N 66 (Henize 1956) is the largest and most luminous H II region in the Small Magellanic Cloud (SMC). It is also known as DEM S103 (Davies et al. 1976) or NGC 346; the latter designates indifferently the H II region and its ionizing cluster. A bright emission region (that we will call N 66 in what follows) is along and to the SW of an oblique (SE-NW) "bar" (Fig. 1). The H II region is limited on the SW side by a well-defined arc. A more compact H II region at (J2000)=00h 59m 16s, (J2000)=-72o 10´ is N 66A. A supernova remnant is located to the East of the region. A dense cluster of massive young stars excites N 66, but there are also young stars outside, as the ionizing stars of N 66A. Massey et al. (1989) have performed an extensive study of the stellar content of the region, which contains at least 33 O stars, including 11 of type O6.5 or earlier. 22 of these O stars are contained in the central star cluster, and the others are isolated or in small groups. Fig. 1 is a 60 sec OIII image obtained with EMMI/NTT on December 1995, and extracted from the ESO NTT archive through the ESO Science Archive Facility. The image was reduced using reference files obtained during the same observing run using a Tek 20482048 CCD, covering a field of view 9.2´ 8.6´ with a pixel size of 0.27 ".
N 66 has been observed at many wavelengths. In particular Contursi et al. (2000, hereafter Paper I) have presented and discussed mid-IR spectrophotometric observations of N 66 obtained with the 3232 pixel ISOCAM camera on board the Infrared Space Observatory (ISO) of the European Space Agency. A 6´6´ field was mapped in 7 broad-band filters, and the central 3´3´ have been observed with the Circular Variable Filters (CVFs) as dispersive elements. These observations provided a wealth of data on warm dust, fine-structure lines and Aromatic Infrared Bands (AIBs). Mid-IR emission peaks coincide with the main features of the ionized gas map. Fig. 2 shows the contour map in the ISOCAM LW2 filter (5.0-8.0 µm) which is dominated by the 6.2 and 7.7 µm AIB emission, superimposed on the [O III ] image of Fig. 1. CO(2-1) line observations made with the Schottky receiver of the SEST telescope at La Silla were also presented. These relatively low-sensitivity observations showed that N 66 does not contain much molecular gas, except for a small cloud to the NE of the bar.
The present paper describes and discusses new observations of the region of N 66. The CVF observations of the central peak made with ISO are discussed in another paper (Contursi et al. 2000a), with emphasis on the silicate emission. Sect. 2 presents high-sensitivity CO(2-1) line observations made with the SIS receiver of the SEST, which reveal the presence of molecular gas associated with the H II region. In Sect. 3, we present near-IR maps made in the v=(1-0) S(1) line of H2 and in the adjacent continuum at 2.14 µm. Sect. 4 contains a discussion and Sect. 5 the conclusions.
© European Southern Observatory (ESO) 2000
Online publication: July 13, 2000