PAH emission from the dust lane of an elliptical galaxy with the Spitzer IRS

TL;DR

This study uses spectral mapping with Spitzer and AKARI to reveal that PAH emissions in an elliptical galaxy are predominantly located in the dust lane, indicating their likely origin from merger-driven ISM evolution.

Contribution

It provides the first detailed spatial distribution of PAHs in an elliptical galaxy, linking PAH features to galaxy merger history and ISM evolution.

Findings

PAH 11.3 um emission is mainly from the dust lane.

PAH 17 um emission distribution differs from 11.3 um.

PAHs are likely secondary products from ISM evolution.

Abstract

Spitzer and AKARI observations have found that polycyclic aromatic hydrocarbons (PAHs) are present in nearby elliptical galaxies, but their spatial distributions are still unknown. In order to investigate their distributions, we performed deep spectral mapping observations of the PAH-detected elliptical galaxy NGC4589, a merger remnant with a minor-axis optical dust lane. As a result, we obtain clear evidence that the PAH 11.3 um emission comes predominantly from the dust lane of the galaxy. We also detect molecular hydrogen line emissions from the dust lane. The PAH 17 um emission is distributed differently from the PAH 11.3 um emission, and more similarly to the dust continuum emission. From their distinctive distributions, we suggest that the PAHs responsible for the 11.3 um feature are secondary products through the evolution of the ISM brought in by the merger.