Pub Date : 2025-01-08DOI: 10.3847/2041-8213/ada37f
Wuzheng Guo, Qiumin Wang, Shuo Cao, Marek Biesiada, Tonghua Liu, Yujie Lian, Xinyue Jiang, Chengsheng Mu and Dadian Cheng
In this Letter, we use the latest results from the Dark Energy Spectroscopic Instrument (DESI) survey to measure the Hubble constant. Baryon acoustic oscillation (BAO) observations released by the DESI survey, allow us to determine H0 from the first principles. Our method is purely data-driven and relies on unanchored luminosity distances reconstructed from Type Ia supernovae (SN Ia) data and H(z) reconstruction from cosmic chronometers. Thus, it circumvents calibrations related to the value of the sound horizon size at the baryon drag epoch or intrinsic luminosity of SN Ia. We find at a 68% confidence level, which provides the Hubble constant at an accuracy of 1.3% with minimal assumptions. Our assessments of this fundamental cosmological quantity using the BAO data spanning the redshift range z = 0.51–2.33 agree very well with Planck's results and TRGB results within 1σ. This result is still in a 4.3σ tension with the results of the Supernova H0 for the Equation of State.
{"title":"Newest Measurements of Hubble Constant from DESI 2024 Baryon Acoustic Oscillation Observations","authors":"Wuzheng Guo, Qiumin Wang, Shuo Cao, Marek Biesiada, Tonghua Liu, Yujie Lian, Xinyue Jiang, Chengsheng Mu and Dadian Cheng","doi":"10.3847/2041-8213/ada37f","DOIUrl":"https://doi.org/10.3847/2041-8213/ada37f","url":null,"abstract":"In this Letter, we use the latest results from the Dark Energy Spectroscopic Instrument (DESI) survey to measure the Hubble constant. Baryon acoustic oscillation (BAO) observations released by the DESI survey, allow us to determine H0 from the first principles. Our method is purely data-driven and relies on unanchored luminosity distances reconstructed from Type Ia supernovae (SN Ia) data and H(z) reconstruction from cosmic chronometers. Thus, it circumvents calibrations related to the value of the sound horizon size at the baryon drag epoch or intrinsic luminosity of SN Ia. We find at a 68% confidence level, which provides the Hubble constant at an accuracy of 1.3% with minimal assumptions. Our assessments of this fundamental cosmological quantity using the BAO data spanning the redshift range z = 0.51–2.33 agree very well with Planck's results and TRGB results within 1σ. This result is still in a 4.3σ tension with the results of the Supernova H0 for the Equation of State.","PeriodicalId":501814,"journal":{"name":"The Astrophysical Journal Letters","volume":"14 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2025-01-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142935649","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 : 2025-01-08DOI: 10.3847/2041-8213/ad9c75
S. Srivastav, T.-W. Chen, J. H. Gillanders, L. Rhodes, S. J. Smartt, M. E. Huber, A. Aryan, S. Yang, A. Beri, A. J. Cooper, M. Nicholl, K. W. Smith, H. F. Stevance, F. Carotenuto, K. C. Chambers, A. Aamer, C.R. Angus, M. D. Fulton, T. Moore, I. A. Smith, D. R. Young, T. de Boer, H. Gao, C.-C. Lin, T. Lowe, E. A. Magnier, P. Minguez, Y.-C. Pan and R. J. Wainscoat
Fast X-ray transients (FXTs) are extragalactic bursts of X-rays first identified in archival X-ray data and are now routinely discovered in real time by the Einstein Probe, which is continuously surveying the night sky in the soft (0.5–4 keV) X-ray regime. In this Letter, we report the discovery of the second optical counterpart (AT 2024gsa) to an FXT (EP 240414a). EP 240414a is located at a projected radial separation of 27 kpc from its likely host galaxy at z = 0.4018 ± 0.0010. The optical light curve of AT 2024gsa displays three distinct components. The initial decay from our first observation is followed by a rebrightening episode, displaying a rapid rise in luminosity to an absolute magnitude Mr ∼ −21 after two rest-frame days. While the early optical luminosity and decline rate are similar to those of luminous fast blue optical transients, the color temperature of AT 2024gsa is distinctly red and we show that the peak flux is inconsistent with a thermal origin. The third component peaks at Mi ∼ −19 at ≳16 rest-frame days post-FXT, and is compatible with an emerging supernova. We fit the riz-band data with a series of power laws and find that the decaying components are in agreement with gamma-ray burst afterglow models, and that the rebrightening may originate from refreshed shocks. By considering EP 240414a in context with all previously reported known-redshift FXT events, we propose that Einstein Probe FXT discoveries may predominantly result from (high-redshift) gamma-ray bursts, and thus appear to be distinct from the previously discovered lower-redshift, lower-luminosity population of FXTs.
{"title":"Identification of the Optical Counterpart of the Fast X-Ray Transient EP240414a","authors":"S. Srivastav, T.-W. Chen, J. H. Gillanders, L. Rhodes, S. J. Smartt, M. E. Huber, A. Aryan, S. Yang, A. Beri, A. J. Cooper, M. Nicholl, K. W. Smith, H. F. Stevance, F. Carotenuto, K. C. Chambers, A. Aamer, C.R. Angus, M. D. Fulton, T. Moore, I. A. Smith, D. R. Young, T. de Boer, H. Gao, C.-C. Lin, T. Lowe, E. A. Magnier, P. Minguez, Y.-C. Pan and R. J. Wainscoat","doi":"10.3847/2041-8213/ad9c75","DOIUrl":"https://doi.org/10.3847/2041-8213/ad9c75","url":null,"abstract":"Fast X-ray transients (FXTs) are extragalactic bursts of X-rays first identified in archival X-ray data and are now routinely discovered in real time by the Einstein Probe, which is continuously surveying the night sky in the soft (0.5–4 keV) X-ray regime. In this Letter, we report the discovery of the second optical counterpart (AT 2024gsa) to an FXT (EP 240414a). EP 240414a is located at a projected radial separation of 27 kpc from its likely host galaxy at z = 0.4018 ± 0.0010. The optical light curve of AT 2024gsa displays three distinct components. The initial decay from our first observation is followed by a rebrightening episode, displaying a rapid rise in luminosity to an absolute magnitude Mr ∼ −21 after two rest-frame days. While the early optical luminosity and decline rate are similar to those of luminous fast blue optical transients, the color temperature of AT 2024gsa is distinctly red and we show that the peak flux is inconsistent with a thermal origin. The third component peaks at Mi ∼ −19 at ≳16 rest-frame days post-FXT, and is compatible with an emerging supernova. We fit the riz-band data with a series of power laws and find that the decaying components are in agreement with gamma-ray burst afterglow models, and that the rebrightening may originate from refreshed shocks. By considering EP 240414a in context with all previously reported known-redshift FXT events, we propose that Einstein Probe FXT discoveries may predominantly result from (high-redshift) gamma-ray bursts, and thus appear to be distinct from the previously discovered lower-redshift, lower-luminosity population of FXTs.","PeriodicalId":501814,"journal":{"name":"The Astrophysical Journal Letters","volume":"35 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2025-01-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142935646","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 : 2025-01-08DOI: 10.3847/2041-8213/ada24b
C. M. S. Cohen, G. M. Mason, E. R. Christian, A. C. Cummings, G. A. de Nolfo, M. I. Desai, J. Giacalone, M. E. Hill, A. W. Labrador, R. A. Leske, D. J. McComas, R. L. McNutt Jr, D. G. Mitchell, J. G. Mitchell, G. D. Muro, J. S. Rankin, N. A. Schwadron, M. M. Shen, M. E. Wiedenbeck, Z. G. Xu, G. C. Ho and R. F. Wimmer-Schweingrüber
The 2021 October 28 solar energetic particle (SEP) event was a rare ground level enhancement (GLE) event, where secondary particles from the interactions of SEPs with the Earth’s atmosphere were detected by neutron monitors on the ground. A number of papers have examined the solar signatures, neutron monitor observations, and the characteristics of the SEP protons and electrons for this event. Here we describe the heavy ion signatures, specifically O and Fe, observed by multiple spacecraft. Parker Solar Probe, Solar Terrestrial Relations Observatory-Ahead, and Advanced Composition Explorer were distributed over nearly 60° in solar longitude and 0.4 au in heliocentric distance. Despite their separations, all three spacecraft measured event-integrated O and Fe spectra, well represented by power laws, with nearly the same power-law index of approximately −1.7, which is significantly harder than most large SEP events and many GLE events. Moreover, the Fe/O abundance ratio determined from these spectra was also found to be spatially invariant over the 60° in longitude and 0.4 au in heliocentric distance. Such near uniformity is highly unusual, and only one similar occurrence was found in a previous multispacecraft. The observed Fe/O ratio of 0.39 is higher than typical for large SEP events but not unusual for GLE events.
{"title":"Longitudinal Dependence of Heavy Ion Composition in the 2021 October 28 Ground Level Enhancement Event","authors":"C. M. S. Cohen, G. M. Mason, E. R. Christian, A. C. Cummings, G. A. de Nolfo, M. I. Desai, J. Giacalone, M. E. Hill, A. W. Labrador, R. A. Leske, D. J. McComas, R. L. McNutt Jr, D. G. Mitchell, J. G. Mitchell, G. D. Muro, J. S. Rankin, N. A. Schwadron, M. M. Shen, M. E. Wiedenbeck, Z. G. Xu, G. C. Ho and R. F. Wimmer-Schweingrüber","doi":"10.3847/2041-8213/ada24b","DOIUrl":"https://doi.org/10.3847/2041-8213/ada24b","url":null,"abstract":"The 2021 October 28 solar energetic particle (SEP) event was a rare ground level enhancement (GLE) event, where secondary particles from the interactions of SEPs with the Earth’s atmosphere were detected by neutron monitors on the ground. A number of papers have examined the solar signatures, neutron monitor observations, and the characteristics of the SEP protons and electrons for this event. Here we describe the heavy ion signatures, specifically O and Fe, observed by multiple spacecraft. Parker Solar Probe, Solar Terrestrial Relations Observatory-Ahead, and Advanced Composition Explorer were distributed over nearly 60° in solar longitude and 0.4 au in heliocentric distance. Despite their separations, all three spacecraft measured event-integrated O and Fe spectra, well represented by power laws, with nearly the same power-law index of approximately −1.7, which is significantly harder than most large SEP events and many GLE events. Moreover, the Fe/O abundance ratio determined from these spectra was also found to be spatially invariant over the 60° in longitude and 0.4 au in heliocentric distance. Such near uniformity is highly unusual, and only one similar occurrence was found in a previous multispacecraft. The observed Fe/O ratio of 0.39 is higher than typical for large SEP events but not unusual for GLE events.","PeriodicalId":501814,"journal":{"name":"The Astrophysical Journal Letters","volume":"1 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2025-01-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142935647","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 : 2025-01-08DOI: 10.3847/2041-8213/ada354
Xingyu Zhu, Gary P. Zank, Lingling Zhao and Ashok Silwal
The Parker Solar Probe (PSP) and Wind spacecraft observed the same plasma flow during PSP encounter 15. The solar wind evolves from a sub-Alfvénic flow at 0.08 au to become modestly super-Alfvénic at 1 au. We study the radial evolution of the turbulence properties and deduce the spectral anisotropy based on the nearly incompressible (NI) MHD theory. We find that the spectral index of the z+ spectrum remains unchanged (∼−1.53), while the z− spectrum steepens, the index of which changes from −1.35 to −1.47. The fluctuating kinetic energy is on average greater than the fluctuating magnetic field energy in the sub-Alfvénic flow while smaller in the modestly super-Alfvénic flow. The NI MHD theory well interprets the observed Elsässer spectra. The contribution of 2D fluctuations is nonnegligible for the observed z− frequency spectra for both intervals. Particularly, the magnitudes of 2D and NI/slab fluctuations are comparable in the frequency domain for the modestly super-Alfvénic flow, resulting in a slightly concave shape of z− spectrum at 1 au. We show that, in the wavenumber domain, the power ratio of the observed forward NI/slab and 2D fluctuations is ∼15 at 0.08 au, while it decreases to ∼3 at 1 au, suggesting the growing significance of the 2D fluctuations as the turbulence evolves in low Mach number solar wind.
{"title":"Radial Evolution of MHD Turbulence Anisotropy in Low Mach Number Solar Wind","authors":"Xingyu Zhu, Gary P. Zank, Lingling Zhao and Ashok Silwal","doi":"10.3847/2041-8213/ada354","DOIUrl":"https://doi.org/10.3847/2041-8213/ada354","url":null,"abstract":"The Parker Solar Probe (PSP) and Wind spacecraft observed the same plasma flow during PSP encounter 15. The solar wind evolves from a sub-Alfvénic flow at 0.08 au to become modestly super-Alfvénic at 1 au. We study the radial evolution of the turbulence properties and deduce the spectral anisotropy based on the nearly incompressible (NI) MHD theory. We find that the spectral index of the z+ spectrum remains unchanged (∼−1.53), while the z− spectrum steepens, the index of which changes from −1.35 to −1.47. The fluctuating kinetic energy is on average greater than the fluctuating magnetic field energy in the sub-Alfvénic flow while smaller in the modestly super-Alfvénic flow. The NI MHD theory well interprets the observed Elsässer spectra. The contribution of 2D fluctuations is nonnegligible for the observed z− frequency spectra for both intervals. Particularly, the magnitudes of 2D and NI/slab fluctuations are comparable in the frequency domain for the modestly super-Alfvénic flow, resulting in a slightly concave shape of z− spectrum at 1 au. We show that, in the wavenumber domain, the power ratio of the observed forward NI/slab and 2D fluctuations is ∼15 at 0.08 au, while it decreases to ∼3 at 1 au, suggesting the growing significance of the 2D fluctuations as the turbulence evolves in low Mach number solar wind.","PeriodicalId":501814,"journal":{"name":"The Astrophysical Journal Letters","volume":"1 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2025-01-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142935648","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 : 2025-01-07DOI: 10.3847/2041-8213/ad9b26
A. Rodríguez-Kamenetzky, A. Pasetto, C. Carrasco-González, L. F. Rodríguez, J. L. Gómez, G. Anglada, J. M. Torrelles, N. R. C. Gomes, S. Vig and J. Martí
Highly collimated outflows (jets) are observed across a wide range of astrophysical systems involving the accretion of material onto central objects, from supermassive black holes in active galaxies to proto-brown dwarfs and stellar-mass black holes. Despite the diversity of their driving sources, it is believed that all jets are different manifestations of a single universal phenomenon. However, a unified explanation for their ejection and collimation remains elusive. In this study we present the first rotation measure analysis of the polarized synchrotron emission ever performed in a protostellar radio jet, which allows us to reveal its true 3D magnetic structure. Unlike extragalactic radio jets, which often exhibit faint counterjets, protostellar radio jets allow both the jet and the counterjet to be analyzed. This exceptional circumstance allows us to unveil the magnetic field structure of both components. Our findings provide the first solid evidence for a helical magnetic field within a protostellar jet, supporting the universality of the jet collimation mechanism.
{"title":"Helical Magnetic Field in a Massive Protostellar Jet","authors":"A. Rodríguez-Kamenetzky, A. Pasetto, C. Carrasco-González, L. F. Rodríguez, J. L. Gómez, G. Anglada, J. M. Torrelles, N. R. C. Gomes, S. Vig and J. Martí","doi":"10.3847/2041-8213/ad9b26","DOIUrl":"https://doi.org/10.3847/2041-8213/ad9b26","url":null,"abstract":"Highly collimated outflows (jets) are observed across a wide range of astrophysical systems involving the accretion of material onto central objects, from supermassive black holes in active galaxies to proto-brown dwarfs and stellar-mass black holes. Despite the diversity of their driving sources, it is believed that all jets are different manifestations of a single universal phenomenon. However, a unified explanation for their ejection and collimation remains elusive. In this study we present the first rotation measure analysis of the polarized synchrotron emission ever performed in a protostellar radio jet, which allows us to reveal its true 3D magnetic structure. Unlike extragalactic radio jets, which often exhibit faint counterjets, protostellar radio jets allow both the jet and the counterjet to be analyzed. This exceptional circumstance allows us to unveil the magnetic field structure of both components. Our findings provide the first solid evidence for a helical magnetic field within a protostellar jet, supporting the universality of the jet collimation mechanism.","PeriodicalId":501814,"journal":{"name":"The Astrophysical Journal Letters","volume":"73 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2025-01-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142935044","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 : 2025-01-06DOI: 10.3847/2041-8213/ada1ce
Christopher E. O’Connor, Dong Lai
Chemical evidence indicates that an appreciable fraction of Sun-like stars have engulfed rocky planets during their main-sequence lifetimes. We investigate whether the tidal evolution and destruction of ultra–short-period planets (USPs) can explain this phenomenon. We develop a simple parameterized model for the formation and engulfment of USPs in a population of main-sequence stars. With this model, it is possible to reproduce both the observed occurrence rate of USPs and the frequency of planet-engulfing Sun-like stars for a reasonable range of USP formation rates and tidal decay lifetimes. Our results support a theory of USP formation through gradual inward migration over many gigayears and suggest that engulfment occurs ~0.1–1 Gyr after formation. This lifetime is set by tidal dissipation in the USP itself instead of the host star, due to the perturbing influence of external companions. If USP engulfment is the main source of pollution among Sun-like stars, we predict a correlation between pollution and compact multiplanet systems; some 5%–10% of polluted stars should have a transiting planet of mass ≳ 5M⊕ and period ~4–12 days. We also predict an anticorrelation between pollution and USP occurrence.
{"title":"Metal Pollution in Sun-like Stars from Destruction of Ultra–short-period Planets","authors":"Christopher E. O’Connor, Dong Lai","doi":"10.3847/2041-8213/ada1ce","DOIUrl":"https://doi.org/10.3847/2041-8213/ada1ce","url":null,"abstract":"Chemical evidence indicates that an appreciable fraction of Sun-like stars have engulfed rocky planets during their main-sequence lifetimes. We investigate whether the tidal evolution and destruction of ultra–short-period planets (USPs) can explain this phenomenon. We develop a simple parameterized model for the formation and engulfment of USPs in a population of main-sequence stars. With this model, it is possible to reproduce both the observed occurrence rate of USPs and the frequency of planet-engulfing Sun-like stars for a reasonable range of USP formation rates and tidal decay lifetimes. Our results support a theory of USP formation through gradual inward migration over many gigayears and suggest that engulfment occurs ~0.1–1 Gyr after formation. This lifetime is set by tidal dissipation in the USP itself instead of the host star, due to the perturbing influence of external companions. If USP engulfment is the main source of pollution among Sun-like stars, we predict a correlation between pollution and compact multiplanet systems; some 5%–10% of polluted stars should have a transiting planet of mass ≳ 5<italic toggle=\"yes\">M</italic><sub>⊕</sub> and period ~4–12 days. We also predict an anticorrelation between pollution and USP occurrence.","PeriodicalId":501814,"journal":{"name":"The Astrophysical Journal Letters","volume":"14 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2025-01-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142929820","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 : 2025-01-06DOI: 10.3847/2041-8213/ad99d2
Feng Long, 凤 龙, Ilaria Pascucci, Adrien Houge, Andrea Banzatti, Klaus M. Pontoppidan, Joan Najita, Sebastiaan Krijt, Chengyan Xie, Joe Williams, Gregory J. Herczeg, 雷歌 沈, Sean M. Andrews, Edwin Bergin, Geoffrey A. Blake, María José Colmenares, Daniel Harsono, Carlos E. Romero-Mirza, Rixin Li, 日新 李, Cicero X. Lu, Paola Pinilla, David J. Wilner, Miguel Vioque, Ke Zhang and the JDISCS collaboration
We present a JWST MIRI/MRS spectrum of the inner disk of WISE J044634.16–262756.1B (hereafter J0446B), an old (∼34 Myr) M4.5 star but with hints of ongoing accretion. The spectrum is molecule-rich and dominated by hydrocarbons. We detect 14 molecular species (H2, CH3, CH4, C2H2, 13CCH2, C2H4, C2H6, C3H4, C4H2, C6H6, HCN, HC3N, CO2, and 13CO2) and two atomic lines ([Ne ii] and [Ar ii]), all observed for the first time in a disk at this age. The detection of spatially unresolved H2 and Ne gas strongly supports that J0446B hosts a long-lived primordial disk, rather than a debris disk. The marginal H2O detection and the high C2H2/CO2 column density ratio indicate that the inner disk of J0446B has a very carbon-rich chemistry, with a gas-phase C/O ratio ≳2, consistent with what has been found in most primordial disks around similarly low-mass stars. In the absence of significant outer disk dust substructures, inner disks are expected to first become water-rich due to the rapid inward drift of icy pebbles and evolve into carbon-rich as outer disk gas flows inward on longer timescales. The faint millimeter emission in such low-mass star disks implies that they may have depleted their outer icy pebble reservoir early and already passed the water-rich phase. Models with pebble drift and volatile transport suggest that maintaining a carbon-rich chemistry for tens of Myr likely requires a slowly evolving disk with α-viscosity ≲10−4. This study represents the first detailed characterization of disk gas at ∼30 Myr, strongly motivating further studies into the final stages of disk evolution.
{"title":"The First JWST View of a 30-Myr-old Protoplanetary Disk Reveals a Late-stage Carbon-rich Phase","authors":"Feng Long, 凤 龙, Ilaria Pascucci, Adrien Houge, Andrea Banzatti, Klaus M. Pontoppidan, Joan Najita, Sebastiaan Krijt, Chengyan Xie, Joe Williams, Gregory J. Herczeg, 雷歌 沈, Sean M. Andrews, Edwin Bergin, Geoffrey A. Blake, María José Colmenares, Daniel Harsono, Carlos E. Romero-Mirza, Rixin Li, 日新 李, Cicero X. Lu, Paola Pinilla, David J. Wilner, Miguel Vioque, Ke Zhang and the JDISCS collaboration","doi":"10.3847/2041-8213/ad99d2","DOIUrl":"https://doi.org/10.3847/2041-8213/ad99d2","url":null,"abstract":"We present a JWST MIRI/MRS spectrum of the inner disk of WISE J044634.16–262756.1B (hereafter J0446B), an old (∼34 Myr) M4.5 star but with hints of ongoing accretion. The spectrum is molecule-rich and dominated by hydrocarbons. We detect 14 molecular species (H2, CH3, CH4, C2H2, 13CCH2, C2H4, C2H6, C3H4, C4H2, C6H6, HCN, HC3N, CO2, and 13CO2) and two atomic lines ([Ne ii] and [Ar ii]), all observed for the first time in a disk at this age. The detection of spatially unresolved H2 and Ne gas strongly supports that J0446B hosts a long-lived primordial disk, rather than a debris disk. The marginal H2O detection and the high C2H2/CO2 column density ratio indicate that the inner disk of J0446B has a very carbon-rich chemistry, with a gas-phase C/O ratio ≳2, consistent with what has been found in most primordial disks around similarly low-mass stars. In the absence of significant outer disk dust substructures, inner disks are expected to first become water-rich due to the rapid inward drift of icy pebbles and evolve into carbon-rich as outer disk gas flows inward on longer timescales. The faint millimeter emission in such low-mass star disks implies that they may have depleted their outer icy pebble reservoir early and already passed the water-rich phase. Models with pebble drift and volatile transport suggest that maintaining a carbon-rich chemistry for tens of Myr likely requires a slowly evolving disk with α-viscosity ≲10−4. This study represents the first detailed characterization of disk gas at ∼30 Myr, strongly motivating further studies into the final stages of disk evolution.","PeriodicalId":501814,"journal":{"name":"The Astrophysical Journal Letters","volume":"7 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2025-01-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142935084","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 : 2025-01-06DOI: 10.3847/2041-8213/ad9bb2
Weijie Sun, Mitsuo Oka, Marit Øieroset, Drew L. Turner, Tai Phan, Ian J. Cohen, Xiaocan Li, Jia Huang, Andy W. Smith, James A. Slavin, Gangkai Poh, Kevin J. Genestreti, Dan Gershman, Kyunghwan Dokgo, Guan Le, Rumi Nakamura and James L. Burch
Electrons are accelerated to high, nonthermal energies during explosive energy-release events in space, such as magnetic reconnection. However, the properties and acceleration mechanisms of relativistic electrons directly associated with the reconnection X-line are not well understood. This study utilizes Magnetospheric Multiscale (MMS) measurements to analyze the flux and spectral features of subrelativistic to relativistic (∼80–560 keV) electrons during a magnetic reconnection event in Earth’s magnetotail. This event provided a unique opportunity to measure the electrons directly energized by the X-line as MMS stayed in the separatrix layer, where the magnetic field directly connects to the X-line, for approximately half of the observation period. Our analysis revealed that the fluxes of relativistic electrons were clearly enhanced within the separatrix layer, and the highest flux was directed away from the X-line, which suggested that these electrons originated directly from the X-line. Spectral analysis showed that these relativistic electrons deviated from the main plasma sheet population and exhibited an “ankle” feature similar to that observed in galactic cosmic rays. The contribution of “ankle” electrons to the total electron energy density increased from 0.1% to 1% in the separatrix layer though the spectral slopes did not exhibit clear variations. Further analysis indicated that while these relativistic electrons originated from the X-line, they experienced a nonnegligible degree of scattering during transport. These findings provide clear evidence that magnetic reconnection in Earth’s magnetotail can efficiently energize relativistic electrons directly at the X-line, providing new insights into the complex processes governing electron dynamics during magnetic reconnection.
{"title":"Relativistic Electron Acceleration and the “Ankle” Spectral Feature in Earth’s Magnetotail Reconnection","authors":"Weijie Sun, Mitsuo Oka, Marit Øieroset, Drew L. Turner, Tai Phan, Ian J. Cohen, Xiaocan Li, Jia Huang, Andy W. Smith, James A. Slavin, Gangkai Poh, Kevin J. Genestreti, Dan Gershman, Kyunghwan Dokgo, Guan Le, Rumi Nakamura and James L. Burch","doi":"10.3847/2041-8213/ad9bb2","DOIUrl":"https://doi.org/10.3847/2041-8213/ad9bb2","url":null,"abstract":"Electrons are accelerated to high, nonthermal energies during explosive energy-release events in space, such as magnetic reconnection. However, the properties and acceleration mechanisms of relativistic electrons directly associated with the reconnection X-line are not well understood. This study utilizes Magnetospheric Multiscale (MMS) measurements to analyze the flux and spectral features of subrelativistic to relativistic (∼80–560 keV) electrons during a magnetic reconnection event in Earth’s magnetotail. This event provided a unique opportunity to measure the electrons directly energized by the X-line as MMS stayed in the separatrix layer, where the magnetic field directly connects to the X-line, for approximately half of the observation period. Our analysis revealed that the fluxes of relativistic electrons were clearly enhanced within the separatrix layer, and the highest flux was directed away from the X-line, which suggested that these electrons originated directly from the X-line. Spectral analysis showed that these relativistic electrons deviated from the main plasma sheet population and exhibited an “ankle” feature similar to that observed in galactic cosmic rays. The contribution of “ankle” electrons to the total electron energy density increased from 0.1% to 1% in the separatrix layer though the spectral slopes did not exhibit clear variations. Further analysis indicated that while these relativistic electrons originated from the X-line, they experienced a nonnegligible degree of scattering during transport. These findings provide clear evidence that magnetic reconnection in Earth’s magnetotail can efficiently energize relativistic electrons directly at the X-line, providing new insights into the complex processes governing electron dynamics during magnetic reconnection.","PeriodicalId":501814,"journal":{"name":"The Astrophysical Journal Letters","volume":"76 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2025-01-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142935054","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 : 2025-01-06DOI: 10.3847/2041-8213/ada252
A. M. Matthews, W. D. Cotton, W. M. Peters, L. Marchetti, T. H. Jarrett, J. J. Condon, J. M. van der Hulst, M. Moloko
Galaxy formation theory identifies superwinds as a key regulator of star formation rates, galaxy growth, and chemical enrichment. Thermal and radiation pressure are known to drive galactic-scale winds in dusty starbursting galaxies (e.g., M82), but modern numerical simulations have recently highlighted that cosmic-ray (CR)–driven winds may be especially important in normal galaxies with modest star formation rate surface densities. However, CR-driven winds have yet to be conclusively observed—leaving significant uncertainty in their detailed microphysics. We present MeerKAT radio continuum and H i spectral-line observations of one such normal galaxy, NGC 1532; a nearby (D ~ 15 Mpc) and nearly edge-on (i ≳ 80°) spiral galaxy tidally interacting with its smaller elliptical companion, NGC 1531. We find magnetized, highly ordered radio-continuum loops extending ~10 kpc above and below the disk, visibly connecting discrete star-forming regions in the disk to the center. The deep MeerKAT H i observations place an upper limit on the column density of neutral gas coincident with the outflow of NH I ≲ 3 × 1019 cm−2. Unlike previously observed outflows—for which ejected gas and dust can be traced across multiple wavelengths—the loops in NGC 1532 show no detectable signs of dust or gas coincident with the radio emission far from the disk. We explore multiple possible mechanisms for driving this magnetic wind and favor an explanation where CR pressure plays a significant role in launching these outflows.
星系形成理论认为超风是恒星形成率、星系生长和化学富集的关键调节因素。众所周知，热压和辐射压是尘埃星爆星系（如 M82）中星系尺度风的驱动力，但现代数值模拟最近强调，宇宙射线（CR）驱动的风在恒星形成率表面密度适中的正常星系中可能尤其重要。然而，CR 驱动的风尚未被最终观测到，因此其详细的微观物理特性还存在很大的不确定性。我们展示了对这样一个正常星系--NGC 1532 的 MeerKAT 射电连续波和 H i 谱线观测结果；NGC 1532 是一个邻近（D ~ 15 Mpc）、近边缘（i ≳ 80°）的螺旋星系，与其较小的椭圆伴星系 NGC 1531 发生潮汐相互作用。我们发现磁化的、高度有序的射电连续环在圆盘上下延伸了 ~10 kpc，明显地将圆盘中离散的恒星形成区与中心连接起来。通过对 MeerKAT H i 的深度观测，中性气体柱密度的上限与 NH I ≲ 3 × 1019 cm-2 的外流相吻合。与之前观测到的外流不同，NGC 1532中的环带在远离磁盘的射电辐射中没有发现可检测到的尘埃或气体的迹象，而喷出的气体和尘埃可以在多个波长上被追踪到。我们探讨了驱动这种磁风的多种可能机制，并倾向于一种解释，即CR压力在启动这些外溢流时发挥了重要作用。
{"title":"A Galactic-scale Magnetized Wind around a Normal Star-forming Galaxy","authors":"A. M. Matthews, W. D. Cotton, W. M. Peters, L. Marchetti, T. H. Jarrett, J. J. Condon, J. M. van der Hulst, M. Moloko","doi":"10.3847/2041-8213/ada252","DOIUrl":"https://doi.org/10.3847/2041-8213/ada252","url":null,"abstract":"Galaxy formation theory identifies superwinds as a key regulator of star formation rates, galaxy growth, and chemical enrichment. Thermal and radiation pressure are known to drive galactic-scale winds in dusty starbursting galaxies (e.g., M82), but modern numerical simulations have recently highlighted that cosmic-ray (CR)–driven winds may be especially important in normal galaxies with modest star formation rate surface densities. However, CR-driven winds have yet to be conclusively observed—leaving significant uncertainty in their detailed microphysics. We present MeerKAT radio continuum and H <sc>i</sc> spectral-line observations of one such normal galaxy, NGC 1532; a nearby (<italic toggle=\"yes\">D</italic> ~ 15 Mpc) and nearly edge-on (<italic toggle=\"yes\">i</italic> ≳ 80°) spiral galaxy tidally interacting with its smaller elliptical companion, NGC 1531. We find magnetized, highly ordered radio-continuum loops extending ~10 kpc above and below the disk, visibly connecting discrete star-forming regions in the disk to the center. The deep MeerKAT H <sc>i</sc> observations place an upper limit on the column density of neutral gas coincident with the outflow of <italic toggle=\"yes\">N</italic><sub>H I</sub> ≲ 3 × 10<sup>19</sup> cm<sup>−2</sup>. Unlike previously observed outflows—for which ejected gas and dust can be traced across multiple wavelengths—the loops in NGC 1532 show no detectable signs of dust or gas coincident with the radio emission far from the disk. We explore multiple possible mechanisms for driving this magnetic wind and favor an explanation where CR pressure plays a significant role in launching these outflows.","PeriodicalId":501814,"journal":{"name":"The Astrophysical Journal Letters","volume":"1 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2025-01-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142929822","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 : 2025-01-06DOI: 10.3847/2041-8213/ad99d3
Gabriella Agazie, Akash Anumarlapudi, Anne M. Archibald, Zaven Arzoumanian, Jeremy G. Baier, Paul T. Baker, Bence Bécsy, Laura Blecha, Adam Brazier, Paul R. Brook, Sarah Burke-Spolaor, J. Andrew Casey-Clyde, Maria Charisi, Shami Chatterjee, Tyler Cohen, James M. Cordes, Neil J. Cornish, Fronefield Crawford, H. Thankful Cromartie, Kathryn Crowter, Megan E. DeCesar, Paul B. Demorest, Heling Deng, Lankeswar Dey, Timothy Dolch, David Esmyol, Elizabeth C. Ferrara, William Fiore, Emmanuel Fonseca, Gabriel E. Freedman, Emiko C. Gardiner, Nate Garver-Daniels, Peter A. Gentile, Kyle A. Gersbach, Joseph Glaser, Deborah C. Good, Kayhan Gültekin, Jeffrey S. Hazboun, Ross J. Jennings, Aaron D. Johnson, Megan L. Jones, David L. Kaplan, Luke Zoltan Kelley, Matthew Kerr, Joey S. Key, Nima Laal, Michael T. Lam, William G. Lamb, Bjorn Larsen, T. Joseph W. Lazio, Natalia Lewandowska, Rafael R. Lino dos Santos, Tingting Liu, Duncan R. Lorimer, Jing Luo, Ryan S. Lynch, Chung-Pei Ma, Dustin R. Mad..
The NANOGrav 15 yr data provide compelling evidence for a stochastic gravitational-wave (GW) background at nanohertz frequencies. The simplest model-independent approach to characterizing the frequency spectrum of this signal consists of a simple power-law fit involving two parameters: an amplitude A and a spectral index γ. In this Letter, we consider the next logical step beyond this minimal spectral model, allowing for a running (i.e., logarithmic frequency dependence) of the spectral index, . We fit this running-power-law (RPL) model to the NANOGrav 15 yr data and perform a Bayesian model comparison with the minimal constant-power-law (CPL) model, which results in a 95% credible interval for the parameter β consistent with no running, , and an inconclusive Bayes factor, . We thus conclude that, at present, the minimal CPL model still suffices to adequately describe the NANOGrav signal; however, future data sets may well lead to a measurement of nonzero β. Finally, we interpret the RPL model as a description of primordial GWs generated during cosmic inflation, which allows us to combine our results with upper limits from Big Bang nucleosynthesis, the cosmic microwave background, and LIGO–Virgo–KAGRA.
{"title":"The NANOGrav 15 yr Data Set: Running of the Spectral Index","authors":"Gabriella Agazie, Akash Anumarlapudi, Anne M. Archibald, Zaven Arzoumanian, Jeremy G. Baier, Paul T. Baker, Bence Bécsy, Laura Blecha, Adam Brazier, Paul R. Brook, Sarah Burke-Spolaor, J. Andrew Casey-Clyde, Maria Charisi, Shami Chatterjee, Tyler Cohen, James M. Cordes, Neil J. Cornish, Fronefield Crawford, H. Thankful Cromartie, Kathryn Crowter, Megan E. DeCesar, Paul B. Demorest, Heling Deng, Lankeswar Dey, Timothy Dolch, David Esmyol, Elizabeth C. Ferrara, William Fiore, Emmanuel Fonseca, Gabriel E. Freedman, Emiko C. Gardiner, Nate Garver-Daniels, Peter A. Gentile, Kyle A. Gersbach, Joseph Glaser, Deborah C. Good, Kayhan Gültekin, Jeffrey S. Hazboun, Ross J. Jennings, Aaron D. Johnson, Megan L. Jones, David L. Kaplan, Luke Zoltan Kelley, Matthew Kerr, Joey S. Key, Nima Laal, Michael T. Lam, William G. Lamb, Bjorn Larsen, T. Joseph W. Lazio, Natalia Lewandowska, Rafael R. Lino dos Santos, Tingting Liu, Duncan R. Lorimer, Jing Luo, Ryan S. Lynch, Chung-Pei Ma, Dustin R. Mad..","doi":"10.3847/2041-8213/ad99d3","DOIUrl":"https://doi.org/10.3847/2041-8213/ad99d3","url":null,"abstract":"The NANOGrav 15 yr data provide compelling evidence for a stochastic gravitational-wave (GW) background at nanohertz frequencies. The simplest model-independent approach to characterizing the frequency spectrum of this signal consists of a simple power-law fit involving two parameters: an amplitude A and a spectral index γ. In this Letter, we consider the next logical step beyond this minimal spectral model, allowing for a running (i.e., logarithmic frequency dependence) of the spectral index, . We fit this running-power-law (RPL) model to the NANOGrav 15 yr data and perform a Bayesian model comparison with the minimal constant-power-law (CPL) model, which results in a 95% credible interval for the parameter β consistent with no running, , and an inconclusive Bayes factor, . We thus conclude that, at present, the minimal CPL model still suffices to adequately describe the NANOGrav signal; however, future data sets may well lead to a measurement of nonzero β. Finally, we interpret the RPL model as a description of primordial GWs generated during cosmic inflation, which allows us to combine our results with upper limits from Big Bang nucleosynthesis, the cosmic microwave background, and LIGO–Virgo–KAGRA.","PeriodicalId":501814,"journal":{"name":"The Astrophysical Journal Letters","volume":"76 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2025-01-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142935047","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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