ALMA PI science with subarrays - Making ALMA observations post WSU even more efficient

The Wide Sensitivity Upgrade (WSU) project for ALMA will increase the sensitivity of observations with larger instantaneous spectral bandwidths, improved receiver performances, and better correlator quantization. However, certain aspects of ALMA observations post WSU could even further be improved by implementing a sub-array observing mode for PI science - simultaneous observations using subgroups of antennas of the ALMA main array. The impact of such an observing mode would be particularly strong on multi-wavelength studies, the investigation of transient phenomena, and time domain astronomy, as well as coordinated observations with other facilities. This poster will present some typical science cases and specific programs that could benefit from a PI sub-array observing mode, with a potential for further increasing the efficiency of ALMA observations in the post-WSU era.