Groundbreaking observations carried out in Chile using a new type of radio telescope have lead to the discovery of 10 massive new galaxy clusters.  Among the team of international scientists contributing to that discovery, described in a paper published in the November 10 issue of Astrophysical Journal, was Haverford astronomer Bruce Partridge and several of his students.

Now an emeritus professor of astronomy, Partridge, who began teaching at Haverford in 1970, has been involved with the Atacama Cosmology Telescope (ACT), from its very beginning more than six years ago.“It is a massive structure, with a six-meter antenna housed in a large reflective“basket” at 17,250 feet in the Andes,” says Partridge of the telescope, which is located in Chile's Atacama Desert, known as one of the driest places on Earth.

The high and dry conditions are crucial because ACT collects millimeter-length radio waves, which are obscured by atmospheric moisture.  Those millimeter waves are what allowed researchers to discern the“shadows” of the galaxy clusters on the cosmic microwave background radiation (CMB).  The galaxy clusters revealed by this research are the largest stable systems in the Universe, containing up to 1000 individual galaxies and vast amounts of hot gas.

Partridge, whose own research has employed radio astronomy to answer questions about the origin and evolution of galaxies and clusters of galaxies, has long been interested in CMB radiation, which is the“heat” left over from the Big Bang.  He was one of the first scientists to search for fluctuations in its intensity, which can offer information about the early history of the Universe.  Partridge was also closely involved from the beginning with the Planck Satellite (which is measuring the CMB from a million miles out)  and was present for its launch in 2009.

With the ACT project, whose main research centers are located at Princeton, Rutgers, Penn and several Chilean Universities, Partridge's primary role has been to make supporting observations at radio frequencies below those used at ACT to help determine what kinds of radio sources ACT is picking up. “These are mostly distant radio galaxies, and most of my supporting observations were made at the Very Large Array of telescopes in New Mexico,” Partridge says.  Aiding him in those observations have been Anna Sajina, a postdoctoral fellow who has been a visiting professor at Haverford, and several Haverford astronomy students. Among them:  Quentin Sherman '12, Ben Walter '13, and Nick Vechik and Tyler Evans, both Class of 2010.

Evans, a physics and astronomy major, got to travel to the ACT facility in Chile last January, with the help of funding from Haverford, Partridge's research grant and Princeton University, where he had spent a summer working on instrument design. “Mostly I worked on maintenance and upkeep on the telescope,” says Evans, who is currently pursuing a Ph.D. in astronomy at Swinburne University in Melbourne, Australia. “They shut down operations from the end of January through the beginning of March, because that is the time of year when there is the most moisture in the atmosphere there and it is hardest to make good observations.  So, while I was at the site I was mostly taking calibrations and making sure that the telescope was in good order to be shut down.”

“It is a measure of the skills and maturity of our students that Tyler was handed responsibilities normally reserved for postdocs and graduate students,” says Partridge. “It is a measure of the ACT team spirit that he got to do interesting stuff like calibrations, while the ACT team leader, Lyman Page, and I spent the next couple of weeks working on vacuum pumps, nailing up siding and wiping soot off the generators.  But who'd miss a chance to eat real Chilean empanadas, drive to work through herds of llamas and drink coca tea to fight the altitude?”

--Eils Lotozo