Star and stellar cluster formation: ALMA-SKA synergies

Abstract

A SKA time-domain survey of star forming regions will produce well sampled radio lightcurves of hundreds of sources per star forming region. As is the case for infrared light-curves of young sources, these will undoubtably have a range of properties, tracing and constraining a range of phenomena. For example, the identification of rotationally modulated emission will provide the first observational constraints on the rotation rates of embedded protostars. Observations of theflickering of HII regions will trace the inflow of material around the highest mass objects while flare activity in these, and other, sources can trace the final infall of material on to the central protostars. These observations can not only constrain the properties of the accretion but also the stochastic heating of the circumstellar regions which can surpress fragmentation (e.g. Krumholz et al. 2007), leading to the formation of more massive stars. Looking forward to full SKA the factor 10 enhancement in sensitivity will enable studies of smaller (and therefore also shorter time scale) flux variations. Full SKA will also make stellar clusters to beyond the Galactic centre accessible to detailed time-domain studies, probing star formation over a much wider range of environments. The enhanced resolution of SKA will allow studies of the changes in morphology of the sources during their variation in flux, provide stronger constraints on the mechanisms involved and the models for the emission. Building a comprehensive model for the formation of both low-mass and high-mass stars requires understanding the evolution of gas and dust from molecular clouds down through clumps and cores and eventually on to the forming stars. This is only possible with the combination of ALMA to trace the cool molecular gas and dust and SKA to follow this material into the inner circumstellar regions. The radio light-curves which SKA will produce for hundreds of sources in star forming regions out to 5 kpc will provide the first detailed insight across a wide range of stellar masses of the transient energetic phenomena occurring on the small spatial scales close to the central star. These light curves will for the first time provide a systematic survey which can study the magnetospheric interactions in young binary systems, tracing episodic accretion, the origin of outflows and potentially constrain the rotation rates of deeply embedded sources.