During the epoch of assembly of large disk galaxies, the turbulent velocity of the gas in the disks was falling with time, as first the thick disk formed 10 to 12 Gyr ago, and then the thin disk presumably began to form as the turbulent velocity became lower.

RR Lyrae (RRL) variable stars are ideal for probing the dynamics and chemical properties at this epoch of disk assembly (redshifts z = 0.8 to 3) as they are very old stars (8 to 13 Gyr), and their characteristic light curves make them easy to recognise against the background of younger disk stars at low Galactic latitudes.

Old RRL stars have been found in small numbers in the thin and thick disk, but have not yet been used as probes of the early phase of disk formation due to the difficulty in observing such a large area at infrared wavelengths.

The extinction from dust in the plane of the Galaxy is low at 1.65 micron (0.17A(V)). The light curve amplitudes for the common RRL variables are about 0.3 magnitudes, with periods mostly between 0.4 to 0.8 days, which, when combined with the low extinction, makes them easy to detect. Thus, as DREAMS is operating in the infrared, we will find RRL stars in the old thin disk and thick disk out to distances of at least 5 kpc.