Far‐Infrared Imaging of NGC 55

Abstract

We present images of the galaxy NGC 55 at 24, 70, and 160 μm obtained with the Multiband Imaging Photometer for Spitzer (MIPS) instrument on board the Spitzer Space Telescope. The new images display the far infrared emission in unprecedented detail and demonstrate that the infrared morphology differs dramatically from that at shorter wavelengths. The most luminous emission region in the galaxy is marginally resolved at 24 μm and has a projected separation of nearly 520 pc from the peak emission in the optical and near-infrared. This region is responsible for ~9% of the total emission at 24 μm and is likely a young star formation region. We show that this and other compact sources account for more than one-third of the total 24 μm emission. We compute a total infrared luminosity for NGC 55 of 1.2 × 109 L⊙. The star formation rate implied by our measurements is 0.22 M⊙ yr-1. We demonstrate that the cold dust is more extended than the warm dust in NGC 55—the minor-axis scale heights are 0.32, 0.43, and 0.49 kpc at 24, 70, and 160 μm, respectively. The dust temperature map shows a range of temperatures that are well correlated with the 24 μm surface brightness, from 20 K in low surface brightness regions to 26 K in high surface brightness regions.