Astronomers ask 'where are all the dwarf galaxies?' | sci-english.blogspot.com

Cosmic Web Stripping | sci-english.blogspot.com

Astronomers of the international CLUES collaboration have identified "Cosmic Web Stripping" as a new way of explaining the famous missing dwarf problem: the lack of observed dwarf galaxies compared with that predicted by the theory of Cold Dark Matter and Dark Energy.

High-precision observations over the last two decades have indicated that our Universe consists of about 75% Dark Energy, 20% Dark Matter and 5% ordinary matter. Galaxies and matter in the universe clump in an intricate network of filaments and voids, known as the Cosmic Web. Computer experiments on massive supercomputers have shown that in such a Universe a huge number of small "dwarf" galaxies weighing just one thousandth of the Milky Way should have formed in our cosmic neighbourhood. Yet only a handful of these galaxies are observed orbiting around the Milky Way. The observed scarcity of dwarf galaxies is a major challenge to our understanding of galaxy formation.
An international team of researchers has studied this issue within the Constrained Local UniversE Simulations project (CLUES). The CLUES simulations use the observed positions and peculiar velocities of galaxies within Tens of Millions of light years of the Milky Way to accurately simulate the local environment of the Milky Way. "The main goal of this project is to simulate the evolution of the Local Group -- the Andromeda and Milky Way galaxies and their low-mass neighbours -- within their observed large scale environment," said Stefan Gottlöber of the Leibniz Institute for Astrophysics Potsdam.
Analysing the CLUES simulations, the astronomers have now found that some of the far-out dwarf galaxies in the Local Group move with such high velocities with respect to the Cosmic Web that most of their gas can be stripped and effectively removed. They call this mechanism "Cosmic Web Stripping," since it is the pancake and filamentary structure of the cosmos that is responsible for depleting the dwarfs' gas supply.
"These dwarfs move so fast that even the weakest membranes of the Cosmic Web can rip off their gas," explained Alejandro Benítez LLambay, PhD student at the Instituto de Astronomía Teórica y Experimental of the Universidad Nacional de Córdoba in Argentina, and first author of the publication of this study. Without a large gas reservoir out of which to form stars, these dwarf galaxies should be so small and dim that they would be hardly be visible today. The missing dwarfs may simply be too faint to see.

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Story Source:
The above story is based on materials provided by Leibniz-Institut für Astrophysik Potsdam (AIP). Note: Materials may be edited for content and length.

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Journal Reference:

1. Alejandro Benítez-Llambay, Julio F. Navarro, Mario G. Abadi, Stefan Gottlöber, Gustavo Yepes, Yehuda Hoffman, Matthias Steinmetz. Dwarf Galaxies and the Cosmic Web. The Astrophysical Journal, 2013; 763 (2): L41 DOI: 10.1088/2041-8205/763/2/L41

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3-D map of the adolescent universe | sci-english.blogspot.com

3D map of the cosmic web at a distance of 10.8 billion years from Earth | sci-english.blogspot.com

 

Using extremely faint light from galaxies 10.8-billion light years away, scientists have created one of the most complete, three-dimensional maps of a slice of the adolescent universe. The map shows a web of hydrogen gas that varies from low to high density at a time when the universe was made of a fraction of the dark matter we see today.

The new study, led by Khee-Gan Lee and his team at the Max Planck Institute for
Astronomy in conjunction with researchers at Berkeley Lab and UC Berkeley, will be
published in an upcoming issue of Astrophysical Journal Letters.
In addition to providing a new map of part of the universe at a young age, says David Schlegel of Berkeley Lab, the work demonstrates a novel technique for high-resolution universe maps. The new technique, which uses distant galaxies to backlight hydrogen gas, might inform future mapping projects, he says. One such project could be the proposed Dark Energy Spectroscopic Instrument (DESI). Managed by Berkeley Lab, DESI has the goal of producing the most complete map of the universe yet.
"DESI was designed without the possibility of extracting such information from the most distant, faint galaxies," says Schlegel, "Now that we know this is possible, DESI promises to be even more powerful."
The first big 3D map of the universe was created using data from the Sloan Digital Sky Survey (SDSS), which began in 1998. Over the years, the survey has provided data to make a high-resolution map of the nearby universe, within about 1-billion light years. Recent telescope upgrades have stretched our ability to map the universe to about 6-billion light years, but, according to Schlegel, it's a fairly crude map with incomplete data in some areas. The next generation of maps will come from the DESI project, scheduled to begin operation in 2018 pending funding. DESI will allow scientists to visualize 10 times the volume of SDSS and will extend about 10-billion light years away.
Artist's impression illustrating the technique of Lyman-alpha tomography: as light from distant background galaxies (yellow arrows) travel through the Universe towards Earth, they are imprinted by the absorption signatures from hydrogen gas tracing in the foreground cosmic web. By observing a number of background galaxies in a small patch of the sky, astronomers were able to create a 3D map of the cosmic web using a technique similar to medical computer tomography (CT) scans. Credit: Khee-Gan Lee (MPIA) and Casey Stark (UC Berkeley)
Beyond 10-billion light years, says Schlegel, the expectation was that the map would become sparse. The reason: astronomers planned to use a familiar technique that uses the bright light of quasars, which are, unfortunately, scattered and few. The technique uses a phenomenon called Lyman-alpha forest absorption, which relies on the fact that vast clouds of hydrogen exist between Earth and distant quasars and galaxies. At a certain distance, as measured by the red shift of the light, astronomers can determine the density of hydrogen, based on the absorption of quasar light. The problem is that this only provides information about the presence of hydrogen along the line of sight, not over a larger volume of space.
"It's a pretty weird map because it's not really 3D," explains Schlegel. "It's all these skewers; we don't have a picture of what's between the quasars, just what's along the skewers."
The researchers believe their new technique, which uses the faint light of numerous distant galaxies instead of that of sparse quasars, can fill in the gaps between these skewers.
Before this study, no one knew if galaxies further than 10-billion light years away could provide enough light to be useful, Schlegel says. But earlier this year, the team collected four hours of data on the Keck-1 telescope during a brief break in cloudy skies. "It turned out to be enough time to prove we could do this," Schlegel says.
Of course, the galaxies' light was indeed exceedingly faint. In order to use it for a map, the researchers needed to develop algorithms to subtract light from the sky that would otherwise drown out the galactic signals. Schlegel developed the algorithm to do this, while Casey Stark and Martin White of UC Berkeley modified an existing algorithm, called a Wiener filter, to create the 3D map within a minute on a standard laptop computer.
Because the project was a proof-of-concept, the researchers are planning future Keck-1 telescope time to extend the volume of space they map. "This technique is pretty efficient and it wouldn't take a long time to obtain enough data to cover volumes hundreds of millions of light years on a side," says Khee-Gan Lee.
This research was supported by the U.S. Department of Energy's Office of Science and used the facilities of the National Energy Research Scientific Computing Center (NERSC) located at Berkeley Lab.
- See more at: http://newscenter.lbl.gov/2014/10/16/a-3d-map-of-the-adolescent-universe/#sthash.nCKqf8Tn.dpuf

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Story Source:
The above story is based on materials provided by Berkeley Laboratory. The original article was written by Kate Greene. Note: Materials may be edited for content and length.

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