First detection of the field star overdensity in the Perseus arm

Aims. The main goal of this study is to detect the stellar overdensity associated with the Perseus arm in the anticenter direction. Methods. We used the physical parameters derived from Strömgren photometric data to compute the surface density distribution as a function of galactocentric distance for different samples of intermediate young stars. The radial distribution of the interstellar absorption has also been derived. Results. We detected the Perseus arm stellar overdensity at 1.6 ± 0.2 kpc from the Sun with a significance of 4–5σ and a surface density amplitude of around 10%, slightly depending on the sample used. Values for the radial scale length of the Galactic disk have been simultaneously fitted obtaining values in the range [2.9,3.5] kpc for the population of the B4–A1 stars. Moreover, the interstellar visual absorption distribution is congruent with a dust layer in front of the Perseus arm. Conclusions. This is the first time that the presence of the Perseus arm stellar overdensity has been detected through individual star counts, and its location matches a variation in the dust distribution. The offset between the dust lane and the overdensity indicates that the Perseus arm is placed inside the co-rotation radius of the Milky Way spiral pattern.