PHANGS–JWST First Results: Massive Young Star Clusters and New Insights from JWST Observations of NGC 1365

Whitmore, Bradley C.; Chandar, Rupali; Rodríguez, María Margarita; Lee, Janice; Emsellem, Éric; Floyd, Matthew; Kim, Hwi; Kruijssen, J. M. Diederik; Mok, Angus; Sormani, Mattia C.; Boquien, M.; Dale, Daniel A.; Faesi, Christopher M.; Henny, Kiana F.; Hannon, Stephen; Thilker, David A.; White, R. L.; Barnes, Ashley; Bigiel, Frank; Chevance, Mélanie; Henshaw, Jonathan D.; Klessen, Ralf S.; Leroy, Adam K.; Liu, Daizhong; Maschmann, Daniel; Meidt, Sharon E.; Rosolowsky, Erik; Schinnerer, E.; Sun, Jiayi; Watkins, Elizabeth J.; Williams, Thomas G.

doi:10.3847/2041-8213/acae94

Cited by 19 publications

(35 citation statements)

References 56 publications

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“…Similar values of t fb,21 μm and t obsc have been measured using ages of stellar clusters and their association with neighboring GMCs (Whitmore et al 2014;Grasha et al 2018Grasha et al , 2019, as well as using H II region morphologies (Hannon et al 2019(Hannon et al , 2022. We note that the "heavily obscured phase" is also referred to as "embedded" in other works in this Issue, which report qualitatively similar durations of this phase (Rodriguez et al 2022;Whitmore et al 2023).…”

Section: Duration Of Thesupporting

confidence: 84%

PHANGS–JWST First Results: Duration of the Early Phase of Massive Star Formation in NGC 628

Kim¹,

Chevance

Kruijssen

et al. 2023

ApJL

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The earliest stages of star formation, when young stars are still deeply embedded in their natal clouds, represent a critical phase in the matter cycle between gas clouds and young stellar regions. Until now, the high-resolution infrared observations required for characterizing this heavily obscured phase (during which massive stars have formed, but optical emission is not detected) could only be obtained for a handful of the most nearby galaxies. One of the main hurdles has been the limited angular resolution of the Spitzer Space Telescope. With the revolutionary capabilities of the James Webb Space Telescope (JWST), it is now possible to investigate the matter cycle during the earliest phases of star formation as a function of the galactic environment. In this Letter, we demonstrate this by measuring the duration of the embedded phase of star formation and the implied time over which molecular clouds remain inert in the galaxy NGC 628 at a distance of 9.8 Mpc, demonstrating that the cosmic volume where this measurement can be made has increased by a factor of >100 compared to Spitzer. We show that young massive stars remain embedded for 5.1 − 1.4 + 2.7 Myr ( 2.3 − 1.4 + 2.7 Myr of which being heavily obscured), representing ∼20% of the total cloud lifetime. These values are in broad agreement with previous measurements in five nearby (D < 3.5 Mpc) galaxies and constitute a proof of concept for the systematic characterization of the early phase of star formation across the nearby galaxy population with the PHANGS–JWST survey.

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Section: Duration Of Thesupporting

confidence: 84%

PHANGS–JWST First Results: Duration of the Early Phase of Massive Star Formation in NGC 628

Kim¹,

Chevance

Kruijssen

et al. 2023

ApJL

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“…This picture has been borne out in other systems (e.g., Kim et al 2021). Our data broadly support this picture; from the visual inspection, the compact 21 μm bright sources detected by JWST in these targets appear to be primarily starforming regions hosting high-mass star formation, though relatively few sources are associated with a truly optically dark phase (see also Kim et al 2023;Whitmore et al 2023). In this section, we quantify this impression by examining the associations between the 21 μm sources and other star formation tracers and then examining embedded sources.…”

Section: Properties Of the 21 μM Sourcessupporting

confidence: 80%

“…In NGC 1365, there is a tail of sources at high luminosity, which consists of the sources in the nuclear star-forming ring of this system that are not included in the fit. These high-mass young sources are explored further in Whitmore et al (2023).…”

Section: Sed Fitting and Derived Propertiesmentioning

confidence: 99%

PHANGS–JWST First Results: The 21 μm Compact Source Population

Hassani

Rosolowsky

Leroy

et al. 2023

ApJL

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We use PHANGS–James Webb Space Telescope (JWST) data to identify and classify 1271 compact 21 μm sources in four nearby galaxies using MIRI F2100W data. We identify sources using a dendrogram-based algorithm, and we measure the background-subtracted flux densities for JWST bands from 2 to 21 μm. Using the spectral energy distribution (SED) in JWST and HST bands plus ALMA and MUSE/VLT observations, we classify the sources by eye. Then we use this classification to define regions in color–color space and so establish a quantitative framework for classifying sources. We identify 1085 sources as belonging to the ISM of the target galaxies with the remainder being dusty stars or background galaxies. These 21 μm sources are strongly spatially associated with H ii regions (>92% of sources), while 74% of the sources are coincident with a stellar association defined in the HST data. Using SED fitting, we find that the stellar masses of the 21 μm sources span a range of 102–104 M ⊙ with mass-weighted ages down to 2 Myr. There is a tight correlation between attenuation-corrected Hα and 21 μm luminosity for L ν,F2100W > 1019 W Hz−1. Young embedded source candidates selected at 21 μm are found below this threshold and have M ⋆ < 103 M ⊙.

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“…Kim et al (2023) used JWST mid-IR imaging, combined with Hα and CO imaging, of the nearby star-forming galaxy NGC 628 to infer that the embedded phase of star formation lasts about 5 Myr, during the first half of which dust obscuration is so high that the Hα emission is not detectable. In a complementary fashion, Whitmore et al (2023) combined HST optical with JWST near-and mid-IR medium and broadband imaging of the galaxy NGC 1365 to conclude that massive (M∼10 6 M e ) stellar clusters in this galaxy remain completely or partially obscured for about 4 ± 1 Myr. However, Linden et al (2023), Kim et al (2023), and Whitmore et al (2023) do not have information on the infrared hydrogen recombination lines, which are key for constraining the ages of young stellar clusters when these are marginally detected or undetected at optical wavelengths.…”

Section: Introductionmentioning

confidence: 99%

“…In a complementary fashion, Whitmore et al (2023) combined HST optical with JWST near-and mid-IR medium and broadband imaging of the galaxy NGC 1365 to conclude that massive (M∼10 6 M e ) stellar clusters in this galaxy remain completely or partially obscured for about 4 ± 1 Myr. However, Linden et al (2023), Kim et al (2023), and Whitmore et al (2023) do not have information on the infrared hydrogen recombination lines, which are key for constraining the ages of young stellar clusters when these are marginally detected or undetected at optical wavelengths. Clearly, more investigations are needed to obtain a census of the fraction of dust-embedded star formation in galaxies and address its implications for the efficacy of pre-SN feedback.…”

Section: Introductionmentioning

confidence: 99%

Dust-buried Compact Sources in the Dwarf Galaxy NGC 4449

Calzetti

Linden

McQuaid

et al. 2023

ApJ

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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 A V > 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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PHANGS–JWST First Results: Massive Young Star Clusters and New Insights from JWST Observations of NGC 1365

Cited by 19 publications

References 56 publications

PHANGS–JWST First Results: Duration of the Early Phase of Massive Star Formation in NGC 628

PHANGS–JWST First Results: Duration of the Early Phase of Massive Star Formation in NGC 628

PHANGS–JWST First Results: The 21 μm Compact Source Population

Dust-buried Compact Sources in the Dwarf Galaxy NGC 4449

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