Hydrostatic equilibrium of gas, extent of cosmic ray confinement, and radio emission in the Galaxy

The question of whether or not our and other normal galaxies have some sort of halo - an extended region containing, in particular, cosmic rays - has been discussed for no less than 25 years. Such a “cosmic ray halo” (CRH) appears as a radio-halo, although the absence of the latter is not evidence against the presence of CRH. the point is that the relativistic electrons responsible for the radio emission from the radio-halo undergo synchrotron and Compton losses which are practically absent in the case of the cosmic-ray proton-nuclear component. Possibly because the discussion concerning the existence of the radio-halo in the Galaxy has lasted for years it has acquired a particular character. the latter is clearly reflected in the report by Baldwin (1976) who emphasized that: ȜIn this discussion so far I have avoided the use of the phrase Ȝradio-haloȝ. It arouses antagonism in otherwise placid astronomers and many sought to deny its existence …ȝ Such a situation evidently reflects the difficulties that arise in detecting the radio-halo of our own Galaxy when account is taken of other confusing galactic sources as well as of the metagalactic background.

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On the Relationship Between Recent Measurements of Cosmic Ray Electrons, Nonthermal Radio Emission from the Galaxy, and the Solar Modulation of Cosmic Rays

Australian Journal of Physics ◽

10.1071/ph680845 ◽

1968 ◽

Vol 21 (6) ◽

pp. 845 ◽

Cited By ~ 27

Author(s):

WR Webber

Keyword(s):

Cosmic Rays ◽

Radio Emission ◽

Electron Spectrum ◽

Cosmic Ray ◽

Solar Modulation ◽

Nonthermal Radio ◽

The Galaxy ◽

Nonthermal Radio Emission ◽

Modulation Parameter ◽

The Relationship

Utilizing recent measurements of the cosmic ray electron spectrum at the Earth and the effects of solar modulation on this spectrum, possible limits on the local interstellar electron spectrum have been determined. Synchrotron emission from these interstellar electrons is then compared with the local (disk) volume emissivity of nonthermal radio emission as deduced from a study of radio intensity profiles along the galactic equator. The detailed spectrum and magnitude of radio emissivity can be reproduced from the electron spectrum only for very stringent, conditions on the magnitude of the local interstellar magnetic field, and the amount of solar modulation of cosmic rays. Specifically it is found that B -L "'" 7 !-,G, and the residual modulation parameter KR "'" 0�75 GV. If solar modulation effects on the cosmic ray electron component are negligible then an implausibly high local field of "'" 20 !-,G is required.

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Radio emission, cosmic ray electrons, and the production of gamma-rays in the Galaxy

The Astrophysical Journal ◽

10.1086/157761 ◽

1980 ◽

Vol 236 ◽

pp. 448 ◽

Cited By ~ 42

Author(s):

W. R. Webber ◽

G. A. Simpson ◽

H. V. Cane

Keyword(s):

Radio Emission ◽

Gamma Rays ◽

Cosmic Ray ◽

The Galaxy

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Can the Local Bubble explain the radio background?

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/stab131 ◽

2021 ◽

Vol 502 (2) ◽

pp. 2807-2814

Author(s):

Martin G H Krause ◽

Martin J Hardcastle

Keyword(s):

Magnetic Field ◽

Energy Density ◽

Radio Emission ◽

Magnetic Energy ◽

Cosmic Ray ◽

Observational Constraints ◽

Local Bubble ◽

Magnetic Energy Density ◽

Magnetic Field Model ◽

Radio Background

ABSTRACT The ARCADE 2 balloon bolometer along with a number of other instruments have detected what appears to be a radio synchrotron background at frequencies below about 3 GHz. Neither extragalactic radio sources nor diffuse Galactic emission can currently account for this finding. We use the locally measured cosmic ray electron population, demodulated for effects of the Solar wind, and other observational constraints combined with a turbulent magnetic field model to predict the radio synchrotron emission for the Local Bubble. We find that the spectral index of the modelled radio emission is roughly consistent with the radio background. Our model can approximately reproduce the observed antenna temperatures for a mean magnetic field strength B between 3 and 5 nT. We argue that this would not violate observational constraints from pulsar measurements. However, the curvature in the predicted spectrum would mean that other, so far unknown sources would have to contribute below 100 MHz. Also, the magnetic energy density would then dominate over thermal and cosmic ray electron energy density, likely causing an inverse magnetic cascade with large variations of the radio emission in different sky directions as well as high polarization. We argue that this disagrees with several observations and thus that the magnetic field is probably much lower, quite possibly limited by equipartition with the energy density in relativistic or thermal particles (B = 0.2−0.6 nT). In the latter case, we predict a contribution of the Local Bubble to the unexplained radio background at most at the per cent level.

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

Proceedings of the International Astronomical Union ◽

10.1017/s1743921320003476 ◽

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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The Origin and Dynamical Effects of the Magnetic Fields and Cosmic Rays in the Disk of the Galaxy

Symposium - International Astronomical Union ◽

10.1017/s0074180900004873 ◽

1970 ◽

Vol 39 ◽

pp. 168-183

Author(s):

E. N. Parker

Keyword(s):

Magnetic Field ◽

Cosmic Rays ◽

Magnetic Fields ◽

Dynamical Behavior ◽

Cosmic Ray ◽

Interested Reader ◽

Written Text ◽

The Galaxy ◽

Basic Ideas ◽

The Magnetic Field

The topic of this presentation is the origin and dynamical behavior of the magnetic field and cosmic-ray gas in the disk of the Galaxy. In the space available I can do no more than mention the ideas that have been developed, with but little explanation and discussion. To make up for this inadequacy I have tried to give a complete list of references in the written text, so that the interested reader can pursue the points in depth (in particular see the review articles Parker, 1968a, 1969a, 1970). My purpose here is twofold, to outline for you the calculations and ideas that have developed thus far, and to indicate the uncertainties that remain. The basic ideas are sound, I think, but, when we come to the details, there are so many theoretical alternatives that need yet to be explored and so much that is not yet made clear by observations.

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