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Emma V. Ryan-Weber

Publications and source records attributed to Emma V. Ryan-Weber.

At least 19 recordsLinked to original sources
arXiv2026

Forest without Trees is still Fruitful: Constraints on the thermal state of the neutral IGM at $z\approx5.6$ with the 21-cm forest power spectrum

Neutral regions of the intergalactic medium (IGM) during the Epoch of Reionization (EoR) remain largely unexplored due to the limitations of existing probes. Owing to discoveries of numerous high-redshift radio-bright sources, the 21-cm forest, a series of absorption features imprinted by the neutral IGM in the spectra of such sources, now offers an attractive probe of the thermal and ionization state of the predominantly neutral IGM at $z\gtrsim5.5$. We analyse archival upgraded Giant Metrewave Radio Telescope (uGMRT) observations of J352-15, the brightest known radio-loud quasar in the EoR ($z=5.82$), to measure the one-dimensional (1D) power spectrum of the 21-cm forest. By comparing the observed power spectrum with forward-modelled synthetic spectra generated from cosmological simulations spanning a wide range of ionization and X-ray pre-heating scenarios, we perform Bayesian inference even in the absence of a statistical detection. We also present an independent Murchison Widefield Array measurement, although its lower sensitivity prevents competitive constraints. Using uGMRT, we achieve a sensitivity of $3.62\,\rm mJy\,beam^{-1}$ per $6.1\,\rm kHz$ channel. While we do not detect the 21-cm forest statistically, the null detection jointly constrains the mean neutral hydrogen fraction, $\langle x_{\rm HI}\rangle$, and the mean temperature of the neutral IGM, $\langle T_{\rm HI}\rangle$. At the $68\%$ credible level, our analysis disfavours cold and substantially neutral IGM models at $z\approx5.6$, including models with $\langle T_{\rm HI}\rangle \lesssim 27\,\rm K$ for $\langle x_{\rm HI}\rangle=0.1$. These limits probe parameter space allowed by existing Ly$α$ and 21-cm observations, indicating substantial pre-heating of the neutral IGM above the adiabatic cooling floor. This demonstrates that the 21-cm forest has entered the regime of observationally informative statistics.

astro-ph.CO↗
arXiv2025

An extremely metal-poor Lyman $α$ emitter candidate at $z=6$ revealed through absorption spectroscopy

We report the discovery of a Lyman $α$ emitter (LAE) candidate in the immediate foreground of the quasar PSO J158-14 at $z_{\rm QSO}=6.0685$ at a projected distance $\sim29\ {\rm pkpc}$ that is associated with an extremely metal-poor absorption system. This system was found in archival observations of the quasar field with the Very Large Telescope/Multi-Unit Spectroscopic Explorer (VLT/MUSE) and was previously missed in searches of absorption systems using quasar absorption line spectroscopy as it imparts no detectable metal absorption lines on the background quasar spectrum. The detected Ly$α$ emission line at a redshift of $z_{\rm LAE}=6.0323$ is well aligned with the outer edge of the quasar's proximity zone and can plausibly cause its observed damping wing if it is associated with a proximate sub-damped Ly$α$ absorption system with a column density of $\log {N_{\rm HI} / {\rm cm}^{-2}} \approx 19.7$. A $>10$ hour medium-resolution spectrum of the quasar observed with the Magellan/Folded-port InfraRed Echellette (FIRE) and VLT/X-Shooter spectrographs reveals a metallicity constraint of ${\rm [Z/H]} < -3$. Such low metallicity makes this system an extremely metal-poor galaxy candidate and provides an exciting site to study possible signatures of Population III stars.

astro-ph.GA↗
arXiv2024

Damping Wing-Like Features in the Stacked Ly$α$ Forest: Potential Neutral Hydrogen Islands at $z<6$

Recent quasar absorption line observations suggest that reionization may end as late as $z \approx 5.3$. As a means to search for large neutral hydrogen islands at $z<6$, we revisit long dark gaps in the Ly$β$ forest in VLT/X-Shooter and Keck/ESI quasar spectra. We stack the Ly$α$ forest corresponding to both edges of these Ly$β$ dark gaps and identify a damping wing-like extended absorption profile. The average redshift of the stacked forest is $z=5.8$. By comparing these observations with reionization simulations, we infer that such a damping wing-like feature can be naturally explained if these gaps are at least partially created by neutral islands. Conversely, simulated dark gaps lacking neutral hydrogen struggle to replicate the observed damping wing features. Furthermore, this damping wing-like profile implies that the volume-averaged neutral hydrogen fraction must be $\langle x_{\rm HI} \rangle \geq 6.1 \pm 3.9\%$ at $z = 5.8$. Our results offer robust evidence that reionization extends below $z=6$.

astro-ph.CO↗
arXiv2022

Lyman Continuum Galaxy Candidates in COSMOS

Star-forming galaxies are the sources likely to have reionized the universe. As we cannot observe them directly due to the opacity of the intergalactic medium at $z\gtrsim5$, we study $z\sim3\text{--}5$ galaxies as proxies to place observational constraints on cosmic reionization. Using new deep \textit{Hubble Space Telescope} rest-frame UV F336W and F435W imaging (30-orbit, $\sim40$~arcmin$^2$, $\sim29\text{--}30$~mag depth at 5$σ$), we attempt to identify a sample of Lyman continuum galaxies (LCGs). These are individual sources that emit ionizing flux below the Lyman break ($<912~\textÅ$). This population would allow us to constrain cosmic reionization parameters such as the number density and escape fraction ($f_{\rm esc}$) of ionizing sources. We compile a comprehensive parent sample that does not rely on the Lyman-break technique for redshifts. We present three new spectroscopic candidates at $z\sim3.7\text{--}4.4$, and 32 new photometric candidates. The high-resolution multi-band HST imaging and new Keck/Low Resolution Imaging Spectrometer (LRIS) redshifts make these promising spectroscopic LCG candidates. Using both a traditional and probabilistic approach, we find the most likely $f_{\rm esc}$ values for the three spectroscopic LCG candidates are $>100\%$, and therefore not physical. We are unable to confirm the true nature of these sources with the best available imaging and direct blue Keck/LRIS spectroscopy. More spectra, especially from the new class of 30 m telescopes, will be required to build a statistical sample of LCGs to place firm observational constraints on cosmic reionization.

astro-ph.GA↗
arXiv2020

The role of galaxies and AGN in reionising the IGM -- III : IGM-galaxy cross-correlations at z~6 from 8 quasar fields with DEIMOS and MUSE

We present improved results of the measurement of the correlation between galaxies and the intergalactic medium (IGM) transmission at the end of reionisation. We have gathered a sample of $13$ spectroscopically confirmed Lyman-break galaxies (LBGs) and $21$ Lyman-$α$ emitters (LAEs) at angular separations $20'' \lesssim θ\lesssim 10'$ ($\sim 0.1-4$ pMpc at $z\sim 6$) from the sightlines to $8$ background $z\gtrsim 6$ quasars. We report for the first time the detection of an excess of Lyman-$α$ transmission spikes at $\sim 10-60$ cMpc from LAEs ($3.2σ$) and LBGs ($1.9σ$). We interpret the data with an improved model of the galaxy-Lyman-$α$ transmission and two-point cross-correlations which includes the enhanced photoionisation due to clustered faint sources, enhanced gas densities around the central bright objects and spatial variations of the mean free path. The observed LAE(LBG)-Lyman-$α$ transmission spike two-point cross-correlation function (2PCCF) constrains the luminosity-averaged escape fraction of all galaxies contributing to reionisation to $\langle f_{\rm esc} \rangle_{M_{\rm UV}<-12} = 0.14_{-0.05}^{+0.28}\,(0.23_{-0.12}^{+0.46})$. We investigate if the 2PCCF measurement can determine whether bright or faint galaxies are the dominant contributors to reionisation. Our results show that a contribution from faint galaxies ($M_{\rm UV} > -20 \, (2σ)$) is necessary to reproduce the observed 2PCCF and that reionisation might be driven by different sub-populations around LBGs and LAEs at $z\sim 6$.

astro-ph.GA↗
arXiv2019

The Evolution of O I over 3.2 < z < 6.5: Reionization of the Circumgalactic Medium

We present a survey for metal absorption systems traced by neutral oxygen over $3.2 < z < 6.5$. Our survey uses Keck/ESI and VLT/X-Shooter spectra of 199 QSOs with redshifts up to 6.6. In total we detect 74 O I absorbers, of which 57 are separated from the background QSO by more than 5000 km/s. We use a maximum likelihood approach to fit the distribution of O I $λ$1302 equivalent widths in bins of redshift, and from this determine the evolution in number density of absorbers with $W_{1302} > 0.05$ angstroms. We find that the number density does not monotonically increase with decreasing redshift, as would naively be expected from the buildup of metal-enriched circumgalactic gas with time. The number density over $4.9 < z < 5.7$ is a factor of 1.7--4.1 lower (68% confidence) than over $5.7 < z < 6.5$, with a lower value at $z < 5.7$ favored with 99% confidence. This decrease suggests that the fraction of metals in a low-ionization phase is larger at $z \sim 6$ than at lower redshifts. Absorption from highly ionized metals traced by C IV is also weaker in higher-redshift O I systems, supporting this picture. The evolution of O I absorbers implies that metal-enriched circumgalactic gas at $z \sim 6$ is undergoing an ionization transition driven by a strengthening ultraviolet background. This in turn suggests that the reionization of the diffuse intergalactic medium may still be ongoing at or only recently ended by this epoch.

astro-ph.GA↗
arXiv2018

The CGM and IGM at z$\sim$5: metal budget and physical connection

We present further results of a survey for absorption line systems in the spectra of four high redshift quasars (5.79 $\le$ z$_{\textrm{em}}$ $\le$ 6.13) obtained with the ESO Very Large Telescope X-Shooter. We identify 36 $\textrm{CIV}$ and 7 $\textrm{SiIV}$ systems with a $\ge$ 5$σ$ significance. The highest redshift $\textrm{CIV}$ and $\textrm{SiIV}$ absorbers identified in this work are at z = 5.80738 $\pm$ 0.00017 and z = 5.77495 $\pm$ 0.00038, respectively. We compute the comoving mass density of $\textrm{SiIV}$ ($Ω_{\textrm{SiIV}}$) and find that it evolves from $Ω_{\textrm{SiIV}}$ = 4.3$^{+2.1}_{-2.1}$ $\times$10$^{-9}$ at = 5.05 to $Ω_{\textrm{SiIV}}$ = 1.4$^{+0.6}_{-0.4}$ $\times$10$^{-9}$ at = 5.66. We also measure $Ω_{\textrm{CIV}}$ = 1.6$^{+0.4}_{-0.1}$ $\times$10$^{-8}$ at = 4.77 and $Ω_{\textrm{CIV}}$ = 3.4$^{+1.6}_{-1.1}$ $\times$10$^{-9}$ at = 5.66. We classify our $\textrm{CIV}$ absorber population by the presence of associated $\textit{low}$ and/or $\textit{high ionisation}$ systems and compute their velocity width ($Δ$v$_{90}$). We find that all $\textrm{CIV}$ systems with $Δ$v$_{90}$ > 200 kms$^{-1}$ have associated $\textit{low ionisation}$ systems. We investigate two such systems, separated by 550 physical kpc along a line of sight, and find it likely that they are both tracing a multi-phase medium where hot and cold gas is mixing at the interface between the CGM and IGM. We further discuss the \textrm{MgII} systems presented in a previous work and we identify 5 $\textrm{SiII}$, 10 $\textrm{AlII}$, 12 $\textrm{FeII}$, 1 $\textrm{CII}$, 7 $\textrm{MgI}$ and 1 $\textrm{CaII}$ associated transitions. We compute the respective comoving mass densities in the redshift range 2 to 6, as allowed by the wavelength coverage.

astro-ph.GA↗
arXiv2018

Probing the nature of Dark Matter through the metal enrichment of the intergalactic medium

We focus on exploring the metal enrichment of the intergalactic medium (IGM) in Cold and Warm (1.5 and 3 keV) Dark Matter (DM) cosmologies, and the constraints this yields on the DM particle mass, using a semi-analytic model, Delphi, that jointly tracks the Dark Matter and baryonic assembly of galaxies at $z \simeq 4-20$ including both Supernova and (a range of) reionization feedback (models). We find that while ${\rm M_{UV}} \geq -15$ galaxies contribute half of all IGM metals in the Cold Dark Matter model by $z \simeq 4.5$, given the suppression of low-mass halos, larger halos with ${\rm M_{UV}} \leq -15$ provide about 80\% of the IGM metal budget in 1.5 keV Warm Dark Matter models using two different models for the metallicity of the interstellar medium. Our results also show that the only models compatible with two different high-redshift data sets, provided by the evolving Ultra-Violet luminosity function at $z \simeq 6-10$ and IGM metal density (e.g. Simcoe et al. 2011), are standard Cold Dark Matter and 3 keV Warm DM that do not include any reionization feedback; a combination of the UV LF and the Diaz et al. (2016) points provides a weaker constraint, allowing Cold and 3 keV and 1.5 keV Warm DM models with SN feedback only, as well as CDM with complete gas suppression of all halos with $v_{circ} \leq 30\, {\rm km\, s^{-1}}$. Tightening the error bars on the IGM metal enrichment, future observations, at $z \geq 5.5$, could therefore represent an alternative way of shedding light on the nature of Dark Matter.

astro-ph.GA↗
arXiv2017

The comoving mass density of MgII from $z\sim2$ to $5.5$

We present the results of a survey for intervening MgII absorbers in the redshift range z $\simeq$2-6 in the foreground of four high redshift quasar spectra, 5.79$\le z_{em}\le$6.133, obtained with the ESO VLT X-shooter. We identify 24 absorbers at $\ge 5σ$ significance in the equivalent width range 0.117$\le W_{2796}\le 3.655\unicode{xC5}$ with the highest redshift absorber at $z=4.89031\pm4\times10^{-5}$. For weak ($W_{2796}<0.3\unicode{xC5}$) systems, we measure an incidence rate $dN/dz$=1.35$\pm$0.58 at =2.34 and find that it almost doubles to $dN/dz$=2.58$\pm$0.67 by =4.81. Weak absorbers exceeds the number expected from an exponential fit to stronger systems ($W_{2796}>0.3\unicode{xC5}$). We find that there must be significant evolution in the absorption halo properties of MgII absorbers with $W_{2796} >0.1\unicode{xC5}$ by =4.77 and/or that they are associated with galaxies with luminosities beyond the limits of the current luminosity function at z $\sim$5. We find that the incidence rate of strong MgII absorbers ($W_{2796}>1.0\unicode{xC5}$) can be explained if they are associated with galaxies with $L\ge0.29L_{\ast}$ and/or their covering fraction increases. If they continue to only be associated with galaxies with $L\ge0.50L_{\ast}$ then their physical cross section ($σ_{phys}$) increases from 0.015 Mpc$^2$ at z=2.3 to 0.041 Mpc$^2$ at =4.77. We measure $Ω_{MgII}$=2.1$^{+6.3}_{-0.6}\times10^{-8}$, 1.9$^{+2.9}_{-0.2}\times10^{-8}$, 3.9$^{+7.1}_{-2.4}\times10^{-7}$ at =2.48, 3.41, 4.77, respectively. At =4.77, $Ω_{MgII}$ exceeds the value expected from $Ω_{HI}$ estimated from the global metallicity of DLAs at z $\simeq$4.85 by a factor of $\sim$44 suggesting that either MgII absorbers trace both ionised and neutral gas and/or are more metal rich than the average DLA at this redshift.

astro-ph.GA↗
arXiv2015

Large-scale environment of $z\sim 5.7$ CIV absorption systems -II. Spectroscopy of Lyman-$α$ emitters

The flow of baryons to and from a galaxy, which is fundamental for galaxy formation and evolution, can be studied with galaxy-metal absorption system pairs. Our search for galaxies around CIV absorption systems at $z\sim5.7$ showed an excess of photometric Lyman-$α$ emitter (LAE) candidates in the fields J1030+0524 and J1137+3549. Here we present spectroscopic follow-up of 33 LAEs in both fields. In the first field, three out of the five LAEs within 10$h^{{-}1}$ projected comoving Mpc from the CIV system are within $\pm500$ km s$^{{-}1}$ from the absorption at $z_{\text{CIV}}=5.7242\pm0.0001$. The closest candidate (LAE 103027+052419) is robustly confirmed at $212.8^{+14}_{-0.4}h^{-1}$ physical kpc from the CIV system. In the second field, the LAE sample is selected at a lower redshift ($Δz\sim0.04$) than the CIV absorption system as a result of the filter transmission and, thus, do not trace its environment. The observed properties of LAE 103027+052419 indicate that it is near the high-mass end of the LAE distribution, probably having a large HI column density and large-scale outflows. Therefore, our results suggest that the CIV system is likely produced by a star-forming galaxy which has been injecting metals into the intergalactic medium since $z>6$. Thus, the CIV system is either produced by LAE 103027+052419, implying that outflows can enrich larger volumes at $z>6$ than at $z\sim3.5$, or an undetected dwarf galaxy. In either case, CIV systems like this one trace the ionized intergalactic medium at the end of cosmic hydrogen reionization and may trace the sources of the ionizing flux density.

astro-ph.GA↗
arXiv2015

Evidence of patchy hydrogen reionization from an extreme Ly$α$ trough below redshift six

We report the discovery of an extremely long ($\sim$110 Mpc/$h$) and dark ($τ_{\rm eff} \gtrsim 7$) Ly$α$ trough extending down to $z \simeq 5.5$ towards the $z_{\rm em} \simeq 6.0$ quasar ULAS J0148+0600. We use these new data in combination with Ly$α$ forest measurements from 42 quasars at $4.5 \le z_{\rm em} \le 6.4$ to conduct an updated analysis of the line-of-sight variance in the intergalactic Ly$α$ opacity over $4 \le z \le 6$. We find that the scatter in transmission among lines of sight near $z \sim 6$ significantly exceeds theoretical expectations for either a uniform ultraviolet background (UVB) or simple fluctuating UVB models in which the mean free path to ionizing photons is spatially invariant. The data, particularly near $z \simeq 5.6$-5.8, instead require fluctuations in the volume-weighted hydrogen neutral fraction that are a factor of 3 or more beyond those expected from density variations alone. We argue that these fluctuations are most likely driven by large-scale variations in the mean free path, consistent with expectations for the final stages of inhomogeneous hydrogen reionization. Even by $z \simeq 5.6$, however, a large fraction of the data are consistent with a uniform UVB, and by $z \sim 5$ the data are fully consistent with opacity fluctuations arising solely from the density field. This suggests that while reionization may be ongoing at $z \sim 6$, it has fully completed by $z \sim 5$.

astro-ph.CO↗
arXiv2014

Large-scale environment of z~5.7 CIV absorption systems I: projected distribution of galaxies

Metal absorption systems are products of star formation. They are believed to be associated with massive star forming galaxies, which have significantly enriched their surroundings. To test this idea with high column density CIV absorption systems at z~5.7, we study the projected distribution of galaxies and characterise the environment of CIV systems in two independent quasar lines-of-sight: J103027.01+052455.0 and J113717.73+354956.9. Using wide field photometry (~80x60h$^{-1}$ comoving Mpc), we select bright (Muv(1350Å)<-21.0 mag.) Lyman break galaxies (LBGs) at z~5.7 in a redshift slice Δz~0.2 and we compare their projected distribution with z~5.7 narrow-band selected Lyman alpha emitters (LAEs, Δz~0.08). We find that the CIV systems are located more than 10h$^{-1}$ projected comoving Mpc from the main concentrations of LBGs and no candidate is closer than ~5h$^{-1}$ projected comoving Mpc. In contrast, an excess of LAEs -lower mass galaxies- is found on scales of ~10h$^{-1}$ comoving Mpc, suggesting that LAEs are the primary candidates for the source of the CIV systems. Furthermore, the closest object to the system in the field J1030+0524 is a faint LAE at a projected distance of 212h$^{-1}$ physical kpc. However, this work cannot rule out undiscovered lower mass galaxies as the origin of these absorption systems. We conclude that, in contrast with lower redshift examples (z<3.5), strong CIV absorption systems at z~5.7 trace low-to-intermediate density environments dominated by low-mass galaxies. Moreover, the excess of LAEs associated with high levels of ionizing flux agrees with the idea that faint galaxies dominate the ionizing photon budget at this redshift.

astro-ph.GA↗
arXiv2014

Lyman continuum galaxies and the escape fraction of Lyman break galaxies

Lyman break galaxies (LBGs) at z ~ 3-4 are targeted to measure the fraction of Lyman continuum (LyC) flux that escapes from high redshift galaxies. However, z ~ 3-4 LBGs are identified using the Lyman break technique which preferentially selects galaxies with little or no LyC. We re-examine the standard LBG selection criteria by performing spectrophotometry on composite spectra constructed from 794 U_nGR-selected z ~ 3 LBGs from the literature while adding LyC flux of varying strengths. The modified composite spectra accurately predict the range of redshifts, properties, and LyC flux of LBGs in the literature that have spectroscopic LyC measurements while predicting the existence of a significant fraction of galaxies outside the standard selection region. These galaxies, termed Lyman continuum galaxies (LCGs), are expected to have high levels of LyC flux and are estimated to have a number density ~30-50 percent that of the LBG population. We define R_obs(U_n) as the relative fraction of observed LyC flux, integrated from 912A to the shortest restframe wavelength probed by the U_n filter, to the observed non-ionising flux (here measured at 1500A). We use the 794 spectra as a statistical sample for the full z ~ 3 LBG population, and find R_obs(U_n) = 5.0 +1.0/-0.4 (4.1 +0.5/-0.3) percent, which corresponds to an intrinsic LyC escape fraction of f_esc = 10.5 +2.0/-0.8 (8.6 +1.0/-0.6) percent (contamination corrected). From the composite spectral distributions we estimate R_obs(U_n) ~16 +/-3, f_esc ~33 +/-7 percent for LCGs and R_obs(U_n) ~8 +/-3, f_esc ~16 +/-4 percent for the combined LBG + LCG z ~ 3 sample. All values are measured in apertures defined by the UV continuum and do not include extended and/or offset LyC flux. A complete high redshift galaxy census and total emergent LyC flux is essential to quantify the contribution of galaxies to the epoch of reionisation.

astro-ph.GA↗
arXiv2013

The Smooth MgII gas distribution through the interstellar/extra-planar/halo interface

We report the first measurements of MgII absorption systems associated with spectroscopically confirmed z~0.1 star-forming galaxies at projected distances of D<6kpc. We demonstrate the data are consistent with the well known anti-correlation between rest-frame MgII equivalent width, Wr(2796), and impact parameter, D, represented by a single log-linear relation derived by Nielsen et al. (MAGIICAT) that converges to ~2A at D=0kpc. Incorporating MAGIICAT, we find that the halo gas covering fraction is unity below D~25kpc. We also report that our D<6kpc absorbers are consistent with the Wr(2796) distributions of the Milky Way interstellar medium (ISM) and ISM+halo. In addition, quasar sight-lines of intermediate redshift galaxies with 6<D<25kpc have an equivalent width distribution similar to that of the Milky Way halo, implying that beyond ~6kpc, quasar sight-lines are likely probing halo gas and not the ISM. As inferred by the Milky Way and our new data, the gas profiles of galaxies can be fit by a single log-linear Wr(2796)-D relation out to large scales across a variety of gas-phase conditions and is maintained through the halo/extra-planar/ISM interfaces, which is remarkable considering their kinematic complexity. These low redshift, small impact parameter absorption systems are the first steps to bridge the gap between quasar absorption-line studies and HI observations of the CGM.

astro-ph.CO↗
arXiv2013

HST/COS Spectra of Three QSOs That Probe The Circumgalactic Medium of a Single Spiral Galaxy: Evidence for Gas Recycling and Outflow

We have used the Cosmic Origins Spectrograph (COS) to obtain far-UV spectra of three closely-spaced QSO sight lines that probe the circumgalactic medium (CGM) of an edge-on spiral galaxy, ESO 157-49, at impact parameters of 74 and 93 kpc near its major axis and 172 kpc along its minor axis. H I Lyα absorption is detected at the galaxy redshift in the spectra of all three QSOs, and metal lines of Si III, Si IV, and C IV are detected along the two major-axis sight lines. Photoionization models of these clouds suggest metallicities close to the galaxy metallicity, cloud sizes of ~1 kpc, and gas masses of ~10^4 solar masses. Given the high covering factor of these clouds, ESO 157-49 could harbor ~2x10^9 solar masses of warm CGM gas. We detect no metals in the sight line that probes the galaxy along its minor axis, but gas at the galaxy metallicity would not have detectable metal absorption with ionization conditions similar to the major-axis clouds. The kinematics of the major-axis clouds favor these being portions of a "galactic fountain" of recycled gas, while two of the three minor-axis clouds are constrained geometrically to be outflowing gas. In addition, one of our QSO sight lines probes a second more distant spiral, ESO 157-50, along its major axis at an impact parameter of 88 kpc. Strong H I Lyα and C IV absorption only are detected in the QSO spectrum at the redshift of ESO 157-50.

astro-ph.CO↗
arXiv2012

Super-luminous supernovae at redshifts of 2.05 and 3.90

A rare class of `super-luminous' supernovae that are about ten or more times more luminous at their peaks than other types of luminous supernovae has recently been found at low to intermediate redshifts. A small subset of these events have luminosities that evolve slowly and result in radiated energies of around 10^51 ergs or more. Therefore, they are likely examples of `pair-instability' or `pulsational pair-instability' supernovae with estimated progenitor masses of 100 - 250 times that of the Sun. These events are exceedingly rare at low redshift, but are expected to be more common at high redshift because the mass distribution of the earliest stars was probably skewed to high values. Here we report the detection of two super-luminous supernovae, at redshifts of 2.05 and 3.90, that have slowly evolving light curves. We estimate the rate of events at redshifts of 2 and 4 to be approximately ten times higher than the rate at low redshift. The extreme luminosities of super-luminous supernovae extend the redshift limit for supernova detection using present technology, previously 2.36, and provide a way of investigating the deaths of the first generation of stars to form after the Big Bang.

astro-ph.CO↗
arXiv2011

A galaxy as the source of a Civ absorption system close to the epoch of reionization

We find a bright (L_{UV}=2.5 L*_{z=6}) Lyman alpha emitter at redshift z=5.719 at a projected distance of 79 physical kpc from a strong triply ionized carbon (Civ) absorption system at redshift z=5.7238 previously reported in the spectrum of the z_{em} = 6.309 QSO SDSS J1030+0524. This is the highest redshift galaxy-absorber pair detected to-date, supporting the idea that galaxy-wide outflows were already in place at the end of the epoch of reionization. The proximity of this object makes it the most likely source of metals, consistent with models of outflows at lower redshift where significant observational evidence relates metal absorption systems with galaxies hosting outflows. In a typical outflow scenario, a wind of 200 km/s, active since the universe was only 0.6 Gyr old (z ~8.4), could eject metals out to 79 kpc at z=5.719. Although the origin of metals in the intergalactic medium (IGM) is still under debate, our results are consistent with predictions from cosmological simulations which reproduce the evolution of the cosmic density of Civ, from z ~ 6 to the present day based on outflow-driven enrichment of the IGM. We also report two more Lyman alpha emitters in this field, at z=5.973\pm 0.002 and z=5.676\pm 0.002 respectively, the former confirming the original identification by Stiavelli et al. Our results suggest that the colour cut typically used to identify i-dropouts (i_{775}-z_{850}>1.3) misses a non-negligible fraction of blue galaxies with faint UV continuum at z \geq 5.7.

astro-ph.CO↗
arXiv2009

A downturn in intergalactic CIV as redshift 6 is approached

We present the results of the largest survey to date for intergalactic metals at redshifts z > 5, using near-IR spectra of nine QSOs with emission redshifts z(em) > 5.7. We find, for the first time, a change in the comoving mass density of C IV ions as we look back to redshifts z > 5. At a mean = 5.76, we deduce Omega(C IV)=(4.4+/-2.6)x10^(-9) which implies a drop by a factor of about 3.5 compared to the value at z < 4.7, after accounting for the differing sensitivities of different surveys. The observed number of C IV doublets is also lower by a similar factor, compared to expectations for a non-evolving column density distribution of absorbers. These results point to a rapid build-up of intergalactic C IV over a period of only 300 Myr; such a build-up could reflect the accumulation of metals associated with the rising levels of star formation activity from z = 9 indicated by galaxy counts, and/or an increasing degree of ionisation of the intergalactic medium (IGM), following the overlap of ionisation fronts from star-forming regions. If the value of Omega(C IV) we derive is typical of the IGM at large, it would imply a metallicity Z(IGM) = 10^(-4) Z(Sun). The early-type stars responsible for synthesising these metals would have emitted only about one Lyman continuum photon per baryon prior to z = 5.8; such a background is insufficient to keep the IGM ionised and we speculate on possible factors which could make up the required shortfall.

astro-ph.CO↗