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- Calzetti, Daniela, et al.
(author)
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Dust-buried Compact Sources in the Dwarf Galaxy NGC 4449
- 2023
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In: Astrophysical Journal. - : American Astronomical Society. - 0004-637X .- 1538-4357. ; 946:1
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Journal article (peer-reviewed)abstract
- Multiwavelength images from the Hubble Space Telescope covering the wavelength range 0.27–1.6 μm show that the central area of the nearby dwarf galaxy NGC 4449 contains several tens of compact sources that are emitting in the hydrogen recombination line Paβ (1.2818 μm) but are only marginally detected in Hα (0.6563 μm) and undetected at wavelengths λ ≤ 0.55 μm. An analysis of the spectral energy distributions (SEDs) of these sources indicates that they are likely relatively young stellar clusters heavily attenuated by dust. The selection function used to identify the sources prevents meaningful statistical analyses of their age, mass, and dust extinction distributions. However, these cluster candidates have ages ∼5–6 Myr and AV > 6 mag, according to their SED fits, and are extremely compact, with typical deconvolved radii of 1 pc. The dusty clusters are located at the periphery of the dark clouds within the galaxy and appear to be partially embedded. Density and pressure considerations indicate that the H ii regions surrounding these clusters may be stalled, and that pre-supernova (pre-SN) feedback has not been able to clear the clusters of their natal cocoons. These findings are in potential tension with existing models that regulate star formation with pre-SN feedback, since pre-SN feedback acts on short timescales, ≲4 Myr, for a standard stellar initial mass function. The existence of a population of dusty stellar clusters with ages >4 Myr, if confirmed by future observations, paints a more complex picture for the role of stellar feedback in controlling star formation.
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- McQuaid, Timothy, et al.
(author)
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The Timescales of Star Cluster Emergence : The Case of NGC 4449
- 2024
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In: Astrophysical Journal. - 0004-637X .- 1538-4357. ; 967:2
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Journal article (peer-reviewed)abstract
- We survey the young star cluster population in the dwarf galaxy NGC 4449 with the goal of investigating how stellar feedback may depend on the clusters' properties. Using ultraviolet (UV)–optical–near-infrared photometry obtained with the Hubble Space Telescope, we have recovered 99 compact sources exhibiting emission in the Paβ hydrogen recombination line. Our analysis reveals these sources possess masses of 102 < M⊙ < 105, ages of 1–20 Myr, and a color excess E(B − V) in the range 0–1.4. After selecting clusters with masses above 3000 M⊙ to mitigate stochastic sampling of the stellar initial mass function, we find that our IR-selected clusters have a median mass ∼ 7 × 103 M⊙ and remain embedded in their surrounding gas and dust for 5–6 Myr. In contrast, line-emitting sources selected from existing UV/optical catalogs have a median mass ∼ 3.5 × 104 M⊙ and have cleared their surroundings by 4 Myr. We further find that the environment in NGC 4449 has too low pressure to drive these differences. We interpret these findings as evidence that the clearing timescale from presupernova and supernova feedback is cluster mass dependent. Even in clusters with masses ∼ 7000 M⊙, stochastic sampling of the upper end of the stellar initial mass function is present, randomly decreasing the number of massive stars available to inject energy and momentum into the surrounding medium. This effect may increase the clearing timescales in these clusters by decreasing the effectiveness of both presupernova and supernova feedback; neither models nor observations have so far explored such dependence explicitly. Future studies and observations with, e.g., the JWST, will fill this gap.
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