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Session 76 - Star Formation in Galaxies.
Display session, Friday, January 09
Exhibit Hall,
We have obtained 8--18\mu m images of the Luminous Infrared Galaxies (LIGs) Mrk 231, Arp 220 amp; NGC 7469 with the UCSD Long Wavelength Imaging Spectrometer (LWS; and Puetter, 1993, Proc. S.P.I.E., 1946, pp. 610-621) on the W. M. Keck Telescope. Pixon-based image reconstruction techniques (Puetter, 1995, Int. J. Image Sys. amp; Tech., 6, pp. 314-331) have been employed to achieve sub-diffraction limited resolution (\sim 50mas). The twin nuclei of Arp 220 are clearly distinguished in the raw data. The mid-infrared flux-density ratios of the two nuclei, compared with data from the near-infrared (Graham, et al 1990, ApJL, 354, L5) and VLBI images (Smith, Lonsdale, Diamond amp; Lonsdale, 1997, ApJL, in press) suggest that star formation is actively continuing in the Western nucleus while activity in the Eastern nucleus has decreased significantly, although the histories of the two nuclei may have been similar.
Our images of the Sy 1 galaxy NGC 7469 clearly show the star-formation ring surrounding the Seyfert nucleus. Comparison will be made between our mid-infrared images and the 3.6cm radio data (Condon, et al. 1991, ApJ, 378, 65). The nucleus is marginally resolved at 50mas resolution, implying a physical size of about 15pc, comparable to the size of the compact VLBI core (Lonsdale, Smith amp; Lonsdale 1995, BAAS, 38, 1359) and suggesting that the active nucleus and warm-dust emitting region may be physically related.
The three galaxies represent a sequence from dominant Starburst (Arp 220) to AGN (Mrk 231); speculations for LIG evolution will be briefly discussed.
This work has been supported by the NSF, NASA, CARA and the W. M. Keck Foundation, to whom we express our thanks.
