Ionization Structure Research Articles

Bidimensional Exploration of the warm-Temperature Ionised gaS (BETIS)

The extraplanar diffuse ionised gas (eDIG) is a key component for understanding the feedback processes that connect galactic discs and their halos. In this paper, we present the second study of the Bidimensional Exploration of the warm-Temperature Ionised Gas (BETIS) project, the aim of which is to explore the possible ionisation mechanisms and characteristics of the eDIG. We use a sample of eight edge-on galaxies observed with the Multi-Unit Spectroscopic Explorer (MUSE) integral field spectrograph (IFS) and apply the methodology developed in the first paper of the BETIS project for obtaining binned emission line maps. We find that the vertical and radial profiles of the [N II]/Hα, [S II]/Hα, [O III]/Hβ, and [O I]/Hα ratios depict a complex ionisation structure within galactic halos – which is influenced by the spatial distribution of H II regions across the galactic plane as observed from our line of sight–, with Lyman continuum photon leakage from OB associations constituting the main ionisation source. Moreover, the electron temperature and S+/S ionisation ratio also exhibit a dependency on the distribution of H II regions within the galactic discs. Our analysis excludes low-mass, hot, and evolved stars (HOLMES) as viable candidates for secondary ionisation sources to elucidate the unusual behaviour of the line ratios at greater distances from the galactic midplane. In contrast, we ascertain that shocks induced in the interstellar medium by star formation(SF)-related feedback mechanisms represent a promising secondary ionisation source of the eDIG. We present a suite of models integrating ionisation mechanisms arising from fast shocks and photoionisation associated with star formation. When applied to the classical Baldwin–Phillips–Terlevich (BPT) diagrams, these models reveal that the ionisation budget of the eDIG ranges from 20% to 50% across our sample, with local variations of up to 20% within individual galaxy halos. This contribution correlates with the presence of filaments and other structural components observed within galaxy halos. The presence of shocks is additionally supported by the observation of a high density of high [O I]/Hα ratios, which is characteristic of shock-compressed ionised gas, and is likely induced by feedback from regions of intense SF within the galactic disc. These results demonstrate consistency across all galaxies analysed in this sample.

Morphology of NGC 6886 Using IFU Data

Abstract In this paper, we report the first investigation of NGC 6886 utilizing IFU data, allowing us to build a more comprehensive morphological study based on many emission lines. NGC 6886 is a young planetary nebula featuring emission lines with varying levels of excitation. Using data from Potsdam Multi-Aperture Spectrophotometer (PMAS), we construct an integrated spectra and identify 27 emission lines. We calculate the flux ratio of each line relative to Hβ. Lines stronger than Hβ are [OIII] 5007, [OIII] 4959, [NII] 6584, Hα 6563, [NII] 6548, and [NeIII] 3869. We also construct 16 emission line maps to examine the morphology and ionization structure of NGC 6886 and we show that there are two geometrical structures within the nebula.

SDSS-V Local Volume Mapper (LVM): A glimpse into Orion

The Orion Molecular Cloud complex, one of the nearest (D = 406 pc) and most extensively studied massive star-forming regions, is ideal for constraining the physics of stellar feedback, but its sim 12 deg diameter on the sky requires a dedicated approach to mapping ionized gas structures within and around the nebula. The Sloan Digital Sky Survey (SDSS-V) Local Volume Mapper (LVM) is a new optical integral field unit (IFU) that will map the ionized gas within the Milky Way and Local Group galaxies, covering 4300 deg$^2$ of the sky with the new LVM Instrument (LMV-I). We showcase optical emission line maps from LVM covering 12 deg$^2$ inside of the Orion belt region, with 195,000 individual spectra combined to produce images at 0.07 pc (35.3 resolution. This is the largest IFU map made (to date) of the Milky Way, and contains well-known nebulae (the Horsehead Nebula, Flame Nebula, IC 434, and IC 432), as well as ionized interfaces with the neighboring dense Orion B molecular cloud. We resolve the ionization structure of each nebula, and map the increase in both the and line ratios at the outskirts of nebulae and along the ionization front with Orion B. line emission is only spatially resolved within the center of the Flame Nebula and IC 434, and our sim 0.1 pc scale line ratio diagrams show how variations in these diagnostics are lost as we move from the resolved to the integrated view of each nebula. We detect ionized gas emission associated with the dusty bow wave driven ahead of the star sigma Orionis, where the stellar wind interacts with the ambient interstellar medium. The Horsehead Nebula is seen as a dark occlusion of the bright surrounding photo-disassociation region. This small glimpse into Orion only hints at the rich science that will be enabled by the LVM.

Photoionization analysis of chemodynamical dwarf galaxies simulations. II. Detailed calculation of diffuse ionizing radiation

ABSTRACT Active star formation in dwarf galaxies shapes the morphology of the surrounding nebular environment and ensures the non-uniformity of the chemical elements spatial distribution in it due to the superwind region expansion. Ionizing radiation within the nebular gas produces observed emission lines used for modelling and diagnostics. We introduce a multicomponent photoionization modelling (MPhM) approach that incorporates detailed calculation of diffuse ionizing radiation (DCDIR) based on chemodynamical simulations (ChDSs). Our models aim to replicate crucial emission line intensity ratios within the observed range, employing a thin dense shell between the superwind region and the outer nebular environment to address ChDSs resolution limitations, which render them insensitive to the presence of a superwind shock. MPhM-generated emission line spectra within a small central synthetic aperture and a thin long-slit exhibit excellent agreement with observations, confirming the accuracy of the ionization structure of the nebular environment obtained using the MPhM + DCDIR approach. However, the outward-only approximation fails to reproduce the dwarf galaxies ionization structure. We determined the oxygen abundance using the $T_e$- and $R_{23}$-methods based on emission lines from MPhM + DCDIR. The resulting abundances align well with values obtained by averaging over the ‘observed’ volume within synthetic apertures, weighted by mass. The escape fraction of ionizing photons from the dwarf galaxy was found to be larger than that obtained using the outward-only approximation. Employing Kennicutt’s calibration corrected for near-UV data, the star formation rate (SFR) was calculated using the ${\rm H}\,\alpha$ luminosity from MPhM + DCDIR. The resulting SFR value is nearly 33 per cent higher than the true one.

Radiative transfer of 21-cm line through ionised cavities in an expanding universe

Abstract The optical depth parameterisation is typically used to study the 21-cm signals associated with the properties of the neutral hydrogen (H i) gas and the ionisation morphology during the Epoch of Reionisation (EoR), without solving the radiative transfer equation. To assess the uncertainties resulting from this simplification, we conduct explicit radiative transfer calculations using the cosmological 21-cm radiative transfer (C21LRT) code and examine the imprints of ionisation structures on the 21-cm spectrum. We consider a globally averaged reionisation history and implement fully ionised cavities (H ii bubbles) of diameters d ranging from 0.01 Mpc to 10 Mpc at epochs within the emission and the absorption regimes of the 21-cm global signal. The single-ray C21LRT calculations show that the shape of the imprinted spectral features are primarily determined by d and the 21-cm line profile, which is parametrised by the turbulent velocity of the H i gas. It reveals the spectral features tied to the transition from ionised to neutral regions that calculations based on the optical depth parametrisation were unable to capture. We also present analytical approximations of the calculated spectral features of the H ii bubbles. The multiple-ray calculations show that the apparent shape of a H ii bubble (of d = 5 Mpc at z = 8), because of the finite speed of light, differs depending on whether the bubble’s ionisation front is stationary or expanding. Our study shows the necessity of properly accounting for the effects of line-continuum interaction, line broadening and cosmological expansion to correctly predict the EoR 21-cm signals.

Photo-ionization structures of Planetary Nebula IC 2003 with [WR] central star

We present ionization structures of IC 2003, a planetary nebula with [WR] central star, using a 1-D dusty photo-ionization code: ”CLOUDY 17.03”. The photo-ionization model is constrained by archival UV emission line fluxes, medium-resolution optical spectroscopy, IRAS25μm flux, absolute Hβ flux, and the mean angular size of the nearly spherical optical nebula. To constrain the carbon abundance and the effect of photo-electric heating in the ionized gas, we used UV emission lines. We considered an amorphous carbon dust grain with MRN and KMH size distributions to address the importance of photo-electric heating in the ionized nebula. We show that KMH grain size distribution with quantum dust heating reproduces the observations quite well. We construct the ionization structures of different elements at their different ionization stages in the nebula. We derive the physical properties of the planetary nebula and its chemical composition, as well as the parameters of its central star. The estimated nebular dust-to-gas mass ratio is 2.37×10-3, and the enhanced photo-electric heating yielded by small dust grains is 9.4% of the total heating. We considered the H-poor model atmosphere for the central star; the effective temperature of the central star is 177 kK, the specific gravity log(g) is 6, and its luminosity (L∗) is 6425 L⊙. The derived central star parameters plotted on stellar evolutionary tracks correspond to a central star mass of 0.636 M⊙ and to a progenitor mass of 3.26 M⊙.

PDRs4All

Context. JWST has taken the sharpest and most sensitive infrared (IR) spectral imaging observations ever of the Orion Bar photodis-sociation region (PDR), which is part of the nearest massive star-forming region the Orion Nebula, and often considered to be the ‘prototypical’ strongly illuminated PDR. Aims. We investigate the impact of radiative feedback from massive stars on their natal cloud and focus on the transition from the H II region to the atomic PDR – crossing the ionisation front (IF) –, and the subsequent transition to the molecular PDR – crossing the dissociation front (DF). Given the prevalence of PDRs in the interstellar medium and their dominant contribution to IR radiation, understanding the response of the PDR gas to far-ultraviolet (FUV) photons and the associated physical and chemical processes is fundamental to our understanding of star and planet formation and for the interpretation of any unresolved PDR as seen by JWST. Methods. We used high-resolution near-IR integral field spectroscopic data from NIRSpec on JWST to observe the Orion Bar PDR as part of the PDRs4All JWST Early Release Science programme. We constructed a 3″ × 25″’ spatio-spectral mosaic covering 0.97– 5.27 μm at a spectral resolution R of ~2700 and an angular resolution of 0.075″–0.173″. To study the properties of key regions captured in this mosaic, we extracted five template spectra in apertures centred on the three H2 dissociation fronts, the atomic PDR, and the H II region. This wealth of detailed spatial-spectral information was analysed in terms of variations in the physical conditions-incident UV field, density, and temperature – of the PDR gas. Results. The NIRSpec data reveal a forest of lines including, but not limited to, He I, H I , and C I recombination lines; ionic lines (e.g. Fe III and Fe II); O I and N I fluorescence lines; aromatic infrared bands (AIBs, including aromatic CH, aliphatic CH, and their CD counterparts); pure rotational and ro-vibrational lines from H2; and ro-vibrational lines from HD, CO, and CH+, with most of them having been detected for the first time towards a PDR. Their spatial distribution resolves the H and He ionisation structure in the Huygens region, gives insight into the geometry of the Bar, and confirms the large-scale stratification of PDRs. In addition, we observed numerous smaller-scale structures whose typical size decreases with distance from θ1 Ori C and IR lines from C I , if solely arising from radiative recombination and cascade, reveal very high gas temperatures (a few 1000 K) consistent with the hot irradiated surface of small-scale dense clumps inside the PDR. The morphology of the Bar, in particular that of the H2 lines, reveals multiple prominent filaments that exhibit different characteristics. This leaves the impression of a ‘terraced’ transition from the predominantly atomic surface region to the CO-rich molecular zone deeper in. We attribute the different characteristics of the H2 filaments to their varying depth into the PDR and, in some cases, not reaching the C+/C/CO transition. These observations thus reveal what local conditions are required to drive the physical and chemical processes needed to explain the different characteristics of the DFs and the photochemical evolution of the AIB carriers. Conclusions. This study showcases the discovery space created by JWST to further our understanding of the impact radiation from young stars has on their natal molecular cloud and proto-planetary disk, which touches on star and planet formation as well as galaxy evolution.

Cloud-by-cloud multiphase investigation of the circumgalactic medium of low-redshift galaxies

ABSTRACT The pervasive presence of warm gas in galaxy haloes suggests that the circumgalactic medium (CGM) is multiphase in its ionization structure and complex in its kinematics. Some recent state-of-the-art cosmological galaxy simulations predict an azimuthal dependence of CGM metallicities. We investigate the presence of such a trend by analysing the distribution of gas properties in the CGM around 47 z < 0.7 galaxies from the Multiphase Galaxy Halos Survey determined using a cloud-by-cloud, multiphase, ionization modelling approach. We identify three distinct populations of absorbers: cool clouds (T ∼ 104.1 K) in photoionization equilibrium, warm–hot collisionally ionized clouds (T ∼ 104.5–105 K) affected by time-dependent photoionization, and hotter clouds (T ∼ 105.4–106 K) with broad O vi and Ly α absorption consistent with collisional ionization. We find that fragmentation can play a role in the origin of cool clouds, that warm–hot clouds are out of equilibrium due to rapid cooling, and that hotter clouds are representative of virialized halo gas in all but the lowest mass galaxies. The metallicities of clouds do not depend on the azimuthal angle or other galaxy properties for any of these populations. At face value, this disagrees with the simplistic model of the CGM with bipolar outflows and cold-mode planar accretion. However, the number of clouds per sightline is significantly larger close to the minor and major axes. This implies that the processes of outflows and accretion are contributing to these CGM cloud populations, and our sightlines are probing gas of mixed origins at all azimuthal angles in these low-redshift galaxies.

Ionizable Lipids from Click Reactions for Lipid Nanoparticle Assembling and mRNA Delivery.

Ionizable lipid-containing lipid nanoparticles (LNPs) are regarded as promising nonviral vectors for gene therapy delivery systems. Rationale design of the ionizable lipid structure based on initial screening of ionizable lipid molecule libraries combined with systematic comparison and analysis on the physical chemical parameters related to delivery efficiency greatly accelerated the discovery of novel LNP candidates for delivering various nucleic acid therapeutics like mRNAs (mRNAs). Based on the copper-catalyzed azide-alkyne click reaction, which is highly efficient and biocompatible, we were able to obtain the lipid molecule library containing a common triazole moiety between different lipid tails and various substituents as hydrophilic head groups. Herein, we systematically investigated the change of pKa values of different ionizable lipid molecules with different substituents as head groups in the click-based lipid library, mapping the pKa value change to different steps in the process of the LNP assembly and mRNA delivery. Systematic analyses on the data including the pKa value of the ionized lipids and the encapsulation and delivery efficiency of mRNA in LNPs with these ionized lipids provided the possibility of rational design on the head and tail structure for the triazole containing ionized lipids to realize highly efficient delivery of different mRNAs.

Large-scale excess H i absorption around z ≈ 4 galaxies detected in a background galaxy spectrum in the MUSE eXtremely deep field

ABSTRACT Observationally mapping the relation between galaxies and the intergalactic medium (IGM) is of key interest for studies of cosmic reionization. Diffuse hydrogen gas has typically been observed in H i Lyman-α (Lyα) absorption in the spectra of bright background quasars. However, it is important to extend these measurements to background galaxies as quasars become increasingly rare at high redshift and rarely probe closely separated sight lines. Here, we use deep integral field spectroscopy in the MUSE eXtremely Deep Field to demonstrate the measurement of the Lyα transmission at z ≈ 4 in absorption to a background galaxy at z = 4.77. The H i transmission is consistent with independent quasar sight lines at similar redshifts. Exploiting the high number of spectroscopic redshifts of faint galaxies (500 between z = 4.0–4.7 within a radius of 8 arcmin) that are tracers of the density field, we show that Lyα transmission is inversely correlated with galaxy density, i.e. transparent regions in the Lyα forest mark underdense regions at z ≈ 4. Due to large-scale clustering, galaxies are surrounded by excess H i absorption over the cosmic mean out to 4 cMpc/h70. We also find that redshifts from the peak of the Lyα line are typically offset from the systemic redshift by +170 km s−1. This work extends results from z ≈ 2–3 to higher redshifts and demonstrates the power of deep integral field spectroscopy to simultaneously measure the ionization structure of the IGM and the large-scale density field in the early Universe.

Thiophene-based lipids for mRNA delivery to pulmonary and retinal tissues

Lipid nanoparticles (LNPs) largely rely on ionizable lipids to yield successful nucleic acid delivery via electrostatic disruption of the endosomal membrane. Here, we report the identification and evaluation of ionizable lipids containing a thiophene moiety (Thio-lipids). The Thio-lipids can be readily synthesized via the Gewald reaction, allowing for modular lipid design with functional constituents at various positions of the thiophene ring. Through the rational design of ionizable lipid structure, we prepared 47 Thio-lipids and identified some structural criteria required in Thio-lipids for efficient mRNA (messenger RNA) encapsulation and delivery in vitro and in vivo. Notably, none of the tested lipids have a pH-response profile like traditional ionizable lipids, potentially due to the electron delocalization in the thiophene core. Placement of the tails and localization of the ionizable headgroup in the thiophene core can endow the nanoparticles with the capability to reach various tissues. Using high-throughput formulation and barcoding techniques, we optimized the formulations to select two top lipids-20b and 29d-and investigated their biodistribution in mice. Lipid 20b enabled LNPs to transfect the liver and spleen, and 29d LNP transfected the lung and spleen. Unexpectedly, LNP with lipid 20b was especially potent in mRNA delivery to the retina with no acute toxicity, leading to the successful delivery to the photoreceptors and retinal pigment epithelium in non-human primates.

Exploring the high abundance discrepancy in the planetary nebula IC 4663

This article presents an in-depth analysis of integral field unit spectroscopy performed on the Galactic planetary nebula (PN) IC 4663, with a primary focus on investigating its physical characteristics, chemical composition, and morphological properties. The examination involved the utilization of a series of emission-line maps representing various elements and ionization zones, allowing for a comprehensive assessment of morphological and ionization structure of IC 4663. The majority of these maps depict an overall elliptical shape, featuring a relatively faint core at the center. Emanating from this core are two distinct and illuminated lobes extending in opposite directions, forming a conspicuous double-lobed configuration. The chemical analysis conducted on IC 4663 has revealed that the PN is rich in both helium and nitrogen, characterized by an N/O ratio exceeding 0.5, classifying it as a Peimbert type I nebula. Furthermore, the presence of a notably intense He II emission line at λ4686, in conjunction with the existence of high-excitation lines within the nebular spectrum, indicate its classification as a high-excitation class nebula. The computation of O2+, N2+, and N3+ through optical recombination lines has unveiled extreme abundance discrepancy factors, with values of 39.0 ± 6 for O2+ and 37.0 ± 9 for N2+ and N3+. These findings suggest the possibility that the central star of IC 4663 may be part of a binary system with a sub-stellar companion, potentially engaged in a common envelope interaction. Recent astrometric data derived from the Gaia mission further indicate a significant likelihood of interaction between the asymptotic giant branch halo of the PN and its surrounding interstellar medium, particularly in the southeast direction.

X-ray polarization properties of partially ionized equatorial obscurers around accreting compact objects

ABSTRACT We present the expected X-ray polarization signal resulting from distant reprocessing material around black holes. Using a central isotropic power-law emission at the centre of the simulated model, we add distant equatorial and axially symmetric media that are covering the central accreting sources. We include partial ionization and partial transparency effects, and the impact of various polarization and steepness of the primary radiation spectrum. The results are obtained with the Monte Carlo code STOKES that considers both line and continuum processes and computes the effects of scattering and absorption inside static homogenous wedge-shaped and elliptical toroidal structures, varying in relative size, composition and distance to the source. We provide first order estimates for parsec-scale reprocessing in Compton-thin and Compton-thick active galactic nuclei, as well as winds around accreting stellar-mass compact objects, for observer’s inclinations above and below the grazing angle. The resulting reprocessed polarization can reach tens of per cent with either parallel or perpendicular orientation with respect to the axis of symmetry, depending on subtle details of the geometry, density, and ionization structure. We also show how principal parameters constrained from X-ray spectroscopy or polarimetry in other wavelengths can lift the shown degeneracies in X-ray polarization. We provide an application example of the broad modelling discussion by revisiting the recent IXPE 2–8 keV X-ray polarimetric observation of the accreting stellar-mass black hole in Cygnus X-3 from the perspective of partial transparency and ionization of the obscuring outflows.

Characterizing the origin band spectrum of isoquinoline with resonance enhanced multiphoton ionization and electronic structure calculations.

We report the experimental resonance enhanced multiphoton ionization spectrum of isoquinoline between 315 and 310nm, along with correlated electronic structure calculations on the ground and excited states of this species. This spectral region spans the origin transitions to a π-π* excited state, which previous work has suggested to be vibronically coupled with a lower lying singlet n-π* state. Our computational results corroborate previous density functional theory calculations that predict the vertical excitation energy for the n-π* state to be higher than the π-π* state; however, we find an increase in the C-N-C angle brings the n-π* state below the energy of the π-π* state. The calculations find two out-of-plane vibrational modes of the n-π* state, which may be brought into near resonance with the π-π* state as the C-N-C bond angle increases. Therefore, the C-N-C bond angle may be important in activating vibronic coupling between the states. We fit the experimental rotational contour with a genetic algorithm to determine the excited state rotational constants and orientation of the transition dipole moment. The fits show a mostly in-plane polarized transition, and the projection of the transition dipole moment in the a-b plane is about 84° away from the a axis. These results are consistent with the prediction of our electronic structure calculations for the transition dipole moment of the π-π* excited state.

A MUSE/VLT spatially resolved study of the emission structure of Green Pea galaxies

Green Pea galaxies (GPs) present among the most intense starbursts known in the nearby Universe. These galaxies are regarded as local analogs of high-redshift galaxies, making them a benchmark in the understanding of the star formation processes and the galactic evolution in the early Universe. In this work, we performed an integral field spectroscopic (IFS) study for a set of 24 GPs to investigate the interplay between its ionized interstellar medium (ISM) and the massive star formation that these galaxies present. Observations were taken in the optical spectral range (λ4750 Å–λ9350 Å) with the MUSE spectrograph attached to the 8.2 m telescope VLT. Spatial extension criteria were employed to verify which GPs are spatially resolved in the MUSE data cubes. We created and analyzed maps of spatially distributed emission lines (at different stages of excitation), continuum emission, and properties of the ionized ISM (e.g., ionization structure indicators, physical-chemical conditions, dust extinction). We also took advantage of our IFS data to produce integrated spectra of selected galactic regions in order to study their physical-chemical conditions. Maps of relevant emission lines and emission line ratios show that higher-excitation gas is preferentially located in the center of the galaxy, where the starburst is present. The continuum maps, with an average angular extent of 4″, exhibit more complex structures than the emission line maps. However, the [O III]λ5007 Å emission line maps tend to extend beyond the continuum images (the average angular extent is 5.5″), indicating the presence of low surface brightness ionized gas in the outer parts of the galaxies. Hα/Hβ, [S II]/Hα, and [O I]/Hα maps trace low-extinction, optically thin regions. The line ratios [O III]/Hβ and [N II]/Hα span extensive ranges, with values varying from 0.5 dex to 0.9 dex and from −1.7 dex to −0.8 dex, respectively. Regarding the integrated spectra, the line ratios were fit to derive physical properties including the electron densities ne = 30 − 530 cm−3, and, in six GPs with a measurable [O III]λ4363 Å line, electron temperatures of Te = 11 500 K–15 500 K, so the direct method was applied in these objects to retrieve metallicities 12 + log(O/H)≃8. We found the presence of the high-ionizing nebular He IIλ4686 Å line in three GPs, where two of them present among the highest sSFR values (> 8 × 108 yr−1) in this sample. Non-Wolf-Rayet (WR) features are detected in these galaxy spectra.

Avalanches and the Distribution of Reconnection Events in Magnetized Circumstellar Disks

Cosmic rays produced by young stellar objects can potentially alter the ionization structure, heating budget, chemical composition, and accretion activity in circumstellar disks. The inner edges of these disks are truncated by strong magnetic fields, which can reconnect and produce flaring activity that accelerates cosmic radiation. The resulting cosmic rays can provide a source of ionization and produce spallation reactions that alter the composition of planetesimals. These reconnection and particle acceleration processes are analogous to the physical processes that produce flaring in and the heating of stellar coronae. Flaring events on the surface of the Sun exhibit a power-law distribution of energy, reminiscent of those measured for earthquakes and avalanches. Numerical lattice reconnection models are capable of reproducing the observed power-law behavior of solar flares under the paradigm of self-organized criticality. One interpretation of these experiments is that the solar corona maintains a nonlinear attractor—or “critical”—state by balancing energy input via braided magnetic fields and output via reconnection events. Motivated by these results, we generalize the lattice reconnection formalism for applications in the truncation region of magnetized disks. Our numerical experiments demonstrate that these nonlinear dynamical systems are capable of both attaining and maintaining criticality in the presence of Keplerian shear and other complications. The resulting power-law spectrum of flare energies in the equilibrium attractor state is found to be nearly universal in magnetized disks. This finding indicates that magnetic reconnection and flaring in the inner regions of circumstellar disks occur in a manner similar to the activity on stellar surfaces. These results, in turn, have ramifications for the spallation-driven injection of radionuclides in planetesimals, disk ionization, and the subsequent planetary formation process.

Quasars and the Intergalactic Medium at Cosmic Dawn

Quasars at cosmic dawn provide powerful probes of the formation and growth of the earliest supermassive black holes (SMBHs) in the Universe, their connections to galaxy and structure formation, and the evolution of the intergalactic medium (IGM) at the epoch of reionization (EoR). Hundreds of quasars have been discovered in the first billion years of cosmic history, with the quasar redshift frontier extended to z ∼ 7.6. Observations of quasars at cosmic dawn show the following: ▪The number density of luminous quasars declines exponentially at z > 5, suggesting that the earliest quasars emerge at z ∼ 10; the lack of strong evolution in their average spectral energy distribution indicates a rapid buildup of the active galactic nucleus environment.▪Billion-solar-mass black holes (BHs) already exist at z > 7.5; they must form and grow in less than 700 Myr, by a combination of massive early BH seeds with highly efficient and sustained accretion.▪The rapid quasar growth is accompanied by strong star formation and feedback activity in their host galaxies, which show diverse morphological and kinetic properties, with typical dynamical mass lower than that implied by the local BH/galaxy scaling relations.▪Hi absorption in quasar spectra probes the tail end of cosmic reionization at z ∼ 5.3–6 and indicates the EoR midpoint at 6.9 < z < 7.6, with large spatial fluctuations in IGM ionization. Observations of heavy element absorption lines suggest that the circumgalactic medium also experiences evolution in its ionization structure and metal enrichment during the EoR.

Hierarchical Model of Weak Polyelectrolytes with Ionization and Conformation Consistency

Conventional models of weak polyelectrolytes are formulated in terms of either an average degree of ionization or a rigid polymer conformation. While the decoupling of segment-level ionization and polymer structure simplifies the theoretical procedure and is beneficial from a computational perspective, it misses intrachain correlations (i.e., interactions beyond adjacent monomers) that are important for systems at a low polymer concentration with strong electrostatic interactions. In this work, we propose a hierarchical method that incorporates the liquid-state theories with the site-binding model to account for the effects of the local ionic environment on both inter- and intrachain correlations. A wormlike-chain model is introduced to describe the coupling of polymer conformation and monomeric ionization with the long-range electrostatic interactions accounted for by using the Gibbs–Bogoliubov variational principle. Through an extensive comparison of the theoretical predictions with experimental titration curves for poly(acrylic acid) in different alkali chloride solutions, we demonstrate that the hierarchical model is able to quantify the charging behavior of weak polyelectrolytes over a broad range of solution conditions.

The Roles of Dust Growth in the Temperature Evolution and Snow Line Migration in Magnetically Accreting Protoplanetary Disks

The temperature structure of protoplanetary disks provides an important constraint on where in the disks rocky planets like our own form. Recent nonideal magnetohydrodynamical (MHD) simulations have shown that the internal Joule heating associated with magnetically driven disk accretion is inefficient at heating the disk midplane. A disk temperature model based on the MHD simulations predicts that in a disk around a solar-mass young star, the water snow line can move inside the current Earth’s orbit within 1 Myr after disk formation. However, the efficiency of the internal Joule heating depends on the disk’s ionization and opacity structures, both of which are governed by dust grains. In this study, we investigate these effects by combining the previous temperature model for magnetically accreting disks with a parameterized model for the grain size and vertical distribution. Grain growth enhances the gas ionization fraction and thereby allows Joule heating to occur closer to the midplane. However, growth beyond 10 μm causes a decrease in the disk opacity, leading to a lower midplane temperature. The combination of these two effects results in the midplane temperature being maximized when the grain size is in the range 10–100 μm. Grain growth to millimeter sizes can also delay the snow line’s migration to the 1 au orbit by up to a few million years. We conclude that accounting for dust growth is essential for accurately modeling the snow line evolution and terrestrial planet formation in magnetically accreting protoplanetary disks.

UM 462, a local green pea galaxy analogue under the MUSE magnifying glass

Context. Stellar feedback in high-redshift galaxies plays an important, if not dominant, role in the re-ionisation epoch of the Universe. Because of their extreme star formation (SF), the relatively closer green pea (GP) galaxies are postulated as favorite local laboratories, and analogues to those high-redshift galaxies. However, at their typical redshift of z ∼ 0.2, the most intimate interaction between stars and the surrounding interstellar medium cannot be disentangled. Detailed studies of blue compact dwarf (BCD) galaxies sharing properties with GP galaxies are necessary to anchor our investigations on them. Aims. We want to study in detail UM 462, which is a BCD with emission line ratios and equivalent widths, stellar mass, and metallicity similar to those observed in GP galaxies, and thus it is ideally suited as a corner stone and reference galaxy. Methods. We use high-quality optical integral field spectroscopy data obtained with MUSE on the ESO Very Large Telescope. Results. The electron density (ne) and temperature (Te) were mapped. Median Te decreases according to the sequence [S III] → [N II] → He I. Furthermore, Te([S III]) values are ∼13 000 K, and uniform within the uncertainties over an area of ∼20″ × 8″ (∼1.4 kpc × 0.6 kpc). The total oxygen abundance by means of the direct method is 12 + log(O/H) ∼ 8.02 and homogenous all over the galaxy within the uncertainties, which is in stark contrast with the metallicities derived from several strong line methods. This result calls for a systematic study to identify the best strategy to determine reliable metallicities at any location within a galaxy. The strong line ratios used in the BPT diagrams and other ratios tracing the ionisation structure were mapped. They are compatible with plasma ionised by massive hot stars. However, there is a systematic excess in the [O I]/Hα ratio, suggesting an additional mechanism or a complex relative configuration of gas and stars. The velocity field for the ionised gas presents receding velocities in the east and approaching velocities in the west and south-west with velocity differences of Δv ∼ 40 km s−1, but it is not compatible with simple rotation. The most striking feature is a velocity stratification in the area towards the north with redder velocities in the high ionisation lines and bluer velocities in the low ionisation lines. This is the only area with velocity dispersions clearly above the MUSE instrumental width, and it is surrounded by two ∼1 kpc-long structures nicknamed ‘the horns’. We interpret the observational evidence in that area as a fragmented super-bubble fruit of the stellar feedback and it may constitute a preferred channel through which Lyman continuum photons from the youngest generation of stars can escape. The galaxy luminosity is dominated by a young (i.e. ∼6 Myr) stellar population that contributes only 10% to the stellar mass, as derived from the modelling of the stellar continuum. The most recent SF seems to propagate from the outer to the inner parts of the galaxy, and then from east to west. We identified a supernova remnant and Wolf-Rayet stars – as traced by the red bump – that support this picture. The direction of the propagation implies the presence of younger Wolf-Rayet stars at the maximum in Hα. These may be detected by deep observations of the blue bump (not covered here). Conclusions. The ensemble of results exemplifies the potential of 2D detailed spectroscopic studies of dwarf star-forming galaxies at high spatial resolution as a key reference for similar studies on primeval galaxies.