OUT THERE 



Celestial MUSYC 



Cosmic ABCs keep astronomers spellbound. 



By Charles Liu 



Acronyms are everywhere, al- 

 phabetically infecting daily 

 life, IMHO (in my humble 

 opinion). So perhaps we astrono- 

 mers can be forgiven for slid- 

 ing down the slippery slope 

 of cryptic capital letters: 

 MHD (magnetohydrodyna- 

 mics), SETI (search for extra- 

 terrestrial intelligence), LGM 

 (little green men). 



Overall, though, we're pret- 

 ty good at keeping things un- 

 acronymed, giving fairly sim- 

 ple names to cosmic phenom- 

 ena. A reddish star that's really 

 big, for instance, is called a red 

 giant; a whitish star that's real- 

 ly small is a white dwarf. But 

 it's back to the ABCs when we 

 name our scientific projects, 

 from the strictly functional 

 (VLT for Very Large Tele- 

 scope) to the embarrassingly 

 cute (LALA for Large Area Ly- 

 man- Alpha survey). 



Lest you think I'm blame- 

 lessly poking fun at my col- 

 leagues, I freely admit my own 

 recent foray into acronymic 

 vanity. A couple of years ago, 

 I was invited to join a major 

 international scientific collaboration 

 that would examine four widely sep- 

 arated patches of sky, each a little larg- 

 er than the size of the full moon. The 

 survey would make images at many 

 wavelengths of electromagnetic radia- 

 tion (infrared, all the colors of visible 

 light, ultraviolet, and X-ray) with the 

 goal of examining how populations of 

 galaxies changed with the passage of 

 cosmic time. 



As work progressed on this ambitious 



cosmic survey, we realized we needed 

 a public name for our project. Mem- 

 bers of the team ruminated on this 

 question for days, weeks, even months. 



Who knows how much highly trained 

 scientific brainpower was siphoned 

 away from studying the mysteries of 

 creation for the creation of acronyms? 

 Finally, after dozens of candidates were 

 proposed, everyone agreed that the 

 acronym for our survey would ac- 

 knowledge the two primary institu- 

 tions in the collaboration: Yale Uni- 

 versity, and the University of Chile, in 

 Santiago. One question remained. 

 Would it be the Multiwavelength 



Survey by Chile-Yale (MUSCY), or 

 the Multiwavelength Survey by Yale- 

 Chile (MUSYC)? In the end, though a 

 MUSCY survey might smell good 

 enough, we agreed that MUSYC 

 would sound much more harmonious. 



Its whimsical name notwithstanding, 

 MUSYC has moved forward rapid- 

 ly. And perhaps not surprisingly, the 

 objects we have studied so far are gen- 

 erally referred to by their acronyms: 

 AGN, DRGs, and LAEs. AGN, active 

 galactic nuclei, are supermassive black 

 holes that act as gravitational dynamos 

 at the hearts of galaxies, con- 

 verting the potential energy of 

 infilling matter into powerful 

 outflowing jets and electro- 

 magnetic radiation. DRGs, 

 distant red galaxies, are, well, 

 galaxies that are distant (be- 

 tween 8 and 12 billion light- 

 years from Earth) and red, 

 emitting so much more red 

 light than blue light that it 

 sometimes looks as if their stars 

 are older than the universe it- 

 self [see "Seeing Red," by Charles 

 Liu, March 2005]. 



LAEs — Lyman-alpha emit- 

 ting galaxies or Lyman-alpha 

 emitters — are particularly in- 

 triguing as markers of cosmic 

 evolution, because they have no 

 obvious counterparts in the lo- 

 cal universe (AGN and DRGs 

 at cosmic distances — many bil- 

 lions of light-years away — have 

 similar counterparts closer by). 

 LAEs get their name from the 

 American physicist Theodore 

 Lyman, who in the early twen- 

 tieth century discovered that hydrogen 

 gas emits ultraviolet light. LAEs are 

 small, young, and bursting with new 

 stars. According to a study led by Eric 

 Gawiser, a postdoctoral fellow at Yile 

 and one of MUSYC s principal investi- 

 gators, they appear to be the primitive 

 progenitors of modern, mainstream 

 galaxies such as our own Milky Way. 



When an atom is struck by another 

 atom or a sufficiently powerful pho- 

 ton, the sudden influx of energy can 



September 2006 NATURAL history 



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