arXiv subjects

John M. O'Meara

Publications and source records attributed to John M. O'Meara.

At least 55 records · Page 3Linked to original sources

arXiv2018

A New Measurement of the Temperature Density Relation of the IGM From Voigt Profile Fitting

We decompose the Lyman-α (Lyα) forest of an extensive sample of 74 high signal-to-noise ratio and high-resolution quasar spectra into a collection of Voigt profiles. Absorbers located near caustics in the peculiar velocity field have the smallest Doppler parameters, resulting in a low-$b$ cutoff in the $b$-$N_{\text{HI}}$ set by the thermal state of intergalactic medium (IGM). We fit this cutoff as a function of redshift over the range $2.0\leq z \leq 3.4$, which allows us to measure the evolution of the IGM temperature-density ($T= T_0 (ρ/ ρ_0)^{γ-1}$) relation parameters $T_0$ and $γ$. We calibrate our measurements against Ly$α$ forest simulations, using 21 different thermal models of the IGM at each redshift, also allowing for different values of the IGM pressure smoothing scale. We adopt a forward-modeling approach and self-consistently apply the same algorithms to both data and simulations, propagating both statistical and modeling uncertainties via Monte Carlo. The redshift evolution of $T_0$ shows a suggestive peak at $z=2.8$, while our evolution of $γ$ is consistent with $γ\simeq 1.4$ and disfavors inverted temperature-density relations. Our measured evolution of $T_0$ and $γ$ are generally in good agreement with previous determinations in the literature. Both the peak in the evolution of $T_0$ at $z = 2.8$, as well as the high temperatures $T_0\simeq 15000-20000\,$K that we observe at $2.4 < z < 3.4$, strongly suggest that a significant episode of heating occurred after the end of HI reionization, which was most likely the cosmic reionization of HeII.

astro-ph.CO↗

arXiv2018

The COS CGM Compendium (CCC). I: Survey Design and Initial Results

We present a neutral hydrogen-selected absorption-line survey of gas with HI column densities 15 2 orders of magnitude at any given N(HI), indicating a wide range of metallicities (from solar to <1/100 solar). In the range 16.2<log N(HI)<17, there is a gap in the N(MgII) distribution corresponding to gas with ~10% solar metallicity, consistent with the gap seen in the previously identified bimodal metallicity distribution in this column density regime. Less than 3% of the absorbers in our sample show no detectable metal absorption, implying truly-pristine gas at z<1 is uncommon. We find [FeII/MgII] = -0.4+/-0.3, and since alpha-enhancement can affect this ratio, dust depletion is extremely mild.

astro-ph.GA↗

arXiv2018

Origin of Metals around Galaxies I: Catalogs of Metal-line Absorption Doublets from High-Resolution Quasar Spectra

We present the first paper of the series Origin of Metals around Galaxies (OMG) aimed to study the origin of the metals observed in the circumgalactic and intergalactic media. In this work we extract and build the catalogs of metal absorbers that will be used in future analyses, and make our results publicly available to the community. We design a fully automatic algorithm to search for absorption metal-line doublets of the species CIV, NV, SiIV and MgII in high-resolution ($R\gtrsim30\,000$) quasar spectra without human intervention, and apply it to the high-resolution and signal-to-noise ratio spectra of 690 quasars, observed with the UVES and HIRES instruments. We obtain $5\,656$ CIV doublets, $7\,919$ doublets of MgII, $2\,258$ of SiIV, and 239 of NV, constituting the largest high-resolution metal-doublet samples to date, and estimate the dependence of their completeness and purity on various doublet parameters such as equivalent width and redshift, using real and artificial quasar spectra. The catalogs include doublets with rest-frame line equivalent widths down to a few ${\rm mÅ}$, all detected at a significance above 3$σ$, and covering the redshifts between $1<z \lesssim 5$, properties that make them useful for a wide range of chemical evolution studies.

astro-ph.GA↗

arXiv2018

The spectral and environment properties of $z\sim2.0-2.5$ quasar pairs

We present the first results from our survey of intervening and proximate Lyman limit systems (LLSs) at $z$$\sim$2.0-2.5 using the Wide Field Camera 3 on-board the Hubble Space Telescope. The quasars in our sample are projected pairs with proper transverse separations $R_\perp$$\leq$150 kpc and line of sight velocity separations $\lesssim$11,000 km/s. We construct a stacked ultraviolet (rest-frame wavelengths 700-2000Å) spectrum of pairs corrected for the intervening Lyman forest and Lyman continuum absorption. The observed spectral composite presents a moderate flux excess for the most prominent broad emission lines, a $\sim$30% decrease in flux at $λ$=800-900Å compared to a stack of brighter quasars not in pairs at similar redshifts, and lower values of the mean free path of the HI ionizing radiation for pairs ($λ_{\rm mfp}^{912}=140.7\pm20.2~h_{70}^{-1}$Mpc) compared to single quasars ($λ_{\rm mfp}^{912}=213.8\pm28~h_{70}^{-1}$Mpc) at the average redshift $z\simeq2.44$. From the modelling of LLS absorption in these pairs, we find a higher ($\sim$20%) incidence of proximate LLSs with $\log N_{\rm HI}\geq17.2$ at $δv$$<$5,000 km/s compared to single quasars ($\sim$6%). These two rates are different at the 5$σ$ level. Moreover, we find that optically-thick absorbers are equally shared between foreground and background quasars. Based on these pieces of evidence, we conclude that there is a moderate excess of gas absorbing Lyman continuum photons in our closely-projected quasar pairs compared to single quasars. We argue that this gas arises mostly within large-scale structures or partially neutral regions inside the dark matter haloes where these close pairs reside.

astro-ph.GA↗

arXiv2017

The LUVOIR Ultraviolet Multi-Object Spectrograph (LUMOS): Instrument Definition and Design

The Large Ultraviolet / Optical / Infrared Surveyor (LUVOIR) is one of four large mission concepts currently undergoing community study for consideration by the 2020 Astronomy and Astrophysics Decadal Survey. The LUVOIR Ultraviolet Multi-Object Spectrograph, LUMOS, is being designed to support all of the UV science requirements of LUVOIR, from exoplanet host star characterization to tomography of circumgalactic halos to water plumes on outer solar system satellites. LUMOS offers point source and multi-object spectroscopy across the UV bandpass, with multiple resolution modes to support different science goals. The instrument will provide low (R = 8,000-18,000) and medium (R = 30,000-65,000) resolution modes across the far-ultraviolet (FUV: 100-200 nm) and near-ultraviolet (NUV: 200-400 nm) windows, and a very low resolution mode (R = 500) for spectroscopic investigations of extremely faint objects in the FUV. Imaging spectroscopy will be accomplished over a 3 x 1.6 arcminute field-of-view by employing holographically-ruled diffraction gratings to control optical aberrations, microshutter arrays (MSA), advanced optical coatings for high-throughput in the FUV, and next generation large-format photon-counting detectors. The spectroscopic capabilities of LUMOS are augmented by an FUV imaging channel (100-200nm, 13 milliarcsecond angular resolution, 2 x 2 arcminute field-of-view) that will employ a complement of narrow and medium-band filters. We present an overview of LUMOS' observing modes and estimated performance curves for effective area, spectral resolution, and imaging performance. Example "LUMOS 100-hour Highlights" observing programs are presented to demonstrate the potential power of LUVOIR's ultraviolet spectroscopic capabilities.

astro-ph.IM↗

arXiv2017

Flux sensitivity requirements for the detection of Lyman continuum radiation drop-ins from star-forming galaxies below redshifts of 3

Flux estimates for ionizing radiation escaping from star-forming galaxies with characteristic UV luminosities ($L^{*}_{1500(1+z)}$) derived from GALEX and the VIMOS-VLT Deep Survey, are presented as a function of redshift and assumed escape fraction. These estimates offer guidance to the design of instrumentation and observing strategies, be they spectroscopic or photometric, attempting to detect LyC escaping star-forming galaxies for redshifts $ z < 3$. Examples are given that relate the absolution escape fraction ($f^{e}_{LyC}$) of ionizing photons, integrated over the entire extreme UV (EUV) bandpass, to the relative escape fraction ($f^{e}_{900}$) observed just shortward of the ionization edge at 911.8 Å as a function of HI, HeI, and HeII column densities. We find that for $\log{N_{HI}(cm^{-2})} \gtrsim 17.0$ $f^{e}_{LyC}$ is significantly greater than $f^{e}_{900}$. Detection of LyC "drop-ins" in the rest-frame EUV will provide enhanced fidelity to determinations of the integrated fraction of ionizing photons $f^{e}_{LyC}$ that escape star-forming galaxies and contribute to the meta-galactic ionizing background.

astro-ph.GA↗

arXiv2017

Project AMIGA: A Minimal Covering Factor for Optically Thick Circumgalactic Gas Around the Andromeda Galaxy

We present a deep search for HI 21-cm emission from the gaseous halo of Messier 31 as part of Project AMIGA, a large program Hubble Space Telescope program to study the circumgalactic medium of the Andromeda galaxy. Our observations with the Robert C. Byrd Green Bank Telesope target sight lines to 48 background AGNs, more than half of which have been observed in the ultraviolet with the Cosmic Origins Spectrograph, with impact parameters $25 \lesssim ρ\lesssim 330$ kpc ($0.1 \lesssim ρ/ R_{\rm vir} \lesssim 1.1$). We do not detect any 21-cm emission toward these AGNs to limits of $N({\rm HI}) \approx 4 \times10^{17}$ cm$^{-2}$ ($5σ$, per 2 kpc diameter beam). This column density corresponds to an optical depth of $\sim2.5$ at the Lyman limit, thus our observations overlap with absorption line studies of Lyman limit systems at higher redshift. Our non-detections place a limit on the covering factor of such optically-thick gas around M31 to $f_c < 0.051$ (at 90\% confidence) for $ρ\leq R_{\rm vir}$. While individual clouds have previously been found in the region between M31 and M33, the covering factor of strongly optically-thick gas is quite small. Our upper limits on the covering factor are consistent with expectations from recent cosmological "zoom" simulations. Recent COS-Halos ultraviolet measurements of \HI\ absorption about an ensemble of galaxies at $z \approx 0.2$ show significantly higher covering factors within $ρ\lesssim 0.5 R_{\rm vir}$ at the same $N({\rm H I})$, although the metal ion-to-H I ratios appear to be consistent with those seen in M31.

astro-ph.GA↗

arXiv2017

Andromeda's Parachute: A Bright Quadruply Lensed Quasar at z=2.377

We present Keck Cosmic Web Imager spectroscopy of the four putative images of the lensed quasar candidate J014709+463037 recently discovered by Berghea et al. (2017). The data verify the source as a quadruply lensed, broad absorption-line quasar having z_S = 2.377 +/- 0.007. We detect intervening absorption in the FeII 2586, 2600, MgII 2796, 2803, and/or CIV 1548, 1550 transitions in eight foreground systems, three of which have redshifts consistent with the photometric-redshift estimate reported for the lensing galaxy (z_L ~ 0.57). By virtue of their positions on the sky, the source images probe these absorbers over transverse physical scales of ~0.3-21 kpc, permitting assessment of the variation in metal-line equivalent width W_r as a function of sight-line separation. We measure differences in W_r,2796 of <40% across all sight-line pairs subtending 7-21 kpc, suggestive of a high degree of spatial coherence for MgII-absorbing material. W_r,2600 is observed to vary by >50% over the same scales across the majority of sight-line pairs, while CIV absorption exhibits a wide range in W_r,1548 differences of ~5-80% within transverse distances less than ~3 kpc. J014709+463037 is one of only a handful of z > 2 quadruply lensed systems for which all four source images are very bright (r = 15.4-17.7 mag) and are easily separated in ground-based seeing conditions. As such, it is an ideal candidate for higher-resolution spectroscopy probing the spatial variation in the kinematic structure and physical state of intervening absorbers.

astro-ph.GA↗

arXiv2017

The Second Data Release of the KODIAQ Survey

We present and make publicly available the second data release (DR2) of the Keck Observatory Database of Ionized Absorption toward Quasars (KODIAQ) survey. KODIAQ DR2 consists of a fully-reduced sample of 300 quasars at 0.07 < z_em < 5.29 observed with HIRES at high resolution (36,000 <= R <= 103,000). DR2 contains 831 spectra available in continuum normalized form, representing a sum total exposure time of ~4.9 megaseconds on source. These co-added spectra arise from a total of 1577 individual exposures of quasars taken from the Keck Observatory Archive (KOA) in raw form and uniformly processed. DR2 extends DR1 by adding 130 new quasars to the sample, including additional observations of QSOs in DR1. All new data in DR2 were obtained with the single-chip Tektronix TK2048 CCD configuration of HIRES in operation between 1995 and 2004. DR2 is publicly available to the community, housed as a higher level science product at the KOA and in the igmspec database (v03).

astro-ph.GA↗

arXiv2017

Predominantly Low Metallicities Measured in a Stratified Sample of Lyman Limit Systems at z=3.7

We measured metallicities for 33 z=3.4-4.2 absorption line systems drawn from a sample of H I-selected-Lyman limit systems (LLSs) identified in Sloan Digital Sky Survey (SDSS) quasar spectra and stratified based on metal line features. We obtained higher-resolution spectra with the Keck Echellette Spectrograph and Imager, selecting targets according to our stratification scheme in an effort to fully sample the LLS population metallicity distribution. We established a plausible range of H I column densities and measured column densities (or limits) for ions of carbon, silicon, and aluminum, finding ionization-corrected metallicities or upper limits. Interestingly, our ionization models were better constrained with enhanced $α$-to-aluminum abundances, with a median abundance ratio of [$α$/Al]=0.3. Measured metallicities were generally low, ranging from [M/H]=-3 to -1.68, with even lower metallicities likely for some systems with upper limits. Using survival statistics to incorporate limits, we constructed the cumulative distribution function (CDF) for LLS metallicities. Recent models of galaxy evolution propose that galaxies replenish their gas from the low-metallicity intergalactic medium (IGM) via high-density H I "flows" and eject enriched interstellar gas via outflows. Thus, there has been some expectation that LLSs at the peak of cosmic star formation ($z\approx3$) might have a bimodal metallicity distribution. We modeled our CDF as a mix of two Gaussian distributions, one reflecting the metallicity of the IGM and the other representative of the interstellar medium of star-forming galaxies. This bimodal distribution yielded a poor fit. A single Gaussian distribution better represented the sample with a low mean metallicity of [M/H] $\approx -2.5$.

astro-ph.GA↗

arXiv2016

The Cosmic Evolution of the Metallicity Distribution of Ionized Gas Traced by Lyman Limit Systems

We present the first results from our KODIAQ Z survey aimed to determine the metallicity distribution and physical properties of the z>2 partial and full Lyman limit systems (pLLSs and LLSs; 16.2<log N(HI)<19), which are probed of the interface regions between the intergalactic medium (IGM) and galaxies. We study 31 HI-selected pLLSs and LLSs at 2.3<z<3.3 observed with Keck/HIRES in absorption against background QSOs. We compare the column densities of metal-ions to HI and use photoionization models to assess the metallicity. The metallicity distribution of the pLLSs/LLSs at 2.3<z<3.3 is consistent with a unimodal distribution peaking at [X/H]=-2. The metallicity distribution of these absorbers therefore evolves markedly with z since at z<1 it is bimodal with peaks at [X/H]=-1.8 and -0.3. There is a substantial fraction (25-41%) of pLLSs/LLSs with metallicities well below those of damped Lya absorbers (DLAs) at any studied z from z<1 to z~2-4, implying reservoirs of metal-poor cool, dense gas in the IGM/galaxy interface at all z. However, the gas probed by pLLSs and LLSs is rarely pristine, with a fraction 3-18% for pLLSs/LLSs with [X/H]<-3. We find C/alpha enhancement in several pLLSs and LLSs in the metallicity range -2<[X/H]<-0.5, where C/alpha is 2-5 times larger than observed in Galactic metal-poor stars or high redshift DLAs at similar metallicities. This is likely caused by preferential ejection of carbon from metal-poor galaxies into their surroundings.

astro-ph.GA↗

arXiv2016

Low-metallicity Absorbers Account for Half of the Dense Circumgalactic Gas at z < 1

We present an analysis of the metallicity distribution of the dense circumgalactic medium (CGM) of galaxies at 0.1 < z < 1.1 as probed by partial Lyman limit systems (pLLSs, 16.1 < log N(H I) < 17.2) and LLSs (17.2 < log N(H I) < 17.7 in our sample). The new H I-selected sample, drawn from our HST COS G140L snapshot survey of 61 QSOs, has 20 pLLSs and 10 LLSs. Combined with our previous survey, we have a total of 44 pLLSs and 11 LLSs. We find that the metallicity distribution of the pLLSs is bimodal at z < 1, with a minimum at [X/H] = -1. The low-metallicity peak comprises (57 +/- 8)% of the pLLSs and is centered at [X/H] ~ -1.87 (1.3% solar metallicity), while the high-metallicity peak is centered at [X/H] ~ -0.32 (48% solar metallicity). Although the sample of LLSs is still small, there is some evidence that the metallicity distributions of the LLSs and pLLSs are different, with a far lower fraction of very metal-poor ([X/H] < -1.4) LLSs than pLLSs. The fraction of LLSs with [X/H] < -1 is similar to that found in pLLSs (~56%). However, higher H I column density absorbers (log N(H I) > 19.0) show a much lower fraction of metal-poor gas; therefore, the metallicity distribution of gas in and around galaxies depends sensitively on N(H I) at z < 1. We interpret the high-metallicity ([X/H] > -1) pLLSs and LLSs as arising in outflows, recycling winds, and tidally-stripped gas around galaxies. The low-metallicity pLLSs and LLSs imply that the CGM of z < 1 galaxies is also host to a substantial mass of cool, dense, low-metallicity gas that may ultimately accrete onto the galaxies.

astro-ph.GA↗

arXiv2016

MUSE searches for galaxies near very metal-poor gas clouds at z~3: new constraints for cold accretion models

We report on the search for galaxies in the proximity of two very metal-poor gas clouds at z~3 towards the quasar Q0956+122. With a 5-hour MUSE integration in a ~500x500 kpc^2 region centred at the quasar position, we achieve a >80% complete spectroscopic survey of continuum-detected galaxies with m<25 mag and Lyα emitters with luminosity L>3e41 erg/s. We do not identify galaxies at the redshift of a z~3.2 Lyman limit system (LLS) with log Z/Zsun = -3.35 +/- 0.05, placing this gas cloud in the intergalactic medium or circumgalactic medium of a galaxy below our sensitivity limits. Conversely, we detect five Lyα emitters at the redshift of a pristine z~3.1 LLS with log Z/Zsun < -3.8, while ~0.4 sources were expected given the z~3 Lyα luminosity function. Both this high detection rate and the fact that at least three emitters appear aligned in projection with the LLS suggest that this pristine cloud is tracing a gas filament that is feeding one or multiple galaxies. Our observations uncover two different environments for metal-poor LLSs, implying a complex link between these absorbers and galaxy halos, which ongoing MUSE surveys will soon explore in detail. Moreover, in agreement with recent MUSE observations, we detected a ~90 kpc Lyα nebula at the quasar redshift and three Lyα emitters reminiscent of a "dark galaxy" population.

astro-ph.GA↗

arXiv2015

Possible Population III Remnants at Redshift 3.5

The first stars, known as Population III (PopIII), produced the first heavy elements, thereby enriching their surrounding pristine gas. Previous detections of metals in intergalactic gas clouds, however, find a heavy element enrichment larger than $1/1000$ times that of the solar environment, higher than expected for PopIII remnants. In this letter we report the discovery of a Lyman limit system (LLS) at $z=3.53$ with the lowest metallicity seen in gas with discernable metals, $10^{-3.41\pm0.26}$ times the solar value, at a level expected for PopIII remnants. We make the first relative abundance measurement in such low metallicity gas: the carbon-to-silicon ratio is $10^{-0.26\pm0.17}$ times the solar value. This is consistent with models of gas enrichment by a PopIII star formation event early in the Universe, but also consistent with later, Population II enrichment. The metals in all three components comprising the LLS, which has a velocity width of 400 km s$^{-1}$, are offset in velocity by $\sim+6$ km s$^{-1}$ from the bulk of the hydrogen, suggesting the LLS was enriched by a single event. Relative abundance measurements in this near-pristine regime open a new avenue for testing models of early gas enrichment and metal mixing.

astro-ph.GA↗

arXiv2015

The physical properties of z>2 Lyman limit systems: new constraints for feedback and accretion models

We study the physical properties of a homogeneous sample of 157 optically-thick absorption line systems at redshifts ~1.8-4.4, selected from a high-dispersion spectroscopic survey of Lyman limit systems (LLSs). By means of multiple ionisation models and Bayesian techniques, we derive the posterior probability distribution functions for the density, metallicity, temperature, and dust content of the absorbing gas. We find that z>2 LLSs are highly ionised with ionisation parameters between -3 2 are characterised by a broad unimodal distribution over >4 orders of magnitude, with a peak at log Z/Zsun~-2. LLSs are metal poor, significantly less enriched than DLAs, with ~70% of the metallicity PDF below log Z/Zsun<-1.5. The median metallicity of super LLSs with log N(HI)>19 rapidly evolves with redshift, with a ten-fold increase between z~2.1-3.6 (~1.5 Gyr). Based on this sample, we find that LLSs at z=2.5-3.5 account for ~15% of all the metals produced by UV-selected galaxies. The implications for theories of cold gas accretion and metal ejection from galaxies are also discussed.

astro-ph.GA↗

arXiv2015

A Deep Search For Faint Galaxies Associated With Very Low-redshift C IV Absorbers: II. Program Design, Absorption-line Measurements, and Absorber Statistics

To investigate the evolution of metal-enriched gas over recent cosmic epochs as well as to characterize the diffuse, ionized, metal-enriched circumgalactic medium (CGM), we have conducted a blind survey for C IV absorption systems in 89 QSO sightlines observed with the Hubble Space Telescope (HST) Cosmic Origins Spectrograph (COS). We have identified 42 absorbers at z < 0.16, comprising the largest uniform blind sample size to date in this redshift range. Our measurements indicate an increasing C IV absorber number density per comoving path length (dN/dX = 7.5 +/- 1.1) and modestly increasing mass density relative to the critical density of the Universe (Omega(C IV) = 10.0 +/- 1.5 x 10^-8 ) from z ~ 1.5 to the present epoch, consistent with predictions from cosmological hydrodynamical simulations. Furthermore, the data support a functional form for the column density distribution function that deviates from a single power-law, also consistent with independent theoretical predictions. As the data also probe heavy element ions in addition to C IV at the same redshifts, we identify, measure, and search for correlations between column densities of these species where components appear aligned in velocity. Among these ion-ion correlations, we find evidence for tight correlations between C II and Si II, C II and Si III, and C IV and Si IV, suggesting that these pairs of species arise in similar ionization conditions. However, the evidence for correlations decreases as the difference in ionization potential increases. Finally, when controlling for observational bias, we find only marginal evidence for a correlation (86.8% likelihood) between the Doppler line width b(C IV) and column density N(C IV).

astro-ph.GA↗

arXiv2015

The Keck+Magellan Survey for Lyman Limit Absorption III: Sample Definition and Column Density Measurements

We present an absorption-line survey of optically thick gas clouds -- Lyman Limit Systems (LLSs) -- observed at high dispersion with spectrometers on the Keck and Magellan telescopes. We measure column densities of neutral hydrogen NHI and associated metal-line transitions for 157 LLSs at z=1.76-4.39 restricted to 10^17.3 < NHI < 10^20.3. An empirical analysis of ionic ratios indicates an increasing ionization state of the gas with decreasing NHI and that the majority of LLSs are highly ionized, confirming previous expectations. The Si^+/H^0 ratio spans nearly four orders-of-magnitude, implying a large dispersion in the gas metallicity. Fewer than 5% of these LLSs have no positive detection of a metal transition; by z~3, nearly all gas that is dense enough to exhibit a very high Lyman limit opacity has previously been polluted by heavy elements. We add new measurements to the small subset of LLS (~5-10) that may have super-solar abundances. High Si^+/Fe^+ ratios suggest an alpha-enhanced medium whereas the Si^+/C^+ ratios do not exhibit the super-solar enhancement inferred previously for the Lya forest.

astro-ph.CO↗

arXiv2015

The Neutral Hydrogen Cosmological Mass Density at z=5

We present the largest homogeneous survey of $z>4.4$ damped Lyman-$α$ systems (DLAs) using the spectra of 163 QSOs that comprise the Giant Gemini GMOS (GGG) survey. With this survey we make the most precise high-redshift measurement of the cosmological mass density of neutral hydrogen, $Ω_{\rm HI}$. At such high redshift important systematic uncertainties in the identification of DLAs are produced by strong intergalactic medium absorption and QSO continuum placement. These can cause spurious DLA detections, result in real DLAs being missed, or bias the inferred DLA column density distribution. We correct for these effects using a combination of mock and higher-resolution spectra, and show that for the GGG DLA sample the uncertainties introduced are smaller than the statistical errors on $Ω_{\rm HI}$. We find $Ω_{\rm HI}=0.98^{+0.20}_{-0.18}\times10^{-3}$ at $\langle z\rangle=4.9$, assuming a 20% contribution from lower column density systems below the DLA threshold. By comparing to literature measurements at lower redshifts, we show that $Ω_{\rm HI}$ can be described by the functional form $Ω_{\rm HI}(z)\propto(1+z)^{0.4}$. This gradual decrease from $z=5$ to $0$ is consistent with the bulk of HI gas being a transitory phase fuelling star formation, which is continually replenished by more highly-ionized gas from the intergalactic medium, and from recycled galactic winds.

astro-ph.CO↗