How collisionless are solar wind electrons? The role of skewed kappa distributions in the solar wind heat-flux transport

Solar wind electrons are the main carriers of thermal conduction in the Heliosphere. Electron thermal conduction provides an important source of energy transport away from the Sun, and it is also the source for the electron heat-flux instability. The skewness of the electron distribution function can provide the free energy necessary to drive this micro-instability. Here, we analyze solar wind electrons in situ data at 1 AU, and show that collisional and collisionless effects can coexist and share dominance in the regulation of the heat-flux observed in situ in the solar wind, depending on the temperature radial profile and solar wind speed. Calculations of collisionless plasma instabilities driven by electrons modeled as a non-thermal skewed kappa distribution suggests that the heat-flux instability threshold marginally bounds solar wind heat-flux observations in fast speed streams. In contrast, for slow solar wind the collisional transport effects statistically increases and the heat-flux regulation is shared between collisional and collisionless effects.