One of the standout features of the J-PLUS survey is the filter known as J0660, one of the 12 narrowband filters used by the JAST80 telescope at the Observatorio Astrofísico de Javalambre (OAJ). This filter is part of the J-PLUS project, a survey of the nearby universe observable from the Northern Hemisphere. Conceived as an unprecedented survey, it aims to characterize tens of millions of galaxies and stars in the Milky Way. But what exactly is J0660, and why is it important?

J0660 is the filter that enables the detection of what is known in physics as H-alpha emission. This emission, visible in the red region of the electromagnetic spectrum, corresponds to one of the spectral lines of hydrogen and is a clear indicator of star formation processes. Therefore, this filter allows the J-PLUS survey to detect regions in the nearby universe where new stars are being born. With this filter, researchers can detect emission from galaxies located up to around 220 million light-years away.

The novelty lies in the development of a pipeline—an automated set of computational tools—led by Dr. Rahna Payyasseri at CEFCA. This pipeline, called J-SHE (J-PLUS Spatially resolved Hα Emission line), selects and processes the latest J-PLUS data to construct detailed, spatially resolved maps of H-alpha emission in galaxies.

These new maps make it possible to explore how star formation varies across different regions of a galaxy and how it relates to factors such as galaxy mass or structure. The goal is to study star formation and galactic structures with an unprecedented level of detail. The method has been validated using spectroscopic data from the MUSE–PHANGS, CALIFA, and MaNGA projects, and has also made it possible to build a cross-matched catalog with those studies.

Thanks to the 12 custom-designed filters of J-PLUS, the J-SHE tool also enables the characterization of the energy distribution of forming stellar populations. This allows researchers not only to identify where stars are forming, but also to estimate how many are forming and how old they are.

The narrowband imaging of the J-PLUS project offers a significant advantage over traditional techniques such as spectroscopy, which require long observation times and are usually limited to a small sample of selected galaxies. With J-PLUS, it is possible to study thousands of galaxies and their full structure much more efficiently, advancing our understanding of how young stars form. The large area covered by J-PLUS—spanning thousands of square degrees of the sky—combined with the automated J-SHE techniques, will deliver an Hα atlas of thousands of galaxies, providing one of the most detailed and extensive views to date of how galaxies grow in the local Universe.

This study has been published in the journal Astronomy & Astrophysics (A&A). J-SHE is part of CEFCA’s J-IFU research project, funded by the Spanish State Research Agency under grant PID2021-124918NA-C43.

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