Here I review some of the things we know about dust in the high redshift (z 2) universe. This review is meant to be an introduction to the literature. While by necessity incomplete, it is my hope that the reader will get an appreciation for some of the activity of the field and the researchers involved.
To many extraglactic astronomers and cosmologists dust is at best a nuisance. However, it is fairly ubiquitous and perilous to ignore. For example, Blakeslee et al. (2003), following on from Aguirre (1999) and Goobar et al. (2002), show that the distinctive signature of cosmological acceleration in the differential Hubble diagram can also be mimicked with a model containing gray dust having fixed spatial density in the intergalactic medium (IGM). While there are a variety of reasons to believe that the effects are not significant (e.g. Aguirre & Haimann 2000; Paerels et al. 2002; also cf. Section 2.4 below), it is too early to totally rule out the gray dust model.
As in the local universe, dust is highly correlated with star formation. Since all studies show that the co-moving star formation rate density (SFRD) monotonically increases with z out to a redshift of at least 1 (e.g. Madau et al. 1996) we expect that dust may be increasingly important at higher redshift (Calzetti & Heckman 1999). Dust is especially important in interpreting the cosmic star formation history as shown in so called "Madau Plots" of SFRD(z). In some early studies dust was ignored leading to a view that SFRD(z) peaked around z ~ 1 and declined towards higher redshift (e.g. Madau et al. 1996). It is now recognized that most of the UV emission from high-z star formation is at least somewhat obscured by dust (e.g. Madau, Pozzetti, & Dickinson 1998; Pettini et al. 1998) leading to SFRD(z) plots that flatten for z 1 (e.g. Calzetti 1999).
Since observations of high-z star forming galaxies are somewhat easier in the rest-frame UV than in the rest-frame far-infrared (FIR), it is of interest to know if star formation rates can be recovered from rest-frame UV observations through suitable application of reddening laws. More importantly we must ask whether the numerous high-redshift galaxies detected in the rest frame UV are really significant in terms of the total star formation happening in the early universe.
This review is broken into two main sections. Section 2 reviews dust content of the species in the "high-z zoo". Section 3 reviews the evidence for galaxy scale reddening laws working at z > 2 and considers the debate as to whether the majority of star formation is totally hidden from the rest-frame UV and optical at high redshift. Section 4 briefly summarizes breaking news and the expected progress in the field.