The Baldwin Effect is real and has important implications for the emission-line regions of quasars. Additional work will be needed if we are to fully extract the meaning of this correlation. The existence of an ionization dependence in the BE provides important clues to the underlying physics. Variations in the BE across line profiles, possible differences between radio-loud and radio-quiet BEs, and constraints resulting from the intrinsic BE will also play a role in sharpening our understanding of this phenomenon. A clearer understanding of the physical basis for the BE would gratify quasar enthusiasts while strengthening the credibility of using this phenomenon for calibrating cosmological diagnostics.
Several avenues of inquiry would be of particular value for making
progress in our understanding. Large data sets with well-defined
selection criteria and uniform follow-up would aid in refining BE
measurements and their relation to radio properties and the ionizing
SED. The Sloan Digital Sky
Survey and surveys with the new generation
of X-ray telescopes (AXAF, XMM) can be expected to deliver
appropriate samples, while the burgeoning number of 8-m class telescopes
will in principle make it possible to obtain follow-up spectroscopy
with the high signal-to-noise ratio necessary for reliable and reproducible
line measurements. X-ray studies will also be important for probing
the X-ray BE with well-defined samples, while exploring the connection
between K
behavior and the UV lines.
Beyond simply searching for the BE, it is now time to vigorously pursue the origins of dispersion in the correlation. The substantial scatter has raised large questions about the suitability of the BE as a cosmological tool. Multiparameter and principal-components investigations offer powerful tools for extracting the full details of correlated phenomenology, which in turn can serve as inspiration and testbeds for the construction of detailed physical interpretations. The future promise of the Baldwin Effect as an entree to understanding quasars and cosmology appears bright.
Acknowledgements
We thank our hosts for organizing the meeting. Their hospitality was in the best Chilean tradition. Our colleagues provided valuable commentary and lively discussion, which helped us all improve our understanding of this important but complex topic in quasar research. We wish to also thank Brad Peterson and Mike Brotherton for providing helpful comments on a draft of this manuscript. Figures 1, 2, and 4 are reproduced with the generous permission of the original authors, Jack Baldwin, Paul Francis, & Anne Kinney, respectively. Support for our research is provided by the NSF to PSO through grant AST-9529324, and by NASA to JCS through grants NAG-3563 and NAG-3690.