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Adaptive optics with a Laser For Astronomy
3D integral field spectroscopy
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K-band images of the PSF and galaxy are shown below, at a pixel size of 0.125" (field of view ~4"). The PSF is shown to 10% of its peak, and compared to this, the extended nature of the galaxy nucleus is clear. The data were obtained during a period when the coherence timescale of the seeing was very short. In both cases, although the wavefront reference star had a magnitude V=10.2, it was 45" due west - rather too far - and we were only able to reach a resolution of 0.5". The PSF is shown to 10% of its peak, and compared to this, the extended nature of the galaxy nucleus is clear.
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| These images of the galaxy have been masked, keeping only those pixels with enough signal to noise to measure the equivalent width of the CO absorption |  |
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The spectrum of the central 1" of the galaxy's nucleus is shown below. The only clear features are the absorption lines of CO (longward of 2.3 microns) and perhaps also Na and Ca, which are signatures of late-type giant stars; there are no emission lines. A model, composed of template K-type red giant and supergiant stars, has been fitted - the difference between this and the observed spectrum is shown underneath. It would seem that no hot young stars are needed, and the conclusion appears to be that this LINER nucleus houses evolved starburst, perhaps 50-100 million years after the star formation has ceased.
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Infact the optical spectrum (from Ho, Filippenko & Sargent 1995) is also dominated by late-type stars. But it does provide hints that there could be young blue stars - which would be clearer in a UV spectrum - and shows that there are at least a few emission lines. For a more detailed discussion see our contribution to the SPIE 4007 meeting.
Data reduced & figures drawn by L. E. Tacconi-Garman & R. Davies