The Minimum Universal Metal Density between Redshifts of 1.5 and 5.5

Songaila, A.

doi:10.1086/324761

Cited by 241 publications

(428 citation statements)

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“…they retain their heavy elements. Second, the nearly constant (2 z 5, Z ≈ 3.5 × 10 −4 Z ) metallicity of the low column density IGM (Songaila 2001) is naturally explained by the decreasing efficiency of metal loss from larger galaxies. Early pollution from low-mass galaxies allows a sufficient time for metals to cool after ejection; however, the majority of metals in LBG halos at lower redshifts are still too hot to be detected.…”

Section: Discussionmentioning

confidence: 99%

Cosmic metal enrichment

Ferrara¹

2008

Proc. IAU

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Abstract. I review the present understanding of the process by which the universe has been enriched in the course of its history with heavy elements produced by stars and transported into the surrounding intergalactic medium. This process goes under the name of "cosmic metal enrichment" and presents some of the most challenging puzzles in present day physical cosmology. These are reviewed along with some proposed explanations that all together form a coherent working scenario.Keywords. (galaxies:) intergalactic medium, cosmology: theory, galaxies: high-redshift PreliminariesAfter the Big Bang the cosmic gas had a composition which was (virtually) free of heavy elements. Yet, every single parcel of gas that we can probe today with our most powerful telescopes shows the sign of considerable amounts of metals, up to the highest redshift. When these metals where first produced, by what sources, and how these atomic species traveled away from their production sites are among the most challenging puzzles in current cosmological scenarios.A very simple, and yet robust, estimate of the amount of metals present at the end of reionization can be made. This is based on the fact that the sources of heavy elements and photons with energy > 1 Ryd responsible for hydrogen reionization are massive stars. Hence, as we know that reionization was complete by redshift z = 6, we can compute the metallicity of the cosmic gas associated with the ionizing photons required to reionize the universe, in the hypothesis that such process has been powered by stellar radiation. Obviously, as different type of sources, as quasars and/or decaying/annihilating dark matter particles may have contributed, the result of this simple exercise is an upper limit to the amount of metals. However, many arguments suggest that stars are by far the most viable reionization source candidates. In this case, we find that the mean metallicity of the cosmic gas (in practice, the intergalactic medium [IGM] which contains most of the baryons) at z = 6 iswhere y is the mean supernova metal yield, ν is the number of supernovae per unit stellar mass formed, C ≈ 1 − 10 is the IGM clumping factor and η is the number of ionizing photons per baryon into stars. The above result has been derived for a Salpeter stellar IMF but the value of Z is only mildly dependent on such quantity. The main point is that metal production associated with cosmic reionization is already substantial and comparable with the value derived from QSO absorption line experiments at lower redshifts. The next question concerns the sources that predominantly produced the metals and photons. Current data from a number of different experiments including CMB polarization anisotropies, Lyα and Lyβ Gunn-Peterson tests, cosmic star formation history and 86 available at https://www.cambridge.org/core/terms. https://doi

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Section: Discussionmentioning

confidence: 99%

Cosmic metal enrichment

Ferrara¹

2008

Proc. IAU

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“…It is also relatively straightforward to model because it arises in gas that is optically thin to ionizing photons and lies far enough away from galaxies that the local radiation field may be neglected to first order. Its overall mass density is robustly observed to decline slowly with increasing redshift (Songaila 2001;Becker et al 2009;Ryan-Weber et al 2009;D'Odorico et al 2010D'Odorico et al , 2013Simcoe et al 2011;Becker et al 2011;Cooksey et al 2013). Numerous studies have shown that the observed decline can readily be accommodated by numerical simulations (Oppenheimer & Davé 2006;Oppenheimer et al 2009;Cen & Chisari 2011).…”

Section: Introductionmentioning

confidence: 93%

“…Intergalactic C IV and C II absorbers are observed along sightlines to quasars out to the highest redshifts probed (Songaila 2001;Ryan-Weber et al 2006;Becker et al 2009;Ryan-Weber et al 2009;Simcoe et al 2011;D'Odorico et al 2013;Becker et al 2011). They occur naturally in cosmological hydrodynamic simulations in which galactic outflows expel metals out to the virial radius and beyond (Theuns et al 2002;Cen et al 2005; Oppenheimer & Davé 2006, 2008Oppenheimer et al 2009;Cen & Chisari 2011), opening up the possibility of using models to interpret them as tracers of star formation, outflows, and the ultraviolet ionizing background (UVB).…”

Section: Introductionmentioning

confidence: 99%

The reionization of carbon

Finlator

Thompson

Huang

et al. 2015

Monthly Notices of the Royal Astronomical Society

109

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Observations suggest that C II was more abundant than C IV in the intergalactic medium towards the end of the hydrogen reionization epoch (z ∼ 6). This transition provides a unique opportunity to study the enrichment history of intergalactic gas and the growth of the ionizing background (UVB) at early times. We study how carbon absorption evolves from z = 10-5 using a cosmological hydrodynamic simulation that includes a self-consistent multifrequency UVB as well as a well-constrained model for galactic outflows to disperse metals. Our predicted UVB is within ∼ 2-4× of that from Haardt & Madau (2012), which is fair agreement given the uncertainties. Nonetheless, we use a calibration in post-processing to account for Lyman-α forest measurements while preserving the predicted spectral slope and inhomogeneity. The UVB fluctuates spatially in such a way that it always exceeds the volume average in regions where metals are found. This implies both that a spatially-uniform UVB is a poor approximation and that metal absorption is not sensitive to the epoch when HII regions overlap globally even at column densites of 10 12 cm −2 . We find, consistent with observations, that the C II mass fraction drops to low redshift while C IV rises owing the combined effects of a growing UVB and continued addition of carbon in low-density regions. This is mimicked in absorption statistics, which broadly agree with observations at z = 6-3 while predicting that the absorber column density distributions rise steeply to the lowest observable columns. Our model reproduces the large observed scatter in the number of low-ionization absorbers per sightline, implying that the scatter does not indicate a partially-neutral Universe at z ∼ 6.

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“…Songaila 2001;Boksenberg et al 2003;Simcoe 2011;Cooksey et al 2013). While the shape of the C IV equivalent width frequency distribution function appears to remain the same, the total cosmic mass density in C 3+ ions is found to increase from z = 4 to z ≈ 1.5 by a factor of 2 (e.g.…”

Section: Introductionmentioning

confidence: 97%

Mining circumgalactic baryons in the low-redshift universe

Liang

Chen

2014

Monthly Notices of the Royal Astronomical Society

143

229

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This paper presents an absorption-line study of the multiphase circumgalactic medium (CGM) based on observations of Lyα, C II, C IV, Si II, Si III, and Si IV absorption transitions in the vicinities of 195 galaxies at redshift z < 0.176. The galaxy sample is established based on a cross-comparison between public galaxy and QSO survey data and is characterized by a median redshift of z = 0.041, a median projected distance of d = 362 kpc to the sightline of the background QSO, and a median stellar mass of log (M star /M ) = 9.7 ± 1.1. Comparing the absorber features identified in the QSO spectra with known galaxy properties has led to strong constraints for the CGM absorption properties at z < ∼ 0.176. First, abundant hydrogen gas is observed out to d ∼ 500 kpc, well beyond the dark matter halo radius R h of individual galaxies, with a mean covering fraction of ≈ 60%. In contrast, no heavy elements are detected at d > ∼ 0.7 R h from either low-mass dwarfs or high-mass galaxies. The lack of detected heavy elements in low-and high-ionization states suggests that either there exists a chemical enrichment edge at d ≈ 0.7 R h or gaseous clumps giving rise to the observed absorption lines cannot survive at these large distances. Considering all galaxies at d > R h leads to a strict upper limit for the covering fraction of heavy elements of ≈ 3% (at a 95% confidence level) over d = (1 − 9) R h . At d < R h , differential covering fraction between low-and high-ionization gas is observed, suggesting that the CGM becomes progressively more ionized from d < 0.3 R h to larger distances. Comparing CGM absorption observations at low and high redshifts shows that at a fixed-fraction of R h the CGM exhibits stronger mean absorption at z = 2.2 than at z ∼ 0 and that the distinction is most pronounced in low-ionization species traced by C II and Si II absorption lines. We discuss possible pseudo-evolution of the CGM as a result of misrepresentation of halo radius, and present a brief discussion on the implications of these findings.

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The Minimum Universal Metal Density between Redshifts of 1.5 and 5.5

Cited by 241 publications

References 35 publications

Cosmic metal enrichment

Cosmic metal enrichment

The reionization of carbon

Mining circumgalactic baryons in the low-redshift universe

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