CfA: Most Complete 3-D Map of Local Universe

[bystander]

Astronomers Unveil Most Complete 3-D Map of Local Universe
Harvard Smithsonian Center for Astrophysics | 2011 May 25

[url=http://www.cfa.harvard.edu/news/2011/pr201116_images.html][b]The 2MASS Redshift Survey (2MRS) [i](Credit: T.H. Jarrett (IPAC/SSC))[/i][/b][/url]

---

---

Today, astronomers unveiled the most complete 3-D map of the local universe (out to a distance of 380 million light-years) ever created. Taking more than 10 years to complete, the 2MASS Redshift Survey (2MRS) also is notable for extending closer to the Galactic plane than previous surveys - a region that's generally obscured by dust.

Karen Masters (University of Portsmouth, UK) presented the new map today in a press conference at the 218th meeting of the American Astronomical Society.

"The 2MASS Redshift Survey is a wonderfully complete new look at the local universe - particularly near the Galactic plane," Masters said. "We're also honoring the legacy of the late John Huchra, an astronomer at the Harvard-Smithsonian Center for Astrophysics, who was a guiding force behind this and earlier galaxy redshift surveys."

A galaxy's light is redshifted, or stretched to longer wavelengths, by the expansion of the universe. The farther the galaxy, the greater its redshift, so redshift measurements yield galaxy distances - the vital third dimension in a 3-D map.

2MRS chose galaxies to map from images made by the Two-Micron All-SkySurvey (2MASS). This survey scanned the entire sky in three near-infrared wavelength bands. Near-infrared light penetrates intervening dust better than visible light, allowing astronomers to see more of the sky. But without adding redshifts, 2MASS makes only a 2-D image. Some of the galaxies mapped had previously-measured redshifts, and Huchra started painstakingly measuring redshifts for the others in the late 1990s using mainly two telescopes: one at the Fred Lawrence Whipple Observatory on Mt. Hopkins, AZ, and one at the Cerro Tololo Inter-American Observatory in Chile. The last observations were completed by 2MRS observers on these telescopes shortly after Huchra's death in October 2010.

Robert Kirshner, Huchra's colleague at the Center for Astrophysics (CfA), said, "John loved doing redshift surveys and he loved the infrared. He had the insight to tell when infrared technology, formerly the province of the experts, was ripe for routine use in a big project."

"John was instrumental in setting up the 2MASS telescope at Mount Hopkins, seeing the infrared side of the project through, and making a much more complete survey of the local universe. It's a wonderful tribute to John that his colleagues have finished the infrared-selected galaxy redshift survey that John started," he added.

The 2MRS mapped in detail areas previously hidden behind our Milky Way to better understand the impact they have on our motion. The motion of the Milky Way with respect to the rest of the universe has been a puzzle ever since astronomers were first able to measure it and found it couldn't be explained by the gravitational attraction from any visible matter. Massive local structures, like the Hydra-Centaurus region (the "Great Attractor") were previously hidden almost behind the Milky Way but are now shown in great detail by 2MRS.

http://asterisk.apod.com/viewtopic.php?f=9&t=23947

[bystander]

The Earth is not at Rest
Smithsonian Astrophysical Observatory
Weekly Science Update | 2012 Apr 13

[i]A plot of the location in the sky of galaxies between about 280-420 million light-years of Earth. Distances are color coded with red, blue, and green representing equal bins of increasing distance in this range. A new study has measured the distances of 97.6% of galaxies within about one billion light-years of Earth. (Credit: J. Huchra et al. 2012)[/i]

---

---

The Earth is not at rest. It orbits the Sun, which in turn orbits the center of the Milky Way Galaxy, which in turn moves within the Local Group of Galaxies - a collection of about fifty four galaxies in our "neighborhood" (that is, within about ten million light-years of Earth). The Local Group itself is "falling" toward the Virgo Cluster of Galaxies, a set of over one thousand galaxies about fifty million lights years away in the direction of the constellation of Virgo, and whose gravity pulls the Milky Way. After the cosmic microwave background radiation was discovered in 1960, astronomers began searching for signs of these motions of Earth with respect to the background light. First hints came in the mid-1970s and 1980s, and signaled a serious problem: the measured motion of the Earth with respect to the cosmic background was considerably smaller than the sum of all the movements listed above. One possible solution was that our understanding of the distribution of galaxies was incorrect.

John P. Huchra, the distinguished CfA astronomer who tragically passed away eighteen months ago at the age of 61, was a pioneer in the study of the large scale structure of the universe. Together with his colleagues, he helped map the locations in space of nearly 20,000 of the nearest galaxies, revealing that the universe was not uniformly sprinkled with galaxies. Instead, the local universe appears to have a structure dominated by tremendous filaments, sheets and voids, including what became known as "the Great Wall," a thin sheet of galaxies about 600 million light-years wide, 250 million light-years high, and 30 million light-years deep - one of the largest known structures in the universe. The discovery helped resolve the mystery of the measured motion of Earth with respect to the cosmic background by finding these large structures and their gravitational influences. But even with this landmark effort, most of the galaxies in the larger neighborhood remained unstudied. Moreover, the precision of the results was considerably worse than the precision from newer cosmic background instruments, as breakthroughs like the acceleration of the universe helped confirm and fill out the larger cosmological picture.

During the ten years before his death, John had been working on another huge and significant project: studying each one of 44,599 galaxies seen in the infrared 2MASS survey to determine its distance, and so place it in an enlarged, much more complete and precise three-dimensional map of the universe near the Earth. This month that paper was published; his team of nineteen collaborators, to honor his leadership and scholarship, and his memory, made him the posthumous first author.

The paper uses new spectroscopic observations of eleven thousand galaxies, and archival spectra of the rest, to obtain a distance catalog that is 97.6% complete over 91% of the sky (to certain well-defined limits). It is an unprecedented accounting of all of the normal matter within about one billion light-years of Earth; in addition, it catalogs the morphological types of a nearly complete subsample of 20,860 galaxies. The result refines and completes the earlier work in an extremely uniform, deep, and unbiased survey of the nearby universe, and is a fitting tribute to the memory of this pioneering astronomer and admired colleague.

The 2MASS Redshift Survey — Description and Data Release - John P. Huchra et al

• Astrophysical Journal Supplement 199(2) 26 (2012 Apr) DOI: 10.1088/0067-0049/199/2/26
  arXiv.org > astro-ph > arXiv:1108.0669 > 02 Aug 2011 (v1) 19 Dec 2011 (v2)

<< Previous Science Update