Using analytical models and cosmological N-body simulations, we study the free–free radio emission from ionized gas in clusters and groups of galaxies. The results obtained with the simulations are compared with analytical predictions based on the mass function and scaling relations. Earlier works based on analytical models have shown that the average free–free signal from small haloes (galaxies) during and after the reionization time could be detected with future experiments as a distortion of the cosmic microwave background (CMB) spectrum at low frequencies (ν 1013 h−1 M⊙ is less than 10 per cent the signal from the more abundant and colder smaller mass haloes. However, the individual signal from the massive haloes could be detected with future experiments opening the door for a new window to study the intracluster medium.

We acknowledge partial financial support from the Ministerio de Ciencia e Innovación project AYA2007-68058-C03-02. PPP acknowledges support from the Spanish Ministerio de Educación y Ciencia and CSIC for an I3P grant. PPP also acknowledges support from the programme of ‘Estancias Breves’, grants 22007ESTI3P- 00493 and 009ESTCSIC-01386. CBacknowledges partial support for this work by the AS/INAF agreement I/072/09/0 for the Planck LFI Activity of Phase E2 and the ASI contract I/016/07/0 COFIS. RKS acknowledges the support of grant NFS-AST 0908241. SRK acknowledges support by the MICINN under the Consolider-Ingenio, SyeC projectCSD-2007-00050.YAacknowledges financial support from project AYA2007-67965-C03-03.

10 páginas, 7 figuras.-- El Pdf del artículo es la versión pre-print: arXiv:1006.2243v2

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