Spinning dust emission from ultrasmall silicates: emissivity and polarization spectrum

TL;DR

This study investigates the potential of ultrasmall silicate grains to produce anomalous microwave emission (AME) and its polarization, suggesting they could be a significant source of AME in the galaxy.

Contribution

It introduces the idea that spinning ultrasmall silicate grains can generate AME and models their emissivity and polarization spectrum, expanding beyond the commonly assumed PAHs.

Findings

Spinning silicate nanoparticles can produce strong rotational emission.

Polarization fraction can reach up to 20% for certain parameters.

Parameter space identified where silicates explain observed AME and polarization.

Abstract

Anomalous microwave emission (AME) is an important Galactic foreground of Cosmic Microwave Background (CMB) radiation. It is believed that the AME arises from rotational emission by spinning polycyclic aromatic hydrocarbons (PAHs) in the interstellar medium (ISM). In this paper, we assume that a population of ultrasmall silicate grains may exist in the ISM, and quantify rotational emissivity from these tiny particles and its polarization spectrum. We found that spinning silicate nanoparticles can produce strong rotational emission when those small grains follow a log-normal size distribution. The polarization fraction of spinning dust emission from tiny silicates increases with decreasing the dipole moment per atom ($\beta$) and can reach $P\sim 20\%$ for $\beta\sim 0.1$D at grain temperature of 60 K. We identify a parameter space $(\beta,Y_{Si})$ for silicate nanoparticles in which its rotational emission can adequately reproduce both the observed AME and the polarization of the AME, without violating the observational constraints by the ultraviolet extinction and polarization of starlight. Our results reveal that rotational emission from spinning silicate may be an important source of the AME.