SIMBAD references

We present observations from our continuing studies of the earliest stages of massive star cluster evolution. In this paper, radio observations from the Very Large Array at 0.7, 1.3, 2, 3.6, and 6 cm are used to map the radio spectral energy distributions and model the physical properties of the ultrayoung embedded super-star clusters in Henize 2-10. The 0.7 cm flux densities indicate that the young embedded star clusters that are powering the radio-detected ``ultradense (UD) H II regions'' have masses greater than ∼10⁵ M_☉. We model the radio spectral energy distributions as both constant-density H II regions and H II regions with power-law electron density gradients. These models suggest that the UD H II regions have radii ranging between ∼2 and 4 pc and average electron densities of ∼10³-10⁴/cm3 (with peak electron densities reaching values of ∼10⁵-10⁶/cm3). The pressures implied by these densities are P/k_B∼10⁷-10¹⁰/cm3 K, several orders of magnitude higher than typical pressures in the Galactic interstellar medium. The inferred H II masses in the UD H II regions are ~(2-8)x10³ M_☉; these values are less than 5% of the embedded stellar masses and anomalously low when compared with optically visible young clusters. We suggest that these low H II mass fractions may be a result of the extreme youth of these objects.