LONDON: Astronomers are studying rising galaxies in the early years of the world using a unique Hubble Space Telescope survey, and they presented a host of results at the winter meeting of the American Astronomical Society.
The survey, known as 3D-HST and led by Pieter van Dokkum (Yale University), fleshes out an existing set of Hubble images with spectroscopy, adding a third dimension to a previously two-dimensional view.
Hubble spent about a month collecting near-infrared spectra of galaxies living in a universe less than half its current age. The short observing time netted an incredible amount of data: “The unique ‘slitless’ nature of the 3D-HST observations provides simultaneous high-quality spectra of everything in the HST field-of-view,” says Gabriel Brammer (Space Telescope Science Institute).
The precise distance measurements add a third dimension to tens of thousands of galaxies detected in CANDELS, Hubble’s single largest observing program, featured in Sky & Telescope’s June 2014 issue.
In a younger universe, star formation and the galaxies’ growth spurts that accompany it are at their peak. By measuring galaxies’ spectra, the 3D-HST team homes in on galaxies’ hey-day to learn about their masses and star-formation histories. Combining those data with observations at other wavelengths, such as X-ray and radio, researchers have started exploring how galaxies formed their stars and why they stopped.
Erica Nelson (Yale University) has been using 3D-HST to analyze the shapes and structures of star-forming galaxies similar to the Milky Way. Since stars ionize hydrogen gas in their vicinity, creating an H-alpha spectral line (which may be familiar to solar observers who view the Sun through H-alpha filters), tracking H-alpha emission traces the birth of stars.
Nelson mapped H-alpha in a thousand disk galaxies in a universe half its current age. She found that these galaxies grow by forming stars along their entire pancake-like structures. That’s unlike the precursors to modern-day elliptical galaxies, also studied with 3D-HST, which first form stars in their central bulges before star formation spreads outward.
