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Lyman alpha-emitting galaxies
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Astronomers probing the distant Universe have found the building blocks of spiral galaxies like our Milky Way.
They discovered ancient galaxies, about one-tenth the size of the Milky Way, which were among the first to form in the Universe.
Over billions of years, galaxies like these merged to form much bigger spiral galaxies such as our own.
The findings were outlined at a meeting of the American Astronomical Society in Austin, Texas.

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RE: Young galaxies
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Astronomers have found a new population of faint protogalaxies by taking the most sensitive spectroscopic survey ever of a time when the universe was only 15% of its present age.

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Hydrogen atoms in distant galaxies and in the intergalactic medium absorb or release photons of light at specific wavelengths producing characteristic absorption or emission lines when the light is dispersed into a spectrum. These are spectra of likely protogalaxies seen when the universe was at 15% of its present age. They show the Lyman alpha emission line region characteristic of a population of low mass, weakly star-forming galaxies commonly believed to be the building blocks of bright present day galaxies. Michael Rauch, George Becker and colleagues found these objects, which are about ten times fainter than any galaxies ever seen in ground-based observations.

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Protogalaxies
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Astronomers have found a new population of faint protogalaxies by taking the most sensitive spectroscopic survey ever of a time when the universe was only 15% of its present age. These objects are the probable building blocks of galaxies today, including our own Milky Way. The discovery substantiates a popular theory of galaxy formation. The research, conducted by Michael Rauch and George Becker of the Carnegie Observatories with colleagues, will be published in the March 1, 2008, issue of the Astrophysical Journal.

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RE: Young galaxies
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Tiny galaxies that may be the first building blocks of galaxies like the Milky Way have turned up in an extremely long exposure of the early universe, reveal new observations by one of the world's largest telescopes.
Because light takes time to travel to us, we see the most distant objects as they were billions of years ago, when the universe was just a small fraction of its present age of 13.7 billion years.
Now, a marathon observation with the 8.2-metre Antu telescope, part of the Very Large Telescope (VLT) observatory in Paranal, Chile, has provided an unprecedented view of tiny galaxies that were present just 2 billion years after the big bang.


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Title: A Population of Faint Extended Line Emitters and the Host Galaxies of Optically Thick QSO Absorption Systems
Authors: Michael Rauch, Martin Haehnelt, Andrew Bunker, George Becker, Francine Marleau, James Graham, Stefano Cristiani, Matt J. Jarvis, Cedric Lacey, Simon Morris, Celine Peroux, Huub Roettgering, Tom Theuns

We have conducted a long slit search for low surface brightness Lyman-alpha emitters at redshift 2.67 < z < 3.75. A 92 hour long exposure with VLT/FORS2 down to a 1-sigma surface brightness detection limit of 8x10^-20 erg/cm2/s/sqarcsec yielded a sample of 27 single line emitters with fluxes of a few times 10^-18 erg/s/cm2. We present arguments that most objects are indeed Lyman-alpha. The large comoving number density, the large covering factor, dN/dz ~ 0.2-1, and the often extended Lyman-alpha emission suggest that the emitters be identified with the elusive host population of damped Lyman-alpha systems (DLAS) and high column density Lyman limit systems. A small inferred star formation rate, perhaps supplanted by cooling radiation, appears to energetically dominate the Lyman-alpha emission, and is consistent with the low metallicity, low dust content, and theoretically inferred low masses of DLAS, and with the relative lack of success of earlier searches for their optical counterparts.

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Young building blocks of galaxies similar to the Milky Way have been spotted for the first time by astronomers, giving a tantalizing glimpse of how our stellar backyard may have formed.
The discovery of 27 "teenagers," or proto-galaxies, is further evidence that galaxies like the Milky Way were created by the clumping of smaller clouds of gas and dust, researchers reported Wednesday.


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ESO's VLT takes the search for young galaxies to new limits
Staring for the equivalent of every night for two weeks at the same little patch of sky with ESO's Very Large Telescope, an international team of astronomers has found the extremely faint light from teenage galaxies billions of light years away. These galaxies, which the research team believes are the building blocks of normal galaxies like our Milky Way, had eluded detection for three decades, despite intensive searches.
The team, led by Martin Haehnelt of the University of Cambridge, UK, Michael Rauch and George Becker of the Observatories of the Carnegie Institution, USA, and Andy Bunker of the Anglo-Australian Observatory, reports their results in the 1 March 2008 issue of the Astrophysical Journal.

"This is the first time that the sky has been searched to this depth and the unrivalled sensitivity of the picture taken with the VLT was key to succeeding" - Martin Haehnelt .

Experts have long speculated that galaxies like ours were created by the amalgamation of proto-galaxies early in the history of the Universe, but the light from these fragments was so faint that astronomers had struggled to prove they were there at all. Astronomers thought that the teenage galaxies must be out there because they were blocking part of the light from objects even further away in space.

"Previous attempts have usually been frustrated by the difficulty of detecting extremely faint objects: the amount of time required even with an 8-metre class telescope like the VLT considerably exceeds typical observing time awards. We have thus exploited the periods of less good weather with the FORS2 spectrograph at the VLT, taking advantage of the service observing mode" - George Becker.

In service mode, ESO staff astronomers at Paranal are responsible for carrying out the actual observations, taking all the specific requirements into account.

"We were actually trying to measure a faint signal from intergalactic gas caused by the cosmic ultraviolet background radiation. But as often happens in science, we got a surprise and found something we weren't looking for - dozens of faint, discrete objects emitting radiation from neutral hydrogen in the so-called Lyman alpha line, a fundamental signature of protogalaxies" - Michael Rauch .

27Teens_e1
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Credit ESO
A 92-hour long spectrum Two-dimensional spectrum obtained in 92 hours of exposure time, showing the
line emitter candidates. The quasar absorption lines are visible close to the centre of the image.


The same small patch of sky, centred on a quasar, was observed between 2004 and 2006 for an unprecedented 92 hours, the equivalent of about 12 complete nights, allowing the astronomers to obtain a spectrum of the Universe when it was only 2 billion years old.
The result of this search is the detection of 27 faint objects. The weak light signal that the team has detected from these distant objects implies low star formation rates and a small amount of chemical enrichment, suggesting that they are indeed at an early stage of formation.

"The properties of the emitters seem to provide an excellent match to those of 'Damped Lyman Alpha Systems', the main reservoir of neutral hydrogen in the far Universe. This suggests that the objects found are the long-sought counterparts of the DLAS in emission. The new observations confirm theoretical research proposing that galaxies like our own have formed by the amalgamation of small proto-galaxies early on in the history of the Universe" - Andy Bunker.

"What makes our discovery particularly exciting is that it opens the route to find large numbers of building blocks of normal galaxies and that we will now be able to study in detail how galaxies like our Milky Way have come together" - Martin Haehnelt.

Source ESO

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