Astronomy & Astrophysics manuscript no. irwin c ESO 2018 October 25, 2018 PAHs in the Halo of NGC 5529 J. A. Irwin1, H. Kennedy1, T. Parkin1, and S. Madden2 1 Dept. of Physics, Engineering Physics, & Astronomy, Queen’s University, Kingston, Canada, K7L 3N6 e-mail:
[email protected] 2 CEA/Saclay, Service d’Astrophysique, Orme des Merisiers, Bˆatiment 709, 91191 Gif-sur-Yvette cedex, France e-mail:
[email protected] Received 00 month 0000; accepted 00 month 0000 ABSTRACT We present sensitive ISO λ 6.7 µm 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 ≈ 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 Hα 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.