Pub Date : 2026-03-23DOI: 10.3847/1538-4357/ae4c59
Shiru Zheng, Baitian Tang, Long Wang, Jose G. Fernandez-Trincado, Ruoyun Huang, Xia Li and XiaoDong Li
ω Centauri, the remnant nucleus of an accreted dwarf galaxy, is a unique laboratory for studying complex stellar populations. The recently discovered Fimbulthul stream provides a fossil record of its ongoing tidal dissolution. In this work, we investigate the spatial distributions of metal-rich and metal-poor populations within ω Centauri and its stream to constrain the cluster’s formation history. Using synthetic photometry from Gaia DR3 XP spectra, we classify stars via a support vector classifier. The spatial distributions are then compared to a scaling N-body simulation performed with the PeTar code. Our analysis reveals no significant radial gradient in population ratios within the cluster, though the metal-rich stars may be slightly more extended. The population ratio in the tidal stream is consistent with that of the present-day cluster, albeit with large uncertainties. Our simulation indicates that any initial radial gradient must have been shallow, with a maximum fraction difference less than 0.15. Both observational and dynamical results suggest that the metal-rich population is not formed in a centrally concentrated manner. By combining our results and existing literature, we propose a new formation scenario for ω Centauri.
{"title":"Spatial Property of Multiple Metallic Populations in the Tidal Stream of ω Centauri","authors":"Shiru Zheng, Baitian Tang, Long Wang, Jose G. Fernandez-Trincado, Ruoyun Huang, Xia Li and XiaoDong Li","doi":"10.3847/1538-4357/ae4c59","DOIUrl":"https://doi.org/10.3847/1538-4357/ae4c59","url":null,"abstract":"ω Centauri, the remnant nucleus of an accreted dwarf galaxy, is a unique laboratory for studying complex stellar populations. The recently discovered Fimbulthul stream provides a fossil record of its ongoing tidal dissolution. In this work, we investigate the spatial distributions of metal-rich and metal-poor populations within ω Centauri and its stream to constrain the cluster’s formation history. Using synthetic photometry from Gaia DR3 XP spectra, we classify stars via a support vector classifier. The spatial distributions are then compared to a scaling N-body simulation performed with the PeTar code. Our analysis reveals no significant radial gradient in population ratios within the cluster, though the metal-rich stars may be slightly more extended. The population ratio in the tidal stream is consistent with that of the present-day cluster, albeit with large uncertainties. Our simulation indicates that any initial radial gradient must have been shallow, with a maximum fraction difference less than 0.15. Both observational and dynamical results suggest that the metal-rich population is not formed in a centrally concentrated manner. By combining our results and existing literature, we propose a new formation scenario for ω Centauri.","PeriodicalId":501813,"journal":{"name":"The Astrophysical Journal","volume":"1 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2026-03-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147495327","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 : 2026-03-23DOI: 10.3847/1538-4357/ae42bf
Sahana Kumar, Eric Y. Hsiao, Chris Ashall, Peter Hoeflich, Eddie Baron, Mark M. Phillips, Maryam Modjaz, Abigail Polin, Nidia Morrell, Christopher R. Burns, Jing Lu, Melissa Shahbandeh, Lindsey A. Kwok, Lluis Galbany, M. D. Stritzinger, Carlos Contreras, James M. DerKacy, T. Hoover, Syed A. Uddin, Saurabh W. Jha, Huangfei Xiao, K. Krisciunas and N. B. Suntzeff
Producing stable 58Ni in Type Ia supernovae (SNe Ia) requires sufficiently high-density conditions that are not predicted for all origin scenarios, so examining the distribution of 58Ni using the near-infrared (NIR) [Ni II] 1.939 μm line may observationally distinguish between possible progenitors and explosion mechanisms. We present 79 telluric-corrected NIR spectra of 22 low-redshift SNe Ia from the Carnegie Supernova Project-II, ranging from +50 to +505 days, including 31 previously unpublished spectra. We introduce the Gaussian Peak Ratio, a detection parameter that confirms the presence of the NIR [Ni II] 1.939 μm line in eight SNe in our sample. Nondetections occur at earlier phases (≤+100 days) when the NIR Ni line has not emerged yet or in low signal-to-noise spectra, yielding inconclusive results. Subluminous 86G-like SNe Ia show the earliest NIR Ni features around ∼+50 days, whereas normal-bright SNe Ia do not exhibit NIR Ni until ∼+150 days. NIR Ni features detected in our sample have low peak velocities (v ∼ 1200 km s−1) and narrow line widths (≤3500 km s−1), indicating stable 58Ni is centrally located. This implies high-density burning conditions in the innermost regions of SNe Ia and could be due to higher mass progenitors (i.e., near-Mch). NIR spectra of the nearly two dozen SNe Ia in our sample are compared to various model predictions and paired with early-time properties to identify ideal observation windows for future SNe Ia discovered by upcoming surveys with Rubin-LSST or the Roman Space Telescope.
在Ia型超新星（SNe Ia）中产生稳定的58Ni需要足够高密度的条件，这并不是所有起源情景都能预测到的，因此使用近红外（NIR） [Ni II] 1.939 μm线检查58Ni的分布可以在观测上区分可能的祖细胞和爆炸机制。我们展示了来自卡内基超新星项目ii的22颗低红移超新星Ia的79个大地校正近红外光谱，范围从+50到+505天，包括31个以前未发表的光谱。我们引入高斯峰值比（Gaussian Peak Ratio）这一检测参数，证实了样品中8个SNe中近红外[Ni II] 1.939 μm谱线的存在。未检测发生在早期阶段（≤+100天），此时近红外镍线尚未出现或在低信噪比光谱中，产生不确定的结果。亚发光的86g型Ia型超新星在~ +50天左右显示出最早的近红外Ni特征，而正常明亮的Ia型超新星直到~ +150天才显示出近红外Ni特征。在我们的样品中检测到的近红外Ni特征具有低峰速度（v ~ 1200 km s−1）和窄线宽度（≤3500 km s−1），表明稳定的58Ni位于中心。这意味着在超新星Ia最内层区域有高密度的燃烧条件，可能是由于更高质量的祖星系（即接近mch）。我们将样本中近24颗Ia型超新星的近红外光谱与各种模型预测进行了比较，并与早期属性进行了配对，以确定鲁宾- lsst或罗马太空望远镜即将进行的调查中发现的Ia型超新星的理想观测窗口。
{"title":"The Search for Stable Nickel: Investigating the Origins of Type Ia Supernovae with Late-time Near-infrared Spectroscopy from the Carnegie Supernova Project-II","authors":"Sahana Kumar, Eric Y. Hsiao, Chris Ashall, Peter Hoeflich, Eddie Baron, Mark M. Phillips, Maryam Modjaz, Abigail Polin, Nidia Morrell, Christopher R. Burns, Jing Lu, Melissa Shahbandeh, Lindsey A. Kwok, Lluis Galbany, M. D. Stritzinger, Carlos Contreras, James M. DerKacy, T. Hoover, Syed A. Uddin, Saurabh W. Jha, Huangfei Xiao, K. Krisciunas and N. B. Suntzeff","doi":"10.3847/1538-4357/ae42bf","DOIUrl":"https://doi.org/10.3847/1538-4357/ae42bf","url":null,"abstract":"Producing stable 58Ni in Type Ia supernovae (SNe Ia) requires sufficiently high-density conditions that are not predicted for all origin scenarios, so examining the distribution of 58Ni using the near-infrared (NIR) [Ni II] 1.939 μm line may observationally distinguish between possible progenitors and explosion mechanisms. We present 79 telluric-corrected NIR spectra of 22 low-redshift SNe Ia from the Carnegie Supernova Project-II, ranging from +50 to +505 days, including 31 previously unpublished spectra. We introduce the Gaussian Peak Ratio, a detection parameter that confirms the presence of the NIR [Ni II] 1.939 μm line in eight SNe in our sample. Nondetections occur at earlier phases (≤+100 days) when the NIR Ni line has not emerged yet or in low signal-to-noise spectra, yielding inconclusive results. Subluminous 86G-like SNe Ia show the earliest NIR Ni features around ∼+50 days, whereas normal-bright SNe Ia do not exhibit NIR Ni until ∼+150 days. NIR Ni features detected in our sample have low peak velocities (v ∼ 1200 km s−1) and narrow line widths (≤3500 km s−1), indicating stable 58Ni is centrally located. This implies high-density burning conditions in the innermost regions of SNe Ia and could be due to higher mass progenitors (i.e., near-Mch). NIR spectra of the nearly two dozen SNe Ia in our sample are compared to various model predictions and paired with early-time properties to identify ideal observation windows for future SNe Ia discovered by upcoming surveys with Rubin-LSST or the Roman Space Telescope.","PeriodicalId":501813,"journal":{"name":"The Astrophysical Journal","volume":"13 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2026-03-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147495321","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 : 2026-03-20DOI: 10.3847/1538-4357/ae4c89
Xiaolei Li, Kai Liao and Xuheng Ding
This study introduces an innovative framework aimed at overcoming the ongoing issue of mass-sheet degeneracy (MSD) in time-delay cosmography by incorporating observations of both gravitationally lensed and unlensed Type Ia supernovae (SNe Ia). By simultaneously using lensing magnification measurements μobs and cosmic distance ratios (Ds/Dds), we develop a Bayesian framework capable of breaking the MSD. Specifically, we reconstruct the distance–redshift and magnitude–redshift relations from unlensed SNe Ia using Gaussian process to avoid dependence on specific cosmological models. Our framework shows substantial efficacy in resolving the MSD by imposing constraints on the MSD parameter λ. Furthermore, we extend this framework to analyze multiple gravitational lensing systems. The results show strong agreement with the fiducial MSD parameters used in the data simulation, confirming our method’s effectiveness in mitigating the MSD. Ultimately, this technique enables the derivation of corrected time-delay distance measurements under the MSD, improving the precision of cosmological parameters inferred from strong lensing systems.
{"title":"Breaking the Mass-sheet Degeneracy in Time-delay Cosmography with Lensed and Unlensed Type Ia Supernovae","authors":"Xiaolei Li, Kai Liao and Xuheng Ding","doi":"10.3847/1538-4357/ae4c89","DOIUrl":"https://doi.org/10.3847/1538-4357/ae4c89","url":null,"abstract":"This study introduces an innovative framework aimed at overcoming the ongoing issue of mass-sheet degeneracy (MSD) in time-delay cosmography by incorporating observations of both gravitationally lensed and unlensed Type Ia supernovae (SNe Ia). By simultaneously using lensing magnification measurements μobs and cosmic distance ratios (Ds/Dds), we develop a Bayesian framework capable of breaking the MSD. Specifically, we reconstruct the distance–redshift and magnitude–redshift relations from unlensed SNe Ia using Gaussian process to avoid dependence on specific cosmological models. Our framework shows substantial efficacy in resolving the MSD by imposing constraints on the MSD parameter λ. Furthermore, we extend this framework to analyze multiple gravitational lensing systems. The results show strong agreement with the fiducial MSD parameters used in the data simulation, confirming our method’s effectiveness in mitigating the MSD. Ultimately, this technique enables the derivation of corrected time-delay distance measurements under the MSD, improving the precision of cosmological parameters inferred from strong lensing systems.","PeriodicalId":501813,"journal":{"name":"The Astrophysical Journal","volume":"13 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2026-03-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147489954","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 : 2026-03-20DOI: 10.3847/1538-4357/ae3164
Guodong Li, Roberto J. Assef, W.N. Brandt, Matthew J. Temple, Franz E. Bauer, Marcin Marculewicz, Swayamtrupta Panda, Alessandro Peca, Claudio Ricci, Gordon T. Richards, Sarath Satheesh-Sheeba, Chao-Wei Tsai, Jingwen Wu and Ilsang Yoon
The Legacy Survey of Space and Time (LSST), being conducted by the Vera C. Rubin Observatory, is a wide-field multiband survey that will revolutionize our understanding of extragalactic sources through its unprecedented combination of area and depth. While the LSST survey strategy is still being finalized, the Rubin Observatory team has generated a series of survey simulations using the LSST Operations Simulator to explore the optimal survey strategy that best accommodates the majority of scientific goals. In this study, we utilize the latest simulated data and the Metrics Analysis Framework to predict the number of quasars detectable by LSST in each band and evaluate the impact of different survey strategies. We find that the number of quasars and lower-luminosity active galactic nuclei (AGNs) detected in the baseline strategy (v4.3.1) in the redshift range z = 0.3–6.7 will be highest in the i band (about 12 million) and lowest in the u band (about 6 million). Over 70% of quasars are expected to be detected within the first year in all bands, as LSST will have already reached the break in the luminosity function at most redshifts. With a limiting magnitude of 25.7 (26.9) mag, we expect to detect 184 (199) million AGNs in the z band (r band) over the 10 yr survey, with quasars constituting only 6% of the total AGNs in each band. This arises because, considering that the luminosities of most low-luminosity AGNs are affected by contamination from their host galaxies, we set a magnitude threshold when predicting the number of quasars. We find that variations in the u-band strategy can impact the number of quasar detections. Specifically, the difference between the baseline strategy and that with the largest total exposure in u is 15%. In contrast, changes in rolling strategies, Deep Drilling Field strategies, weather conditions, and Target of Opportunity observations result in variations below 2%. These results provide valuable insights for optimizing approaches to maximize the scientific output of quasar studies.
由Vera C. Rubin天文台进行的遗产时空调查（LSST）是一项宽视场多波段调查，通过其前所未有的面积和深度结合，将彻底改变我们对河外资源的理解。虽然LSST调查策略仍在最后确定，但鲁宾天文台团队已经使用LSST操作模拟器生成了一系列调查模拟，以探索最适合大多数科学目标的最佳调查策略。在这项研究中，我们利用最新的模拟数据和度量分析框架来预测LSST在每个波段可探测到的类星体数量，并评估不同调查策略的影响。我们发现，在基线策略（v4.3.1）中，在红移z = 0.3-6.7范围内探测到的类星体和低亮度活动星系核（agn）的数量在i波段最高（约1200万），在u波段最低（约600万）。预计超过70%的类星体将在第一年在所有波段被探测到，因为LSST在大多数红移时已经达到了光度函数的中断。在极限星等为25.7（26.9）等的情况下，我们预计在10年的调查中，将在z波段（r波段）探测到1.84（1.99）亿个agn，类星体仅占每个波段agn总数的6%。这是因为，考虑到大多数低亮度agn的亮度受到其宿主星系污染的影响，我们在预测类星体数量时设置了一个星等阈值。我们发现u波段策略的变化会影响类星体探测的数量。具体来说，基线策略与最大总暴露量之间的差异为15%。相比之下，滚动策略、深钻场策略、天气条件和机会目标观测的变化导致的变化低于2%。这些结果为优化方法以最大化类星体研究的科学产出提供了有价值的见解。
{"title":"Predicting Quasar Counts Detectable in the LSST Survey","authors":"Guodong Li, Roberto J. Assef, W.N. Brandt, Matthew J. Temple, Franz E. Bauer, Marcin Marculewicz, Swayamtrupta Panda, Alessandro Peca, Claudio Ricci, Gordon T. Richards, Sarath Satheesh-Sheeba, Chao-Wei Tsai, Jingwen Wu and Ilsang Yoon","doi":"10.3847/1538-4357/ae3164","DOIUrl":"https://doi.org/10.3847/1538-4357/ae3164","url":null,"abstract":"The Legacy Survey of Space and Time (LSST), being conducted by the Vera C. Rubin Observatory, is a wide-field multiband survey that will revolutionize our understanding of extragalactic sources through its unprecedented combination of area and depth. While the LSST survey strategy is still being finalized, the Rubin Observatory team has generated a series of survey simulations using the LSST Operations Simulator to explore the optimal survey strategy that best accommodates the majority of scientific goals. In this study, we utilize the latest simulated data and the Metrics Analysis Framework to predict the number of quasars detectable by LSST in each band and evaluate the impact of different survey strategies. We find that the number of quasars and lower-luminosity active galactic nuclei (AGNs) detected in the baseline strategy (v4.3.1) in the redshift range z = 0.3–6.7 will be highest in the i band (about 12 million) and lowest in the u band (about 6 million). Over 70% of quasars are expected to be detected within the first year in all bands, as LSST will have already reached the break in the luminosity function at most redshifts. With a limiting magnitude of 25.7 (26.9) mag, we expect to detect 184 (199) million AGNs in the z band (r band) over the 10 yr survey, with quasars constituting only 6% of the total AGNs in each band. This arises because, considering that the luminosities of most low-luminosity AGNs are affected by contamination from their host galaxies, we set a magnitude threshold when predicting the number of quasars. We find that variations in the u-band strategy can impact the number of quasar detections. Specifically, the difference between the baseline strategy and that with the largest total exposure in u is 15%. In contrast, changes in rolling strategies, Deep Drilling Field strategies, weather conditions, and Target of Opportunity observations result in variations below 2%. These results provide valuable insights for optimizing approaches to maximize the scientific output of quasar studies.","PeriodicalId":501813,"journal":{"name":"The Astrophysical Journal","volume":"115 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2026-03-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147489943","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 : 2026-03-20DOI: 10.3847/1538-4357/ae459b
Sanaea C. Rose, James C. Lombardi, Elena González Prieto, Fulya Kıroğlu and Frederic A. Rasio
Nuclear star clusters represent some of the most extreme collisional environments in the Universe. A nuclear star cluster like that of the Milky Way harbors a supermassive black hole at its center, which accelerates stars to high speeds (≳100–1000 km s−1) in a region where millions of other stars reside. Direct collisions occur in such high-density environments, where they can shape the stellar populations and influence the evolution of the cluster. We present a suite of a couple hundred high-resolution smoothed-particle hydrodynamics (SPH) simulations of collisions between 1 M⊙ stars, at impact speeds representative of galactic nuclei. We use our SPH dataset to develop physically motivated fitting formulae for predicting collision outcomes. While collision-driven mass loss has been examined in detail in the literature, we present a new framework for understanding the effects of “hit-and-run” collisions on a star’s trajectory. We demonstrate that the change in stellar velocity follows the tidal-dissipation limit for grazing encounters, while the deflection angle is well-approximated by point-particle dynamics for periapses ≳0.3 times the stellar radii. We use our SPH dataset to test two machine learning (ML) algorithms, k-nearest neighbors and neural networks, for predicting collision outcomes. We find that the neural network outperforms k-nearest neighbors and delivers results on par with and in some cases exceeding the accuracy of our fitting formulae. We conclude that both fitting formulae and ML have merits for modeling collisions in dense stellar environments; however, ML may prove more effective as the parameter space of initial conditions expands.
核星团代表了宇宙中一些最极端的碰撞环境。像银河系这样的核星团在其中心有一个超大质量黑洞，在数百万其他恒星居住的区域，它将恒星加速到高速（约100-1000 km s - 1）。直接碰撞发生在这种高密度的环境中，在那里它们可以塑造恒星种群并影响星团的演化。我们提出了一套几百个高分辨率的光滑粒子流体动力学（SPH）模拟，模拟了1m⊙恒星之间的碰撞，碰撞速度代表了星系核。我们使用SPH数据集开发用于预测碰撞结果的物理动机拟合公式。虽然碰撞驱动的质量损失已经在文献中进行了详细的研究，但我们提出了一个新的框架来理解“肇事逃逸”碰撞对恒星轨迹的影响。我们证明了恒星速度的变化遵循擦掠相遇的潮汐耗散极限，而偏转角是由点粒子动力学很好地近似于约圆约0.3倍的恒星半径。我们使用SPH数据集来测试两种机器学习（ML）算法，k近邻和神经网络，用于预测碰撞结果。我们发现，神经网络优于k近邻，并且提供的结果与我们拟合公式的准确性相当，在某些情况下甚至超过了我们拟合公式的准确性。我们得出结论，拟合公式和机器学习对于模拟密集恒星环境中的碰撞都有优点；然而，随着初始条件参数空间的扩大，ML可能会被证明是更有效的。
{"title":"Modeling Stellar Collisions in Galactic Nuclei Using Hydrodynamic Simulations and Machine Learning","authors":"Sanaea C. Rose, James C. Lombardi, Elena González Prieto, Fulya Kıroğlu and Frederic A. Rasio","doi":"10.3847/1538-4357/ae459b","DOIUrl":"https://doi.org/10.3847/1538-4357/ae459b","url":null,"abstract":"Nuclear star clusters represent some of the most extreme collisional environments in the Universe. A nuclear star cluster like that of the Milky Way harbors a supermassive black hole at its center, which accelerates stars to high speeds (≳100–1000 km s−1) in a region where millions of other stars reside. Direct collisions occur in such high-density environments, where they can shape the stellar populations and influence the evolution of the cluster. We present a suite of a couple hundred high-resolution smoothed-particle hydrodynamics (SPH) simulations of collisions between 1 M⊙ stars, at impact speeds representative of galactic nuclei. We use our SPH dataset to develop physically motivated fitting formulae for predicting collision outcomes. While collision-driven mass loss has been examined in detail in the literature, we present a new framework for understanding the effects of “hit-and-run” collisions on a star’s trajectory. We demonstrate that the change in stellar velocity follows the tidal-dissipation limit for grazing encounters, while the deflection angle is well-approximated by point-particle dynamics for periapses ≳0.3 times the stellar radii. We use our SPH dataset to test two machine learning (ML) algorithms, k-nearest neighbors and neural networks, for predicting collision outcomes. We find that the neural network outperforms k-nearest neighbors and delivers results on par with and in some cases exceeding the accuracy of our fitting formulae. We conclude that both fitting formulae and ML have merits for modeling collisions in dense stellar environments; however, ML may prove more effective as the parameter space of initial conditions expands.","PeriodicalId":501813,"journal":{"name":"The Astrophysical Journal","volume":"146 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2026-03-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147489946","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}
We investigate starburst-driven galactic outflows in low-mass galaxies ( ) at cosmic noon using high-resolution 3D hydrodynamical simulations based on a framework that can reproduce the multiphase outflows in M82. The simulations produce starbursts lasting 20–30 Myr, with peak star formation rates of 2–68 M⊙ yr−1. The outflow properties vary strongly with time, radial distance to the galaxy center, stellar mass, and gas fraction, exhibiting velocities of 50–1000 km s−1, mass outflow rates of 0.3–20 M⊙ yr−1, and mass loading factors, ηM, of 0.24–6.26. The cool phase (8000 < T ≤ 2 × 104 K) dominates the outflows, and the properties of the cool and warm phases are broadly consistent with observations. At M* = 109.5M⊙, the average ηM for the total, cool, and warm phases is ∼1.2, 0.75, and 0.25, respectively. The mass loading factor decreases with increasing galaxy stellar mass, but increases with star formation rate. Given strong temporal and spatial evolution, the scaling slopes from limited samples should be treated with caution. Our total ηM values are higher than FIRE-2 by 0.06 dex but lower than EAGLE and TNG50 by 0.50 and 0.84 dex, respectively. Accounting for methodological differences in the outflow measurements reduces these gaps to 0.2–0.4 dex, suggesting that part of the discrepancy between observations and simulations reported in the literature may arise from inconsistent definitions and measurement methods, though differences in individual phases persist. Larger observational and simulation samples, together with consistent methods for measuring outflow properties, are required to draw robust conclusions about the scaling relations of galactic outflows.
{"title":"Properties of Galactic Outflows Driven by Starburst at Cosmic Noon: Insights from Hydrodynamical Simulations","authors":"Huan Chen, Weishan Zhu, Xue-Fu Li, Tian-Rui Wang, Antonios Katsianis and Long-Long Feng","doi":"10.3847/1538-4357/ae45a8","DOIUrl":"https://doi.org/10.3847/1538-4357/ae45a8","url":null,"abstract":"We investigate starburst-driven galactic outflows in low-mass galaxies ( ) at cosmic noon using high-resolution 3D hydrodynamical simulations based on a framework that can reproduce the multiphase outflows in M82. The simulations produce starbursts lasting 20–30 Myr, with peak star formation rates of 2–68 M⊙ yr−1. The outflow properties vary strongly with time, radial distance to the galaxy center, stellar mass, and gas fraction, exhibiting velocities of 50–1000 km s−1, mass outflow rates of 0.3–20 M⊙ yr−1, and mass loading factors, ηM, of 0.24–6.26. The cool phase (8000 < T ≤ 2 × 104 K) dominates the outflows, and the properties of the cool and warm phases are broadly consistent with observations. At M* = 109.5M⊙, the average ηM for the total, cool, and warm phases is ∼1.2, 0.75, and 0.25, respectively. The mass loading factor decreases with increasing galaxy stellar mass, but increases with star formation rate. Given strong temporal and spatial evolution, the scaling slopes from limited samples should be treated with caution. Our total ηM values are higher than FIRE-2 by 0.06 dex but lower than EAGLE and TNG50 by 0.50 and 0.84 dex, respectively. Accounting for methodological differences in the outflow measurements reduces these gaps to 0.2–0.4 dex, suggesting that part of the discrepancy between observations and simulations reported in the literature may arise from inconsistent definitions and measurement methods, though differences in individual phases persist. Larger observational and simulation samples, together with consistent methods for measuring outflow properties, are required to draw robust conclusions about the scaling relations of galactic outflows.","PeriodicalId":501813,"journal":{"name":"The Astrophysical Journal","volume":"52 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2026-03-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147489948","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 : 2026-03-20DOI: 10.3847/1538-4357/ae4692
Andrei M. Beloborodov
When a fast radio burst (FRB) expands from its source through a surrounding tenuous plasma, it strongly heats and compresses the plasma at radii up to ∼1014 cm. The likely central engines of FRBs are magnetars, and their ambient plasma at radii r ≫ 1010 cm is a magnetized e± wind. We formulate basic equations of the FRB–plasma interaction, solve them numerically, and describe the physical picture of the interaction. We find the following: (1) FRBs emitted at r < rstoch ∼ 1012 cm induce fast stochastic heating and strong compression of the wind, sweeping it like a broom. The outcome of this interaction is determined by the energy losses of the radio wave; we evaluate the parameter space where FRBs survive and escape. (2) At radii r > rstoch, the FRB induces regular particle oscillations in the radio wave with the standard strength parameter a, and drives a compression wave in the wind. At r > r⋆ ∼ 1013 cm, the compression wave becomes locally quasi steady, with compression factor 1 + a2. FRBs avoid damping if they are released into the wind medium outside rdamp ∼ 1011 cm.
{"title":"Compression Fronts from Fast Radio Bursts","authors":"Andrei M. Beloborodov","doi":"10.3847/1538-4357/ae4692","DOIUrl":"https://doi.org/10.3847/1538-4357/ae4692","url":null,"abstract":"When a fast radio burst (FRB) expands from its source through a surrounding tenuous plasma, it strongly heats and compresses the plasma at radii up to ∼1014 cm. The likely central engines of FRBs are magnetars, and their ambient plasma at radii r ≫ 1010 cm is a magnetized e± wind. We formulate basic equations of the FRB–plasma interaction, solve them numerically, and describe the physical picture of the interaction. We find the following: (1) FRBs emitted at r < rstoch ∼ 1012 cm induce fast stochastic heating and strong compression of the wind, sweeping it like a broom. The outcome of this interaction is determined by the energy losses of the radio wave; we evaluate the parameter space where FRBs survive and escape. (2) At radii r > rstoch, the FRB induces regular particle oscillations in the radio wave with the standard strength parameter a, and drives a compression wave in the wind. At r > r⋆ ∼ 1013 cm, the compression wave becomes locally quasi steady, with compression factor 1 + a2. FRBs avoid damping if they are released into the wind medium outside rdamp ∼ 1011 cm.","PeriodicalId":501813,"journal":{"name":"The Astrophysical Journal","volume":"60 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2026-03-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147489949","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 : 2026-03-20DOI: 10.3847/1538-4357/ae47e6
Bin-Hui Chen, Juntai Shen and Paola Di Matteo
Bars are among the most prominent galactic structures, yet their formation mechanisms remain incompletely understood. They can form either internally, via dynamical instabilities, or externally, triggered by interactions with other galaxies. The impact of mergers on bar formation and survival, however, has not been thoroughly investigated. To explore the influence of mergers on bars, we construct a suite of N-body merger pairs where a Gaia-Sausage-Enceladus-like radially biased satellite disk galaxy merges with a central disk galaxy during its bar formation. With the central galaxy fixed, the satellite varies in merger parameters: the mass ratio m/M relative to the central galaxy, the impact parameter b, and the orbital inclination angle θi relative to the central disk. We find that the bar survival probability decreases with increasing m/M. Mergers with m/M ≲ 1/10 generally preserve the forming bar, whereas those with m/M ≥ 1/2 tend to destroy it, producing more early-type-like remnants. For intermediate mass ratios (1/5 ≤ m/M ≤ 1/3), several models yield “weakening bars,” in which the bar survives the merger but gradually decays during subsequent secular evolution, possibly due to interactions between nested double bars formed from merger debris. In contrast to m/M, b and θi have only secondary and stochastic effects on bar survival. The different influences of these three merger parameters can be naturally explained by the tidal force exerted by the satellite on the forming bar, which tends to weaken the bar when the satellite crosses it nearly perpendicular to its major axis.
条状星系是最突出的星系结构之一，但它们的形成机制仍不完全清楚。它们可以通过动态不稳定性在内部形成，也可以通过与其他星系的相互作用在外部形成。然而，合并对酒吧形成和生存的影响尚未得到彻底调查。为了探索合并对棒子的影响，我们构建了一组n体合并对，其中一个类似盖亚-香肠-恩克拉多斯的径向偏置卫星盘星系在其棒子形成过程中与一个中心盘星系合并。在中心星系固定的情况下，卫星的合并参数发生变化：相对于中心星系的质量比m/ m、撞击参数b、相对于中心盘的轨道倾角θi。我们发现棒材的生存概率随着m/ m的增加而降低。m/ m > 1/10的合并通常保留了形成棒材，而m/ m≥1/2的合并则倾向于破坏形成棒材，产生更多早期类型的残余物。对于中等质量比（1/5≤m/ m≤1/3），几个模型得出“弱化柱”，其中柱在合并中幸存下来，但在随后的长期演化中逐渐衰减，可能是由于由合并碎片形成的嵌套双柱之间的相互作用。与m/ m相比，b和θi对杆的生存只有次要和随机的影响。这三个合并参数的不同影响可以很自然地用卫星对形成棒施加的潮汐力来解释，当卫星几乎垂直于其长轴穿过时，潮汐力往往会削弱形成棒。
{"title":"Bar Formation during a Gaia-Sausage-Enceladus-like Merger Event","authors":"Bin-Hui Chen, Juntai Shen and Paola Di Matteo","doi":"10.3847/1538-4357/ae47e6","DOIUrl":"https://doi.org/10.3847/1538-4357/ae47e6","url":null,"abstract":"Bars are among the most prominent galactic structures, yet their formation mechanisms remain incompletely understood. They can form either internally, via dynamical instabilities, or externally, triggered by interactions with other galaxies. The impact of mergers on bar formation and survival, however, has not been thoroughly investigated. To explore the influence of mergers on bars, we construct a suite of N-body merger pairs where a Gaia-Sausage-Enceladus-like radially biased satellite disk galaxy merges with a central disk galaxy during its bar formation. With the central galaxy fixed, the satellite varies in merger parameters: the mass ratio m/M relative to the central galaxy, the impact parameter b, and the orbital inclination angle θi relative to the central disk. We find that the bar survival probability decreases with increasing m/M. Mergers with m/M ≲ 1/10 generally preserve the forming bar, whereas those with m/M ≥ 1/2 tend to destroy it, producing more early-type-like remnants. For intermediate mass ratios (1/5 ≤ m/M ≤ 1/3), several models yield “weakening bars,” in which the bar survives the merger but gradually decays during subsequent secular evolution, possibly due to interactions between nested double bars formed from merger debris. In contrast to m/M, b and θi have only secondary and stochastic effects on bar survival. The different influences of these three merger parameters can be naturally explained by the tidal force exerted by the satellite on the forming bar, which tends to weaken the bar when the satellite crosses it nearly perpendicular to its major axis.","PeriodicalId":501813,"journal":{"name":"The Astrophysical Journal","volume":"33 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2026-03-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147489951","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 : 2026-03-20DOI: 10.3847/1538-4357/ae48f0
Zhi-wen Li, 志 文 李, Ming Yang, 明 杨, Biwei Jiang, 碧 沩 姜, Yi Ren and 逸 任
Red supergiants (RSGs) are crucial for studying the properties and evolution of massive stars. It is representative to conduct a census of RSGs across the Local Group, which spans a broad metallicity range. However, identifying RSGs in distant and metal-poor galaxies remains challenging, mainly due to contamination of foreground dwarfs and observational limitations. In this work, we perform point-spread function photometry on publicly released JWST/NIRCam images of five Local Group galaxies: NGC 6822, Sextans A, NGC 300, Wolf–Lundmark–Melotte (WLM), and IC 1613 using the DOLPHOT NIRCam module. We find an optimal color–color diagram (CCD) for metal-poor environments, that is F115W–F200W versus F356W–F444W, which clearly separates RSGs from foreground dwarfs. By using the CCD, we identify 208, 135, and 22 RSG candidates in NGC 6822, Sextans A, and NGC 300, respectively, free from contamination by foreground dwarfs and oxygen-rich asymptotic giant branch stars (O-AGBs). In addition, 40 and 14 RSG candidates are directly selected on the CMD in WLM and IC 1613, respectively. Compared with previous works, the number of RSG candidates within the same luminosity range and sky region increases significantly, demonstrating the advantages of JWST in constructing a more complete RSG sample in the Local Group thanks to its high spatial resolution and photometric quality. In addition, catalogs of O-AGBs and carbon-rich AGBs are provided as byproducts.
{"title":"Identifying Red Supergiants in the Local Group Using JWST Photometry. I. NGC 6822, Sextans A, NGC 300, Wolf–Lundmark–Melotte, and IC 1613","authors":"Zhi-wen Li, 志 文 李, Ming Yang, 明 杨, Biwei Jiang, 碧 沩 姜, Yi Ren and 逸 任","doi":"10.3847/1538-4357/ae48f0","DOIUrl":"https://doi.org/10.3847/1538-4357/ae48f0","url":null,"abstract":"Red supergiants (RSGs) are crucial for studying the properties and evolution of massive stars. It is representative to conduct a census of RSGs across the Local Group, which spans a broad metallicity range. However, identifying RSGs in distant and metal-poor galaxies remains challenging, mainly due to contamination of foreground dwarfs and observational limitations. In this work, we perform point-spread function photometry on publicly released JWST/NIRCam images of five Local Group galaxies: NGC 6822, Sextans A, NGC 300, Wolf–Lundmark–Melotte (WLM), and IC 1613 using the DOLPHOT NIRCam module. We find an optimal color–color diagram (CCD) for metal-poor environments, that is F115W–F200W versus F356W–F444W, which clearly separates RSGs from foreground dwarfs. By using the CCD, we identify 208, 135, and 22 RSG candidates in NGC 6822, Sextans A, and NGC 300, respectively, free from contamination by foreground dwarfs and oxygen-rich asymptotic giant branch stars (O-AGBs). In addition, 40 and 14 RSG candidates are directly selected on the CMD in WLM and IC 1613, respectively. Compared with previous works, the number of RSG candidates within the same luminosity range and sky region increases significantly, demonstrating the advantages of JWST in constructing a more complete RSG sample in the Local Group thanks to its high spatial resolution and photometric quality. In addition, catalogs of O-AGBs and carbon-rich AGBs are provided as byproducts.","PeriodicalId":501813,"journal":{"name":"The Astrophysical Journal","volume":"85 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2026-03-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147489952","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 : 2026-03-20DOI: 10.3847/1538-4357/ae47e9
Jeonghoon Lim, 정훈 임, Jacob B. Simon, Rixin Li, 日新 李, Olivia Brouillette, David G. Rea and Wladimir Lyra
The streaming instability (SI) is a leading mechanism for planetesimal formation, driving the aerodynamic concentration of solids in protoplanetary disks. The SI triggers strong clumping (i.e., strong enough for clumps to collapse) when the solid-to-gas column density ratio, Z, exceeds a threshold, Zcrit. This threshold depends on the dimensionless stopping time, τs. Although the strong-clumping threshold has been explored over the last decade, it has been determined largely through 2D axisymmetric simulations. In this work, we perform a suite of 3D, vertically stratified simulations to establish a clumping threshold across 10−3 ≤ τs ≤ 1.0. Additionally, we study SI-driven concentration that is unique to 3D. We find that Zcrit is as low as ≈0.002 at τs = 0.1 and exceeds ≈0.03 at τs = 10−3. Compared to 2D, our 3D results yield lower Zcrit for τs > 0.02, but higher for τs ≤ 0.02, with a sharp transition between τs = 0.02 and 0.03. This transition correlates with the midplane density ratio (ϵ): ϵ < 1 where 3D gives lower thresholds, and ϵ > 1 where 3D gives higher thresholds. We also find a filaments-in-filaments structure when ϵ < 1, which enhances clumping compared to 2D. By contrast, when ϵ > 1 and τs ≤ 0.03, dust filaments in 3D do not drift inward, suppressing filament mergers and strong clumping. In 2D, filaments drift inward regardless of ϵ, triggering strong clumping easier in this regime. Our results underscore the necessity of 3D simulations for accurately capturing SI-driven concentration and building the strong-clumping threshold.
{"title":"The Streaming Instability in 3D: Conditions for Strong Clumping","authors":"Jeonghoon Lim, 정훈 임, Jacob B. Simon, Rixin Li, 日新 李, Olivia Brouillette, David G. Rea and Wladimir Lyra","doi":"10.3847/1538-4357/ae47e9","DOIUrl":"https://doi.org/10.3847/1538-4357/ae47e9","url":null,"abstract":"The streaming instability (SI) is a leading mechanism for planetesimal formation, driving the aerodynamic concentration of solids in protoplanetary disks. The SI triggers strong clumping (i.e., strong enough for clumps to collapse) when the solid-to-gas column density ratio, Z, exceeds a threshold, Zcrit. This threshold depends on the dimensionless stopping time, τs. Although the strong-clumping threshold has been explored over the last decade, it has been determined largely through 2D axisymmetric simulations. In this work, we perform a suite of 3D, vertically stratified simulations to establish a clumping threshold across 10−3 ≤ τs ≤ 1.0. Additionally, we study SI-driven concentration that is unique to 3D. We find that Zcrit is as low as ≈0.002 at τs = 0.1 and exceeds ≈0.03 at τs = 10−3. Compared to 2D, our 3D results yield lower Zcrit for τs > 0.02, but higher for τs ≤ 0.02, with a sharp transition between τs = 0.02 and 0.03. This transition correlates with the midplane density ratio (ϵ): ϵ < 1 where 3D gives lower thresholds, and ϵ > 1 where 3D gives higher thresholds. We also find a filaments-in-filaments structure when ϵ < 1, which enhances clumping compared to 2D. By contrast, when ϵ > 1 and τs ≤ 0.03, dust filaments in 3D do not drift inward, suppressing filament mergers and strong clumping. In 2D, filaments drift inward regardless of ϵ, triggering strong clumping easier in this regime. Our results underscore the necessity of 3D simulations for accurately capturing SI-driven concentration and building the strong-clumping threshold.","PeriodicalId":501813,"journal":{"name":"The Astrophysical Journal","volume":"6 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2026-03-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147490136","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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