Geofyzikální ústav Akademie věd ČR, v.v.i.


Vavryčuk - 2016 - Impact of galactic and intergalactic dust on the stellar EBL.

Vavryčuk - 2016 - Impact of galactic and intergalactic dust on the stellar EBL.

Václav Vavryčuk, a researcher of the Institute of Geopyhsics of Czech Academy of Science, investigated an impact of galactic and intergalactic dust on the extragalactic background light.

Current theories assume that the low intensity of the stellar extragalactic background light (stellar EBL) is caused by finite age of the Universe because the finite-age factor limits the number of photons that have been pumped into the space by galaxies and thus the sky is dark in the night. We oppose this opinion and show that two main factors are responsible for the extremely low intensity of the observed stellar EBL. The first factor is a low mean surface brightness of galaxies, which causes a low luminosity density in the local Universe. The second factor is light extinction due to absorption by galactic and intergalactic dust. Dust produces a partial opacity of galaxies and of the Universe. The galactic opacity reduces the intensity of light from more distant background galaxies obscured by foreground galaxies. The inclination-averaged values of the effective extinction AV for light passing through a galaxy is about 0.2 mag. This causes that distant background galaxies become apparently faint and do not contribute to the EBL significantly. In addition, light of distant galaxies is dimmed due to absorption by intergalactic dust. Even a minute intergalactic opacity of 1×10−2 mag per Gpc is high enough to produce significant effects on the EBL. As a consequence, the EBL is comparable with or lower than the mean surface brightness of galaxies. Comparing both extinction effects, the impact of the intergalactic opacity on the EBL is more significant than the obscuration of distant galaxies by partially opaque foreground galaxies by factor of 10 or more. The absorbed starlight heats up the galactic and intergalactic dust and is further re-radiated at IR, FIR and micro-wave spectrum. Assuming static infinite universe with no galactic or intergalactic dust, the stellar EBL should be as high as the surface brightness of stars. However, if dust is considered, the predicted stellar EBL is about 290 nWm−2sr−1 , which is only 5 times higher than the observed value. Hence, the presence of dust has higher impact on the EBL than currently assumed. In the expanding universe, the calculated value of the EBL is further decreased, because the obscuration effect and intergalactic absorption become more pronounced at high redshifts when the matter was concentrated at smaller volume than at present.

Link to the publication.