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Ashes of Creation: JWST Uncovers Silicate Dust in Massive Star Clusters

Daniel Maschmann, Bradley C. Whitmore, David A. Thilker, Ivan Gerasimov, Simon C. O. Glover, B. T. Draine, Bret Lehmer, Varun Bajaj, Sumit Sarbadhicary, Médéric Boquien, G. C. Sloan, Tony D. Weinbeck, Daniel A. Dale, Kiana Henny, Kirsten L. Larson, M. Jimena Rodríguez, Robert Kennicutt, Amirnezam Amiri, Ashley. T. Barnes, Torsten Böker, Martha Boyer, Daizhong Liu, Oleg V. Egorov, Hwihyun Kim, Ralf S. Klessen, Thomas S. -Y. Lai, Janice C. Lee, Adam K. Leroy, Sean T. Linden, Julia Roman-Duval, Karin Sandstrom, Eva Schinnerer, J. D. Smith, Leonardo Úbeda, Stefanie Walch, E. Watkins, Thomas G. Williams, Yixian Cao

TL;DR

This study uses JWST and HST data to identify a rare class of massive star clusters that exhibit a pronounced $10~\mu m$ silicate emission after clearing natal dust. By defining a robust excess metric, $E_{10~\mu m}$, and cross-referencing with multiwavelength catalogs, the authors assemble a sample of 22 clusters ($M_* > 10^5\,M_\odot$) across 12 galaxies. Through SED modeling with CIGALE and consideration of alternative mechanisms (RSG/YHG/LBV winds, SNe ejecta, and shocks), they find that pure dust continuum cannot explain the strongest emitters (max $E_{10~\mu m}^{\max}=1.27$), implying intrinsic silicate emission from internal dust production. The findings suggest that multiple, potentially rare processes operate in the most massive clusters, with IR spectroscopy required to pinpoint the dominant sources and their implications for the baryonic cycle in galaxies.

Abstract

Dust production is a fundamental aspect of the baryonic cycle of star formation. It is known that dust is injected into the interstellar medium during early star formation by supernovae and later on by evolved stars. From individual objects, these mechanisms are well understood, but the overall dust production in star clusters at different evolutionary stages is still challenging to quantify. We present 22 massive (> 105M$_{\odot}$) extra galactic star clusters with ages between 3 and 100 Myr exhibiting a compact dust morphology seen with JWST-MIRI. We only find PAH features associated with one star cluster and nineteen have already cleared themselves from their natal dust. Their main characteristic is a significant enhancement at 10$μ$m, which is likely due to silicate emission and cannot be explained by ionized gas. We discuss several possible explanations including dust production from evolved stars such as red super giants, more exotic star types like yellow hypergiants and luminous blue variable stars. Stochastic dust injection from supernovae or a single supernova in dense gas can also create significant silicate emission. However, for this scenario secondary tracers such as a X-ray signal are expected which we only observe in three star clusters. We find the most luminous 10$μ$m emitter to be the three most massive star clusters (> 106M$_{\odot}$) which is at least a magnitude stronger than any known stellar sources indicating a rare mechanism that only appears at extreme masses and a short lifetime.

Ashes of Creation: JWST Uncovers Silicate Dust in Massive Star Clusters

TL;DR

This study uses JWST and HST data to identify a rare class of massive star clusters that exhibit a pronounced silicate emission after clearing natal dust. By defining a robust excess metric, , and cross-referencing with multiwavelength catalogs, the authors assemble a sample of 22 clusters () across 12 galaxies. Through SED modeling with CIGALE and consideration of alternative mechanisms (RSG/YHG/LBV winds, SNe ejecta, and shocks), they find that pure dust continuum cannot explain the strongest emitters (max ), implying intrinsic silicate emission from internal dust production. The findings suggest that multiple, potentially rare processes operate in the most massive clusters, with IR spectroscopy required to pinpoint the dominant sources and their implications for the baryonic cycle in galaxies.

Abstract

Dust production is a fundamental aspect of the baryonic cycle of star formation. It is known that dust is injected into the interstellar medium during early star formation by supernovae and later on by evolved stars. From individual objects, these mechanisms are well understood, but the overall dust production in star clusters at different evolutionary stages is still challenging to quantify. We present 22 massive (> 105M) extra galactic star clusters with ages between 3 and 100 Myr exhibiting a compact dust morphology seen with JWST-MIRI. We only find PAH features associated with one star cluster and nineteen have already cleared themselves from their natal dust. Their main characteristic is a significant enhancement at 10m, which is likely due to silicate emission and cannot be explained by ionized gas. We discuss several possible explanations including dust production from evolved stars such as red super giants, more exotic star types like yellow hypergiants and luminous blue variable stars. Stochastic dust injection from supernovae or a single supernova in dense gas can also create significant silicate emission. However, for this scenario secondary tracers such as a X-ray signal are expected which we only observe in three star clusters. We find the most luminous 10m emitter to be the three most massive star clusters (> 106M) which is at least a magnitude stronger than any known stellar sources indicating a rare mechanism that only appears at extreme masses and a short lifetime.

Paper Structure

This paper contains 33 sections, 9 equations, 13 figures, 4 tables.

Table of Contents

  1. Introduction
  2. Data
  3. HST and JWST Imaging Observations
  4. Star Cluster Catalogs
  5. IR-Identified Stellar Sources
  6. Known $10~\mu m$ Emitters in the Milky Way
  7. SNR catalogs and Chandra X-ray Observations
  8. Source Identification and Photometry
  9. Source Detection
  10. Justification of Detection Algorithm
  11. Photometry
  12. Verification of Background Effects
  13. H$\alpha$ Equivalent width
  14. Selection of Star Clusters with Enhanced $10~\mu m$ Emission
  15. Quantifying $10~\mu m$ excess
  16. ...and 18 more sections

Figures (13)

  • Figure 1: MIRI rgb image of a $120\hbox{$^{\prime\prime}$}\times60\hbox{$^{\prime\prime}$}$ cutout of NGC 1566 constructed with the bands F770W (blue), F1000W (green), F1130W (red). We show a $10\hbox{$^{\prime\prime}$}\times10\hbox{$^{\prime\prime}$}$ zoom-in of a compact star cluster exhibiting a strong $10~\mu m$ emission and therefore appears green in the rgb image. This object will be identified in Sect. \ref{['sec:seclection']} as NGC 1566-4. We show on the right the SED with photometric measurements (see Sect. \ref{['ssec:photometry']}) of the three MIRI bands and the cutouts in gray-scales on top with the same stretch.
  • Figure 2: $10\mu$m excess, E$_{\rm 10\mu m}$, as a function of the absolute AB magnitude in the F1000W band, M$_{\rm F1000W}$. We show all detected sources in gray that have S/N$\geq 3$ in the F770W, F1000W and F1130W MIRI bands. In crowded regions we show grayscale contours to better visualize the density. All cross-matched star clusters from maschmann_phangs-hst_2024 are marked with black diamonds and sources that do not show any optical counterpart are marked with black circles. The black dashed line indicates the maximal value of E$_{\rm 10\mu m}$ that can be predicted by simple dust models as described in detail in Section \ref{['sec:model_predict']}. The $10\mu$m-emitters selected for this work are highlighted by red diamonds. For reference, we indicate with purple contours PAH-emitters that have been selected in rodriguez_tracing_2025, and with red, green and blue stars the stars categorized by hassani25. Orange stars indicate SNRs from the catalogs of winkler_optical_2021 and li_discovery_2024, and yellow markers show known stars exhibiting strong silicate features. In order to visualize the SED shape of PAH emitters and $10\mu$m emitters we show each of these objects in the top left and right, respectively: We show a $5\hbox{$^{\prime\prime}$}\times5\hbox{$^{\prime\prime}$}$rgb-cutout of the MIRI bands F770W (blue), F1000W (green), F1130W (red) and their corresponding SED.
  • Figure 3: Spatial distribution of $10~\mu$m emitters in their host galaxies. The overview images of the host galaxies are composed of HST BVI bands. Each source is shown in detail with two $7\hbox{$^{\prime\prime}$}\times7\hbox{$^{\prime\prime}$}$rgb cutouts: one HST with B (blue), V (green) and H$\alpha$ (red) marked by a red frame and one JWST MIRI with a cyan frame and composed of F770W (blue) F1000W (green) and F1130W (red). The two sources in NGC 3627 are both shown with one single $10\hbox{$^{\prime\prime}$}\times10\hbox{$^{\prime\prime}$}$ zoom-in as they are so close together. In all MIRI zoom-in panels we mark the $10~\mu$m emitters with a red crosshair and indicate the source number.
  • Figure 4: SED for all $10~\mu$m emitters presented in groups of the four morphological classifications discussed in Section \ref{['ssec:morph_class']}. We show the entire available photometric SED including observations with HST, JWST NIRCAM and MIRI. For each morphological group we show at least two objects with $7\hbox{$^{\prime\prime}$}\times7\hbox{$^{\prime\prime}$}$rgb cutouts of HST, NIRCAM and MIRI on the right. The HST images are composed with B (blue), V (green) and H$\alpha$ (red), the NIRCAM images with F200W (blue) F300M (green) and F335M (red) and the MIRI images with F770W (blue) F1000W (green) and F1130W (red). We furthermore show a zoom-in into the mid-IR of all objects in NGC 5194 and highlight the position of silicate emission at 10 and 18 $\mu$m.
  • Figure 5: MIR SED in units of luminosity for all $10~\mu m$ emitting star clusters and selected stellar sources (See Sect. \ref{['ssec:stars_milky']}). We show the ISO spectra of the star systems $\eta$ Carinae, the YHG IRC+10420, the RSG HV 888 and the post-AGB star IRAS 18062+2410. We also show the SED points of the young star cluster Westerlund 1 observed with SOFIA. We display the SEDs of the star cluster sample with gray and highlight the three brightest star clusters with black thicker lines.
  • ...and 8 more figures