The Minimum Universal Metal Density between Redshifts of 1.5 and 5.5

By A. Songaila. 2001

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It appears that the Lyα forest is becoming thick at a redshift of about 5.5, cutting off the higher redshift intergalactic medium from view in neutral hydrogen. However, the effects of star formation at higher redshift are still readable in the intergalactic metal lines. In this Letter, I use observations of 32 quasars with emission redshifts in the range 2.31-5.86 to study the evolution of the intergalactic metal density from z = 1.5 to z = 5.5. The C IV column density distribution function is consistent with being invariant throughout this redshift range. From direct integration, I determine ΩC iv to be in the range (2.5-7) × 10-8 and ΩSi iv in the range (0.9-3) × 10-8 between z = 1.5 and z = 5. The metallicity at z = 5 exceeds 3.5 × 10-4, which in turn implies that this fraction of the universal massive star formation took place beyond this redshift. This is sufficient to have ionized the intergalactic medium.

Subfields: Astronomy and Astrophysics

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Quasar Feedback: The Missing Link in Structure Formation (2004, background): “Analyses of C iv lines in quasar absorption spectra uncover an IGM that has been widely and inhomogenously enriched with stellar material (e.g., Cowie et al. 1995; Rauch et al. 1997) out to very high redshifts (Songaila 2001) and turbulently ‘‘stirred’’ at z 3 (Rauch et al. 2001).”
Simulations of Cosmic Chemical Enrichment (2006, background): “(iii) Tracing the orbits of gas particles, we found that ∼20 per cent of all baryons are ejected at least once from galaxies into the IGM.”
Feedback and recycled wind accretion: assembling the z= 0 galaxy mass function (2009, background): “Winds ejecting galactic ISM have the added benefit of chemically enriching the IGM, where metal absorption lines are observed to be common (e.g. Songaila & Cowie 1996; Songaila 2001; Schaye et al. 2003; Simcoe et al. 2004; Adelberger et al. 2005).”
CANDELS: THE COSMIC ASSEMBLY NEAR-INFRARED DEEP EXTRAGALACTIC LEGACY SURVEY (2011, unknown): “Moreover, the IGM was seeded with metals to Z ≈ 4 × 10−4 within the first billion years, and the energy released by the stars that produced these metals appears sufficient to reionize the IGM (Songaila 2001; Ryan-Weber et al. 2006).”
The First Cosmic Structures and Their Effects (2004, background): “The “no evolution” trend seems to extend to even higher redshifts, as already pointed out by Songaila (2001) (and further supported by Pettini et al. 2003), who concluded as well that the C IV column density distribution function is consistent with being invariant throughout the redshift range z =…”
The Detectability of the First Stars and Their Cluster Enrichment Signatures (2003, background): “…progress has been made recently in the determination of the metal content of the IGM both observationally (Ellison et al. 2000; Schaye et al. 2000; Songaila 2001) and theoretically (Gnedin & Ostriker 1997; Ferrara, Pettini, & Shchekinov 2000; Cen & Bryan 2001; Scannapieco & Broadhurst 2001;…”
The Distribution of Metallicity in the Intergalactic Medium at z ~ 2.5: O VI and C IV Absorption in the Spectra of Seven QSOs (2003, methodology): “The first calculation takes a direct sum of the observed C iv column densities, as in Songaila (2001): ΩC IV = 1 ρc mC IV ∑ NC IV,i c H0 ∑ ∆Xi .”
Evolution of the Intergalactic Opacity: Implications for the Ionizing Background, Cosmic Star Formation, and Quasar Activity (2008, background): “The abundance of intergalactic metals as traced by CIV appears consistent with being constant from z ∼ 2 to perhaps z ∼ 6 (Songaila 2001; Pettini et al. 2003; Ryan-Weber et al. 2006), suggestive of an early period of nucleosynthetic activity that may be at odds with estimates of the SFR density…”
New Observations of the Interstellar Medium in the Lyman Break Galaxy MS 1512–cB58 (2001, background): “Together with the wide range of ages of LBGs deduced by Shapley et al. (2001), these results may help explain the presence of metals in the Ly forest up to the highest redshifts probed (z = 5; Songaila 2001).”
The Age-Metallicity Relation of the Universe in Neutral Gas: The First 100 Damped Lyα Systems (2003, background): “We also emphasize that the lower bound to the metallicity of the DLA ([M/H]≈ −2.6) is significantly higher than the metallicities typically attributed to the Lyα forest (e.g. Songaila 2001).”
Reionization of Hydrogen and Helium by Early Stars and Quasars (2002, background): “In addition to the above constraints, observations suggest that the IGM was metal enriched by z 6 (Songaila 2001) to a level that would lead to a Scalo stellar mass function (Bromm et al. 2001) if new galaxies formed out of it.”
Cosmological simulations of intergalactic medium enrichment from galactic outflows (2006, methodology): “The CDD is observed to fairly accurately follow a steep power law (Ellison et al. 2000; Songaila 2001).”
Galaxies and Intergalactic Matter at Redshift z ~ 3: Overview (2002, background): “The constant observed intergalactic CIV density at redshifts 1.5 < z < 5.5 may imply that metal enrichment of the intergalactic medium occurred at z > 5.5 and not at the lower redshifts we have observed (Songaila 2001).”
The Low-z Intergalactic Medium. III. H I and Metal Absorbers at z < 0.4 (2007, methodology): “Similarly, Songaila (1997, 2001) inferred ΩCIV ≈ (2−7)×10−8 at z = 3.0−3.5.”
The First Stars (2003, background): “To account for the widespread presence of metals in the Lyα forest at z ∼ 4–5 (e.g., Songaila 2001, Schaye et al. 2003), star formation in low-mass systems at z 10 has been proposed (e.g., Madau et al. 2001, Mori et al. 2002, Wada & Venkatesan 2003).”
Observational Constraints on Cosmic Reionization (2006, background): “Songaila (2001, 2005) and Pettini et al. (2003) found that the total CIV abundance Ω(CIV) does not significantly evolve over 1.5 < z < 5.5.”
THE DISCOVERY AND ANALYSIS OF VERY METAL-POOR STARS IN THE GALAXY (2005, background): “Indeed, J.H. Wise & T. Abel (submitted) appeal to the explosions of the very first (super-massive) stars that formed in the early Universe to account for the large amount of carbon found in studies of Lyman-alpha-forest clouds at high redshift (e.g., Songaila 2001).”
Two populations of metal-free stars in the early Universe (2006, methodology): “One of the most important developments concerns the discovery of a metallicity floor in the Ly-α forest of the order 10−3 Z⊙ in the redshift range z ≃ 2 – 6, which cannot be explained by galactic outflows of normal Pop I/II galaxies (e.g. Songaila 2001; Aguirre et al. 2005).”
The physics of the intergalactic medium (2007, background): “…(Aracil et al., 2004; Barlow and Tytler, 1998; Bergeron et al., 1994; Bergeron and Stasinska, 1986; Cowie and Songaila, 1998; Cowie et al., 1995; Ellison et al., 2000; Pieri et al., 2006; Scannapieco et al., 2006b; Simcoe et al., 2006; Songaila, 2001, 2005, 2006; Songaila and Cowie, 1996).”