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Science Aided by Deconvolution

There is another category of scientific results where deconvolution plays a significant role, even when the final measurements use another technique. This operates on the principle that if you don't know it's there, you can't measure it. In many cases, deconvolved images are important in knowing what analysis technique to use for the problem at hand, and whether in fact another technique might be more appropriate. Several examples come to mind from the realm of galaxy structure and evolution.

Central Peaks in Galaxy Profiles

The presence of strong central concentrations in the starlight of galaxies is important in understanding their dynamics, and in searching for the massive compact objects thought to exist in (at least) active galactic nuclei. They have been probed using combinations of modelling and deconvolution in several galaxies. From an early science verification image, Lauer et al. 1991 found a strong central peak in the previously undistinguished galaxy NGC 7457. Further PC observations confirmed ground-based measurements of a central ``spike'' in M87 (Lauer et al. 1992a), and showed that the central concentration is more pronounced that could have been demonstrated from ground-based data alone. A similar concentration also appears in the Local Group elliptical M32 (Lauer et al. 1992b). Pending spectroscopic observations post-COSTAR, galaxies with these features are the best candidates for hosting massive central black holes. It is noteworthy that this signature is not uniquely linked to nuclear activity, suggesting that the prerequisites for such activity are more common than its actual occurrence.

The core of the Andromeda galaxy, M31, has also been suspected to harbor a massive central object from ground-based spectroscopic data (Dressler &Richstone, 1988, Kormendy 1988). The HST images analyzed by Lauer et al. (1993) show an unexpectedly complex situation - two cores of different scale size and brightness, separated by 0.49 arcseconds. This discovery accounts for a long-standing puzzle, the offset of the brightness peak of M31 from the isophotal center (Nieto et al. 1986). This nucleus was observed using the Stratoscope II balloon-borne telescope (Light et al. 1974), which showed this central asymmetry; had their image been somewhat deeper the character of the nucleus might have become apparent. The double core of M31 poses outstanding theoretical questions. The most likely explanation is that the more compact object is the remnant core of a galaxy that has merged with M31; to have such a configuration last long enough to have a reasonable chance of our observing it probably requires that both nuclei harbor massive black holes. These conclusions could have been reached from modeling and fitting alone, but deconvolution was a strong aid in knowing what to fit.

Modelling Galaxy Images

For more distant galaxies, structural parameters are often better estimated by model-fitting (Schade &Elson 1993) - once deconvolution has given assurance that there is not too much nonaxisymmetric structure. Even in fitting multicomponent models to the aberrated data in a sense, a deconvolved image can give initial values for the parameters that vastly speeds convergence to the best-fit set (Windhorst et al. 1993a, 1993b). Results from such procedures include an angular-size - redshift relation for field galaxies (Griffiths et al. 1994) and identification of weak disks in early-type galaxies (Keel &Windhorst 1993).

Next: Current Challenges Up: Scientific Results from Deconvolved Previous: HST Science: Structure
Fri Apr 15 18:23:31 EDT 1994