Mid-IR and CO Observations of the IR/X-Ray Luminous Seyfert I Galaxy NGC985: The Making or Breaking of a ULIRG?

Abstract

We describe ISO and BIMA observations of the z=0.04 Seyfert 1 ring galaxy NGC985 which suggest close parallels with some quasar host galaxies. NGC985 contains two closely spaced nuclei embedded in an R${}^{1/4}$--law stellar bulge and an outer ring, evidence of an ongoing merger. The system contains \~1.8x10^{10}Msolar of highly disturbed molecular gas which lies in an asymmetric bar-like structure with the peak in observed CO column densities significantly offset from the compact double nucleus. In contrast to this, the ISO observations show strong dust emission centered on the AGN, located in one of the two nuclei. Fainter CO, MIR, and radio continuum emission provide a glimpse of the complexities of star formation in the outer ring. An analysis of the kinematics of the main CO emission reveal evidence for two dynamically distinct molecular components within NGC985. The first is a set of isolated super-giant molecular clouds (SGMCs) which are concentrated within 9-10kpc of the active nucleus. Although randomly distributed about the center, the clouds may form part of a clumpy highly-disturbed disk which may be either just forming around double-nucleus (the making of a ULIRG), or alternatively may be in the process of being disrupted-perhaps as a result of a powerful nuclear outflow (the breaking of a ULIRG). A second major concentration of CO lies offset from the double-nucleus in a dynamically coherent ridge of emission in which powerful star formation is occurring. We tentatively associate CO emission with two out of six UV absorption-lines seen in the blue wing of the very broad Lyman alpha emission. Such an association would imply a complex inter-relationship between the nuclear CO cloud population in colliding systems, and AGN-driven winds.

22 pages, 12 figures. Accepted for publication in the Astrophysical Journal on Sep. 24, 2001. A version of the paper with higher resolution figures from http://www.astro.cornell.edu/~vassilis/papers/ngc985.ps.gz

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