Xiaohui Fan Discusses Discovering Distant Quasars

Fast Moving Front Commentary, September 2010

Xiaohui Fan

Article: Constraining the evolution of the ionizing background and the epoch of reionization with z similar to 6 quasars. II. A sample of 19 quasars

Authors: Fan, XH, et al.
Journal: ASTRON J, 132 (1): 117-136 JUL 2006
Addresses:Univ Arizona, Steward Observ, Tucson, AZ 85721 USA.
Univ Arizona, Steward Observ, Tucson, AZ 85721 USA.
Princeton Univ Observ, Princeton, NJ 08544 USA.
Univ Calif Davis, Dept Phys, Davis, CA 95616 USA.
(Addresses have been truncated)

Xiaohui Fan talks with ScienceWatch.com and answers a few questions about this month's Fast Moving Fronts paper in the field of Space Science.

SW: Why do you think your paper is highly cited?

For two reasons: first, the paper addressed one of the frontier questions in astrophysics—"When did the so-called "cosmic reionization" take place in the universe?" This refers to the process that transformed the thermal state of the universe resulting from the formation of the first generation of stars and galaxies a few hundred million years after the Big Bang. Second, it did so by presenting the analysis at the time the largest and most complete dataset, a sample of 19 distant quasars which are all about 13 billion light years away.

SW: Does it describe a new discovery, methodology, or synthesis of knowledge?

This is a follow-up work of a main discovery we made in 2001/2002. At that time, we discovered the Gunn-Peterson absorption. Gunn and Peterson (1965) predicted that spectra of quasars at or beyond reionization will exhibit a complete absorption feature, which was first confirmed by a distant quasar we discovered in 2001. The 2006 work here presented a much large dataset, and a more detailed analysis to map the evolution of quasar spectra during that epoch.

SW: Would you summarize the significance of your paper in layman's terms?

"...e Sloan Digital Sky Survey, which is the largest and most ambitious survey of the deep Universe."

Our work established that the universe went through a very rapid transition at about or slightly before one billion years after the Big Bang. This transition is a result of the earliest generation of objects—galaxies and quasars—being formed in the Universe. Therefore, it is directly related to the question of when the first objects, or first light, appeared in the Universe after the Big Bang.

SW: How did you become involved in this research, and how would you describe the particular challenges, setbacks, and successes that you've encountered along the way?

This work was the result of a long-term project. It was based on data obtained in the Sloan Digital Sky Survey, which is the largest and most ambitious survey of the deep Universe. We started studies of quasars in the Sloan Survey from 1998. This work is really one of the highlight of our decade-long project, which started out when I was still a graduate student.

The most challenging aspect is certainly how to discover these distant quasars, which required us to look through databases of hundred of millions of objects. It is literally looking for needles in a haystack.

SW: Where do you see your research leading in the future?

We are still continuing the studies of the "reionization epoch" and the formation of first objects in the Universe. What we concluded in our 2006 paper was that we were only detecting the end of this important epoch, and to find out exactly when the first light happened, we have to look even deeper in space and time. This is the focus of our research in the future.

SW: Do you foresee any social or political implications for your research?

Not specifically about this research. But I think the big picture question is one that is as old as our civilization: How did the Universe begin? How does it evolve? How did complex structure of the world that we live in (for astronomers, that means stars, planets, galaxies etc.) come about?End

Xiaohui Fan
Professor of Astronomy
Steward Observatory
The University of Arizona
Tucson, AZ, USA




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