Simulating radiative feedback and star cluster formation in GMCs – II. Mass dependence of cloud destruction and cluster properties
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abstract
The process of radiative feedback in Giant Molecular Clouds (GMCs) is an
important mechanism for limiting star cluster formation through the heating and
ionization of the surrounding gas. We explore the degree to which radiative
feedback affects early ($\lesssim$5 Myr) cluster formation in GMCs having
masses that range from 10$^{4-6}$ M$_{\odot}$ using the FLASH code. The
inclusion of radiative feedback lowers the efficiency of cluster formation by
20-50\% relative to hydrodynamic simulations. Two models in particular ---
5$\times$10$^4$ and 10$^5$ M$_{\odot}$ --- show the largest suppression of the
cluster formation efficiency, corresponding to a factor of $\sim$2. For these
clouds only, the internal energy, a measure of the energy injected by radiative
feedback, exceeds the gravitational potential for a significant amount of time.
We find a clear relation between the maximum cluster mass, M$_{cl,max}$, formed
in a GMC of mass M$_{GMC}$; M$_{cl,max}\propto$ M$_{GMC}^{0.81}$. This scaling
result suggests that young globular clusters at the necessary scale of $10^6
M_{\odot}$ form within host GMCs of masses near $\sim 5 \times 10^7 M_{\odot}$.
We compare simulated cluster mass distributions to the observed embedded
cluster mass function ($dlog(N)/dlog(M) \propto M^{\beta}$ where $\beta$ = -1)
and find good agreement ($\beta$ = -0.99$\pm$0.14) only for simulations
including radiative feedback, indicating this process is important in
controlling the growth of young clusters. However, the high star formation
efficiencies, which range from 16-21\%, and high star formation rates compared
to locally observed regions suggest other feedback mechanisms are also
important during the formation and growth of stellar clusters.
