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We present 3D radiation-hydrodynamical (RHD) simulations of star cluster formation and evolution in massive, self-gravitating clouds, whose dust columns are optically thick to infrared (IR) photons. We use VETTAM – a recently developed, novel RHD algorithm, which uses the Variable Eddington Tensor closure – to model the IR radiation transport through the cloud. We also use realistic temperature (T) dependent IR opacities (κ) in our simulations, improving upon earlier works in this area, which used either constant IR opacities or simplified power laws (κ ∝  T 2). We investigate the impact of the radiation pressure of these IR photons on the star formation efficiency of the cloud, and its potential to drive dusty winds. We find that IR radiation pressure is unable to regulate star formation or prevent accretion on to the star clusters, even for very high gas surface densities (⁠|$\Sigma \gt 10^5 \, \mathrm{M}_{\odot } \, \mathrm{pc}^{-2}$|⁠), contrary to recent semi-analytic predictions and simulation results using simplified treatments of the dust opacity. We find that the commonly adopted simplifications of κ ∝  T 2 or constant κ for the IR dust opacities leads to this discrepancy, as those approximations overestimate the radiation force. By contrast, with realistic opacities that take into account the microphysics of the dust, we find that the impact of IR radiation pressure on star formation is very mild, even at significantly high dust-to-gas ratios (∼3 times solar), suggesting that it is unlikely to be an important feedback mechanism in controlling star formation in the ISM. [ABSTRACT FROM AUTHOR]

We study radiation pressure due to Ly α line photons, obtaining and exploring analytical expressions for the force-multiplier, M F(N H, Z) = F α/(L α/ c), as a function of gas column density, N H, and metallicity, Z , for both dust-free and dusty media, employing a WKB approach for the latter case. Solutions for frequency offset emission to emulate non-static media moving with a bulk velocity v have also been obtained. We find that, in static media, Ly α pressure dominates over both photoionization and dust-mediated UV radiation pressure in a very wide parameter range (16 < log  N H < 23; −4 < log [ Z / Z ⊙] < 0). For example, it overwhelms the other two forces by |$\lower.5ex\hbox{$\,\, \buildrel\gt \over \sim \,\,$}10$| (300) times in standard (low- Z) star-forming clouds. Thus, in agreement with previous studies, we conclude that Ly α pressure plays a dominant role in the initial acceleration of the gas around luminous sources, and must be implemented in galaxy formation, evolution and outflow models and simulations. [ABSTRACT FROM AUTHOR]