Astronomy and Astrophysics – Astronomy
Scientific paper
Jan 1997
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1997mnras.284..365p&link_type=abstract
Monthly Notices of the Royal Astronomical Society, Volume 284, Issue 2, pp. 365-375.
Astronomy and Astrophysics
Astronomy
25
Methods: Data Analysis - Methods: Numerical - Galaxies: Individual: Ngc 5643 - Galaxies: Stellar Content
Scientific paper
In this paper, we present a new solution of the stellar population synthesis problem using as primary information the equivalent width of the absorption lines observed in the spectra of, say, a galaxy. It is shown that this problem leads to a formulation akin to the maximum entropy method so successfully applied in image analysis and elsewhere. Emphasis is placed on the fact that it is a certain type of inverse problem for which many local solutions do exist. Among these local solutions there generally exists a global solution which is difficult to obtain in practice. A new method to search for this solution is proposed. First we solve a problem that is slightly different from the original one but which possesses a unique solution. Then we return to the original problem using that solution as a starting point of a local exploration. Because the change between the two formulations gets smaller as the errors in the data get smaller, we have great confidence that the solution we find in this way is an efficient one. As this solution may not be physical, we argue that either (1) the errors in the observations are too big for any method to work properly or (2) it is the signature of an inadequate stellar base. We then explore all boundaries by removing one or more stars from the data base and retain only those truncated data bases for which the solution is physical. The final solution (called the GPG solution) is that solution which minimizes a certain distance criterion. We have tested our method against noise in the data by Monte Carlo simulations and found it to be generally unbiased and to have a small dispersion around the true value for signal-to-noise ratio as low as 10. This property holds true at very low signal-to-noise ratio for stellar contributions greater than approximately 10 per cent. An example of the new method for the study of the active galaxy NGC 5643 is given.
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