Observing the influence of the youngest super Star clusters in NGC 1569: Keck brackett α spectroscopy

Daniel P. Cohen*, Jean L. Turner*, Sara C. Beck, S. Michelle Consiglio

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review


We report Keck–NIRSPEC observations of the Brackett α 4.05 μm recombination line across the two candidate embedded super star clusters (SSCs) in NGC 1569. These SSCs power a bright H II region and have been previously detected as radio and mid-infrared sources. Supplemented with high-resolution VLA mapping of the radio continuum along with IRTF–TEXES spectroscopy of the [S IV] 10.5 μm line, the Brackett α data provide new insight into the dynamical state of gas ionized by these forming massive clusters. Near-infrared sources detected in 2 μm images from the slit-viewing Camera are matched with Gaia sources to obtain accurate celestial coordinates and slit positions to within ∼0´´ . 1. Br α is detected as a strong emission peak powered by the less luminous infrared source, MIR1 (LIR ∼ 2 × 107 L). The second candidate SSC MIR2 is more luminous (LIR ≳ 4 × 108 L) but exhibits weak radio continuum and Br α emission, suggesting the ionized gas is extremely dense (ne ≳ 105 cm−3), corresponding to hypercompact H II regions around newborn massive stars. The Br α and [S IV] lines across the region are both remarkably symmetric and extremely narrow, with observed line widths ∆v ≃ 40 km s−1, full width at half-maximum. This result is the first clear evidence that feedback from NGC 1569’s youngest giant clusters is currently incapable of rapid gas dispersal, consistent with the emerging theoretical paradigm in the formation of giant star clusters.

Original languageEnglish
Pages (from-to)2187-2194
Number of pages8
JournalMonthly Notices of the Royal Astronomical Society
Issue number2
StatePublished - 1 May 2021


FundersFunder number
National Science Foundation2006433
National Aeronautics and Space Administration
W. M. Keck Foundation
University of California
Veterinary Laboratories Agency


    • Galaxies: individual: NGC 1569
    • Galaxies: irregular
    • Galaxies: kinematics and dynamics
    • Galaxies: star clusters: general
    • Galaxies: starburst
    • H II regions


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