The initial mass function and stellar content of NGC 3603

Hwankyung Sung*, Michael S. Bessell

*Corresponding author for this work

    Research output: Contribution to journalArticlepeer-review

    82 Citations (Scopus)


    We present UBVRI and Hα photometry of the extremely compact, starburst cluster NGC 3603. Ground-based images, Hubble Space Telescope (HST) archival data, as well as Chandra X-ray data have been used for this study. We present, for the first time, optical color-magnitude diagrams (CMDs) for the stars in the cluster core down to V= 22 mag. A well-defined main sequence (MS) as well as low-mass pre-main-sequence (PMS) stars can clearly be seen in the CMDs. This result confirms the finding by Eisenhauer et al. that low-mass stars are forming in the starburst cluster. We also derive an age (1 ± 1 Myr) and distance of the cluster (V0 - MV= 14.2 ± 0.2 mag, i.e., d = 6.9 ± 0.6 kpc). The interstellar reddening shows a minimum value [E(B- V) = 1.25 mag] at the core (r ≤ 0.′12) and increases rapidly up to E(B-V) ≈ 1.8 mag or even higher with increasing distance from the center, which suggests the presence of a wind-driven cavity near the cluster center as found by Frogel et al. and Clayton. We also determine the radius of the cluster (r ≈ 2′) from the surface-density profile of bright stars and X-ray sources. To investigate the initial mass function (IMF) of the cluster, we performed a completeness test for the core region. Using the theoretical mass-luminosity relation of MS as well as PMS stars, we derived the IMF of stars imaged with the HST/PC1. The surface density of stars in the core is enormously high and decreases gradually with increasing distance from the center. The slope of the IMF also shows radial variation: fairly flat in the core (T = -0.5 ± 0.1 at r ≤ 0.′1) and gradually steepening (Γ = -0.8 ± 0.2 at r = 0.′1 - 0.′2 and Γ = -1.2 ± 0.2 at r > 0.′2 of HST/PC1). The stars in the halo region of NGC 3603 (outside of HST/PC1) seem to be slightly older (age ≈ 5 Myr) and presumably formed before the stars in the core.

    Original languageEnglish
    Pages (from-to)1014-1028
    Number of pages15
    JournalAstronomical Journal
    Issue number2 1778
    Publication statusPublished - Feb 2004


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