MEGARA-IFU detection of extended He II λ4686 nebular emission in the central region of NGC1569 and its ionization budget

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Gil de Paz, Armando
Castillo Morales, África
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Oxford Univ. Press
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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 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 semi-circular arc of ∼40 pc width and ∼150 pc diameter around the super star cluster A (SSC-A). The A_(V) 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 A_(V)=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 mass of (5.5±0.5)×105 Mꙩ.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.
© 2020 The Author(s). Artículo firmado por 24 autores. It is a pleasure to thank the anonymous referee for thoughtful comments that lead to a significant improvement of the manuscript. This publication is based on data obtained with the MEGARA instrument at the Gran Telescopio Canarias, installed in the Spanish Observatorio del Roque de los Muchachos, in the island of La Palma. MEGARA has been built by a Consortium led by the Universidad Complutense de Madrid (Spain) and that also includes the Instituto de Astrofísica, Óptica y Electrónica (México), Instituto de Astrofísica de Andalucía (CSIC, Spain) and the Universidad Politécnica de Madrid (Spain). MEGARA is funded by the Consortium institutions, GRANTECAN S.A. and European Regional Development Funds (ERDF), through Programa Operativo Canarias FEDER 2014-2020. We thank CONACyT for the research grants CB-A1-S25070 (YDM), CB-A1-S-22784 (DRG), and CB-A1-S-28458 (SS). VMAGG is funded by UNAM DGAPA PAPIIT project number IA100318. Authors acknowledge financial support from the Spanish MINECO under grant numbers AYA2016-79724-C4-4-P, AYA2016-75808-R, AYA2017- 90589-REOT and RTI2018-096188-B-I00.
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