Integral Field Spectroscopy of the cometary starburst galaxy NGC 4861
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Oxford University Press
Stars: WolfRayetGalaxies: evolutionGalaxies: individual: NGC 4861: Markarian 59Galaxies: starburst
Nathan Roche and others, Integral Field Spectroscopy of the cometary starburst galaxy NGC 4861, Monthly Notices of the Royal Astronomical Society, Volume 523, Issue 1, July 2023, Pages 270–285, [https://doi.org/10.1093/mnras/stad1219]
SponsorshipCentro Astronómico Hispano en Andalucía; IPAC; National Aeronautics and Space Administration NASA; European Commission PTDC/FIS-AST/29245/2017, UID/FIS/04434/2019 EC; European Space Agency ESA; Ministerio de Economía y Competitividad PID2019-107408GB-C44 MINECO; Ministerio de Ciencia e Innovación MICINN; Junta de Andalucía CEX2021-001131-S, P18-FR-2664; Agencia Estatal de Investigación AEI; Instituto de Astrofísica de Andalucía PID2020-112949GB-I00 CAB (INTA-CSIC IAA
Using the PMAS Integral Field Unit on the Calar Alto 3.5 m telescope, we observed the southern component (Markarian 59) of the ‘cometary’ starburst galaxy NGC 4861. Mrk 59 is centred on a giant nebula and concentration of stars 1 kpc in diameter. Strong H α emission points to a star-formation rate (SFR) at least 0.47 M⊙ yr−1. Mrk 59 has a very high [O III] λ5007/H β ratio, reaching 7.35 in the central nebula, with a second peak at a star-forming hotspot further north. Fast outflows are not detected but nebular motion and galaxy rotation produce relative velocities up to 40 km s−1. Spectral analysis of different regions with ‘Fitting Analysis using Differential evolution Optimization’ (FADO) finds that the stars in the central and ‘spur’ nebulae are very young, ≤ 125 Myr with a large < 10 Myr contribution. Older stars (∼ 1 Gyr) make up the northern disk component, while the other regions show mixtures of 1 Gyr age with very young stars. This and the high specific SFR ∼ 3.5 Gyr−1 imply a bimodal star formation history, with Mrk 59 formed in ongoing starbursts fuelled by a huge gas inflow, turning the galaxy into an asymmetric ‘green pea’ or blue compact dwarf. We map the He II λ4686 emission, and identify a broad component from the central nebula, consistent with the emission of ∼300 Wolf–Rayet stars. About a third of the He II λ4686 flux is a narrow line emitted from a more extended area covering the central and spur nebulae, and may have a different origin.