Texas A&M Astronomers Find Baby Galaxies in Early Universe
COLLEGE STATION —
Armed with a sample of the deepest near-infrared images yet, captured by NASA’s new Wide Field Camera 3 (WFC3) on board the Hubble Space Telescope, Texas A&M University astronomers Dr. Casey Papovich and Dr. Steven Finkelstein along with their collaborators have completed their initial analysis of the light from 35 galaxies formed between 500 and 800 million years after the Big Bang — likely some of the most distant galaxies ever identified.
The new Hubble images, which are being intensely studied by several groups around the world, have opened unprecedented doors for Papovich, Finkelstein and their team — Mauro Giavalisco from the University of Massachusetts, Naveen A. Reddy and Mark Dickinson from the National Optical Astronomy Observatory (NOAO), and Henry C. Ferguson and Anton M. Koekemoer from the Space Telescope Science Institute (STScI) — to delve into just some of the mysteries surrounding the evolution of galaxies that, in turn, can be used to probe conditions at the beginning of the Universe.
Finkelstein recently presented the group’s results — detailed in the paper On the Stellar Populations and Evolution of Star-Forming Galaxies at 6.3 < z < 8.6 available online at http://arxiv.org/abs/0912.1338 — Jan. 6 at the 215th meeting of the American Astronomical Society (AAS) in Washington, D.C.
By comparing the dust and metal content of the newly-discovered galaxies to that of typical local star-forming galaxies, the team found that their galaxies were significantly bluer in appearance, indicating lower “metallicity” and implying smaller amounts of heavier elements, such as carbon, nitrogen, oxygen or iron (which are fused over time in the cores of stars) relative to hydrogen and helium (products of the Big Bang). After comparing them with the bluest nearby galaxies, the team concluded that, while their galaxies were fairly primitive in composition, they did not have zero metallicity, meaning that these galaxies contain stars not unlike those we see today, even though the Universe was only five percent of its current age of 13.7 billion years. This implies that they are not the first-ever galaxies formed after the Big Bang as other international teams of astronomers analyzing the same data have implied.
Papovich explains that these newly-identified galaxies are so far away that they can only viewed with the WFC3, which collects the light from near-infrared wavelengths and enables a deeper look into the Universe. Although the WFC3 can take visible-light images, its capability to detect light just bluer than the eye can see, or the near ultra-violet, and light just redder than the eye can see, or the near-infrared, makes its viewing power unparalleled to anything else.
“These galaxies are completely invisible in optical light,” says Papovich, an observational astronomer and assistant professor in the Texas A&M Department of Physics and Astronomy since 2008. “They are moving away at 97 percent the speed of light, or 180,000 miles per second. These are the most distant things anyone has found. The WFC3 is the only camera that can see them.”
The WFC3 captured the images last August when the Hubble Space Telescope spent nearly three days focusing on a tiny area in the sky less than one percent the angular area of a full moon known as the Hubble Ultra Deep Field (HUDF). The WFC3 is so powerful, it was able to capture objects one billion times fainter than what the human eye can see.
When they found objects apparent in the WFC3 infrared data that were either very red or nonexistent in the optical image of Hubble’s main camera, the Advanced Camera for Surveys (ACS), Papovich and Finkelstein realized that they had come across some of the most distant galaxies ever.
“Our goal was to do a detailed analysis to understand the physical make-up of these galaxies,” says Finkelstein, an astrophysics postdoctoral research associate in Texas A&M’s George P. and Cynthia Woods Mitchell Institute for Fundamental Physics and Astronomy since 2008. “We have been studying in detail over the last few decades or so what galaxies at lower redshifts look like. By comparing them to a higher redshift galaxy, we can really gain a sense of how galaxies are evolving.”
By comparing images of the galaxies’ redshift — the distance the light of a galaxy stretches as the Universe expands that astronomers rank numerically — Finkelstein concluded that these galaxies appear to have a redshift of 7 to 8. Until only a few months ago, the most distant galaxies had a redshift of about 6.5 to 7.
To put it in perspective, the light in the images of the objects Papovich and Finkelstein studied left 13 billion years ago, around the time when the Universe was only 700 million years old.
While not the first galaxies ever formed, Papovich’s and Finkelstein’s discoveries do a hold another important key to understanding the formation of the Universe. By measuring these galaxies’ stellar mass, they found them to be anywhere from one to 10 percent as massive as the Milky Way. Because typical galaxies at only a redshift of 3 are about as massive as the Milky Way, the findings are a substantial indicator of strong evolution in typical galaxies over only one billion years of cosmic time.
Essentially, these newly-discovered galaxies are the building blocks of present-day galaxies.
“Putting all of the pieces above together, it really does look like at redshifts of 7 to 8, we are really probing the era of baby galaxies,” Finkelstein explains. “The larger, Milky-Way-size galaxies that are common at lower redshifts are nowhere to be seen, and everything we see appears to be fairly young and primitive. We have not yet found the infant galaxies, containing the metal-free stars, but with the launch of the James Webb Space Telescope in 2014/2015, we should come awfully close.”
Named after former NASA administrator James E. Webb, renowned for heading the fledgling NASA program from 1961 to 1968, the James Webb Space Telescope (JWST) contains a mirror 6.5 meters in diameter and a sunshield the size of a tennis court. It is specially designed to find the very first galaxies created in the early Universe and to link the Big Bang to our own Milky Way galaxy.
Though Papovich’s and Finkelstein’s analysis of 35 of the most distant galaxies ever found has premier implications regarding the Universe’s origins, the first several hundred million years after the Big Bang still harbor many unanswered questions. Until the first images from the JWST are made available, Papovich and Finkelstein say they will continue to push forward with the resources they do have.
“Between the first 700 million years, there’s stuff that went on that we still want to find out about,” Papovich adds. “We have to go to the limits of the current technology in order to go to the next level.”
Finkelstein will present a public talk on these results next week at the monthly Astronomy Open House, scheduled for Friday (Jan. 29), from 7:30 to 9:30 p.m. at the Texas A&M Campus Observatory.
Learn more about the team’s research as well as additional information regarding Texas A&M Astronomy.
Contact: Chris Jarvis, (979) 845-7246 or email@example.com; Dr. Casey Papovich, (979) 845-7017 or firstname.lastname@example.org; or Dr. Steven Finkelstein, (979) 862-1763 or email@example.com.
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