Tracing the mass during star formation: studies of dust continuum and dense gas

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Shirley, Yancy Leonard

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Currently there exists a gap in our understanding of star formation across the stellar mass spectrum. A putative evolutionary sequence exists for isolated low-mass star formation (M < few M¯) while no clear scheme exists for clustered high-mass star formation. With the advent of submillimeter bolometer arrays, observational tools are now available for pursuing statistical studies of star forming regions. Direct comparisons of the physical environments of low-mass and high-mass cores using dust continuum and dense gas emission provide important observational constraints on the theoretical picture. Two surveys of the deeply embedded phases of lowmass and high-mass star formation were recently carried out at the University of Texas: a Submillimeter Common User Bolometer Array (SCUBA) 450 and 850 µm continuum mapping survey of nearby, low-mass star forming regions and a CS J = 5 → 4 spectral line mapping survey of high-mass star forming regions associated with water masers. Since optically thin dust emission at submillimeter wavelengths traces the mass along the line-of-sight, it is a a powerful diagnostic constraining the density and temperature structure of the envelope of star forming cores. The normalized, azimuthally averaged, intensity profiles and spectral energy distributions of low-mass protostars from the SCUBA survey are modeled using a one dimensional radiative transfer code that accounts for heating from an internal source, heating from the interstellar radiation field, realistic beam effects, and chopping. The results from modeling the submillimeter continuum emission of recent low-mass and high-mass star forming regions are compared. Similarly, the CS J = 5 → 4 transition is an excellent probe of dense gas in high-mass star forming regions since the integrated intensity correlates strongly with the flux of optically thin submillimeter continuum emission. Various properties of high-mass star forming cores (such as the core size, aspect ratio, virial mass, surface density, luminosity-to-mass ratio, and mean pressure) are calculated for 63 sources mapped with the Caltech Submillimeter Observatory. This survey provides a sample from which the properties of the deeply embedded phases of high-mass star formation are determined. The conditions in low-mass and high-mass star forming regions in both surveys are directly compared.





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