Volume 534, October 2011
|Number of page(s)||5|
|Published online||14 October 2011|
Letter to the Editor
Possible detection of the M 31 rotation in WMAP data⋆
Dipartimento di FisicaUniversità del Salento, via per Arnesano, 73100
2 INFN, Sez. di Lecce, via per Arnesano, 73100 Lecce, Italy
3 Yerevan Physics Institute and Yerevan State University, Yerevan, Armenia
4 Institut für Theoretische Physik, Universität Zürich, Winterthurerstrasse 190, 8057 Zürich, Switzerland
5 Centre for Advanced Mathematics and Physics, National University of Sciences and Technology, Rawalpindi, Pakistan
6 Dipartimento di Fisica “E.R. Caianiello”, Università degli Studi di Salerno, Fisciano, Italy
Accepted: 19 September 2011
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.
Key words: galaxies: general / galaxies: individual: M 31 / galaxies: halos
Table 1 and Figs. 4, 5 are available in electronic form at http://www.aanda.org
© ESO, 2011
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