MEGARA-IFU detection of extended He ii λ4686 nebular emission in the central region of NGC 1569 and its ionization budget

• Published in: Monthly notices of the Royal Astronomical Society Vol. 498; no. 1; pp. 1496 - 1514
• Main Authors: Mayya, Y D, Carrasco, E, Gómez-González, V M A, Zaragoza-Cardiel, J, Gil de Paz, A, Ovando, P A, Sánchez-Cruces, M, Lomelí-Núñez, L, Rodríguez-Merino, L, Rosa-González, D, Silich, S, Tenorio-Tagle, G, Bruzual, G, Charlot, S, Terlevich, R, Terlevich, E, Vega, O, Gallego, J, Iglesias-Páramo, J, Castillo-Morales, A, García-Vargas, M L, Gómez-Alvarez, P, Pascual, S, Pérez-Calpena, A
• Format: Journal Article
• Language: English
• Published: Oxford University Press 11-10-2020; Oxford University Press (OUP): Policy P - Oxford Open Option A
• Subjects: Sciences of the Universe; stars: emission line; galaxies: individual (NGC 1569); galaxies: star clusters; Astrophysics - Astrophysics of Galaxies; galaxies: individual (NGC 1569)
• ISSN: 0035-8711; 1365-2966
• DOI: 10.1093/mnras/staa2335

ABSTRACT
We here report the detection of extended He ii λ4686 nebular emission in the central region of NGC 1569 using the integral field spectrograph MEGARA at the 10.4 m Gran Telescopio Canarias. The observations cover a field of view (FoV) of 12.5 arcsec × 11.3 arcsec at a seeing-limited spatial resolution of ∼15 pc and at a spectral resolution of R = 6000 in the wavelength range 4330–5200 Å. The emission extends over a semicircular arc of ∼40 pc width and ∼150 pc diameter around the superstar cluster A (SSC-A). The AV derived using Balmer decrement varies from the Galactic value of 1.6 mag to a maximum of ∼4.5 mag, with a mean value of 2.65 ± 0.60 mag. We infer 124 ± 11 Wolf–Rayet (WR) stars in SSC-A using the He ii λ4686 broad feature and AV = 2.3 mag. The He+ ionizing photon rate from these WR stars is sufficient to explain the luminosity of the He ii nebula. The observationally determined total He+ and H0 ionizing photon rates, their ratio, and the observed number of WR stars in SSC-A are all consistent with the predictions of simple stellar population models at an age of 4.0 ± 0.5 Myr and a mass of (5.5 ± 0.5) × 105 M⊙. Our observations reinforce the absence of WR stars in SSC-B, the second most massive cluster in the FoV. None of the other locations in our FoV where He ii λ4686 emission has been reported from narrow-band imaging observations contain WR stars.