http://arxiv.org/abs/1403.0007
Over the last decade and a half, an avalanche of new data from multiwavelength imaging and spectroscopic surveys has revolutionized our view of galaxy formation and evolution. Making sense of it all and fitting it together into a coherent picture remains one of astronomy’s great challenges. Here we review the range of complementary techniques and theoretical tools that are allowing astronomers to map the cosmic history of star formation, heavy element production, and reionization of the universe from the cosmic “dark ages” to the present epoch. A consistent picture is emerging from modern galaxy surveys, whereby the star formation rate density peaked about 3.5 Gyr after the Big Bang, at redshift 1.9, and declined exponentially at later times, with an e-folding timescale of 3.9 Gyr. Half of the stellar mass observed today was formed before redshift 1.3. Less than 1% of today’s stars formed during the epoch of reionization, at redshift greater than 6. Under the simple assumption of a universal initial mass function, the global stellar mass density inferred at any epoch matches reasonably well the time integral of all the preceding star formation activity, although a mild disagreement may still point to unresolved issues with the measurements, or to deviations in the stellar initial mass function from conventional assumptions. The assembly histories of the stellar component of galaxies and their central black holes were quite similar, offering evidence for the co-evolution of black holes and their host galaxies. The rise of the mean metallicity of the universe to about 0.001 solar by redshift six, one Gyr after the Big Bang, appears to have been accompanied by the production of fewer than ten hydrogen Lyman-continuum photons per baryon, a rather tight budget for cosmological deionization.
P. Madau and M. Dickinson
Tue, 4 Mar 14
32/61