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Conservation translocations, intentional movements of species to protect against extinction, have become widespread in recent decades and are projected to increase further as biodiversity loss continues worldwide. The literature abounds with analyses to inform translocations and assess whether they are successful, but the fundamental question of whether they should be initiated at all is rarely addressed formally. We used decision analysis to assess northern leopard frog reintroduction in northern Idaho, with success defined as a population that persists for at least 50 years. The Idaho Department of Fish and Game was the decision maker (i.e., the agency that will use this assessment to inform their decisions). Stakeholders from government, indigenous groups, academia, land management agencies, and conservation organizations also participated. We built an age-structured population model to predict how management alternatives would affect probability of success. In the model, we explicitly represented epistemic uncertainty around a success criterion (probability of persistence) characterized by aleatory uncertainty. For the leading alternative, the mean probability of persistence was 40%. The distribution of the modelling results was bimodal, with most parameter combinations resulting in either very low (<5%) or relatively high (>95%) probabilities of success. Along with other considerations, including cost, the Idaho Department of Fish and Game will use this assessment to inform a decision regarding reintroduction of northern leopard frogs. Conservation translocations may benefit greatly from more widespread use of decision analysis to counter the complexity and uncertainty inherent in these decisions. History: This paper has been accepted for the Decision Analysis Special Issue on Further Environmental Sustainability. Funding: This work was supported by the Wilder Institute/Calgary Zoo, the U.S. Fish and Wildlife Service [Grant F18AS00095], the NSF Idaho EPSCoR Program and the National Science Foundation [Grant OIA-1757324], and the Hunt Family Foundation. Supplemental Material: The online appendix is available at https://doi.org/10.1287/deca.2023.0472 . 

We present a new upper limit on the cosmic molecular gas density atz= 2.4–3.4 obtained using the first year of observations from the CO Mapping Array Project (COMAP). COMAP data cubes are stacked on the 3D positions of 243 quasars selected from the Extended Baryon Oscillation Spectroscopic Survey (eBOSS) catalog, yielding a 95% upper limit for flux from CO(1–0) line emission of 0.129 Jy km s⁻¹. Depending on the balance of the emission between the quasar host and its environment, this value can be interpreted as an average CO line luminosity$L_{\mathrm{CO}}^{\prime }$of eBOSS quasars of ≤1.26 × 10¹¹K km pc²s⁻¹, or an average molecular gas density${\rho }_{{\mathrm{H}}_2}$in regions of the Universe containing a quasar of ≤1.52 × 10⁸M_⊙cMpc⁻³. The$L_{\mathrm{CO}}^{\prime }$upper limit falls among CO line luminosities obtained from individually targeted quasars in the COMAP redshift range, and the${\rho }_{{\mathrm{H}}_2}$value is comparable to upper limits obtained from other line intensity mapping (LIM) surveys and their joint analyses. Further, we forecast the values obtainable with the COMAP/eBOSS stack after the full 5 yr COMAP Pathfinder survey. We predict that a detection is probable with this method, depending on the CO properties of the quasar sample. Based on the achieved sensitivity, we believe that this technique of stacking LIM data on the positions of traditional galaxy or quasar catalogs is extremely promising, both as a technique for investigating large galaxy catalogs efficiently at high redshift and as a technique for bolstering the sensitivity of LIM experiments, even with a fraction of their total expected survey data.

 

We measure the mean free path ($\lambda _{\rm mfp,H\, \small {I}}$), photoionization rate ($\langle \Gamma _{\rm H\, \small {I}} \rangle$), and neutral fraction ($\langle f_{\rm H\, \small {I}} \rangle$) 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 modelled 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 $\Gamma _{\rm H\, \small {I}}$ 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-modelling the  Lyα forest and comparing the effective optical depth ($\tau _{\rm eff, H\, \small {I}}$) distribution in simulations and observations. The final uncertainties in our measured parameters account for the uncertainties due to thermal parameters, modelling parameters, observational systematics, and cosmic variance. Our best-fitting parameters show significant evolution with redshift such that $\lambda _{\rm mfp,H\, \small {I}}$ and $\langle f_{\rm H\, \small {I}} \rangle$ decreases and increases by a factor ∼6 and ∼104, respectively from z ∼ 5 to z ∼ 6. By comparing our $\lambda _{\rm mfp,H\, \small {I}}$, $\langle \Gamma _{\rm H\, \small {I}} \rangle$ and $\langle f_{\rm H\, \small {I}} \rangle$ evolution with that in state-of-the-art Aton radiative transfer simulations and the Thesan and CoDa-III simulations, we find that our best-fitting parameter evolution is consistent with a model in which reionization completes by z ∼ 5.2. Our best-fitting model that matches the $\tau _{\rm eff, H\, \small {I}}$ distribution also reproduces the dark gap length distribution and transmission spike height distribution suggesting robustness and accuracy of our measured parameters.

 

We explore how the assumption of ionization equilibrium modulates the modeled intergalactic medium at the end of the hydrogen epoch of reionization using the cosmological radiation hydrodynamicTechnicolor Dawnsimulation. In neutral and partially ionized regions where the metagalactic ultraviolet background is weak, the ionization timescalet_ion≡ Γ⁻¹exceeds the Hubble time. Assuming photoionization equilibrium in such regions artificially boosts the ionization rate, accelerating reionization. By contrast, the recombination timet_rec<t_ionin photoionized regions, with the result that assuming photoionization equilibrium artificially increases the neutral hydrogen fraction. Using snapshots in the range 8 ≥z≥ 5, we compare the predicted Lyαforest (LAF) flux power spectrum with and without the assumption of ionization equilibrium. Small scales (k> 0.1 rad s km⁻¹) exhibit reduced power from 7 ≤z≤ 5.5 in the ionization equilibrium case, while larger scales are unaffected. This occurs for the same reasons: ionization equilibrium artificially suppresses the neutral fraction in self-shielded gas and boosts ionizations in voids, suppressing small-scale fluctuations in the ionization field. When the volume-averaged neutral fraction drops below 10⁻⁴, the signature of nonequilibrium ionizations on the LAF disappears. Comparing with recent observations indicates that these nonequilibrium effects are not yet observable in the LAF flux power spectrum.

 

Proximity zones of high-redshift quasars are unique probes of their central supermassive black holes as well as the intergalactic medium (IGM) 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 ultraviolet magnitudes of M1450 ∼ −27 and black hole masses of 109–1010 M⊙. Our inferred proximity zone sizes are 2–7 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 ∼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, that in turn will help probe the seed mass and formation redshift of supermassive black holes.

 

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

 

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-α 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-α 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-α forest, such as flat-bottom or double-dip absorption profiles.

 

Abstract Traditional large-scale models of reionization usually employ simple deterministic relations between halo mass and luminosity to predict how reionization proceeds. We here examine the impact on modeling reionization of using more detailed models for the ionizing sources as identified within the 100 h −1 Mpc cosmological hydrodynamic simulation S imba , coupled with postprocessed radiative transfer. Comparing with simple (one-to-one) models, the main difference with using S imba sources is the scatter in the relation between dark matter halos and star formation, and hence ionizing emissivity. We find that, at the power spectrum level, the ionization morphology remains mostly unchanged, regardless of the variability in the number of sources or escape fraction. In particular, the power spectrum shape remains unaffected and its amplitude changes slightly by less than 5%–10%, throughout reionization, depending on the scale and neutral fraction. Our results show that simplified models of ionizing sources remain viable to efficiently model the structure of reionization on cosmological scales, although the precise progress of reionization requires accounting for the scatter induced by astrophysical effects. 

We measure escape fractions, fesc, of ionizing radiation from galaxies in the sphinx suite of cosmological radiation-hydrodynamical simulations of reionization, resolving haloes with $M_{\rm vir}\gtrsim 7.5 \times 10^7 \ {\rm {M}_{\odot }}$ with a minimum cell width of ≈10 pc. Our new and largest 20 co-moving Mpc wide volume contains tens of thousands of star-forming galaxies with halo masses up to a few times 1011 M⊙. The simulated galaxies agree well with observational constraints of the ultraviolet (UV) luminosity function in the Epoch of Reionization. The escape fraction fluctuates strongly in individual galaxies over time-scales of a few Myr, due to its regulation by supernova and radiation feedback, and at any given time a tiny fraction of star-forming galaxies emits a large fraction of the ionizing radiation escaping into the intergalactic medium. Statistically, fesc peaks in intermediate-mass, intermediate-brightness, and low-metallicity galaxies (M* ≈ 107 M⊙, M1500 ≈ −17, Z ≲ 5 × 10−3 Z⊙), dropping strongly for lower and higher masses, brighter and dimmer galaxies, and more metal-rich galaxies. The escape fraction correlates positively with both the short-term and long-term specific star formation rate. According to sphinx, galaxies too dim to be yet observed, with ${M_{1500}}\gtrsim -17$, provide about 55 per cent of the photons contributing to reionization. The global averaged fesc naturally decreases with decreasing redshift, as predicted by UV background models and low-redshift observations. This evolution is driven by decreasing specific star formation rates over cosmic time.