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Abstract: The UV radiation from a quasar leaves a characteristic pattern in thedistribution of ionized hydrogen throughout the surrounding space. This patternor light echo propagates through the intergalactic medium at the speed oflight, and can be observed by its imprint on the Ly-alpha forest spectra ofbackground sources. As the echo persists after the quasar has switched off, itoffers the possibility of searching for dead quasars, and constraining theirluminosities and lifetimes. We outline a technique to search for andcharacterize these light echoes. To test the method, we create artificialLy-alpha forest spectra from cosmological simulations at z=3, apply lightechoes and search for them. We show how the simulations can also be used toquantify the significance level of any detection. We find that light echoesfrom the brightest quasars could be found in observational data. Withabsorption line spectra of 100 redshift z~3-3.5 quasars or galaxies in a 1square degree area, we expect that ~10 echoes from quasars with B bandluminosities L B=3x10^45 ergs-s exist that could be found at 95% confidence,assuming a quasar lifetime of ~10^7 yr. Even a null result from such a searchwould have interesting implications for our understanding of quasarluminosities and lifetimes.



Autor: Eli Visbal CMU, Rupert A. C. Croft CMU

Fuente: https://arxiv.org/



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