scholarly journals Spiral structure of the Galaxy Derived from the Hat Creek survey of neutral hydrogen

1970 ◽  
Vol 38 ◽  
pp. 126-139 ◽  
Author(s):  
H. Weaver
Keyword(s):  
Pitch Angle ◽  
Spiral Structure ◽  
Neutral Hydrogen ◽  
The Sun ◽  
General Picture ◽  
Contour Maps ◽  
The Galaxy ◽  
External Galaxies ◽  
Perseus Arm ◽  
Spiral Arm

The extensive Hat Creek survey of neutral hydrogen combined with southern observations provides the basis for a new discussion of the spiral structure of the galaxy. The purpose of this investigation is to provide a general picture of the galaxy. It is found that the pitch of the spiral arms is approximately 12°.5 and that there are many spurs and interarm features as we observe in external galaxies.The sun is not located in a major spiral arm, but rather in a spur or offshoot originating near or at the Sagittarius arm, which is a major structure in the galaxy. The young stars in the general vicinity of the sun delineate this spur, not a major arm structure. The stars and the gas are in agreement in indicating a large pitch angle (20°–25°) for this local structure, which differs from the smaller pitch angle for the arms which form the system as a whole.In the presentation a computer-produced movie of the galaxy based on Hat Creek hydrogen contour maps similar to those in Figure 1 was shown. It was used to illustrate generally the complexity of the gas structure and, in particular, to show (i) observational aspects of the spur in which the sun is located and (ii) the point of origin of the so-called Perseus arm.

Local stellar distribution and galactic spiral structure

1970 ◽  
Vol 38 ◽  
pp. 189-198 ◽  
Author(s):  
S. W. McCuskey
Keyword(s):  
Spiral Structure ◽  
The Sun ◽  
Long Period ◽  
Classical Cepheids ◽  
Galactic Clusters ◽  
The Galaxy ◽  
Galactic Spiral Structure ◽  
Ob Associations ◽  
Galactic Spiral ◽  
Spiral Arm

Aside from the well-known spiral arm tracers such as the OB associations, young galactic clusters, WR stars and possibly the long-period classical cepheids, the more common stars in the neighborhood of the sun within 2 kpc show little or no relationship to the local spiral structure of the galaxy.

scholarly journals Interpretation of the apparent anomalies of the Galactic structure

1985 ◽  
Vol 106 ◽  
pp. 305-308
Author(s):  
T. Jaakkola ◽  
N. Holsti ◽  
P. Teerikorpi
Keyword(s):  
Spiral Structure ◽  
Neutral Hydrogen ◽  
Hii Regions ◽  
Galactic Structure ◽  
Circular Motion ◽  
The Sun ◽  
The South ◽  
The North ◽  
Perseus Arm ◽  
Strong Curvature

In maps of the galactic structure based on the kinematical method (Fig. 1) several systematically heliocentric anomalies are found: 1. Assuming purely circular motion, the spiral arms are more tightly wound and the extent of neutral hydrogen is smaller in the northern galactic hemisphere than in the southern one. 2. With separate rotation curves for the north and the south, the arms become anomalously circular. 3. Consequently, there is a striking discrepancy with the stellar spiral structure. 4. There are long straight portions in the arms pointing towards the Sun. 5. There are abrupt knee-like features in the south. 6. Some arms seem to affect the structure of other, outer arms. 7. Conspicuously strong curvature of the arms is found in the north. 8. The HI-density is enhanced at symmetric longitudes on the far side. 9. With the northern rotation model HII-regions and HI avoid the southern tangential circle. 10. The Perseus Arm is displaced at 1 = 180°.

scholarly journals The Magellanic Stream as a probe of the galactic halo

1979 ◽  
Vol 84 ◽  
pp. 574-574
Author(s):  
R. J. Cohen ◽  
R. D. Davies ◽  
I. F. Mirabel
Keyword(s):  
Galactic Halo ◽  
Neutral Hydrogen ◽  
The Sun ◽  
Typical Size ◽  
Stellar Component ◽  
Large Velocity ◽  
The Galaxy ◽  
Magellanic Stream

Recent observations of the Magellanic Stream can be used to set limits on a possible hot halo surrounding the Galaxy. The observations are described in detail elsewhere (Mirabel, Cohen & Davies, submitted to Mon. Not. R. astr. Soc.). Briefly, the neutral hydrogen in the northern end of the Magellanic Stream is concentrated in narrow filaments which contain small elongated clouds of typical size 0°.4 × 0°.6. These clouds have a large velocity halfpower width (25 km s−1 and are gravitationally unstable, unless there is a massive low luminosity stellar component. If we consider only the observed gas the expansion age of a typical cloud is 6 × 105 D years, where D is the distance in kpc from the Sun, and this falls at least a factor of ten short of the age of the Stream predicted by current models. This strongly suggests that some containment mechanism is operating.

scholarly journals Interarm islands in the Milky Way – the one near the Cygnus spiral arm

2020 ◽  
Vol 494 (1) ◽  
pp. 1134-1142
Author(s):  
Jacques P Vallée
Keyword(s):  
Observational Data ◽  
Milky Way ◽  
Young Stars ◽  
H Ii Regions ◽  
Spiral Arms ◽  
The Galaxy ◽  
The One ◽  
Loop 2 ◽  
Perseus Arm ◽  
Spiral Arm

ABSTRACT This study extends to the structure of the Galaxy. Our main goal is to focus on the first spiral arm beyond the Perseus arm, often called the Cygnus arm or the ‘Outer Norma’ arm, by appraising the distributions of the masers near the Cygnus arm. The method is to employ masers whose trigonometric distances were measured with accuracy. The maser data come from published literature – see column 8 in Table 1 here, having been obtained via the existing networks (US VLBA, the Japanese VERA, the European VLBI, and the Australian LBA). The new results for Cygnus are split in two groups: those located near a recent CO-fitted global model spiral arm and those congregating within an ‘interarm island’ located halfway between the Perseus arm and the Cygnus arm. Next, we compare this island with other similar interarm objects near other spiral arms. Thus, we delineate an interarm island (6 × 2 kpc) located between the two long spiral arms (Cygnus and Perseus arms); this is reminiscent of the small ‘Local Orion arm’ (4 × 2 kpc) found earlier between the Perseus and Sagittarius arms and of the old ‘Loop’ (2 × 0.5 kpc) found earlier between the Sagittarius and Scutum arms. Various arm models are compared, based on observational data (masers, H II regions, H I gas, young stars, CO 1–0 gas).

scholarly journals High Velocity Neutral Hydrogen Clouds

1974 ◽  
Vol 60 ◽  
pp. 599-616
Author(s):  
R. D. Davies
Keyword(s):  
High Velocity ◽  
Spiral Structure ◽  
Neutral Hydrogen ◽  
Magellanic Clouds ◽  
Galactic Rotation ◽  
Velocity Pattern ◽  
Tidal Interactions ◽  
The Galaxy ◽  
High Velocity Clouds

A review is given of the observations of neutral hydrogen high velocity clouds (|ν| > 80 km s−1) in and near the Galaxy. The positive and negative clouds are seen to have different distributions in the sky, following roughly the velocity pattern of galactic rotation. A characteristic of the majority of the clouds is their distribution in elongated bands or strings. The various theories of origin of HVCs are discussed; the possible role of the tidal interactions between the Magellanic Clouds and the Galaxy is emphasized. Tests are suggested to distinguish between the Oort theory of the infall of intergalactic material and theories which envisage the HVCs as originating in the outermost spiral structure.

scholarly journals A multiwavelength study of spiral structure in galaxies. I. General characteristics in the optical

2020 ◽  
Vol 493 (1) ◽  
pp. 390-409
Author(s):  
Sergey Savchenko ◽  
Alexander Marchuk ◽  
Aleksandr Mosenkov ◽  
Konstantin Grishunin
Keyword(s):  
Pitch Angle ◽  
Spiral Structure ◽  
Wavelength Dependence ◽  
Sloan Digital Sky Survey ◽  
Galactocentric Distance ◽  
Distinctive Features ◽  
Sky Survey ◽  
Grand Design ◽  
Generation Mechanisms ◽  
Spiral Arm

ABSTRACT Different spiral generation mechanisms are expected to produce different morphological and kinematic features. In this first paper in a series, we carefully study the parameters of spiral structure in 155 face-on spiral galaxies, selected from the Sloan Digital Sky Survey, in the three gri bands. We use a method for deriving a set of parameters of spiral structure, such as the width of the spiral arms, their fraction to the total galaxy luminosity, and their colour, which have not been properly studied before. Our method is based on an analysis of a set of photometric cuts perpendicular to the direction of a spiral arm. Based on the results of our study, we compare the main three classes of spirals: grand design, multi-armed, and flocculent. We conclude that: (i) for the vast majority of galaxies (86 per cent), we observe an increase of their arm width with Galactocentric distance; (ii) more luminous spirals in grand design galaxies exhibit smaller variations of the pitch angle with radius than those in less luminous grand design spirals; (iii) grand design galaxies show less difference between the pitch angles of individual arms than multi-armed galaxies. Apart from these distinctive features, all three spiral classes do not differ significantly by their pitch angle, arm width, width asymmetry, and environment. Wavelength dependence is found only for the arm fraction. Therefore, observationally we find no strong difference (except for the view and number of arms) between grand design, multi-armed, and flocculent spirals in the sample galaxies.

scholarly journals A motion picture film of galactic 21-cm line emission

1970 ◽  
Vol 38 ◽  
pp. 122-125 ◽  
Author(s):  
G. Westerhout
Keyword(s):  
Galactic Plane ◽  
Line Emission ◽  
Neutral Hydrogen ◽  
Hydrogen Distribution ◽  
Motion Picture Film ◽  
Contour Maps ◽  
Latitude Range ◽  
The Galaxy ◽  
Line Survey ◽  
Line Work

Since 1964 we have been observing 21-cm line profiles in a new survey of the neutral hydrogen distribution in the neighborhood of the galactic plane with the 300-foot radio telescope of the National Radio Astronomy Observatory in Green Bank, W.Va. This is the largest telescope available for 21-cm line work; it has a beamwidth of 10 min of arc and is equipped with an excellent line receiver. Since it seems unlikely that an extensive hydrogen-line survey will be made with any larger telescope, we felt that for reference purposes a concerted effort should be made to obtain as many 21-cm data as possible pertaining to the structure of the Galaxy with this telescope. The data have been presented in the form of contour maps giving the intensity of the 21-cm line radiation as a function of right-ascension and velocity at constant declination. A series of contour maps was distributed to the astronomical community in 1966 as the first edition of the Maryland–Green Bank Galactic 21-cm Line Survey. The second edition, containing 1200 pages and approximately 1800 maps, was distributed in the summer and fall of 1969. It is expected that additional contour maps, completing the survey as originally planned, covering a latitude range from bII = +1° to −1°, lII = 11° to 235° (bII = +3° to −3° between lII = 100° and 145°), will be finished by the summer of 1970. Scans were made across the galactic equator with a stationary telescope, so that the declination is constant through each scan; the declination intervals varied from 4 to 6 min of arc. Eventually, we plan to cover a strip from bII = +5° to −5° between lII = 11° and 235°, containing 225000 independent points at intervals of 6 min of arc, with an effective beamwidth of 12.5 min of arc, a velocity resolution of 2 km s-1, and a total of 1.2 × 108 individual intensities.

scholarly journals A comparison of the Andromeda and Milky Way galaxies

1985 ◽  
Vol 106 ◽  
pp. 423-430
Author(s):  
Paul Hodge
Keyword(s):  
Pitch Angle ◽  
Milky Way ◽  
Spiral Structure ◽  
Type A ◽  
Detailed Comparison ◽  
Basic Properties ◽  
Density Enhancement ◽  
The Galaxy ◽  
Optical Tracers

A comparison of some of the basic properties of M31 and the Milky Way indicates that in almost every respect M31 is larger than the Galaxy. It is more luminous, redder, more massive, and of earlier Hubble type. A detailed comparison of the spiral structure, based on optical tracers, for comparable areas in the outer parts of each galaxy shows differences in the arm spacings, in density enhancement, and in pitch angle.

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