The Enrichment History of the Intergalactic Medium—Measuring the C IV/H I Ratio in the Lyα Forest

By Sara L. Ellison, A. Songaila, Joop Schaye, M. Pettini. 2000

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We have obtained an exceptionally high signal-to-noise, high-resolution spectrum of the gravitationally lensed quasar Q1422+231. A total of 34 C IV systems are identified, several of which had not been seen in previous spectra. Voigt profiles are fitted to these C IV systems and to the entire Lyα forest in order to determine column densities, b-values, and redshifts for each absorption component. The column density distribution for C IV is found to be a power law with index α = 1.44 ± 0.05, down to at least log N(C IV) = 12.3. We use simulations to estimate the incompleteness correction and find that there is in fact no evidence for flattening of the power law down to log N(C IV) = 11.7—a factor of 10 lower than previous measurements. In order to determine whether the C IV enrichment extends to even lower column density H I clouds, we utilize two analysis techniques to probe the low column density regime in the Lyα forest. First, a composite stacked spectrum is produced by combining the data for Q1422+231 and another bright QSO, APM 08279+5255. The signal-to-noise ratio of the stacked spectrum is 1250, and yet no resultant C IV absorption is detected. We discuss the various problems that affect the stacking technique and focus in particular on a random velocity offset between H I and its associated C IV which we measure to have a dispersion of σv = 17 km s-1. It is concluded that, in our data, this offset results in an underestimate of the amount of C IV present by a factor of about 2, and this technique is therefore not sufficiently sensitive to probe the low column density Lyα clouds to meaningful metallicities. Second, we use measurements of individual pixel optical depths of Lyα and corresponding C IV lines. We compare the results obtained from this optical depth method with analyses of simulated spectra enriched with varying C IV enrichment recipes. From these simulations, we conclude that more C IV than is currently directly detected in Q1422+231 is required to reproduce the optical depths determined from the data, consistent with the conclusions drawn from consideration of the power-law distribution.

Subfields: Astronomy and Astrophysics

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Citations in the corpus

Simulations of Pregalactic Structure Formation with Radiative Feedback (2000, background): “Observations of quasar spectra (Ellison et al. 1999, Ellison et al. 2000) suggest that metallicities possibly as high as logCIV/HI = −2.6 may be present even in the low column density logNHI < 14.5 Lyman alpha forest.”
Cosmological simulations of intergalactic medium enrichment from galactic outflows (2006, background): “The CDD is observed to fairly accurately follow a steep power law (Ellison et al. 2000; Songaila 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): “1997b, ApJ, 481, 601 Rauch, M., Miralda-Escude, J., Sargent, W. L. W., Barlow, T. A., Weinberg, D. H., Hernquist, L., Katz, N., Cen, R., & Ostriker, J. P. 1997c, ApJ, 489, 7 Rauch, M., Sargent, W. L. W., & Barlow, T. A. 2001, ApJ, 554, 823 Rauch, M., Sargent, W. L. W., Womble, D. S., & Barlow, T. A.”
The Evolution of the Intergalactic Medium (2015, methodology): “The first is the so-called pixel optical depth method (Cowie & Songaila 1998; Ellison et al. 2000; Aguirre, Schaye & Theuns 2002), which tabulates at fixed optical depth in H i Lyα the optical depth of a given metal ion at the same location in the IGM, correcting for noise and other contaminants.”
The Detectability of the First Stars and Their Cluster Enrichment Signatures (2003, background): “Tremendous 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…”
The enrichment of the intergalactic medium with adiabatic feedback – I. Metal cooling and metal diffusion (2009, background): “…S IV and O VI) in quasar spectra show that the intergalactic medium (IGM) far outside large galaxies (ρ/ρmean < 10) is enriched (e.g. Songaila & Cowie 1996; Davé et al. 1998; Ellison et al. 2000; Schaye et al. 2000; Pettini et al. 2003; Schaye et al. 2003; Aguirre et al. 2004; Simcoe et al. 2004).”
THE GASEOUS ENVIRONMENT OF HIGH-z GALAXIES: PRECISION MEASUREMENTS OF NEUTRAL HYDROGEN IN THE CIRCUMGALACTIC MEDIUM OF z ∼ 2–3 GALAXIES IN THE KECK BARYONIC STRUCTURE SURVEY (2012, background): “In addition, studies of the distribution of metal absorption lines in the “IGM” often consider metallic species associated with HI absorbers of log(NHI) & 14.5 (Cowie et al. 1995; Songaila & Cowie 1996; Ellison et al. 2000; Carswell et al. 2002; Simcoe 2011).”
Reionization by Hard Photons. I. X-Rays from the First Star Clusters (2000, methodology): “Theoretical models of shock acceleration, in which e/p is a free parameter, often set e/p D 1%È5% for consistency with cosmicray experiments (Ellison & Reynolds 1991 ; Ellison et al. 2000).”
DEMOGRAPHICS AND PHYSICAL PROPERTIES OF GAS OUTFLOWS/INFLOWS AT 0.4 < z < 1.4 (2012, background): “…of the circumgalactic medium by winds probably started very early in cosmic history based on the properties of metal-line systems at high-redshift (Meyer & York 1987; Lu 1991; Songaila & Cowie 1996; Ellison et al. 2000; Schaye et al. 2003; Simcoe et al. 2006; Martin et al. 2010; Simcoe 2011).”
The Luminosity-Metallicity Relation, Effective Yields, and Metal Loss in Spiral and Irregular Galaxies (2002, background): “(The widespread observation of metals in the IGM at high redshifts [Ellison et al. 2000] suggests that the metallicity in the outer regions of galaxies is unlikely to be zero.)”
Constraints on Warm Dark Matter from Cosmological Reionization (2001, background): “5)Z_et al. 1995 ; Lu et al. 1998 ; Cowie & Songaila 1998 ; Ellison et al. 2000 ; Prochaska & Wolfe 2000) observed in low column density Lyman-a absorbers, assuming that the metallicity of these systems is representative of the average metallicity of the IGM.”
On the onset of galactic winds in quiescent star forming galaxies (2007, background): “Observations of the Lyα forest clouds show that they are metal enriched fromZ ≃ 10−3 up to 10−2 Z⊙ (Songaila & Cowie 1996, Ellison et al. 2000).”
The Reionization of the Universe by the First Stars and Quasars (2000, background): “…quasars has revealed that the low-density IGM has been enriched to a metal abundance (by mass) of ZIGM ∼ 10−2.5(±0.5)Z , where Z = 0.019 is the solar metallicity (Meyer & York 1987; Tytler et al. 1995; Songaila & Cowie 1996; Lu et al 1998; Cowie & Songaila 1998; Songaila 1997; Ellison et al. 2000).”
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).”
The Minimum Universal Metal Density between Redshifts of 1.5 and 5.5 (2001, background): “…arising from the diffuse IGM has been extensively analyzed at redshift z ∼ 3 (Cowie et al. 1995, Tytler et al. 1995, Songaila 1997, Songaila 1998, Ellison et al. 2000) and some information is also available from investigations of O VI at lower redshift (Burles & Tytler 1996, Tripp, Savage &…”
Constraints on star formation driven galaxy winds from the mass–metallicity relation at z= 0 (2010, background): “The IGM is enriched as early asz > 3 (Songaila & Cowie 1996; Ellison et al. 2000; Schaye et al. 2003), and if this material is re-accreted onto galaxies at later epochs it could have a significant effect on the shape and normalization of thez = 0 mass-metallicity relation.”
The First Cosmic Structures and Their Effects (2004, result): “Ellison et al. (1999, 2000) re-examined the problem and found that both approaches suffer from limitations which had not been properly taken into account in previous analysis.”
The Dust Opacity of Star‐forming Galaxies (2001, background): “…fraction, >50%, of the baryons at z≈3 (Rauch et al. 1997); its metallicity at z∼2.5–3 is ∼0.2–1% Z⊙ down to column densities N(HI)∼1014.5 cm−2 (Tytler et al. 1995; Songaila & Cowie 1996; Ellison et al. 1999), while metallicity values at lower column densities remain uncertain (Ellison et al. 2000).”
A unified model for AGN feedback in cosmological simulations of structure formation (2007, background): “…therefore pollute a sizable fraction of the volume of the intergalactic medium (IGM) with metals, to a level of 10−3 − 10−2 of the Solar metallicity, in agreement with a number of observational findings (e.g. Rauch et al., 1997; Cowie & Songaila, 1998; Schaye et al., 2000; Ellison et al., 2000).”