scholarly journals 37. Galactic radio emission and the distribution of discrete sources: Introductory Lecture

1957 ◽  
Vol 4 ◽  
pp. 211-217
Author(s):  
R. Hanbury Brown
Keyword(s):  
Radio Emission ◽  
Thermal Emission ◽  
Wave Length ◽  
Black Body ◽  
Interstellar Gas ◽  
Ionized Gas ◽  
Introductory Lecture ◽  
The Galaxy ◽  
Image Position ◽  
Galactic Radio

At wave-lengths greater than about 1 metre the majority of the radio emission which is observed from the Galaxy cannot be explained in terms of thermal emission from ionized interstellar gas. This conclusion is widely accepted and is based on observations of the equivalent temperature of the sky and the spectrum of the radiation. The spectrum at metre wave-lengths is of the general form: where TA is the equivalent black-body temperature of a region of sky and λ is the wave-length. The exponent n varies with direction but lies between about 2·5 and 2·8, and is thus significantly greater than the value of 2·0 which is the maximum to be expected for thermal emission from an ionized gas. Furthermore, the value of TA is about 1050K. at 15 metres and thus greatly exceeds the electron temperature expected in H 11 regions.At centimetre wave-lengths it is likely that the majority of the radiation observed originates in thermal emission from ionized gas; however, the present discussion is limited to a range of wave-lengths from about 1 to 10 metres where the ionized gas in the Galaxy is believed to be substantially transparent and where the origin of most of the radiation is believed to be non-thermal.

scholarly journals Galactic and extra-galactic radio frequency radiation due to sources other than the thermal and 21-cm emission of the interstellar gas

1958 ◽  
Vol 5 ◽  
pp. 37-43
Author(s):  
R. Hanbury Brown
Keyword(s):  
Thermal Emission ◽  
Wave Length ◽  
Black Body ◽  
Interstellar Gas ◽  
Ionized Gas ◽  
Radio Frequency Radiation ◽  
The Galaxy ◽  
Image Position ◽  
Galactic Radio ◽  
Frequency Radiation

At wave-lengths greater than about one metre the majority of the radio emission which is observed from the Galaxy cannot be explained in terms of thermal emission from ionized interstellar gas. This conclusion is widely accepted and is based on observations of the equivalent temperature of the sky and the spectrum of the radiation. The spectrum at metre wave-lengths is of the general form: where TA is the equivalent black-body temperature of a region of sky and A is the wave-length. The exponent n varies with direction but lies between about 2·5 and 2·8, and is thus significantly greater than the value of 2·0 which is the maximum to be expected for thermal emission from an ionized gas. Furthermore the value of TA is about 1050 K at 15 m and thus greatly exceeds the electron temperature expected in H 11 regions.At centimetre wave-lengths it is likely that the majority of the radiation observed originates in thermal emission from ionized gas; however, the present discussion is limited to a range of wave-lengths from about 1 m to 10 m where the ionized gas in the Galaxy is believed to be substantially transparent and where the origin of most of the radiation is believed to be non-thermal.

scholarly journals Study of the Magnetic Field of the Galaxy using Correlation Functions of the Intensity of Synchrotron Background Radio Emission

1996 ◽  
Vol 169 ◽  
pp. 615-616
Author(s):  
V.R. Shoutenkov
Keyword(s):  
Magnetic Field ◽  
Radio Emission ◽  
Correlation Functions ◽  
Theoretical Calculations ◽  
Angular Separation ◽  
Field Studies ◽  
Position Angle ◽  
The Galaxy ◽  
Image Position ◽  
The Magnetic Field

The possibility to study magnetic field of the Galaxy calculating correlation or structure functions of synchrotron background radio emission have been known long ago (Kaplan and Pikel'ner (1963); Getmantsev (1958)). But this method had not been as popular as other methods of magnetic field studies. However theoretical calculations made by Chibisov and Ptuskin (1981) showed that correlation functions of intensity of synchrotron background radio emission can give a lot of valuable information about galactic magnetic fields because of the intensity of synchrotron background radio emission depends on H⊥. According to this theory correlation C(θ, φ) and structure S(θ, φ) functions of intensity, as functions of angular separation θ between two lines of sight and position angle φ on the sky between this two lines of sight, can be presented as a sum of isotropic (not dependent from angle φ) and anisotropic parts:

scholarly journals 79. Radio emission from the moon and the nature of its surface

1957 ◽  
Vol 4 ◽  
pp. 406-407 ◽  
Author(s):  
V. S. Troitzky ◽  
S. E. Khaikin
Keyword(s):  
Radio Emission ◽  
Attenuation Coefficient ◽  
Wave Length ◽  
Degree Of Polarization ◽  
Lunar Phase ◽  
Radio Waves ◽  
The Moon ◽  
Subsolar Point ◽  
Image Position ◽  
Academy Of Sciences

A theoretical study of the integral radio emission of the moon, measured at the wave-length of 3·2 cm. (Zelinskaja and Troitzky[1]; Kajdanovsky, Turusbekov and Khaikin[2]), was carried out at the Gorky radio astronomical station ‘Zimenky’ and at the Physical Institute of the Academy of Sciences of the U.S.S.R. The following expression for the average radio temperature of the entire lunar disk, as a function of the lunar phase, Ωt, was obtained (Troitzky, 1954) [3]: Here tan ξ = δ/(1 + δ) and δ = β/κ, where β is the attenuation coefficient of the thermal wave, κ the power attenuation coefficient of the radio wave. Further, Tm = 374°K. is the temperature of the subsolar point, Tn is the temperature at the lunar midnight, Θ = Tm – Tn and k0 is the reflexion coefficient of radio waves for vertical incidence (k0 ≈ 0–1). The numerical coefficients in equation (1) were obtained as a result of averaging the Fresnel reflexion coefficients over the whole disk. The degree of polarization of the total radio emission was calculated and was found to be about 4 %.

scholarly journals 41. The spherical component of the galactic radio emission

1957 ◽  
Vol 4 ◽  
pp. 233-237
Author(s):  
J. E. Baldwin
Keyword(s):  
Radio Emission ◽  
Brightness Temperature ◽  
Radio Telescope ◽  
Galactic Plane ◽  
Wave Length ◽  
Spherical Component ◽  
Long Wave ◽  
Half Power ◽  
Right Ascension ◽  
Galactic Radio

As part of the programme of observations with the large Cambridge radio telescope, a survey of the integrated radio emission has been made using one of the four elements of the interferometer. At a wave-length of 3·7 metres this aerial has beam-widths to half-power points of 2° in right ascension and 15° in declination. The use of a long wave-length makes it possible to obtain accurate measurements of the brightness temperature of the sky in regions away from the galactic plane. It is with the radiation from these regions that this paper is primarily concerned.

scholarly journals Solar radiation in the radio spectrum - I. Radiation from the quiet sun

1948 ◽  
Vol 193 (1032) ◽  
pp. 44-59 ◽  
Keyword(s):  
Effective Temperature ◽  
Collision Frequency ◽  
Wave Length ◽  
Radio Spectrum ◽  
Quantum Mechanical ◽  
Ionized Gas ◽  
M Wave ◽  
Lorentz Theory ◽  
Mechanical Expression ◽  
Galactic Radio

The theory of the emission of thermal radiation from the solar envelope at radio-frequencies is worked out in detail. The Lorentz theory of absorption is used in conjunction with Kirchhoff’s law to derive the effective temperature of the various regions of the solar disk over the radio spectrum. A maximum effective temperature approaching 10 6 °C is found in the vicinity of 1 m. wave-length. Limb brightening occurs at centimetre wave-lengths. It is shown that Gaunt’s quantum mechanical expression for free-free emission yields results almost identical with the classical treatment, provided Chapman and Cowling’s expression for the collision frequency in a fully ionized gas is used in the latter treatment. It is suggested that it may be preferable to treat problems of solar and galactic radio noise by classical methods, particularly when the refractive index of the medium departs appreciably from unity.

scholarly journals Observations of the galactic radio emission between 1.5 and 10 MHz from the Alouette Satellite

1965 ◽  
Vol 23 ◽  
pp. 319-326
Author(s):  
T. R. Hartz
Keyword(s):  
Radio Emission ◽  
Local Electron ◽  
Frequency Curve ◽  
Sweep Frequency ◽  
The Earth ◽  
Galactic Emission ◽  
The Galaxy ◽  
Noise Measurements ◽  
Galactic Radio Emission ◽  
Galactic Radio

Since September 29, 1962, a sweep-frequency receiver covering the range 0.5 to 12 MHz has been operating in a 1000 km height, 80.5° inclination orbit about the earth for about 5 hours a day on the average. Only a very small portion of the data has yet been analyzed, and from this the spectrum of the galactic radio emission between 1.5 and 5 MHz has been determined fairly reliably, but it has not been possible from these data to extend this up to 10 MHz with any accuracy. Although there is no provision for absolute gain calibration of the receiver in flight, the data are so consistent as to give confidence to the pre-flight calibration. The greatest uncertainty hinges on the effects of the ionization on the antenna impedances. To evaluate these, galactic noise measurements have been made under a variety of local electron densities and different magnetic field strengths : these values have then been extrapolated to zero electron density and the free space values obtained by this extrapolation procedure are taken as a measure of the galactic emission. At 2.3 MHz the brightest region of the galaxy is centred on the south galactic pole and has a temperature of about 1.8 × 107 °K. The lowest temperature, about 5.0 × 106 °K, at 2.3 MHz was found for the region centred on R. A. 9 hr., dec + 75°. At this same frequency the brightness temperature versus frequency curve has a elope of — 1.7; at 1.5 MHz the slope is — 1.3 and at 5.0 MHz the slope is — 2.2.

Radio-Frequency Radiation from the Constellation of Cygnus

1952 ◽  
Vol 5 (1) ◽  
pp. 17 ◽  
Author(s):  
JH Piddington ◽  
HC Minnett
Keyword(s):  
Thermal Emission ◽  
Limited Extent ◽  
Interstellar Gas ◽  
Radio Frequency Radiation ◽  
Diffuse Source ◽  
Cygnus A ◽  
The Galaxy ◽  
New Evidence ◽  
Spiral Arm ◽  
Frequency Radiation

Observations are described of the radiation from portion of the constellation of Cygnus at frequencies of 1210 and 3000 Mc/s. Two sources of radiation were observed at the lower frequency, one being the well-known "radio star ", Cygnus-A. The other was a diffuse source of limited extent which might be called a " radio nebula ". Neither source could be observed at the higher frequency. The properties of both sources, particularly their spectra, are discussed and it is shown that earlier discrepancies in observations of the Cygnus region may be explained. The diffuse source coincides in position with the secondary maximum in the lower frequency galactic contours, which Bolton and Westfold (1950a, 1950b) have interpreted as a spiral arm of the Galaxy. The new evidence suggests that the source is probably due to thermal emission from clouds of ionized interstellar gas, possibly in the region of γ Cygni and having a temperature and electron density of the order of 104 �K, and 10 cm-3 respectively.

scholarly journals Some new observations relating to galactic radio sources and background structure

1964 ◽  
Vol 20 ◽  
pp. 107-114 ◽  
Author(s):  
E. R. Hill
Keyword(s):  
Radio Emission ◽  
Radio Telescope ◽  
Milky Way ◽  
Angular Resolution ◽  
Spectral Information ◽  
Radio Sources ◽  
Background Structure ◽  
The Galaxy ◽  
Galactic Radio

A survey of the distribution of radio emission at wavelengths of 75 and 20 cm along an extensive section of the Southern Milky Way has recently been carried out by M. Komesaroff and myself using the 210-foot radio telescope at Parkes. The area surveyed ranges from lII = 280 to 355° and extends on the average to 6 degrees either side of the plane. The beamwidths of the aerial at 75 and 20 cm are 50 and 14 min arc respectively. Observations at the shorter wavelength offer a picture of this section of the Galaxy at considerably higher angular resolution than hitherto available, while the 75-cm observations are expected to make a useful contribution to our spectral information.

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.

The GLEAM 4-Jy Sample: The brightest radio-sources in the southern sky

2019 ◽  
Vol 15 (S356) ◽  
pp. 375-375
Author(s):  
Sarah White
Keyword(s):  
Radio Emission ◽  
Active Galactic Nuclei ◽  
Visual Inspection ◽  
Low Frequency ◽  
Galactic Nuclei ◽  
Radio Sources ◽  
Relativistic Jets ◽  
The Galaxy ◽  
Murchison Widefield Array ◽  
Past Activity

AbstractLow-frequency radio emission allows powerful active galactic nuclei (AGN) to be selected in a way that is unaffected by dust obscuration and orientation of the jet axis. It also reveals past activity (e.g. radio lobes) that may not be evident at higher frequencies. Currently, there are too few “radio-loud” galaxies for robust studies in terms of redshift-evolution and/or environment. Hence our use of new observations from the Murchison Widefield Array (the SKA-Low precursor), over the southern sky, to construct the GLEAM 4-Jy Sample (1,860 sources at S151MHz > 4 Jy). This sample is dominated by AGN and is 10 times larger than the heavily relied-upon 3CRR sample (173 sources at S178MHz > 10 Jy) of the northern hemisphere. In order to understand how AGN influence their surroundings and the way galaxies evolve, we first need to correctly identify the galaxy hosting the radio emission. This has now been completed for the GLEAM 4-Jy Sample – through repeated visual inspection and extensive checks against the literature – forming a valuable, legacy dataset for investigating relativistic jets and their interplay with the environment.

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