332 Highlights in modern observational cosmology
Figure 11.8.Illustration of the photometric redshift technique on a variety of intermediate
and high redshift galaxies (Giallongoet al1998). The data points are broad-band
photometric meaurements in BVRIK filters used to constrain the spectral energy
distribution of galaxies, thus estimating their redshift.
SFR density. By using photometric redshifts (possibly supported by a subset of
spectroscopic measurements), one can thus trace thestar formation historyin the
distant universe. Madauet al(1998) exploited this method to measure the global
SFR at 0. 5 .z.4 using HDF and ground-based surveys. This measurement has
been repeated by many others in recent years (e.g. Steidelet al1999), and most of
the debate has focused on the critical role ofdustwhich is surely present in high-
zgalaxies and is very effective in absorbing UV radiation. To some extent all
UV-based SFR measurements are biased low due to dust extinction (e.g. Steidel