Determination of parameters of the spiral structure of the galaxy from the radio emission of neutral hydrogen at 21 CM. I. Linear theory. Nonresonance region

Astrophysics ◽  
1979 ◽  
Vol 14 (4) ◽  
pp. 361-365
Author(s):  
V. G. Berman ◽  
Yu. N. Mishurov
Keyword(s):  
Radio Emission ◽  
Linear Theory ◽  
Spiral Structure ◽  
Neutral Hydrogen ◽  
The Galaxy ◽  
Determination Of Parameters

scholarly journals Observational description of the warp in our galaxy

1979 ◽  
Vol 84 ◽  
pp. 493-499 ◽  
Author(s):  
A. P. Henderson
Keyword(s):  
Southern Hemisphere ◽  
Northern Hemisphere ◽  
Outer Region ◽  
Neutral Hydrogen ◽  
Reduction Stage ◽  
University Of Maryland ◽  
The Galaxy ◽  
Region 10 ◽  
The University

In 1975 F. J. Kerr and P. F. Bowers of the University of Maryland made a full coverage survey of the neutral hydrogen in the southern hemisphere between ±10° latitude from 240° to 350° in longitude. This survey taken with the CSIRO 18 meter telescope is still in the reduction stage but when completed it will provide an ideal complement to the full ±10° coverage of the northern sky by H. Weaver and D. R. W. Williams (1973). The possibility of a unified analysis of the outer region of the Galaxy has inspired this present study. The plan here is to use the ±10° Weaver-Williams survey in the region 10° < ℓ < 130°; the ±30° extension to this survey (H. Weaver and D. R. W. Williams, 1974) in the region 115° < ℓ < 245° and finally the Kerr-Bowers survey, 240° < ℓ < 350°. Since the latter survey is incompletely reduced at this time we have only used profiles at 5° intervals in longitude and thereby have produced a preliminary determination of the plane in the southern hemisphere. The northern hemisphere determination is complete.

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.

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 Quantifying EoR delay spectrum contamination from diffuse radio emission

2020 ◽  
Vol 494 (3) ◽  
pp. 3712-3727 ◽  
Author(s):  
Adam E Lanman ◽  
Jonathan C Pober ◽  
Nicholas S Kern ◽  
Eloy de Lera Acedo ◽  
David R DeBoer ◽  
...  
Keyword(s):  
Radio Emission ◽  
Large Scale ◽  
Power Spectra ◽  
Neutral Hydrogen ◽  
Spectral Structure ◽  
Wide Field ◽  
Electromagnetic Simulations ◽  
The Galaxy ◽  
Spectral Weighting ◽  
The Universe

ABSTRACT The 21 cm hyperfine transition of neutral hydrogen offers a promising probe of the large-scale structure of the universe before and during the Epoch of Reionization (EoR), when the first ionizing sources formed. Bright radio emission from foreground sources remains the biggest obstacle to detecting the faint 21 cm signal. However, the expected smoothness of foreground power leaves a clean window in Fourier space where the EoR signal can potentially be seen over thermal noise. Though the boundary of this window is well defined in principle, spectral structure in foreground sources, instrumental chromaticity, and choice of spectral weighting in analysis all affect how much foreground power spills over into the EoR window. In this paper, we run a suite of numerical simulations of wide-field visibility measurements, with a variety of diffuse foreground models and instrument configurations, and measure the extent of contaminated Fourier modes in the EoR window using a delay-transform approach to estimate power spectra. We also test these effects with a model of the Hydrogen Epoch of Reionization Array (HERA) antenna beam generated from electromagnetic simulations, to take into account further chromatic effects in the real instrument. We find that foreground power spillover is dominated by the so-called pitchfork effect, in which diffuse foreground power is brightened near the horizon due to the shortening of baselines. As a result, the extent of contaminated modes in the EoR window is largely constant over time, except when the Galaxy is near the pointing centre.

Distribution and systematic motions of neutral hydrogen

1967 ◽  
Vol 31 ◽  
pp. 143-160 ◽  
Author(s):  
P. O. Lindblad
Keyword(s):  
Recent Work ◽  
Large Scale ◽  
Galactic Plane ◽  
Neutral Hydrogen ◽  
Structural Features ◽  
Frequency Resolution ◽  
Narrow Strip ◽  
The Galaxy ◽  
Scale Motion ◽  
Determination Of Parameters

Recent work on the rotation curve of the Galaxy has confirmed the large-scale asymmetry of the motion of neutral hydrogen. In addition it seems that the radial velocities at the subcentral points of the lines of sight vary with longitude in a rather unsmooth manner. These irregularities of the motions may be associated with the distribution of matter in spiral arms. Large-scale systematic deviations from circular motion, ranging up to at least 30 km/sec in the outer regions of the Galaxy, are shown by observations across the anti-centre.Thus it presumably is impossible to describe the velocity field of the gas in terms of a simple general model, or to derive the force field without simultaneously solving the distribution problem. We may have to construct for each region, or for each separate feature of galactic structure, a special model that explains its radial-velocity properties. All these models must of course be in mutual agreement.The most coherent picture of the large-scale motion of the interstellar hydrogen is still given by the early Dutch and Australian surveys. A number of surveys with higher resolution are at present well on their way, although most of them are limited to a rather narrow strip along the galactic equator.In the interpretation of line profiles some method of analysis into Gaussian components is increasingly used, especially as an aid in following different structural features in diagrams giving velocity as a function of galactic longitude or latitude, and in separating these features in regions of velocity overlap. Applications of this technique and of simple model-making are demonstrated in connection with a discussion of the local and outer structure of the Galaxy.Large-scale deviations from the galactic plane as found in recent work indicate that the ‘bending’ of the plane may be a complicated phenomenon. New observations outlining the true character of this bending are necessary for a decision between the different theories about these deviations.The need for surveys with high frequency resolution and extending away from the galactic plane is emphasized. Optical identifications of members of the various structural features are highly desirable as an independent determination of parameters of structural models.

Places of formation of young and moderately young stars

1967 ◽  
Vol 31 ◽  
pp. 323-329 ◽  
Author(s):  
Bengt Strömgren
Keyword(s):  
Spiral Structure ◽  
Narrow Band ◽  
Accurate Determination ◽  
Young Stars ◽  
Photoelectric Photometry ◽  
Peculiar Velocities ◽  
Stellar Ages ◽  
The Galaxy ◽  
Perseus Arm

Narrow-band photoelectric photometry can furnish classification indices allowing accurate determination of stellar ages. From these ages, together with well-determined space motions, the places of formation of stars, and their relationship to the spiral structure of the Galaxy, may be determined. This procedure has been successfully followed for 52 B8–B9 stars within 200 pc from the Sun. It turns out that seven of these have originated in the Perseus Arm, with local peculiar velocities of about 22 km/sec.A simple model is developed describing places of star formation in the Perseus Arm and velocities at formation. The distribution of space velocities and of ages for stars formed according to this model appears to be in agreement with observation.

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