Galactic Radiation at Radio Frequencies. III. Galactic Structure

1950 ◽  
Vol 3 (2) ◽  
pp. 251
Author(s):  
JG Bolton ◽  
KC Westfold
Keyword(s):  
Radio Frequency ◽  
Spiral Galaxy ◽  
Galactic Structure ◽  
The Sun ◽  
Frequency Data ◽  
Spiral Form ◽  
The Galaxy ◽  
Radio Frequencies ◽  
Optical Evidence ◽  
Galactic Radiation

From radio-frequency observations it is deduced that the sun is situated in or near an arm of a spiral galaxy. The first part of this paper consists of an analysis of the radio-frequency data followed by the presentation of optical evidence in favour of a spiral form. The sense of rotation of the Galaxy -that of the spiral unwinding- is in accordance with the theories of Lindblad and Milne.

scholarly journals An investigation of galactic radiation in the radio spectrum

1948 ◽  
Vol 192 (1030) ◽  
pp. 425-445 ◽  
Keyword(s):  
Reference Signal ◽  
Galactic Structure ◽  
General Distribution ◽  
Method Of Successive Approximations ◽  
Galactic Centre ◽  
Finite Width ◽  
Main Body ◽  
Astronomical Data ◽  
The Galaxy ◽  
Galactic Radiation

An investigation of the distribution of the sources of galactic radiation at 64 Mcyc./sec. is described. Methods are discussed by which the characteristics of the receiving antenna were measured and by which the magnitude of the received galactic power was estimated by comparison with a reference signal of similar amplitude characteristics. The method of analysis of results is described in detail, with emphasis on the need for allowing for the finite width of the main cone of reception of signal power and for the sensitivity of the antenna to signal sources outside the main cone. The necessary corrections are effected by a method of successive approximations, and contours of the distribution of the signal source between declinations + 50° and — 30° are derived. The results are expressed in terms of power flux and also of effective aerial temperature. Possible sources of error are discussed and an accuracy better than 1.2 db. (30 %) is expected for the regions of highest radiation intensity. Reference is made to the fluctuations observed in the radiations coming from Cygnus. The correlation of the derived distribution of galactic radiations with other astronomical data is discussed with special reference to the galactic structure. It is shown that correlation with the near galactic structure, as indicated by the general distribution of visible sources of light, is not very good, but that a more satisfactory correlation is obtained with data which are believed to be characteristic of the structure of the galaxy as a whole. The bias to the south of the galactic circle shown by radiation sources in the vicinity of the galactic centre is especially significant. Various relevant astronomical data are collected together in the accompanying diagrams. The bearing of these correlations on the question of the nature of the source of radiation is examined. It is shown that they do not clearly favour any one theory, and that neither a simple theory in terms of a distributed source in interstellar gas nor one in terms of discrete centres of radiation analogous to sunspots appears adequate to account for the observed phenomena. It is suggested that sources of both types contribute to the observed radiation and that, in general, they must be very distant and associated with the main body of the galaxy.

scholarly journals The origin of the belt of galactic radio waves

1959 ◽  
Vol 9 ◽  
pp. 571-573
Author(s):  
Harriet Tunmer
Keyword(s):  
Spiral Galaxy ◽  
Equatorial Plane ◽  
Cosmic Radio ◽  
Total Emission ◽  
Radio Waves ◽  
Optical Studies ◽  
The Galaxy ◽  
Optical Evidence ◽  
Galactic Radio

Most of the background of cosmic radio waves comes from our own Galaxy. In the equatorial plane this origin is evident, and the obvious features can be directly related to the Galaxy's structure. Away from the plane the emission comes from a roughly spherical halo, which accounts for most of the total emission from the Galaxy. Some features in this part of the sky are not evident from optical studies; the most important is a circular belt of emission passing not far from the center and the anti-center. It is impossible that this should be extragalactic in origin, since it is more than twice as bright as the brightest estimates of the whole galactic component, and optical evidence would be expected of such a major irregularity in the distribution of the galaxies, or indeed of a single spiral galaxy close to or enveloping our own. We turn therefore to a suggestion of an origin in our own Galaxy.

scholarly journals III. Local Galactic Structure

1985 ◽  
Vol 19 (1) ◽  
pp. 407-409
Keyword(s):  
Milky Way ◽  
Gamma Ray ◽  
Galactic Structure ◽  
Solar Neighbourhood ◽  
The Sun ◽  
X Ray ◽  
The Galaxy

This section contains work dealing with the Milky Way characteristics in the solar neighbourhood and supported by observations with wavelengths shorter than 1 mm. Thus, results are collected from gamma-ray, X-ray, UV, optical and IR observations in the different subsections. These are (1) the volume closest to the sun, (2) more distant objects at low galactic latitudes, and (3) objects at high galactic latitudes. Overall properties of the Galaxy and evolutionary effects are presented in Section IV.

scholarly journals B. Models of the Galaxy

1985 ◽  
Vol 19 (1) ◽  
pp. 423-425
Keyword(s):  
Observational Data ◽  
Rotational Velocity ◽  
Galactic Structure ◽  
The Sun ◽  
Circular Velocity ◽  
The Galaxy

Reviews of implications of the recent observational data concerning the galactic structure were given by Bok (33.013.022) and Blitz et al. (33.155.115).The recent data of the rotational velocity in the Galaxy were discussed by Blitz (33.155.023) and Knapp (33.155.053). A method to derive the circular velocity at the sun was proposed by Lynden-Bell and Frenk (30.155.053).

scholarly journals Can Galactic GMCs be Identified from l-v Diagrams?

1989 ◽  
Vol 8 ◽  
pp. 587-588
Author(s):  
David S. Adler ◽  
William W. Roberts
Keyword(s):  
Numerical Simulations ◽  
Spiral Galaxy ◽  
Molecular Cloud ◽  
Cloud System ◽  
The Sun ◽  
Interstellar Gas ◽  
The Past ◽  
The Galaxy

Identifying the spiral nature of the distribution of gas in the Galaxy has been a subject of much research in the past thirty years. The position of the sun in the disk of the Galaxy presents us with a problem of perspective: how does one identify the cloud system from within the system? Longitude-velocity (l-v) diagrams have been used to try to determine the distribution of interstellar gas, but problems inherent in the methods have been pointed out previously (Burton 1971). Recent Galactic CO surveys have been used in attempts to map the distribution of molecular cloud complexes in the disk of the Galaxy (Dame, et al. 1986). Here, we use numerical simulations of the molecular cloud system in a spiral galaxy to consider the following question: to what extent can concentrations of emission in the l-v diagram (LVCs) be considered complexes of gas in the disk of the Galaxy (GMCs)?

scholarly journals II. The Galaxy

1959 ◽  
Vol 7 ◽  
pp. 65-80
Author(s):  
N. G. Roman
Keyword(s):  
Globular Clusters ◽  
Planetary Nebulae ◽  
Stellar Populations ◽  
Galactic Structure ◽  
Galactic Rotation ◽  
The Sun ◽  
Important Region ◽  
The Galaxy ◽  
Efficient Selection ◽  
Selection Of

The region within about a kiloparsec of the sun contains no globular clusters, and few associations, planetary nebulae, novae, or Cepheids; the interpretation of 21-cm observations is complicated by peculiar motions which are comparable with galactic rotation effects. Nevertheless, this is an extremely important region for the study of galactic structure. Not only are all distance calibrations ultimately based on objects near the sun, but only in this region do we have the resolution necessary to examine the detail of galactic structure and only here can we study the numerous fainter members of the various stellar populations. As elsewhere, the problems are two-fold, the efficient selection of those objects whose study is the most informative and the choice of the methods of obtaining the greatest amount of information about those objects.

scholarly journals Two uneven sisters

2018 ◽  
Vol 620 ◽  
pp. A108
Author(s):  
B. Vollmer ◽  
C. Pappalardo ◽  
M. Soida ◽  
A. Lançon
Keyword(s):  
Spiral Galaxy ◽  
Galactic Disk ◽  
Pressure Profile ◽  
Galactic Structure ◽  
Virgo Cluster ◽  
Radio Continuum ◽  
Continuum Emission ◽  
Free Region ◽  
Ram Pressure ◽  
The Galaxy

Since the Virgo cluster is the closest galaxy cluster in the northern hemisphere, galaxy interactions can be observed in it at kiloparsec resolution. The spiral galaxy NGC 4388 underwent a ram-pressure stripping event ∼200 Myr ago caused by its highly eccentric orbit within the Virgo cluster. This galaxy fulfills all diagnostic criteria for having undergone active ram-pressure stripping in the recent past: it has a strongly truncated HI and Hα disk, an asymmetric ridge of polarized radio continuum emission, extended extraplanar gas toward the opposite side of the ridge of polarized radio continuum emission, and has undergone a recent (a few hundred million years ago) quenching of its star formation activity in the outer, gas-free galactic disk. We made dynamical simulations of the ram-pressure stripping event to investigate the influence of galactic structure on the observed properties of NGC 4388. The combination of a deep optical spectrum of the outer gas-free region of the galactic disk together with deep HI, Hα, far-ultraviolet, and polarized radio continuum data allows us to constrain numerical simulations to derive the temporal ram-pressure profile, the three-dimensional velocity vector of the galaxy, and the time since peak ram pressure with a high level of confidence. From the simulations, an angle between the ram-pressure wind and the galactic disk of 30° is derived. The galaxy underwent peak ram pressure ∼240 Myr ago. The observed asymmetries in the disk of NGC 4388 are not caused by the present action of ram pressure, but by the resettling of gas that has been pushed out of the galactic disk during the ram-pressure stripping event. For the detailed reproduction of multi-wavelength observations of a spiral galaxy that undergoes or underwent a ram-pressure stripping event, galactic structure, such as spiral arms for example, must be taken into account.

Galactic orbits of stars

1966 ◽  
Vol 25 ◽  
pp. 93-97
Author(s):  
Richard Woolley
Keyword(s):  
Globular Cluster ◽  
Potential Field ◽  
High Velocity ◽  
Velocity Vector ◽  
Variable Stars ◽  
The Sun ◽  
Proper Motions ◽  
Rr Lyrae ◽  
The Galaxy

It is now possible to determine proper motions of high-velocity objects in such a way as to obtain with some accuracy the velocity vector relevant to the Sun. If a potential field of the Galaxy is assumed, one can compute an actual orbit. A determination of the velocity of the globular clusterωCentauri has recently been completed at Greenwich, and it is found that the orbit is strongly retrograde in the Galaxy. Similar calculations may be made, though with less certainty, in the case of RR Lyrae variable stars.

Bipolar outflow of gas in the spiral galaxy NGC 3079

1986 ◽  
Vol 64 (4) ◽  
pp. 531-535 ◽  
Author(s):  
Nebojsa Duric ◽  
E. R. Seaquist
Keyword(s):  
Spectral Index ◽  
Spiral Galaxy ◽  
Central Region ◽  
Qualitative Description ◽  
Radio Continuum ◽  
Large Array ◽  
Very Large Array ◽  
Bipolar Outflow ◽  
The Galaxy

Very large array, radio-continuum observations of the edge-on spiral galaxy NGC 3079 are presented. The observations reveal that the nucleus has windlike properties and that the central region of the galaxy exhibits an unusual figure-eight morphology that shows evidence of severe depolarization and a flattening spectral index away from the nucleus. A qualitative description of a model is presented to account for the observed radio properties. It is shown that a wind-driven shock propagating away from the nucleus and focused by the ambient disk gas can give rise to the observed morphology.

Neural Network Generative Models for Radio Frequency Data

2021 ◽  
Author(s):  
Joseph Carmack ◽  
Amit Bhatia ◽  
Josh Robinson ◽  
John Majewski ◽  
Scott Kuzdeba
Keyword(s):  
Neural Network ◽  
Radio Frequency ◽  
Generative Models ◽  
Frequency Data
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