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Blobrana


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Pristine gas
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Astronomers' pristine gas discovery among top scientific breakthroughs of 2011

The discovery by UC Santa Cruz astronomers of pristine clouds of gas formed shortly after the Big Bang is among the scientific breakthroughs of the year featured in year-end issues of Science and Physics World magazines.
Astronomy professor J. Xavier Prochaska and graduate student Michele Fumagalli, along with John O'Meara of Saint Michael's College in Vermont, reported in November the first ever detection of clouds of the primordial gas that formed in the first few minutes after the Big Bang.
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Blobrana


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Primordial gas
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Pristine Gas From The Big Bang

Two clumps of primordial gas from the dawn of time have been detected in deep space by astronomers using the 10-meter telescopes at the W. M. Keck Observatory.
The gas clouds are too diffuse to form stars and show virtually no signs of containing any "metals," which is astronomer-speak for all elements heavier than hydrogen and helium - the two simplest and lightest elements in the universe. In fact the only elements astronomers have detected in the clouds are hydrogen and its heavier isotope, deuterium.
The lack of metals strongly suggests that the gases are reservoirs of the pristine material left over from the Big Bang.
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Blobrana


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Pristine Gas
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Title: Detection of Pristine Gas Two Billion Years after the Big Bang
Authors: Michele Fumagalli, John M. O'Meara, J. Xavier Prochaska

In the current cosmological model, only the three lightest elements were created in the first few minutes after the Big Bang; all other elements were produced later in stars. To date, however, heavy elements have been observed in all astrophysical environments. We report the detection of two gas clouds with no discernible elements heavier than hydrogen. These systems exhibit the lowest heavy-element abundance in the early universe and thus are potential fuel for the most metal poor halo stars. The detection of deuterium in one system at the level predicted by primordial nucleosynthesis provides a direct confirmation of the standard cosmological model. The composition of these clouds further implies that the transport of heavy elements from galaxies to their surroundings is highly inhomogeneous.

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Blobrana


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Posts: 131433
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Primordial gas
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Astronomers find clouds of primordial gas from the early universe

For the first time, astronomers have found pristine clouds of the primordial gas that formed in the first few minutes after the Big Bang. The composition of the gas matches theoretical predictions, providing direct evidence in support of the modern cosmological explanation for the origins of elements in the universe.
Only the lightest elements, mostly hydrogen and helium, were created in the Big Bang. Then a few hundred million years passed before clumps of this primordial gas condensed to form the first stars, where heavier elements were forged. Until now, astronomers have always detected "metals" (their term for all elements heavier than hydrogen and helium) wherever they have looked in the universe.
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Blobrana


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RE: Lyman-limit systems
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Astronomers shed light on early stars in cosmos

After decades of scouring the universe, astronomers finally have found two immense clouds of gas that are pristine - free of the metals fired out into the cosmos by stars.
The findings, published Thursday on the journal Science's website, provide the first solid detection of primitive, uncontaminated gas and support the longstanding theory as to how the chemical elements were formed in the early universe. It is these types of pure gas clouds that formed the first stars.
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Blobrana


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Title: Absorption line systems in simulated galaxies fed by cold streams 
Authors: Michele Fumagalli, J. Xavier Prochaska, Daniel Kasen, Avishai Dekel, Daniel Ceverino, Joel R. Primack
(Version v2)

Hydro cosmological simulations reveal that massive galaxies at high redshift are fed by long narrow streams of merging galaxies and a smoother component of cold gas. We post-process seven high-resolution simulated galaxies with radiative transfer to study the absorption characteristics of the gas in galaxies and streams, in comparison with the statistics of observed absorption-line systems. We find that much of the stream gas is ionised by UV radiation from background and local stellar sources, but still optically thick (N_HI > 10^17 cm^-2) so that the streams appear as Lyman-limit systems (LLSs). At z>3, the fraction of neutral gas in streams becomes non-negligible, giving rise to damped Lyman-alpha (DLA) absorbers as well. The gas in the central and incoming galaxies remains mostly neutral, responsible for DLAs. Within one (two) virial radii, the covering factor of optically thick gas is 30% of the observed absorbers in the foreground of quasars, the rest possibly arising from smaller galaxies or the intergalactic medium. The mean metallicity in the streams is ~1% solar, much lower than in the galaxies. The simulated galaxies reproduce the Lyalpha-absorption equivalent widths observed around Lyman-break galaxies, but they severely underpredict the equivalent widths in metal lines, suggesting that the latter may arise from outflows. We conclude that the observed metal-poor LLSs are likely detections of the predicted cold streams. Revised analysis of the observed LLSs kinematics and simulations with more massive outflows in conjunction with the inflows may enable a clearer distinction between the signatures of the various gas modes.

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