Pristine Gas Research Articles

Surface Defect Generation on SnO2 Nanoparticles Using High-Energy Ball Milling for H2S Gas Sensor Applications

Hydrogen sulfide (H2S) is a highly toxic and dangerous gas with a flammable and corrosive nature, making the development of reliable gas sensors for its detection vital. This study investigated the enhancement in H2S gas sensing performance of commercial SnO2 powders after high-energy milling. SnO2 powders were subjected to high-energy milling for 30, 60, and 90 min and then were characterized using advanced techniques to evaluate their morphology, chemical composition, and crystallinity. The response of a pristine SnO2 gas sensor, and ones where the SnO2 was milled for 30, 60 and 90 min, were 2.46, 2.27, 3.01, and 1.98, respectively, to 10 ppm H2S at 300°C. Thus, the H2S gas sensing results revealed that the SnO2 powders milled for 60 min exhibited the highest sensing performance. This improvement in H2S sensing performance was attributable to the reduced particle sizes achieved through the high-energy milling process, which increased the surface area and created defects on the surface of the SnO2 particles, thereby enhancing the interaction between the gas molecules and sensor material. The smaller morphological size of the particles and surface defects subsequently promoted the resistance modulation crucial for H2S gas detection. This study demonstrates that high-energy ball milling can effectively boost the gas-sensing features of SnO2 powders. The findings can provide guidance for enhancing the gas-sensing capabilities of other resistive sensors.

Spatially resolved emission lines in galaxies at 4 < z < 10 from the JADES survey: evidence for enhanced central star formation

We present the first statistical investigation of spatially resolved emission-line properties in a sample of 63 low-mass galaxies at $4 z<10$ using James Webb Space Telescope (JWST)/NIRSpec Micro Shutter Assembly (MSA) data from the JWST Advanced Deep Extragalactic (JADES) survey, focusing on deep, spatially resolved spectroscopy in the GOODS-S extragalactic field. By performing a stacking of the 2D spectra of the galaxies in our sample, we find an increasing or flat radial trend with increasing radius for and a decreasing trend for the blended spectral complex ( (3--4 sigma significance). These results are still valid when stacking the sample in two redshift bins (i.e. $4 z<5.5$ and $5.5 z<10$). The comparison with star-formation photoionisation models suggests that the ionisation parameter increases by $ 0.5$ dex with redshift. Under the hypothesis that radial variations in ( are dominated by trends in we find a tentative metallicity gradient that increases with radius (i.e. `inverted') in both redshift bins. Moreover, our analysis reveals strong negative gradients for the equivalent width of (7sigma significance). This trend persists even after removing known active galactic nucleus candidates, and is therefore consistent with a radial gradient primarily in stellar age and secondarily in metallicity. Taken together, our results suggest that the sample is dominated by active central star formation, with possibly inverted metallicity gradients sustained by recent episodes of accretion of pristine gas or strong radial flows. Deeper observations and larger samples are needed to confirm these preliminary results and to validate our interpretation.

Oxygen Abundance Throughout the Dwarf Starburst Galaxy IC 10

Measurements of oxygen abundance throughout galaxies provide insight to the formation histories and ongoing processes. Here we present a study of the gas-phase oxygen abundance in the H ii regions and diffuse gas of the nearby starburst dwarf galaxy, IC 10. Using the Keck Cosmic Web Imager at W. M. Keck Observatory, we map the central region of IC 10 from 3500 to 5500 Å. The auroral [O III] 4363 Å line is detected with a high signal-to-noise ratio in 12 of 46 H II regions observed, allowing for direct measurement of the oxygen abundance, yielding a median and standard deviation of 12+log(O/H)=8.37±0.25 . We investigate trends between these directly measured oxygen abundances and other H II region properties, finding weak negative correlations with the radius, velocity dispersion, and luminosity. We also find weak negative correlations between the oxygen abundance and the derived quantities of turbulent pressure and ionized gas mass, and a moderate correlation with the derived dynamical mass. Strong line, R 23 abundance estimates are used in the remainder of the H II regions and on a resolved spaxel-by-spaxel basis. There is a large offset between the abundances measured with R 23 and the auroral line method. We find that the R 23 method is unable to capture the large range of abundances observed via the auroral line measurements. The extent of this variation in the measured abundances further indicates a poorly mixed interstellar medium in IC 10, which is not typical of dwarf galaxies and may be partly due to the ongoing starburst, accretion of pristine gas, or a late stage merger.

Strain effects on electronic structure and optics of al-Doped monolayer GaS

This comprehensive study utilises rigorous first-principles calculations to meticulously investigate the influence of uniaxial tensile strain on the electronic configuration and optical behaviours of aluminium-doped gallium sulphide. The study highlights the modulation of electrical properties and optical responses in Al-doped monolayer GaS through the application of tensile strain. Notably, with increasing tensile strain, the bandgap value of the pristine GaS exhibits a pronounced decline, whereas the Al-doped variant maintains a more stable bandgap. A deeper exploration of the state density reveals the emergence of novel electronic states and energy levels in both the pristine and Al-doped monolayer GaS systems as tensile strain is applied. Crucially, the stabilising effect of the doped Al atoms minimises variations in the state density profiles of the Al-doped monolayer GaS systems, in contrast to their pristine counterparts. This result implies that fine control of the electrical structure and optical characteristics of Al-doped monolayer GaS may be achieved by the application of uniaxial tensile strain. The optoelectronic characteristics of GaS and its doped systems are explained in detail by these discoveries, which also offer a crucial theoretical foundation and direction for the use of these materials in optoelectronic devices.

The JWST-PRIMAL archival survey. A JWST/NIRSpec reference sample for the physical properties and Lyman-alpha absorption and emission of ~ 600 galaxies at z = 5:0 - 13:4

One of the surprising early findings with has been the discovery of a strong ``roll-over'' or a softening of the absorption edge of in a large number of galaxies at \(z 6\), in addition to systematic offsets from photometric redshift estimates and fundamental galaxy scaling relations. This has been interpreted as strong cumulative damped absorption (DLA) wings from high column densities of neutral atomic hydrogen ( signifying major gas accretion events in the formation of these galaxies. To explore this new phenomenon systematically, we assembled the PRImordial gas Mass AssembLy (PRIMAL) legacy survey of 584 galaxies at $z=5.0-13.4$, designed to study the physical properties and gas in and around galaxies during the reionization epoch. We characterized this benchmark sample in full and spectroscopically derived the galaxy redshifts, metallicities, star formation rates, and ultraviolet (UV) slopes. We defined a new diagnostic, the damping parameter to measure and quantify the net effect of emission strength, the fraction in the intergalactic medium, or the local column density for each source. The survey is based on the spectroscopic DAWN Archive (DJA-Spec). We describe DJA-Spec in this paper, detailing the reduction methods, the post-processing steps, and basic analysis tools. All the software, reduced spectra, and spectroscopically derived quantities and catalogs are made publicly available in dedicated repositories. We find that the fraction of galaxies showing strong integrated DLAs with $N_ HI $ only increases slightly from $ 60<!PCT!>$ at $z 6$ up to $ 65-90<!PCT!>$ at $z>8$. Similarly, the prevalence and prominence of emission is found to increase with decreasing redshift, in qualitative agreement with previous observational results. Strong emitters (LAEs) are predominantly found to be associated with low-metallicity and UV faint galaxies. By contrast, strong DLAs are observed in galaxies with a variety of intrinsic physical properties, but predominantly at high redshifts and low metallicities. Our results indicate that strong DLAs likely reflect a particular early assembly phase of reionization-era galaxies, at which point they are largely dominated by pristine gas accretion. At $z=8-10$, this gas gradually cools and forms into stars that ionize their local surroundings, forming large ionized bubbles and producing strong observed emission at $z<8$.

Fe2O3-Co3O4 nanocomposite gas sensor for ethanol sensing studies

This study focused on pristine Fe2O3, pristine Co3O4, and Fe2O3-Co3O4 composite using the Pechini sol-gel method for ethanol gas sensing applications. Advanced characterization techniques were used to analyze the phase, morphology, and composition of the synthesized materials. Gas sensors were then fabricated and used for ethanol gas sensing at different temperatures. The results indicated that Fe2O3-Co3O4 composite gas sensor crystallized at 600 °C, had higher response compared to both pristine Fe2O3 and pristine Co3O4 gas sensors. The composite sensor manifested a high response of 26.2–100 ppm ethanol at 250 °C, while maximum responses of pristine Co3O4 gas sensor was only 4.4 at 200 °C and that of pristine Fe2O3 sensor was 11.4 at 300 °C. The boosted sensing performance of the composite sensor was related to the formation of p-n heterojunctions between Co3O4 and Fe2O3 in composite sensor, the formation of dangling bonds at interfaces, and high intrinsic ethanol sensing properties of Fe2O3.

Two-process Model and Residual Abundance Analysis of the Milky Way Massive Satellites

The “two-process model” is a promising technique for interpreting stellar chemical abundance data from large-scale surveys (e.g., the Sloan Digital Sky Survey IV/V and the Galactic Archeology with HERMES survey), enabling more quantitative empirical studies of differences in chemical enrichment history between galaxies without relying on detailed yield and evolution models. In this work, we fit two-process model parameters to (1) a luminous giant Milky Way (MW) sample and (2) stars comprising the Sagittarius dwarf galaxy (Sgr). We then use these two sets of model parameters to predict the abundances of 14 elements of stars belonging to the MW and in five of its massive satellite galaxies, analyzing the residuals between the predicted and observed abundances. We find that the model fit to (1) results in large residuals (0.1–0.3 dex) for most metallicity-dependent elements in the metal-rich ([Mg/H] > −0.8) stars of the satellite galaxies. However, the model fit to (2) results in small or no residuals for all elements across all satellite galaxies. Therefore, despite the wide variation in [X/Mg]–[Mg/H] abundance patterns of the satellite galaxies, the two-process framework provides an accurate characterization of their abundance patterns across many elements, but these multielement patterns are systematically different between the dwarf galaxy satellites and the MW disks. We consider a variety of scenarios for the origin of this difference, highlighting the possibility that a large inflow of pristine gas to the MW disk diluted the metallicity of star-forming gas without changing abundance ratios.

Study on highly selective NO2 gas sensors based on (Fe, Mo)-doped monolayer WSe2

The two-dimensional (2D) material WSe2 is frequently employed in gas sensors due to its excellent electrical properties. However, the weak interaction between the pristine WSe2 and gas molecules limits its application. Therefore, in this paper, the adsorption behavior of transition metal X (X = Fe, Mo) atom-doped monolayers WSe2 on H and O atoms and molecules of NO2, HCN, and CO gases is investigated to gain insights into the physical mechanisms of adsorbent-substrate interactions. Doping significantly improves the adsorption properties between the substrate and the gas molecules, with the best adsorption showing for NO2 gas molecules and O atoms. The relationship between transition metals and the improvement of adsorption performance is explored by the center position of transition metal d orbitals in different systems, and it is found that the higher the center position of the transition metal d band, the stronger the adsorption between adsorbent and substrate. Compared to pristine WSe2, Mo atom doping in the transition metal doped system has higher adsorption sensitivity to gas molecules and exhibits highly selective adsorption and chemisorption behaviors through high adsorption energies and electron transfer to NO2 molecules. It is demonstrated that X (X = Fe, Mo) doped WSe2 can be used as a gas-sensitive material for efficient gas detection.

Recent Advances in Engineering of 2D Layered Metal Chalcogenides for Resistive-Type Gas Sensor.

2D nanomaterials have triggered widespread attention in sensing applications. Especially for 2D layered metal chalcogenides (LMCs), the unique semiconducting properties and high surface area endow them with great potential for gas sensors. The assembly of 2D LMCs with guest species is an effective functionalization method to produce the synergistic effects of hybridization for greatly enhancing the gas-sensing properties. This review starts with the synthetic techniques, sensing properties, and principles, and then comprehensively compiles the advanced achievements of the pristine 2D LMCs gas sensors. Key advances in the development of the functionalization of 2D LMCs for enhancing gas-sensing properties are categorized according to the spatial architectures. It is systematically discussed in three aspects: surface, lattice, and interlayer, to comprehend the benefits of the functionalized 2D LMCs from surface chemical effect, electronic properties, and structure features. The challenges and outlooks for developing high-performance 2D LMCs-based gas sensors are also proposed.

The imprint of the first stars on the faint end of the white dwarf luminosity function

ABSTRACT Population III stars are characterized by extremely low metallicities as they are thought to be formed from a pristine gas in the early Universe. Although the existence of Population III stars is widely accepted, the lack of direct observational evidence hampers the study of the nature of the putative stars. In this article, we explore the possibilities of constraining the nature of the oldest stars by using the luminosity function of their remnants – white dwarfs. We study the formation and evolution of white dwarf populations by following star formation in a Milky Way-like galaxy using the semi-analytic model a-sloth. We derive the white dwarf luminosity function by applying a linear initial-final mass relation and Mestel’s cooling model. The obtained luminosity function is generally in agreement with available observations and theoretical predictions – with an exponential increase to a maximum of $M_{\mathrm{abs}} = 16$ and a sudden drop for $M_{\mathrm{abs}} \gt 16$. We explore the uncertainties of our model and compare them to the observational estimates. We adopt two different models of the initial mass function of Population III stars to show that the faint end of the luminosity function imprints the signature of Population III remnants. If the feature is detected in future observations, it would provide a clue to Population III stars and would also be an indirect evidence of low- to intermediate-mass Population III stars. We discuss the challenges and prospects for detecting the signatures.

Stability of bubble-particle hetero-coagulates accessed by atomic force microscopy to understand the froth flotation of agglomerating hydrophobic fines

The key microprocesses, which determine the efficiency in froth flotation are the formation and breakage of particle-bubble hetero-coagulates. Agglomeration can be used to increase the recovery of fine particles < 20 µm. Here the stability of hetero-coagulates consisting of agglomerates and gas bubble determines the process performance. Therefore, the stability of agglomerate-bubble hetero-coagulates was accessed by atomic force microscopy (AFM) on particle-laden gas bubbles, agglomerates and pristine gas bubbles without particles in the interface. The force and work of adhesion from AFM measurements were compared to the detaching force and the detaching energy that act on agglomerate-bubble and particle-bubble hetero-coagulates under turbulent conditions, similar to those in a flotation cell. This comparison provides the maximum size of agglomerates and single particles that can remain attached to the gas bubbles at a given energy dissipation rate. The results suggest that the size of agglomerates attached to gas bubbles can grow beyond the Kolmogorov length, which limits the size of agglomerates under turbulent conditions. The findings are supported by in-line probe images of agglomerate-bubble hetero-coagulates that were captured in an aerated stirred tank under turbulent conditions. It was further shown that the particle detachment from particle-laden bubbles is governed by the deformation of the underlying gas bubble and the local particle coverage.

JADES

Finding the first generation of stars formed out of pristine gas in the early Universe, known as Population III (PopIII) stars, is one of the most important goals of modern astrophysics. Recent models have suggested that PopIII stars may form in pockets of pristine gas in the halo of more evolved galaxies. We present NIRSpec integral field spectroscopy and micro-shutter array spectroscopic observations of the region around GN-z11, an exceptionally luminous galaxy atz = 10.6, that reveal a greater than 5σdetection of a feature consistent with being HeIIλ1640 emission at the redshift of GN-z11. The very high equivalent width of the putative HeII emission in this clump (log(EWrest(HeII)/Å) = 1.79−0.25+0.15) and a lack of metal lines can be explained in terms of photoionisation by PopIII stars, while photoionisation by PopII stars is inconsistent with the data. The high equivalent width would also indicate that the putative PopIII stars likely have an initial mass function with an upper cutoff reaching at least 500M⊙. The PopIII bolometric luminosity inferred from the HeII line would be ∼7 × 109 L⊙, which would imply a total stellar mass formed in the burst of ∼2 × 105 M⊙. We find that photoionisation by the active galactic nucleus (AGN) in GN-z11 cannot account for the HeII luminosity observed in the clump but can potentially be responsible for an additional HeII emission observed closer to GN-z11. We also consider the possibility of in situ photoionisation by an accreting direct collapse black hole hosted by the HeII clump. We find that this scenario is less favoured, but it remains a possible alternative interpretation. We also report the detection of a Lyαhalo stemming out of GN-z11 and extending out to ∼2 kpc as well as resolved funnel-shaped CIII emission likely tracing the ionisation cone of the AGN.

Temperature and humidity effects on the acetone gas sensing of pristine and Pd-doped WO3 clusters: A transition state theory study.

The performance of pristine and Pd-doped WO3 acetone gas sensors is calculated theoretically and compared with available experimental results. Temperature, humidity, and acetone concentration variation are considered in the present work. Transition state theory calculates Gibbs free energy of transition, including its components enthalpy and entropy of transition or activation. The variation of Pd doping concentration is used to obtain the maximum response and lowest response time for the optimum performance of the gas sensor. The present theory considers the reduction of acetone gas concentration as acetone reaches its autoignition temperature. Acceptable agreement between theory and experiment is obtained. The acceptance includes the decrease of Gibbs free energy with doping percentage, variation of temperature exponent to the power twelve in the considered reactions, and reduction of response time with the increase of temperature. Density functional theory at the B3LYP level is used. 6-311G** basis set (for O atoms) and SDD (for heavy Pd and W atoms) are used to optimize the structures examined in the present work. The Gaussian 09 program and accompanying software were used to perform the current tasks.

Long-Term Stability Test for Femtosecond Laser-Irradiated SnO2-Nanowire Gas Sensor for C7H8 Gas Sensing

In this study, femtosecond (FS) laser irradiation with different laser energy densities of 138, 276, and 414 mJ/cm2 is applied to SnO2-nanowire (NW) gas sensors, and the effect of the FS laser irradiation on the gas sensor response toward toluene (C7H8) gas is investigated. The FS laser irradiation causes oxygen deficiency in the SnO2 NWs and forms SnO and SnOx. Moreover, an embossing surface with multiple nano-sized bumps is created on the SnO2 NW surface because of the FS laser irradiation. The FS laser-irradiated SnO2-NW gas sensor exhibits superior sensing performance compared with the pristine SnO2-NW gas sensor. Moreover, the FS laser energy density significantly affects gas-sensing performance, and the highest sensor response is achieved by the gas sensor irradiated at 138 mJ/cm2. The long-term stability test of the laser-irradiated SnO2-NW gas sensor is performed by comparing fresh and 6-month-old gas sensors in different gas concentrations and relative humidity levels. Comparable gas-sensing behaviors are examined between the fresh and 6-month-old gas sensor, and this verifies the robustness of the laser-irradiated SnO2-NW gas sensor.

Ancient stellar populations in the outskirts of nearby grand-design spirals: Investigation of their star formation histories

Context. The main sequence (MS) of star-forming galaxies (SFGs) is the tight relation between the galaxy stellar mass (M⋆) and its star formation rate (SFR) and was observed up to z ∼ 6. The MS relation can be used as a reference for understanding the differences among galaxies, which are characterised by different rates of stellar production (starbursts, SFGs, and passive galaxies), and those inside a galaxy that is made up of different components (bulge, disk, and halo). To investigate peculiar features found in our galaxies sample in more depth, we focus here on their star formation history (SFH). Aims. The SFHs are a fundamental tool for revealing the galaxy path from the earlier stages of formation to the present time. The various phases of galaxy evolution are imprinted on the source spectrum globally and locally. Thus, we are able to interpret the dynamical origin of the spirals quantitatively and distinguish between in situ or ex situ formation processes. Methods. We performed a spectral energy distribution fitting procedure that accounted for the energetic balance between UV (observed) and far-IR (optically obscured) radiation on a sample of eight nearby face-on grand-design spiral galaxies from the DustPedia sample. This approach allowed us to study the spatially resolved MS of the sample and to recover the past SFH by accounting for attenuation due to the presence of dust. By exploiting the BAGPIPES code, we constrained the SFHs for each galaxy with a delayed exponentially declining model to derive their mass-weighted age (tMW). Results. The spiral galaxies in our sample have similar radial tMW trends overall. A central old region (tMW up to ∼7 Gyr, consistent with the presence of a bulge for various systems) is followed by younger regions in which the disks are still forming stars (tMW ∼ 4 Gyr). At larger distances from the centre of the galaxies, tMW increases mildly in general. Strikingly, in two galaxies (NGC4321 and NGC5194), we found a steep increase in tMW that reached levels similar to those of the bulge. These old stellar populations in the very galaxy outskirts, which are also detectable as “quenched rings” below the spatially resolved MS, is unexpected. We discuss their potential origin by considering the different gas phases (HI and H2) of the source with the most prominent quenched ring, NGC4321, and argue for two main possibilities: (1) some environmental effect (e.g. starvation) could affect the outer edge of the galaxies or (2) the circumgalactic medium of sources outside of high-density clusters might have stopped to supply pristine gas to the galaxy (e.g. if its specific angular moment is too high for being accreted).

Detecting Population III Stars through Tidal Disruption Events in the Era of JWST and Roman

The first-generation metal-free stars, referred to as Population III (Pop III) stars, are believed to be the first objects to form out of the pristine gas in the very early Universe. Pop III stars have different structures from the current generation of stars and are important for generating heavy elements and shaping subsequent star formation. However, it is very challenging to directly detect Pop III stars given their high redshifts and short lifetimes. In this Letter, we propose a novel method for detecting Pop III stars through their tidal disruption events (TDEs) by massive black holes. We model the emission properties and calculate the expected rates for these unique TDEs in the early Universe at z ∼ 10. We find that Pop III star TDEs have much higher mass fallback rates and longer evolution timescales compared to solar-type star TDEs in the local Universe, which enhances the feasibility of their detection, although a good survey strategy will be needed for categorizing these sources as transients. We further demonstrate that a large fraction of the flare emissions are redshifted to infrared wavelengths, which can be detected by the JWST and the Nancy Grace Roman Space Telescope (Roman). Last but not least, we find a promising Pop III star TDE detection rate of up to a few tens per year using Roman, based on our current understanding of the black hole mass function in the early Universe.

Simulations of early structure formation: Properties of halos that host primordial star formation

Context.Population III (pop III) stars were born in halos characterised by a pristine gas composition. In such a halo, once the gas density reachesnH ∼ 1 cm−3, molecular cooling leads to the collapse of the gas and the birth of pop III stars. Halo properties, such as the chemical abundances, mass, and angular momentum can affect the collapse of the gas, thereby leading to the pop III initial mass function (IMF) of star formation.Aims.We want to study the properties of primordial halos and how halos that host early star formation differ from other types of halos. The aim of this study is to obtain a representative population of halos at a given redshift hosting a cold and massive gas cloud that enables the birth of the first stars.Methods.We investigated the growth of primordial halos in a ΛCDM Universe in a large cosmological simulation. We used the hydrodynamic code RAMSESand the chemical solver KROMEto study halo formation with non-equilibrium thermochemistry. We then identified structures in the dark and baryonic matter fields, thereby linking the presence or absence of dense gas clouds to the mass and the physical properties of the hosting halos.Results.In our simulations, the mass threshold for a halo for hosting a cold dense gas cloud is ≃7 × 105 M⊙and the threshold in the H2mass fraction is found to be ≃2 × 10−4. This is in agreement with previous works. We find that the halo history and accretion rate play a minor role. Here, we present halos with higher HD abundances, which are shown to be colder, as the temperature in the range between 102 − 104 cm−3depends on the HD abundance to a large extent. The higher fraction of HD is linked to the higher spin parameter that is seen for the dense gas.

Improved NH3 Gas Sensing Performance of Femtosecond‐Laser Textured Silicon by the Decoration of Au Nanoparticles

The escalating environmental concerns have stimulated the demand for NH3 gas sensors, which are indispensable for real‐time data collection in pollution monitoring. To address this need, optimized NH3 sensor based on femtosecond‐laser textured silicon decorated with Au nanoparticles (Au‐NP) is designed. The morphologies and microstructures of the fabricated samples are characterized by scanning electron microscopy (SEM) and X‐ray diffraction (XRD) technologies. The gas‐sensing results demonstrated that the modification of Au‐NPs significantly enhances the NH3 gas‐sensing performances. Specifically, the sensor based on the textured silicon decorated with Au NPs exhibits a remarkable response of 16.02% toward 20 ppm NH3, which is 4.7 times higher than that of the pristine textured silicon gas sensor at room temperature. In addition, it also demonstrates shortened response and recovery time (26 s/98 s), showing good selectivity and long‐term availability. The enhanced NH3‐sensing mechanism of the sensor is elucidated, mainly due to the synergistic effect of textured silicon and Au NPs. These contribute to the development of portable, wearable, and intelligent sensor equipment.

Deciphering Lyman-α emission deep into the epoch of reionization

During the epoch of reionization, the first galaxies were enshrouded in pristine neutral gas, with one of the brightest emission lines in star-forming galaxies, Lyman α (Lyα), expected to remain undetected until the Universe became ionized. Providing an explanation for the surprising detection of Lyα in these early galaxies is a major challenge for extragalactic studies. Recent James Webb Space Telescope observations have reignited the debate about whether residence in an overdensity of galaxies is a sufficient and necessary condition for Lyα to escape. Here, we take unique advantage of both high-resolution and high-sensitivity images from the James Webb Space Telescope Near Infrared Camera to show that all galaxies in a sample of Lyα emitters with redshift >7 have close companions. We exploit on-the-fly radiative-transfer magnetohydrodynamical simulations with cosmic ray feedback to show that galaxies with frequent mergers have very bursty star formation histories that drives episodes of high intrinsic Lyα emission and facilitates the escape of Lyα photons along channels cleared of neutral gas. We conclude that the rapid buildup of stellar mass through mergers presents a compelling solution to the long-standing puzzle of the detection of Lyα emission deep in the epoch of reionization.

The dual role of outflows in quenching satellites of low-mass hosts: NGC 3109

ABSTRACT While dwarf galaxies observed in the field are overwhelmingly star forming, dwarf galaxies in environments as dense or denser than the Milky Way are overwhelmingly quenched. In this paper, we explore quenching in the lower density environment of the Small-Magellanic-Cloud-mass galaxy NGC 3109 (M$_* \sim 10^8 \, \text{M}_\odot$), which hosts two known dwarf satellite galaxies (Antlia and Antlia B), both of which are ${\rm H}\, \rm{\small I}$ deficient compared to similar galaxies in the field and have recently stopped forming stars. Using a new semi-analytic model in concert with the measured star formation histories and gas masses of the two dwarf satellite galaxies, we show that they could not have been quenched solely by direct ram pressure stripping of their interstellar media, as is common in denser environments. Instead, we find that separation of the satellites from pristine gas inflows, coupled with stellar-feedback-driven outflows from the satellites (jointly referred to as the starvation quenching model), can quench the satellites on time-scales consistent with their likely infall times into NGC 3109’s halo. It is currently believed that starvation is caused by ‘weak’ ram pressure that prevents low-density, weakly bound gas from being accreted on to the dwarf satellite, but cannot directly remove the denser interstellar medium. This suggests that star-formation-driven outflows serve two purposes in quenching satellites in low-mass environments: outflows from the host form a low-density circumgalactic medium that cannot directly strip the interstellar media from its satellites, but is sufficient to remove loosely bound gaseous outflows from the dwarf satellites driven by their own star formation.