Kuiper widefield infrared camera far-infrared imaging of the galactic center: The circumnuclear disk revealed

We present images of the Galactic center in the dust continuum at 31.5 and 37.7 mu m obtained with the Kuiper Widefield Infrared Camera on the Kuiper Airborne Observatory. The raw images have a spatial resolution of similar t o 8 ".5 and cover a region roughly 10' (R.A.) by 24' (decl.) in extent. Her e we discuss the innermost 2'.8 x 3'.6 (6.9 x 9.1 pc) regions roughly cente red on Sagittarius A*, where the high signal-to-noise ratio permits image r estoration to similar to 3 ".6-5 ".7 spatial resolution at 31.5 and 37.7 mu m, respectively. These images clearly delineate the warm dust in the "mini spiral" but also show an elliptical structure centered on Sgr A* and inters ecting the minispiral at the western are that we identify as the photodisso ciated inner rim of the circumnuclear disk (CND) or ring. This is the first image of the complete disk and the first image of both the minispiral and CND in a single tracer, thereby permitting detailed studies of the intimate association between these two structures. The 31.5/37.7 mu m color tempera ture map indicates that most of the far-UV flux required to heat the dust g rains must come from centrally located sources. The cluster of He I emissio n-line stars recently identified near Sgr A* is sufficient to provide half the heating for the far-IR ring and minispiral structures, the balance like ly being provided by O and B stars associated with the cluster. We also fin d similar to 16 color temperature peaks distributed within the CND that we suggest are the locations of early type (B4 to O9) main-sequence stars. To match the observed far-IR fluxes from the ring, we require an unusually hig h 30-40 mu m dust grain emissivity and/or an usually high UV albedo. The far-IR morphology is reproduced by a simple model: an inclined (i simil ar to 65 degrees), slightly elliptical (e similar to 0.06) torus with one f ocus at Sgr A* and two streamers on parabolic orbits with foci at Sgr A*. T he torus has an inner radius of 1.58 pc, is similar to 0.4 pc thick, and co nsists of clumpy cloudlets with characteristic sizes less than 0.15 pc. The northern streamer is identified with the northern arm, and the east-west ( EW) streamer is identified with the bar and eastern arm structures seen in both their [Ne II] fine-structure line emission and the radio continuum. Th e northern arm is traced in the far-IR continuum from regions similar to 1. 4 pc outside of the far-IR ring to its apparent intersection with the EW st reamer. The eastern CND is not detected in the radio continuum because of e xtinction by the intervening northern arm, which therefore must be nearly i n the plane of the CND. Extensions of the EW streamer outside of the CND ar e apparent to the east and especially to the northwest. The EW streamer lie s similar to 85 degrees out of the plane of the CND and is on a parobolic o rbit focused on Sgr A* at a distance of 0.33 pc, with its apex well in fron t of or behind Sgr A*.