scholarly journals A Survey of OH in the Galactic Centre Region

1996 ◽  
Vol 169 ◽  
pp. 311-316
Author(s):  
P.J. Boyce ◽  
R. J. Cohen
Keyword(s):  
Central Region ◽  
Molecular Clouds ◽  
Radio Continuum ◽  
Continuum Emission ◽  
Galactic Centre ◽  
Molecular Gas ◽  
The Galaxy ◽  
Centre Region ◽  
Line Survey ◽  
The Continuum

The galactic centre contains the largest concentration of molecular clouds in the Galaxy. The clouds in the central region are unusual in having large linewidths and masses, and large non-circular motions. Previous surveys of their distribution in the central region have been carried out in OH (Robinson & McGee 1970; Cohen & Few 1976), H2CO (Whiteoak & Gardner 1979; Cohen & Few 1981), CO (Bania 1977; Dame et al. 1987; Bally et al. 1987, 1988) and CS (Bally et al. 1987, 1988). The OH groundstate lines at 18cm wavelength have certain advantages for such a survey. The OH lines appear in absorption against the galactic centre continuum sources, and against the continuum emission from the disk of the Galaxy. The absorption spectra are sensitive to relatively small molecular column densities. In addition they can give information on the relative positions of the molecular gas and the radio continuum sources. This paper describes results from an absorption line survey of the galactic centre region in the OH main lines at 1667.359 MHz and 1665.402 MHz (Boyce & Cohen 1994).

Interstellar gas in the central region of the Galaxy

1967 ◽  
Vol 31 ◽  
pp. 239-251 ◽  
Author(s):  
F. J. Kerr
Keyword(s):  
Central Region ◽  
Galactic Plane ◽  
Neutral Hydrogen ◽  
Continuum Emission ◽  
Galactic Centre ◽  
Interstellar Gas ◽  
Hydrogen Recombination ◽  
The Galaxy ◽  
Centre Region ◽  
The Relationship

A review is given of information on the galactic-centre region obtained from recent observations of the 21-cm line from neutral hydrogen, the 18-cm group of OH lines, a hydrogen recombination line at 6 cm wavelength, and the continuum emission from ionized hydrogen.Both inward and outward motions are important in this region, in addition to rotation. Several types of observation indicate the presence of material in features inclined to the galactic plane. The relationship between the H and OH concentrations is not yet clear, but a rough picture of the central region can be proposed.

scholarly journals Radio Continuum Observations of the Barred Galaxy NGC 4314

1987 ◽  
Vol 115 ◽  
pp. 626-627 ◽  
Author(s):  
J.A. García-Barreto ◽  
P. Pişmiş
Keyword(s):  
Angular Resolution ◽  
Radio Continuum ◽  
Continuum Emission ◽  
No Emission ◽  
The Galaxy ◽  
Thermal Origin ◽  
Linearly Polarized ◽  
Barred Spiral Galaxy ◽  
Compact Sources ◽  
The Continuum

VLA observations have been made of the continuum emission at 20-cm from the barred spiral galaxy NGC 4314 with an angular resolution of 3.5 arcseconds that corresponds to a linear scale of approximately 156 pc at a distance to the galaxy. This resolution was sufficient to resolve the central region into several compact sources. The radiation is linearly polarized which may indicate a non-thermal origin. No emission was detected from the extended bar to a level of 130 Jy.

scholarly journals The Galactic Centre - a laboratory for starburst galaxies (?)

2011 ◽  
Vol 7 (S284) ◽  
pp. 371-378
Author(s):  
Roland M. Crocker
Keyword(s):  
Star Formation ◽  
Cosmic Rays ◽  
Gamma Ray ◽  
Galactic Disk ◽  
Starburst Galaxies ◽  
Radio Continuum ◽  
Galactic Centre ◽  
Molecular Gas ◽  
Thermal Activity ◽  
The Galaxy

AbstractThe Galactic centre – as the closest galactic nucleus – holds both intrinsic interest and possibly represents a useful analogue to starburst nuclei which we can observe with orders of magnitude finer detail than these external systems. The environmental conditions in the GC – here taken to mean the inner 200 pc in diameter of the Milky Way – are extreme with respect to those typically encountered in the Galactic disk. The energy densities of the various GC ISM components are typically ~two orders of magnitude larger than those found locally and the star-formation rate density ~three orders of magnitude larger. Unusually within the Galaxy, the Galactic centre exhibits hard-spectrum, diffuse TeV (=1012 eV) gamma-ray emission spatially coincident with the region's molecular gas. Recently the nuclei of local starburst galaxies NGC 253 and M82 have also been detected in gamma-rays of such energies. We have embarked on an extended campaign of modelling the broadband (radio continuum to TeV gamma-ray), non- thermal signals received from the inner 200 pc of the Galaxy. On the basis of this modelling we find that star-formation and associated supernova activity is the ultimate driver of the region's non-thermal activity. This activity drives a large-scale wind of hot plasma and cosmic rays out of the GC. The wind advects the locally-accelerated cosmic rays quickly, before they can lose much energy in situ or penetrate into the densest molecular gas cores where star-formation occurs. The cosmic rays can, however, heat/ionize the lower density/warm H2 phase enveloping the cores. On very large scales (~10 kpc) the non-thermal signature of the escaping GC cosmic rays has probably been detected recently as the spectacular ‘Fermi bubbles’ and corresponding ‘YWMAP haze’.

The Galactic Centre

1974 ◽  
Vol 60 ◽  
pp. 539-547 ◽  
Author(s):  
J. H. Oort
Keyword(s):  
Central Region ◽  
Molecular Clouds ◽  
Direct Evidence ◽  
Galactic Plane ◽  
High Rate ◽  
Small Scale ◽  
Galactic Centre ◽  
Molecular Gas ◽  
Complicated Structure ◽  
Sgr A

The phenomena displayed by the interstellar medium in the galactic centre are considered. The asymmetries shown by the features between 1 and 3 kpc from the centre together with the presence of material lying out of the galactic plane favour the expulsion hypothesis for their origin. The nuclear disk shows a perturbation which might have resulted from such expulsion. The dense molecular clouds in the disk may well be considered as the most direct evidence that matter is expelled from the nucleus and that this occurs at a high rate. The +50 km s-1 feature in the direction of Sgr A may be the most recently expelled body of molecular gas. New observations of the central radio source, Sgr A, have revealed details on a very small scale, and the infrared core also shows a complicated structure. Probably a number of individual concentrations of gas and dust are present. While the position of the actual nucleus seems now to have been defined to within a few arcseconds, no indication has yet been found concerning its nature nor concerning the mechanism that enables it to expel the vast expanding masses of gas observed in the central region.

scholarly journals Molecular Gas Distribution and Dynamics in the Central Region of Galaxies

1994 ◽  
Vol 140 ◽  
pp. 293-299
Author(s):  
Sumio Ishizuki
Keyword(s):  
High Resolution ◽  
Central Region ◽  
Large Scale ◽  
Starburst Galaxies ◽  
Radio Continuum ◽  
Continuum Emission ◽  
Molecular Gas ◽  
Gas Distribution

AbstractTo investigate the relation between a large-scale stellar bar and circumnuclear starburst, the CO (J=1→0) emission of circumnuclear regions of three starburst galaxies NGC2782, NGC3504, and M83 (NGC5236) have been mapped with the Nobeyama Millimeter Array. The high resolution CO (J=1→0) images indicate that the molecular gas in the three starburst galaxies is located interior to the innermost ends of the paired straight dust lanes. The molecular gas at the small radii is associated with their circumnuclear starburst sites which are indicated by radio continuum emission.

scholarly journals Radio Observations of the AGN and Gas in Low Surface Brightness Galaxies

2006 ◽  
Vol 2 (S235) ◽  
pp. 90-90
Author(s):  
M. Das ◽  
K. O'Neil ◽  
N. Kantharia ◽  
S. N. Vogel ◽  
S. S. McGaugh
Keyword(s):  
Surface Brightness ◽  
Continuum Emission ◽  
Molecular Gas ◽  
Gas Distribution ◽  
Continuum Source ◽  
Low Surface Brightness ◽  
The Galaxy ◽  
Low Surface Brightness Galaxies ◽  
Lsb Galaxies ◽  
The Continuum

AbstractLSB galaxies have low metallicities, diffuse stellar disks, and massive HI disks. We have detected molecular gas in two giant LSB galaxies, UGC 6614 and F568-6. A millimeter continuum source has been detected in UGC 6614 as well. At centimeter wavelengths we have detected and mapped the continuum emission from the giant LSB galaxy 1300+0144. The emission is extended about the nucleus and is most likely originating from the AGN in the galaxy. The HI gas distribution and velocity field in 1300+0144 was also mapped. The HI disk extends well beyond the optical disk and appears lopsided in the intensity maps.

FST Observations of NGC 4945 and the Circinus Galaxy

1985 ◽  
Vol 6 (2) ◽  
pp. 171-174 ◽  
Author(s):  
J. B. Whiteoak ◽  
J. D. Bunton
Keyword(s):  
Spectral Line ◽  
Central Region ◽  
Small Diameter ◽  
Continuum Emission ◽  
Line Profiles ◽  
Large Velocity ◽  
The Galaxy ◽  
Extended Emission ◽  
The Continuum

AbstractThe Fleurs synthesis telescope, which provides 20 arcsec resolution at 1.4 GHz, was used to map the continuum emission in NGC 4945 and the Circinus galaxy. Both objects have prominent small-diameter radio nuclei, containing 50% to 75% of the total intensity, superimposed on extended emission associated with the outer regions of the galaxies. The scale of the nuclei, together with the large velocity widths of the associated spectral-line profiles, are not unlike those encountered in the central region of the Galaxy.

scholarly journals Molecular gas kinematics of the CMZ: Great oaks from little acorns grow

2016 ◽  
Vol 11 (S322) ◽  
pp. 85-89
Author(s):  
Jonathan D. Henshaw
Keyword(s):  
Star Formation ◽  
Velocity Field ◽  
Molecular Clouds ◽  
Extreme Environment ◽  
Galactic Centre ◽  
Molecular Gas ◽  
Evolutionary Sequence ◽  
Gas Kinematics ◽  
Gravitational Instabilities ◽  
The Galaxy

AbstractThe central molecular zone (CMZ) hosts some of the most massive and dense molecular clouds and star clusters in the Galaxy, offering an important window into star formation under extreme conditions. Star formation in this extreme environment may be closely linked to the 3-D distribution and orbital dynamics of the gas. Here I discuss how our new, accurate description of the {l,b,v} structure of the CMZ is helping to constrain its 3-D geometry. I also present the discovery of a highly-regular, corrugated velocity field located just upstream from the dust ridge molecular clouds (which include G0.253+0.016 and Sgr B2). The extremes in this velocity field correlate with a series of massive (~ 104 M⊙) cloud condensations. The corrugation wavelength (~23 pc) and cloud separation (~8 pc) closely agree with the predicted Toomre (~17 pc) and Jeans (~6 pc) lengths, respectively. I conclude that gravitational instabilities are driving the formation of molecular clouds within the Galactic Centre gas stream. Furthermore, I suggest that these seeds are the historical analogues of the dust ridge molecular clouds – possible progenitors of some of the most massive and dense molecular clouds in the Galaxy. If our current best understanding for the 3-D geometry of this system is confirmed, these clouds may pinpoint the beginning of an evolutionary sequence that can be followed, in time, from cloud condensation to star formation.

Observations of the continuum near the galactic centre

1967 ◽  
Vol 31 ◽  
pp. 405
Author(s):  
F. J. Kerr
Keyword(s):  
Galactic Centre ◽  
The Past ◽  
Centre Region ◽  
The Continuum

A continuum survey of the galactic-centre region has been carried out at Parkes at 20 cm wavelength over the areal11= 355° to 5°,b11= -3° to +3° (Kerr and Sinclair 1966, 1967). This is a larger region than has been covered in such surveys in the past. The observations were done as declination scans.

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