Star formation history, dust attenuation and extragalactic background light

At any given epoch, the Extragalactic Background Light (EBL) carries imprints of integrated star formation activities in the universe till that epoch. On the other hand, in order to estimate the EBL, when direct observations are not possible, one requires an accurate estimation of the star formation rate density (SFRD) and the dust attenuation ($A_ν$) in galaxies. Here, we present a 'progressive fitting method' that determines global average SFRD($z$) and $A_ν(z)$ for any given extinction curve by using the available multi-wavelength multi-epoch galaxy luminosity function measurements. Using the available observations, we determine the best fitted combinations of SFRD($z$) and $A_ν(z)$, in a simple fitting form, up to $z\sim8$ for five well known extinction curves. We find, irrespective of the extinction curve used, the $z$ at which the SFRD($z$) peaks is higher than the $z$ above which $A_ν(z)$ begins to decline. For each case, we compute the EBL from ultra-violet to the far-infrared and optical depth ($τ_γ$) encountered by the high energy $γ$-rays due to pair production upon collisions with these EBL photons. We compare these with measurements of the local EBL, $γ$-ray horizon and $τ_γ$ measurements using Fermi-LAT. All these and the comparison of independent SFRD($z$) and $A_ν(z)$ measurements from the literature with our predictions favor the extinction curve similar to that of Large Magellanic Cloud Supershell.

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