Disk Galaxies: Our Fascinating Cosmic Habitats

Galaxies are the fundamental building blocks of the Universe. Gas-rich spiral disk galaxies are the cosmic islands where stars and planets form and where the chemical buildings blocks of life are generated. However, despite their importance, we are still far from a detailed understanding of their structure and the processes that drive their evolution.

I will discuss some of the fascinating puzzles of disk galaxies that are currently a major focus of astrophysical research. These include the surprisingly inefficient rate of star formation, which is essential for our Sun and Solar System to be able to form, 4.5 billion years ago. Another the mystery of the nature of dark matter, without which we believe no galaxy to be able to form in the first place.

I will focus especially on new observations of galaxies in the early Universe, 3 Gyrs after the big bang. This was the era with the peak of the cosmic star formation rate. It was the time of rapid galaxy assembly and the epoch where galaxy morphology were established. These observations show a diversity of galactic systems with physical properties that are unparalleled in the present Universe. Very gas-rich, extended, fast rotating and highly turbulent galactic disks have been found, dominated by gigantic star-forming gas clumps. Very surprisingly, no signature of dark matter is found in these galaxies.

These observations open a fascinating window into early galaxy evolution. They reveal a rich variety of dynamical processes that at the moment are far from being understood.