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Session 68 - Disk Galaxies.
Display session, Wednesday, January 15
The barred spiral galaxy NGC 3351 and the ovally distorted spiral galaxy NGC 5248 have well-known circumnuclear hotspots. We obtained J and K band observations of their central 100" using the KPNO 2.1m + COB with 0.2" pixels. In both galaxies, the hotspots are approximately evenly spaced around a circumnuclear ring, with a separation between them equal to about three times their diameter. This spacing is consistent with their formation by large-scale gravitational collapse along the periphery of the ring. In NGC 3351, two of the hotspots are slightly offset from published CO peaks. The Toomre Q parameter determined from the gas data is 1.1, which is consistent with the collapse model. The circumnuclear ring, when deprojected to correct for inclination, is elliptical and aligned parallel to the large scale stellar bar. The (J-K) map shows twin peaks and another faint ring structure at a radius of 2" (corresponding to 100 pc), considerably smaller than the circumnuclear ring. The K band morphology of NGC 5248 is very similar to the published ultraviolet HST image, with hotspots on small spiral arcs that form a ring-like structure. We compared our calibrated (J-K) colors with published instantaneous and burst models to determine ages, and compared individual hotspot luminosities with published cluster luminosity-mass models to determine masses.
Program listing for Wednesday