A radio method of searching for fine structure in H 11 regions

1967 ◽  
Vol 31 ◽  
pp. 237
Author(s):  
O. B. Slee
Keyword(s):  
Fine Structure ◽  
Radio Emission ◽  
Electron Density ◽  
Path Length ◽  
Low Frequency ◽  
Radio Sources ◽  
Average Electron Density ◽  
Scale Size ◽  
Average Electron ◽  
Radio Method

Fine structure with a scale size of about 10-3pc in the galactic ionized hydrogen may scatter the low-frequency radio emission of extragalactic sources with intrinsically small angular diameters, thus making them apparently large. For example, application of the Chandrasekhar scattering formula to a path length of 100 pc through an H 11 region with an average electron density of 0·1 cm-3, and structure of scale size 10-3pc filling 1% of the volume, results in a scattering to half-brightness points of 8″ (arc) at 38 MHz. Radio sources with apparent angular sizes of this amount should be partially resolved by an interferometer with an effective baseline of about 10 000 wavelengths.

scholarly journals Emission Nebulae as Radio Sources

1956 ◽  
Vol 9 (2) ◽  
pp. 218 ◽  
Author(s):  
BY Mills ◽  
AG Little ◽  
KV Sheridan
Keyword(s):  
Electron Temperature ◽  
Electron Density ◽  
Radio Telescope ◽  
Optical Data ◽  
Radio Sources ◽  
Pencil Beam ◽  
Orion Nebula ◽  
Average Electron Density ◽  
Average Electron ◽  
Bright Emission

Attempts have been made to detect 14 bright emission nebulae at a wavelength of 3?5 m using a pencil-beam radio telescope with a beamwidth of 50 min of arc. Of these nebulae, six were probably observed in emission, seven were undetectable, and one, NGC 6357, was observed in absorption; radio isophotes were obtained for NGC 2237 and NGC 3372. Radio and optical data have been combined to estimate electron densities, masses, and sometimes the electron temperature of many of the nebulae. Values range from an electron density of 3 cm?3 and a mass of 3�10. solar masses for the outer regions of the 30 Doradus complex to an average electron density of 500 cm?3 and a mass of 20 solar masses for the Orion Nebula. Temperatures generally appear to be in the neighbourhood of 10,000 �K, except in the case of NGC 6357, for which 6500 �K is estimated.

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.

scholarly journals X-ray phase determination by the principle of minimum charge

1999 ◽  
Vol 55 (3) ◽  
pp. 489-499 ◽  
Author(s):  
Veit Elser
Keyword(s):  
Electron Density ◽  
Diffraction Data ◽  
Global Minimum ◽  
Unit Cell ◽  
Electronic Charge ◽  
Total Charge ◽  
Phase Determination ◽  
X Ray ◽  
Average Electron Density ◽  
Average Electron

When the electron density in a crystal or a quasicrystal is reconstructed from its Fourier modes, the global minimum value of the density is sensitively dependent on the relative phases of the modes. The set of phases that maximizes the value of the global minimum corresponds, by positivity of the density, to the density having the minimum total charge that is consistent with the measured Fourier amplitudes. Phases that minimize the total electronic charge (i.e. the average electron density) have the additional property that the lowest minima of the electron density become exactly degenerate and proliferate within the unit cell. The large number of degenerate minima have the effect that density maxima are forced to occupy ever smaller regions of the unit cell. Thus, by minimization of the electronic charge, the atomicity of the electron density is enhanced as well. Charge minimization applied to simulated crystalline and quasicrystalline diffraction data successfully reproduces the correct phases starting from random initial phases.

scholarly journals Pulsar distances, spiral structure and the interstellar medium

1970 ◽  
Vol 38 ◽  
pp. 178-181 ◽  
Author(s):  
B. Y. Mills
Keyword(s):  
Interstellar Medium ◽  
Electron Density ◽  
Supernova Remnants ◽  
Spiral Structure ◽  
Radio Continuum ◽  
Average Electron Density ◽  
Uniform Medium ◽  
The Mean ◽  
Average Electron

The distances of all pulsars are calculated on the assumption that they are immersed in a uniform medium of average electron density 0.06 cm−3. It then appears that the pulsars are concentrated towards the local and Sagittarius spiral features and that their mean height above the plane is consistent with that of known supernova remnants. The mean distances appear to be approximately correct, but individual distances are uncertain by about a factor of two. Evidence from radio continuum results supports this model of the ionized interstellar medium.

scholarly journals Low Frequency Absorption in Isotropic World Models

1967 ◽  
Vol 20 (4) ◽  
pp. 445 ◽  
Author(s):  
AD Payne
Keyword(s):  
Electron Density ◽  
Low Frequency ◽  
Radio Sources ◽  
Electron Density And Temperature ◽  
Discrete Radio Sources

The present paper is concerned with the free�free absorption by intergalactic ionized hydrogen of the radiation from discrete radio sources. The absorption for different world models has been calculated as a function of redshift, electron density, and temperature.

Effects of Synchrotron Loss on the Low-Frequency Spectra of Extragalactic Radio Sources with Inhomogeneities

2002 ◽  
Vol 199 ◽  
pp. 231-232
Author(s):  
N. Tsvyk
Keyword(s):  
Fine Structure ◽  
Low Frequency ◽  
New Method ◽  
Radio Sources ◽  
Frequency Spectra ◽  
Extragalactic Radio Sources ◽  
Spectrum Measurements

In this work we explain the integrated spectrum measurements (Braude et.al.,1978—1995) in terms of the synchrotron theory and the the recent measurements of radio fine structure in different classes of sources (Carilli et.al.,1991). This provides a new method of investigating extragalactic radio sources

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