The PHANGS-H α survey

We present PHANGS-H α , a narrowband imaging survey that maps H α emission over a sample of 65 nearby massive star-forming galaxies. The data were obtained using the MPG-ESO 2.2-meter telescope at La Silla and the du Pont 2.5-meter telescope at Las Campanas Observatory, within the framework of the multi-wavelength cloud-scale (50–100 pc) resolution mapping of molecular gas and star formation conducted by the Physics at High Angular resolution in Nearby GalaxieS (PHANGS) collaboration. PHANGS-H α complements the published PHANGS-ALMA, PHANGS-MUSE, PHANGS-HST, and PHANGS-JWST surveys, providing an anchor point for the photometric and astrometric calibration of these datasets, as well as samples of H II regions and star formation rate maps for the bulk of the PHANGS sample. We describe the observations, data processing, and calibration of the PHANGS-H α dataset, as well as the procedures used to derive emission-line fluxes from narrowband imaging. A subset of galaxies with available spectroscopic Ha mapping from the PHANGS-MUSE survey serves as the basis of a detailed comparison with the narrowband photometry presented here. This comparison informs a set of best practices for the processing of narrowband H α imaging, which we subsequently apply to the full dataset.