Star formation 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 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).

Star-forming galaxy in the nearby Universe from J-PLUS DR1

Figure 1. Star-forming galaxy in the nearby Universe from J-PLUS DR1. The left image is a color composite from the gri filters. The central image presents the flux excess in the J0660 filter after accounting for a linear continuum defined with the r and i bands. The right panel presents the J-PLUS photo-spectra of the emission regions in the galaxy. The derived physical properties are labelled in the panel. Figure from Vilella-Rojo et al. 2020, submitted.

MEASURING Hα FLUX WITH J-PLUS PHOTOMETRIC DATA

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

This work uses J-PLUS EDR and Science Verification Data. The updated analysis including J-PLUS DR1 information is shown in Fig. 2.

Comparison between the Hα flux measured with J-PLUS photometry and from SDSS and CALIFA spectra. Distribution of the ration between photometric and spectroscopic flux.

Figure 2. Left panel: Comparison between the Hα flux measured with J-PLUS photometry and from SDSS (cyan) and CALIFA (orange) spectra. This figure includes data from J-PLUS DR1 and Science Verification Data. Right panel: Distribution of the ration between photometric and spectroscopic flux. The distribution is described as a Gaussian with median of 1.02 and dispersion of 0.27. Update version of Figure 7 in Logroño-García et al. 2019.