The position of the Sun in the Milky Way makes it almost impossible to study the structure of the Galaxy along its disk, since it is filled with gas and dust. The study of the halo, nevertheless, still harbours a large amount of information about the formation of the Galaxy and the environment in which a giant spiral galaxy evolves. J-PLUS will be able to fit the spectra of all the stars observed in the halo of the Milky Way, creating a unique catalogue of stars with their physical parameters.
J-PLUS provides 12 photometric points for each observed pixel in the ~ 8500 deg² covered by the survey. With the broad-band filters tracing the global shape of the spectral energy distribution (SED), and the narrow-band filters covering several particular and important features of the SED at z < 0.015, such as the 4000A break and the nebular emission of Ha and [OII], J-PLUS has unique capabilities to study the spatially resolved properties of nearby galaxies.
The J-PLUS photometric system is well suited to study the properties of nearby galaxies (z < 0.015), where the 4000A break, and the Ha and [OII] prominent emission lines are covered by the filter set. At higher redshifts, both the lines and the break depart from the narrow-band filters and they are only observed with the standard broad-band filters. However, there are a few redshift windows beyond the nearby Universe that can be explored with J-PLUS.
The scientific legacy of J-PLUS is primarily expected to probe galaxy evolution processes in the local Universe. However, given its outstanding large area and filter array design, J-PLUS also allows to tackle key cosmological issues.