PAHs in the Halo of NGC 5529

TL;DR

This study detects the most extensive PAH halo in a normal galaxy, NGC 5529, revealing its structure, origin, and relation to galaxy environment and halo gas, using sensitive mid-infrared observations.

Contribution

First detection of an extensive PAH halo in a normal galaxy, demonstrating its structure, origin, and correlation with halo gas and galaxy environment.

Findings

PAH halo has a scale height of 3.7 kpc

PAHs detected up to 10 kpc from the galaxy plane

Halo PAHs are likely long-lived and originate from disk outflows

Abstract

We present sensitive ISO $\lambda 6.7 \mu$m observations of the edge-on galaxy, NGC 5529, finding an extensive MIR halo around NGC 5529. The emission is dominated by PAHs in this band. The PAH halo has an exponential scale height of 3.7 kpc but can still be detected as far as $\approx 10$ kpc from the plane to the limits of the high dynamic range (1770/1) data. This is the most extensive PAH halo yet detected in a normal galaxy. This halo shows substructure and the PAHs likely originate from some type of disk outflow. PAHs are long-lived in a halo environment and therefore continuous replenishment from the disk is not required (unless halo PAHs are also being destroyed or removed), consistent with the current low SFR of the galaxy. The PAHs correlate spatially with halo H$\alpha$ emission, previously observed by Miller & Veilleux (2003); both components are likely excited/ionized by in-disk photons that are leaking into the halo. The presence of halo gas may be related to the environment of NGC 5529 which contains at least 17 galaxies in a small group of which NGC 5529 is the dominant member. Of these, we have identified two new companions from the SDSS.