Revealing Potential Initial Mass Function Variations with Metallicity: JWST Observations of Young Open Clusters in a Low-metallicity Environment
We present the substellar mass function of star-forming clusters (≃0.1 Myr old) in a low-metallicity environment (≃−0.7 dex). We performed deep JWST/NIRCam and MIRI imaging of two star-forming clusters in Digel Cloud 2, a star-forming region in the outer Galaxy ( R _G ≳ 15 kpc). The very high sensit...
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2024-01-01
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| Online Access: | https://doi.org/10.3847/1538-4357/ad73a2 |
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| author | Chikako Yasui Natsuko Izumi Masao Saito Ryan M. Lau Naoto Kobayashi Michael E. Ressler |
| author_facet | Chikako Yasui Natsuko Izumi Masao Saito Ryan M. Lau Naoto Kobayashi Michael E. Ressler |
| author_sort | Chikako Yasui |
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| description | We present the substellar mass function of star-forming clusters (≃0.1 Myr old) in a low-metallicity environment (≃−0.7 dex). We performed deep JWST/NIRCam and MIRI imaging of two star-forming clusters in Digel Cloud 2, a star-forming region in the outer Galaxy ( R _G ≳ 15 kpc). The very high sensitivity and spatial resolution of JWST enable us to resolve cluster members clearly down to a mass detection limit of 0.02 M _⊙ , enabling the first detection of brown dwarfs in low-metallicity clusters. A total of 52 and 91 sources were extracted in mass- A _V -limited samples in the two clusters, from which initial mass functions (IMFs) were derived by model-fitting the F200W band luminosity function, resulting in IMF peak masses (hereafter M _C ) $\mathrm{log}{M}_{C}/{M}_{\odot }\simeq -1.5\pm 0.5$ for both clusters. Although the uncertainties are rather large, the obtained M _C values are lower than those in any previous study ( $\mathrm{log}{M}_{C}/{M}_{\odot }\sim -0.5$ ). Comparison with the local open clusters with similar ages to the target clusters (∼10 ^6 –10 ^7 yr) suggests a metallicity dependence of M _C , with lower M _C at lower metallicities, while the comparison with globular clusters, with similarly low metallicities but considerably older (∼10 ^10 yr), suggests that the target clusters have not yet experienced significant dynamical evolution and remain in their initial physical condition. The lower M _C is also consistent with the theoretical expectation of the lower Jeans mass owing to the higher gas density under such low metallicity. The M _C values derived from observations in such an environment would place significant constraints on the understanding of star formation. |
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| issn | 1538-4357 |
| language | English |
| publishDate | 2024-01-01 |
| publisher | IOP Publishing |
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| series | The Astrophysical Journal |
| spelling | doaj-art-a5fb32156b7c477a9ebb8ef0b25e7c4c2025-08-20T02:18:46ZengIOP PublishingThe Astrophysical Journal1538-43572024-01-01975115210.3847/1538-4357/ad73a2Revealing Potential Initial Mass Function Variations with Metallicity: JWST Observations of Young Open Clusters in a Low-metallicity EnvironmentChikako Yasui0https://orcid.org/0000-0003-3579-7454Natsuko Izumi1https://orcid.org/0000-0003-1604-9127Masao Saito2https://orcid.org/0000-0003-0769-8627Ryan M. Lau3https://orcid.org/0000-0003-0778-0321Naoto Kobayashi4https://orcid.org/0000-0003-4578-2619Michael E. Ressler5https://orcid.org/0000-0001-5644-8830National Astronomical Observatory of Japan , 2-21-1 Osawa, Mitaka, Tokyo 181-8588, Japan ; ck.yasui@gmail.comInstitute of Astronomy and Astrophysics , Academia Sinica, No. 1, Section 4, Roosevelt Road, Taipei 10617, TaiwanNational Astronomical Observatory of Japan, National Institutes of Natural Sciences , 2-21-1 Osawa, Mitaka, Tokyo 181-8588, Japan; Department of Astronomical Science, School of Physical Science, SOKENDAI (The Graduate University for Advanced Studies) , 2-21-1 Osawa, Mitaka, Tokyo 181-8588, JapanNSF’s National Optical-Infrared Astronomy Research Laboratory , 950 North Cherry Avenue, Tucson, AZ 85719, USAInstitute of Astronomy, School of Science, University of Tokyo , 2-21-1 Osawa, Mitaka, Tokyo 181-0015, Japan; Kiso Observatory, Institute of Astronomy, School of Science, University of Tokyo , 10762-30 Mitake, Kiso-machi, Kiso-gun, Nagano 397-0101, JapanJet Propulsion Laboratory, California Institute of Technology , 4800 Oak Grove Drive, Pasadena, CA 91109, USAWe present the substellar mass function of star-forming clusters (≃0.1 Myr old) in a low-metallicity environment (≃−0.7 dex). We performed deep JWST/NIRCam and MIRI imaging of two star-forming clusters in Digel Cloud 2, a star-forming region in the outer Galaxy ( R _G ≳ 15 kpc). The very high sensitivity and spatial resolution of JWST enable us to resolve cluster members clearly down to a mass detection limit of 0.02 M _⊙ , enabling the first detection of brown dwarfs in low-metallicity clusters. A total of 52 and 91 sources were extracted in mass- A _V -limited samples in the two clusters, from which initial mass functions (IMFs) were derived by model-fitting the F200W band luminosity function, resulting in IMF peak masses (hereafter M _C ) $\mathrm{log}{M}_{C}/{M}_{\odot }\simeq -1.5\pm 0.5$ for both clusters. Although the uncertainties are rather large, the obtained M _C values are lower than those in any previous study ( $\mathrm{log}{M}_{C}/{M}_{\odot }\sim -0.5$ ). Comparison with the local open clusters with similar ages to the target clusters (∼10 ^6 –10 ^7 yr) suggests a metallicity dependence of M _C , with lower M _C at lower metallicities, while the comparison with globular clusters, with similarly low metallicities but considerably older (∼10 ^10 yr), suggests that the target clusters have not yet experienced significant dynamical evolution and remain in their initial physical condition. The lower M _C is also consistent with the theoretical expectation of the lower Jeans mass owing to the higher gas density under such low metallicity. The M _C values derived from observations in such an environment would place significant constraints on the understanding of star formation.https://doi.org/10.3847/1538-4357/ad73a2Brown dwarfsInitial mass functionJames Webb Space TelescopeMetallicityOpen star clustersStar formation |
| spellingShingle | Chikako Yasui Natsuko Izumi Masao Saito Ryan M. Lau Naoto Kobayashi Michael E. Ressler Revealing Potential Initial Mass Function Variations with Metallicity: JWST Observations of Young Open Clusters in a Low-metallicity Environment The Astrophysical Journal Brown dwarfs Initial mass function James Webb Space Telescope Metallicity Open star clusters Star formation |
| title | Revealing Potential Initial Mass Function Variations with Metallicity: JWST Observations of Young Open Clusters in a Low-metallicity Environment |
| title_full | Revealing Potential Initial Mass Function Variations with Metallicity: JWST Observations of Young Open Clusters in a Low-metallicity Environment |
| title_fullStr | Revealing Potential Initial Mass Function Variations with Metallicity: JWST Observations of Young Open Clusters in a Low-metallicity Environment |
| title_full_unstemmed | Revealing Potential Initial Mass Function Variations with Metallicity: JWST Observations of Young Open Clusters in a Low-metallicity Environment |
| title_short | Revealing Potential Initial Mass Function Variations with Metallicity: JWST Observations of Young Open Clusters in a Low-metallicity Environment |
| title_sort | revealing potential initial mass function variations with metallicity jwst observations of young open clusters in a low metallicity environment |
| topic | Brown dwarfs Initial mass function James Webb Space Telescope Metallicity Open star clusters Star formation |
| url | https://doi.org/10.3847/1538-4357/ad73a2 |
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