J-PAS: A value-added catalogue of optical line intensities for nebular emission galaxies (JOLINES)

TL;DR

The paper introduces JOLINES, a value-added catalogue of optical emission-line fluxes for galaxies observed with J-PAS precursors (miniJPAS, J-NEP) and the J-PAS EDR, derived through SED fitting with $CIGALE$ to accurately reconstruct continua in narrow-band photometry. The authors validate the approach with mock catalogs and synthetic spectra from DESI, and demonstrate consistency with external spectroscopic measurements, achieving typical dispersions around $\sim$0.3 dex for bright lines and reliable results for $EW$ above about 20 Å. The first release includes thousands of sources with robust measurements for key lines (e.g., H$\alpha$+[NII], [OIII]$\lambda$5007, [OII]$\lambda$3727) and provides a framework to disentangle blends using adjacent filters and theoretical line ratios. JOLINES enables population-wide studies of star formation, AGN activity, and ISM conditions in the local universe, with future data releases expected to expand the samples and improve completeness.

Abstract

We present the value-added catalogue JOLINES (J-PAS optical line intensities for nebular emission galaxies), which provides emission-line fluxes in galaxies at from the spectrophotometric catalogues of miniJPAS, J-NEP and the J-PAS early data release (EDR). This catalogue will be updated with future data releases, offering a growing resource for the study of emission-line galaxies. To obtain reliable emission-line fluxes from narrow-band photometry, we employed spectral energy distribution (SED) fitting using CIGALE, a robust tool that reconstructs the continuum emission and ensures accurate flux measurements. This method effectively mitigates uncertainties associated with direct continuum subtraction techniques, and systematics such as absorption components in the emission lines. We validate our approach using simulated observations of galaxy spectra with added noise, testing the method's performance across different equivalent width (EW) regimes and emission-line strengths. Additionally, we compare the recovered emission-line fluxes with spectroscopic measurements from the Sloan Digital Sky Survey (SDSS) and the Dark Energy Spectroscopic Instrument (DESI). Our results show a tight correlation between photometric and spectroscopic fluxes, particularly for bright emission lines, with a typical dispersion of $\sim$0.3 dex. Reliable fluxes are obtained for emission lines with EW $\gtrsim20\, \rm{\mathring{A}}$, in agreement with previous empirical studies. The current catalogue comprises approximately 13,900 sources with reliable flux measurements in the H$α$+[NII] complex and 7,200 in [OIII]$λ5007$, ensuring statistically robust samples for the brightest optical emission lines. This resource will be expanded in future J-PAS releases, facilitating large-scale studies of star formation, AGN activity, and galaxy evolution.

Figures (9)

• Figure 1: Transmission profile of three J-PAS filters: J0530 (dashed grey line), J0540 (solid yellow line), and J0550 (dotted grey line). A flux measurement for a certain emission line (green arrow) from Table \ref{['tab_lines']} is provided when the observed wavelength falls on the top 5% maximum transmission of the square filters (orange and red solid line), whereas filters with lines falling at the transmission profile wings ($> 5\%$; shaded grey area) are flagged as contaminated and discarded for the continuum fitting. Note that those cases will have a measurement in one of the adjacent filters, which always overlap at the maximum transmission (in red).
• Figure 2: Best-fit SED obtained with CIGALE for the miniJPAS galaxy 2241--19112. The upper panel displays the observed fluxes (purple circles), the best-fit fluxes derived from the fitting (red dots), the stellar continuum before (dashed blue line) and after (solid yellow line) applying dust attenuation, the nebular line plus continuum emission (solid green line), and the total model (solid black line). The lower panel presents the relative differences between the observed and modelled fluxes.
• Figure 3: Extraction of emission-line fluxes from the photospectrum of the galaxy 2241--19112, using the CIGALE best-fit model for the continuum subtraction. Left: the observed photospectrum (coloured dots) is compared with the best-fit model (solid light-grey line) and its corresponding continuum (solid dark grey line). The solid green step line indicates the synthetic photometry for the best-fit continuum distribution obtained for the J-PAS filters. Right: dots show the continuum-subtracted photospectrum, in colour for filters including lines in Table \ref{['tab_lines']}, in grey for continuum filters used in the SED fitting. Dotted black lines indicate the $3\sigma$ uncertainty, derived from the scatter in the residual values of the continuum-subtracted photospectrum. The solid light-grey line shows the emission-line spectrum for the CIGALE best-fit model.
• Figure 4: The upper panels show density plots of the emission-line fluxes for [Oiii]$\lambda4959,5007$ (a) and H$\alpha$ + [Nii]$\lambda6548,6583$ (b) derived from the mock catalogue spectra with the J-PAS filter system, using the SED-fitting-based continuum subtraction method described in Section \ref{['obs']}. The J-PAS fluxes are compared with the input line fluxes in the mock catalogue. The lower panels show the line flux ratios between the J-PAS line fluxes and the mock input fluxes for [Oiii]$\lambda 4959,5007$ (c) and H$\alpha$ + [Nii]$\lambda 6548,6583$ (d), plotted as a function of the mock equivalent width of [Oiii]$\lambda 5007$ and H$\alpha$, respectively. In dashed grey style, we show the one-to-one lines in the upper panels and the constant unity value in the lower panels. The side vertical panels in (c) and (d) show the marginal distribution (grey histogram) and the corresponding Gaussian fit (dashed red line) of the J-PAS to mock line flux ratios. In all panels, the black contours represent the 1, 10, 50, 90, and 99% percentiles of the two-dimensional probability distribution.
• Figure 5: Same as Fig. \ref{['fig_mock']}, but comparing the J-PAS fluxes obtained from the synthetic photometry of DESI EDR spectra with the spectroscopic line fluxes from the FastSpecFit value-added catalogue (moustakas23; Moustakas et al. in prep.). Panels (a) and (b) show the density plots for [Oiii]$\lambda4959,5007$ and H$\alpha$+[Nii]$\lambda6548,6583$, respectively. Panels (c) and (d) display the corresponding J-PAS to spectroscopic flux ratios as a function of the spectroscopic equivalent widths.