The rotation of galactic halos is a particularly difficult subject to be dealt with. It has been shown that CMB data toward nearby galaxies can be used to probe the galactic halo rotation and can be ascribed to cold molecular clouds populating the halos. We present some methods to study the physical properties and distribution of such molecular gas clouds in the M31 galaxy halo.
Galactic halos are of great importance for our understanding of both the dark matter nature and primordial non-Gaussianity in the perturbation spectrum, a powerful discriminant of the physical mechanisms that generated the cosmological fluctuations observed today. In this paper we analyze Planck data towards the galaxy M104 (Sombrero) and find an asymmetry in the microwave temperature which extends up to about 1 0 from the galactic center. This frequency-independent asymmetry is consistent with that induced by the Doppler effect due to the galactic rotation and we find a probability of less than about 0.2% that it is due to a random fluctuation of the microwave background. In addition, Planck data indicate the relatively complex dynamics of the M104 galactic halo, and this appears to be in agreement with previous studies. In view of our previous analysis of the dark halos of nearby galaxies, this finding confirms the efficiency of the method used in revealing and mapping the dark halos around relatively nearby edge-on galaxies.
Rotation of galactic objects has been seen in the CMB that could be ascribed to molecular hydrogen clouds with, or without, dust contamination and contamination from other sources. We model the clouds using the canonical ensemble for pure molecular hydrogen, a mixture of hydrogen helium and or dust, in order to constrain the physical parameters of these clouds. Since, the clouds are cold, we justify the use of the canonical ensemble by explicitly calculating the interaction between the hydrogen molecules and the CMB photons and determining the time required for thermal equilibrium to be reached, and show that there is enough time for the equilibrium to be attained.
The rotation of the galactic halos is a fascinating topic which is still waiting to be addressed. Planck data have shown the existence of a temperature asymmetry towards the halo of several nearby galaxies, such as M31, NGC 5128, M33, M81 and M82. However, the cause of this asymmetry is an open problem. A possibility to explain the observed effect relies on the presence of "cold gas clouds" populating the galactic halos, which may be the answer to the so-called missing baryon problem. Here, we present a technique to estimate an upper limit to the rotational velocity of the halo of some nearby spiral galaxies using both their dynamical masses and the Planck data.
The analysis of WMAP and Planck CMB data has shown the presence of temperature asymmetries towards the halos of several galaxies, which is probably due to the rotation of clouds present in these halos about the rotational axis of the galaxies. It had been proposed that these are hydrogen clouds that should be in equilibrium with the CMB. However, standard theory did not allow equilibrium of such clouds at the very low CMB temperature, but it was recently shown that the equilibrium could be stable. This still does not prove that the cloud concentration and that the observed temperature asymmetry is due to clouds in equilibrium with the CMB. To investigate the matter further, it would be necessary to trace the evolution of such clouds, which we call “virial clouds”, from their formation epoch to the present, so as to confront the model with the observational data. The task is to be done in two steps: (1) from the cloud formation before the formation of first generation of stars; (2) from that time to the present. In this paper we deal with the first step leaving the second one to a subsequent analysis.
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