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Extragalactic Cosmic Radio Background
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Title: Is there an unaccounted excess Extragalactic Cosmic Radio Background?
Authors: Ravi Subrahmanyan, Ramanath Cowsik

Analyses of measurements of the distribution of absolute brightness temperature over the radio sky have led recently to suggestions that there exists a substantial unexplained extragalactic radio background. Consequently, there have been numerous attempts to place constraints on plausible origins for the `excess'. We suggest here this expectation of a large extragalactic background, over and above that contributed by the sources observed in the surveys, is based on an extremely simple geometry adopted to model the Galactic emission and the procedure adopted in the estimation of the extragalactic contribution. In this paper, we derive the extragalactic radio background from wide-field radio images by using a more realistic modelling of the Galactic emission and decompose the sky maps at 150, 408, and 1420 MHz into anisotropic Galactic and isotropic extragalactic components. The anisotropic Galactic component is assumed to arise from a highly flattened spheroid representing the thick disc, embedded in a spherical halo, both centered at the Galactic center, along with Galactic sources, filamentary structures, Galactic loops and spurs. All components are constrained to be positive and the optimisation scheme minimises the sky area occupied by the complex filaments. We show that in contrast to the simple modelling of the Galactic emission as a plane parallel slab, the more realistic modelling yields estimates for the uniform extragalactic brightness that is consistent with expectations from known extragalactic radio source populations.

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Blobrana


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RE: Extragalactic background light
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Detection of the cosmic gamma ray horizon: Measures all the light in the universe since the Big Bang

How much light has been emitted by all galaxies since the cosmos began? After all, almost every photon (particle of light) from ultraviolet to far infrared wavelengths ever radiated by all galaxies that ever existed throughout cosmic history is still speeding through the Universe today. If we could carefully measure the number and energy (wavelength) of all those photons - not only at the present time, but also back in time - we might learn important secrets about the nature and evolution of the Universe, including how similar or different ancient galaxies were compared to the galaxies we see today.
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Blobrana


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Posts: 131433
Date:
Extragalactic Gamma-ray Background
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Title: A New Result on the Origin of the Extragalactic Gamma-ray Background
Authors: Ming Zhou, Jiancheng Wang

In the paper, we continually use the method of image stacking to study the origin of the extragalactic gamma-ray background (EGB) at GeV bands, and find that the Faint Images of the Radio Sky at Twenty centimetres (FIRST) sources undetected by the Large Area Telescope on the Fermi Gamma-ray Space Telescope can contribute about (56±6)% of the EGB. Because the FIRST is a flux limited sample of radio sources with incompleteness at the faint limit, we consider that the point-sources, including blazars, non-blazar AGNs, starburst galaxies, could produce a much larger fraction of the EGB.

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Blobrana


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Posts: 131433
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RE: Extragalactic background light
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NASA'S Fermi Measures Cosmic 'Fog' Produced By Ancient Starlight

Astronomers using data from NASA's Fermi Gamma-ray Space Telescope have made the most accurate measurement of starlight in the universe and used it to establish the total amount of light from all the stars that have ever shone, accomplishing a primary mission goal.
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The diffuse extragalactic background light (EBL) is all the accumulated radiation in the Universe due to star formation processes, plus a contribution from active galactic nuclei (AGNs). This radiation covers the wavelength range between ~ 0.1-1000 microns (these are the ultraviolet, optical, and infrared regions of the electromagnetic spectrum). The EBL is part of the diffuse extragalactic background radiation (DEBRA), which by definition covers the overall electromagnetic spectrum. After the cosmic microwave background, the EBL produces the second-most energetic diffuse background, thus being essential for understanding the full energy balance of the universe.
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MAGIC discovers the most distant very-high energy gamma-ray emission from an accreting supermassive black hole.
The MAGIC (Major Atmospheric Gamma-ray Imaging Cherenkov) telescope has detected emission of very high energy gamma rays from the active nucleus of the 3C279 galaxy. The quasar's distance is more than five billion light years (roughly half the radius of the Universe) from the Earth, more than twice the distance of objects previously observed with this kind of radiation.

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