scholarly journals 4.13. A high velocity molecular cloud near the center of the Galaxy

1998 ◽  
Vol 184 ◽  
pp. 193-194 ◽  
Author(s):  
Tomoharu Oka ◽  
Tetsuo Hasegawa ◽  
Glenn J. White ◽  
Fumio Sato ◽  
Masato Tsuboi ◽  
...  
Keyword(s):  
High Velocity ◽  
Molecular Cloud ◽  
Molecular Clouds ◽  
Galactic Center ◽  
Galactic Disk ◽  
External Pressure ◽  
Galactic Bulge ◽  
Physical Conditions ◽  
Large Velocity ◽  
The Galaxy

Molecular clouds in the Galactic center region are characterised by their large velocity widths and physical conditions which differ from clouds in the Galactic disk (e.g., Morris 1996). These clouds may not be gravitationally bound, but in equilibrium with the high external pressure in the Galactic bulge (Spergel & Blitz 1992, Oka et al. 1997a).

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 Disk-halo interactions: molecular clouds in the Galactic center

2013 ◽  
Vol 9 (S303) ◽  
pp. 177-181
Author(s):  
D. Riquelme ◽  
J. Martín-Pintado ◽  
R. Mauersberger ◽  
S. Martín ◽  
L. Bronfman
Keyword(s):  
Molecular Cloud ◽  
Molecular Clouds ◽  
Large Scale ◽  
Galactic Center ◽  
Galactic Disk ◽  
Isotopic Ratio ◽  
Small Scale ◽  
Kinetic Temperature ◽  
Temperature Regimes ◽  
Gas Accretion

AbstractWe study the disk-halo interaction, in the context of orbits and Giant Molecular loops (GMLs) in the Galactic center (GC) region. From a large scale survey of the central kpc of the Galaxy, in SiO J = (2 − 1), HCO+J = (1 − 0) and H13CO+J = (1 − 0) molecular emission, we identify shock regions traced by the enhancement of the SiO. These positions were studied using the 12C/13C isotopic ratio to trace gas accretion/ejection. We found a systematically higher 12C/13C isotopic ratio (> 40) toward the GMLs and the x1 orbits than for the GC standard molecular clouds (20–25). The high isotopic ratios are consistent with the accretion of the gas from the halo and from the outskirts of the Galactic disk. From multi-transitional observations of NH3, we derive two kinetic temperature regimes (one warm at ∼150 K and one cold at ∼40 K) for all the positions, except for the GMLs positions where only the warm component is present. The fractional abundances derived from the different molecules support the shock origin for the heating mechanism in the GC. We also present a detailed study of one molecular cloud placed in the foot points of two giant molecular loops, where two of the previously selected positions are placed. Using the 22m Mopra telescope we mapped the molecular cloud M − 3.8 + 0.9 in 3-mm molecular lines. The data show structures at small scale in SiO emission, with narrower line profiles than those of, e.g, HCO+ or HCN, which indicate that the shocks are dynamically confined. The data also show clear differences between different molecular tracers, e.g., between the SiO and HCO+ emission, which would indicate differences in the physical properties and chemistry within the cloud.

scholarly journals Kinematics of the Ultra-High-Velocity Gas in the Expanding Molecular Shell Adjacent to the W44 Supernova Remnant

2016 ◽  
Vol 11 (S322) ◽  
pp. 151-153
Author(s):  
Masaya Yamada ◽  
Tomoharu Oka ◽  
Kunihiko Tanaka ◽  
Mariko Nomura ◽  
Shunya Takekawa ◽  
...  
Keyword(s):  
High Velocity ◽  
Molecular Cloud ◽  
Molecular Clouds ◽  
Supernova Remnant ◽  
Molecular Gas ◽  
Close Inspection ◽  
Essential Properties ◽  
Large Velocity ◽  
Intensity Ratios

High-velocity compact cloud (HVCC) is a peculiar category of molecular clouds detected in the central molecular zone of our Galaxy (Oka et al. 1998, 2007, and 2012). They are characterized by compact appearances (d < 5 pc) and very large velocity widths (Δ V > 50 km s−1). Some of them show high CO J=3–2/J=1–0 intensity ratios (≥ 1.5), indicating that they consist of dense and warm molecular gas. Dispite a number of efforts, we have not reached a comprehensive interpretation of HVCCs. Recently, we detected an extraordinaly broad velocity width feature, the ‘Bullet’, in the molecular cloud interacting with the W44 supernova remnant. The Bullet shares essential properties with HVCCs. Because of its proximity, a close inspection of the Bullet must contribute to the understanding of HVCCs.

scholarly journals Two New Views of the Galactic Center

1996 ◽  
Vol 169 ◽  
pp. 283-284 ◽  
Author(s):  
D.T. Jaffe ◽  
R. Plume ◽  
S. Pak
Keyword(s):  
Interstellar Medium ◽  
High Velocity ◽  
Molecular Clouds ◽  
Large Scale ◽  
Galactic Center ◽  
Molecular Gas ◽  
The Galaxy ◽  
Physical Effects ◽  
Velocity Dispersions ◽  
Internal Velocity

The inner few hundred parsecs of the Galactic Center contains ∼10% of the molecular ISM in the Galaxy. The conditions in this gas are significantly different from those in molecular clouds elsewhere in the Galaxy. Typical temperatures, densities, and internal velocity dispersions are higher (Güesten 1989). There is also evidence for a large amount of molecular gas which is not bound to distinct clouds (Stark et al. 1989). High velocity bulk gas motions and velocity discontinuities open up the possibility of a role for powerful large-scale shocks in ISM excitation. The very different nature of the dense ISM in the inner Galaxy make it useful as a laboratory for physical effects in the interstellar medium and a proving ground for ideas about the interaction of gas and stars in the nuclei of other galaxies.

scholarly journals The diffuse molecular component in the nuclear bulge of the Milky Way

2018 ◽  
Vol 610 ◽  
pp. A43 ◽  
Author(s):  
D. Riquelme ◽  
L. Bronfman ◽  
R. Mauersberger ◽  
R. Finger ◽  
C. Henkel ◽  
...  
Keyword(s):  
Galactic Center ◽  
Galactic Disk ◽  
Molecular Complexes ◽  
Low Density ◽  
Galactic Bulge ◽  
The Galaxy ◽  
Bulge Region ◽  
Complex Chemistry ◽  
Diffuse Clouds ◽  
Gas Component

Context. The bulk of the molecular gas in the central molecular zone (CMZ) of the Galactic center region shows warm kinetic temperatures, ranging from >20 K in the coldest and densest regions (n ~ 104-5 cm-3) up to more than 100 K for densities of about n ~ 103 cm-3. Recently, a more diffuse, hotter (n ~ 100 cm-3, T ~ 250 K) gas component was discovered through absorption observations of H3+. This component may be widespread in the Galactic center, and low density gas detectable in absorption may be present even outside the CMZ along sightlines crossing the extended bulge of the Galaxy. Aim. We aim to observe and characterize diffuse and low density gas using observations of 3-mm molecular transitions seen in absorption. Methods. Using the Atacama Large (sub)Millimeter Array (ALMA) we observed the absorption against the quasar J1744-312, which is located toward the Galactic bulge region at (l, b) = (−2°.13, −1°.0), but outside the main molecular complexes. Results. ALMA observations in absorption against the J1744-312 quasar reveal a rich and complex chemistry in low density molecular and presumably diffuse clouds. We detected three velocity components at ~0, −153, and −192 km s−1. The component at ~0 km s−1 could represent gas in the Galactic disk while the velocity components at −153, and −192 km s−1 likely originate from the Galactic bulge. We detected 12 molecules in the survey, but only 7 in the Galactic bulge gas.

scholarly journals Helium abundances in inner Galaxy planetary nebulae

2009 ◽  
Vol 5 (S268) ◽  
pp. 171-172
Author(s):  
Oscar Cavichia ◽  
Roberto D. D. Costa ◽  
Walter J. Maciel
Keyword(s):  
Galactic Center ◽  
Galactic Disk ◽  
Planetary Nebulae ◽  
Galactic Bulge ◽  
The Galaxy ◽  
Good Agreement

AbstractNew helium abundances of planetary nebulae located towards the bulge of the Galaxy were derived, based on observations made at OPD (Brazil). We present accurate helium abundances for 56 PNe located towards the galactic bulge. The data show good agreement with other results in the literature, in the sense that the distribution of the abundances is similar to previous works. Furthermore, the radial helium gradient is extended towards the galactic center. The results show that no trend can be identified when comparing the internal gradient (R ≤ 4 kpc) to the whole galactic disk.

scholarly journals The Age of Old Galactic Populations

1998 ◽  
Vol 11 (1) ◽  
pp. 560-561
Author(s):  
M. Grenon
Keyword(s):  
High Velocity ◽  
Radial Velocities ◽  
Thick Disk ◽  
Early Evolution ◽  
Galactic Bulge ◽  
Colour Class ◽  
The Galaxy ◽  
Nearby Stars

As a preparation to the HIPPARCOS mission, a large observing programme on NLTT stars (propermotion > 0.18 ″/yr) was started in Genevaphotometry. The original programme consists of 10047 stars brighter than mR = 11.5, or mR = 12.5 if of colour class m. Among them, 7813 targets could be included in the HIPPARCOS programme, selected according to their observability and internal priorities in favour of large parallaxe stars (photometric distances < 100 pc) and high-velocity stars. The bulk of new nearby, halo, mild-metal poor and SMR stars in the HIP Catalogue originates from this proposal (N° 139). No less than 208 new nearby stars with π ≥ 40 mas were discovered south of δ +10°, the closest has π(HIP)= 182 mas. Radial velocities were obtained with CORAVEL at OHP and ESO. Most aspects of the early evolution of the Galaxy may be addressed with this sample. Here we discuss, as examples, the ages of the thick disk and of the galactic bulge.

scholarly journals Mapping the 13CO/C18O abundance ratio in the massive star-forming region G29.96−0.02

2018 ◽  
Vol 617 ◽  
pp. A14 ◽  
Author(s):  
S. Paron ◽  
M. B. Areal ◽  
M. E. Ortega
Keyword(s):  
Molecular Clouds ◽  
Abundance Ratio ◽  
High Mass ◽  
Local Thermal Equilibrium ◽  
Mass Star ◽  
Galactocentric Distance ◽  
Star Forming ◽  
Physical Conditions ◽  
The Galaxy ◽  
Molecular Abundances

Aims. Estimating molecular abundances ratios from directly measuring the emission of the molecules toward a variety of interstellar environments is indeed very useful to advance our understanding of the chemical evolution of the Galaxy, and hence of the physical processes related to the chemistry. It is necessary to increase the sample of molecular clouds, located at different distances, in which the behavior of molecular abundance ratios, such as the 13CO/C18O ratio, is studied in detail. Methods. We selected the well-studied high-mass star-forming region G29.96−0.02, located at a distance of about 6.2 kpc, which is an ideal laboratory to perform this type of study. To study the 13CO/C18O abundance ratio (X13∕18) toward this region, we used 12CO J = 3–2 data obtained from the CO High-Resolution Survey, 13CO and C18O J = 3–2 data from the 13CO/C18O (J = 3–2) Heterodyne Inner Milky Way Plane Survey, and 13CO and C18O J = 2–1 data retrieved from the CDS database that were observed with the IRAM 30 m telescope. The distribution of column densities and X13∕18 throughout the extension of the analyzed molecular cloud was studied based on local thermal equilibrium (LTE) and non-LTE methods. Results. Values of X13∕18 between 1.5 and 10.5, with an average of about 5, were found throughout the studied region, showing that in addition to the dependency of X13∕18 and the galactocentric distance, the local physical conditions may strongly affect this abundance ratio. We found that correlating the X13∕18 map with the location of the ionized gas and dark clouds allows us to suggest in which regions the far-UV radiation stalls in dense gaseous components, and in which regions it escapes and selectively photodissociates the C18O isotope. The non-LTE analysis shows that the molecular gas has very different physical conditions, not only spatially throughout the cloud, but also along the line of sight. This type of study may represent a tool for indirectly estimating (from molecular line observations) the degree of photodissociation in molecular clouds, which is indeed useful to study the chemistry in the interstellar medium.

scholarly journals The Massive Dark Corona Of Our Galaxy

1996 ◽  
Vol 173 ◽  
pp. 175-176
Author(s):  
K.C. Freeman
Keyword(s):  
Rotation Curve ◽  
Spiral Galaxies ◽  
Galactic Center ◽  
Galactic Disk ◽  
Galactic Rotation ◽  
Rotation Curves ◽  
Stellar Component ◽  
The Galaxy ◽  
Galactic Rotation Curve

From their rotation curves, most spiral galaxies appear to have massive dark coronas. The inferred masses of these dark coronas are typically 5 to 10 times the mass of the underlying stellar component. I will review the evidence that our Galaxy also has a dark corona. Our position in the galactic disk makes it difficult to measure the galactic rotation curve beyond about 20 kpc from the galactic center. However it does allow several other indicators of the total galactic mass out to very large distances. It seems clear that the Galaxy does indeed have a massive dark corona. The data indicate that the enclosed mass within radius R increases like M(R) ≈ R(kpc) × 1010M⊙, out to a radius of more than 100 kpc. The total galactic mass is at least 12 × 1011M⊙.

scholarly journals Measurements of Isotopic Abundances in Interstellar Clouds

1980 ◽  
Vol 87 ◽  
pp. 397-404 ◽  
Author(s):  
Arno A. Penzias
Keyword(s):  
Molecular Clouds ◽  
General Framework ◽  
Galactic Center ◽  
Galactic Plane ◽  
Giant Molecular Clouds ◽  
Interstellar Clouds ◽  
The Galaxy ◽  
Isotopic Abundances ◽  
Si Isotopes

While an examination of the available data reveals some seemingly contradictory results, a general framework having the following outlines can be put forward:1. With the exception of the two galactic center sources SgrA and SgrB, the relative isotopic abundances exhibited by the giant molecular clouds in our Galaxy exhibit few, if any, significant variations from the values obtained by averaging the data from all these sources.2. The 13C/12C and 14N/15N abundance ratios are ∼130% and ∼150%, respectively, of their terrestrial values throughout the galactic plane and somewhat higher, ∼300%, near the galactic center.3. The 16O/18O and 17O/18O abundance ratios are ∼130% and ∼160%, respectively, of their terrestrial values throughout the Galaxy, although the former may be somewhat lower near the galactic center.4. The S and Si isotopes have generally terrestrial abundances.

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