Last week an international group of astronomers unveiled the most complete 3-D map of the local Universe to great worldwide fanfare, not to mention the immense pride of one of the map’s creators, Texas A&M astronomer Lucas Macri.
Macri, assistant professor of physics and astronomy and a member of Texas A&M’s George P. and Cynthia Woods Mitchell Institute for Fundamental Physics and Astronomy, is one of the leading members of the team that created the map, which contains galaxies as far as a billion light-years from Earth. Known as the 2MASS Redshift Survey (2MRS), it is the result of a decade-long effort initiated by an astronomical legend, the late Dr. John Huchra, a longtime astronomer at the Harvard-Smithsonian Center for Astrophysics.
Karen Masters (University of Portsmouth, United Kingdom) presented the new map in a Wednesday (May 26) press conference at the 218th meeting of the American Astronomical Society, crediting Huchra for his masterpiece.
“The 2MASS Redshift Survey is a wonderfully complete new look at the local Universe, particularly near the Galactic plane [a region generally obscured by dust],” Masters said. “We’re also honoring the legacy of the late John Huchra, who was the leader and 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.
The 2MRS team chose 45,000 galaxies based on images made by the 2 Micron All-Sky Survey (2MASS). This survey scanned the entire sky in three near-infrared wavelength bands. Near-infrared light, which Macri notes we feel as heat, penetrates intervening dust better than visible light, allowing astronomers to see more of the sky. The dust can be thought of as cosmic smoke, and observing in the near-infrared allows us to clear away the smoke to see the Universe clearly.
However, without adding redshifts, 2MASS makes only a 2-D image. Many of the galaxies mapped had previously-measured redshifts, but 11,000 new ones were measured by Huchra, Macri and collaborators starting in the late 1990s using mainly two telescopes: one at the Fred Lawrence Whipple Observatory on Mount Hopkins, Ariz., and one at the Cerro Tololo Inter-American Observatory in Chile. The last observations were completed shortly after Huchra’s death in October 2010.
Macri, who is the corresponding author in the resulting paper that will soon be published, completed his doctorate in astronomy at Harvard in 2001 under Huchra, who put the CfA on the international astronomical map 25 years ago with one of the first redshift surveys.
“The focus of 2MRS is to answer how much dark matter is there in the local Universe — out to about 400 million light years in radius — and to understand why the Milky Way is moving through the Universe at its present speed and direction,” Macri said.
The 2MRS mapped in detail areas previously hidden behind our Milky Way. 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.
Macri noted that Texas A&M astronomers are involved in another historical mapping project, the Hobby-Eberly Telescope Dark Energy Experiment (HETDEX), an international collaboration led by The University of Texas at Austin to investigate dark energy in the early universe. The $34 million project will harness the extensive light-gathering power of the world’s third-largest telescope, the Hobby-Eberly Telescope, and the world’s premier survey spectrograph being assembled and aligned at Texas A&M to produce the largest map of the Universe to date by pinpointing the positions of more than one million far-off galaxies in three dimensions. The goal is to measure how the Universe expands over time, revealing unprecedented information about dark energy, and to measure the “geometry” of our Universe to very high precision to give astronomers direct information about the state of the Universe at a time less than one second after the Big Bang.
“HETDEX will give us a 3-D map of a large volume of the Universe, but it will ‘only’ cover 1 percent of the surface of the entire sky,” Macri said. “For comparison, 2MRS covers 95 percent of the entire sky out to a very shallow depth — astronomically speaking, of course — of 400 million light-years, yielding a volume that is about 1,000 times smaller than the one to be surveyed by HETDEX. If you compare a survey of the Universe to a study of the Earth, HETDEX would be the equivalent of getting very deep geological information for two regions covering an area about 7 times the size of Texas, whereas 2MRS would be akin to mapping the near-surface features of our planet — mountains, coastlines, ocean rifts, etc. — for 95 percent of its surface. Just as both types of geological surveys are useful for answering different questions about the Earth, 2MRS and HETDEX complement each other in our study of the Universe.”
Macri, a joint holder of the Mitchell-Heep-Munnerlyn Career Enhancement Professorship in Physics and Astronomy, joined the Texas A&M faculty in 2008 after spending six years as a postdoctoral Hubble Fellow and Goldberg Fellow at the National Optical Astronomy Observatory (NOAO) in Arizona. His research focuses on the extragalactic distance scale, resolved stellar populations and near-field cosmology. He is an expert in Cepheid variables, which he studies using the Hubble Space Telescope, the Gemini North telescope and other observatories. In addition to authoring more than 50 referred publications, he is a member of the SH0ES team, an international collaboration that is using Cepheid variables — specifically, measurements of their luminosity — to help refine the Hubble constant and thereby narrow alternative explanations for dark energy in the Universe.
Learn more about the 2MASS Redshift Survey.
Find more information about Macri’s research and astronomy at Texas A&M.
News release includes significant contributions from the Harvard-Smithsonian Center for Astrophysics.