Synthetic photometry of OB star clusters with stochastically sampled IMFs: analysis of models and HST observations
Résumé
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 = 10 3 , 10 4 , and 10 5 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 (< 10 4 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 = 10 5 M ; and b) the largest spread in stochastic magnitudes occurs when Wolf-Rayet stars are present. 2) For M i = 10 5 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% and > 30% to the total emission in the V and I bands, respectively. 3) Age-dating OB-star clusters via deterministic tracks in the U-B vs. V-I plane is highly uncertain at Z = 0.014 for M i ∼ 10 3 M and Z = 0.002 for M i ∼ 10 3 − 10 5 M. 4) For low-mass clusters, the V-band extinction derived with stochastic models significantly depends on the value of log(U S). 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 characterising the true variance in the number of stars per mass bin in nature.
| Origine | Fichiers produits par l'(les) auteur(s) |
|---|