* Astronomy

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Galaxy Formation

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New research resolves conflict in theory of how galaxies form

For more than two decades, the cold dark matter theory has been used by cosmologists to explain how the smooth universe born in the big bang more than 13 billion years ago evolved into the filamentary, galaxy-rich cosmic web that we see today.
There's been just one problem: the theory suggested most galaxies should have far more stars and dark matter at their cores than they actually do. The problem is most pronounced for dwarf galaxies, the most common galaxies in our own celestial neighbourhood. Each contains less than 1 percent of the stars found in large galaxies such as the Milky Way.
Now an international research team, led by a University of Washington astronomer, reports Jan. 14 in Nature that it resolved the problem using millions of hours on supercomputers to run simulations of galaxy formation (1 million hours is more than 100 years). The simulations produced dwarf galaxies very much like those observed today by satellites and large telescopes around the world.
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Title: The Origin of the Hubble Sequence in Lambda-CDM Cosmology
Authors: Andrew J. Benson (1), Nick Devereux (2) ((1) California Institute of Technology, (2) Embry-Riddle Aeronautical University)
(2 Dec 2009, version, v2)

The Galform semi-analytic model of galaxy formation is used to explore the mechanisms primarily responsible for the three types of galaxies seen in the local universe: bulge, bulge+disk and disk, identified with the visual morphological types E, S0/a-Sbc, and Sc-Scd, respectively. With a suitable choice of parameters the Galform model can accurately reproduce the observed local K_s-band luminosity function (LF) for galaxies split by visual morphological type. The successful set of model parameters is used to populate the Millennium Simulation with 9.4 million galaxies and their dark matter halos. The resulting catalogue is then used to explore the evolution of galaxies through cosmic history. The model predictions concur with recent observational results including the galaxy merger rate, the star formation rate and the seemingly anti-hierarchical evolution of ellipticals. However, the model also predicts significant evolution of the elliptical galaxy LF that is not observed. The discrepancy raises the possibility that samples of z~1 galaxies which have been selected using colour and morphological criteria may be contaminated with galaxies that are not actually ellipticals.

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Distant Galaxies Grow "Inside-out" and Through Minor Mergers

Looking into the distant universe, astronomers look into the past. Observations of distant galaxies directly reveal those galaxies as they once were. They also indicate indirectly the stages of development that result in the nearby galaxies that are typical of our own Milky Way and other older galaxies today.
Christopher Conselice (University of Nottingham, UK) and collaborators used the Near Infrared Imager (NIRI) with the adaptive optics system Altair and laser guide stars on the Gemini North telescope to investigate galaxies at redshifts from z =1 to 2 (when the universe was only 25 to 40% of its current age). They show that the massive galaxies of their sample tended to be extremely compact. These instruments afford high angular resolution, which is essential to measure fine spatial scales in the distant galaxies. In a sense, the galaxies grow "inside-out," adding mass to the outer regions beyond an initial dense core.
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Bristol Uni study reveals origins of galaxies
Stars and giant structures which have been spotted for the first time around the Andromeda Galaxy are probably the remnants of smaller galaxies, a study says.
A team of astronomers including experts from Bristol University have undertaken the biggest survey of the galaxy, covering a region of nearly a million light years wide.

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A team of astronomers has measured the motions of stars in a very distant galaxy for the first time and discovered they are whizzing around at astonishingly high speeds - about one million miles per hour, or twice the speed at which the Sun circles our own Milky Way galaxy. The finding offers new insights into how these early galaxies may have evolved into the more familiar ones we see in the nearby universe.

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Cosmic "blobs" have helped pinpoint a crucial stage in galaxy and black hole evolution, suggests research led by Durham University.
The blobs - huge brightly glowing reservoirs of hydrogen gas in the early Universe - were discovered ten years ago but little was known about their power source.
Using data from NASAs Chandra X-Ray Observatory and other telescopes, the Durham-led researchers found that a significant source of their power came from radiation associated with supermassive black holes within the blobs that are partially obscured by dense layers of dust and gas.
Bursts of star formation also provided power to the blobs which were seen at a time when the Universe was only 2 billion years old, the researchers found.

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Elizabeth Barton Discusses Galaxy Formation and Evolution (UC Irvine)

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Elizabeth Barton, assistant professor of physics and astronomy at UC Irvine, studies galaxy and star formation, galaxy evolution, and the development of large optical and infrared telescopes. Barton is a member of the executive board of UCI's Center for Cosmology, and she is a member of the Science Advisory Committee for the Thirty Meter Telescope project.

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Streams of Stars Provide "Missing Link" in the Evolution of Galaxy Disks
Using NASA's Spitzer Space Telescope, an international team of astronomers has discovered streams of young stars flowing from their natal cocoons in distant galaxies. These distant rivers of stars provide an answer to one of astronomy's most fundamental puzzles: how do young stars that form clustered together in dense clouds of dust and gas disperse to form the large, smooth distribution seen in the disks of spiral galaxies like the Milky Way?

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Using space and ground telescopes, astronomers looked back to when the universe was only 800 million years old and found something that was out of proportion and out of time. It was gaseous and big, and it emitted a certain type of radiation, said study lead author Masami Ouchi, an astronomer at the Carnegie Observatories in Pasadena, California.

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