Mid-Infrared and CO Observations of the Infrared/X-Ray Luminous Seyfert 1 Galaxy NGC 985: The Making or Breaking of a ULIRG?

February 2002 • 2002ApJ...566..682A

Authors • Appleton, P. N. • Charmandaris, V. • Gao, Yu • Combes, F. • Ghigo, F. • Horellou, C. • Mirabel, I. F.

Abstract • We describe Infrared Space Observatory (ISO)1 and BIMA observations of the z=0.04 Seyfert 1 ring galaxy NGC 985 which suggest close parallels with some quasar host galaxies. NGC 985 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 ~1.8×10¹⁰ M_solar of highly disturbed molecular gas which lies in an asymmetric barlike 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 active galactic nucleus (AGN), located in one of the two nuclei. Fainter CO, mid-infrared (MIR), and radio continuum emission provides a glimpse of the complexities of star formation in the outer ring. An analysis of the kinematics of the main CO emission reveals evidence for two dynamically distinct molecular components within NGC 985. The first is a set of isolated supergiant molecular clouds (SGMCs) which are concentrated within 9-10 kpc 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 an ultraluminous infrared galaxy [ULIRG]) or alternatively 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 Lyα emission. Such an association would imply a complex interrelationship between the nuclear CO cloud population in colliding systems and AGN-driven winds.

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Phil Appleton

Senior Scientist