干旱区生态环境知识资源中心

Near-infrared images in the J and K’ bands of two edge-on late-type galaxies, NGC 3556 and NGC 4244, were obtained with the newly developed common-use instrument for infrared imaging and spectroscopy at the Okayama Astrophysical Observatory (OASIS). These images were analyzed to yield the surface-photometric and model parameters for the global structure of these Scd galaxies. NGC 3556 shows a disk and a bar-like structure, both of which have an approximately exponential surface-brightness distribution. The absorption feature of NGC 3556 is complex, and only the most prominent central dark lane of A(J) < 0.5 was taken into the modeling. NGC 4244 comprises a disk and a weak bulge, both having an approximately exponential surface-brightness distribution, suffering under negligible internal absorption by a faint dark lane of A(J) < 0.1. Global models of the 3-D emissivity structure and absorption layer have been constructed to reproduce the observed main features. The global models indicate that both galaxies are optically thin in the V band when seen face on (tau(0,V) < 0.4), with the reservation of a possible presence of locally opaque structures in NGC 3556. Brief discussions are given concerning the insufficiency of simple absorption-layer models and the strong contrast between the two Scd galaxies regarding their interstellar matter and star-forming activities.