SDSS-V LVM: Detectability of Wolf-Rayet stars and their He II ionizing flux in low-metallicity environments
Year: 2025
Type: article
Abstract: The Small Magellanic Cloud (SMC) is the nearest low-metallicity dwarf galaxy. Its proximity and low reddening has enabled us to detect its Wolf-Rayet (WR) star population with 12 known objects. Quantitative spectroscopy of the stars revealed half of these WR stars to be strong sources of He II ionizing flux, but the average metallicity of the SMC is below where WR bumps are usually detected in integrated galaxy spectra showing nebular He II emission. Utilizing the Local Volume Mapper (LVM) integral-field spectroscopic survey, we investigate regions around the six SMC WN3h stars, whose winds are optically thin at ≥54 eV, allowing these energetic photons to escape. Focusing on He II 4686 Å, we show that the broad stellar wind component, the strongest optical diagnostic of WN3h stars, is diluted within 24 pc in the integrated spectra, making such WR stars hard to detect in unresolved low-metallicity regions. In addition, we compare the He II ionizing flux from LVM with the values inferred from the stellar atmosphere code PoWR and find that in nearly all cases, the stars emit more than enough hard ionizing photons to explain the observed He II nebular emission. We conclude that early-type WN stars with comparably thin winds are viable sources to produce the observed He II ionizing flux in low-metallicity galaxies. The easy dilution of the stellar signatures can explain the rareness of WR bump detections at 12 + log O/H < 8.0, while at the same time providing major candidates for the observed excess of nebular He II emission. This is challenging for population synthesis models across all redshifts as the evolutionary path toward this observed WR population at low metallicity remains enigmatic.
Authors: G. González-Torà, A. A. C. Sander, E. Egorova, R. R. Lefever, V. Ramachandran, O. V. Egorov, J. Josiek, E. C. Schösser, M. Bernini-Peron, K. Kreckel, A. Wofford, O. G. Telford, P. Senchyna, C. Leitherer, F.-H. Liang, G. A. Blanc, N. Drory, J. G. Fernández-Trincado, E. J. Johnston, A. J. Mejía-Narváez, S. F. Sanchez
Institutions: Heidelberg University, Universidad Nacional Autónoma de México, Carnegie Institution for Science, Carnegie Observatories, Space Telescope Science Institute, University of Chile, McDonald Observatory, The University of Texas at Austin, Universidad Católica del Norte, Universidad Diego Portales
Language: English
Subfield: Astronomy and Astrophysics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: green
Funders: Bundesministerium für Wirtschaft und Klimaschutz, National Science Foundation, Alfred P. Sloan Foundation, Yale University, Carnegie Institution of Washington, Ohio State University, California Institute of Technology, Harvard University, Aspen Center for Physics, Johns Hopkins University, New Mexico State University, Space Telescope Science Institute, Flatiron Health, European Commission, Deutsche Forschungsgemeinschaft, École Polytechnique Fédérale de Lausanne, University of Toronto, Ministerio de Ciencia e Innovación, Universidad Nacional Autónoma de México, Yunnan University, Nanjing University, China National Textile and Apparel Council, Leibniz-Institut für Astrophysik Potsdam, Agencia Nacional de Investigación y Desarrollo, Max-Planck-Institut für Astronomie, University of Illinois at Urbana-Champaign, University of Colorado Boulder, Smithsonian Astrophysical Observatory, Leibniz-Gemeinschaft, Dirección General de Asuntos del Personal Académico, Universidad Nacional Autónoma de México, National Astronomical Observatories, Chinese Academy of Sciences
Awards: G2595738051, G3625898673, G3690828678, G411753437, G4348055450, Erstellung eines mehrdimensionalen Frameworks zur Kalibrierung von WolfRayetartigen Massenausflüssen, G5737963569, Entschlüsselung der Grundpfeiler unseres Universums: Anwendung und Entwicklung von Sternatmosphären der nächsten Generation, G7135376007, G7237102553, Programs on Critical Problems in Physics, Astrophysics and Biophysics at the Aspen Center for Physics, G8278124175, CENTRO DE ASTROFISICA Y TECNOLOGIAS AFINES (CATA)
OpenAlex ID: W7110965830
FWCI:
Cites:
Cited by:
Related to: