Possible detection of the M 31 rotation in WMAP data

Abstract

Data on the cosmic microwave background (CMB) radiation by the Wilkinson Microwave Anisotropy Probe (WMAP) had a profound impact on the understanding of a variety of physical processes in the early phases of the Universe and on the estimation of the cosmological parameters. Here, the 7-year WMAP data are used to trace the disk and the halo of the nearby giant spiral galaxy M 31. We analyzed the temperature excess in three WMAP bands (W, V, and Q) by dividing the region of the sky around M 31 into several concentric circular areas. An asymmetry in the mean microwave temperature in the M 31 disk along the direction of the M 31 rotation is observed with a temperature contrast up to 130 μK/pixel. We also find a temperature asymmetry in the M 31 halo, which is much weaker than for the disk, up to a galactocentric distance of about 10 • ( 120 kpc) with a peak temperature contrast of about 40 μK/pixel. We studied the robustness of these possible detections by considering 500 random control fields in the real WMAP maps and simulating 500 sky maps from the best-fitted cosmological parameters. By comparing the obtained temperature contrast profiles with the real ones towards the M 31 galaxy, we find that the temperature asymmetry in the M 31 disk is fairly robust, while the effect in the halo is weaker. Although the confidence level of the signal is not high, if estimated purely statistically, which could be expected due to the weakness of the effect, the geometrical structure of the temperature asymmetry points towards a definite effect modulated by the rotation of the M 31 halo. This result might open a new way to probe these relatively less studied galactic objects using high-accuracy CMB measurements, such as those with the Planck satellite or planned balloon-based experiments, which could prove or disprove our conclusions.

Planckconfirmation of the disk and halo rotation of M 31

“…1 clearly shows the temperature asymmetry profile in the two regions of the disk of M 31. These profiles agree with the results obtained previously by using the WMAP data (De Paolis et al 2011) 2 . Moreover, the shape of the two profiles is clearly mirrored, as expected if the effect is due to a Doppler modulation induced by the rotation of the M 31 disk.…”

“…Ascertaining the degree to which galactic halos rotate with respect to the disks is a particularly difficult task to accomplish, even for the closest galaxy to the Milky Way: M 31 (Courteau et al 2011). A novel approach in studying the rotation of the disk and halo of nearby galaxies (particularly the M 31 galaxy) has been discussed in De Paolis et al (2011). By using the seven-year WMAP data, a possible temperature asymmetry was found both in the M 31 disk and in the halo in the direction of the rotation of M 31, which indicates a Doppler-induced effect.…”

“…By adopting the geometry described in Fig. 1 in De Paolis et al (2011) and extending the analysis to about 20…”

Planckrevealed bulk motion of Centaurus A lobes

“…We would also like to mention that this kind of mean temperature asymmetry method first applied to study the M 31 galaxy (De Paolis et al 2011, 2014, applied here to the giant radio lobes of Cen A, can become a conventional tool for studying of internal motions, especially toward nearby galaxies, in the microwaves. As for the case of the SZ effect or, e.g., for the Kolmogorov stochasticity parameter (Gurzadyan et al 2009, and references therein), software for an automatic analysis by correlating galaxy surveys and CMB data may be developed.…”

“…Motivated by the discussion above and by the unique tool that is provided by data in the microwave region of the electromagnetic spectrum to probe the large-scale temperature asymmetries toward nearby astronomical systems, in this Letter we study the Cen A system using Planck data and following the same approach adopted in De Paolis et al (2011Paolis et al ( , 2014 for the M 31 galaxy.…”