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Astron. Astrophys. 357, 1-6 (2000)

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5. Conclusions

Previous studies on galaxy formation have evaluated the global distortion of a population of galaxies in the virialised regime. In these studies, the global Compton parameter was found to be very small, and smaller than the COBE-FIRAS value. In contrast, our model focuses on a regime in which proto-galaxies undergo a BH formation phase. During this phase, the proto-galactic matter is shock-heated up to a few [FORMULA] K and cools down to [FORMULA] K. CMB photons undergo inverse Compton scattering on the heated gas. In addition, galaxy peculiar motions induce temperature anisotropies through the SZ kinetic effect. We have estimated the global Compton parameter due to a population of proto-galaxies and the expected power spectrum of the induced secondary anisotropies. We find that there are four main parameters that control our model: the fraction f of BH-seeded proto-galaxies, the fraction [FORMULA] of the spheroid mass in the BH, the steepness of the density profile [FORMULA] and the gas core radius [FORMULA]. The comparison between our predictions and the COBE-FIRAS observation constrains these parameters. Given the observed fraction of seeded galaxies, [FORMULA]%, our results put rather strong constraints on the density profile and on [FORMULA]. Indeed, our predictions agree with the observations whatever p if the density profile is an approximation to a King profile. On the contrary, if the density profile is isothermal, then the core radius must be at least 30 times smaller than the virial radius and the BH-to-spheroid mass ratio has to be small, of the order of [FORMULA]. The computations in the two extreme cosmological models show that the global Compton parameter due to proto-galaxies is not very sensitive to [FORMULA].

We compare the power spectra of the different contributions to the temperature anisotropies. Our results show that the SZ effect of the very early shock-heated proto-galaxies could constitute the major source of CMB distortions on very small scales (arcsecond and sub-arcsecond scales). The anisotropies are likely to be detected and measured by future long baseline interferometers such as ALMA. The shock heating is likely to contribute to the re-heating of the proto-galactic gas, which plays a role in galaxy formation theory. Blanchard et al. (1992) used preheating to modify the galaxy luminosity function, suppressing and finally delaying dwarf galaxy formation. We do not take into account this effect in our model, therefore, our results should be taken as an upper limit to the proto-galaxy contribution in terms of secondary anisotropies.

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© European Southern Observatory (ESO) 2000

Online publication: May 3, 2000