scholarly journals Hydrogen motions in the central region of the Galaxy

1964 ◽  
Vol 20 ◽  
pp. 183-186 ◽  
Author(s):  
B. F. Burke ◽  
M. A. Tuve
Keyword(s):  
Radio Telescope ◽  
Cross Sections ◽  
Central Region ◽  
Galactic Plane ◽  
Circular Motion ◽  
Galactic Centre ◽  
Strong Deviation ◽  
The Galaxy

The 21-cm hydrogen radiation near the galactic plane exhibits strong deviation from circular motion over longitudes within 30° or so of the galactic centre. In order to extend the observations first made by Rougoor and Oort,* the Carnegie multichannel H-line spectrograph was used with our 60-foot radio telescope at Derwood, Maryland, in order to confirm the Leiden work and extend observations to more southern longitudes. Cross-sections extending ±2° in latitude were taken every 2° in longitude from lII=−26°8 to lII=+2°2 and a series of points along the galactic equator were taken every 1° over the same range. Effort has been concentrated on the southern extension of the observations, which agree well with the Leiden observations over the section in common, but which carry the observations nearly 20° farther south in longitude.

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.

A CO Survey of the Southern Galactic Plane

1981 ◽  
Vol 4 (2) ◽  
pp. 243-247 ◽  
Author(s):  
W. H. McCutcheon ◽  
B. J. Robinson ◽  
J. B. Whiteoak
Keyword(s):  
Northern Hemisphere ◽  
Atomic Hydrogen ◽  
Molecular Hydrogen ◽  
Large Scale ◽  
Galactic Plane ◽  
Galactic Centre ◽  
Hydrogen Distribution ◽  
Millimetre Wave ◽  
The Galaxy ◽  
Wave Emission

Millimetre-wave emission from the CO molecule has proven to be an extremely useful probe of the cold, dense clouds of molecular hydrogen in the Galaxy. Previous studies of the large-scale distribution of CO in the galactic plane (Scoville and Solomon 1975; Burton et al. 1975; Bash and Peters 1976; Burton and Gordon 1978; Solomon et al. 1979b; Cohen et al. 1980) have all been of the northern hemisphere and primarily at longitudes 0° ≤ l ≥ 80°. These studies have revealed the striking characteristic that the CO, and by implication molecular hydrogen clouds, are concentrated in a ring extending from 4 to 8 kpc from the galactic centre. This is in sharp contrast to the atomic hydrogen distribution, which is fairly constant over the extended region from 4 to 13 kpc but correlates well with other Population I indicators.

scholarly journals Local Stellar Kinematics from RAVE data – V. Kinematic Investigation of the Galaxy with Red Clump Stars

2014 ◽  
Vol 31 ◽  
Author(s):  
S. Karaali ◽  
S. Bilir ◽  
S. Ak ◽  
E. Yaz Gökçe ◽  
Ö. Önal ◽  
...  
Keyword(s):  
Velocity Component ◽  
Galactic Plane ◽  
Radial Distance ◽  
Vertical Direction ◽  
Space Velocity ◽  
Galactic Centre ◽  
Galactic Rotation ◽  
Stellar Kinematics ◽  
The Galaxy ◽  
Red Clump

AbstractWe investigated the space velocity components of 6 610 red clump (RC) stars in terms of vertical distance, Galactocentric radial distance and Galactic longitude. Stellar velocity vectors are corrected for differential rotation of the Galaxy which is taken into account using photometric distances of RC stars. The space velocity components estimated for the sample stars above and below the Galactic plane are compatible only for the space velocity component in the direction to the Galactic rotation of the thin disc stars. The space velocity component in the direction to the Galactic rotation (Vlsr) shows a smooth variation relative to the mean Galactocentric radial distance (Rm), while it attains its maximum at the Galactic plane. The space velocity components in the direction to the Galactic centre (Ulsr) and in the vertical direction (Wlsr) show almost flat distributions relative to Rm, with small changes in their trends at Rm ~ 7.5 kpc. Ulsr values estimated for the RC stars in quadrant 180° < l ⩽ 270° are larger than the ones in quadrants 0° < l ⩽ 90° and 270° < l ⩽ 360°. The smooth distribution of the space velocity dispersions reveals that the thin and thick discs are kinematically continuous components of the Galaxy. Based on the Wlsr space velocity components estimated in the quadrants 0° < l ⩽ 90° and 270° < l ⩽ 360°, in the inward direction relative to the Sun, we showed that RC stars above the Galactic plane move towards the North Galactic Pole, whereas those below the Galactic plane move in the opposite direction. In the case of quadrant 180° < l ⩽ 270°, their behaviour is different, i.e. the RC stars above and below the Galactic plane move towards the Galactic plane. We stated that the Galactic long bar is the probable origin of many, but not all, of the detected features.

scholarly journals A 200 pc Ring of Molecular Gas and an Outburst in the Galaxy M82

1987 ◽  
Vol 115 ◽  
pp. 614-620
Author(s):  
N. Nakai ◽  
M. Hayashi ◽  
T. Hasegawa ◽  
Y. Sofue ◽  
T. Handa ◽  
...  
Keyword(s):  
Star Formation ◽  
Central Region ◽  
Intensity Distribution ◽  
Energy Supply ◽  
Galactic Plane ◽  
Ring Structure ◽  
Molecular Gas ◽  
The Galaxy ◽  
Expansion Energy ◽  
Two Peaks

The CO (J=1-0) emission in M82 has been mapped with the Nobeyama 45-m telescope. The CO intensity distribution in the central region is resolved into two peaks. An axisymmetric model reveals a ring structure of molecular gas at a distance of 80-400 pc (centered near 200 pc) from the nucleus. This “200-pc ring” corresponds to just the region of a star formation burst. The molecular gas in M82 is also expanding out of the galactic plane with a velocity of 100-500 km s−1. The expansion energy of (0.1-1.4) x 1056 erg can be explained by the energy supply of supernovae in the central region.

scholarly journals Magnesium and silicon in interstellar dust: X-ray overview

2020 ◽  
Vol 641 ◽  
pp. A149
Author(s):  
D. Rogantini ◽  
E. Costantini ◽  
S. T. Zeegers ◽  
M. Mehdipour ◽  
I. Psaradaki ◽  
...  
Keyword(s):  
Cross Sections ◽  
Interstellar Dust ◽  
Galactic Centre ◽  
X Rays ◽  
Dust Grains ◽  
Large Reservoir ◽  
X Ray ◽  
Synchrotron Facility ◽  
The Galaxy ◽  
X Ray Binaries

Context. The dense Galactic environment is a large reservoir of interstellar dust. Therefore, this region represents a perfect laboratory to study the properties of cosmic dust grains. X-rays are the most direct way to detect the interaction of light with dust present in these dense environments. Aims. The interaction between the radiation and the interstellar matter imprints specific absorption features on the X-ray spectrum. We study them with the aim of defining the chemical composition, the crystallinity, and structure of the dust grains that populate the inner regions of the Galaxy. Methods. We investigated the magnesium and the silicon K-edges detected in the Chandra /HETG spectra of eight bright X-ray binaries, distributed in the neighbourhood of the Galactic centre. We modelled the two spectral features using accurate extinction cross-sections of silicates, which we measured at the synchrotron facility Soleil, France. Results. Near the Galactic centre, magnesium and silicon show abundances similar to the solar ones and they are highly depleted from the gas phase (δMg > 0.90 and δSi > 0.96). We find that amorphous olivine with a composition of MgFeSiO4 is the most representative compound along all lines of sight according to our fits. The contribution of Mg-rich silicates and quartz is low (less than 10%). On average we observe a percentage of crystalline dust equal to 11%. For the extragalactic source LMC X-1, we find a preference for forsterite, a magnesium-rich olivine. Along this line of sight we also observe an under-abundance of silicon ASi∕ALMC = 0.5 ± 0.2.

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).

scholarly journals Planetary nebulae in the central region of the Galaxy

1964 ◽  
Vol 20 ◽  
pp. 41-45 ◽  
Author(s):  
L. Perek
Keyword(s):  
Central Region ◽  
Surface Brightness ◽  
Large Scale ◽  
Direct Determination ◽  
Planetary Nebulae ◽  
Galactic Centre ◽  
Large Numbers ◽  
The Galaxy ◽  
Objective Prism

Planetary nebulae are convenient objects for studying the large-scale structure of the Galaxy. Firstly, they are easily recognized up to considerable distances on plates taken through an objective prism, and secondly, methods have been devised by various authors to determine their distances from two observable quantities: angular diameter and surface brightness. The importance of the subsystem of planetary nebulae has been accentuated especially by the discoveries by Minkowski and Haro of large numbers of planetaries in the direction of the galactic centre. The distribution of planetaries on the sphere suggests that they are connected with the galactic nucleus, but no direct determination of their distances, which would either confirm or contradict this statement, is available. The most serious obstacle in studying the subsystem of planetaries is the lack of observing data. The aim of the reported paper (Perek 1963) is to give a tentative outline of the distribution of planetaries in space based on extensive new observing material.

scholarly journals On Non-Spherical Models for Spiral Galaxy Gravitation Potential Yielding Flat Rotation Curve

2021 ◽  
Author(s):  
Swagatam Sen
Keyword(s):  
Spiral Galaxies ◽  
Galactic Plane ◽  
Rotation Velocity ◽  
Radial Symmetry ◽  
Galactic Centre ◽  
Spherically Symmetric ◽  
Annular Disk ◽  
Spherical Models ◽  
The Galaxy ◽  
Flat Rotation Curve

Abstract A two component model of gravitation potential for spiral galaxies has been proposed which couples a spherically symmetric component with a second component that observes planar radial symmetry on the galactic plane and vanishes outside an annular disk beyond the edge of galaxy's effective radius. It is shown that such a model for potential satisfying Poisson Equation would produce rotation velocity curve towards the edge of the galaxy which is flat over distance from the galactic centre. This relationship, which is experimentally observed in many spiral galaxies, is shown as a consequence of classical understanding of gravity and specific symmetry of the gravitational potential without any extrinsic requirement of dark matter. It is also demonstrated that this potential directly yields a relationship between inner mass of the galaxy and terminal rotation velocity, which has been empirically observed and known as Baryonic Tully-Fisher relations. Furthermore a direct test has been proposed for experimental verification of the proposed theory.

scholarly journals A balloon-borne X-ray survey of the central region of the galaxy

1968 ◽  
Vol 46 (10) ◽  
pp. S444-S447 ◽  
Author(s):  
Elihu Boldt ◽  
Henry Doong ◽  
Peter Serlemitsos ◽  
Guenter Riegler
Keyword(s):  
Central Region ◽  
Proportional Counter ◽  
Galactic Center ◽  
Galactic Plane ◽  
Cesium Iodide ◽  
X Rays ◽  
Scintillation Crystal ◽  
X Ray ◽  
Gas Proportional Counter ◽  
The Galaxy

A balloon-borne X-ray survey of the galactic plane in the region of the galactic center was made from Australia during December 1966. The photon events recorded by a detector composed of a krypton gas proportional counter and a cesium iodide scintillation crystal are used to determine the spectrum of hard X-rays from the vicinity of Sgr XR-1.

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.

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