Voigt Profile Fitting Research Articles

Detecting Novel Damped Lyα Absorbers in the Intergalactic Medium

Damped Lyα (DLA) absorbers are a class of quasar absorption line systems that can be used to trace hydrogen evolution and study gas, composition, kinematics, and stellar formation in galaxies or the intergalactic medium in the early universe. In this study, the number of DLA absorbers found with a deep learning algorithm is augmented using metal Mg ii absorbers as signposts. The artificial training data was generated by inserting synthetic absorption lines into spectra. Using previously identified DLAs as a test set, the model returned a 94.6% accuracy score and 1197 new DLA absorbers, which nearly doubles the previously known number of samples within the search catalog. Additionally, the column density and Doppler broadening are measured on the newly found DLA absorbers through Voigt profile fitting.

FLAME: Fitting Lyman-alpha absorption lines using machine learning

We introduce FLAME, a machine-learning algorithm designed to fit Voigt profiles to H i Lyman-alpha ( absorption lines using deep convolutional neural networks. FLAME integrates two algorithms: the first determines the number of components required to fit absorption lines, and the second calculates the Doppler parameter $b$, the H i column density N$_ HI $, and the velocity separation of individual components. For the current version of FLAME, we trained it on low-redshift forests observed with the far-ultraviolet gratings of the Cosmic Origin Spectrograph (COS) on board the Hubble Space Telescope (HST). Using these data, we trained FLAME on sim $10^6$ simulated Voigt profiles ---which we forward-modeled to mimic absorption lines observed with HST-COS--- in order to classify lines as either single or double components and then determine Voigt profile-fitting parameters. FLAME shows impressive accuracy on the simulated data, identifying more than 98<!PCT!> (90<!PCT!>) of single (double) component lines. It determines $b$ values within $ (15)$ km s$^ $ and log $N_ HI cm ^2$ values within $ 0.3 (0.8)$ for 90<!PCT!> of the single (double) component lines. However, when applied to real data, FLAME's component classification accuracy drops by sim 10<!PCT!>. Nevertheless, there is reasonable agreement between the $b$ and HI $ distributions obtained from traditional Voigt profile-fitting methods and FLAME's predictions. Our mock HST-COS data analysis, designed to emulate real data parameters, demonstrates that FLAME is able to achieve consistent accuracy comparable to its performance with simulated data. This finding suggests that the drop in FLAME's accuracy when used on real data primarily arises from the difficulty in replicating the full complexity of real data in the training sample. In any case, FLAME's performance validates the use of machine learning for Voigt profile fitting, underscoring the significant potential of machine learning for detailed analysis of absorption lines.

The BarYon Cycle project (ByCycle): identifying and localizing Mg ii metal absorbers with machine learning

ABSTRACT The upcoming ByCycle project on the VISTA/4MOST multi-object spectrograph will offer new prospects of using a massive sample of ∼1 million high spectral resolution (R = 20 000) background quasars to map the circumgalactic metal content of foreground galaxies (observed at R = 4000–7000), as traced by metal absorption. Such large surveys require specialized analysis methodologies. In the absence of early data, we instead produce synthetic 4MOST high-resolution fibre quasar spectra. To do so, we use the TNG50 cosmological magnetohydrodynamical simulation, combining photo-ionization post-processing and ray tracing, to capture Mg ii (λ2796, λ2803) absorbers. We then use this sample to train a convolutional neural network (CNN) which searches for, and estimates the redshift of, Mg ii absorbers within these spectra. For a test sample of quasar spectra with uniformly distributed properties ($\lambda _{\rm {Mg\, {\small II},2796}}$, $\rm {EW}_{\rm {Mg\, {\small II},2796}}^{\rm {rest}} = 0.05\!-\!5.15$ Å, $\rm {SNR} = 3\!-\!50$), the algorithm has a robust classification accuracy of 98.6 per cent and a mean wavelength accuracy of 6.9 Å. For high signal-to-noise (SNR) spectra ($\rm {SNR \gt 20}$), the algorithm robustly detects and localizes Mg ii absorbers down to equivalent widths of $\rm {EW}_{\rm {Mg\, {\small II},2796}}^{\rm {rest}} = 0.05$ Å. For the lowest SNR spectra ($\rm {SNR=3}$), the CNN reliably recovers and localizes EW$_{\rm {Mg\, {\small II},2796}}^{\rm {rest}}$ ≥0.75 Å absorbers. This is more than sufficient for subsequent Voigt profile fitting to characterize the detected Mg ii absorbers. We make the code publicly available through GitHub. Our work provides a proof-of-concept for future analyses of quasar spectra data sets numbering in the millions, soon to be delivered by the next generation of surveys.

MUSEQuBES: the relation between Ly α emitters and C iv absorbers at z ≈ 3.3

ABSTRACT We present a detailed study of the column density and covering fraction profiles of C iv absorption around 86 redshift z ≈ 3.3 Ly α emitters (LAEs) detected in eight Multi-Unit Spectroscopic Explorer (MUSE) fields of 1 arcmin × 1 arcmin centred on eight bright background quasars as part of the MUSE Quasar-field Blind Emitters Survey (MUSEQuBES). Using Voigt profile fitting of all the C iv absorbers detected along these eight sightlines, we generated a ‘blind’ absorber catalogue consisting of 489 C iv absorption components. We cross-matched this blind C iv catalogue with the MUSE-detected LAE catalogue and found a significant enhancement of C iv components within ≈±400 $\rm km\, s^{-1}$ of the systemic redshifts of the LAEs. Neither the C iv column density (N) nor the Doppler parameter (b) of individual C iv components shows any significant anticorrelation with impact parameter (ρ) of the LAEs in the 68 percentile range of 90 ≤ ρ ≤ 230 physical kpc (pkpc). We find a covering fraction of ≈60 per cent for a threshold $N(\rm{C{\small IV}})$ of 1012.5 cm−2, which is roughly twice as high as in random regions. The C iv covering fraction remains constant at $\approx\!{50}{{\ \rm per\, cent}}$ for impact parameters in the range of 150–250 pkpc (≈3–6R200). Using the covering fraction profile, we constrain the LAE–C iv absorber two-point correlation function, and obtain $r_0 = 3.4^{+1.1}_{-1.0}$ comoving Mpc and $\gamma = 1.2^{+0.2}_{-0.3}$ for a threshold $N(\rm{C{\small IV}})$ of 1013.0 cm−2. The C iv covering fraction is found to be enhanced for the LAEs that are part of a ‘pair/group’ compared to the isolated ones.

Harvesting the Ly α forest with convolutional neural networks

ABSTRACT We develop a machine learning based algorithm using a convolutional neural network (CNN) to identify low H i column density Ly α absorption systems (log NH i/cm−2 < 17) in the Ly α forest, and predict their physical properties, such as their H i column density (log NH i/cm−2), redshift (zH i), and Doppler width (bH i). Our CNN models are trained using simulated spectra (S/N ≃ 10), and we test their performance on high quality spectra of quasars at redshift z ∼ 2.5−2.9 observed with the High Resolution Echelle Spectrometer on the Keck I telescope. We find that ${\sim}78{{\ \rm per\ cent}}$ of the systems identified by our algorithm are listed in the manual Voigt profile fitting catalogue. We demonstrate that the performance of our CNN is stable and consistent for all simulated and observed spectra with S/N ≳ 10. Our model can therefore be consistently used to analyse the enormous number of both low and high S/N data available with current and future facilities. Our CNN provides state-of-the-art predictions within the range 12.5 ≤ log NH i/cm−2 < 15.5 with a mean absolute error of Δ(log NH i/cm−2) = 0.13, Δ(zH i) = 2.7 × 10−5, and Δ(bH i) = 4.1 km s−1. The CNN prediction costs < 3 min per model per spectrum with a size of 120 000 pixels using a laptop computer. We demonstrate that CNNs can significantly increase the efficiency of analysing Ly α forest spectra, and thereby greatly increase the statistics of Ly α absorbers.

Performance of ESPRESSO’S high-resolution 4 × 2 binning for characterising intervening absorbers towards faint quasars

As of October 2021 (Period 108), the European Southern Observatory (ESO) offers a new mode of the ESPRESSO spectrograph designed to use the high-resolution grating with 4 × 2 binning (spatial by spectral; HR42 mode), with the specific objective of observing faint targets with a single Unit Telescope at Paranal. We validated the new HR42 mode using four hours of on-target observations of the quasar J0003-2603, known to host an intervening metal-poor absorber along the line of sight. The capabilities of the ESPRESSO HR42 mode (resolving power R ≈ 137 000) were evaluated by comparing them to a UVES spectrum of the same target with a similar integration time but lower resolving power (R ≈ 48 000). For both data sets, we tested the ability to decompose the velocity profile of the intervening absorber using Voigt profile fitting and extracted the total column densities of C IV, N I, Si II, Al II, Fe II, and Ni II. With ≈3× the resolving power and ≈2× lower signal-noise ratio (S/N) for a nearly equivalent exposure time, the ESPRESSO data is able to just as accurately characterise the individual components of the absorption lines as the comparison UVES data, but it has the added bonus of identifying narrower components not detected by UVES. For UVES to provide similar spectral resolution (R > 100 000; 0.3″ slit) and the broad wavelength coverage of ESPRESSO, the Exposure Time Calculator (ETC) supplied by ESO estimates 8 h of exposure time spread over two settings, requiring double the time investment compared to that of ESPRESSO’s HR42 mode whilst not properly sampling the UVES spectral resolution element. Thus, ESPRESSO’s HR42 mode offers nearly triple the resolving power of UVES (0.8″ slit to match typical ambient conditions at Paranal) and provides more accurate characterisation of quasar absorption features for an equivalent exposure time.

Metallicities of outer halo M31 globular clusters from integrated light calcium-II triplet spectroscopy

ABSTRACT This paper presents [Fe/H] ratios for globular clusters (GCs) in the outer halo of the Andromeda Galaxy, M31, based on moderate-resolution, integrated light (IL) spectroscopy of the calcium-II triplet (CaT) lines. The CaT strengths are measured by fitting Voigt profiles to the lines and integrating those profiles; integrations of defined bandpasses are also considered. The [Fe/H] ratios are determined using an empirical calibration with CaT line strength, as derived from another sample of M31 GCs that were previously studied at high-resolution. The [Fe/H] ratios for the new GCs reveal that the outer halo GCs are indeed generally more metal-poor than typical inner halo GCs, though there are several more metal-rich GCs that look to have been accreted from dwarf satellites. The metallicities of these GCs also place important constraints on the nature of the substructure in the outer halo and the dwarf satellites that created this substructure.

D-depleted water isotopic measurement with a miniaturized cavity ring-down spectrometer aiming for exploration of lunar water

A miniaturized cavity ring-down spectrometer (mini-CRDS) with 5 cm cavity length using a near-infrared laser diode was developed, aiming for exploration of lunar water. This mini-CRDS enables us to measure a water vapor sample of limited amount at low pressure (< 100 Pa) by an unique mechanism using Peltier element modules that changes the resonance point to interpolate the gap of the free spectral range (FSR) of the cavity. We measured aqua samples with different D/H ratios and applied Voigt profile fitting to the absorption spectra, then obtained a calibration line of HDO isotope. The signal to noise ratio (SNR) of HDO peak at δD = − 980‰ was 7.17, which was enough higher than the detection limit of 3.

Sharpening quasar absorption lines with ESPRESSO. Temperature of warm gas at z ~ 2, constraints on the Mg isotopic ratio, and structure of cold gas at z ~ 0.5

Aims. We aim to study several key physical properties of quasar absorption-line systems that are subtly encoded in their absorption profiles and have not yet been thoroughly investigated or constrained. Methods. We analysed a high-resolution (R = 140 000) spectrum of the bright quasar HE 0001−2340 (zem = 2.26) obtained with ESPRESSO, which was recently installed at the Very Large Telescope. We analysed three systems at z = 0.45, z = 1.65, and z = 2.19 using multiple-component Voigt-profile fitting. We also compared our spectrum with those obtained with VLT/UVES, covering a total period of 17 years. Results. We disentangle turbulent and thermal broadening in many components spread over about 400 km s−1 in the z ≈ 2.19 sub-damped Lyman-α system. We derive an average temperature of 16 000 ± 1300 K, which is about twice the canonical value of the warm neutral medium in the Galactic interstellar medium (ISM). A comparison with other high-z, low-metallicity absorbers reveals an anti-correlation between gas temperature and total H I column density. Although requiring confirmation, this could be the first observational evidence of a thermal decrease with galactocentric distance; in other words, we may be witnessing a thermal transition between the circumgalactic medium and the cooler ISM. We revisit the Mg isotopic ratios at z = 0.45 and z = 1.65 and constrain them to be ξ = (26Mg + 25Mg)/24Mg &lt; 0.6 and &lt; 1.4 in these two systems, respectively. These values are consistent with the standard solar ratio; that is, we do not confirm strong enhancement of heavy isotopes previously inferred from UVES data. Finally, we confirm the partial coverage of the quasar emission-line region by a Fe I-bearing cloud in the z = 0.45 system and present evidence for velocity substructure of the gas that has Doppler parameters of the order of only ∼0.3 km s−1. This agrees well with the low kinetic temperature of T ∼ 100 K inferred from modelling of the gas physical conditions. Conslusions. This work demonstrates the unique insight provided by high-fidelity, high-resolution optical spectrographs on large telescopes when used to investigate the thermal state of the gas in and around galaxies as well as its spatial and velocity structure on small scales, and to constrain the associated stellar nucleosynthetic history.

A Polarization-Insensitive Recirculating Delayed Self-Heterodyne Method for Sub-Kilohertz Laser Linewidth Measurement

A polarization-insensitive recirculating delayed self-heterodyne method (PI-RDSHM) is proposed and demonstrated for the precise measurement of sub-kilohertz laser linewidths. By a unique combination of Faraday rotator mirrors (FRMs) in an interferometer, the polarization-induced fading is effectively reduced without any active polarization control. This passive polarization-insensitive operation is theoretically analyzed and experimentally verified. Benefited from the recirculating mechanism, a series of stable beat spectra with different delay times can be measured simultaneously without changing the length of delay fiber. Based on Voigt profile fitting of high-order beat spectra, the average Lorentzian linewidth of the laser is obtained. The PI-RDSHM has advantages of polarization insensitivity, high resolution, and less statistical error, providing an effective tool for accurate measurement of sub-kilohertz laser linewidth.

Mg ii Absorbers in High-resolution Quasar Spectra. I. Voigt Profile Models

Abstract We present the Voigt profile (VP) models, column densities, Doppler b parameters, kinematics, and distribution of components for 422 Mg ii absorbers found in a survey of 249 HIRES and UVES quasar spectra. The equivalent width range of the sample is 0.006 ≤ W r (2796) ≤ 6.23 Å and the redshift range is 0.19 ≤ z ≤ 2.55, with a mean of . Based on historical precedent, we classified 180 absorbers as weak systems (W r (2796) &lt; 0.3 Å) and 242 as strong systems (W r (2796) ≥ 0.3 Å). Assuming a minimum number of significant components per system, the VP fitting, yielded a total of 2989 components, with an average of 2.7 and 10.3 components found for the weak and strong Mg ii subsamples, respectively. The VP component line density for the full sample is 8.62 ± 0.23 clouds Å−1. The distribution of VP component column density over the range 12.4 ≤ log N(Mg ii) ≤ 17.0 cm−2 is well modeled with a power-law slope of −1.45 ± 0.01. The median Doppler b parameters are 4.5 ± 3.5 km s−1, 6.0 ± 4.5 km s−1, and 5.7 ± 4.4 km s−1 for the weak, strong, and full samples. We modeled the probability of component velocity splitting (the two-point velocity correlation function) of our full sample using a three-component composite Gaussian function. Our resulting velocity dispersions are σ 1 = 25.4 km s−1, σ 2 = 68.7 km s−1, and σ 3 = 207.1 km s−1. These data provide an excellent database for studying the cosmic evolution of Mg ii absorber kinematic evolution.

Probing the thermal state of the intergalactic medium at z &amp;gt; 5 with the transmission spikes in high-resolution Ly α forest spectra

ABSTRACT We compare a sample of five high-resolution, high S/N Ly α forest spectra of bright 6 &amp;lt; z &amp;lt; ∼6.5 QSOs aimed at spectrally resolving the last remaining transmission spikes at z &amp;gt; 5 with those obtained from mock absorption spectra from the Sherwoodand Sherwood–Relics simulation suites of hydrodynamical simulations of the intergalactic medium (IGM). We use a profile-fitting procedure for the inverted transmitted flux, 1 − F, similar to the widely used Voigt profile fitting of the transmitted flux F at lower redshifts, to characterize the transmission spikes that probe predominately underdense regions of the IGM. We are able to reproduce the width and height distributions of the transmission spikes, both with optically thin simulations of the post-reionization Universe using a homogeneous UV background and full radiative transfer simulations of a late reionization model. We find that the width of the fitted components of the simulated transmission spikes is very sensitive to the instantaneous temperature of the reionized IGM. The internal structures of the spikes are more prominent in low temperature models of the IGM. The width distribution of the observed transmission spikes, which require high spectral resolution (≤ 8 km s−1) to be resolved, is reproduced for optically thin simulations with a temperature at mean density of T0 = (11 000 ± 1600, 10 500 ± 2100, 12 000 ± 2200) K at z = (5.4, 5.6, 5.8). This is weakly dependent on the slope of the temperature-density relation, which is favoured to be moderately steeper than isothermal. In the inhomogeneous, late reionization, full radiative transfer simulations where islands of neutral hydrogen persist to z ∼ 5.3, the width distribution of the observed transmission spikes is consistent with the range of T0 caused by spatial fluctuations in the temperature–density relation.

Temperature dependence of collisional broadening and shift for the Kr 4p6S01→5p[3/2]2 electronic transition.

Temperature scaling of collisional broadening parameters for krypton (absorber) 4p6S01→5p[3/2]2 electronic transition centered at 107.3 nm in the presence of major combustion species (perturber) is investigated. The absorption spectrum in the vicinity of the transition is obtained from the fluorescence due to the two-photon excitation scan of krypton. Krypton was added in small amounts to major combustion species such as CH4, CO2, N2, and air, which then heated to elevated temperatures when flowed through a set of heated coils. In a separate experimental campaign, laminar premixed flat flame product mixtures of methane combustion were employed to extend the investigations to higher temperature ranges relevant to combustion. Collisional full width half maximum (FWHM) (wC) and shift (δC) were computed from the absorption spectrum by synthetically fitting Voigt profiles to the excitation scans, and their corresponding temperature scaling was determined by fitting power-law temperature dependencies to the wC and δC data for each perturber species. The temperature exponents of wC and δC for all considered combustion species (perturbers) were -0.73 and -0.6, respectively. Whereas the temperature exponents of wC are closer to the value (-0.7) predicted by the dispersive interaction collision theory, the corresponding exponents of δC are in between the dispersive interaction theory and the kinetic theory of hard-sphere collisions. Comparison with existing literature on broadening parameters of NO, OH, and CO laser-induced fluorescence spectra reveal interesting contributions from non-dispersive interactions on the temperature exponent.

Quantum mechanics at high redshift – Modelling Damped Lyman–α absorption systems

Abstract For around 100 years, hydrogen spectral modelling has been based on Voigt profile fitting. The semi-classical Voigt profile is based on a 2-level atom approximation. Whilst the Voigt profile is excellent for many circumstances, the accuracy is insufficient for very high column density damped Lyman-α absorption systems. We have adapted the quantum-mechanical Kramers-Heisenberg model to include thermal broadening, producing a new profile, the KHT profile. Interactions involving multiple discrete atomic levels and continuum terms, not accounted for in the Voigt model, generate asymmetries in the Lyman line wings. If not modelled, this can lead to significant systematics in parameter estimation when modelling real data. There are important ramifications in particular for measurements of the primordial deuterium abundance. However, the KHT model is complicated. We therefore present a simplified formulation based on Taylor series expansions and look-up tables, quantifying the impact of the approximations made. The KHT profile has been implemented within the widely-used VPFIT code.

Three- and two-point spatial correlations of intergalactic medium at z ∼ 2 using projected quasar triplets

ABSTRACT We present analysis of two- and three-point correlation functions of Lyα forest (at 2 ≤ z ≤ 2.5) using X-Shooter spectra of three background quasar triplets probing transverse separations of 0.5–1.6 pMpc. We present statistics based on transmitted flux and clouds identified using Voigt profile fitting. We show that the observed two-, three-point correlation functions and reduced three-point correlation (i.e. Q) are well reproduced by our simulations. We assign probabilities for realizing all the observed correlation properties simultaneously using our simulations. Our simulations suggest an increase in correlation amplitudes and Q with increasing NH i. We roughly see this trend in the observations too. We identify a concurrent gap of 17Å (i.e. 14.2 h−1 cMpc, one of the longest reported) wide along one of the triplets. Such gap is realized only in 14.2 per cent of our simulated sightlines and most of the time belongs to a void in the matter distribution. In the second triplet, we detect Damped Lyα systems (DLAs) along all three sightlines (with spatial separations 0.64 to 1.6 pMpc) within a narrow redshift interval (i.e. Δz = 0.088). Detection of a foreground quasar (∼1 pMpc from the triplet sightlines) and excess partial Lyman Limit systems (with NH i in the range $10^{16-17.2} \, \mathrm{cm}^{-2}$) around these DLAs suggest that we may be probing a large overdense region. We also report positive C iv–C iv correlations up to ∼500 km s−1 only in the longitudinal direction. Additionally, we conclude a positive C iv–Lyα correlations for higher NH i thresholds (${\gt}10^{15}\, \mathrm{cm}^{-2}$) up to a scale of ∼1000 km s−1 both in transverse and longitudinal directions.

Laser frequency noise characterization by self-heterodyne with both long and short delay.

We propose a novel approach to laser frequency noise characterization by delayed self-heterodyne. Compared with the traditional treatment, our method applies to both long and short delay, corresponding to uncorrelated and correlated self-heterodyne. In the case of long delay, it overcomes the influence of 1/f noise on the intrinsic linewidth extraction from a broadened spectrum, and the results are more accurate than Voigt profile fitting. For short delayed correlated heterodyne, it eliminates artifact peaks at multiples of the reciprocal of delay time introduced by transferring measured RF phase noise to laser phase noise, thus extending the measurement range. In addition, it calibrates the frequency noise overestimation caused by a finite noise floor. This method remains valid when the delay and the coherence time are comparable. Experimental results are presented to demonstrate the effectiveness of the proposed approach in characterizing lasers with intrinsic linewidth ranging from sub-100Hz to megahertz.

Cesium atomic Doppler broadening thermometry for room temperature measurement

Atomic Doppler broadening thermometry (DBT) is potentially an accurate and practical approach for thermodynamic temperature measurement. However, previous reported atomic DBT had a long acquisition time and had only been proved at the triple point of water, 0°C, for the purpose of determination of the Boltzmann constant. This research implemented the cesium atomic DBT for fast room temperature measurement. The Cs133 D1 (6S1/2 → 6p1/2 transition) line was measured by direct laser absorption spectroscopy, and the quantity of thermal-induced linewidth broadening was precisely retrieved by the Voigt profile fitting algorithm. The preliminary results showed the proposed approach had a 4 min single-scan acquisition time and 0.2% reproducibility. It is expected that the atomic DBT could be used as an accurate, chip-scale, and calibration-free temperature sensor and standard.

Estimation of the temperature-density relation in the intergalactic medium at z ∼ 2 – 4 via Lyα forest

Quasar spectra provide a unique opportunity to investigate the intergalactic medium at high redshifts. The spectral analysis of the Lya forest allows us to constrain the effective equation of state of the intergalactic medium and its changes during the evolution of the Universe. Based on the Voigt profile fitting of Lya forest lines in 50 high-resolution QSO spectra obtained at Keck telescope we present new measurements of the power-law index γ of temperature-density relation in IGM for six redshift bins in the range z = 1.6 – 3.7. We find that the IGM state is close to isothermal (γ ≈ 1) at z ∼ 3 which may indicate that HeII reionization occurred at this redshift.

A New Measurement of the Temperature–density Relation of the IGM from Voigt Profile Fitting

Abstract We decompose the Lyman-α (Lyα) forest of an extensive sample of 75 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– distribution set primarily by the thermal state of the intergalactic medium (IGM). We fit this cutoff as a function of redshift over the range , which allows us to measure the evolution of the IGM temperature–density ( ) relation parameters T 0 and γ. We calibrate our measurements against mock Lyα forest data generated using 26 hydrodynamic simulations with different thermal histories from the THERMAL suite, also encompassing 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 (γ) shows a suggestive peak (dip) at z = 2.9 (z = 3). Our measured evolution of T 0 and γ is 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 that we observe at 2.4 &lt; z &lt; 3.4, strongly suggest that a significant episode of heating occurred after the end of H i reionization, which was most likely the cosmic reionization of He ii.

DLA and sub-DLA metallicity evolution: A case study of absorbers towards Q0338-0005

The damped and sub-damped Lyα systems (DLAs and sub-DLAs) traced in absorption against bright background quasars represent the main reserve of neutral hydrogen at high redshifts. We used the archival Very Large Telescope (VLT) instrument Ultraviolet and Visual Echelle Spectrograph (UVES) high-resolution data of Q 0338-0005 (zem=3.049) to study the abundances of the DLA (zabs=2.2298) and sub-DLA (zabs=2.7457) along the line of sight. We estimated column densities of H i and various elements present in the DLA and sub-DLA through Voigt profile fitting. The DLA throgh shows the Lyα emission from its host galaxy. We derive the metallicities of the DLA and sub-DLA with [Zn/H] =−0.67±0.18 and [S/H] =−1.45±0.17, respectively. We compared our abundances of the DLA and sub-DLA with other high-resolution DLA and sub-DLA metallicities and find that both populations show an overall increase of metallicity with decreasing redshift. However, sub-DLAs have higher metallicities than the DLAs.