Observing the influence of the youngest super star clusters in NGC 1569: Keck Brackett $\alpha$ spectroscopy

Abstract

We report Keck-NIRSPEC observations of the Brackett $\alpha$ 4.05 $\mu$m recombination line across the two candidate embedded super star clusters (SSCs) in NGC 1569. These SSCs power a bright HII 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 [SIV] 10.5 $\mu$m line, the Brackett $\alpha$ spectra data provide new insight into the dynamical state of gas ionized by these forming massive clusters. NIR sources detected in 2 $\mu$m images from the Slit-viewing Camera are matched with GAIA sources to obtain accurate celestial coordinates and slit positions to within $\sim 0.1^{\prime \prime }$. Br$\alpha$ is detected as a strong emission peak powered by the less luminous infrared source, MIR1 ($L_{\mathrm{IR}}\sim 2\times 10^7{L}_{\odot }$). The second candidate SSC MIR2 is more luminous ($L_{\mathrm{IR}}\gtrsim 4\times 10^8{L}_{\odot }$) but exhibits weak radio continuum and Br$\alpha$ emission, suggesting the ionized gas is extremely dense ($n_e\gtrsim 10^5$ cm${}^{-3}$), corresponding to hypercompact HII regions around newborn massive stars. The Br$\alpha$ and [SIV] lines across the region are both remarkably symmetric and extremely narrow, with observed line widths $\Delta v\simeq 40$ km s${}^{-1}$, FWHM. 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.

arXiv commentAccepted for publication in MNRAS 2021 Feb 26; 9 pages, 7 figures

References in corpus (41)

• Gaia Data Release 2. Summary of the contents and survey properties
• The Gaia mission
• Multiple Stellar Populations in Globular Clusters
• The Hubble Space Telescope UV Legacy Survey of Galactic Globular Clusters. I. Overview of the Project and Detection of Multiple Stellar Populations
• TEXES: A Sensitive High-Resolution Grating Spectrograph for the Mid-Infrared
• On Radiation Pressure in Static, Dusty HII Regions
• ISM Properties in Low-Metallicity Environments II. The Dust Spectral Energy Distribution of NGC 1569
• The Star Clusters in the Starburst Irregular Galaxy NGC 1569
• Gas expulsion in massive star clusters? Constraints from observations of young and gas-free objects
• (Sub)millimetre emission from NGC 1569: an abundance of very small grains
• Highly efficient star formation in NGC 5253 possibly from stream-fed accretion
• Gemini GMOS/IFU spectroscopy of NGC 1569 - I: Mapping the properties of a young star cluster and its environment
• The Very Massive Star Content of the Nuclear Star Clusters in NGC 5253
• The Brightest Young Star Clusters in NGC 5253
• Molecular Gas and the Young Starburst in NGC 5253, Revisited
• An extragalactic supernebula confined by gravity
• The Birth of a Super Star Cluster: NGC 5253
• The Stellar and Gas Kinematics of the LITTLE THINGS Dwarf Irregular Galaxy NGC 1569
• ALMA Detects CO(3-2) within a Super Star Cluster in NGC5253
• Gas expulsion vs gas retention: what process dominates in young massive clusters?
• Catastrophic Cooling in Superwinds: Line Emission and Non-equilibrium Ionization
• Two Thresholds for Globular Cluster Formation and their Dominance of Star Formation in the Early-Universe
• Multifrequency radio continuum observations of NGC 1569: Evidence for a convective wind
• Gas expulsion vs gas retention in young stellar clusters II: effects of cooling and mass segregation
• A search for radio supernovae and supernova remnants in the region of NGC1569's super star clusters
• A Radio Continuum Study of Dwarf Galaxies: 6 cm imaging of Little Things
• HST/ACS Photometry of Old Stars in NGC 1569: The Star Formation History of a Nearby Starburst
• Infrared Narrow-Band Tomography of the Local Starburst NGC 1569 with LBT/LUCIFER
• Exploring the Dust Content of Galactic Winds With Herschel. II. Nearby Dwarf Galaxies
• Brackett Lines from the Super Star Cluster Nebulae in He 2-10
• Ionized Gas Motions and the Structure of Feedback Near a Forming Globular Cluster in NGC 5253
• On the early evolution of massive star clusters: the case of cloud D1 and its embedded cluster in NGC 5253
• Extreme Star Formation
• Ionized Gas Kinematics at High Resolution. II: Discovery of a Double Infrared Cluster in II Zw 40
• A Spatially Resolved Radio Spectral Index Study of the Dwarf Irregular Galaxy NGC\,1569
• Recombination Lines of Embedded Star Clusters
• Enhanced dust emissivity power-law index along the western H$\alpha$ filament of NGC 1569
• Probing the interstellar medium of NGC1569 with Herschel
• Ionized Gas Kinematics at High Resolution V: [NeII], Multiple Clusters, High Efficiency Star Formation and Blue Flows in He 2-10
• Probing the Super Star Cluster Environment of NGC 1569 Using FISICA
• Ultra-Compact H II Regions and the Early Lives of Massive Stars