Mapping the core of the Tarantula Nebula with VLT-MUSE – III. A template for metal-poor starburst regions in the visual and far-ultraviolet

Abstract

ABSTRACT We present the integrated VLT-MUSE spectrum of the central 2 × 2 arcmin2 (30 × 30 pc2) of NGC 2070, the dominant giant H ii region of the Tarantula Nebula in the Large Magellanic Cloud, together with an empirical far-ultraviolet spectrum constructed via LMC template stars from the ULLYSES survey and Hubble Tarantula Treasury Project UV photometry. NGC 2070 provides a unique opportunity to compare results from individual stellar populations (e.g. VLT FLAMES Tarantula Survey) in a metal-poor starburst region to the integrated results from the population synthesis tools Starburst99, Charlot & Bruzual, and BPASS. The metallicity of NGC 2070 inferred from standard nebular strong line calibrations is ∼0.4 ± 0.1 dex lower than obtained from direct methods. The Hα inferred age of 4.2 Myr from Starburst99 is close to the median age of OB stars within the region, although individual stars span a broad range of 1–7 Myr. The inferred stellar mass is close to that obtained for the rich star cluster R136 within NGC 2070, although this contributes only 21 per cent to the integrated far-UV continuum. He ii λ1640 emission is dominated by classical WR stars and main sequence WNh + Of/WN stars. Around 18 per cent of the NGC 2070 far UV continuum flux arises from very massive stars with ≥100 M⊙, including several very luminous Of supergiants. None of the predicted population synthesis models at low metallicities are able to successfully reproduce the far-UV spectrum of NGC 2070. We attribute issues to the treatment of mass-loss in very massive stars, the lack of contemporary empirical metal-poor templates, plus WR stars produced via binary evolution.