Column (1): Object name. Column (2): Column density and integrated intensity of molecular cloud. Column (3): Luminosity of Hα emission obtained with HST (Whitmore et al. 2010). Column (4): The radius of the object. The radius of the protocluster is defined as the size where the integrated intensity decreases to 50% of the peak integrated intensity. Radii of parent clouds of SSC B1 and the emerging cluster are assumed to be geometric means of radii of the two protoclusters. Column (5): M_parent is molecular mass inside of the radius projected to have been within the radius based on extrapolation from ALMA4 and ALMA5. The CO cloud masses of SSC B1 and the emerging cluster are given by [(the average |$N_{\rm H_{2}}$| of ALMA4 and ALMA5) − (the present |$N_{\rm H_{2}}$| toward SSC B1|$/$|emerging cluster)] × πR². Column (6): Ionized gas mass derived by using the relationship between Hα luminosity and ionized gas mass |$M_{\rm gas \ ionized} = 0.98\times 10^{9} (\frac{L_{\rm H\alpha }}{10^{43}\:\mbox{erg}\:\mbox{s}^{-1}}) {(\frac{n_{\rm e}}{100\:\mbox{cm}^{-3}})}^{-1}$| (Osterbrock & Ferland 2006). L_Hα is the luminosity of Hα [erg s⁻¹] and n_e is assumed to be 100 cm⁻³. Column (7): Total stellar mass of the cluster (Whitmore et al. 2010).

Minimum value for SSC B1 and the emerging cluster, and maximum value for the protocluster candidates.

Errors of M_parent are derived from three times uncertainty of X_CO factor.