Calibration of hybrid resolved star formation rate recipes based on PHANGS–MUSE Hα and Hβ maps

¹ INAF – Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, 50125 Florence, Italy
e-mail: francesco.belfiore@inaf.it
² Department of Astronomy, The Ohio State University, 140 West 18th Avenue, Columbus, OH 43210, USA
³ Department of Physics and Astronomy, McMaster University, 1280 Main St. West, Hamilton, ON L8S 4M1, Canada
⁴ Canadian Institute for Theoretical Astrophysics (CITA), University of Toronto, 60 St George Street, Toronto, ON M5S 3H8, Canada
⁵ Argelander-Institut für Astronomie, Universität Bonn, Auf dem Hügel 71, 53121 Bonn, Germany
⁶ Centro de Astronomía (CITEVA), Universidad de Antofagasta, Avenida Angamos 601, Antofagasta, Chile
⁷ Max-Planck-Institut für extraterrestrische Physik (MPE), Giessenbachstrasse 1, 85748 Garching, Germany
⁸ Departamento de Astronomía, Universidad de Chile, Camino del Observatorio 1515, Las Condes, Santiago, Chile
⁹ Department of Physics and Astronomy, University of Wyoming, Laramie, WY 82071, USA
¹⁰ Astronomisches Rechen-Institut, Zentrum für Astronomie der Universität Heidelberg, Mönchhofstraße 12-14, 69120 Heidelberg, Germany
¹¹ Universität Heidelberg, Zentrum für Astronomie, Institut für theoretische Astrophysik, Albert-Ueberle-Straße 2, 69120 Heidelberg, Germany
¹² Research School of Astronomy and Astrophysics, Australian National University, Canberra, ACT 2611, Australia
¹³ ARC Centre of Excellence for All Sky Astrophysics in 3 Dimensions (ASTRO 3D), Stromlo Mount, Australia
¹⁴ International Centre for Radio Astronomy Research, University of Western Australia, 7 Fairway, Crawley, 6009 WA, Australia
¹⁵ Universität Heidelberg, Interdisziplinäres Zentrum für Wissenschaftliches Rechnen, Im Neuenheimer Feld 205, 69120 Heidelberg, Germany
¹⁶ Observatorio Astronómico Nacional (IGN), C/Alfonso XII, 3, 28014 Madrid, Spain
¹⁷ Departamento de Física de la Tierra y Astrofísica, Universidad Complutense de Madrid, 28040, Madrid, Spain
¹⁸ Instituto de Física de Partículas y del Cosmos IPARCOS, Facultad de CC Físicas, UCM, 28040, Madrid, Spain
¹⁹ Max-Planck-Institute for Astronomy, Königstuhl 17, 69117 Heidelberg, Germany

Received: 1 September 2022
Accepted: 10 November 2022

Abstract

Mapping star-formation rates (SFR) within galaxies is key to unveiling their assembly and evolution. Calibrations exist for computing the SFR from a combination of ultraviolet and infrared bands for galaxies as integrated systems, but their applicability to sub-galactic (kiloparsec) scales remains largely untested. We used integral field spectroscopy of 19 nearby (D < 20 Mpc) galaxies obtained by PHANGS–MUSE to derive accurate Balmer decrements (Hα/Hβ) and attenuation-corrected Hα maps. We combined this information with mid-infrared maps from WISE at 22 μm and ultraviolet maps from GALEX in the far-UV band to derive SFR surface densities in nearby galaxies on resolved (kiloparsec) scales. Using the Hα attenuation-corrected SFR as a reference, we find that hybrid recipes from the literature overestimate the SFR in regions of low SFR surface density, low specific star-formation rate (sSFR), low attenuation, and old stellar ages. We attribute these trends to heating of the dust by old stellar populations (IR cirrus). We calibrated this effect by proposing functional forms for the coefficients in front of the IR term that depend on band ratios sensitive to the sSFR. These recipes return SFR estimates that agree with those in the literature at high sSFR (log(sSFR/yr⁻¹) >  − 9.9). Moreover, they lead to negligible bias and < 0.16 dex scatter when compared to our reference attenuation-corrected SFR from Hα. These calibrations prove reliable as a function of physical scale. In particular, they agree within 10% with the attenuation corrections computed from the Balmer decrement on 100 pc scales. Despite small quantitative differences, our calibrations are also applicable to integrated galaxy scales probed by the MaNGA survey, but with a larger scatter (up to 0.22 dex). Observations with JWST open up the possibility to calibrate these relations in nearby galaxies with cloud-scale (∼100 pc) resolution mid-IR imaging.