Near-Infrared Imaging of Ultraluminous IRAS Galaxies

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Session 44 -- Radio Galaxies, Jets and Disks
Display presentation, Wednesday, 9:20-6:30, Pauley Room

[44.01] Near-Infrared Imaging of Ultraluminous IRAS Galaxies

Jason A. Surace, Lee Armus (Caltech), James R. Graham (University of California at Berkeley), K. Matthews (Caltech), Joseph M. Mazzarella (IPAC-Caltech), G. Neugebauer, B.T. Soifer (Caltech)

We present images in the J (1.25$\mu$m), H (1.65$\mu$m), and K (2.2$\mu$m) bands of 11 ultraluminous infrared galaxies (L$_{ir} > 10^{12}$\hbox{L$_\odot$}) selected from the IRAS Bright Galaxy Sample (BGS, Soifer et al., 1987) and the Warm Galaxy Sample (Sanders et al., 1988). We have used these images to create 2-dimensional colormaps and to derive multiple-aperture near-infrared colors. Of the 7 sources with Seyfert 1.8-2 or LINER optical spectra, 3 have very red nuclei which are most easily interpreted as enshrouded AGN cores (A$_{v} = 3-6$ mag) with varying amounts of hot dust emission (600-1000 K), 3 have near-infrared nuclear colors indicative of reddened young stars mixed with hot dust, and one galaxy, IRAS 15206+3342, has colors similar to the mean PG QSO colors. Including Arp 220 (Mazzarella et al. 1992) and Mrk 273 (Armus et al. 1993), which were previously found to have very red nuclei, this brings the number of ultraluminous BGS galaxies with narrow optical lines suspected of having dust-enshrouded AGN to 5 out of 8. Additionally, the circum-nuclear colors of 4 of our sample galaxies are indicative of a large population of young stars obscured by varying amounts of dust. This suggests that the galaxies may contain both an AGN and a circum-nuclear starburst. We will discuss these new data in the light of theories concerning the power sources in ultraluminous infrared galaxies and their possible evolution into optical QSOs.

The data were obtained using the 5m Hale telescope at Palomar Observatory. This work is supported by the NSF and NASA.

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