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. Briefly, these include the abundance of the large collapsed, virialised structures in the Universe (galaxy groups and clusters), the clustering of galaxies of different types in different environments and at different cosmological epochs, the rate of the gravitational growth of structure in the Universe, and the interplay of the Large Scale Structure with the Cosmic Microwave Background radiation (hereafter CMB). These prospects are based upon the fact that J-PLUS will be between one and two magnitudes deeper than the Sloan Sky Digital Survey (SDSS), and will count with more, narrower photometric bands than the photometric version of SDSS, yielding a higher resolution in the galaxy spectra. As a result, we foresee an improved redshift accuracy for J-PLUS with respect to SDSS. Moreover, we expect to obtain thin redshift slices corresponding to the narrow band filters present in the J-PLUS filter tray.

Outline of the cosmological milestones for J-PLUS:

1. J-PLUS will provide a deep and uniform catalogue of clusters and groups of galaxies. These structures constitute interesting systems from both the astrophysical and cosmological points of view: they are extreme, very rare systems, rich in physical phenomena, whose properties are highly dependent on the expansion history of the Universe and the nature of the dark matter.
2. With J-PLUS it will be possible to identify a variety of different galaxy populations, with different physical properties at different cosmic times. The measurements of the clustering of the angular distribution of each population can provide the typical mass of the halos hosting those galaxies. Furthermore, given the large area sampled by J-PLUS, it can also tell us about (possible) deviations from Gaussianity of the initial distribution of density and energy in the very young universe. More detailed analyses of each population will improve our understanding on how galaxies assemble and how star formation activity takes place in them. In particular, the narrow band filters of J-PLUS will allow us to explore the properties of massively star-forming galaxies, both in the local universe and at high redshifts, by detecting emission lines in their spectra. These extreme sources have only been found serendipitously in smaller area surveys. J-PLUS will thus provide the largest catalogue of these galaxies, allowing us to study their nature in a cosmological galaxy formation scenario.


Figure 1. Map of the intensity anisotropies of the Cosmic Microwave Background radiation, as seen by the Planck satellite (image credit: ESA/Planck).

3. By means of a joint study of J-PLUS data with existing maps of the CMB angular anisotropies (like those provided by the Planck satellite), it will be possible to address a number of astrophysical and cosmological problems of very different nature. For instance, we will be able to estimate the amount of thermal energy contained in the ionized gas in galaxy clusters and groups of J-PLUS by measuring how the CMB spectrum becomes distorted as this radiation flies through those structures. These same effect should/may take place in other environments, like quasars or line emission galaxies, and this will be tested on a large cosmological volume by searching for those sources in J-PLUS data. Likewise, it will be also possible to test whether the gravitational potential fields (as they are sampled by J-PLUS galaxies) distort the CMB as predicted theoretically in different scenarios. All these cosmological tests will shed new light on our understanding of the physical processes taking place in our Universe.