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Accounting for the absence of anomalous microwave emission in the M 31 halo

Francesco De Paolis, Faryal Naseem, Noraiz Tahir

TL;DR

The study addresses the origin of CMB temperature asymmetries observed toward galactic halos, focusing on whether anomalous microwave emission (AME) from spinning halo dust in M31 can explain the signal. It builds a physically motivated halo-dust model with an NFW-like density profile, constrains dust temperature and radiative flux using IRAS data, and computes the AME-induced temperature shift via line-of-sight integration, then compares it to Planck SMICA measurements. The key finding is that AME from halo dust contributes at most about 7% of the observed asymmetry, with even smaller contributions beyond ~20 kpc, while rkSZ remains negligible; this disfavors AME as the primary cause and points to other mechanisms, such as cold/virial halo gas, as more plausible drivers. The results place quantitative limits on halo dust content and spinning-dust emission, informing baryon census in halos and the interpretation of halo dynamics.

Abstract

The discovery of a temperature asymmetry in the cosmic microwave background (CMB) data towards various galaxies has opened a window for a deeper comprehension of galactic halos. A crucial step forward is that of estimating the fraction of missing baryons in the halos, but it relies on understanding the real cause of the observed CMB temperature asymmetry since many effects might give a non-negligible contribution. Here, we analyzed the contribution played by the anomalous microwave emission (AME) from halo dust grains in the halo of the M 31 galaxy. Assuming either amorphous carbon and silicates dust grains with size ranging from $0.01~μ$m to about $0.3~μ$m and mass in the range $10^{-14} - 10^{-13}$ g, we estimated the total mass, distribution, and diffuse emission in the $100\,μ$m band of the Infrared Astronomical Satellite (IRAS). Then, we estimated the temperature asymmetry induced by the rotation of the M 31 halo and compared the obtained values with the \textit{Planck}'s SMICA-processed data. We find that the AME cannot account for the measured CMB temperature asymmetry, with its contribution constrained to $\lesssim 7\%$, thereby indicating that additional physical mechanisms must be responsible for the observed signal.

Accounting for the absence of anomalous microwave emission in the M 31 halo

TL;DR

The study addresses the origin of CMB temperature asymmetries observed toward galactic halos, focusing on whether anomalous microwave emission (AME) from spinning halo dust in M31 can explain the signal. It builds a physically motivated halo-dust model with an NFW-like density profile, constrains dust temperature and radiative flux using IRAS data, and computes the AME-induced temperature shift via line-of-sight integration, then compares it to Planck SMICA measurements. The key finding is that AME from halo dust contributes at most about 7% of the observed asymmetry, with even smaller contributions beyond ~20 kpc, while rkSZ remains negligible; this disfavors AME as the primary cause and points to other mechanisms, such as cold/virial halo gas, as more plausible drivers. The results place quantitative limits on halo dust content and spinning-dust emission, informing baryon census in halos and the interpretation of halo dynamics.

Abstract

The discovery of a temperature asymmetry in the cosmic microwave background (CMB) data towards various galaxies has opened a window for a deeper comprehension of galactic halos. A crucial step forward is that of estimating the fraction of missing baryons in the halos, but it relies on understanding the real cause of the observed CMB temperature asymmetry since many effects might give a non-negligible contribution. Here, we analyzed the contribution played by the anomalous microwave emission (AME) from halo dust grains in the halo of the M 31 galaxy. Assuming either amorphous carbon and silicates dust grains with size ranging from m to about m and mass in the range g, we estimated the total mass, distribution, and diffuse emission in the m band of the Infrared Astronomical Satellite (IRAS). Then, we estimated the temperature asymmetry induced by the rotation of the M 31 halo and compared the obtained values with the \textit{Planck}'s SMICA-processed data. We find that the AME cannot account for the measured CMB temperature asymmetry, with its contribution constrained to , thereby indicating that additional physical mechanisms must be responsible for the observed signal.
Paper Structure (5 sections, 8 equations, 2 figures, 2 tables)

This paper contains 5 sections, 8 equations, 2 figures, 2 tables.

Table of Contents

  1. Introduction
  2. Distribution of halo dust grains
  3. Infrared emission from halo dust towards M 31
  4. Temperature asymmetry contribution by AME
  5. Results and conclusions

Figures (2)

  • Figure 1: M 31 halo profiles of the dust grain density (blue curve), dust mass (orange curve), circular velocity (green curve), and optical depth (red curve).
  • Figure 2: Left Panel: Planck's SMICA map of the temperature excess within 135 kpc towards M 31. Right Panel: IRAS dust excitation map at $100\,\mu$m within 135 kpc.