Pub Date : 2026-03-25DOI: 10.3847/1538-4357/ae4a28
Sho Shibata and Andre Izidoro
While recent planet-formation models broadly reproduce the observed population of super-Earths and mini-Neptunes, as well as the bimodal radius distribution (the “radius valley”), it remains unclear whether all these planets share a common rocky composition (a single population of planets) or instead comprise two distinct populations—rocky planets and icy planets (two populations of planets). The inferred eccentricity–radius relation, which shows a modest peak near the radius valley, provides a useful diagnostic for distinguishing between these scenarios. Here, we use N-body simulations to examine how the radii and eccentricities of close-in planets depend on the masses and orbital configurations of their progenitor protoplanets. We find that final planetary eccentricities scale with the system initial Safronov number. In two-population systems, energy equipartition between rocky and relatively more massive icy protoplanets creates a strong eccentricity contrast between the two groups, which appears as a peak near the radius valley. This signature does not appear if planetary systems are composed exclusively of rocky planets (with or without H-rich atmospheres), as assumed in photoevaporation and core-powered mass loss models. Because the eccentricity–radius relation traces a dichotomy in the underlying protoplanet mass distribution—most plausibly arising from formation at different disk locations—our results suggest that a significant fraction of mini-Neptunes are water-worlds. The observed radius and eccentricity distributions may reflect a mixture of systems that host exclusively rocky planets, systems dominated by icy planets, and systems with both rocky and icy planets.
{"title":"Elevated Eccentricities in the Radius Valley Hint at Water-rich Mini-Neptunes","authors":"Sho Shibata and Andre Izidoro","doi":"10.3847/1538-4357/ae4a28","DOIUrl":"https://doi.org/10.3847/1538-4357/ae4a28","url":null,"abstract":"While recent planet-formation models broadly reproduce the observed population of super-Earths and mini-Neptunes, as well as the bimodal radius distribution (the “radius valley”), it remains unclear whether all these planets share a common rocky composition (a single population of planets) or instead comprise two distinct populations—rocky planets and icy planets (two populations of planets). The inferred eccentricity–radius relation, which shows a modest peak near the radius valley, provides a useful diagnostic for distinguishing between these scenarios. Here, we use N-body simulations to examine how the radii and eccentricities of close-in planets depend on the masses and orbital configurations of their progenitor protoplanets. We find that final planetary eccentricities scale with the system initial Safronov number. In two-population systems, energy equipartition between rocky and relatively more massive icy protoplanets creates a strong eccentricity contrast between the two groups, which appears as a peak near the radius valley. This signature does not appear if planetary systems are composed exclusively of rocky planets (with or without H-rich atmospheres), as assumed in photoevaporation and core-powered mass loss models. Because the eccentricity–radius relation traces a dichotomy in the underlying protoplanet mass distribution—most plausibly arising from formation at different disk locations—our results suggest that a significant fraction of mini-Neptunes are water-worlds. The observed radius and eccentricity distributions may reflect a mixture of systems that host exclusively rocky planets, systems dominated by icy planets, and systems with both rocky and icy planets.","PeriodicalId":501813,"journal":{"name":"The Astrophysical Journal","volume":"95 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2026-03-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147506472","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2026-03-25DOI: 10.3847/1538-4357/ae4d3e
Tadahiro Kimura and Tim Lichtenberg
The interaction between a magma ocean and a primordial atmosphere is increasingly recognized as a key process in shaping planetary envelope compositions. This coupling should strongly influence gas accretion, yet its role during the disk-embedded stage remains poorly constrained. We develop a time-dependent model that couples solid accretion, nebular gas accretion, and water enrichment and partitioning through magma–atmosphere interactions, along with post-disk thermal evolution and escape. We find that, for super-Earth-mass planets, water production is generally limited by the magma oxygen budget and typically ceases before disk dispersal. Subsequent nebular gas accretion dilutes the envelope toward hydrogen-dominated compositions, largely independent of the initial magma redox state. This establishes an upper bound on the envelope water fraction—the oxygen exhaustion limit—primarily set by the reactive oxygen inventory and the planet mass. After disk dispersal, degassing increases the water fraction only in Earth-mass planets undergoing strong escape, while super-Earths exhibit little change because surface pressures are hardly affected by escape. Magma–atmosphere coupling alone therefore cannot maintain water-rich envelopes in sub-Neptunes and produces a strong mass–composition relation imposed by the oxygen exhaustion limit. Highly enriched sub-Neptunes would therefore imply additional mechanisms such as late volatile delivery or post-disk giant impacts. The relation between planetary radius and envelope composition offers a means to infer magma properties, providing a pathway to connect present-day observables with early formation histories.
{"title":"Water Enrichment of Forming Sub-Neptune Envelopes Limited by Oxygen Exhaustion","authors":"Tadahiro Kimura and Tim Lichtenberg","doi":"10.3847/1538-4357/ae4d3e","DOIUrl":"https://doi.org/10.3847/1538-4357/ae4d3e","url":null,"abstract":"The interaction between a magma ocean and a primordial atmosphere is increasingly recognized as a key process in shaping planetary envelope compositions. This coupling should strongly influence gas accretion, yet its role during the disk-embedded stage remains poorly constrained. We develop a time-dependent model that couples solid accretion, nebular gas accretion, and water enrichment and partitioning through magma–atmosphere interactions, along with post-disk thermal evolution and escape. We find that, for super-Earth-mass planets, water production is generally limited by the magma oxygen budget and typically ceases before disk dispersal. Subsequent nebular gas accretion dilutes the envelope toward hydrogen-dominated compositions, largely independent of the initial magma redox state. This establishes an upper bound on the envelope water fraction—the oxygen exhaustion limit—primarily set by the reactive oxygen inventory and the planet mass. After disk dispersal, degassing increases the water fraction only in Earth-mass planets undergoing strong escape, while super-Earths exhibit little change because surface pressures are hardly affected by escape. Magma–atmosphere coupling alone therefore cannot maintain water-rich envelopes in sub-Neptunes and produces a strong mass–composition relation imposed by the oxygen exhaustion limit. Highly enriched sub-Neptunes would therefore imply additional mechanisms such as late volatile delivery or post-disk giant impacts. The relation between planetary radius and envelope composition offers a means to infer magma properties, providing a pathway to connect present-day observables with early formation histories.","PeriodicalId":501813,"journal":{"name":"The Astrophysical Journal","volume":"4 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2026-03-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147506558","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2026-03-25DOI: 10.3847/1538-4357/ae474f
Lena Komarova, Mauro Stefanon, Andrés Laza-Ramos, Hiddo S.B. Algera, Manuel Aravena, Rychard Bouwens, Rebecca Bowler, Elisabete da Cunha, Pratika Dayal, Andrea Ferrara, Rebecca Fisher, Themiya Nanayakkara, Lucie E. Rowland, Sander Schouws, Renske Smit, Laura Sommovigo, Daniel P. Stark and Paul van der Werf
Measuring the ionizing photon production efficiency ξion,0—the ratio of the ionizing photon output rate to the UV continuum luminosity LUV—in galaxies at z > 6 is crucial for constraining their contribution to cosmic reionization. We present integrated and spatially resolved measurements of ξion,0 for 12 exceptionally bright (MUV ∼ −22 mag) star-forming galaxies at z ∼ 7 from the Reionization Era Bright Emission Line Survey (REBELS). These measurements are based on JWST NIRSpec/Integral Field Unit PRISM spectroscopy, probing the rest-frame UV and optical regime. Notably, in 8 of the 12 galaxies, the spectral coverage includes Hα, enabling self-consistent dust attenuation estimates in both the ionized gas and stellar continuum via the Balmer decrement and rest-UV slope, respectively. We find global values ranging from 25.19 ± 0.11 to 25.61 ± 0.11, with a weighted mean of 25.44 ± 0.15, consistent with the canonical value of ∼25.3. Using a sample of 25 star-forming clumps within these galaxies, we explore local variations in the ionizing photon production efficiency, finding a broader range, from 24.52 ± 0.21 to 26.18 ± 0.61. We identify strong correlations between ξion,0 and the specific star formation rate, star formation surface density, Hβ equivalent width, and stellar mass. Clumps with the highest ξion,0 exhibit EW0(Hβ) ≥ 150 Å, consistent with young stellar ages. From previous Lyα measurements in three galaxies, we estimate a typical Lyα escape fraction of fesc,Lyα ∼ 2%, suggesting similar or lower escape fractions for LyC photons. Combining this with our Hα measurements, we infer ionized bubble sizes ∼1 pMpc, aligned with expectations from Lyα-detected systems and reionization models.
{"title":"REBELS-IFU: Spatially Resolved Ionizing Photon Production Efficiencies of 12 Bright Galaxies in the Epoch of Reionization","authors":"Lena Komarova, Mauro Stefanon, Andrés Laza-Ramos, Hiddo S.B. Algera, Manuel Aravena, Rychard Bouwens, Rebecca Bowler, Elisabete da Cunha, Pratika Dayal, Andrea Ferrara, Rebecca Fisher, Themiya Nanayakkara, Lucie E. Rowland, Sander Schouws, Renske Smit, Laura Sommovigo, Daniel P. Stark and Paul van der Werf","doi":"10.3847/1538-4357/ae474f","DOIUrl":"https://doi.org/10.3847/1538-4357/ae474f","url":null,"abstract":"Measuring the ionizing photon production efficiency ξion,0—the ratio of the ionizing photon output rate to the UV continuum luminosity LUV—in galaxies at z > 6 is crucial for constraining their contribution to cosmic reionization. We present integrated and spatially resolved measurements of ξion,0 for 12 exceptionally bright (MUV ∼ −22 mag) star-forming galaxies at z ∼ 7 from the Reionization Era Bright Emission Line Survey (REBELS). These measurements are based on JWST NIRSpec/Integral Field Unit PRISM spectroscopy, probing the rest-frame UV and optical regime. Notably, in 8 of the 12 galaxies, the spectral coverage includes Hα, enabling self-consistent dust attenuation estimates in both the ionized gas and stellar continuum via the Balmer decrement and rest-UV slope, respectively. We find global values ranging from 25.19 ± 0.11 to 25.61 ± 0.11, with a weighted mean of 25.44 ± 0.15, consistent with the canonical value of ∼25.3. Using a sample of 25 star-forming clumps within these galaxies, we explore local variations in the ionizing photon production efficiency, finding a broader range, from 24.52 ± 0.21 to 26.18 ± 0.61. We identify strong correlations between ξion,0 and the specific star formation rate, star formation surface density, Hβ equivalent width, and stellar mass. Clumps with the highest ξion,0 exhibit EW0(Hβ) ≥ 150 Å, consistent with young stellar ages. From previous Lyα measurements in three galaxies, we estimate a typical Lyα escape fraction of fesc,Lyα ∼ 2%, suggesting similar or lower escape fractions for LyC photons. Combining this with our Hα measurements, we infer ionized bubble sizes ∼1 pMpc, aligned with expectations from Lyα-detected systems and reionization models.","PeriodicalId":501813,"journal":{"name":"The Astrophysical Journal","volume":"15 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2026-03-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147506467","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2026-03-25DOI: 10.3847/1538-4357/ae473a
Elise Fuller, Sean D. Johnson, Jonathan Stern, Hsiao-Wen Chen, Ena Choi, Claude-André Faucher-Giguère, Massimo Gaspari, Andy Goulding, Jenny Greene, Timothy M. Heckman, Jennifer I-Hsiu Li, Zhuoqi Liu, Nishant Mishra, Kristina Nyland, Kate Rowlands, Gwen C. Rudie, Evan Schneider, Dominika Wylezalek and Nadia L. Zakamska
Feedback from active galactic nuclei (AGN) is widely acknowledged to regulate the growth of massive galaxies, though its driving mechanisms are debated. Prevailing theories suggest that AGN-driven outflows are driven either by radiation pressure acting directly on the dusty interstellar medium (ISM) or by hot winds entraining cooler ISM gas, but the relative contribution of each mechanism remains uncertain. By combining optical emission line measurements with highly ionized UV emission lines, it is possible to constrain whether the pressure source applied to ionized clouds is primarily radiation or primarily hydrodynamic, and thus constrain the dominant driver. This study presents the first multiobject analysis of far-UV spectra from galactic-scale AGN-driven outflows in obscured quasars, based on Cosmic Origins Spectrograph observations of five low-redshift targets. By comparing narrow-line region UV emission-line ratios to theoretical models that vary the importance of the two pressure sources, we find that three out of five targets fall within the radiation-pressure-dominated regime. A fourth target exhibits intermediate emission-line ratios that suggest radiation pressure and pressure from a hot wind are both dynamically important. Finally, the lowest-luminosity object in our sample may have a dynamically important hot wind component, but nondetections prevent a clear conclusion in this case. These results suggest radiation pressure dominates circumnuclear narrow-line region cloud dynamics, but pressure from a hot wind also plays a role in some cases. This is consistent with AGN feedback scenarios mediated by radiation pressure or a short-lived hot wind phase that dissipates after initially accelerating outflows.
{"title":"Under Pressure: Ultraviolet Emission-line Ratios as Barometers of Active Galactic Nuclei Feedback Mechanisms","authors":"Elise Fuller, Sean D. Johnson, Jonathan Stern, Hsiao-Wen Chen, Ena Choi, Claude-André Faucher-Giguère, Massimo Gaspari, Andy Goulding, Jenny Greene, Timothy M. Heckman, Jennifer I-Hsiu Li, Zhuoqi Liu, Nishant Mishra, Kristina Nyland, Kate Rowlands, Gwen C. Rudie, Evan Schneider, Dominika Wylezalek and Nadia L. Zakamska","doi":"10.3847/1538-4357/ae473a","DOIUrl":"https://doi.org/10.3847/1538-4357/ae473a","url":null,"abstract":"Feedback from active galactic nuclei (AGN) is widely acknowledged to regulate the growth of massive galaxies, though its driving mechanisms are debated. Prevailing theories suggest that AGN-driven outflows are driven either by radiation pressure acting directly on the dusty interstellar medium (ISM) or by hot winds entraining cooler ISM gas, but the relative contribution of each mechanism remains uncertain. By combining optical emission line measurements with highly ionized UV emission lines, it is possible to constrain whether the pressure source applied to ionized clouds is primarily radiation or primarily hydrodynamic, and thus constrain the dominant driver. This study presents the first multiobject analysis of far-UV spectra from galactic-scale AGN-driven outflows in obscured quasars, based on Cosmic Origins Spectrograph observations of five low-redshift targets. By comparing narrow-line region UV emission-line ratios to theoretical models that vary the importance of the two pressure sources, we find that three out of five targets fall within the radiation-pressure-dominated regime. A fourth target exhibits intermediate emission-line ratios that suggest radiation pressure and pressure from a hot wind are both dynamically important. Finally, the lowest-luminosity object in our sample may have a dynamically important hot wind component, but nondetections prevent a clear conclusion in this case. These results suggest radiation pressure dominates circumnuclear narrow-line region cloud dynamics, but pressure from a hot wind also plays a role in some cases. This is consistent with AGN feedback scenarios mediated by radiation pressure or a short-lived hot wind phase that dissipates after initially accelerating outflows.","PeriodicalId":501813,"journal":{"name":"The Astrophysical Journal","volume":"14 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2026-03-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147506468","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2026-03-24DOI: 10.3847/1538-4357/ae4e21
Florine Masson and Laura C. Parker
The time since a galaxy first became a satellite is central to understanding how environment drives galaxy evolution, yet it cannot be measured directly. Using the TNG300 and TNG-Cluster simulations, we track satellites from z = 1 to z = 0 and derive a simple, redshift-dependent prescription for infall time based on position in projected phase space and stellar mass, via symbolic regression. The resulting calibration provides continuous, observation-ready estimates of Tinf across projected phase space. In projected phase space, is often well described by two components, and we provide analytic expressions for the corresponding characteristic timescales. This framework can be applied directly to spectroscopic samples to infer environmental histories in galaxy groups and clusters.
{"title":"Calibrating Galaxy Infall Times in Groups and Clusters with IllustrisTNG Simulations","authors":"Florine Masson and Laura C. Parker","doi":"10.3847/1538-4357/ae4e21","DOIUrl":"https://doi.org/10.3847/1538-4357/ae4e21","url":null,"abstract":"The time since a galaxy first became a satellite is central to understanding how environment drives galaxy evolution, yet it cannot be measured directly. Using the TNG300 and TNG-Cluster simulations, we track satellites from z = 1 to z = 0 and derive a simple, redshift-dependent prescription for infall time based on position in projected phase space and stellar mass, via symbolic regression. The resulting calibration provides continuous, observation-ready estimates of Tinf across projected phase space. In projected phase space, is often well described by two components, and we provide analytic expressions for the corresponding characteristic timescales. This framework can be applied directly to spectroscopic samples to infer environmental histories in galaxy groups and clusters.","PeriodicalId":501813,"journal":{"name":"The Astrophysical Journal","volume":"14 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2026-03-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147506559","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2026-03-24DOI: 10.3847/1538-4357/ae43ee
Mukremin Kilic, Pierre Bergeron, Adam Moss, Simon Blouin, Matthew J. Green, Gracyn Jewett, Manuel Barrientos, Alexander L. Albright and Warren R. Brown
We present a detailed model atmosphere analysis of hot white dwarfs in the Dark Energy Spectroscopic Instrument (DESI) Data Release 1. Our sample includes 19,321 unique targets with GBP − GRP ≤ 0. We use the DESI spectra along with Gaia parallaxes and Sloan Digital Sky Survey (SDSS), Pan-STARRS, and SkyMapper photometry to perform spectroscopic and photometric fits. We find a significant discrepancy between the photometric and spectroscopic masses for DA white dwarfs (a systematic offset of 0.05–0.06 M⊙), indicating problems with the broad hydrogen line profiles in DESI spectroscopy data. Our photometric fits are consistent with a peak at the canonical mass of 0.6 M⊙. A remarkable feature of the mass distribution is the prevalence of magnetic white dwarfs among the ultramassive DA population and that of warm DQs in the non-DA distribution. We identify 70 DQs in the DESI hot white dwarf sample, including nine DAQs with carbon and hydrogen atmospheres. We constrain the ratio of non-DA to DA white dwarfs as a function of temperature, and discuss the implications for the spectral evolution of white dwarfs in the temperature range of 105–104 K. We also discuss unusual objects in the sample, including metal-rich white dwarfs and extremely low-mass white dwarfs. This analysis provides the first look at the large sample of Gaia-selected white dwarf candidates that will be observed with multiplexed spectroscopic surveys such as DESI, SDSS-V, the 4 m Multi-Object Spectroscopic Telescope, and the William Herschel Telescope Enhanced Area Velocity Explorer over the next several years.
{"title":"A Detailed Model Atmosphere Analysis of Hot White Dwarfs in DESI DR1","authors":"Mukremin Kilic, Pierre Bergeron, Adam Moss, Simon Blouin, Matthew J. Green, Gracyn Jewett, Manuel Barrientos, Alexander L. Albright and Warren R. Brown","doi":"10.3847/1538-4357/ae43ee","DOIUrl":"https://doi.org/10.3847/1538-4357/ae43ee","url":null,"abstract":"We present a detailed model atmosphere analysis of hot white dwarfs in the Dark Energy Spectroscopic Instrument (DESI) Data Release 1. Our sample includes 19,321 unique targets with GBP − GRP ≤ 0. We use the DESI spectra along with Gaia parallaxes and Sloan Digital Sky Survey (SDSS), Pan-STARRS, and SkyMapper photometry to perform spectroscopic and photometric fits. We find a significant discrepancy between the photometric and spectroscopic masses for DA white dwarfs (a systematic offset of 0.05–0.06 M⊙), indicating problems with the broad hydrogen line profiles in DESI spectroscopy data. Our photometric fits are consistent with a peak at the canonical mass of 0.6 M⊙. A remarkable feature of the mass distribution is the prevalence of magnetic white dwarfs among the ultramassive DA population and that of warm DQs in the non-DA distribution. We identify 70 DQs in the DESI hot white dwarf sample, including nine DAQs with carbon and hydrogen atmospheres. We constrain the ratio of non-DA to DA white dwarfs as a function of temperature, and discuss the implications for the spectral evolution of white dwarfs in the temperature range of 105–104 K. We also discuss unusual objects in the sample, including metal-rich white dwarfs and extremely low-mass white dwarfs. This analysis provides the first look at the large sample of Gaia-selected white dwarf candidates that will be observed with multiplexed spectroscopic surveys such as DESI, SDSS-V, the 4 m Multi-Object Spectroscopic Telescope, and the William Herschel Telescope Enhanced Area Velocity Explorer over the next several years.","PeriodicalId":501813,"journal":{"name":"The Astrophysical Journal","volume":"86 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2026-03-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147506684","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2026-03-24DOI: 10.3847/1538-4357/ae43eb
Javiera K. Díaz-Berríos, Catherine Walsh and Ewine F. van Dishoeck
The material in planet-forming disks determines the composition of planets; hence, it is crucial to understand the physical and chemical processes that set the abundance and distribution of key volatiles. James Webb Space Telescope observations of disks around very low-mass (∼0.1 M⊙) stars (VLMSs) have revealed their hydrocarbon-rich inner regions (e.g., C2H2), with column densities significantly higher than predicted. We employ chemical kinetics models using the physical structure of the inner disk around an M dwarf star with an X-ray luminosity of LX ∼ 1029 erg s−1. We adopt initial abundances that mimic the effects of carbon enhancement and oxygen depletion (C/O from 0.44 to 87.47) and quantify how the abundances and distributions of key volatiles respond. The column density and number of molecules ( ) of hydrocarbons and oxygen-bearing species are highly sensitive to the C/O ratio, with the largest increases in hydrocarbons occurring when carbon increases by a factor of 2, and/or oxygen decreases by a factor of 10, relative to solar. In the IR-emitting region (Tgas > 200 K), a range of C/O ratios can reproduce the observed and ratios relative to CO2. The disk-integrated molecular ratio with respect to CO2 is highly sensitive to the underlying C/O ratio. However, our results apply only to a source with a single X-ray luminosity value at the middle of that observed for VLMSs; hence, a degeneracy between the stellar LX and the C/O ratio cannot be discarded. Nonetheless, our findings support that an enhanced C/O is required to drive the hydrocarbon-rich chemistry observed in the inner disks around VLMSs.
{"title":"Quantifying the C/O Ratio in the Planet-forming Environments around Very Low-mass Stars","authors":"Javiera K. Díaz-Berríos, Catherine Walsh and Ewine F. van Dishoeck","doi":"10.3847/1538-4357/ae43eb","DOIUrl":"https://doi.org/10.3847/1538-4357/ae43eb","url":null,"abstract":"The material in planet-forming disks determines the composition of planets; hence, it is crucial to understand the physical and chemical processes that set the abundance and distribution of key volatiles. James Webb Space Telescope observations of disks around very low-mass (∼0.1 M⊙) stars (VLMSs) have revealed their hydrocarbon-rich inner regions (e.g., C2H2), with column densities significantly higher than predicted. We employ chemical kinetics models using the physical structure of the inner disk around an M dwarf star with an X-ray luminosity of LX ∼ 1029 erg s−1. We adopt initial abundances that mimic the effects of carbon enhancement and oxygen depletion (C/O from 0.44 to 87.47) and quantify how the abundances and distributions of key volatiles respond. The column density and number of molecules ( ) of hydrocarbons and oxygen-bearing species are highly sensitive to the C/O ratio, with the largest increases in hydrocarbons occurring when carbon increases by a factor of 2, and/or oxygen decreases by a factor of 10, relative to solar. In the IR-emitting region (Tgas > 200 K), a range of C/O ratios can reproduce the observed and ratios relative to CO2. The disk-integrated molecular ratio with respect to CO2 is highly sensitive to the underlying C/O ratio. However, our results apply only to a source with a single X-ray luminosity value at the middle of that observed for VLMSs; hence, a degeneracy between the stellar LX and the C/O ratio cannot be discarded. Nonetheless, our findings support that an enhanced C/O is required to drive the hydrocarbon-rich chemistry observed in the inner disks around VLMSs.","PeriodicalId":501813,"journal":{"name":"The Astrophysical Journal","volume":"18 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2026-03-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147506573","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2026-03-24DOI: 10.3847/1538-4357/ae4bd7
Samuel Crowe, Yisheng Tu, Zhi-Yun Li, Jeong-Gyu Kim and John Bally
Recent James Webb Space Telescope observations of H ii regions in the Central Molecular Zone (CMZ) have shown a highly filamentary morphology distinct from H ii regions in other parts of the Galaxy. We present magnetohydrodynamic (MHD) simulations of strongly magnetized (plasma-β ≪ 1) H ii region evolution that investigate and describe the formation of these ionized gas filaments. H ii region evolution has been simulated in a 30 pc3 box, in distinct models with preplaced overdensities in the ambient medium and overdensities that have been generated with driven turbulence. We find that when these overdensities are seeded in the ambient medium before the birth of the ionizing source, the photoionized plasma stripped off of these dense blobs is funneled into long filaments along the magnetic field lines. The length and emission measure of these ionized gas filaments are similar to the filaments observed in the CMZ. Given that these filaments are effectively magnetically confined flows of photoionized gas, their density and curvature are influenced by the density of the blob and the geometry of the configuration.
{"title":"MHD Simulations of Strongly Magnetized H ii Region Evolution: Evidence for Ionized Gas Filamentation","authors":"Samuel Crowe, Yisheng Tu, Zhi-Yun Li, Jeong-Gyu Kim and John Bally","doi":"10.3847/1538-4357/ae4bd7","DOIUrl":"https://doi.org/10.3847/1538-4357/ae4bd7","url":null,"abstract":"Recent James Webb Space Telescope observations of H ii regions in the Central Molecular Zone (CMZ) have shown a highly filamentary morphology distinct from H ii regions in other parts of the Galaxy. We present magnetohydrodynamic (MHD) simulations of strongly magnetized (plasma-β ≪ 1) H ii region evolution that investigate and describe the formation of these ionized gas filaments. H ii region evolution has been simulated in a 30 pc3 box, in distinct models with preplaced overdensities in the ambient medium and overdensities that have been generated with driven turbulence. We find that when these overdensities are seeded in the ambient medium before the birth of the ionizing source, the photoionized plasma stripped off of these dense blobs is funneled into long filaments along the magnetic field lines. The length and emission measure of these ionized gas filaments are similar to the filaments observed in the CMZ. Given that these filaments are effectively magnetically confined flows of photoionized gas, their density and curvature are influenced by the density of the blob and the geometry of the configuration.","PeriodicalId":501813,"journal":{"name":"The Astrophysical Journal","volume":"18 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2026-03-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147506697","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2026-03-24DOI: 10.3847/1538-4357/ae4bd3
Usman Saeed and Hamid Saleem
The excitation of electrostatic drift waves in the solar chromosphere, transition region (TR), and corona is investigated using collisionless kinetic theory for hot ion plasma. Real frequencies and growth rates of drift waves are computed choosing various observed values of temperatures Tj (where j = e, i) and ambient magnetic field corresponding to different possible wavelengths of drift waves in the absence and presence of field-aligned constant electron velocity . Numerical estimates of growth rates reveal that obliquely propagating low-frequency electrostatic drift waves are prevalent in all three regions where short-scale density gradients are anticipated to exist. These waves exhibit instabilities across a broader range of wavelengths and frequencies in the chromosphere, while in the TR and corona they are generally damped but can grow within a narrow window of parameter values. The findings suggest that drift waves are preferentially excited in the lower layer and subsequently damp in the upper layers, transferring energy to surrounding particles. The field-aligned constant electron flow further enhances the wave growth rates in these regions. The results of this investigation predict that the drift wave is a promising candidate for heating the upper solar atmosphere: the TR and corona.
利用热离子等离子体的无碰撞动力学理论研究了太阳色球、过渡区和日冕中静电漂移波的激发。选择温度Tj（其中j = e, i）和环境磁场的不同观测值，在没有和存在场向恒定电子速度的情况下，计算漂移波的实际频率和增长率。增长率的数值估计表明，在预计存在短尺度密度梯度的所有三个地区，斜传播的低频静电漂移波普遍存在。在色球中，这些波在更宽的波长和频率范围内表现出不稳定性，而在TR和日冕中，它们通常是阻尼的，但可以在一个狭窄的参数值窗口内增长。研究结果表明，漂移波在下层优先受到激发，随后在上层受到阻尼，将能量传递给周围的粒子。场向恒定电子流进一步提高了这些区域的波增长速率。本研究结果预测，漂移波是加热太阳上层大气：TR和日冕的一个有希望的候选者。
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Pub Date : 2026-03-24DOI: 10.3847/1538-4357/ae4c49
Ben R. Gordon, Helena Buschermöhle, Wata Tubthong, David V. Martin, Sean Smallets, Grace Masiello and Liz Bergeron
Confirmation of the first exomoon remains elusive. Although several exomoon candidates exist around single stars, there are currently no candidates around circumbinary planets (CBPs). Most CBPs are thought to form far from the host binary and migrate through the protoplanetary disk. Therefore, an exomoon of a CBP represents a fascinating yet complex and evolving four-body system. Their existence (or absence) would shed light on the robustness of moon formation and evolution in dynamically active planetary systems. In this work, we simulate the orbital evolutions of exomoons around migrating CBPs. We show that for fully migrated CBPs, a moon is capable of surviving the migration if it is formed within ∼5%–10% of the planet’s Hill radius, well within the currently proposed range at which moons are thought to settle in the planetary disk for giant planets. Of the moons that remained gravitationally bound to their host planet postmigration, 18% lie within the habitable zone, supporting the potential for circumbinary habitability, even if all currently known CBPs are gas giants. Meanwhile, 38% of moons escape their host planet early in the migration and become long-period CBPs (i.e a multiplanet circumbinary system). Nearly one-third of exomoons collide with their host planet, and 1% are ejected from the system entirely. This last class presents another pathway for producing free-floating planetary-mass objects, like those discovered recently and expected from the Roman microlensing survey.
{"title":"Exomoons of Circumbinary Planets","authors":"Ben R. Gordon, Helena Buschermöhle, Wata Tubthong, David V. Martin, Sean Smallets, Grace Masiello and Liz Bergeron","doi":"10.3847/1538-4357/ae4c49","DOIUrl":"https://doi.org/10.3847/1538-4357/ae4c49","url":null,"abstract":"Confirmation of the first exomoon remains elusive. Although several exomoon candidates exist around single stars, there are currently no candidates around circumbinary planets (CBPs). Most CBPs are thought to form far from the host binary and migrate through the protoplanetary disk. Therefore, an exomoon of a CBP represents a fascinating yet complex and evolving four-body system. Their existence (or absence) would shed light on the robustness of moon formation and evolution in dynamically active planetary systems. In this work, we simulate the orbital evolutions of exomoons around migrating CBPs. We show that for fully migrated CBPs, a moon is capable of surviving the migration if it is formed within ∼5%–10% of the planet’s Hill radius, well within the currently proposed range at which moons are thought to settle in the planetary disk for giant planets. Of the moons that remained gravitationally bound to their host planet postmigration, 18% lie within the habitable zone, supporting the potential for circumbinary habitability, even if all currently known CBPs are gas giants. Meanwhile, 38% of moons escape their host planet early in the migration and become long-period CBPs (i.e a multiplanet circumbinary system). Nearly one-third of exomoons collide with their host planet, and 1% are ejected from the system entirely. This last class presents another pathway for producing free-floating planetary-mass objects, like those discovered recently and expected from the Roman microlensing survey.","PeriodicalId":501813,"journal":{"name":"The Astrophysical Journal","volume":"10 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2026-03-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147506746","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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