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Published January 2022 | Published + Accepted Version
Journal Article Open

Synthetic photometry of OB star clusters with stochastically sampled IMFs: analysis of models and HST observations

Abstract

We present a pilot library of synthetic NUV, U, B, V, and I photometry of star clusters with stochastically sampled IMFs and ionized gas for initial masses, M_i = 10³, 10⁴, and 10⁵ M⊙; t = 1, 3, 4, and 8 Myr; Z = 0.014 and Z = 0.002; and log(U_S) = −2 and −3. We compare the library with predictions from deterministic models and observations of isolated low-mass (<10⁴ M⊙) star clusters with co-spatial compact H II regions. The clusters are located in NGC 7793, one of the nearest galaxies observed as part of the HST LEGUS and Hα-LEGUS surveys. (1) For model magnitudes that only account for the stars: (a) the residual |deterministic mag - median stochastic mag| can be ≥0.5 mag, even for M_i = 10⁵ M⊙; and (b) the largest spread in stochastic magnitudes occurs when Wolf–Rayet stars are present. (2) For M_i = 10⁵ M⊙: (a) the median stochastic mag with gas can be >1.0 mag more luminous than the median stochastic magnitude without gas; and (b) nebular emission lines can contribute with >50 per cent and >30 per cent to the total emission in the V and I bands, respectively. (3) Age-dating OB-star clusters via deterministic tracks in the U-B versus V-I plane is highly uncertain at Z = 0.014 for M_i ∼ 10³ M⊙ and Z = 0.002 for M_i ∼ 10³–10⁵ M⊙. (4) For low-mass clusters, the V-band extinction derived with stochastic models significantly depends on the value of log(US). (5) The youngest clusters tend to have higher extinction. (6) The majority of clusters have multi-peaked age PDFs. (7) Finally, we discuss the importance of characterizing the true variance in the number of stars per mass bin in nature.

Additional Information

© 2021 The Author(s). Published by Oxford University Press on behalf of Royal Astronomical Society. This article is published and distributed under the terms of the Oxford University Press, Standard Journals Publication Model (https://academic.oup.com/journals/pages/open_access/funder_policies/chorus/standard_publication_model). Accepted 2021 October 8. Received 2021 September 8; in original form 2021 April 1. Published: 19 October 2021. We thank the jury of ROD's M.S. thesis (E. Terlevich, S. Sánchez, L. Aguilar, S. Srinivasan) as well as M. Cerviño and B. Elmegreen for comments and suggestions which have greatly improved the quality of this paper. ROD and AW acknowledge the support of UNAM via grant agreement PAPIIT no. IA-102120. AVG, SC and GB acknowledge support from the ERC via an Advanced Grant under grant agreement no. 321323-NEOGAL. AVG also aknowledges support from the ERC Advanced Grant MIST (FP7/2017-2022, No 742719). MRK acknowledges support from the Australian Research Council's Future Fellowship funding scheme, award FT180100375, and from resources and services provided by the National Computational Infrastructure (NCI), which is supported by the Australian Government. Data Availability: The HST data underlying this article are available in the Mikulski Archive for Space Telescopes at https://mast.stsci.edu/portal/Mashup/Clients/Mast/Portal.html, and can be accessed with the data set identifiers 13364 and 13773. LEGUS high level science products can be found at https://archive.stsci.edu/prepds/legus/dataproducts-public.html.

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Accepted Version - 2110.05595.pdf

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Additional details

Created:
August 22, 2023
Modified:
October 23, 2023