NASA JPL Spitzer | sig10-018 | 18 Aug 2010
Galaxies' Glory Days RevealedAstronomers have found that stars are forming more rapidly in the center of a distant galaxy cluster than at its edges, which is completely reversed from galaxy clusters seen in the local universe. This cluster, designated CLG J02182-05102, is shown in the call-out..
The image combines infrared light from NASA's Spitzer Space Telescope with visible light from Japan's Subaru telescope atop Mauna Kea, Hawaii. This sensitive exposure captures galaxies that are relatively local along side some that date back almost 10 billion years, soon after the Big Bang. The most distant galaxies stand out clearly in the infrared, rendered here in green and red.
What is noteworthy is how many of these galaxies are particularly bright at the longest infrared wavelengths, appearing red in this image. This glow indicates these ancient galaxies are still actively forming stars, even near the core of the cluster. In our local portion of the universe, the cores of galaxy clusters are known to be galactic graveyards full of massive elliptical galaxies composed of old stars.
The group's discovery holds potentially compelling implications that could ultimately reveal more about how such massive galaxies form. Now that they have pinpointed the epoch when galaxy clusters are making the last of their stars, astronomers can focus on understanding why massive assemblies of galaxies transition from very active to passive. The galaxies here may represent a missing link between the active galaxies and the quiescent behemoths that live in the local universe.
Infrared light from Spitzer at wavelengths of 4.5 and 24 microns is rendered in green and red, respectively. Subaru observations of visible light at a wavelength of 0.7 microns are rendered in blue. These data are part of the Spitzer Wide-area InfraRed Extragalactic (SWIRE) survey.
Credit: NASA/JPL-Caltech/K. Tran (Texas A&M)
NASA JPL Spitzer | feature10-14 | 18 Aug 2010
Hidden Star Power RevealedAstronomers have experienced the galactic equivalent of discovering pictures of a mild-mannered grandmother partying as a wild youth. New observations from NASA's Spitzer Space Telescope reveal the early "wild" days of galaxy clusters -- a time when the galaxies were bursting with new stars.
What is particularly striking is the fact that the stellar birth rate is higher in the cluster's center than at its edges -- the exact opposite of what happens in our local portion of the universe, where the cores of galaxy clusters are known to be galactic graveyards.
The discovery, made by an international team of researchers led by Kim-Vy Tran of Texas A&M University, College Station, could ultimately reveal more about how such massive galaxies form.
Tran and her team spent the past four months analyzing images taken by Spitzer, essentially looking back in time nearly 10 billion years at a distant galaxy cluster known as CLG J02182-05102. Mere months after first discovering the cluster and the fact that it is shockingly "modern" in its appearance and size for its age, the team was able to determine that the galaxy cluster produces hundreds to thousands of new stars every year. That is a far higher birth rate than that of galaxies relatively near to us.
"We have revealed the missing link between the active galaxies and the quiescent behemoths that live in the local universe," said Tran.
Texas A&M | College of Science | 18 Aug 2010
Reversal of Fortune: Confirmation of an Increasing Star Formation-Density Relation in a Cluster at z=1.62 - KH Tran et alMuch like quiet, middle-aged baby boomers peacefully residing in some of the world's largest cities, families of some galaxies also have a hidden wild youth that they only now are revealing for the first time, according to research by astronomers at Texas A&M University.
In ongoing observations of one of the Universe's earliest, most distant cluster of galaxies using NASA's Spitzer Space Telescope, an international team of researchers led by Texas A&M's Dr. Kim-Vy Tran has discovered that a significant fraction of those ancient galaxies are still actively forming stars.
Tran, an assistant professor in the Texas A&M Department of Physics and Astronomy and member of the George P. and Cynthia Woods Mitchell Institute for Fundamental Physics and Astronomy, and her team have spent the past 4 months analyzing images taken from the Multiband Imaging Photometer for Spitzer (MIPS), essentially looking back in time nearly 10 billion years at a high red-shift cluster known as CLG J02182-05102. Mere months after first discovering the cluster and the fact that it is shockingly "modern" in its appearance and size despite being observed just 4 billion years after the Big Bang, the Texas A&M-led team was able to determine that the galaxy cluster produces hundreds to thousands of new stars every year -- a far higher birthrate than what is present in nearby galaxies.
What is particularly striking, according to Tran, is the fact that the stellar birthrate is higher in the cluster's center than at the cluster's edges -- the exact opposite of what happens in our local portion of the Universe, where the cores of galaxy clusters are known to be galactic graveyards full of massive elliptical galaxies composed of old stars.
"A well-established hallmark of galaxy evolution in action is how the fraction of star-forming galaxies decreases with increasing galaxy density," explains Tran, lead author of the team's study which appears in The Astrophysical Journal Letters. "In other words, there are more star-forming galaxies in the field than in the crowded cores of galaxy clusters. However, in our cluster, we find many galaxies with star-formation rates comparable to their cousins in the lower-density field environment."
Exactly why this star power increases as galaxies become more crowded remains a mystery. Tran thinks the densely-populated surroundings could lead to galaxies triggering activity in one another, or that all galaxies were extremely active when the Universe was young.
The group's discovery holds potentially compelling implications that could ultimately reveal more about how such massive galaxies form. Observations of nearby galaxy clusters confirm that they are made of stars that are at least 8 to 10 billion years old, which means that CLG J02182-05102 is nearing the end of its hyperactive star-building period.
- Astrophysical Journal Letters 719(2) L126 (20 Aug 2010) DOI: 10.1088/2041-8205/719/2/L126
arXiv.org > astro-ph > arXiv:1005.5126 > 27 May 2010 (v1), 04 Aug 2010 (v2)