isothermal equation of state. The sound speed, $c_{\rm s}$, equals $0.3\,\mathrm{km\, s^{-1}}$, which corresponds to a temperature of approximately 25 K for all particles. The isothermal equation of state can be justified by considering the cooling time scale: $$\label{eq:cooling_tau_eda1}
\tau_{\rm cool} = \frac{\frac{3}{2}k_{B}T}{n \Lambda(n,T)}$$ where $n$ is the number density, $k_{B}$ the Boltzmann constant, $T$ the temperature and $\Lambda(n,T)$ the cooling rate. For $T$ = 25K and $n \geq 10^3 \mathrm{cm}^{-3}$, the cooling time scale $\tau_{\rm cool} \lesssim 16$ years, assuming $\Lambda \approx 10^{-26} \mathrm{erg \ cm^3 \ s^{-1}}$ [@neufeld95]. Any departure from the equilibrium temperature of 25K will therefore be restored quickly with respect to our simulation time scale. We discuss the parameters and assumptions for the ISM and the disc separately below in Sec. \[sec:ism\_eda1\] and \[sec:disc\_eda1\], respectively.

### Interstellar Medium {#sec:ism_eda1}

By adopting a temperature of 25 K, we assume that cooling of the ISM is much more efficient than the radiative transfer of heat from nearby stars. It has been suggested that the Lyman-Werner flux plays an important role in the formation of multiple populations [@conroy11], but a survey on 130 young massive clusters have shown little to no ionized gas [@bastian13]. Young massive clusters are 