Pub Date : 2026-01-12DOI: 10.1051/0004-6361/202557588
Martin W. Ochmann, Edward M. Cackett, Lukas Diehl, Keith Horne, Malte A. Probst, Wolfram Kollatschny
Context. Reverberation mapping (RM) is a powerful tool to determine the extent, structure, and kinematics of the broad-line region (BLR) of active galactic nuclei (AGNs). So far, RM of the BLR has only been performed for recombination lines responding to the varying ionizing continuum.Aims. We tested whether O I λ8446, attributed to Bowen fluorescence driven by Lyβ pumping, varied on short (day- to week-long) timescales during a 2016 Hubble Space Telescope/Space Telescope Imaging Spectrograph (HST/STIS) campaign of NGC 4593, and examined how it relates to other emission lines and the ionizing UV continuum.Methods. We quantified the variability of O I λ8446 by its root-mean-square (rms) amplitude. We then extracted integrated light curves of O I λ8446 and other UV and optical emission lines, and compared them with each other and the UV continuum light curve using correlation analyses. In addition, we used archival near-infrared spectra to assess the dominant excitation mechanism of O I λ8446.Results. We detect, for the first time, variability in O I λ8446 on day timescales. The fractional rms amplitude is ∼4% over the 4-week campaign. The O I λ8446 light curve reverberates with a delay of ∼2.5 days relative to Lyα, used as a proxy for Lyβ, detected at a false-alarm probability of 0.6% (significance of ∼2.8σ) under our adopted null hypothesis. It closely tracks Hα with only a minor additional delay of ∼0.3 days, placing its emission region at essentially the same distance as the Balmer-line weighted BLR. Line ratios indicate that Lyβ pumping is the dominant excitation mechanism for O I λ8446.Conclusions. Our results establish O I λ8446 as the first Bowen fluorescence line to be reverberation-mapped, responding directly to variations in the Lyβ flux. We propose that in future campaigns targeting AGNs with larger BLRs, O I could enable dual-driver RM using both the continuum and the pumping line as drivers.
上下文。混响映射（RM）是确定活动星系核（agn）宽线区域（BLR）的范围、结构和运动学的有力工具。到目前为止，BLR的RM只对响应不同电离连续体的重组谱线进行了研究。在2016年哈勃太空望远镜/太空望远镜成像光谱仪（HST/STIS）对NGC 4593的观测中，我们测试了O I λ8446是否在短时间（一天到一周）内发生变化，并研究了它与其他发射线和电离紫外线连续体的关系。我们通过其均方根（rms）振幅量化了O I λ8446的变异性。然后提取O I λ8446和其他紫外和光学发射线的积分光曲线，并利用相关分析将它们与紫外连续光曲线进行比较。此外，我们利用档案近红外光谱分析了O I λ8446的主要激发机制。我们首次探测到O I λ8446在日时间尺度上的变化。在4周的活动中，分数均方根振幅为~ 4%。O I λ8446光曲线相对于Lyα的反射延迟为~ 2.5天，用作Lyβ的代表，在我们采用的零假设下检测到0.6%的假警报概率（显著性为~ 2.8σ）。它密切跟踪Hα，只有0.3天的微小延迟，使其发射区域与巴尔默线加权BLR的距离基本相同。线比表明，Lyβ泵送是O I λ8446的主要激励机制。我们的结果确定O I λ8446是第一个被混响映射的Bowen荧光线，直接响应Lyβ通量的变化。我们建议，在未来针对具有更大blr的agn的活动中，O I可以使用连续体和泵送管线作为驱动器来启用双驱动器RM。
{"title":"First reverberation mapping of a Bowen fluorescence line","authors":"Martin W. Ochmann, Edward M. Cackett, Lukas Diehl, Keith Horne, Malte A. Probst, Wolfram Kollatschny","doi":"10.1051/0004-6361/202557588","DOIUrl":"https://doi.org/10.1051/0004-6361/202557588","url":null,"abstract":"<i>Context.<i/> Reverberation mapping (RM) is a powerful tool to determine the extent, structure, and kinematics of the broad-line region (BLR) of active galactic nuclei (AGNs). So far, RM of the BLR has only been performed for recombination lines responding to the varying ionizing continuum.<i>Aims.<i/> We tested whether O I <i>λ<i/>8446, attributed to Bowen fluorescence driven by Ly<i>β<i/> pumping, varied on short (day- to week-long) timescales during a 2016 Hubble Space Telescope/Space Telescope Imaging Spectrograph (HST/STIS) campaign of NGC 4593, and examined how it relates to other emission lines and the ionizing UV continuum.<i>Methods.<i/> We quantified the variability of O I <i>λ<i/>8446 by its root-mean-square (rms) amplitude. We then extracted integrated light curves of O I <i>λ<i/>8446 and other UV and optical emission lines, and compared them with each other and the UV continuum light curve using correlation analyses. In addition, we used archival near-infrared spectra to assess the dominant excitation mechanism of O I <i>λ<i/>8446.<i>Results.<i/> We detect, for the first time, variability in O I <i>λ<i/>8446 on day timescales. The fractional rms amplitude is ∼4% over the 4-week campaign. The O I <i>λ<i/>8446 light curve reverberates with a delay of ∼2.5 days relative to Ly<i>α<i/>, used as a proxy for Ly<i>β<i/>, detected at a false-alarm probability of 0.6% (significance of ∼2.8<i>σ<i/>) under our adopted null hypothesis. It closely tracks H<i>α<i/> with only a minor additional delay of ∼0.3 days, placing its emission region at essentially the same distance as the Balmer-line weighted BLR. Line ratios indicate that Ly<i>β<i/> pumping is the dominant excitation mechanism for O I <i>λ<i/>8446.<i>Conclusions.<i/> Our results establish O I <i>λ<i/>8446 as the first Bowen fluorescence line to be reverberation-mapped, responding directly to variations in the Ly<i>β<i/> flux. We propose that in future campaigns targeting AGNs with larger BLRs, O I could enable dual-driver RM using both the continuum and the pumping line as drivers.","PeriodicalId":8571,"journal":{"name":"Astronomy & Astrophysics","volume":"81 1","pages":"L11"},"PeriodicalIF":6.5,"publicationDate":"2026-01-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145956525","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2026-01-09DOI: 10.1051/0004-6361/202558391
Ana Mitrašinović, Marko Grozdanović, Ana Lalović, Milena Jovanović, Michal Bílek, Nataša Pavlov, Alexei V. Moiseev, Dmitry V. Oparin
The search for “dark galaxies”, a key prediction of the lambda cold dark matter, has yielded few viable candidates. Recently, FAST J0139+4328 was reported as the first isolated dark galaxy in the nearby universe, based on a neutral hydrogen (HI) detection and a non-detection in the Pan-STARRS1 survey. To verify the nature of this candidate, we obtained deep optical imaging, using the 1.4 m Milanković and 0.6 m Nedeljković telescopes, and spectroscopic follow-up of the field. We report the unambiguous discovery of a low-surface-brightness (LSB) optical counterpart at the location of the HI cloud. Furthermore, the detection of Hα emission via the 6 m Big Telescope Alt-Azimuthal (BTA) confirms that the stellar system lies at a redshift consistent with the HI source, establishing their physical association. Through detailed photometry and employing color-dependent mass-to-light scaling relations, we derive a total stellar mass of M★ = (7.2 ± 3.7)×106M⊙, about an order of magnitude higher than the previously estimated upper limit. Using the literature HI mass, this implies a gas-to-stellar mass ratio of MHI/M★ = 11.5 ± 6.4. Our findings demonstrate that FAST J0139+4328 is not a dark galaxy but an extremely gas-rich LSB dwarf galaxy, whose stellar component was simply below the detection limit of the Pan-STARRS1 survey. This reclassification resolves the status of this prominent dark galaxy candidate and underscores the necessity of deep optical follow-up to classify faint HI-selected systems.
寻找“暗星系”，这是λ冷暗物质的一个关键预测，但几乎没有找到可行的候选星系。最近，FAST J0139+4328被报道为附近宇宙中第一个孤立的暗星系，基于中性氢（HI）探测和Pan-STARRS1调查中的非探测。为了验证这一候选天体的性质，我们使用1.4 m milankovovic和0.6 m nedeljkovovic望远镜获得了深度光学成像，并对该区域进行了光谱跟踪。我们报告在HI云的位置明确发现了低表面亮度（LSB）光学对应物。此外，通过6米大望远镜（BTA）探测到的Hα发射证实了恒星系统与HI源的红移一致，建立了它们的物理联系。通过详细的光度测定和使用与颜色相关的质量-光比例关系，我们得出了M★=（7.2±3.7）×106 M⊙的总恒星质量，比先前估计的上限高出一个数量级。根据文献HI质量，这意味着气体与恒星的质量比为MHI/M★= 11.5±6.4。我们的发现表明FAST J0139+4328不是一个黑暗星系，而是一个极度富含气体的LSB矮星系，其恒星成分低于Pan-STARRS1调查的检测极限。这种重新分类解决了这个突出的暗星系候选者的地位，并强调了对微弱的hi选择系统进行深度光学跟踪的必要性。
{"title":"Discovery of a galaxy associated with the HI cloud FAST J0139+4328","authors":"Ana Mitrašinović, Marko Grozdanović, Ana Lalović, Milena Jovanović, Michal Bílek, Nataša Pavlov, Alexei V. Moiseev, Dmitry V. Oparin","doi":"10.1051/0004-6361/202558391","DOIUrl":"https://doi.org/10.1051/0004-6361/202558391","url":null,"abstract":"The search for “dark galaxies”, a key prediction of the lambda cold dark matter, has yielded few viable candidates. Recently, FAST J0139+4328 was reported as the first isolated dark galaxy in the nearby universe, based on a neutral hydrogen (HI) detection and a non-detection in the Pan-STARRS1 survey. To verify the nature of this candidate, we obtained deep optical imaging, using the 1.4 m <i>Milanković<i/> and 0.6 m <i>Nedeljković<i/> telescopes, and spectroscopic follow-up of the field. We report the unambiguous discovery of a low-surface-brightness (LSB) optical counterpart at the location of the HI cloud. Furthermore, the detection of H<i>α<i/> emission via the 6 m Big Telescope Alt-Azimuthal (BTA) confirms that the stellar system lies at a redshift consistent with the HI source, establishing their physical association. Through detailed photometry and employing color-dependent mass-to-light scaling relations, we derive a total stellar mass of <i>M<i/><sub>★<sub/> = (7.2 ± 3.7)×10<sup>6<sup/> <i>M<i/><sub>⊙<sub/>, about an order of magnitude higher than the previously estimated upper limit. Using the literature HI mass, this implies a gas-to-stellar mass ratio of <i>M<i/><sub>HI<sub/>/<i>M<i/><sub>★<sub/> = 11.5 ± 6.4. Our findings demonstrate that FAST J0139+4328 is not a dark galaxy but an extremely gas-rich LSB dwarf galaxy, whose stellar component was simply below the detection limit of the Pan-STARRS1 survey. This reclassification resolves the status of this prominent dark galaxy candidate and underscores the necessity of deep optical follow-up to classify faint HI-selected systems.","PeriodicalId":8571,"journal":{"name":"Astronomy & Astrophysics","volume":"12 1","pages":""},"PeriodicalIF":6.5,"publicationDate":"2026-01-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145920087","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2026-01-09DOI: 10.1051/0004-6361/202557621
József M. Benkő
Context. Recent studies have shown that the irregular O−C variations observed in many non-Blazhko RR Lyrae stars may result from random, cycle-to-cycle (C2C) variations in their light curves. However, centuries-long data series reveal that the O−C diagrams of Blazhko stars exhibit particularly large-amplitude, irregular variations.Aims. In this letter, we extend the previous investigation of non-Blazhko stars to Kepler Blazhko stars to explore the role of C2C variations in the O−C diagrams.Methods. We derived the O−C diagrams from Kepler space telescope light curves using a precise template-fitting method. Based on their Fourier analyses, we also constructed residual O−C diagrams that were pre-whitened for frequencies associated with the Blazhko effect. We then fitted the same statistical models to both types of O−Cs that we had previously applied to non-Blazhko stars.Results. The optimal statistical model includes the C2C variation for 74% of the O−C curves in our Blazhko sample, and the parameter describing the strength of the C2C variation is significantly larger than that obtained for non-Blazhko stars. This may explain the strong irregular O−C variations previously observed in Blazhko stars. Furthermore, we found a strong positive correlation between the C2C variation strength and the amplitude of the frequency-modulation component of the Blazhko effect, indicating a connection between the two phenomena.
{"title":"Connections between the cycle-to-cycle light curve and O−C variations of the Blazhko RR Lyrae stars","authors":"József M. Benkő","doi":"10.1051/0004-6361/202557621","DOIUrl":"https://doi.org/10.1051/0004-6361/202557621","url":null,"abstract":"<i>Context.<i/> Recent studies have shown that the irregular O−C variations observed in many non-Blazhko RR Lyrae stars may result from random, cycle-to-cycle (C2C) variations in their light curves. However, centuries-long data series reveal that the O−C diagrams of Blazhko stars exhibit particularly large-amplitude, irregular variations.<i>Aims.<i/> In this letter, we extend the previous investigation of non-Blazhko stars to <i>Kepler<i/> Blazhko stars to explore the role of C2C variations in the O−C diagrams.<i>Methods.<i/> We derived the O−C diagrams from <i>Kepler<i/> space telescope light curves using a precise template-fitting method. Based on their Fourier analyses, we also constructed residual O−C diagrams that were pre-whitened for frequencies associated with the Blazhko effect. We then fitted the same statistical models to both types of O−Cs that we had previously applied to non-Blazhko stars.<i>Results.<i/> The optimal statistical model includes the C2C variation for 74% of the O−C curves in our Blazhko sample, and the parameter describing the strength of the C2C variation is significantly larger than that obtained for non-Blazhko stars. This may explain the strong irregular O−C variations previously observed in Blazhko stars. Furthermore, we found a strong positive correlation between the C2C variation strength and the amplitude of the frequency-modulation component of the Blazhko effect, indicating a connection between the two phenomena.","PeriodicalId":8571,"journal":{"name":"Astronomy & Astrophysics","volume":"131 1","pages":""},"PeriodicalIF":6.5,"publicationDate":"2026-01-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145920088","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2026-01-08DOI: 10.1051/0004-6361/202557600
S. Boula, A. Mastichiadis, D. Kazanas
Blazars, a subclass of radio-loud active galactic nuclei with relativistic jets aligned close to our line of sight, emit highly variable nonthermal radiation across the electromagnetic spectrum. The physical origin of their emission and the blazar sequence remain open questions. We present a self-consistent two-zone leptonic model in which relativistic electrons accelerate in a compact region, losing energy via synchrotron and inverse Compton processes, and escape into a larger zone permeated by an external photon field associated with magnetohydrodynamic winds from the accretion disk. By varying only the mass accretion rate onto the central black hole, the model naturally reproduces the blazar sequence, including Compton dominance, γ-ray spectral indices, and the positions of synchrotron and inverse Compton peaks, while variations in the secondary parameters account for the observed spread in the data. Flat-spectrum radio quasars exhibit strong external Compton emission from the extended zone, whereas BL Lac objects are dominated by synchrotron and synchrotron self-Compton emission from the compact acceleration region. This framework highlights the key role of accretion rate and spatially structured emission zones in shaping blazar spectra and provides a unified interpretation of their diverse phenomenology.
{"title":"A one-parameter two-zone leptonic model for the blazar sequence","authors":"S. Boula, A. Mastichiadis, D. Kazanas","doi":"10.1051/0004-6361/202557600","DOIUrl":"https://doi.org/10.1051/0004-6361/202557600","url":null,"abstract":"Blazars, a subclass of radio-loud active galactic nuclei with relativistic jets aligned close to our line of sight, emit highly variable nonthermal radiation across the electromagnetic spectrum. The physical origin of their emission and the blazar sequence remain open questions. We present a self-consistent two-zone leptonic model in which relativistic electrons accelerate in a compact region, losing energy via synchrotron and inverse Compton processes, and escape into a larger zone permeated by an external photon field associated with magnetohydrodynamic winds from the accretion disk. By varying only the mass accretion rate onto the central black hole, the model naturally reproduces the blazar sequence, including Compton dominance, <i>γ<i/>-ray spectral indices, and the positions of synchrotron and inverse Compton peaks, while variations in the secondary parameters account for the observed spread in the data. Flat-spectrum radio quasars exhibit strong external Compton emission from the extended zone, whereas BL Lac objects are dominated by synchrotron and synchrotron self-Compton emission from the compact acceleration region. This framework highlights the key role of accretion rate and spatially structured emission zones in shaping blazar spectra and provides a unified interpretation of their diverse phenomenology.","PeriodicalId":8571,"journal":{"name":"Astronomy & Astrophysics","volume":"3 1","pages":""},"PeriodicalIF":6.5,"publicationDate":"2026-01-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145920089","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2026-01-08DOI: 10.1051/0004-6361/202557202
Leandro Abaroa, Gustavo E. Romero, Valentí Bosch-Ramon
The Large High Altitude Air Shower Observatory (LHAASO) has revealed numerous ultrahigh-energy gamma-ray sources of unknown origin. We propose that a fraction of them can be explained by microquasar remnants, i.e., binary systems where mass transfer has ceased and the central engine is quenched. Cosmic rays injected during the active phase of a microquasar may remain confined within its cocoon and subsequently interact with nearby molecular clouds, producing bright gamma-ray emission through pp collisions. Remnants of former super-Eddington systems can act as dark PeVatrons, releasing particles up to ∼10 PeV that illuminate surrounding clouds producing gamma rays reaching hundreds of tera-electron volts. This scenario provides a natural explanation for several unidentified Galactic LHAASO sources.
{"title":"Microquasar remnants as hidden PeVatrons","authors":"Leandro Abaroa, Gustavo E. Romero, Valentí Bosch-Ramon","doi":"10.1051/0004-6361/202557202","DOIUrl":"https://doi.org/10.1051/0004-6361/202557202","url":null,"abstract":"The Large High Altitude Air Shower Observatory (LHAASO) has revealed numerous ultrahigh-energy gamma-ray sources of unknown origin. We propose that a fraction of them can be explained by microquasar remnants, i.e., binary systems where mass transfer has ceased and the central engine is quenched. Cosmic rays injected during the active phase of a microquasar may remain confined within its cocoon and subsequently interact with nearby molecular clouds, producing bright gamma-ray emission through <i>pp<i/> collisions. Remnants of former super-Eddington systems can act as dark PeVatrons, releasing particles up to ∼10 PeV that illuminate surrounding clouds producing gamma rays reaching hundreds of tera-electron volts. This scenario provides a natural explanation for several unidentified Galactic LHAASO sources.","PeriodicalId":8571,"journal":{"name":"Astronomy & Astrophysics","volume":"393 1","pages":""},"PeriodicalIF":6.5,"publicationDate":"2026-01-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145920090","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2026-01-07DOI: 10.1051/0004-6361/202557112
S. Anoardo, A. Mucciarelli, M. Palla, L. Santarelli, C. Lardo, D. Romano
In this study we investigate the chemical enrichment of the rapid neutron-capture process in the Small Magellanic Cloud (SMC). We measured the [Eu/Fe] abundance ratio of 209 giant stars that are confirmed members of the SMC, providing the first extensive dataset of Eu abundances in this galaxy across its full metallicity range, spanning more than 1.5 dex. We compared the Eu abundances with those of Mg and Ba to evaluate the efficiency of the r-process relative to α-capture and s-process nucleosynthesis. The SMC shows enhanced [Eu/Fe] values at all metallicities (comparable with the values measured in the Milky Way) and a clear decline as [Fe/H] increases (from approximately −1.75 dex to approximately −0.5 dex), which is consistent with the onset of Type Ia supernovae. In contrast, [Eu/Mg] is enhanced by about +0.5 dex at all [Fe/H] and thus significantly above the values observed in Milky Way stars, where [Eu/Mg] remains close to the solar value, reflecting comparable production of r-process and α-capture elements. Moreover, [Ba/Eu] increases with metallicity beginning at [Fe/H] ≈ −1.5 dex, namely at a lower metallicity with respect to the Milky Way, where [Ba/Eu] starts to increase around [Fe/H] ≈ −1 dex. Our findings suggest the SMC has a higher production of Eu (with respect to the α-elements) than the Milky Way, but it is still in line with what has been observed in other dwarf systems within the Local Group. We confirm that galaxies with star formation efficiencies lower than the Milky Way have a high [Eu/α], probably indicating stronger efficiency of the delayed sources of the r-process at low metallicities.
{"title":"The chemical DNA of the Magellanic Clouds","authors":"S. Anoardo, A. Mucciarelli, M. Palla, L. Santarelli, C. Lardo, D. Romano","doi":"10.1051/0004-6361/202557112","DOIUrl":"https://doi.org/10.1051/0004-6361/202557112","url":null,"abstract":"In this study we investigate the chemical enrichment of the rapid neutron-capture process in the Small Magellanic Cloud (SMC). We measured the [Eu/Fe] abundance ratio of 209 giant stars that are confirmed members of the SMC, providing the first extensive dataset of Eu abundances in this galaxy across its full metallicity range, spanning more than 1.5 dex. We compared the Eu abundances with those of Mg and Ba to evaluate the efficiency of the <i>r<i/>-process relative to α-capture and <i>s<i/>-process nucleosynthesis. The SMC shows enhanced [Eu/Fe] values at all metallicities (comparable with the values measured in the Milky Way) and a clear decline as [Fe/H] increases (from approximately −1.75 dex to approximately −0.5 dex), which is consistent with the onset of Type Ia supernovae. In contrast, [Eu/Mg] is enhanced by about +0.5 dex at all [Fe/H] and thus significantly above the values observed in Milky Way stars, where [Eu/Mg] remains close to the solar value, reflecting comparable production of <i>r<i/>-process and α-capture elements. Moreover, [Ba/Eu] increases with metallicity beginning at [Fe/H] ≈ −1.5 dex, namely at a lower metallicity with respect to the Milky Way, where [Ba/Eu] starts to increase around [Fe/H] ≈ −1 dex. Our findings suggest the SMC has a higher production of Eu (with respect to the α-elements) than the Milky Way, but it is still in line with what has been observed in other dwarf systems within the Local Group. We confirm that galaxies with star formation efficiencies lower than the Milky Way have a high [Eu/α], probably indicating stronger efficiency of the delayed sources of the <i>r<i/>-process at low metallicities.","PeriodicalId":8571,"journal":{"name":"Astronomy & Astrophysics","volume":"47 1","pages":""},"PeriodicalIF":6.5,"publicationDate":"2026-01-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145920086","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2026-01-06DOI: 10.1051/0004-6361/202554592
Kai Lehman, Nico Schuster, Luisa Lucie-Smith, Nico Hamaus, Christopher T. Davies, Klaus Dolag
Context. Cosmic voids are a promising probe of cosmology for spectroscopic galaxy surveys due to their unique response to cosmological parameters. Their combination with other probes promises to break parameter degeneracies.Aims. Due to simplifying assumptions, analytical models for void statistics represent only a subset of the full void population. We present a set of neural-based emulators for void summary statistics of watershed voids, which retain more information about the full void population than simplified analytical models.Methods. We built emulators for the void size function and void density profiles traced by the halo number density using the QUIJOTE suite of simulations that spans a wide range of the Λ cold dark matter (ΛCDM) parameter space. The emulators replace the computation of these statistics from computationally expensive cosmological simulations. We demonstrate the cosmological constraining power of voids using our emulators, which offer orders-of-magnitude acceleration in parameter estimation, capture more cosmological information compared to analytical models, and produce more realistic posteriors compared to Fisher forecasts.Results. In this QUIJOTE setup, we recover the parameters Ωm and σ8 to within 14.4% and 8.4% accuracy, respectively, using void density profiles. Incorporating additional information from the void size function improves the accuracy for σ8 to 6.8%. We demonstrate the robustness of our approach with respect to two important variables in the underlying simulations: the resolution and the inclusion of baryons. We find that our pipeline is robust to variations in resolution, and we show that the posteriors derived from the emulated void statistics are unaffected by the inclusion of baryons in the Magneticum hydrodynamic simulations. This opens up the possibility of a baryon-independent probe of the large-scale structure.
{"title":"Cosmological inference with cosmic voids and neural network emulators","authors":"Kai Lehman, Nico Schuster, Luisa Lucie-Smith, Nico Hamaus, Christopher T. Davies, Klaus Dolag","doi":"10.1051/0004-6361/202554592","DOIUrl":"https://doi.org/10.1051/0004-6361/202554592","url":null,"abstract":"<i>Context.<i/> Cosmic voids are a promising probe of cosmology for spectroscopic galaxy surveys due to their unique response to cosmological parameters. Their combination with other probes promises to break parameter degeneracies.<i>Aims.<i/> Due to simplifying assumptions, analytical models for void statistics represent only a subset of the full void population. We present a set of neural-based emulators for void summary statistics of watershed voids, which retain more information about the full void population than simplified analytical models.<i>Methods.<i/> We built emulators for the void size function and void density profiles traced by the halo number density using the QUIJOTE suite of simulations that spans a wide range of the Λ cold dark matter (ΛCDM) parameter space. The emulators replace the computation of these statistics from computationally expensive cosmological simulations. We demonstrate the cosmological constraining power of voids using our emulators, which offer orders-of-magnitude acceleration in parameter estimation, capture more cosmological information compared to analytical models, and produce more realistic posteriors compared to Fisher forecasts.<i>Results.<i/> In this QUIJOTE setup, we recover the parameters Ω<sub>m<sub/> and <i>σ<i/><sub>8<sub/> to within 14.4% and 8.4% accuracy, respectively, using void density profiles. Incorporating additional information from the void size function improves the accuracy for <i>σ<i/><sub>8<sub/> to 6.8%. We demonstrate the robustness of our approach with respect to two important variables in the underlying simulations: the resolution and the inclusion of baryons. We find that our pipeline is robust to variations in resolution, and we show that the posteriors derived from the emulated void statistics are unaffected by the inclusion of baryons in the Magneticum hydrodynamic simulations. This opens up the possibility of a baryon-independent probe of the large-scale structure.","PeriodicalId":8571,"journal":{"name":"Astronomy & Astrophysics","volume":"2 1","pages":""},"PeriodicalIF":6.5,"publicationDate":"2026-01-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145908416","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2026-01-06DOI: 10.1051/0004-6361/202555714
Wen-Han Zhou, Yun Zhang, Jiamu Huang, Douglas N. C. Lin
Context. Sgr A★, the supermassive black hole at the center of the Milky Way, exhibits frequent short-duration flares (e.g., with luminosity > 1034 erg s−1) across multiple wavelengths. The origin of the flares is still unknown.Aims. We revisited the role of small planetary bodies, originally from the stellar disk, and their tidally disrupted fragments as a source of flaring activity in Sgr A★. In particular, we refined previous models by incorporating material strength constraints on the tidal disruption limit and by evaluating the evaporation dynamics of the resulting fragments.Methods. We analyzed the tidal fragmentation and gas-induced fragmentation of small planetary bodies with rubble-pile and monolithic structures. Using constraints from recent space missions (e.g., NASA’s OSIRIS-REx and JAXA’s Hayabusa2 missions), we estimated the survivability of fragments under aerodynamic heating and computed their expected luminosity from ablation, modeled as fireball flares analogous to meteor events.Results. We find that planetary fragments can approach as close as 8 R• due to material strength, where R• denotes the gravitational radius consistent with flare locations inferred from observations. The fireball model yields luminosities from 1034 to 1036 erg/s for fragments whose parent bodies are a few kilometers in size. The derived flare frequency–luminosity distribution follows a power law with the power index 1.83, in agreement with observed values (1.65–1.9), while the flare duration scales as tf ∝ L−1/3, consistent with observational constraints. We considered the discovered young stars around Sgr A★ as the planetary reservoir. Given a small-body population analogous in mass to the primordial Kuiper belt and the common existence of close-in super-Earths as well as long-period Neptunes, we show that this planetary reservoir can provide an adequate supply for the observed flares.Conclusions. The tidal disruption and thermal evaporation of small bodies offer a plausible explanation for the observed flare properties of Sgr A★.
{"title":"Tidal disruption and evaporation of rubble-pile and monolithic bodies as a source of flaring activity in Sgr A★","authors":"Wen-Han Zhou, Yun Zhang, Jiamu Huang, Douglas N. C. Lin","doi":"10.1051/0004-6361/202555714","DOIUrl":"https://doi.org/10.1051/0004-6361/202555714","url":null,"abstract":"<i>Context.<i/> Sgr A<sup>★<sup/>, the supermassive black hole at the center of the Milky Way, exhibits frequent short-duration flares (e.g., with luminosity > 10<sup>34<sup/> erg s<sup>−1<sup/>) across multiple wavelengths. The origin of the flares is still unknown.<i>Aims.<i/> We revisited the role of small planetary bodies, originally from the stellar disk, and their tidally disrupted fragments as a source of flaring activity in Sgr A<sup>★<sup/>. In particular, we refined previous models by incorporating material strength constraints on the tidal disruption limit and by evaluating the evaporation dynamics of the resulting fragments.<i>Methods.<i/> We analyzed the tidal fragmentation and gas-induced fragmentation of small planetary bodies with rubble-pile and monolithic structures. Using constraints from recent space missions (e.g., NASA’s OSIRIS-REx and JAXA’s Hayabusa2 missions), we estimated the survivability of fragments under aerodynamic heating and computed their expected luminosity from ablation, modeled as fireball flares analogous to meteor events.<i>Results.<i/> We find that planetary fragments can approach as close as 8 <i>R<i/><sub>•<sub/> due to material strength, where <i>R<i/><sub>•<sub/> denotes the gravitational radius consistent with flare locations inferred from observations. The fireball model yields luminosities from 10<sup>34<sup/> to 10<sup>36<sup/> erg/s for fragments whose parent bodies are a few kilometers in size. The derived flare frequency–luminosity distribution follows a power law with the power index 1.83, in agreement with observed values (1.65–1.9), while the flare duration scales as <i>t<i/><sub>f<sub/> ∝ <i>L<i/><sup>−1/3<sup/>, consistent with observational constraints. We considered the discovered young stars around Sgr A<sup>★<sup/> as the planetary reservoir. Given a small-body population analogous in mass to the primordial Kuiper belt and the common existence of close-in super-Earths as well as long-period Neptunes, we show that this planetary reservoir can provide an adequate supply for the observed flares.<i>Conclusions.<i/> The tidal disruption and thermal evaporation of small bodies offer a plausible explanation for the observed flare properties of Sgr A<sup>★<sup/>.","PeriodicalId":8571,"journal":{"name":"Astronomy & Astrophysics","volume":"18 1","pages":""},"PeriodicalIF":6.5,"publicationDate":"2026-01-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145908414","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-12-24DOI: 10.1051/0004-6361/202555216
Gabriella Di Genova, Nadia Balucani, Luca Mancini, Andrea Giustini, Marzio Rosi, Dimitrios Skouteris, Cecilia Ceccarelli
Context. Dimethyl sulfide (DMS; CH3 SCH3) is an organosulfur compound that has been suggested as a potential biosignature in exoplanetary atmospheres. In addition to its tentative detections toward the sub-Neptune planet K2-18b, DMS has been detected in the coma of the 67/P comet and toward the galactic-center molecular cloud G+0.693-0.027. However, its formation routes have not been characterized yet.Aims. In this work, we aim to investigate five gas-phase reactions (the ion-molecule reactions CH3SH + CH3SH2+, CH3OH + CH3SH2+, CH3SH + CH3OH2+, (CH3)2SH+ + NH3, and the CH3+CH3S radiative association) in order to characterize DMS formation routes in shocked molecular clouds and star-forming regions.Methods. We performed dedicated quantum and kinetics calculations to derive the potential energy surfaces of these reactive systems and evaluate the reaction rate coefficients as a function of temperature to be included in astrochemical models.Results. Among the investigated processes, the reaction between methanethiol (CH3SH) and protonated methanol (CH3OH2+), possibly followed by a gentle proton transfer to ammonia, is a compelling candidate to explain the formation of DMS in the galactic-center molecular cloud G+0.693−0.027. The CH3+CH3S radiative association does not seem to be a very efficient process, with the exclusion of cold clouds, provided that the thiomethoxy (CH3 S) and methyl radical are available.Conclusions. This work does not directly address the potential formation of DMS in the atmospheres of exoplanets. However, it clearly indicates that there are efficient abiotic formation routes of this interesting species. Furthermore, the characterization of the potential energy surface for the CH3+CH3 S radiative association supports the recent suggestion that DMS could be formed via photolysis in exoplanetary atmospheres.
{"title":"Gas-phase formation routes of dimethyl sulfide in the interstellar medium","authors":"Gabriella Di Genova, Nadia Balucani, Luca Mancini, Andrea Giustini, Marzio Rosi, Dimitrios Skouteris, Cecilia Ceccarelli","doi":"10.1051/0004-6361/202555216","DOIUrl":"https://doi.org/10.1051/0004-6361/202555216","url":null,"abstract":"<i>Context<i/>. Dimethyl sulfide (DMS; CH<sub>3<sub/> SCH<sub>3<sub/>) is an organosulfur compound that has been suggested as a potential biosignature in exoplanetary atmospheres. In addition to its tentative detections toward the sub-Neptune planet K2-18b, DMS has been detected in the coma of the 67/P comet and toward the galactic-center molecular cloud G+0.693-0.027. However, its formation routes have not been characterized yet.<i>Aims<i/>. In this work, we aim to investigate five gas-phase reactions (the ion-molecule reactions CH<sub>3<sub/>SH + CH<sub>3<sub/>SH<sub>2<sub/><sup>+<sup/>, CH<sub>3<sub/>OH + CH<sub>3<sub/>SH<sub>2<sub/><sup>+<sup/>, CH<sub>3<sub/>SH + CH<sub>3<sub/>OH<sub>2<sub/><sup>+<sup/>, (CH<sub>3<sub/>)<sub>2<sub/>SH<sup>+<sup/> + NH<sub>3<sub/>, and the CH<sub>3<sub/>+CH<sub>3<sub/>S radiative association) in order to characterize DMS formation routes in shocked molecular clouds and star-forming regions.<i>Methods<i/>. We performed dedicated quantum and kinetics calculations to derive the potential energy surfaces of these reactive systems and evaluate the reaction rate coefficients as a function of temperature to be included in astrochemical models.<i>Results<i/>. Among the investigated processes, the reaction between methanethiol (CH<sub>3<sub/>SH) and protonated methanol (CH<sub>3<sub/>OH<sub>2<sub/><sup>+<sup/>), possibly followed by a gentle proton transfer to ammonia, is a compelling candidate to explain the formation of DMS in the galactic-center molecular cloud G+0.693−0.027. The CH<sub>3<sub/>+CH<sub>3<sub/>S radiative association does not seem to be a very efficient process, with the exclusion of cold clouds, provided that the thiomethoxy (CH<sub>3<sub/> S) and methyl radical are available.<i>Conclusions<i/>. This work does not directly address the potential formation of DMS in the atmospheres of exoplanets. However, it clearly indicates that there are efficient abiotic formation routes of this interesting species. Furthermore, the characterization of the potential energy surface for the CH<sub>3<sub/>+CH<sub>3<sub/> S radiative association supports the recent suggestion that DMS could be formed via photolysis in exoplanetary atmospheres.","PeriodicalId":8571,"journal":{"name":"Astronomy & Astrophysics","volume":"9 1","pages":""},"PeriodicalIF":6.5,"publicationDate":"2025-12-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145823899","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-12-24DOI: 10.1051/0004-6361/202452223
Junia Göller, Philipp Girichidis, Noé Brucy, Glen Hunter, Karin Kjellgren, Robin Tress, Ralf S. Klessen, Simon C. O. Glover, Patrick Hennebelle, Sergio Molinari, Rowan Smith, Juan D. Soler, Mattia C. Sormani, Leonardo Testi
The Milky Way is a complex ecosystem. We can obtain detailed observations of it by probing the physical mechanisms that determine its interstellar medium. For a detailed comparison with observations and to provide theories for missing observables, the Milky Way must be modelled as accurately as possible. However, details of the Galactic structure are not fully defined by observations, which raises the need for more generalised models. With the Rhea simulations, we present a set of Milky Way-like simulations containing detailed physics of the interstellar medium as well as star formation and stellar feedback. We conducted two simulations that differ in the gravitational potential: one fitted to several structural details derived from observations and another that only reproduces the most basic quantities. We find little difference in the overall morphology except for the bar region, which funnels gas towards the Galactic inner region and therefore prevents quenching in the centre. Despite differences with galacto-centric radius, the global star formation rate is almost identical in both setups. A spiral arm potential does not influence properties of groups of formed stars. A bar potential, however, reduces the size and formation time of those associations. We conclude that a spiral arm potential has little influence on star formation in the Galaxy, except for producing long-lived spiral structures instead of transient ones, and that a galactic bar potential has a noticeable influence on star formation, mainly within the innermost 2.5 kpc.
{"title":"Introducing the Rhea simulations of Milky Way-like galaxies","authors":"Junia Göller, Philipp Girichidis, Noé Brucy, Glen Hunter, Karin Kjellgren, Robin Tress, Ralf S. Klessen, Simon C. O. Glover, Patrick Hennebelle, Sergio Molinari, Rowan Smith, Juan D. Soler, Mattia C. Sormani, Leonardo Testi","doi":"10.1051/0004-6361/202452223","DOIUrl":"https://doi.org/10.1051/0004-6361/202452223","url":null,"abstract":"The Milky Way is a complex ecosystem. We can obtain detailed observations of it by probing the physical mechanisms that determine its interstellar medium. For a detailed comparison with observations and to provide theories for missing observables, the Milky Way must be modelled as accurately as possible. However, details of the Galactic structure are not fully defined by observations, which raises the need for more generalised models. With the Rhea simulations, we present a set of Milky Way-like simulations containing detailed physics of the interstellar medium as well as star formation and stellar feedback. We conducted two simulations that differ in the gravitational potential: one fitted to several structural details derived from observations and another that only reproduces the most basic quantities. We find little difference in the overall morphology except for the bar region, which funnels gas towards the Galactic inner region and therefore prevents quenching in the centre. Despite differences with galacto-centric radius, the global star formation rate is almost identical in both setups. A spiral arm potential does not influence properties of groups of formed stars. A bar potential, however, reduces the size and formation time of those associations. We conclude that a spiral arm potential has little influence on star formation in the Galaxy, except for producing long-lived spiral structures instead of transient ones, and that a galactic bar potential has a noticeable influence on star formation, mainly within the innermost 2.5 kpc.","PeriodicalId":8571,"journal":{"name":"Astronomy & Astrophysics","volume":"4 1","pages":""},"PeriodicalIF":6.5,"publicationDate":"2025-12-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145823902","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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