What we've actually been doing
As our last night on the mountain draws to an end, we’re fighting strong winds and occasional technical glitches in the camera control system (solution : turn off, turn back on again) to get images of some of the most useful galaxies we’ve seen yet. One is a more distant version of Bill’s personal touchstone, NGC 3314. I hope you’ve enjoyed the blogs we’ve posted over the last five nights – there will be more to come as the work on all of this fabulous data continues However, you’d be forgiven if you failed to work out from the posts what it is that has been keeping us, or rather Anna in particular, so busy. As the telescope obtains a series of exposures, they are aligned and then stacked together to produce a composite. The raw data looks something like this:
While the galaxy is there, there’s an awful lot of other noise and mess surrounding it. To deal with this, a ‘dark frame’ produced by taking short exposures to measure the noise in the camera is subtracted, along with a flat – a picture of a standard source, usually the inside of the dome lit with light of known wavelengths. Easy to write, but difficult to do, especially when new images are coming by every 30 minutes or so. The result is a vast improvement:
A beautiful crisp, clear image, ready to be combined with its counterpart in the other filter to produce a colour image. At the minute, I’ve been doing this on an ad hoc basis (results below) but eventually this will be done systematically and carefully to produce science ready images. At this point, the real work of modeling and measuring the dust can begin.
In this case, we have a ring/spiral galaxy near an smaller and more distant elliptical (the small blobby thing just to the right of the larger galaxy). It’s interesting to see how similar in colour and appearance the elliptical is to the budge at the centre of the spiral, and how different in colour these assemblages of older stars are to the dusty ring. This, as it turns out, isn’t an ideal system for the study because there isn’t much of an overlap between the two systems, but there is some – and we didn’t know that until we took these exposures.