Disruption of the cloud

Figure 4 shows the HST NICMOS field in 2.15 m continuum, with a few interesting continuum features marked. The previously-known infrared sources IRc3 and IRc4 are seen to be arcs with long diffuse ``tails'' (this was first noted in the work of Stolovy et al 1998); these tails have molecular hydrogen bullets emerging from them. One interpretation of the origin of the tail structures is that they are tunnels created in the cloud by the passage of the bullets; these tunnels are then lit from within by the infrared source(s) embedded in the cloud.

The region marked ``Dark Cloud'' in Figure 4 may be a foreground remnant of denser cloud material, now being disrupted by the outflow. This structure can also be seen in Figure 3b, apparently obscuring some of the fingers in the southwestern part of the outflow. To the west of it lies a further faint area of emission which exhibits significant linear and circular K-band polarization (Geng 1993, Chrysostomou et al 2000--the IRc3 tail also exhibits high polarization). This implies that these regions are being illuminated by the infrared sources within the cloud, possibly through openings created by the passage of the bullets.

North of BN, we find two other structures. The ``Crescent'' appears to be a dense knot of cloud, illuminated from below by BN. Its appearance is reminiscent of the ``pillars'' of the Eagle Nebula (Hester et al 1996). The ``V'' is another continuum structure with some 2 emission. This emission, like that in the Crescent, is almost certainly shock-excited. The coincidence of strong continuum and 2 emission would suggest a fluorescent mechanism for the excitation of the 2, but there is no evidence of a source of sufficient FUV photons in this region. Emerging from the northern end of the ``V'' is a linear 2 feature which Schild et al (1997) speculate is a jet, terminating in a ring. However, the UKIRT Fabry-Perot data does not show an especially high velocity for this region (Schultz & Burton 2001). Schultz et al (1999) speculate that the ``V'' and ``jet'' are the result of the confinement of the flow by the molecular cloud (note the absence of emission in the northwest quadrant of Figure 3b).

© Copyright Astronomical Society of Australia 1997