J-PLUS: Uncovering a large population of extreme [OIII] emitters in the local Universe

Abstract

Over the past decades, several studies have discovered a population of galaxies undergoing very strong star formation events, called extreme emission line galaxies (EELGs). In this work, we exploit the capabilities of the Javalambre Photometric Local Universe Survey (J-PLUS), a wide field multifilter survey, with 2000 square degrees observed. We use it to identify EELGs at low redshift by their [OIII]5007 emission line. We intend to provide with a more complete, deep, and less biased sample of local EELGs. We select objects with an excess of flux in the J-PLUS mediumband $J0515$ filter, which covers the [OIII] line at z$<$0.06. We remove contaminants (stars and higher redshift systems) using J-PLUS and WISE infrared data, with SDSS spectra as a benchmark. We perform spectral energy distribution fitting to estimate the properties of the galaxies: line fluxes, equivalent widths (EWs), masses, etc. We identify 466 EELGs at $\mathrm{z}<0.06$ with [OIII] EW over 300 \textà and $r$-band mag. below 20, of which 411 were previously unknown. Most show compact morphologies, low stellar masses ($\log (M_{\star }/M_{\odot })\sim {8.13}_{-0.58}^{+0.61}$), low dust extinction ($E(B-V)\sim {0.1}_{-0.1}^{+0.2}$), and very young bursts of star formation (${3.0}_{-2.0}^{+2.7}$ Myr). Our method is up to $\sim$ 20 times more efficient detecting EELGs per Mpc${}^3$ than broadband surveys, and as complete as magnitude-limited spectroscopic surveys (and reaching fainter objects). The sample is not directly biased against strong H$\hat{I}\pm$ emitters, in contrast with broadband surveys. We demonstrate the capability of J-PLUS to identify, following a clear selection process, a large sample of previously unknown EELGs showing unique properties. A fraction of them are likely similar to the first galaxies in the Universe, but at a much lower redshift, which makes them ideal targets for follow-up studies.

22 pages, 22 figures. Submitted to Astronomy & Astrophysics