Forming stars in the early universe
The first stars appeared about one hundred million years after the big bang, and ever since then stars and star formation processes have lit up the cosmos. When the universe was about three billion years old, star formation activity peaked at rates about ten times above current levels. Why this happened, and whether the physical processes back then were different from those today or just more active (and why), are among the most pressing questions in astronomy. Since stars are made from gas, the gas content of galaxies is a measure of their star formation potential and (at least in the local universe) the fraction of matter in form of gas, the "gas fraction", is a measure of the star formation capability.
Francesca Civano and a team of her colleagues used the large ALMA millimeter facility to study the gas fractions in a set of forty-five massive galaxies in the cosmic epoch of peak star formation. Although the diagnostic emission lines from the gas were too faint to study, the team used the strong dust continuum as a proxy, arguing from other results that the ratio of gas to dust was reasonably well understood. The gas fractions for this set of galaxies were found to be quite similar to the values in other massive galaxies, which was somewhat of a surprise because some evolutionary trends in gas fraction had been expected. Their other important result is that the relationship between the gas fraction and star formation activity is in good agreement with current models and, according to the scientists, implies that a single star formation prescription applies from the local universe out to at least as early as the peak epoch about three billion years ago.
Source: Harvard-Smithsonian Center for Astrophysics [November 21, 2016]