THE INFRARED PROPERTIES OF EMBEDDED SUPER STAR CLUSTERS: PREDICTIONS FROM THREE-DIMENSIONAL RADIATIVE TRANSFER MODELS

David G. Whelan, Kelsey E. Johnson, Barbara A. Whitney, Remy Indebetouw, Kenneth Wood

Research output: Contribution to journalArticlepeer-review

13 Citations (Scopus)

Abstract

With high-resolution infrared data becoming available that can probe the formation of high-mass stellar clusters for the first time, appropriate models that make testable predictions of these objects are necessary. We utilize a three-dimensional radiative transfer code, including a hierarchically clumped dusty envelope, to study the earliest stages of super star cluster (SSC) evolution. We explore a range of parameter space in geometric sequences that mimic the hypothesized evolution of an embedded SSC. The inclusion of a hierarchically clumped medium can make the envelope porous, in accordance with previous models and supporting observational evidence. The infrared luminosity inferred from observations can differ by a factor of two from the true value in the clumpiest envelopes depending on the viewing angle. The infrared spectral energy distribution also varies with viewing angle for clumpy envelopes, creating a range in possible observable infrared colors and magnitudes, silicate feature depths, and dust continua. General observable features of cluster evolution differ between envelopes that are relatively opaque or transparent to mid-infrared photons. For optically thick envelopes, evolution is marked by a gradual decline of the 9.8 mu m silicate absorption feature depth and a corresponding increase in the visual/ultraviolet flux. For the optically thin envelopes, clusters typically begin with a strong hot dust component and silicates in emission, and these features gradually fade until the mid-infrared polycyclic aromatic hydrocarbon features are predominant. For the models with a smooth dust distribution, the Spitzer MIPS or Herschel PACS [70]-[160] color is a good probe of the stellar mass relative to the total mass or star formation efficiency (SFE). Likewise, the IRAC/MIPS [3.6]-[24] color can be used to constrain the R-in and R-out values of the envelope. However, clumpiness confuses the general trends seen in the smooth dust distribution models, making it harder to determine a unique set of envelope properties. Nevertheless, good diagnostic colors were found for each of the input parameters: again, the [70]-[160] color can be used to separate models with different SFEs; the Spitzer IRAC/MIPS [8.0]-[24] color is able to constrain R-in and R-out values; and the IRAC [3.6]-[5.8] color is sensitive to the fraction of the dust distributed in clumps. Finally, in a comparison of this model set to IRAS data of ultracompact H II regions, we find good agreement, suggesting that these models are physically relevant, and will provide useful diagnostic ability for data sets of resolved, embedded SSCs with the advent of high-resolution infrared telescopes like James Webb Space Telescope.

Original languageEnglish
Article number111
Number of pages13
JournalAstrophysical Journal
Volume729
Issue number2
DOIs
Publication statusPublished - 10 Mar 2011

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