Amount of intergalactic dust: constraints from distant supernovae and the thermal history of the intergalactic medium

In this paper we examine the allowed amount of intergalactic (IG) dust, which is constrained by extinction and reddening of distant Type Ia supernovae (SNe Ia) and the thermal history of the intergalactic medium (IGM) affected by dust photoelectric heating. Based on the observational cosmic star formation history, we find an upper bound of χ, the mass ratio of the IG dust to the total metal in the Universe, as χ≲ 0.1 for 10 Å ≲a≲ 0.1 μm and χ≲ 0.1(a/0.1 μm) for 0.1 ≲a≲ 1 μm, where a is a characteristic grain size of the IG dust. This upper bound of χ∼ 0.1 suggests that the dust-to-metal ratio in the IGM is smaller than the current Galactic value. The corresponding allowed density of the IG dust increases from ∼10⁻³⁴ g cm⁻³ at z= 0 to ∼10⁻³³ g cm⁻³ at z∼ 1, and keeps almost the value toward higher redshift. This causes IG extinction of ≲0.2 mag at the observer's B band for z∼ 1 sources and that of ≲1 mag for higher redshift sources. Furthermore, if E(B–V) ∼ 0.1 mag at the observer's frame against z≳ 1 sources is detected, we can conclude that a typical size of the IG dust is ≲100Å. The signature of the 2175-Å  feature of small graphite may be found as a local minimum at z∼ 2.5 in a plot of the observed E(B–V) as a function of the source redshift. Finally, the IGM mean temperature at z≲ 1 can be still higher than 10⁴ K, provided the size of the IG dust is ≲100 Å.