Star formation in the local Universe
Star-forming galaxies exhibit emission lines. The origin of these lines is the presence of young, bright blue stars embedded in gas and dust, the so called HII regions. These bright stars are short-lived, and their presence implies a recent episode of star formation in the galaxy. The main emission lines in the optical are the hydrogen lines of the Balmer's series (Hα y Hβ), the oxygen lines ([OII] and [OIII]), and the nitrogen lines ([NII] doublet). The properties of these emission lines are related to the star formation rate (SFR; defined as the mass of gas transformed into stars per unit time), the metallicity, and the extinction of the HII regions (Fig. 1).
The narrow-band filter J0660 of J-PLUS covers the Hα and [NII] emission lines at z < 0.017 (d < 73 Mpc), and it is the main source of information to derive the SFR in the nearby Universe with J-PLUS. To measure a robust Hα line flux, a methodology that accounts for the underlying stellar continuum, the dimming due to the dust extinction, and the contribution of the [NII] doublet has been developed. The technical details about the procedure can be found at
Vilella-Rojo et al. 2015: Extracting Hα flux from photometric data
The methodology was tested and validated by comparing J-PLUS Hα fluxes of HII regions with shared spectroscopic information from SDSS and CALIFA. We find that J-PLUS provides an unbiased Hα flux with 20% floor uncertainty, as presented in
Logroño-García et al. 2019: Measuring Hα emission line fluxes in the nearby universe