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Martin G. Haehnelt

Publications and source records attributed to Martin G. Haehnelt.

At least 55 records · Page 3Linked to original sources
arXiv2023

Constraints on the Evolution of the Ionizing Background and Ionizing Photon Mean Free Path at the End of Reionization

The variations in Ly$α$ forest opacity observed at $z>5.3$ between lines of sight to different background quasars are too strong to be caused by fluctuations in the density field alone. The leading hypothesis for the cause of this excess variance is a late, ongoing reionization process at redshifts below six. Another model proposes strong ionizing background fluctuations coupled to a short, spatially varying mean free path of ionizing photons, without explicitly invoking incomplete reionization. With recent observations suggesting a short mean free path at $z\sim6$, and a dramatic improvement in $z>5$ Ly$α$ forest data quality, we revisit this latter possibility. Here we apply the likelihood-free inference technique of approximate Bayesian computation to jointly constrain the hydrogen photoionization rate $Γ_{\rm HI}$ and the mean free path of ionizing photons $λ_{\rm mfp}$ from the effective optical depth distributions at $z=5.0$-$6.1$ from XQR-30. We find that the observations are well-described by fluctuating mean free path models with average mean free paths that are consistent with the steep trend implied by independent measurements at $z\sim5$-$6$, with a concomitant rapid evolution of the photoionization rate.

astro-ph.CO↗
arXiv2023

The Sphinx Public Data Release: Forward Modelling High-Redshift JWST Observations with Cosmological Radiation Hydrodynamics Simulations

The recent launch of JWST has ushered in a new era of high-redshift astronomy by providing detailed insights into the gas and stellar populations of galaxies in the epoch of reionization. Interpreting these observations and translating them into constraints on the physics of early galaxy formation is a complex challenge that requires sophisticated models of star formation and the interstellar medium (ISM) in high-redshift galaxies. To this end, we present Version 1 of the Sphinx$^{20}$ public data release. Sphinx$^{20}$ is a full box cosmological radiation hydrodynamics simulation that simultaneously models the large-scale process of cosmic reionization and the detailed physics of a multiphase ISM, providing a statistical sample of galaxies akin to those currently being observed by JWST. The data set contains $\sim14,000$ mock images and spectra of the stellar continuum, nebular continuum, and 52 nebular emission lines, including Ly$α$, for each galaxy in Sphinx$^{20}$ with a star formation rate $\geq0.3\ {\rm M_{\odot}\ yr^{-1}}$. All galaxy emission has been processed with dust radiative transfer and/or resonant line radiative transfer, and data is provided for ten viewing angles for each galaxy. Additionally, we provide a comprehensive set of intrinsic galaxy properties, including halo masses, stellar masses, star formation histories, and ISM characteristics (e.g., metallicity, ISM gas densities, LyC escape fractions). This paper outlines the data generation methods, presents a comparative analysis with JWST ERS and Cycle 1 observations, and addresses data set limitations. The Sphinx$^{20}$ data release can be downloaded at the following URL: https://github.com/HarleyKatz/SPHINX-20-data

astro-ph.GA↗
arXiv2023

Terrestrial Very-Long-Baseline Atom Interferometry: Workshop Summary

This document presents a summary of the 2023 Terrestrial Very-Long-Baseline Atom Interferometry Workshop hosted by CERN. The workshop brought together experts from around the world to discuss the exciting developments in large-scale atom interferometer (AI) prototypes and their potential for detecting ultralight dark matter and gravitational waves. The primary objective of the workshop was to lay the groundwork for an international TVLBAI proto-collaboration. This collaboration aims to unite researchers from different institutions to strategize and secure funding for terrestrial large-scale AI projects. The ultimate goal is to create a roadmap detailing the design and technology choices for one or more km-scale detectors, which will be operational in the mid-2030s. The key sections of this report present the physics case and technical challenges, together with a comprehensive overview of the discussions at the workshop together with the main conclusions.

hep-ex↗
arXiv2023

The Pandora project. I: the impact of radiation and cosmic rays on baryonic and dark matter properties of dwarf galaxies

Enshrouded in several well-known controversies, dwarf galaxies have been extensively studied to learn about the underlying cosmology, notwithstanding that physical processes regulating their properties are poorly understood. To shed light on these processes, we introduce the Pandora suite of 17 high-resolution (3.5 parsec half-cell side) dwarf galaxy formation cosmological simulations. Commencing with thermo-turbulent star formation and mechanical supernova feedback, we gradually increase the complexity of physics incorporated leading to full-physics models combining magnetism, on-the-fly radiative transfer and the corresponding stellar photoheating, and SN-accelerated cosmic rays. We investigate combinations of these processes, comparing them with observations to constrain what are the main mechanisms determining dwarf galaxy properties. We find hydrodynamical `SN feedback-only' simulations struggle to produce realistic dwarf galaxies, leading either to overquenched or too centrally concentrated, dispersion dominated systems when compared to observed field dwarfs. Accounting for radiation with cosmic rays results in extended and rotationally-supported systems. Spatially `distributed' feedback leads to realistic stellar and HI masses as well as kinematics. Furthermore, resolved kinematic maps of our full-physics models predict kinematically distinct clumps and kinematic misalignments of stars, HI and HII after star formation events. Episodic star formation combined with its associated feedback induces more core-like dark matter central profiles, which our `SN feedback-only' models struggle to achieve. Our results demonstrate the complexity of physical processes required to capture realistic dwarf galaxy properties, making tangible predictions for integral field unit surveys, radio synchrotron emission, and for galaxy and multi-phase interstellar medium properties that JWST will probe.

astro-ph.GA↗
arXiv2023

Measurements of the $z > 5$ Lyman-$α$ forest flux auto-correlation functions from the extended XQR-30 data set

Recently, the Lyman-$α$ (Ly$α$) forest flux auto-correlation function has been shown to be sensitive to the mean free path of hydrogen-ionizing photons, $λ_{\text{mfp}}$, for simulations at $z \geq 5.4$. Measuring $λ_{\text{mfp}}$ at these redshifts will give vital information on the ending of reionization. Here we present the first observational measurements of the Ly$α$ forest flux auto-correlation functions in ten redshift bins from $5.1 \leq z \leq 6.0$. We use a sample of 35 quasar sightlines at $z > 5.7$ from the extended XQR-30 data set, this data has signal-to-noise ratios of $> 20$ per spectral pixel. We carefully account for systematic errors in continuum reconstruction, instrumentation, and contamination by damped Ly$α$ systems. With these measurements, we introduce software tools to generate auto-correlation function measurements from any simulation. For an initial comparison, we show our auto-correlation measurements with simulation models for recently measured $λ_{\text{mfp}}$ values and find good agreements. Further work in modeling and understanding the covariance matrices of the data is necessary to get robust measurements of $λ_{\text{mfp}}$ from this data.

astro-ph.CO↗
arXiv2023

Measuring the photo-ionization rate, neutral fraction and mean free path of HI ionizing photons at $4.9 \leq z \leq 6.0$ from a large sample of XShooter and ESI spectra

We measure the mean free path ($λ_{\rm mfp,HI}$), photo-ionization rate ($\langle Γ_{\rm HI} \rangle$) and neutral fraction ($\langle f_{\rm HI} \rangle$) of hydrogen in 12 redshift bins at $4.85<z<6.05$ from a large sample of moderate resolution XShooter and ESI QSO absorption spectra. The fluctuations in ionizing radiation field are modeled by post-processing simulations from the Sherwood suite using our new code "EXtended reionization based on the Code for Ionization and Temperature Evolution" (EX-CITE). EX-CITE uses efficient Octree summation for computing intergalactic medium attenuation and can generate large number of high resolution $Γ_{\rm HI}$ fluctuation models. Our simulation with EX-CITE shows remarkable agreement with simulations performed with the radiative transfer code Aton and can recover the simulated parameters within $1σ$ uncertainty. We measure the three parameters by forward-modeling the Ly$α$ forest and comparing the effective optical depth ($τ_{\rm eff, HI}$) distribution in simulations and observations. The final uncertainties in our measured parameters account for the uncertainties due to thermal parameters, modeling parameters, observational systematics and cosmic variance. Our best fit parameters show significant evolution with redshift such that $λ_{\rm mfp,HI}$ and $\langle f_{\rm HI} \rangle$ decreases and increases by a factor $\sim 6$ and $\sim 10^{4}$, respectively from $z \sim 5$ to $z \sim 6$. By comparing our $λ_{\rm mfp,HI}$, $\langle Γ_{\rm HI} \rangle$ and $\langle f_{\rm HI} \rangle$ evolution with that in state-of-the-art Aton radiative transfer simulations and the Thesan and CoDa-III simulations, we find that our best fit parameter evolution is consistent with a model in which reionization completes by $z \sim 5.2$.

astro-ph.CO↗
arXiv2023

Investigating the characteristic shape and scatter of intergalactic damping wings during reionization

Ly$α$ damping wings in the spectra of bright objects at high redshift are a useful probe of the ionization state of the intergalactic medium during the reionization epoch. It has recently been noted that, despite the inhomogeneous nature of reionization, these damping wings have a characteristic shape which is a strong function of the volume-weighted average neutral hydrogen fraction of the intergalactic medium. We present here a closer examination of this finding using a simulation of patchy reionization from the Sherwood-Relics simulation suite. We show that the characteristic shape and scatter of the damping wings are determined by the average neutral hydrogen density along the line of sight, weighted by its contribution to the optical depth producing the damping wing. We find that there is a redshift dependence in the characteristic shape due to the expansion of the Universe. Finally, we show that it is possible to differentiate between the shapes of damping wings in galaxies and young (or faint) quasars at different points in the reionization history at large velocity offsets from the point where the transmission first reaches zero.

astro-ph.CO↗
arXiv2023

JWST observations of galaxy damping wings during reionization interpreted with cosmological simulations

Spectra of the highest redshift galaxies taken with JWST are now allowing us to see into the heart of the reionization epoch. Many of these observed galaxies exhibit strong damping wing absorption redward of their Lyman-$α$ emission. These observations have been used to measure the redshift evolution of the neutral fraction of the intergalactic medium and sizes of ionized bubbles. However, these estimates have been made using a simple analytic model for the intergalactic damping wing. We explore the recent observations with models of inhomogeneous reionization from the Sherwood-Relics simulation suite. We carry out a comparison between the damping wings calculated from the simulations and from the analytic model. We find that although the agreement is good on the red side of the Lyman-$α$ emission, there is a discrepancy on the blue side due to residual neutral hydrogen present in the simulations, which saturates the intergalactic absorption. For this reason, we find that it is difficult to reproduce the claimed observations of large bubble sizes at z ~ 7, which are driven by a detection of transmitted flux blueward of the Lyman-$α$ emission. We suggest instead that the observations can be explained by a model with smaller ionized bubbles and larger intrinsic Lyman-$α$ emission from the host galaxy.

astro-ph.GA↗
arXiv2023

Probing Ultra-late Reionization: Direct Measurements of the Mean Free Path over $5<z<6$

The mean free path of ionizing photons, $λ_{\rm mfp}$, is a critical parameter for modeling the intergalactic medium (IGM) both during and after reionization. We present direct measurements of $λ_{\rm mfp}$ from QSO spectra over the redshift range $5<z<6$, including the first measurements at $z\simeq5.3$ and 5.6. Our sample includes data from the XQR-30 VLT large program, as well as new Keck/ESI observations of QSOs near $z \sim 5.5$, for which we also acquire new [C II] 158$μ$m redshifts with ALMA. By measuring the Lyman continuum transmission profile in stacked QSO spectra, we find $λ_{\rm mfp} = 9.33_{-1.80}^{+2.06}$, $5.40_{-1.40}^{+1.47}$, $3.31_{-1.34}^{+2.74}$, and $0.81_{-0.48}^{+0.73}$ pMpc at $z=5.08$, 5.31, 5.65, and 5.93, respectively. Our results demonstrate that $λ_{\rm mfp}$ increases steadily and rapidly with time over $5<z<6$. Notably, we find that $λ_{\rm mfp}$ deviates significantly from predictions based on a fully ionized and relaxed IGM as late as $z=5.3$. By comparing our results to model predictions and indirect $λ_{\rm mfp}$ constraints based on IGM Ly$α$ opacity, we find that the $λ_{\rm mfp}$ evolution is consistent with scenarios wherein the IGM is still undergoing reionization and/or retains large fluctuations in the ionizing UV background well below redshift six.

astro-ph.CO↗
arXiv2023

New quasar proximity zone size measurements at $z\sim 6$ using the enlarged XQR-30 sample

Proximity zones of high-redshift quasars are unique probes of their central supermassive black holes as well as the intergalactic medium in the last stages of reionization. We present 22 new measurements of proximity zones of quasars with redshifts between 5.8 and 6.6, using the enlarged XQR-30 sample of high-resolution, high-SNR quasar spectra. The quasars in our sample have UV magnitudes of $M_{1450}\sim -27$ and black hole masses of $10^9$$\unicode{x2013}$$10^{10}$ M$_\odot$. Our inferred proximity zone sizes are 2$\unicode{x2013}$7 physical Mpc, with a typical uncertainty of less than 0.5 physical Mpc, which, for the first time, also includes uncertainty in the quasar continuum. We find that the correlation between proximity zone sizes and the quasar redshift, luminosity, or black hole mass, indicates a large diversity of quasar lifetimes. Two of our proximity zone sizes are exceptionally small. The spectrum of one of these quasars, with $z=6.02$, displays, unusually for this redshift, damping wing absorption without any detectable metal lines, which could potentially originate from the IGM. The other quasar has a high-ionization absorber $\sim$0.5 pMpc from the edge of the proximity zone. This work increases the number of proximity zone measurements available in the last stages of cosmic reionization to 87. This data will lead to better constraints on quasar lifetimes and obscuration fractions at high redshift, which in turn will help probe the seed mass and formation redshift of supermassive black holes.

astro-ph.GA↗
arXiv2023

The need for obscured supermassive black hole growth to explain quasar proximity zones in the epoch of reionization

Proximity zones of high-redshift quasars are unique probes of supermassive black hole formation, but simultaneously explaining proximity zone sizes and black hole masses has proved to be challenging. We study the robustness of some of the assumptions that are usually made to infer quasar lifetimes from proximity zone sizes. We show that small proximity zones can be readily explained by quasars that vary in brightness with a short duty cycle of $f_\mathrm{duty}\sim 0.1$ and short bright periods of $t_\mathrm{on}\sim 10^4$ yr, even for long lifetimes. We further show that reconciling this with black hole mass estimates requires the black hole to continue to grow and accrete during its obscured phase. The consequent obscured fractions of $\gtrsim$ 0.7 or higher are consistent with low-redshift measurements and models of black hole accretion. Such short duty cycles and long obscured phases are also consistent with observations of large proximity zones, thus providing a simple, unified model for proximity zones of all sizes. The large dynamic range of our simulation, and its calibration to the Lyman-$α$ forest, allows us to investigate the influence of the large-scale topology of reionization and the quasar's host halo mass on proximity zones. We find that incomplete reionization can impede the growth of proximity zones and make them smaller up to 30%, but the quasar host halo mass only affects proximity zones weakly and indirectly. Our work suggests that high-redshift proximity zones can be an effective tool to study quasar variability and black hole growth.

astro-ph.GA↗
arXiv2023

Possible evidence for a large-scale enhancement in the Lyman-$α$ forest power spectrum at redshift $\mathbf{\textit{z}\geq 4}$

Inhomogeneous reionization enhances the 1D Lyman-$α$ forest power spectrum on large scales at redshifts $z\geq4$. This is due to coherent fluctuations in the ionized hydrogen fraction that arise from large-scale variations in the post-reionization gas temperature, which fade as the gas cools. It is therefore possible to use these relic fluctuations to constrain inhomogeneous reionization with the power spectrum at wavenumbers $\log_{10}(k/{\rm km^{-1}\,s})\lesssim -1.5$. We use the Sherwood-Relics suite of hybrid radiation hydrodynamical simulations to perform a first analysis of new Lyman-$α$ forest power spectrum measurements at $4.0\leq z \leq 4.6$. These data extend to wavenumbers $\log_{10}(k/{\rm km^{-1}\,s})\simeq -3$, with a relative uncertainty of $10$--$20$ per cent in each wavenumber bin. Our analysis returns a $2.7σ$ preference for an enhancement in the Lyman-$α$ forest power spectrum at large scales, in excess of that expected for a spatially uniform ultraviolet background. This large-scale enhancement could be a signature of inhomogeneous reionization, although the statistical precision of these data is not yet sufficient for obtaining a robust detection of the relic post-reionization fluctuations. We show that future power spectrum measurements with relative uncertainties of $\lesssim 2.5$ per cent should provide unambiguous evidence for an enhancement in the power spectrum on large scales.

astro-ph.CO↗
arXiv2023

Examining the Decline in the C IV Content of the Universe over 4.3 < z < 6.3 using the E-XQR-30 Sample

Intervening CIV absorbers are key tracers of metal-enriched gas in galaxy halos over cosmic time. Previous studies suggest that the CIV cosmic mass density ($Ω_{\rm CIV}$) decreases slowly over 1.5 $\lesssim z\lesssim$ 5 before declining rapidly at $z\gtrsim$ 5, but the cause of this downturn is poorly understood. We characterize the $Ω_{\rm CIV}$ evolution over 4.3 $\lesssim z\lesssim$ 6.3 using 260 absorbers found in 42 XSHOOTER spectra of $z\sim$ 6 quasars, of which 30 come from the ESO Large Program XQR-30. The large sample enables us to robustly constrain the rate and timing of the downturn. We find that $Ω_{\rm CIV}$ decreases by a factor of 4.8 $\pm$ 2.0 over the ~300 Myr interval between $z\sim$ 4.7 and $z\sim$ 5.8. The slope of the column density (log N) distribution function does not change, suggesting that CIV absorption is suppressed approximately uniformly across 13.2 $\leq$ log N/cm$^{-2}$ < 15.0. Assuming that the carbon content of galaxy halos evolves as the integral of the cosmic star formation rate density (with some delay due to stellar lifetimes and outflow travel times), we show that chemical evolution alone could plausibly explain the fast decline in $Ω_{\rm CIV}$ over 4.3 $\lesssim z\lesssim$ 6.3. However, the CIV/CII ratio decreases at the highest redshifts, so the accelerated decline in $Ω_{\rm CIV}$ at $z\gtrsim$ 5 may be more naturally explained by rapid changes in the gas ionization state driven by evolution of the UV background towards the end of hydrogen reionization.

astro-ph.GA↗
arXiv2023

The Sherwood-Relics simulations: overview and impact of patchy reionization and pressure smoothing on the intergalactic medium

We present the Sherwood-Relics simulations, a new suite of large cosmological hydrodynamical simulations aimed at modelling the intergalactic medium (IGM) during and after the cosmic reionization of hydrogen. The suite consists of over 200 simulations that cover a wide range of astrophysical and cosmological parameters. It also includes simulations that use a new lightweight hybrid scheme for treating radiative transfer effects. This scheme follows the spatial variations in the ionizing radiation field, as well as the associated fluctuations in IGM temperature and pressure smoothing. It is computationally much cheaper than full radiation hydrodynamics simulations and circumvents the difficult task of calibrating a galaxy formation model to observational constraints on cosmic reionization. Using this hybrid technique, we study the spatial fluctuations in IGM properties that are seeded by patchy cosmic reionization. We investigate the relevant physical processes and assess their impact on the z > 4 Lyman-alpha forest. Our main findings are: (i) Consistent with previous studies patchy reionization causes large scale temperature fluctuations that persist well after the end of reionization, (ii) these increase the Lyman-alpha forest flux power spectrum on large scales, and (iii) result in a spatially varying pressure smoothing that correlates well with the local reionization redshift. (iv) Structures evaporated or puffed up by photoheating cause notable features in the Lyman-alpha forest, such as flat-bottom or double-dip absorption profiles.

astro-ph.CO↗
arXiv2022

Probing quasar lifetimes with proximate $21$-centimetre absorption in the diffuse intergalactic medium at redshifts $z\geq 6$

Enhanced ionizing radiation in close proximity to redshift $z\gtrsim 6$ quasars creates short windows of intergalactic Ly$α$ transmission blueward of the quasar Ly$α$ emission lines. The majority of these Ly$α$ near-zones are consistent with quasars that have optically/UV bright lifetimes of $t_{\rm Q}\sim 10^{5}-10^{7}\rm\,yr$. However, lifetimes as short as $t_{\rm Q}\lesssim 10^{4}\rm\,yr$ appear to be required by the smallest Ly$α$ near-zones. These short lifetimes present an apparent challenge for the growth of $\sim 10^{9}\rm\,M_{\odot}$ black holes at $z\gtrsim 6$. Accretion over longer timescales is only possible if black holes grow primarily in an obscured phase, or if the quasars are variable on timescales comparable to the equilibriation time for ionized hydrogen. Distinguishing between very young quasars and older quasars that have experienced episodic accretion with Ly$α$ absorption alone is challenging, however. We therefore predict the signature of proximate 21-cm absorption around $z\gtrsim 6$ radio-loud quasars. For modest pre-heating of intergalactic hydrogen by the X-ray background, where the spin temperature $T_{\rm S} \lesssim 10^{2}\rm\,K$ prior to any quasar heating, we find proximate 21-cm absorption should be observable in the spectra of radio-loud quasars. The extent of the proximate 21-cm absorption is sensitive to the integrated lifetime of the quasar. Evidence for proximate 21-cm absorption from the diffuse intergalactic medium within $2-3\rm\,pMpc$ of a (radio-loud) quasar would be consistent with a short quasar lifetime, $t_{\rm Q}\lesssim 10^{5}\rm\,yr$, and would provide a complementary constraint on models for high redshift black hole growth.

astro-ph.CO↗
arXiv2022

Long Dark Gaps in the Ly$β$ Forest at $z<6$: Evidence of Ultra Late Reionization from XQR-30 Spectra

We present a new investigation of the intergalactic medium (IGM) near reionization using dark gaps in the Lyman-$β$ (Ly$β$) forest. With its lower optical depth, Ly$β$ offers a potentially more sensitive probe to any remaining neutral gas compared to commonly used Ly$α$ line. We identify dark gaps in the Ly$β$ forest using spectra of 42 QSOs at $z_{\rm em}>5.5$, including new data from the XQR-30 VLT Large Programme. Approximately $40\%$ of these QSO spectra exhibit dark gaps longer than $10h^{-1}{\rm Mpc}$ at $z\simeq5.8$. By comparing the results to predictions from simulations, we find that the data are broadly consistent both with models where fluctuations in the Ly$α$ forest are caused solely by ionizing ultraviolet background (UVB) fluctuations and with models that include large neutral hydrogen patches at $z<6$ due to a late end to reionization. Of particular interest is a very long ($L=28h^{-1}{\rm Mpc}$) and dark ($τ_{\rm eff} \gtrsim 6$) gap persisting down to $z\simeq 5.5$ in the Ly$β$ forest of the $z_{\rm}=5.85$ QSO PSO J025$-$11. This gap may support late reionization models with a volume-weighted average neutral hydrogen fraction of $ \langle x_{\rm HI}\rangle \gtrsim 5\%$ by $z=5.6$. Finally, we infer constraints on $\langle x_{\rm HI}\rangle$ over $5.5 \lesssim z \lesssim 6.0$ based on the observed Ly$β$ dark gap length distribution and a conservative relationship between gap length and neutral fraction derived from simulations. We find $\langle x_{\rm HI}\rangle \leq 0.05$, 0.17, and 0.29 at $z\simeq 5.55$, 5.75, and 5.95, respectively. These constraints are consistent with models where reionization ends significantly later than $z = 6$.

astro-ph.CO↗
arXiv2022

Hydrogen reionisation ends by $z=5.3$: Lyman-$α$ optical depth measured by the XQR-30 sample

The presence of excess scatter in the Ly-$α$ forest at $z\sim 5.5$, together with the existence of sporadic extended opaque Gunn-Peterson troughs, has started to provide robust evidence for a late end of hydrogen reionisation. However, low data quality and systematic uncertainties complicate the use of Ly-$α$ transmission as a precision probe of reionisation's end stages. In this paper, we assemble a sample of 67 quasar sightlines at $z>5.5$ with high signal-to-noise ratios of $>10$ per $\leq 15$ km s$^{-1}$ spectral pixel, relying largely on the new XQR-30 quasar sample. XQR-30 is a large program on VLT/X-Shooter which obtained deep (SNR $>20$ per pixel) spectra of 30 quasars at $z>5.7$. We carefully account for systematics in continuum reconstruction, instrumentation, and contamination by damped Ly-$α$ systems. We present improved measurements of the mean Ly-$α$ transmission over $4.9 3.5 σ$). Our results indicate that reionisation-related fluctuations, whether in the UVB, residual neutral hydrogen fraction, and/or IGM temperature, persist in the intergalactic medium until at least $z=5.3$ ($t=1.1$ Gyr after the Big Bang). This is further evidence for a late end to reionisation.

astro-ph.CO↗
arXiv2022

Limits on non-canonical heating and turbulence in the intergalactic medium from the low redshift Lyman-alpha forest

We examine the column density distribution function (CDDF) and Doppler parameter distribution from hydrodynamical simulations and Cosmic Origins Spectrograph (COS) observations of the Lyman-alpha forest at redshift $0\leq z\leq 0.2$. Allowing for a factor of two uncertainty in the metagalactic HI photoionisation rate, our hydrodynamical simulations are in good agreement ($1$-$1.5σ$) with the shape and amplitude of the observed CDDF at HI column densities $10^{13.3}\rm\,cm^{-2}\leq N_{\rm HI}\leq 10^{14.5}\rm\,cm^{-2}$. However, the Doppler widths of the simulated lines remain too narrow with respect to the COS data. We argue that invoking AGN feedback does not resolve this discrepancy. We also disfavour enhanced photoheating rates as a potential solution, as this requires an unphysically hard UV background spectrum. If instead appealing to a non-canonical source of heating, an additional specific heat injection of $u \lesssim 6.9\rm\,eV\,m_{\rm p}^{-1}$ is required at $z\lesssim 2.5$ for gas that has $N_{\rm HI}\simeq 10^{13.5}\rm\,cm^{-2}$ by $z=0.1$. Alternatively, there may be an unresolved line of sight turbulent velocity component of $v_{\rm turb}\lesssim 8.5\rm\,km\,s^{-1}(N_{\rm HI}/10^{13.5}\rm\,cm^{-2})^{0.21}$ for the coldest gas in the diffuse IGM.

astro-ph.CO↗