University of Hertfordshire

From the same journal

From the same journal

By the same authors


  • D. de la Fuente
  • F. Najarro
  • J. Borissova
  • S. Ramírez Alegría
  • M. M. Hanson
  • C. Trombley
  • D. F. Figer
  • B. Davies
  • M. Garcia
  • R. Kurtev
  • M. A. Urbaneja
  • L. C. Smith
  • P. W. Lucas
  • A. Herrero
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Original languageEnglish
Article numberA69
Number of pages23
JournalAstronomy & Astrophysics
Journal publication date1 May 2016
Early online date14 Apr 2016
Publication statusPublished - 1 May 2016


The Dragonfish Nebula has been recently claimed to be powered by a superluminous but elusive OB association. Instead, systematic searches in near-infrared photometric surveys have found many other cluster candidates on this sky region. Among these, the first confirmed young massive cluster was Mercer 30, where Wolf-Rayet stars were found. We perform a new characterization of Mercer 30 with unprecedented accuracy, combining NICMOS/HST and VVV photometric data with multi-epoch ISAAC/VLT H- and K-band spectra. Stellar parameters for most of spectroscopically observed cluster members are found through precise non-LTE atmosphere modeling with the CMFGEN code. Our spectrophotometric study for this cluster yields a new, revised distance of d = (12.4 +- 1.7) kpc and a total of Q = 6.70 x 10^50 Lyman ionizing photons. A cluster age of (4.0 +- 0.8) Myr is found through isochrone fitting, and a total mass of (1.6 +- 0.6) x 10^4 Msol is estimated thanks to our extensive knowledge of the post-main-sequence population. As a consequence, membership of Mercer 30 to the Dragonfish star-forming complex is confirmed, allowing us to use this cluster as a probe for the whole complex, which turns out to be extremely large (400 pc across) and located at the outer edge of the Sagittarius-Carina spiral arm (11 kpc from the Galactic Center). The Dragonfish complex hosts 19 young clusters or cluster candidates (including Mercer 30 and a new candidate presented in this work) and an estimated minimum of 9 field Wolf-Rayet stars. The sum of all these contributions accounts for, at least, 73% of the Dragonfish Nebula ionization and leaves little or no room for the alleged superluminous OB association; alternative explanations are discussed.


This document is the accepted manuscript version of the following article: D. De la Fuente, et al, “Probing the Dragonfish star-forming complex: the ionizing population of the young massive cluster Mercer 30”, Astronomy and Astrophysics, Vol. 589, A69, May 2016. The Version of record is available online at DOI: 10.1051/0004-6361/201528004


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