Primordial Globular Clusters, X-Ray Binaries and Cosmological Reionisation - Astrophysics > Cosmology and Nongalactic AstrophysicsReportar como inadecuado




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Abstract: Globular clusters are dense stellar systems that have typical ages of ~13billion years, implying that they formed at redshifts of z>~6. Massive stars innewly formed or primordial globular clusters could have played an importantrole during the epoch of cosmological reionisation z>~6 as sources ofenergetic, neutral hydrogen ionising UV photons. We investigate whether or notthese stars could have been as important in death as sources of energetic X-rayphotons as they were during their main sequence lives. Most massive stars areexpected to form in binaries, and an appreciable fraction of these as much as~30% will evolve into X-ray luminous L X~10^38 erg-s high-mass X-raybinaries HMXBs. These sources would have made a contribution to the X-raybackground at z>~6. Using Monte Carlo models of a globular cluster, we estimatethe total X-ray luminosity of a population of HMXBs. We compare and contrastthis with the total UV luminosity of the massive stars during their mainsequence lives. For reasonable estimates, we find that the bolometricluminosity of the cluster peaks at ~10^42 erg-s during the first few millionyears, but declines to ~10^41 erg-s after ~5 million years as the most massivestars evolve off the main sequence. From this time onwards, the totalbolometric luminosity is dominated by HMXBs and falls gradually to ~10^40 erg-safter ~50 million years. Assuming a power-law spectral energy distribution forthe HMXBs, we calculate the effective number of neutral hydrogen ionisationsper HMXB and show that HMXBs can be as important as sources of ionisingradiation as massive stars. Finally we discuss the implications of our resultsfor modelling galaxy formation at high redshift and the prospects of usingglobular clusters as probes of reionisation.



Autor: C. Power, G. A. Wynn, C. Combet, M. I. Wilkinson

Fuente: https://arxiv.org/







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