Metal enrichment of the intergalactic medium

Shchekinov, Yu. A.

doi:10.1080/10556790215566

Cited by 8 publications

(2 citation statements)

References 28 publications

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“…From the theoretical point of view three basic models explaining the inhomogeneous metal distribution in the Universe have been described: patchy (unpercolated) distribution of metal-enriched bubbles around active (starburst) galaxies (Nath & Trentham 1997;Gnedin 1998;Ferrara et al 2000); dependence of the metallicity of enriched bubbles on the host galaxy (Nath & Trentham 1997;Gnedin 1998;Ferrara et al 2000;Shchekinov 2002), and inefficient (incomplete) mixing (Dedikov & Shchekinov 2004).…”

Section: Metallicity In the Early Universementioning

confidence: 99%

Planets in the early Universe

Shchekinov¹,

Safonova

Murthy

2013

Astrophys Space Sci

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Several planets have recently been discovered around stars that are old and metal-poor, implying that these planets are also old, formed in the early Universe together with their hosts. The canonical theory suggests that the conditions for their formation could not have existed at such early epochs. In this paper we argue that the required conditions, such as sufficiently high dust-to-gas ratio, could in fact have existed in the early Universe immediately following the first episode of metal production in Pop. III stars, both in metal-enhanced and metaldeficient environments. Metal-rich regions may have existed in multiple isolated pockets of enriched and weakly-mixed gas close to the massive Pop. III stars. Observations of quasars at redshifts z ∼ 5, and gamma-ray bursts at z ∼ 6, show a very wide spread of metals in absorption from [X/H] ≃ −3 to ≃ −0.5. This suggests that physical conditions in the metal-abundant clumps could have been similar to where protoplanets form today. However, planets could have formed even in low-metallicity environments, where formation of stars is expected to proceed due to lower opacity at higher densities. In such cases, the circumstellar accretion disks are expected to rotate faster than their high-metallicity analogues. This in turn can result in the enhancement of dust particles at the disk periphery, where they can coagulate and start forming planetesimals. In conditions with the low initial specific angular momentum of the cloud, radiation from the central protostar can act as a trigger to drive small-scale instabilities with typical masses in the Earth to Jupiter mass range. Discoveries of planets around old metal-poor stars (e.g. HIP 11952, [Fe/H] ∼ −1.95, ∼ 13 Gyr) show that planets did indeed form in the early Universe and this may require modification of our understanding of the physical processes that produce them. This work is an attempt to provide one such heuristic scenario for the physical basis for their existence.

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Section: Metallicity In the Early Universementioning

confidence: 99%

Planets in the early Universe

Shchekinov¹,

Safonova

Murthy

2013

Astrophys Space Sci

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“…Such shock waves are believed to play a significant role in the metal enrichment of the intergalactic medium (IGM). Metals (heavy elements) produced by stars are transported into the IGM by shock waves from galaxies and clusters of galaxies (Gnedin 1998;Madau, Ferrara & Rees 2001;Shchekinov 2002;Aguirre & Schaye 2007;Meiksin 2009). The efficiency of metal ejection depends on many factors and parameters, for example the mass of a parent (for metals) galaxy, the star formation rate and the density profile.…”

Section: Introductionmentioning

confidence: 99%

Thermal instability in a collisionally cooled gas

Vasiliev¹

2011

Monthly Notices of the Royal Astronomical Society

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Non‐equilibrium (time‐dependent) cooling rate and ionization state calculations are presented for a gas behind a shock wave with v ∼ 50–150 km s−1 (Ts∼ 0.5–6 × 105 K). Such shock waves do not lead to the radiative precursor formation; that is, the thermal evolution of a gas behind the shock wave is controlled by collisions only. We have found that the cooling rate in a gas behind a shock wave with v ∼ 50–120 km s−1 (Ts∼ 0.5–3 × 105 K) differs considerably from the cooling rate for a gas cooled from T = 108 K. It is well known that a gas cooled from T = 108 K is thermally unstable for isobaric and isochoric perturbations at K. We studied the thermal instability in a collisionally controlled gas for shock waves with v ∼ 50–150 km s−1. We found that the temperature range within which the post‐shock gas is thermally unstable is significantly modified and depends on both gas metallicity and the ionic composition of the gas before the shock wave. For , the temperature range for which the thermal instability criterion for isochoric perturbations is not fulfilled widens in comparison with that for a gas cooled from T = 108 K, while that for isobaric perturbations remains almost unchanged. For Z ∼ Z⊙, the gas behind a shock wave with km s−1 ( K) is thermally stable to isochoric perturbations during all of its evolution. We have shown that the transition from isobaric to isochoric cooling for a gas with behind a shock wave with Ts= 0.5–3 × 105 K occurs in a gas layer column density layer behind a shock wave than that for a gas cooled from T = 108 K. The ionic states in a gas with Z ∼ 10−3–1 Z⊙ behind shock waves with K demonstrate a significant difference from these in a gas cooled from T = 108 K. Such a difference is thought to be important for the correct interpretation of observational data, but is not very helpful for discriminating thermally stable gas.

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Dust in the IGM: pro and contra

Shchekinov¹,

Nath²

2011

UV Astronomy 2011

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Metal enrichment of the intergalactic medium

Cited by 8 publications

References 28 publications

Planets in the early Universe

Planets in the early Universe

Thermal instability in a collisionally cooled gas

Dust in the IGM: pro and contra

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