JWST and Hubble Observations Reveal Star Cluster Formation and Dust Evolution in NGC 628
Astronomers used Hubble and James Webb Space Telescope observations spanning 0.3–7.7 micrometers to analyze the spectral energy distributions of over 12,000 star clusters in the spiral galaxy NGC 628, deriving their ages, masses, and dust properties. The study finds that young emerging star clusters peak at 3–5 million years in age, with about 12% still heavily embedded in dust, and that clusters clear their surrounding gas and dust within roughly 4 million years. These results constrain the feedback mechanisms that drive star cluster emergence and demonstrate JWST's power to detect short-lived, dust-obscured stellar populations.
A team of astronomers analyzed more than 12,000 optically-selected star clusters, emerging young star clusters (eYSCs), and MIRI-selected sources in the nearby spiral galaxy NGC 628 using combined Hubble Space Telescope and James Webb Space Telescope data covering wavelengths from 0.3 to 7.7 micrometers. Fitting spectral energy distributions with the SED-fitting code CIGALE, they derived cluster ages, masses, extinctions, and dust properties including polycyclic aromatic hydrocarbon (PAH) abundances. Near-infrared-selected eYSC-I and eYSC-II sources — distinguished by compact versus diffuse PAH emission — peak at ages of 3–5 million years, with roughly 12% showing high dust reddening (E(B−V) > 2), confirming the existence of dust-embedded cluster populations during emergence. The distributions of PAH abundance and stellar-to-nebular attenuation ratios suggest an evolutionary sequence in which clusters transition from eYSC-I to eYSC-II as they clear surrounding dust and gas, with a photo-dissociation region clearing timescale of approximately 4 million years. The study also finds that star clusters in NGC 628's spiral arms are systematically more massive and more dust-reddened than those in inter-arm regions, and that F770W-bright MIRI sources preferentially trace the youngest and dustiest cluster populations. The results underscore JWST's unique capability to identify and characterize star clusters during their brief embedded phases and to place observational constraints on stellar feedback processes.
What's missing
The study relies on optically-selected cluster catalogs as its primary sample, which may introduce incompleteness bias against the most heavily dust-embedded clusters that are invisible at optical wavelengths. The generalizability of the ~4 Myr PDR clearing timescale to galaxies with different metallicities, star formation rates, or morphologies remains an open question.
What different sources said
- arXiv astro-phCenter
Feedback in Extragalactic Star Clusters (FEAST): Spectral Energy Distributions and the Physical Properties of Star Clusters in NGC 628 with CIGALE
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