A Two Carrier Families Spectral Profile Model for Anomalous Microwave Emission

Abstract

Abstract We model anomalous microwave emission (AME) spectral profiles from 14 diverse galactic and extragalactic sources. The spectral profile model is an analytic representation of a quantum mechanical model for symmetric top rotational emission. The observed spectral shapes are well fit by superposing two model profiles originating from two distinct carrier families. Each family is composed of numerous, comparably abundant isomers of a parent carrier. The isomers have similar rotational constants, thereby producing continuous, versus resolved line, spectra that are slightly broader than the parent profiles. Ten observations are fit with comparable peak height and peak frequency ratios for the two carrier families, suggesting that AME arises from common carriers. One observation is fit using a single family, attributed to photodissociation of the less stable, smaller molecules for the missing family. Three observations are fit by combining two frequency-shifted model spectra, indicating multiple sources along their sight lines. The derived rotational constants for the two parent carriers are well determined because their rotational temperature is well characterized for the LDN 1622 dark cloud AME source. The rotational constants are consistent with the C36 and C60 fullerenes as the parent carriers. We use a Monte Carlo simulation of fullerene hydrogenation to understand the origins of source variability in the AME model fits. Other potential carriers, polycyclic aromatic hydrocarbons and very small grains, cannot be excluded; however, we find that fulleranes are also viable carriers because their aromatic cages are extremely stable to photodissociation, and their data-derived sizes suggest C36 and C60 parent fullerenes.