AKARI Infrared Observations of the Edge-On Spiral Galaxy NGC 3079

Abstract We present AKARI near- to far-infrared images of the nearby edge-on spiral galaxy NGC 3079 in 10 photometric bands. The spectral energy distribution consists of continuum emission from dust with a single temperature of 28–33 K together with strong mid-infrared emission features from polycyclic aromatic hydrocarbons (PAHs). We derived dust masses of 5.6 $\times$ 10$^{6}\ M$$_{\odot}$ and 1.4 $\times$ 10$^7\ M$$_{\odot}$ for the central 4 kpc region and the whole galaxy, respectively, and found that the gas-to-dust mass ratio is unusually high in the central region ($\sim\ $1100), and even for the whole galaxy ($\sim\ $860). The ratio of the surface brightness distribution at a wavelength of 7$\ \mu$m to that at 11$\ \mu$m suggests that the properties of PAHs have spatial variations. The emission from ionized and neutral PAHs is relatively strong in the center and the disk regions, respectively, suggesting a stronger radiation field, and thus relatively active star formation in the center. Yet, the total infrared luminosities of the galaxy indicate rather low star formation rates. These results suggest that NGC 3079 is in an early-phase starburst stage.