科研之友
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摘要
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 chi, the mass ratio of the IG dust to the total metal in the Universe, as >chiless than or similar to0.1 for 10 Angstromless than or similar toaless than or similar to0.1 mum and chiless than or similar to0.1(a/0.1 mum) for 0.1less than or similar toaless than or similar to1 mum, where a is a characteristic grain size of the IG dust. This upper bound of chisimilar to 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 similar to10(-34) g cm(-3) at z=0 to similar to10(-33) g cm(-3) at zsimilar to1, and keeps almost the value toward higher redshift. This causes IG extinction of less than or similar to0.2 mag at the observer's B band for zsimilar to1 sources and that of less than or similar to1 mag for higher redshift sources. Furthermore, if (B-V)similar to0.1 mag at the observer's frame against zgreater than or similar to1 sources is detected, we can conclude that a typical size of the IG dust is less than or similar to100 Angstrom. The signature of the 2175-Angstrom feature of small graphite may be found as a local minimum at zsimilar to2.5 in a plot of the observed E(B-V) as a function of the source redshift. Finally, the IGM mean temperature at zless than or similar to1 can be still higher than 10(4) K, provided the size of the IG dust is less than or similar to100 Angstrom.
- 出版日期2004-5-11
