Tightening the belt: Constraining the mass and evolution in SDC335

Recent ALMA observations identified one of the most massive star-formingcores yet observed in the Milky Way; SDC335-MM1, within the infrareddark cloud SDC335.579-0.292. Along with an accompanying core MM2, SDC335appears to be in the early stages of its star formation process. In thispaper we aim to constrain the properties of the stars forming withinthese two massive millimetre sources. Observations of SDC335 at 6, 8, 23and 25GHz were made with the ATCA. We report the results of thesecontinuum measurements, which combined with archival data, allow us tobuild and analyse the spectral energy distributions (SEDs) of thecompact sources in SDC335. Three HCHII regions within SDC335 areidentified, two within the MM1 core. For each HCHII region, a free-freeemission curve is fit to the data allowing the derivation of thesources' emission measure, ionising photon flux and electron density.Using these physical properties we assign each HCHII region a ZAMSspectral type, finding two protostars with characteristics of spectraltype B1.5 and one with a lower limit of B1-B1.5. Ancillary data frominfrared to mm wavelength are used to construct free-free componentsubtracted SEDs for the mm-cores, allowing calculation of the bolometricluminosities and revision of the previous gas mass estimates. Themeasured luminosities for the two mm-cores are lower than expected fromaccreting sources displaying characteristics of the ZAMS spectral typeassigned to them. The protostars are still actively accreting,suggesting that a mechanism is limiting the accretion luminosity, wepresent the case for two different mechanisms capable of causing this.Finally, using the ZAMS mass values as lower limit constraints, a finalstellar population for SDC335 was synthesised finding SDC335 is likelyto be in the process of forming a stellar cluster comparable to theTrapezium Cluster and NGC6334 I(N).