Take a look at the challenges being faced at present when trying to detect these intergalactic filaments:
- the densities of the structures predicted by models is expected to be in the range of 10^-6 to 10 ^-4 electrons per cubic centimetre.
- the temperatures are in the range of 10 ^5 to 10^7 K
- the path length of the filamentary structures detected to date, are in the order 10-14.6 Mpc in length!
These filaments must be close to infinite conductivity, and thereby resulting in giant intergalactic frozen-in magnetic fields !
What are the key detection methods ?..
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Filaments are expected to be detected at X-ray wavelengths via thermal bremmstrahlung emission, although some of the first detections have been made by observing 0.65 keV O line in absorption or emission.
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Dietrich et al.(2004) used gravitational lensing to detect the surface mass density of a suspected filament between Abell 222 and Abell 223. This detection was backed up by similar detections in the optical and X-ray bands in the same study.
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This study used a not-thus-far-used data analysis technique, applied to the 2 degree Field Galaxy Redshift Survey (2dFGRS) and ROSAT All-Sky Survey data.
Why haven’t they been detected before ? ...
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Hence, our failure to detect individual filaments of galaxies using current methods is not in conflict with model predictions.
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The new generation of more sensitive X-ray satellites such as Suzaku and upcoming missions should improve the search for such low-density high-temperature sources as these filaments (e.g. Sato et al 2010). Indeed, Kawahara et al. (2011) have presented evidence for a galaxy group forming at the intersection of several filaments of galaxies from Suzaku observations, and further detections from Suzaku hold much promise in this regard.
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Great stuff ! Good on 'em.
Paper here.
Cheers