January 5, 2010
Shown in an extremely broad range of color and showcasing more than 12 billion years of cosmic history, Hubble's recent image is a full-glory cosmic renaissance of the history of the Universe. This image provides a record of the Universe's most exciting formative years, from the birth of stars in the early Universe all the way through the materialization of the Milky Way.
Constructed from mosaics taken with the newly installed Wide Field Camera 3 (WFC3) in fall 2009 and Hubble Space Telescope's Advanced Camera for Surveys (ACS) taken in 2004, the final image combines a broad range of colors, from the ultraviolet, through visible light, into the near infrared. Such a detailed multi-color view of the Universe has never been assembled before at such a level of clarity, accuracy and depth.
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"It's like taking off rose-colored glasses and seeing the Universe in a whole new light, and what we're seeing is fantastic," says Rogier Windhorst, a professor in the School of Earth and Space Exploration, an academic unit of the College of Liberal Arts and Sciences at Arizona State University, and a member of the WFC3 Science Oversight Committee. "We're seeing stars on a galactic scale being born, we're seeing galaxies in formation, galaxies replenished with new fuel for making stars. We're seeing a messy Universe, a Universe in action, and we're seeing it like astronomers have never seen it before."
Hubble's sharp resolution and new color versatility, accomplished by combining data from the two cameras, is allowing astronomers to sort out the various stages of galaxy assembly, from the mature spiral and elliptical galaxies in the foreground, to smaller, fainter, irregularly shaped galaxies that are in general farther away, and hence existed farther back into time. These smaller galaxies are considered the building blocks of the larger galaxies that we see today. The wide range of new colors now observed with WFC3 also allows astronomers to estimate a galaxy's distance from Earth, and reveal information about its stellar populations.
Acquiring this image was much more time intensive than simply pointing and shooting. The data that comes off the telescope is in a raw form that requires processing. The Science Oversight Committee designed a science program to test and demonstrate the science capabilities of the WFC3, referred to as Early Release Science (ERS) data. Windhorst and students in the School of Earth and Space Exploration have been involved in the processing and analyzing the ERS data, spending the better part of July and August calibrating the data and removing background artifacts.
"Certain instrumental effects and cosmetic problems have to be taken out," explains Seth Cohen, a postdoctoral research associate in SESE. "Some artifacts are due to cosmic rays or satellites, while others are due to the detectors themselves. You have to remove all these things before you can do the science. You don't want to mistake the residual effects of these in your image if they are not due to something in your galaxy of interest."
"Your eye is very good at picking out the artifacts, but you have to train a computer to do this and use software to reduce these out," says Michael Rutkowski, a graduate student in SESE who has worked on preparing the image.
The image shows a rich tapestry of 7,500 galaxies stretching back through most of cosmic history. The closest galaxies seen in the foreground emitted their observed light only 0.9 billion years ago. The farthest galaxies, a few of the very faint red specks, are seen as they appeared more than 13 billion years ago, or roughly 650 million years after the Big Bang. This mosaic spans a slice of space that is 10 arc minutes across in its largest diameter, or about one-third of the diameter of the full Moon in the sky.
The new Hubble view highlights a wide variety of stages in the galaxy assembly process. The WFC3 ultraviolet light shows the blue glow of hot, young stars in galaxies teeming with star-birth. The orange light reveals the nearly final assembly stages of massive galaxies about 8 billion to 10 billion years ago. The near infrared reveals the red glow of very distant galaxies – in a few cases as far as 12 billion to 13 billion light years away – whose light has been stretched, like a toy Slinky, from ultraviolet light to longer-wavelength infrared light due to the expansion of the Universe.
The region covers a portion of the Great Observatories Origins Deep Survey's (GOODS) Southern field, first observed by Hubble with the ACS in 2004, and now with Hubble's new WFC3 from September to October 2009.
In this ambitious use of Hubble's observing time, the 2004 ACS exposures totaled over 100 orbits in the optical in this portion of the sky, and the new WFC3 exposures total 104 orbits in the ultraviolet and near-infrared. The image was made from a mosaic of 2x4 WFC3 ultraviolet pointings, and 2x5 WFC3 near-infrared pointings. In just two orbits per pointing, the WFC3 peered deeper into the Universe than comparable near-infrared observations from ground-based telescopes. This set of unique new Hubble observations reveals galaxies to about 27th magnitude in brightness over a factor of 10 in wavelength.
"Having this broad spectrum wavelength coverage allows us to do many different things that we couldn't do before without having deep observations at all these wavelengths at the Hubble resolution," Cohen says.
Astronomers are using this multi-color panorama to trace many details of galaxy formation over cosmic time: the star-formation rate in galaxies, the rate of mergers among galaxies, and the abundance of weak active galactic nuclei, along with many other measurable quantities.
Rutkowski is most excited about the panchromatic nature, particularly the UV capabilities since UV astronomy can't be done from the ground.
"My interest is in elliptical galaxies known as "red and dead galaxies." We believed that there wasn't much going on by way of current star formation in these galaxies, but as the UV becomes more accessible, there are a lot of red and dead galaxies that are actually quite blue. This image suggests that they're neither as red nor as dead as we originally thought."