Marcelo Alvarez is the recipient of the 2013 Jeffrey L. Bishop Fellowship


Alvarez was awarded the Bishop Fellowship for his outstanding work in cosmology, particularly his recent research on how the universe was re-ionized by energetic small galaxies so efficient they eventually could no longer form. He explained his work this way:

“We think the universe was re-ionized about a billion years after the Big Bang which meant that the first stars that formed heated all of the gas and ionized all the hydrogen gas in the universe, and so one question that’s always come up is, ‘were the galaxies that we see enough to ionize the universe, or, is there a hidden population of fainter galaxies that is present but just too faint for us to see that were the main sources of ionizing radiation to re-ionize the universe?”

Alvarez theorized that galaxies in the early universe too small to see with existing technology formed stars just as efficiently as the large galaxies that we see do and in addition released much more of their ionizing radiation into the surrounding space.

“Our theory was that small galaxies have a higher escape fraction, the fraction of the ionizing photons that actually get out of the galaxy, and the idea behind that is that a large galaxy like a spiral galaxy with a flattened disk has many of the stars forming within dense gas clouds that are very large. The starlight that is put out by those stars is absorbed locally within the galaxy and converted into heat or infrared radiation and does not contribute to the re-ionization of the universe. Our theory was that the small galaxies that form are more irregular in morphology and therefore when they form stars the radiation has a much easier time escaping from those galaxies so . . . they could have re-ionized the universe. . . . We don’t see those galaxies now because in a re-ionized universe where the gas has been heated, those small galaxies have a much harder time forming. It’s as though those galaxies re-ionized the universe but they were so good at what they did that they made it difficult for smaller galaxies to form after them, and since most of what we see now is in the re-ionized universe we don’t see those galaxies now.”

His recent publications on the theory of re-ionization include:

“Constraints on the Ionizing Efficiency of the First Galaxies” (Alvarez, Finlator & Trenti, 2012, ApJL, 759, 38).

“The Effect of Absorption Systems on Cosmic Reionization” (Alvarez & Abel, 2012, ApJL, 747, 126).

“The Opacity of the Intergalactic Medium during Reionization: Resolving Small-scale Structure” (Emberson, Thomas & Alvarez, 2013, ApJ, 763, 146).

Alvarez is a Post-Doctoral Fellow at CITA and has been promoted to Senior Research Associate effective September 2013.

The Jeffrey L. Bishop Fellowship is granted every two years for excellence in research in astrophysical dynamics.

Jeffrey Bishop was one of CITA’s first postdoctoral fellows. He was killed in an automobile accident shortly after leaving the Institute and this award was one of several created by his mother, Mrs. Muriel Simmons, to remember his life and work. Her donation is matched by CITA.

Published on: August 23, 2013

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