Pub Date : 2026-04-14DOI: 10.3847/1538-4357/ae5177
Katherine E. Whitaker, Sam E. Cutler, Rupali Chandar, Richard Pan, David J. Setton, Lukas J. Furtak, Rachel Bezanson, Ivo Labbe, Joel Leja, Katherine A. Suess, Bingjie Wang, 冰洁 王, John R. Weaver, Hakim Atek, Gabriel B. Brammer, Robert Feldmann, Natascha M. Förster Schreiber, Karl Glazebrook, Anna de Graaff, Jenny E. Greene, Gourav Khullar, Danilo Marchesini, Michael V. Maseda, Tim B. Miller, Houjun Mo, Lamiya A. Mowla, Themiya Nanayakkara, Erica J. Nelson, Sedona H. Price, Francesca Rizzo, Pieter van Dokkum, Christina C. Williams, Yanzhe Zhang, Yunchong Zhang and Adi Zitrin
Globular clusters (GCs) are some of the oldest bound structures in the Universe, holding clues to the earliest epochs of star formation and galaxy assembly. However, accurate age measurements of ancient clusters are challenging due to the age–metallicity degeneracy. Here, we report the discovery of 36 compact stellar systems within the “Relic,” a massive, quiescent galaxy at z = 2.53. The Relic resides in an overdensity behind the Abell 2744 cluster, with a prominent tidal tail extending towards two low-mass companions. Using deep data from the UNCOVER/MegaScience JWST Surveys, we find that clusters formed in age intervals ranging from 8 Myr up to ∼2 Gyr, suggesting a rich formation history starting at z ∼ 10. While the cluster-based star formation history is broadly consistent with the high past star formation rates derived from the diffuse host galaxy light, one potential discrepancy is a tentative ∼2–3× higher rate in the cluster population for the past Gyr. Taken together with the spatial distribution and low inferred metallicities of these young-to-intermediate age clusters, we may be seeing direct evidence for the accretion of star clusters in addition to their early in situ formation. The cluster masses are high, ∼106–107M⊙, which may explain why we are able to detect them around this likely post-merger galaxy. Overall, the Relic clusters are consistent with being precursors of the most-massive present-day GCs. This unique laboratory enables the first connection between long-lived, high-redshift clusters and local stellar populations, offering insights into the early stages of GC evolution and the broader processes of galaxy assembly.
{"title":"Discovery of Ancient Globular Cluster Candidates in the Relic, a Quiescent Galaxy at z = 2.5","authors":"Katherine E. Whitaker, Sam E. Cutler, Rupali Chandar, Richard Pan, David J. Setton, Lukas J. Furtak, Rachel Bezanson, Ivo Labbe, Joel Leja, Katherine A. Suess, Bingjie Wang, 冰洁 王, John R. Weaver, Hakim Atek, Gabriel B. Brammer, Robert Feldmann, Natascha M. Förster Schreiber, Karl Glazebrook, Anna de Graaff, Jenny E. Greene, Gourav Khullar, Danilo Marchesini, Michael V. Maseda, Tim B. Miller, Houjun Mo, Lamiya A. Mowla, Themiya Nanayakkara, Erica J. Nelson, Sedona H. Price, Francesca Rizzo, Pieter van Dokkum, Christina C. Williams, Yanzhe Zhang, Yunchong Zhang and Adi Zitrin","doi":"10.3847/1538-4357/ae5177","DOIUrl":"https://doi.org/10.3847/1538-4357/ae5177","url":null,"abstract":"Globular clusters (GCs) are some of the oldest bound structures in the Universe, holding clues to the earliest epochs of star formation and galaxy assembly. However, accurate age measurements of ancient clusters are challenging due to the age–metallicity degeneracy. Here, we report the discovery of 36 compact stellar systems within the “Relic,” a massive, quiescent galaxy at z = 2.53. The Relic resides in an overdensity behind the Abell 2744 cluster, with a prominent tidal tail extending towards two low-mass companions. Using deep data from the UNCOVER/MegaScience JWST Surveys, we find that clusters formed in age intervals ranging from 8 Myr up to ∼2 Gyr, suggesting a rich formation history starting at z ∼ 10. While the cluster-based star formation history is broadly consistent with the high past star formation rates derived from the diffuse host galaxy light, one potential discrepancy is a tentative ∼2–3× higher rate in the cluster population for the past Gyr. Taken together with the spatial distribution and low inferred metallicities of these young-to-intermediate age clusters, we may be seeing direct evidence for the accretion of star clusters in addition to their early in situ formation. The cluster masses are high, ∼106–107M⊙, which may explain why we are able to detect them around this likely post-merger galaxy. Overall, the Relic clusters are consistent with being precursors of the most-massive present-day GCs. This unique laboratory enables the first connection between long-lived, high-redshift clusters and local stellar populations, offering insights into the early stages of GC evolution and the broader processes of galaxy assembly.","PeriodicalId":501813,"journal":{"name":"The Astrophysical Journal","volume":"124 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2026-04-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147695393","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 : 2026-04-14DOI: 10.3847/1538-4357/ae4c38
B. Zuckerman
One of the most interesting questions that astronomy can hope to answer is: Are we alone in our Milky Way Galaxy? A detection of an electromagnetic (EM) signal generated by an extraterrestrial technological intelligence, or the presence in our solar system of an alien probe, would answer this question in the negative. Purposeful interstellar communication is a two-way street—the transmitting and receiving technological intelligences (TIs) both need to do their parts. As the receiving TI, our EM search programs should incorporate a model of what a transmitting TI is likely to be doing. Published works on the search for extraterrestrial technological intelligence (SETI) have generally not done so, and thus have often been suboptimally designed. We propose an improved search technique that more closely corresponds to astronomical surveys that have been undertaken for reasons that have nothing to do with SETI. Published non-SETI radio and optical surveys are sufficiently extensive that they already supply meaningful constraints on the prevalence of nearby, purposely communicative alien civilizations. Purposeful communication can also include the sending of spaceships (probes). The absence of evidence for alien probes in the solar system suggests that no alien civilization has passed within ∼100 lt-yr of Earth during the past few billion years.
{"title":"Broadband Searches for Extraterrestrial Technological Intelligence: A New Strategy to Find Nearby Alien Civilizations","authors":"B. Zuckerman","doi":"10.3847/1538-4357/ae4c38","DOIUrl":"https://doi.org/10.3847/1538-4357/ae4c38","url":null,"abstract":"One of the most interesting questions that astronomy can hope to answer is: Are we alone in our Milky Way Galaxy? A detection of an electromagnetic (EM) signal generated by an extraterrestrial technological intelligence, or the presence in our solar system of an alien probe, would answer this question in the negative. Purposeful interstellar communication is a two-way street—the transmitting and receiving technological intelligences (TIs) both need to do their parts. As the receiving TI, our EM search programs should incorporate a model of what a transmitting TI is likely to be doing. Published works on the search for extraterrestrial technological intelligence (SETI) have generally not done so, and thus have often been suboptimally designed. We propose an improved search technique that more closely corresponds to astronomical surveys that have been undertaken for reasons that have nothing to do with SETI. Published non-SETI radio and optical surveys are sufficiently extensive that they already supply meaningful constraints on the prevalence of nearby, purposely communicative alien civilizations. Purposeful communication can also include the sending of spaceships (probes). The absence of evidence for alien probes in the solar system suggests that no alien civilization has passed within ∼100 lt-yr of Earth during the past few billion years.","PeriodicalId":501813,"journal":{"name":"The Astrophysical Journal","volume":"6 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2026-04-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147681746","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 : 2026-04-14DOI: 10.3847/1538-4357/ae56f7
Lorenzo Biasiotti, Paolo Simonetti, Riccardo Spinelli, Stavro L. Ivanovski, Lorenzo Calderone, Federico Dogo, Giovanna Jerse, Sergio Monai and Giovanni Vladilo
HD 20794 d is one of the best examples of a super-Earth planet in the habitable zone of a Sun-like star. Notably, due to the high eccentricity (e = 0.45 ) it partially lies in the conservative habitable zone, suggesting a dynamically variable climate. The system’s proximity (d = 6.0414 ± 0.0028 pc) makes it a high-priority target for future atmospheric characterization via direct imaging and positions HD 20794 d as an ideal benchmark for understanding the potential climate states of eccentric exoplanets. Assuming a rocky composition for HD 20794 d, we employ a seasonal-latitudinal energy balance model, EOS-ESTM, to explore the impact on surface temperature and habitability of climate factors unconstrained by observational data. To do so, first, we narrow ranges of surface pressures and CO2 fractions that enable potentially habitable conditions. Then, we vary the planetary rotation period, axial tilt, and orbital eccentricity. Finally, we evaluate the impact of the stellar UV radiation field on atmospheric stability and prebiotic chemistry. Our simulations indicate that habitable conditions are generally favored in regimes characterized by high-CO2 concentrations and elevated atmospheric pressure. Habitability also increases with higher axial obliquity (up to the point where an equatorial ice belt forms) and with longer rotation periods. We conclude that HD 20794 d can potentially maintain temperate surface conditions with modest seasonal temperature variations over a wide variety of planetary, orbital, and atmospheric conditions. Although no transits have yet been detected, our results underscore the importance of pursuing further observations of this benchmark system.
{"title":"Climates and Habitability of the Eccentric Super-Earth HD 20794 d: A Multi-parametric Investigation","authors":"Lorenzo Biasiotti, Paolo Simonetti, Riccardo Spinelli, Stavro L. Ivanovski, Lorenzo Calderone, Federico Dogo, Giovanna Jerse, Sergio Monai and Giovanni Vladilo","doi":"10.3847/1538-4357/ae56f7","DOIUrl":"https://doi.org/10.3847/1538-4357/ae56f7","url":null,"abstract":"HD 20794 d is one of the best examples of a super-Earth planet in the habitable zone of a Sun-like star. Notably, due to the high eccentricity (e = 0.45 ) it partially lies in the conservative habitable zone, suggesting a dynamically variable climate. The system’s proximity (d = 6.0414 ± 0.0028 pc) makes it a high-priority target for future atmospheric characterization via direct imaging and positions HD 20794 d as an ideal benchmark for understanding the potential climate states of eccentric exoplanets. Assuming a rocky composition for HD 20794 d, we employ a seasonal-latitudinal energy balance model, EOS-ESTM, to explore the impact on surface temperature and habitability of climate factors unconstrained by observational data. To do so, first, we narrow ranges of surface pressures and CO2 fractions that enable potentially habitable conditions. Then, we vary the planetary rotation period, axial tilt, and orbital eccentricity. Finally, we evaluate the impact of the stellar UV radiation field on atmospheric stability and prebiotic chemistry. Our simulations indicate that habitable conditions are generally favored in regimes characterized by high-CO2 concentrations and elevated atmospheric pressure. Habitability also increases with higher axial obliquity (up to the point where an equatorial ice belt forms) and with longer rotation periods. We conclude that HD 20794 d can potentially maintain temperate surface conditions with modest seasonal temperature variations over a wide variety of planetary, orbital, and atmospheric conditions. Although no transits have yet been detected, our results underscore the importance of pursuing further observations of this benchmark system.","PeriodicalId":501813,"journal":{"name":"The Astrophysical Journal","volume":"38 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2026-04-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147682048","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 : 2026-04-14DOI: 10.3847/1538-4357/ae4725
Indrani Das, Shantanu Basu, Nagayoshi Ohashi, Eduard Vorobyov and Yusuke Aso
The observations of protostellar systems show a transition in the radial profile of specific angular momentum (and rotational velocity), as evolving from (vϕ ∼ r−1) in the infalling-rotating envelope to j ∝ r1/2 (vϕ ∼ r −1/2) in the Keplerian disk. We employ global MHD disk simulations of gravitational collapse starting from a supercritical prestellar core, that forms a disk and envelope structure in a self-consistent manner, in order to determine the physics of the envelope–disk transition zone (EnDTranZ). Our results show that the transition from the infalling-rotating envelope to Keplerian disk happens through a jump in the j − r profile, spanning over a finite radial width, which is characterized by the positive local gravitational torques. The outer edge of the EnDTranZ is identified where the radial infall speed (vr) begins a sharp decline in magnitude and j begins a transition from toward j ∼ r1/2. Moving radially inward, the centrifugal radius (rCR) is defined where vϕ first transitions to Keplerian velocity at the disk’s edge. Farther inward of rCR, the model disk develops a super-Keplerian rotation due to self-gravity. The inner edge of EnDTranZ is defined at model centrifugal barrier (rCB) where vr drops to negligible values. Inside rCB, a net negative gravitational torque drives mass accretion onto the protostar. On observational grounds, we identify a jump in the observed j − r profile of class 0/I protostar L1527 IRS for the first time using the ALMA Large Program Early Planet Formation in Embedded Disks (eDisk) data. Comparison with our numerical radial behavior suggests the observed j − r jump serves as a kinematical tracer for the existence of EnDTranZ. Our results offer insights into the observable imprint of angular momentum redistribution mechanisms during star–disk formation.
{"title":"Modeling the Break in the Specific Angular Momentum within the Envelope–Disk Transition Zone","authors":"Indrani Das, Shantanu Basu, Nagayoshi Ohashi, Eduard Vorobyov and Yusuke Aso","doi":"10.3847/1538-4357/ae4725","DOIUrl":"https://doi.org/10.3847/1538-4357/ae4725","url":null,"abstract":"The observations of protostellar systems show a transition in the radial profile of specific angular momentum (and rotational velocity), as evolving from (vϕ ∼ r−1) in the infalling-rotating envelope to j ∝ r1/2 (vϕ ∼ r −1/2) in the Keplerian disk. We employ global MHD disk simulations of gravitational collapse starting from a supercritical prestellar core, that forms a disk and envelope structure in a self-consistent manner, in order to determine the physics of the envelope–disk transition zone (EnDTranZ). Our results show that the transition from the infalling-rotating envelope to Keplerian disk happens through a jump in the j − r profile, spanning over a finite radial width, which is characterized by the positive local gravitational torques. The outer edge of the EnDTranZ is identified where the radial infall speed (vr) begins a sharp decline in magnitude and j begins a transition from toward j ∼ r1/2. Moving radially inward, the centrifugal radius (rCR) is defined where vϕ first transitions to Keplerian velocity at the disk’s edge. Farther inward of rCR, the model disk develops a super-Keplerian rotation due to self-gravity. The inner edge of EnDTranZ is defined at model centrifugal barrier (rCB) where vr drops to negligible values. Inside rCB, a net negative gravitational torque drives mass accretion onto the protostar. On observational grounds, we identify a jump in the observed j − r profile of class 0/I protostar L1527 IRS for the first time using the ALMA Large Program Early Planet Formation in Embedded Disks (eDisk) data. Comparison with our numerical radial behavior suggests the observed j − r jump serves as a kinematical tracer for the existence of EnDTranZ. Our results offer insights into the observable imprint of angular momentum redistribution mechanisms during star–disk formation.","PeriodicalId":501813,"journal":{"name":"The Astrophysical Journal","volume":"316 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2026-04-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147681744","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 : 2026-04-14DOI: 10.3847/1538-4357/ae5180
Joseph L. Hora, Jinyoung K. Noh, Gary J. Melnick, Brandon S. Hensley, Roberta Paladini, Jeong-Eun Lee, Matthew L. N. Ashby, Volker Tolls, Jaeyeong Kim, Michael W. Werner, James J. Bock, Sean Bruton, Shuang-Shuang Chen, Tzu-Ching Chang, Yi-Kuan Chiang, Asantha Cooray, Brendan P. Crill, Ari J. Cukierman, Olivier Doré, Andreas L. Faisst, Zhaoyu Huai, Howard Hui, Woong-Seob Jeong, Miju Kang, Phil M. Korngut, Ho-Gyu Lee, Carey M. Lisse, Daniel C. Masters, Giulia Murgia, Chi H. Nguyen, Zafar Rustamkulov, Ji Yeon Seok, Robin Y. Wen, Yujin Yang and Michael Zemcov
We present some of the first infrared spectral maps acquired by SPHEREx. These maps, which to our knowledge are the largest of their type ever compiled in the near-infrared, reveal multiple strong lines due to interstellar ices and polycyclic aromatic hydrocarbons (PAHs) throughout the Cygnus X and North American Nebula regions. The maps emphasize the strongest features arising from the 3 μm H2O, 4.27 μm CO2, and 4.67 μm CO lines and the 3.28 μm PAH feature, all of which are detected over large areas with complex and filamentary spatial distributions. The ice absorption maps of H2O and CO2 in particular broadly trace dense, cold, and well-shielded regions across Cygnus X, consistent with the established picture of efficient ice formation in dense molecular clouds. The interstellar ice features are also detected abundantly in diffuse absorption over wide areas. The relative strengths of the H2O and CO2 features vary among different lines of sight, indicating possible differences in local physical conditions or chemical variations. The 3.28 μm PAH emission correlates with the emission from the 7.7 and 11.2 μm features but shows small differences that may trace the grain-size distribution and variations in the ambient UV field. SPHEREx all-sky spectral imaging—only a small fraction of which is showcased in this work—will support numerous science investigations, including the structure of the Galaxy, the physics of the interstellar medium, and the chemistry of stars.
{"title":"SPHEREx Widefield Infrared Spectral Mapping of Interstellar Ices and Polycyclic Aromatic Hydrocarbons","authors":"Joseph L. Hora, Jinyoung K. Noh, Gary J. Melnick, Brandon S. Hensley, Roberta Paladini, Jeong-Eun Lee, Matthew L. N. Ashby, Volker Tolls, Jaeyeong Kim, Michael W. Werner, James J. Bock, Sean Bruton, Shuang-Shuang Chen, Tzu-Ching Chang, Yi-Kuan Chiang, Asantha Cooray, Brendan P. Crill, Ari J. Cukierman, Olivier Doré, Andreas L. Faisst, Zhaoyu Huai, Howard Hui, Woong-Seob Jeong, Miju Kang, Phil M. Korngut, Ho-Gyu Lee, Carey M. Lisse, Daniel C. Masters, Giulia Murgia, Chi H. Nguyen, Zafar Rustamkulov, Ji Yeon Seok, Robin Y. Wen, Yujin Yang and Michael Zemcov","doi":"10.3847/1538-4357/ae5180","DOIUrl":"https://doi.org/10.3847/1538-4357/ae5180","url":null,"abstract":"We present some of the first infrared spectral maps acquired by SPHEREx. These maps, which to our knowledge are the largest of their type ever compiled in the near-infrared, reveal multiple strong lines due to interstellar ices and polycyclic aromatic hydrocarbons (PAHs) throughout the Cygnus X and North American Nebula regions. The maps emphasize the strongest features arising from the 3 μm H2O, 4.27 μm CO2, and 4.67 μm CO lines and the 3.28 μm PAH feature, all of which are detected over large areas with complex and filamentary spatial distributions. The ice absorption maps of H2O and CO2 in particular broadly trace dense, cold, and well-shielded regions across Cygnus X, consistent with the established picture of efficient ice formation in dense molecular clouds. The interstellar ice features are also detected abundantly in diffuse absorption over wide areas. The relative strengths of the H2O and CO2 features vary among different lines of sight, indicating possible differences in local physical conditions or chemical variations. The 3.28 μm PAH emission correlates with the emission from the 7.7 and 11.2 μm features but shows small differences that may trace the grain-size distribution and variations in the ambient UV field. SPHEREx all-sky spectral imaging—only a small fraction of which is showcased in this work—will support numerous science investigations, including the structure of the Galaxy, the physics of the interstellar medium, and the chemistry of stars.","PeriodicalId":501813,"journal":{"name":"The Astrophysical Journal","volume":"68 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2026-04-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147681750","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 : 2026-04-14DOI: 10.3847/1538-4357/ae53e4
Amy K. Murphy, Nada Al-Haddad and Noé Lugaz
Small flux ropes (SFRs) observed in the solar wind are transient magnetic field structures with a strong axial field and helical field lines around the core. How these structures evolve as they propagate in the inner heliosphere is still an open question. In this study, we present a list of 68 SFRs observed by Parker Solar Probe between 2018 October and 2021 August. These SFRs were observed at distances ranging from 0.077 to 0.634 au. We examine the expansion characteristics of these SFRs, including the nondimensional expansion parameter. We find that most of these SFRs show no signs of significant expansion, while a small number show signs of contraction. These results provide new information about the potential origin of these structures and their connection to other coronal and interplanetary transients.
{"title":"Expansion Properties of Small Flux Ropes Observed by Parker Solar Probe","authors":"Amy K. Murphy, Nada Al-Haddad and Noé Lugaz","doi":"10.3847/1538-4357/ae53e4","DOIUrl":"https://doi.org/10.3847/1538-4357/ae53e4","url":null,"abstract":"Small flux ropes (SFRs) observed in the solar wind are transient magnetic field structures with a strong axial field and helical field lines around the core. How these structures evolve as they propagate in the inner heliosphere is still an open question. In this study, we present a list of 68 SFRs observed by Parker Solar Probe between 2018 October and 2021 August. These SFRs were observed at distances ranging from 0.077 to 0.634 au. We examine the expansion characteristics of these SFRs, including the nondimensional expansion parameter. We find that most of these SFRs show no signs of significant expansion, while a small number show signs of contraction. These results provide new information about the potential origin of these structures and their connection to other coronal and interplanetary transients.","PeriodicalId":501813,"journal":{"name":"The Astrophysical Journal","volume":"12 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2026-04-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147681752","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 : 2026-04-14DOI: 10.3847/1538-4357/ae5535
Connery J. Chen, Yihan Wang and Bing Zhang
Neutron star (NS) mergers, including both binary NS mergers and black hole–NS mergers, are multimessenger sources detectable in both gravitational wave (GW) and electromagnetic (EM) radiation. The expected EM emission signatures depend on the source’s progenitor, merger remnant, and observer’s line of sight (LoS). Widely discussed EM counterparts of NS mergers have been focused on the gamma-ray (in terms of short-duration gamma-ray bursts) and optical (in terms of kilonova) bands. In this paper, we demonstrate that X-ray emission provides a powerful and complementary probe of post-merger physics and geometry, offering diagnostic signatures across both the prompt and long-term afterglow phases. We consider several binary progenitor and central engine models and investigate X-ray emission signatures from the prompt phase immediately after the merger to the afterglow phase extending years later. For the prompt phase, we devise a general method for computing phenomenological X-ray light curves and spectra for structured jets viewed from any LoS, which can be applied to X-ray observations of NS mergers to constrain the geometry. The geometric constraints can in turn be used to model the afterglow and estimate a peak time and flux—to preemptively determine afterglow characteristics would be monumental for follow-up observation campaigns of future GW sources. Finally, we provide constraints on the time window for X-ray counterpart searches of NS mergers across a range of luminosity distances and detector sensitivities.
{"title":"X-Ray Emission Signatures of Neutron Star Mergers","authors":"Connery J. Chen, Yihan Wang and Bing Zhang","doi":"10.3847/1538-4357/ae5535","DOIUrl":"https://doi.org/10.3847/1538-4357/ae5535","url":null,"abstract":"Neutron star (NS) mergers, including both binary NS mergers and black hole–NS mergers, are multimessenger sources detectable in both gravitational wave (GW) and electromagnetic (EM) radiation. The expected EM emission signatures depend on the source’s progenitor, merger remnant, and observer’s line of sight (LoS). Widely discussed EM counterparts of NS mergers have been focused on the gamma-ray (in terms of short-duration gamma-ray bursts) and optical (in terms of kilonova) bands. In this paper, we demonstrate that X-ray emission provides a powerful and complementary probe of post-merger physics and geometry, offering diagnostic signatures across both the prompt and long-term afterglow phases. We consider several binary progenitor and central engine models and investigate X-ray emission signatures from the prompt phase immediately after the merger to the afterglow phase extending years later. For the prompt phase, we devise a general method for computing phenomenological X-ray light curves and spectra for structured jets viewed from any LoS, which can be applied to X-ray observations of NS mergers to constrain the geometry. The geometric constraints can in turn be used to model the afterglow and estimate a peak time and flux—to preemptively determine afterglow characteristics would be monumental for follow-up observation campaigns of future GW sources. Finally, we provide constraints on the time window for X-ray counterpart searches of NS mergers across a range of luminosity distances and detector sensitivities.","PeriodicalId":501813,"journal":{"name":"The Astrophysical Journal","volume":"16 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2026-04-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147681942","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 : 2026-04-14DOI: 10.3847/1538-4357/ae4c60
Jong-In Park, Jubee Sohn, Margaret J. Geller, Ken J. Rines and Antonaldo Diaferio
We measure galaxy stellar mass functions (SMFs) for nine of the most massive galaxy clusters in the local Universe (0.07 < z < 0.11) using deep and complete spectroscopy from the MAssive Cluster Survey with Hectospec (MACH). We construct the cluster SMFs down to . For comparison, we measure the SMF for field galaxies, complete to , based on Sloan Digital Sky Survey spectroscopy over the same redshift range. The mean MACH SMF shows a shape similar to that of the field SMF but with a significantly higher amplitude at . At , the MACH SMF shows a clear excess, indicating the contribution of massive galaxies, including brightest cluster galaxies (BCGs). Based on homogeneous MACH spectroscopy, we compare SMF shapes for quiescent and star-forming members as a function of the cluster-centric distance. The quiescent SMFs display a curved shape with a peak at ; the star-forming SMFs decline monotonically with increasing stellar mass. We further compare the mean MACH SMF with SMFs derived from similarly massive clusters in the IllustrisTNG-300 simulations. The shape of the observed and simulated SMFs agrees well overall. However, the MACH clusters contain roughly a factor of 2 more galaxies at . These results demonstrate that constructing cluster SMFs from complete spectroscopic samples can test simulations and provide powerful constraints on galaxy formation and evolution in dense environments.
我们使用hetospec （MACH）大质量星系团调查的深度和完整光谱测量了本地宇宙中9个最大质量星系团（0.07 < z < 0.11）的星系恒星质量函数（smf）。我们将集群smf构造为。为了比较，我们测量了场星系的SMF，完全基于斯隆数字巡天光谱，在相同的红移范围内。平均马赫SMF的形状与场SMF相似，但在。在图中，MACH SMF显示出明显的过剩，表明大质量星系的贡献，包括最亮的星系团（bcg）。基于均匀马赫光谱，我们比较了静止和恒星形成成员的SMF形状作为星团中心距离的函数。静态smf呈曲线状，峰值在；恒星形成的smf随恒星质量的增加而单调下降。我们进一步将平均MACH SMF与IllustrisTNG-300模拟中类似大质量集群的SMF进行了比较。观察到的和模拟的smf的形状总体上是一致的。然而，马赫星系团包含了大约2倍的星系。这些结果表明，从完整的光谱样品中构建星系团smf可以测试模拟，并为稠密环境中星系的形成和演化提供强有力的约束。
{"title":"The Stellar Mass Function for Nine Massive Galaxy Clusters in the Local Universe","authors":"Jong-In Park, Jubee Sohn, Margaret J. Geller, Ken J. Rines and Antonaldo Diaferio","doi":"10.3847/1538-4357/ae4c60","DOIUrl":"https://doi.org/10.3847/1538-4357/ae4c60","url":null,"abstract":"We measure galaxy stellar mass functions (SMFs) for nine of the most massive galaxy clusters in the local Universe (0.07 < z < 0.11) using deep and complete spectroscopy from the MAssive Cluster Survey with Hectospec (MACH). We construct the cluster SMFs down to . For comparison, we measure the SMF for field galaxies, complete to , based on Sloan Digital Sky Survey spectroscopy over the same redshift range. The mean MACH SMF shows a shape similar to that of the field SMF but with a significantly higher amplitude at . At , the MACH SMF shows a clear excess, indicating the contribution of massive galaxies, including brightest cluster galaxies (BCGs). Based on homogeneous MACH spectroscopy, we compare SMF shapes for quiescent and star-forming members as a function of the cluster-centric distance. The quiescent SMFs display a curved shape with a peak at ; the star-forming SMFs decline monotonically with increasing stellar mass. We further compare the mean MACH SMF with SMFs derived from similarly massive clusters in the IllustrisTNG-300 simulations. The shape of the observed and simulated SMFs agrees well overall. However, the MACH clusters contain roughly a factor of 2 more galaxies at . These results demonstrate that constructing cluster SMFs from complete spectroscopic samples can test simulations and provide powerful constraints on galaxy formation and evolution in dense environments.","PeriodicalId":501813,"journal":{"name":"The Astrophysical Journal","volume":"59 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2026-04-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147681747","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 : 2026-04-14DOI: 10.3847/1538-4357/ae5488
Lorenzo Marra, Romana Mikušincová, Federico M. Vincentelli, Fiamma Capitanio, Melania Del Santo, Sergio Fabiani, Shifra Mandel, Fabio Muleri, Maxime Parra, Paolo Soffitta, Antonella Tarana, M. Cristina Baglio, Stefano Bianchi, Stéphane Corbel, Enrico Costa, Antonino D’Aì, Barbara De Marco, Michal Dovčiak, Vittoria Elvezia Gianolli, Andrea Gnarini, Maitrayee Gupta, Adam Ingram, Guglielmo Mastroserio, Giorgio Matt, Kaya Mori, Pierre-Olivier Petrucci, Jakub Podgorný, Juri Poutanen, James F. Steiner, Jiří Svoboda, Roberto Taverna, Francesco Tombesi, Swati Ravi, Jérôme Rodriguez, Thomas D. Russell, Alexandra Veledina and Shuo Zhang
We present the first IXPE spectro-polarimetric observation of the black hole candidate MAXI J1744−294, a transient X-ray source observed during a bright 2025 outburst in the Galactic center region. The source has recently been identified as most likely a repeat outburst of the 2016 transient Swift J174540.2−290037. During the ∼150 ks observation, the source was detected in the soft state, and its spectrum was well described by an absorbed multicolor disk with a minor high-energy tail. We did not detect any significant polarization from the source, and hence we derived a 3σ upper limit on the polarization degree of 1.3% in the 2–8 keV energy band. This result is consistent with previous findings for soft-state black hole binaries observed at low to intermediate inclination angles. By comparing the polarization degree upper limit with theoretical predictions for standard accretion disk emission, we constrain the disk inclination to i ≲ 38°–72°, depending on the black hole spin and the disk atmosphere albedo, consistent with inclination estimates obtained during the 2016 outburst of Swift J174540.2−290037.
{"title":"Exploring MAXI J1744−294: IXPE Insights into a Galactic Center X-Ray Transient","authors":"Lorenzo Marra, Romana Mikušincová, Federico M. Vincentelli, Fiamma Capitanio, Melania Del Santo, Sergio Fabiani, Shifra Mandel, Fabio Muleri, Maxime Parra, Paolo Soffitta, Antonella Tarana, M. Cristina Baglio, Stefano Bianchi, Stéphane Corbel, Enrico Costa, Antonino D’Aì, Barbara De Marco, Michal Dovčiak, Vittoria Elvezia Gianolli, Andrea Gnarini, Maitrayee Gupta, Adam Ingram, Guglielmo Mastroserio, Giorgio Matt, Kaya Mori, Pierre-Olivier Petrucci, Jakub Podgorný, Juri Poutanen, James F. Steiner, Jiří Svoboda, Roberto Taverna, Francesco Tombesi, Swati Ravi, Jérôme Rodriguez, Thomas D. Russell, Alexandra Veledina and Shuo Zhang","doi":"10.3847/1538-4357/ae5488","DOIUrl":"https://doi.org/10.3847/1538-4357/ae5488","url":null,"abstract":"We present the first IXPE spectro-polarimetric observation of the black hole candidate MAXI J1744−294, a transient X-ray source observed during a bright 2025 outburst in the Galactic center region. The source has recently been identified as most likely a repeat outburst of the 2016 transient Swift J174540.2−290037. During the ∼150 ks observation, the source was detected in the soft state, and its spectrum was well described by an absorbed multicolor disk with a minor high-energy tail. We did not detect any significant polarization from the source, and hence we derived a 3σ upper limit on the polarization degree of 1.3% in the 2–8 keV energy band. This result is consistent with previous findings for soft-state black hole binaries observed at low to intermediate inclination angles. By comparing the polarization degree upper limit with theoretical predictions for standard accretion disk emission, we constrain the disk inclination to i ≲ 38°–72°, depending on the black hole spin and the disk atmosphere albedo, consistent with inclination estimates obtained during the 2016 outburst of Swift J174540.2−290037.","PeriodicalId":501813,"journal":{"name":"The Astrophysical Journal","volume":"12 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2026-04-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147682047","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 : 2026-04-14DOI: 10.3847/1538-4357/ae5243
Aysha Aamer, Matt Nicholl, Charlotte Angus, Shubham Srivastav, Jeff Cooke, Natasha Van Bemmel, Mark Suhr, Frédérick Poidevin, Stefan Geier, Joseph P. Anderson, Thomas de Boer, Kenneth C. Chambers, Ting-Wan Chen, Mariusz Gromadzki, Claudia P. Gutiérrez, Erkki Kankare, Réka Könyves-Tóth, Chien-Cheng Lin, Thomas B. Lowe, Eugene Magnier, Paolo Mazzali, Kyle Medler, Paloma Minguez, Tomás E. Müller-Bravo and Ben Warwick
Superluminous supernovae (SLSNe) are some of the brightest explosions in the Universe, representing the extremes of stellar deaths. At the upper end of their distribution is SN 2023taz, in a dwarf galaxy at z = 0.407. This is one of the most luminous SLSNe discovered to date with a peak absolute magnitude of Mg,peak = –22.75 ± 0.03 and a lower limit for energy radiated of E = 2.9 × 1051 erg. Magnetar model fits reveal individual parameter values typical of the SLSN population, but the combination of a low B-field and ejecta mass with a short spin period places SN 2023taz in a unusual region of parameter space, accounting for its extreme luminosity. The optical data around peak are consistent with a temperature of ∼17,000 K but SN 2023taz shows a surprising deficit in the UV compared to other events in this temperature range. We find no indication of dust extinction that could plausibly explain the UV deficit. The lower level of UV flux is reminiscent of the absorption seen in lower-luminosity events like SN 2017dwh, where Fe-group elements are responsible for the effect. However, in the case of SN 2023taz, there is no evidence for a larger amount of Fe-group elements which could contribute to line blanketing. Comparing to SLSNe with well-observed UV spectra, an underlying temperature of 8000–9000 K would match the UV spectral slope, but is not consistent with the optical color temperatures of these events. The most likely explanation is enhanced absorption by intermediate-mass elements, challenging previous findings that SLSNe exhibit similar UV absorption line equivalent widths. This highlights the need for expanded UV spectroscopic coverage of SLSNe, especially at early times, to build a framework for interpreting their diversity and to enable classification at higher redshifts where optical observations will exclusively probe rest-frame UV emission.
{"title":"SN 2023taz: Implications for the UV Diversity of Superluminous Supernovae","authors":"Aysha Aamer, Matt Nicholl, Charlotte Angus, Shubham Srivastav, Jeff Cooke, Natasha Van Bemmel, Mark Suhr, Frédérick Poidevin, Stefan Geier, Joseph P. Anderson, Thomas de Boer, Kenneth C. Chambers, Ting-Wan Chen, Mariusz Gromadzki, Claudia P. Gutiérrez, Erkki Kankare, Réka Könyves-Tóth, Chien-Cheng Lin, Thomas B. Lowe, Eugene Magnier, Paolo Mazzali, Kyle Medler, Paloma Minguez, Tomás E. Müller-Bravo and Ben Warwick","doi":"10.3847/1538-4357/ae5243","DOIUrl":"https://doi.org/10.3847/1538-4357/ae5243","url":null,"abstract":"Superluminous supernovae (SLSNe) are some of the brightest explosions in the Universe, representing the extremes of stellar deaths. At the upper end of their distribution is SN 2023taz, in a dwarf galaxy at z = 0.407. This is one of the most luminous SLSNe discovered to date with a peak absolute magnitude of Mg,peak = –22.75 ± 0.03 and a lower limit for energy radiated of E = 2.9 × 1051 erg. Magnetar model fits reveal individual parameter values typical of the SLSN population, but the combination of a low B-field and ejecta mass with a short spin period places SN 2023taz in a unusual region of parameter space, accounting for its extreme luminosity. The optical data around peak are consistent with a temperature of ∼17,000 K but SN 2023taz shows a surprising deficit in the UV compared to other events in this temperature range. We find no indication of dust extinction that could plausibly explain the UV deficit. The lower level of UV flux is reminiscent of the absorption seen in lower-luminosity events like SN 2017dwh, where Fe-group elements are responsible for the effect. However, in the case of SN 2023taz, there is no evidence for a larger amount of Fe-group elements which could contribute to line blanketing. Comparing to SLSNe with well-observed UV spectra, an underlying temperature of 8000–9000 K would match the UV spectral slope, but is not consistent with the optical color temperatures of these events. The most likely explanation is enhanced absorption by intermediate-mass elements, challenging previous findings that SLSNe exhibit similar UV absorption line equivalent widths. This highlights the need for expanded UV spectroscopic coverage of SLSNe, especially at early times, to build a framework for interpreting their diversity and to enable classification at higher redshifts where optical observations will exclusively probe rest-frame UV emission.","PeriodicalId":501813,"journal":{"name":"The Astrophysical Journal","volume":"132 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2026-04-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147681751","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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