Large misalignment between stellar bar and dust pattern in NGC 3488 revealed by Spitzer and SDSS

A large position angle misalignment between the stellar bar and the distribution of dust in the late-type barred spiral NGC 3488 was discovered, using mid-infrared images from the Spitzer Space Telescope and optical images from the sloan digital sky survey (SDSS). The angle between the bar and dust patterns was measured to be 25° ± 2°, larger than most of the misalignments found previously in barred systems based on Hα or H i/CO observations. The stellar bar is bright at optical and 3.6 μm, while the dust pattern is more prominent in the 8 μm band but also shows up in the SDSS u and g-band images, suggesting a rich interstellar medium environment harboring ongoing star formation. This angular misalignment is unlikely to have been caused by spontaneous bar formation. We suggest that the stellar bar and the dust pattern may have different formation histories, and that the large misalignment was triggered by a tidal interaction with a small companion. A statistical analysis of a large sample of nearby galaxies with archival Spitzer data indicates that bar structure such as that seen in NGC 3488 is quite rare in the local Universe.