Walter ◽  
M. Wittkowski
Keyword(s):  
Angular Momentum ◽  
Molecular Clouds ◽  
Vertical Structure ◽  
Galactic Center ◽  
Galactic Plane ◽  
The Galaxy ◽  
Sgr A ◽  
Celestial Sphere ◽  
Inner Region ◽  
Galactic Longitude

Gas and dust in the inner region of the Galaxy are distributed in a flat, disklike structure. We model the dynamics of this material in the framework of an accretion disk approach, and thus determine the efficiency of the radial transport of mass and angular momentum in the inner ∼ 200 pc of the Galactic Plane. Moreover, this allows us to establish the location (coordinates: galactic longitude l and depth normal to the celestial sphere) of molecular clouds from the observed positions (l) and radial velocities (currently, we neglect details of the vertical structure). Ultimately this will yield a map of the distribution of molecular clouds about Sgr A∗.

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 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 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 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 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.

scholarly journals Methanol at the Edge of the Galaxy: New Observations to Constrain the Galactic Habitable Zone

2021 ◽  
Vol 922 (2) ◽  
pp. 106
Author(s):  
J. J. Bernal ◽  
C. D. Sephus ◽  
L. M. Ziurys
Keyword(s):  
Molecular Clouds ◽  
Organic Molecules ◽  
Galactic Center ◽  
Solar Neighborhood ◽  
Habitable Zone ◽  
Line Profiles ◽  
Galactocentric Distance ◽  
Radio Observatory ◽  
The Galaxy ◽  
Co Observations

Abstract The Galactic Habitable Zone (GHZ) is a region believed hospitable for life. To further constrain the GHZ, observations have been conducted of the J = 2 → 1 transitions of methanol (CH3OH) at 97 GHz, toward 20 molecular clouds located in the outer Galaxy (R GC = 12.9–23.5 kpc), using the 12 m telescope of the Arizona Radio Observatory. Methanol was detected in 19 out of 20 observed clouds, including sources as far as R GC = 23.5 kpc. Identification was secured by the measurement of multiple asymmetry and torsional components in the J = 2 → 1 transition, which were resolved in the narrow line profiles observed (ΔV 1/2 ∼ 1–3 km s−1). From a radiative transfer analysis, column densities for these clouds of N tot = 0.1–1.5 × 1013 cm−2 were derived, corresponding to fractional abundances, relative to H2, of f (CH3OH) ∼ 0.2–4.9 × 10−9. The analysis also indicates that these clouds are cold (T K ∼ 10–25 K) and dense (n(H2) ∼ 106 cm−3), as found from previous H2CO observations. The methanol abundances in the outer Galaxy are comparable to those observed in colder molecular clouds in the solar neighborhood. The abundance of CH3OH therefore does not appear to decrease significantly with distances from the Galactic Center, even at R GC ∼ 20–23 kpc. Furthermore, the production of methanol is apparently not affected by the decline in metallicity with galactocentric distance. These observations suggest that organic chemistry is prevalent in the outer Galaxy, and methanol and other organic molecules may serve to assess the GHZ.

scholarly journals Dust absorption and scattering in the silicon K-edge

2019 ◽  
Vol 627 ◽  
pp. A16 ◽  
Author(s):  
S. T. Zeegers ◽  
E. Costantini ◽  
D. Rogantini ◽  
C. P. de Vries ◽  
H. Mutschke ◽  
...  
Keyword(s):  
Interstellar Dust ◽  
Galactic Center ◽  
Interstellar Extinction ◽  
Line Of Sight ◽  
X Rays ◽  
Laboratory Measurements ◽  
Galactocentric Distance ◽  
Synchrotron Facility ◽  
The Galaxy ◽  
Low Mass

Context. The composition and properties of interstellar silicate dust are not well understood. In X-rays, interstellar dust can be studied in detail by making use of the fine structure features in the Si K-edge. The features in the Si K-edge offer a range of possibilities to study silicon-bearing dust, such as investigating the crystallinity, abundance, and the chemical composition along a given line of sight. Aims. We present newly acquired laboratory measurements of the silicon K-edge of several silicate-compounds that complement our measurements from our earlier pilot study. The resulting dust extinction profiles serve as templates for the interstellar extinction that we observe. The extinction profiles were used to model the interstellar dust in the dense environments of the Galaxy. Methods. The laboratory measurements, taken at the Soleil synchrotron facility in Paris, were adapted for astrophysical data analysis and implemented in the SPEX spectral fitting program. The models were used to fit the spectra of nine low-mass X-ray binaries located in the Galactic center neighborhood in order to determine the dust properties along those lines of sight. Results. Most lines of sight can be fit well by amorphous olivine. We also established upper limits on the amount of crystalline material that the modeling allows. We obtained values of the total silicon abundance, silicon dust abundance, and depletion along each of the sightlines. We find a possible gradient of 0.06 ± 0.02 dex/kpc for the total silicon abundance versus the Galactocentric distance. We do not find a relation between the depletion and the extinction along the line of sight.

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