Results

UNSWIRF is a highly versatile facility, as illustrated by some of the first science results achieved. Since being commissioned in 1996 February, it has been awarded a total of 35 nights in its first 3 semesters on the AAT. Among the projects currently underway (or planned) are:

• Imaging and line-ratio mapping of supernova remnants, planetary nebulae, HII regions, photodissociation regions (PDRs), and Herbig-Haro objects.
• Photometry and dynamics of starburst and Seyfert galaxy nuclei.
• Studies of extinction in star formation regions.
• The search for redshifted UV/optical emission from primeval galaxies.

Figure 6 was produced from some of the earliest data obtained with UNSWIRF, and shows the emission from molecular hydrogen at 2.12 m from a photodissociation region not far from the ``Keyhole'' Nebula in Carina. Not surprisingly, this region has earned the (unofficial) designation of the ``Kangaroo'' Nebula. This image was produced using UNSWIRF in its Line Imaging Filter mode, by subtracting a continuum image from a single image taken very near the line peak.

  
Figure 6: Image of the H emission associated with a CO outflow in Carina. The outline of this photodissociation region bears an uncanny resemblance to one of the more abundant inhabitants of the Warrumbungles National Park. The pixel scale is , and the image spans . East is up, and North is to the right in this image.

UNSWIRF is already helping to shed some light on the excitation mechanism for H in PDRs. Figure 7 is a map of the H / H intensity ratio in the reflection nebula Parsamyan 18, obtained from scans of the 2.12 and 2.25 m lines with UNSWIRF (Ryder et al. 1998). Values of the ratio over most of P 18 are indicative of UV-pumped fluorescence, while values approaching 7 or more in the areas marked ``5'' and ``8'' are consistent with an increased gas density and/or a contribution from shocks. The simultaneous velocity information provided by UNSWIRF has allowed us to show that Region ``8'' is almost certainly excited by an outflow source close to P 18, rather than being radiatively excited like the other regions. Similar studies are also being carried out on the ``elephant trunks'' of M16 (Allen et al. 1998a), as well as the ``fingers'' emerging from the core of OMC-1 (Figure 8; Burton & Stone 1998).

  
Figure 7: Grey-scale map of the ratio of the H line at 2.12 m to the H line at 2.25 m in Parsamyan 18, for all points in which a reliable detection () at 2.25 m was achieved. The coordinate system is relative to the position of a V=13.2 B2-3e star, thought to be supplying the UV flux that pumps much of the H emission.

  
Figure 8: Two images of the line emission from OMC-1. Offsets are in arcseconds from the BN object. (left) H line (contours) and adjacent off-line continuum (grey-scale) in the core of OMC-1, showing the clumpy nature of the line emission on arcsecond scales. (right) H emission to the NW of the core (grey-scale), overlaid with contours of [FeII] 1.64 m emission. Several of the [FeII] emitting heads have been identified with HH-object numbers. It can be seen that the fingers also emit in [FeII] as well as in H (see Burton & Stone (1998) for a review of the H emission from OMC-1).

  
Figure 9: Images of the Br line emission from ionised hydrogen (left), and the H 1-0 S(1) line emission from molecular hydrogen (right) in the southern planetary nebula NGC 3132, both imaged with UNSWIRF. Note how well the interface region between the two regimes is defined, and the complex structure of the molecular emission.

One avenue of research to which UNSWIRF is particularly well-suited is the excitation and dynamics of planetary nebulae, both young and evolved. Figure 9 compares the morphology of ionised and warm molecular gas in NGC 3132 (Allen et al. 1998b). A similar study of the H emission in very low excitation (and therefore young) planetary nebulae is also being conducted to complement an H Snapshot survey with WFPC-2 on board the HST (Sahai & Trauger 1996).

Another area of research where UNSWIRF is beginning to make inroads is in the excitation and dynamics of active galactic nuclei and starburst galaxies, normally heavily obscured by dust. Figure 10 shows the inner velocity field, derived from UNSWIRF scans of the H 2.12 m line, in the Circinus galaxy, which is the closest known Type 2 Seyfert galaxy. This has enabled the first direct measure of the rotational velocity gradient near the nucleus of the Circinus galaxy, and allows us to put an upper limit on the mass of the central black hole of  M (Davies et al. 1998).

  
Figure 10: Grey-scale velocity map for the central 30'' of the Circinus galaxy, derived from fitting of UNSWIRF scans to find the wavelength of the H 2.12 m emission line peak. The contours indicate line intensity.

© Copyright Astronomical Society of Australia 1997