Sheth '93 leads Hubble research on galactic bars
A frequent sign of the maturity of a spiral galaxy is the formation of a ribbon of stars and gas that slices across the nucleus, like the slash across a "no smoking" sign.
In a landmark study of more than 2,000 spiral galaxies, a team led by Kartik Sheth '93 found so-called barred spiral galaxies were far less plentiful 7 billion years ago than they are today.
Bars have been forming steadily over the last 7 billion years, more than tripling in number. "The recently forming bars are not uniformly distributed across galaxy masses, however, and this is a key finding from our investigation," Sheth explained. "They are forming mostly in the small, low-mass galaxies, whereas among the most massive galaxies, the fraction of bars was the same in the past as it is today."
The results of the study, part of the largest galaxy census conducted by NASA's Hubble Space Telescope -- the Cosmic Evolution Survey (COSMOS) -- confirm the idea that bars are a sign of galaxies reaching full maturity as the "formative years" end.
The findings, Sheth continued, have important ramifications for galaxy evolution. "We know that evolution is generally faster for more massive galaxies: They form their stars early and fast and then fade into red disks. Low-mass galaxies are known to form stars at a slower pace, but now we see that they also made their bars slowly over time," he said.
Sheth -- a research astronomer at Spitzer Science Center, California Institute of Technology -- led an international team of scientists who analyzed information from COSMOS. COSMOS covers an area of sky nine times larger than the full moon, surveying 10 times more spiral galaxies than previous observations. In support of the Hubble galaxy images, the team derived distances to the galaxies in the COSMOS field using data from Hubble and an assortment of ground-based telescopes.
For more information, see: Barred Spiral Galaxies Are Latecomers to the Universe (HubbleSite)
Image courtesy of: NASA, ESA, K. Sheth (Spitzer Science Center, California Institute of Technology), and P. Capak and N. Scoville (California Institute of Technology)
Information from: Space Telescope Science Institute and Spitzer Science Center