Evidence for the naphthalene cation in a region of the interstellar medium with anomalous microwave emission

TL;DR

This study presents spectroscopic evidence for the naphthalene cation in a region of space with anomalous microwave emission, suggesting polycyclic aromatic hydrocarbons contribute to interstellar phenomena.

Contribution

First detection of naphthalene cation features in an interstellar medium with anomalous microwave emission, linking PAHs to these phenomena.

Findings

Detected spectral features matching naphthalene cation in space.

Estimated 0.008% of carbon in the cloud is in naphthalene cation form.

Supports PAHs as carriers of diffuse interstellar bands and microwave emission.

Abstract

We report high resolution spectroscopy of the moderately reddened (A$_V$=3) early type star Cernis 52 located in a region of the Perseus molecular cloud complex with anomalous microwave emission. In addition to the presence of the most common diffuse interstellar bands (DIBs) we detect two new interstellar or circumstellar bands coincident to within 0.01% in wavelength with the two strongest bands of the naphthalene cation (C$_{10}$H$_{8}^+$) as measured in gas-phase laboratory spectroscopy at low temperatures and find marginal evidence for the third strongest band. Assuming these features are caused by the naphthalene cation, from the measured intensity and available oscillator strengths we find that 0.008 % of the carbon in the cloud could be in the form of this molecule. We expect hydrogen additions to cause hydronaphthalene cations to be abundant in the cloud and to contribute via electric dipole radiation to the anomalous microwave emission. The identification of new interstellar features consistent with transitions of the simplest polycyclic aromatic hydrocarbon adds support to the hypothesis that this type of molecules are the carriers of both diffuse interstellar bands and anomalous microwave emission.