AAO Newsletter October 1996 - Page 3

However, I am convinced that the AAO's record on cost-effectiveness, productivity and quality of scientific output, and potential for the future, strongly argues the case for maintaining the funding at current or even increased levels.

The fact that the AAO exhibits such a strong potential for its future is due to its staff, and notably to Russell Cannon under whose Directorship the AAO has prospered significantly over the last ten years. It is my over-riding priority to ensure that this potential is realised and that the AAO maintains its reputation as a world-leading observatory both in terms of scientific productivity and technological innovation.

Brian Boyle

TFF observation of Halpha/[N II] emission at z = 0.23

Fig. 1 shows example TAURUS Tunable Filter (TTF) observations of Halpha and/or [N II] emission at a redshift of z = 0.23. The observations were made at f/8 during a recent run on the AAT as part of our continuing TTF Galaxy Survey to sample star formation as a function of redshift and environment. This particular galaxy was noted by Couch & Newell (1984; ApJS 56, 143) for its spectrum of strong emission lines, including [O II], [Ne III], [O III], He I, Hgamma and Hbeta. Although this galaxy is an extreme case, emission in other galaxies at much lower levels is detectable. Our observation of emission peaking at around 810 nm is consistent with Halpha/[N II] at the z = 0.232 measured by Couch & Newell for this galaxy.

figure 1

Figure 1: TTF scan showing a galaxy (arrowed) particularly bright in redshifted Halpha and/or [N II] emission. The observations were made in 1.4 to 2.0" seeing with a total exposure time of 1300 s per wavelength slice.

The cover figure shows the same region imaged through the order-sorting filters used by TTF, without the tunable filter in place. The image on the left was taken through a 31 nm bandpass centred at 812 nm. The image on the right is the mean flux received through similar filters of 758/29 and 909/40 nm. The line-to-continuum ratio in this object is sufficiently high for the excess in emission to be noticeable even at these broader bandpasses.

We suspected the presence of Halpha emission on the basis of the intermediate-band images alone. However, it is only with the spectrophotometric capability of TTF that line emission can be confirmed and a redshift obtained. Line absorption is similarly detectable.

The intermediate-band filters of TTF have been customised to avoid the bands of OH nightsky lines spread throughout the near-infrared. They present a sky background that is much darker compared to that in conventional R and I, thereby being useful for intermediate-band photometry on their own (i.e. without TTF). Presently, high resolution imaging (< 15Å bandpass) is limited to four intermediate-band filters spread over R and I (see the TTF web site at


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