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Constraining cosmic ray acceleration in young star clusters using multi-wavelength observations

2018; Oxford University Press; Volume: 479; Issue: 4 Linguagem: Inglês

10.1093/mnras/sty1846

1365-2966

Siddhartha Gupta, Biman B. Nath, Prateek Sharma,

Galaxies: Formation, Evolution, Phenomena

We use 1D and 3D two-fluid cosmic ray (CR) hydrodynamic simulations to investigate the role of CRs in the vicinity of a compact young star cluster. We model a self-gravitating cloud (density profile ρ∝r−1), include important thermal and non-thermal processes, and explore two different CR injection scenarios. We show that if internal shocks in the wind-driving region are the main site for CR acceleration, then the resulting γ-ray luminosity (Lγ) can reach ≈5 per cent of the mechanical luminosity (Lw), independent of the fraction of wind energy (∼1–20 per cent) injected into CRs. In contrast, if the forward/reverse shock of a bubble is the injection site then Lγ increases linearly with the CR injection fraction, as expected analytically. We find that the X-ray luminosity (Lx) in the forward/reverse shock injection scenario is ≳ 10−3Lw, which is ∼10 times larger than in the central wind-driving injection case. We predict the corresponding range of the synchrotron radio luminosity. We show how multi-wavelength observations can constrain the CR parameters. Comparing the predicted multi-wavelength luminosities with those of 30 Doradus and Westerlund 2 we identify the reverse shock as the most probable CR injection site. We do not find significant dynamical impact of CRs in our models.