Star formation rate in the local Universe

The star-forming galaxy UGC09476

The star-forming galaxy UGC09476

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 coled HII regions. These bright stars are sort-lived, and their presence implies a recent episode of star formation in the galaxy. The main emission lines 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 lines are related with the star formation rate (Hα and [OII]), the metallicity, and the extinction.

One of the main scientific goals of J-PLUS is the estimation of the star formation rate (SFR) in the local Universe, both global and spatially resolved (2D studies). The narrow-band filter F660 of J-PLUS covers the Hα and [NII] emission lines at z < 0.015, and it is our main source of information to derive the SFR.

To measure a robust Hα line flux, the contribution of the underlying stellar continuum, the dimming due to the dust extinction, and the contribution of the [NII] doublet have to be estimated. Regarding the stellar continuum, we will estimate it by fitting theoretical stellar templates to the J-PLUS photometry. In the fitting process, the F660 filter is avoided and the broad-band r filter is recursively de-contaminated of the emission lines flux. The dust extinction and the [NII] contribution will be estimated using empirical recipes.

The expected Hα luminosity detection limit with J-PLUS is LHα ~ 10³⁸ erg/s. This limit is one order of magnitude fainter than any previous study in the field and, combined with the large area covered by J-PLUS, more than 20,000 emission lines galaxies at z < 0.015 are expected. This will permit to study with unprecedented detail both the bright and the faint end of the Hα luminosity function and the SFR in the local Universe.

The star-forming galaxy UGC09476: Optical images from SDSS (Sloan Digital Sky Survey) The star-forming galaxy UGC09476: Hα emission measured from the 2D spectra of the CALIFA (Calar Alto Legacy Integral Field Area) survey The star-forming galaxy UGC09476: Expected F660 – r image from J-PLUS photometry. The HII regions with Hα emission will be detected and characterized with J-PLUS data

The star-forming galaxy UGC 09475. Left: Optical images from SDSS (Sloan Digital Sky Survey). Middle: Hα emission measured from the 2D spectra of the CALIFA (Calar Alto Legacy Integral Field Area) survey. Right: Expected F660 – r image from J-PLUS photometry. The HII regions with Hα emission will be detected and characterized with J-PLUS data.