Pub Date : 2025-02-18DOI: 10.1051/0004-6361/202453618
F. Vito, W. N. Brandt, A. Comastri, R. Gilli, F. Bauer, S. Belladitta, G. Chartas, K. Iwasawa, G. Lanzuisi, B. Luo, S. Marchesi, M. Mignoli, F. Ricci, O. Shemmer, C. Spingola, C. Vignali, W. Boschin, F. Cusano, D. Paris
X-ray observations of the optically selected z = 6.025 quasi-stellar object (QSO) CFHQS J164121+375520 (hereafter J1641) revealed that its flux dropped by a factor of ≳7 between 2018, when it was a bright and soft X-ray source, and 2021. Such a strong variability amplitude has not been observed before among z > 6 QSOs, and the underlying physical mechanism was unclear. We carried out a new X-ray and rest-frame UV monitoring campaign of J1641 over 2022–2024. We detected J1641 with Chandra in the 2–7 keV band, while no significant emission is detected at softer X-ray energies, making J1641 an X-ray changing-look QSO at z > 6. Compared with the 2018 epoch, the 0.5–2 keV flux dropped by a factor of > 20. We ascribe this behavior to intervening, and still ongoing, obscuration by Compton-thick gas intercepting our line of sight between 2018 and 2021. The screening material could be an inner disk or a failed nuclear wind whose thickness increased. Another possibility is that we have witnessed an occultation event due to dust-free clouds located at parsec or subparsec scales, similar to those recently invoked to explain the remarkable X-ray weakness of active galactic nuclei discovered by JWST. These interpretations are also consistent with the lack of strong variations in the QSO rest-frame UV light curve over the same period. Future monitoring of J1641 and the possible discovery of other X-ray changing look QSOs at z > 6 will return precious information about the physics of rapid supermassive black hole growth at high redshifts.
{"title":"Intervening nuclear obscuration changing the X-ray look of the z ≈ 6 quasi-stellar object CFHQS J164121+375520","authors":"F. Vito, W. N. Brandt, A. Comastri, R. Gilli, F. Bauer, S. Belladitta, G. Chartas, K. Iwasawa, G. Lanzuisi, B. Luo, S. Marchesi, M. Mignoli, F. Ricci, O. Shemmer, C. Spingola, C. Vignali, W. Boschin, F. Cusano, D. Paris","doi":"10.1051/0004-6361/202453618","DOIUrl":"https://doi.org/10.1051/0004-6361/202453618","url":null,"abstract":"X-ray observations of the optically selected <i>z<i/> = 6.025 quasi-stellar object (QSO) CFHQS J164121+375520 (hereafter J1641) revealed that its flux dropped by a factor of ≳7 between 2018, when it was a bright and soft X-ray source, and 2021. Such a strong variability amplitude has not been observed before among <i>z<i/> > 6 QSOs, and the underlying physical mechanism was unclear. We carried out a new X-ray and rest-frame UV monitoring campaign of J1641 over 2022–2024. We detected J1641 with <i>Chandra<i/> in the 2–7 keV band, while no significant emission is detected at softer X-ray energies, making J1641 an X-ray changing-look QSO at <i>z<i/> > 6. Compared with the 2018 epoch, the 0.5–2 keV flux dropped by a factor of > 20. We ascribe this behavior to intervening, and still ongoing, obscuration by Compton-thick gas intercepting our line of sight between 2018 and 2021. The screening material could be an inner disk or a failed nuclear wind whose thickness increased. Another possibility is that we have witnessed an occultation event due to dust-free clouds located at parsec or subparsec scales, similar to those recently invoked to explain the remarkable X-ray weakness of active galactic nuclei discovered by JWST. These interpretations are also consistent with the lack of strong variations in the QSO rest-frame UV light curve over the same period. Future monitoring of J1641 and the possible discovery of other X-ray changing look QSOs at <i>z<i/> > 6 will return precious information about the physics of rapid supermassive black hole growth at high redshifts.","PeriodicalId":8571,"journal":{"name":"Astronomy & Astrophysics","volume":"129 1","pages":""},"PeriodicalIF":6.5,"publicationDate":"2025-02-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143435711","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 : 2025-02-18DOI: 10.1051/0004-6361/202451818
L. V. Tambovtseva, A. A. Djupvik, V. P. Grinin, H. Weber, H. Bengtsson, H. De Angelis, G. Duszanowicz, D. Heinonen, L. Hermansson, G. Holmberg, T. Karlsson, M. Larsson, J. Warell, T. Wikander
Context. UX Orionis stars are the most active young stars; they undergo sporadic fadings of 2–4 magnitudes in the V-band, due to variable circumstellar extinction caused by a nearly edge-on star–disc system. The long-lasting monitoring of a number of stars of this type with the Nordic Optical Telescope from 2019 to 2024 has given a rich collection of material of high-resolution (R ∼ 25 000) spectra obtained during different brightness states of the stars. In this paper, we present the results of observations for UX Ori itself. Until now only one spectrum of high resolution had been obtained for this star during brightness minimum, making it difficult to do a comprehensive analysis.Aims. Our aim is to analyse how different spectral lines change during such irregular fading events, when the star is going in and out of eclipses, obscured by dust along the line of sight.Methods. For this purpose we provide a comparative analysis of the profiles and equivalent widths of the spectral lines belonging to the different atoms and ions. In addition we compare the results for UX Ori with those made for another target in our sample: RR Tau.Results. Common features of variability are revealed: (1) a strengthening of the Hα line relatively to the continuum during eclipses; (2) the appearance of additional emission on the frequencies of photospheric lines (e.g. FeII, CaII, SiII). The different behaviour of the spectral lines during fading found for UX Ori and RR Tau may be caused by two effects: a different contribution of the scattered light to the stellar flux during eclipses or a less intense disc wind of UX Ori.
{"title":"Observations of UX Ori in deep minima with the Nordic Optical Telescope","authors":"L. V. Tambovtseva, A. A. Djupvik, V. P. Grinin, H. Weber, H. Bengtsson, H. De Angelis, G. Duszanowicz, D. Heinonen, L. Hermansson, G. Holmberg, T. Karlsson, M. Larsson, J. Warell, T. Wikander","doi":"10.1051/0004-6361/202451818","DOIUrl":"https://doi.org/10.1051/0004-6361/202451818","url":null,"abstract":"<i>Context<i/>. UX Orionis stars are the most active young stars; they undergo sporadic fadings of 2–4 magnitudes in the <i>V<i/>-band, due to variable circumstellar extinction caused by a nearly edge-on star–disc system. The long-lasting monitoring of a number of stars of this type with the Nordic Optical Telescope from 2019 to 2024 has given a rich collection of material of high-resolution (R ∼ 25 000) spectra obtained during different brightness states of the stars. In this paper, we present the results of observations for UX Ori itself. Until now only one spectrum of high resolution had been obtained for this star during brightness minimum, making it difficult to do a comprehensive analysis.<i>Aims<i/>. Our aim is to analyse how different spectral lines change during such irregular fading events, when the star is going in and out of eclipses, obscured by dust along the line of sight.<i>Methods<i/>. For this purpose we provide a comparative analysis of the profiles and equivalent widths of the spectral lines belonging to the different atoms and ions. In addition we compare the results for UX Ori with those made for another target in our sample: RR Tau.<i>Results<i/>. Common features of variability are revealed: (1) a strengthening of the Hα line relatively to the continuum during eclipses; (2) the appearance of additional emission on the frequencies of photospheric lines (e.g. FeII, CaII, SiII). The different behaviour of the spectral lines during fading found for UX Ori and RR Tau may be caused by two effects: a different contribution of the scattered light to the stellar flux during eclipses or a less intense disc wind of UX Ori.","PeriodicalId":8571,"journal":{"name":"Astronomy & Astrophysics","volume":"178 1","pages":""},"PeriodicalIF":6.5,"publicationDate":"2025-02-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143435736","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 : 2025-02-18DOI: 10.1051/0004-6361/202452203
Justo Antonio González Villalba, Klaus Dolag, Veronica Biffi
Aims. Our aim is to understand how the interplay between black hole (BH) feedback and merge processes can effectively turn cool-core galaxy clusters into hot-core clusters in the modern universe. Additionally, we also aim to clarify which parameters of the BH feedback model used in simulations can cause an excess of feedback at the scale of galaxy groups while not efficiently suppressing star formation at the scale of galaxy clusters.Methods. To obtain robust statistics of the cool-core population, we compare the modern Universe snapshot (z = 0.25) of the largest Magneticum simulation (Box2b/hr) with the eROSITA eFEDS survey and Planck SZ-selected clusters observed with XMM-Newton. Additionally, we compare the BH feedback injected by the simulation in radio mode with Chandra observations of X-ray cavities, and LOFAR observations of radio emission.Results. We confirm a decreasing trend in cool-core fractions towards the most massive galaxy clusters, which is well reproduced by the Magneticum simulations. This evolution is connected with an increased merge activity that injects high-energy particles into the core region, but it also requires thermalisation and conductivity to enhance mixing through the intra-cluster medium core, where both factors are increasingly efficient towards the high mass end. On the other hand, BH feedback remains as the dominant factor at the scale of galaxy groups, while its relative impact decreases towards the most massive clusters.Conclusions. The problems suppressing star formation in simulations are not caused by low BH feedback efficiencies. They root in the definition of the black hole sphere of influence used to distribute the feedback, which decreases as density and accretion rate increase. Actually, a decreasing BH feedback efficiency towards low-mass galaxy groups is required to prevent overheating. These problems can be addressed in simulations by using relations between accretion rate, cavity power, and cavity reach derived from X-ray observations.
{"title":"How the cool-core population transitions from galaxy groups to massive clusters","authors":"Justo Antonio González Villalba, Klaus Dolag, Veronica Biffi","doi":"10.1051/0004-6361/202452203","DOIUrl":"https://doi.org/10.1051/0004-6361/202452203","url":null,"abstract":"<i>Aims.<i/> Our aim is to understand how the interplay between black hole (BH) feedback and merge processes can effectively turn cool-core galaxy clusters into hot-core clusters in the modern universe. Additionally, we also aim to clarify which parameters of the BH feedback model used in simulations can cause an excess of feedback at the scale of galaxy groups while not efficiently suppressing star formation at the scale of galaxy clusters.<i>Methods.<i/> To obtain robust statistics of the cool-core population, we compare the modern Universe snapshot (<i>z<i/> = 0.25) of the largest Magneticum simulation (<i>Box2b/hr<i/>) with the eROSITA eFEDS survey and Planck SZ-selected clusters observed with XMM-Newton. Additionally, we compare the BH feedback injected by the simulation in radio mode with Chandra observations of X-ray cavities, and LOFAR observations of radio emission.<i>Results.<i/> We confirm a decreasing trend in cool-core fractions towards the most massive galaxy clusters, which is well reproduced by the Magneticum simulations. This evolution is connected with an increased merge activity that injects high-energy particles into the core region, but it also requires thermalisation and conductivity to enhance mixing through the intra-cluster medium core, where both factors are increasingly efficient towards the high mass end. On the other hand, BH feedback remains as the dominant factor at the scale of galaxy groups, while its relative impact decreases towards the most massive clusters.<i>Conclusions.<i/> The problems suppressing star formation in simulations are not caused by low BH feedback efficiencies. They root in the definition of the black hole sphere of influence used to distribute the feedback, which decreases as density and accretion rate increase. Actually, a decreasing BH feedback efficiency towards low-mass galaxy groups is required to prevent overheating. These problems can be addressed in simulations by using relations between accretion rate, cavity power, and cavity reach derived from X-ray observations.","PeriodicalId":8571,"journal":{"name":"Astronomy & Astrophysics","volume":"23 1","pages":""},"PeriodicalIF":6.5,"publicationDate":"2025-02-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143435776","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 : 2025-02-18DOI: 10.1051/0004-6361/202452279
H. P. Wang, S. Poedts, A. Lani, M. Brchnelova, T. Baratashvili, L. Linan, F. Zhang, D. W. Hou, Y. H. Zhou
Context. Magnetohydrodynamic (MHD) solar corona models are critical in the Sun-to-Earth modelling chain and are the most complex and computationally intensive component. Compared to quasi-steady-state corona models that are constrained by a time-invariant magnetogram over a Carrington rotation (CR) period, time-evolving corona models driven by time-varying photospheric magnetograms are more realistic and can maintain more useful information to accurately describe solar wind evolution and forecast coronal mass ejection propagation.Aims. Implicit methods have significantly improved the efficiency of quasi-steady MHD coronal modelling. However, developing efficient time-evolving corona models to improve space weather forecasting is also important. This paper aims to demonstrate that time-evolving corona simulations can be performed efficiently and accurately using an implicit method with relatively large time steps, thus reducing the overall computational cost. We also evaluate differences between coronal structures captured by time-evolving and quasi-steady simulations over a CR period during solar minimum.Methods. We extended the quasi-steady COCONUT model, a global MHD corona model that uses implicit methods to select large time steps, into a time-evolving corona model. Specifically, we used a series of hourly updated photospheric magnetograms to drive the evolution of coronal structures from the solar surface to 25 Rs during two CRs around the 2019 eclipse in an inertial coordinate system. At each time step, the inner-boundary magnetic field was temporal-interpolated and updated from adjacent observation-based magnetograms. We compare the time-evolving and quasi-steady simulations to demonstrate that the differences in these two types of coronal modelling can be obvious even for a solar minimum. The relative differences in radial velocity and density can be over 15% and 25% at 20 Rs during one CR period. We also evaluated the impact of time steps on the simulation results. Using a time step of approximately 10 minutes balances efficiency and necessary numerical stability and accuracy for time-evolving corona simulations around solar minima. The chosen 10-minute time step significantly exceeds the Courant-Friedrichs-Lewy stability condition needed for explicit corona modelling, and the time-evolving COCONUT can thus simulate the coronal evolution during a full CR within only 9 hours (using 1080 CPU cores for 1.5M grid cells).Results. The simulation results demonstrate that time-evolving MHD coronal simulations can be performed efficiently and accurately using an implicit method, offering a more realistic alternative to quasi-steady-state simulations. The fully implicit time-evolving corona model thus promises to simulate the time-evolving corona accurately in practical space weather forecasting.
{"title":"Efficient magnetohydrodynamic modelling of the time-evolving corona by COCONUT","authors":"H. P. Wang, S. Poedts, A. Lani, M. Brchnelova, T. Baratashvili, L. Linan, F. Zhang, D. W. Hou, Y. H. Zhou","doi":"10.1051/0004-6361/202452279","DOIUrl":"https://doi.org/10.1051/0004-6361/202452279","url":null,"abstract":"<i>Context.<i/> Magnetohydrodynamic (MHD) solar corona models are critical in the Sun-to-Earth modelling chain and are the most complex and computationally intensive component. Compared to quasi-steady-state corona models that are constrained by a time-invariant magnetogram over a Carrington rotation (CR) period, time-evolving corona models driven by time-varying photospheric magnetograms are more realistic and can maintain more useful information to accurately describe solar wind evolution and forecast coronal mass ejection propagation.<i>Aims.<i/> Implicit methods have significantly improved the efficiency of quasi-steady MHD coronal modelling. However, developing efficient time-evolving corona models to improve space weather forecasting is also important. This paper aims to demonstrate that time-evolving corona simulations can be performed efficiently and accurately using an implicit method with relatively large time steps, thus reducing the overall computational cost. We also evaluate differences between coronal structures captured by time-evolving and quasi-steady simulations over a CR period during solar minimum.<i>Methods.<i/> We extended the quasi-steady COCONUT model, a global MHD corona model that uses implicit methods to select large time steps, into a time-evolving corona model. Specifically, we used a series of hourly updated photospheric magnetograms to drive the evolution of coronal structures from the solar surface to 25 <i>R<i/><sub>s<sub/> during two CRs around the 2019 eclipse in an inertial coordinate system. At each time step, the inner-boundary magnetic field was temporal-interpolated and updated from adjacent observation-based magnetograms. We compare the time-evolving and quasi-steady simulations to demonstrate that the differences in these two types of coronal modelling can be obvious even for a solar minimum. The relative differences in radial velocity and density can be over 15% and 25% at 20 <i>R<i/><sub>s<sub/> during one CR period. We also evaluated the impact of time steps on the simulation results. Using a time step of approximately 10 minutes balances efficiency and necessary numerical stability and accuracy for time-evolving corona simulations around solar minima. The chosen 10-minute time step significantly exceeds the Courant-Friedrichs-Lewy stability condition needed for explicit corona modelling, and the time-evolving COCONUT can thus simulate the coronal evolution during a full CR within only 9 hours (using 1080 CPU cores for 1.5M grid cells).<i>Results.<i/> The simulation results demonstrate that time-evolving MHD coronal simulations can be performed efficiently and accurately using an implicit method, offering a more realistic alternative to quasi-steady-state simulations. The fully implicit time-evolving corona model thus promises to simulate the time-evolving corona accurately in practical space weather forecasting.","PeriodicalId":8571,"journal":{"name":"Astronomy & Astrophysics","volume":"64 1","pages":""},"PeriodicalIF":6.5,"publicationDate":"2025-02-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143435743","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 : 2025-02-18DOI: 10.1051/0004-6361/202452189
N. K. Bhadari, L. K. Dewangan, O. R. Jadhav, A. Hoque, L. E. Pirogov, P. F. Goldsmith, A. K. Maity, S. Sharma, A. Haj Ismail, T. Baug
Context. Star clusters, including high-mass stars, form within hub-filament systems (HFSs). Observations of HFSs that remain unaffected by feedback from embedded stars are rare yet crucial for understanding the mass inflow process in high-mass star formation. Using the JWST NIRCAM images, a recent study reported that the high-mass protostar G11P1 is embedded in a candidate HFS (G11P1-HFS; < 0.6 pc).Aims. Utilizing ALMA N2H+(1–0) data, we confirm the presence of G11P1-HFS and study the dense gas kinematics.Methods. We analyzed the position–position–velocity (PPV) map and estimated on-sky velocity gradient (Vg) and gravity (ℱg) vectors. We examined the spatial distribution of the gas velocity and the H2 column density.Results. A steep Vg of 5 km s−1 pc−1 and −7 km s−1 pc−1 toward either side of G11P1-hub and a decreasing Vg toward the hub identify G11P1-HFS as a small-scale HFS in its nascent phase. Additionally, the Vg and ℱg align along the filaments, indicating gravity-driven flows.Conclusions. This work highlights the wiggled funnel-shaped morphology of an HFS in PPV space and suggests the importance of sub-filaments or transverse gas flows in mass transportation to the hub.
{"title":"JWST-ALMA study of a hub-filament system in the nascent phase","authors":"N. K. Bhadari, L. K. Dewangan, O. R. Jadhav, A. Hoque, L. E. Pirogov, P. F. Goldsmith, A. K. Maity, S. Sharma, A. Haj Ismail, T. Baug","doi":"10.1051/0004-6361/202452189","DOIUrl":"https://doi.org/10.1051/0004-6361/202452189","url":null,"abstract":"<i>Context.<i/> Star clusters, including high-mass stars, form within hub-filament systems (HFSs). Observations of HFSs that remain unaffected by feedback from embedded stars are rare yet crucial for understanding the mass inflow process in high-mass star formation. Using the JWST NIRCAM images, a recent study reported that the high-mass protostar G11P1 is embedded in a candidate HFS (G11P1-HFS; < 0.6 pc).<i>Aims.<i/> Utilizing ALMA N<sub>2<sub/>H<sup>+<sup/>(1–0) data, we confirm the presence of G11P1-HFS and study the dense gas kinematics.<i>Methods.<i/> We analyzed the position–position–velocity (PPV) map and estimated on-sky velocity gradient (<i>V<i/><sub>g<sub/>) and gravity (ℱ<sub>g<sub/>) vectors. We examined the spatial distribution of the gas velocity and the H<sub>2<sub/> column density.<i>Results.<i/> A steep <i>V<i/><sub>g<sub/> of 5 km s<sup>−1<sup/> pc<sup>−1<sup/> and −7 km s<sup>−1<sup/> pc<sup>−1<sup/> toward either side of G11P1-hub and a decreasing <i>V<i/><sub>g<sub/> toward the hub identify G11P1-HFS as a small-scale HFS in its nascent phase. Additionally, the <i>V<i/><sub>g<sub/> and ℱ<sub>g<sub/> align along the filaments, indicating gravity-driven flows.<i>Conclusions.<i/> This work highlights the wiggled funnel-shaped morphology of an HFS in PPV space and suggests the importance of sub-filaments or transverse gas flows in mass transportation to the hub.","PeriodicalId":8571,"journal":{"name":"Astronomy & Astrophysics","volume":"13 1","pages":""},"PeriodicalIF":6.5,"publicationDate":"2025-02-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143435713","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 : 2025-02-18DOI: 10.1051/0004-6361/202452206
Pratik Lonare, Michele Cantiello, Marco Mirabile, Marilena Spavone, Marina Rejkuba, Michael Hilker, Rebecca Habas, Enrichetta Iodice, Nandini Hazra, Gabriele Riccio
Context. Globular clusters (GCs) offer a valuable tool as a fossil tracer of the formation and evolution of galaxies and their environment. Studying the properties of these stellar systems provides crucial insights into the past formation and interaction events of the galaxies, especially in galaxy group and cluster environments.Aims. We study the properties of globular cluster (GC) candidates in an area of 1.25 × 1.03 sq. degrees centred on the NGC 5018 galaxy group. We use the deep, wide field, and multi-passband (ugr) observations obtained with the VLT Survey Telescope (VST) as part of the VST Elliptical GAlaxy Survey (VEGAS). With a focus on studying small stellar systems (SSS) associated with bright galaxies, this paper constitutes an extension of the VEGAS-SSS series investigating GCs in the NGC 5018 group.Methods. We derived photometric catalogues of compact and extended sources in the area and identified GC candidates using a set of photometric and morphometric selection parameters. A GC candidate catalogue has been provided and inspected using a statistical background decontamination technique, benefiting from the wide area coverage of the data.Results. The 2D distribution map of GC candidates reveals an over-density of sources on the brightest member of the NGC 5018 group. No significant GC over-densities are observed in the other bright galaxies of the group. We report the discovery of a candidate local nucleated low-surface-brightness (LSB) dwarf galaxy that may possibly be engaged in a tidal interaction with NGC 5018. The 2D map also reveals an intra-group GC population aligning with the bright galaxies and along the intra-group light (IGL) component of the group. The radial density profile of GC candidates in NGC 5018 follows the galaxy surface brightness profile. The (g − r) colour profile of GC candidates centred on this galaxy shows no evidence of the well-known colour bimodality; however, it is observed instead in the intra-group population. From the GC luminosity function (GCLF) analysis, we find a low specific frequency, SN = 0.59 ± 0.27 for NGC 5018, which is consistent with previous results based on less deep optical data over a smaller area. This relatively low SN value, coupled with the lack of colour bimodality, might be due to a combination of observational data limitations as well as the post-merger status of NGC 5018, which might host a population of relatively young GCs. For the intra-group GC population, we obtained a lower limit of SN, gr ∼ 0.6. Using the GCLF as a distance indicator, we estimate that NGC 5018 is located 38.0 ± 7.9 Mpc away, which is consistent with values reported in the literature.
{"title":"VEGAS-SSS: An intra-group component in the globular cluster system of the NGC 5018 galaxy group using VST data","authors":"Pratik Lonare, Michele Cantiello, Marco Mirabile, Marilena Spavone, Marina Rejkuba, Michael Hilker, Rebecca Habas, Enrichetta Iodice, Nandini Hazra, Gabriele Riccio","doi":"10.1051/0004-6361/202452206","DOIUrl":"https://doi.org/10.1051/0004-6361/202452206","url":null,"abstract":"<i>Context.<i/> Globular clusters (GCs) offer a valuable tool as a fossil tracer of the formation and evolution of galaxies and their environment. Studying the properties of these stellar systems provides crucial insights into the past formation and interaction events of the galaxies, especially in galaxy group and cluster environments.<i>Aims.<i/> We study the properties of globular cluster (GC) candidates in an area of 1.25 × 1.03 sq. degrees centred on the NGC 5018 galaxy group. We use the deep, wide field, and multi-passband (<i>u<i/><i>g<i/><i>r<i/>) observations obtained with the VLT Survey Telescope (VST) as part of the VST Elliptical GAlaxy Survey (VEGAS). With a focus on studying small stellar systems (SSS) associated with bright galaxies, this paper constitutes an extension of the VEGAS-SSS series investigating GCs in the NGC 5018 group.<i>Methods.<i/> We derived photometric catalogues of compact and extended sources in the area and identified GC candidates using a set of photometric and morphometric selection parameters. A GC candidate catalogue has been provided and inspected using a statistical background decontamination technique, benefiting from the wide area coverage of the data.<i>Results.<i/> The 2D distribution map of GC candidates reveals an over-density of sources on the brightest member of the NGC 5018 group. No significant GC over-densities are observed in the other bright galaxies of the group. We report the discovery of a candidate local nucleated low-surface-brightness (LSB) dwarf galaxy that may possibly be engaged in a tidal interaction with NGC 5018. The 2D map also reveals an intra-group GC population aligning with the bright galaxies and along the intra-group light (IGL) component of the group. The radial density profile of GC candidates in NGC 5018 follows the galaxy surface brightness profile. The (<i>g<i/> − <i>r<i/>) colour profile of GC candidates centred on this galaxy shows no evidence of the well-known colour bimodality; however, it is observed instead in the intra-group population. From the GC luminosity function (GCLF) analysis, we find a low specific frequency, <i>S<i/><sub>N<sub/> = 0.59 ± 0.27 for NGC 5018, which is consistent with previous results based on less deep optical data over a smaller area. This relatively low <i>S<i/><sub>N<sub/> value, coupled with the lack of colour bimodality, might be due to a combination of observational data limitations as well as the post-merger status of NGC 5018, which might host a population of relatively young GCs. For the intra-group GC population, we obtained a lower limit of <i>S<i/><sub>N, gr<sub/> ∼ 0.6. Using the GCLF as a distance indicator, we estimate that NGC 5018 is located 38.0 ± 7.9 Mpc away, which is consistent with values reported in the literature.","PeriodicalId":8571,"journal":{"name":"Astronomy & Astrophysics","volume":"47 1","pages":""},"PeriodicalIF":6.5,"publicationDate":"2025-02-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143435500","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 : 2025-02-18DOI: 10.1051/0004-6361/202452056
Xiaotong Guo, Qiusheng Gu, Guanwen Fang, Yongyun Chen, Nan Ding, Xiaoling Yu, Hongtao Wang
Context. Compton-thick active galactic nuclei (CT-AGNs), characterized by a significant absorption with column densities of NH ≥ 1.5 × 1024 cm−2, emit feeble X-ray radiation and are even undetectable by X-ray instruments, making them difficult to identify. X-ray radiation from AGNs is the predominant source of the cosmic X-ray background (CXB). Based on AGN synthesis models for the CXB, the fraction of CT-AGNs should constitute a substantial portion of AGN population, approximately 30% or more.Aims. The fraction of CT-AGNs discovered in the Cosmological Evolution Survey (COSMOS) is significantly lower than this value. This means that many CT-AGNs may be hidden in AGNs that exhibit low photon counts or that have not been detected by X-ray instruments. This work focuses on identifying CT-AGNs hidden in AGNs with low photon counts.Methods. Firstly, we selected 440 AGNs with abundant multiwavelength data as our sample. Secondly, we analyzed multiwavelength data, extracting crucial physical parameters required for the CT-AGN diagnosis. Finally, we used multiwavelength approaches to identify CT-AGNs.Results. We have successfully identified 18 CT-AGNs in our sample. Among the CT-AGNs, four AGNs show discrepant results across different diagnostic methods. We discuss the potential reasons behind these diagnostic discrepancies. We explore the impact of estimating [O III]λ 5007 luminosities based on [O II]λ 3727 luminosities for the CT-AGN diagnosis. We have also found that the properties of host galaxies for CT-AGNs and non-CT-AGNs do not show significant discrepancies.
{"title":"Identifying Compton-thick AGNs in the COSMOS","authors":"Xiaotong Guo, Qiusheng Gu, Guanwen Fang, Yongyun Chen, Nan Ding, Xiaoling Yu, Hongtao Wang","doi":"10.1051/0004-6361/202452056","DOIUrl":"https://doi.org/10.1051/0004-6361/202452056","url":null,"abstract":"<i>Context.<i/> Compton-thick active galactic nuclei (CT-AGNs), characterized by a significant absorption with column densities of <i>N<i/><sub>H<sub/> ≥ 1.5 × 10<sup>24<sup/> cm<sup>−2<sup/>, emit feeble X-ray radiation and are even undetectable by X-ray instruments, making them difficult to identify. X-ray radiation from AGNs is the predominant source of the cosmic X-ray background (CXB). Based on AGN synthesis models for the CXB, the fraction of CT-AGNs should constitute a substantial portion of AGN population, approximately 30% or more.<i>Aims.<i/> The fraction of CT-AGNs discovered in the Cosmological Evolution Survey (COSMOS) is significantly lower than this value. This means that many CT-AGNs may be hidden in AGNs that exhibit low photon counts or that have not been detected by X-ray instruments. This work focuses on identifying CT-AGNs hidden in AGNs with low photon counts.<i>Methods.<i/> Firstly, we selected 440 AGNs with abundant multiwavelength data as our sample. Secondly, we analyzed multiwavelength data, extracting crucial physical parameters required for the CT-AGN diagnosis. Finally, we used multiwavelength approaches to identify CT-AGNs.<i>Results.<i/> We have successfully identified 18 CT-AGNs in our sample. Among the CT-AGNs, four AGNs show discrepant results across different diagnostic methods. We discuss the potential reasons behind these diagnostic discrepancies. We explore the impact of estimating [O III]<i>λ<i/> 5007 luminosities based on [O II]<i>λ<i/> 3727 luminosities for the CT-AGN diagnosis. We have also found that the properties of host galaxies for CT-AGNs and non-CT-AGNs do not show significant discrepancies.","PeriodicalId":8571,"journal":{"name":"Astronomy & Astrophysics","volume":"1 1","pages":""},"PeriodicalIF":6.5,"publicationDate":"2025-02-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143435737","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}
Context. Fast-moving accretors are a ubiquitous phenomenon in astrophysics. Their interaction with the surrounding gas can leave characteristic imprints on the form of morphological structures like bow shocks, Mach cones, and trails with different densities.Aims. We study how various physical processes affect the flow structure around an accretor with a one-way surface, its accretion rate, and accretion anisotropy. These processes correspond to distinct length scales: the Bondi radius, the stand-off distance of the bow shock, and the Hoyle-Lyttleton radius.Methods. We conducted adiabatic hydrodynamic simulations using a spherical coordinate grid centred on the accretor’s location. By varying the accretor’s (numerical) size across various scales – from much smaller than the stand-off distance to much larger than the Bondi radius – we analyse how the processes on these spatial scales affect the physics of the steady-state flow.Results. All simulations achieve a steady state. When the accretor is smaller than the stand-off distance, a bow shock forms ahead of the object, and a nearly spherically symmetric atmosphere develops within this distance. Accretors smaller than the Hoyle-Lyttleton radius produce a Mach cone, while larger accretors exhibit a supersonic-to-subsonic flow transition on larger scales. Fully resolved simulations align with the Hoyle-Lyttleton theory, showing slightly anisotropic accretion with enhanced inflow from behind the object. In contrast, larger accretors approach the geometrical limit, with accretion primarily from the flow direction and a low-density ‘shadow’ forming behind the object.Conclusions. The accretor’s size greatly influences the small-scale and large-scale morphologies. Resolving the Hoyle-Lyttleton radius is essential for representing large-scale flow characteristics. Resolving the smaller stand-off distance is required only for studying the bow shock in front of the moving object: since the stand-off distance determines the bow shock’s position, its non-resolution does not affect the larger-scale flow morphology.
{"title":"Impact of accretor size on the morphology of supersonic, non-relativistic, axisymmetric Bondi-Hoyle-Lyttleton accretion flows","authors":"Shaghayegh Ashtari Jolehkaran, Lothar Brendel, Rolf Kuiper","doi":"10.1051/0004-6361/202451658","DOIUrl":"https://doi.org/10.1051/0004-6361/202451658","url":null,"abstract":"<i>Context.<i/> Fast-moving accretors are a ubiquitous phenomenon in astrophysics. Their interaction with the surrounding gas can leave characteristic imprints on the form of morphological structures like bow shocks, Mach cones, and trails with different densities.<i>Aims.<i/> We study how various physical processes affect the flow structure around an accretor with a one-way surface, its accretion rate, and accretion anisotropy. These processes correspond to distinct length scales: the Bondi radius, the stand-off distance of the bow shock, and the Hoyle-Lyttleton radius.<i>Methods.<i/> We conducted adiabatic hydrodynamic simulations using a spherical coordinate grid centred on the accretor’s location. By varying the accretor’s (numerical) size across various scales – from much smaller than the stand-off distance to much larger than the Bondi radius – we analyse how the processes on these spatial scales affect the physics of the steady-state flow.<i>Results.<i/> All simulations achieve a steady state. When the accretor is smaller than the stand-off distance, a bow shock forms ahead of the object, and a nearly spherically symmetric atmosphere develops within this distance. Accretors smaller than the Hoyle-Lyttleton radius produce a Mach cone, while larger accretors exhibit a supersonic-to-subsonic flow transition on larger scales. Fully resolved simulations align with the Hoyle-Lyttleton theory, showing slightly anisotropic accretion with enhanced inflow from behind the object. In contrast, larger accretors approach the geometrical limit, with accretion primarily from the flow direction and a low-density ‘shadow’ forming behind the object.<i>Conclusions.<i/> The accretor’s size greatly influences the small-scale and large-scale morphologies. Resolving the Hoyle-Lyttleton radius is essential for representing large-scale flow characteristics. Resolving the smaller stand-off distance is required only for studying the bow shock in front of the moving object: since the stand-off distance determines the bow shock’s position, its non-resolution does not affect the larger-scale flow morphology.","PeriodicalId":8571,"journal":{"name":"Astronomy & Astrophysics","volume":"7 1","pages":""},"PeriodicalIF":6.5,"publicationDate":"2025-02-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143435738","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 : 2025-02-18DOI: 10.1051/0004-6361/202453188
Anagha P. Nitindala, Alexandra Veledina, Juri Poutanen
X-ray polarimetry is a fine tool for probing the accretion geometry and physical processes operating in the proximity of compact objects, such as black holes and neutron stars. Recent discoveries made by the Imaging X-ray Polarimetry Explorer question our understanding of the accretion picture. The observed high levels of X-ray polarization in X-ray binaries and active galactic nuclei are challenging to achieve within the conventional scenarios. We investigate the possibility that a fraction (or even all) of the observed polarized signal arises from scattering in the equatorial accretion disk winds, the slow and extended outflows, which are often detected in these systems via spectroscopic means. We find that wind scattering can reproduce the levels of polarization that are observed in these sources.
X 射线偏振测量法是探测黑洞和中子星等紧凑天体附近的吸积几何形状和物理过程的有效工具。成像 X 射线偏振探测仪的最新发现质疑了我们对吸积情况的理解。在 X 射线双星和活动星系核中观测到的高水平 X 射线偏振，在常规情况下是很难实现的。我们研究了所观测到的偏振信号的一部分（甚至全部）来自赤道吸积盘风散射的可能性，这些风是缓慢而扩展的外流，通常在这些系统中通过光谱手段探测到。我们发现，风散射可以再现在这些源中观测到的极化水平。
{"title":"X-ray polarization from accretion disk winds","authors":"Anagha P. Nitindala, Alexandra Veledina, Juri Poutanen","doi":"10.1051/0004-6361/202453188","DOIUrl":"https://doi.org/10.1051/0004-6361/202453188","url":null,"abstract":"X-ray polarimetry is a fine tool for probing the accretion geometry and physical processes operating in the proximity of compact objects, such as black holes and neutron stars. Recent discoveries made by the Imaging X-ray Polarimetry Explorer question our understanding of the accretion picture. The observed high levels of X-ray polarization in X-ray binaries and active galactic nuclei are challenging to achieve within the conventional scenarios. We investigate the possibility that a fraction (or even all) of the observed polarized signal arises from scattering in the equatorial accretion disk winds, the slow and extended outflows, which are often detected in these systems via spectroscopic means. We find that wind scattering can reproduce the levels of polarization that are observed in these sources.","PeriodicalId":8571,"journal":{"name":"Astronomy & Astrophysics","volume":"31 1","pages":""},"PeriodicalIF":6.5,"publicationDate":"2025-02-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143435709","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 : 2025-02-18DOI: 10.1051/0004-6361/202452368
A. Ferrara, S. Carniani, F. di Mascia, R. J. Bouwens, P. Oesch, S. Schouws
The abundance and blue color of the super-early (redshift z > 10) luminous galaxies discovered by the James Webb Space Telescope (JWST) can be explained if radiation-driven outflows have ejected their dust on kiloparsec-scales. To test this hypothesis, we predict the Atacama Large Millimeter Array (ALMA) detectability of this extended dust component. Based on the observed properties of the galaxy, its observed continuum flux at 88 μm, F88, depends on the dust-to-stellar mass ratio, ξd, and on the extent of the dust distribution, rd. When this is applied to the most distant known galaxy, GS-z14-0 at z = 14.32, the fiducial model (ξd = 1/529) predicts F88fid = 14.9 μJy and a dust extent rd = 1.4 kpc. If the galaxy is very dust rich (ξd = 1/40), F88max = 40.1 μJy. These values are lower (F88fid = 9.5 μJy) if the dust is predominantly made of large grains such as those that form in supernova ejecta. Forthcoming ALMA observations might come very close to constraining the fiducial predictions of the outflow-based attenuation-free model. Other super-early galaxies are predicted to be fainter at 88 μm, mostly because their star formation rate is lower than that of GS-z14-0, with fiducial fluxes in the range 2 − 5.2 μJy.
{"title":"ALMA observations of super-early galaxies: Attenuation-free model predictions","authors":"A. Ferrara, S. Carniani, F. di Mascia, R. J. Bouwens, P. Oesch, S. Schouws","doi":"10.1051/0004-6361/202452368","DOIUrl":"https://doi.org/10.1051/0004-6361/202452368","url":null,"abstract":"The abundance and blue color of the super-early (redshift <i>z<i/> > 10) luminous galaxies discovered by the <i>James Webb<i/> Space Telescope (JWST) can be explained if radiation-driven outflows have ejected their dust on kiloparsec-scales. To test this hypothesis, we predict the Atacama Large Millimeter Array (ALMA) detectability of this extended dust component. Based on the observed properties of the galaxy, its observed continuum flux at 88 μm, <i>F<i/><sub>88<sub/>, depends on the dust-to-stellar mass ratio, <i>ξ<i/><sub><i>d<i/><sub/>, and on the extent of the dust distribution, <i>r<i/><sub><i>d<i/><sub/>. When this is applied to the most distant known galaxy, GS-z14-0 at <i>z<i/> = 14.32, the fiducial model (<i>ξ<i/><sub><i>d<i/><sub/> = 1/529) predicts <i>F<i/><sub>88<sub/><sup>fid<sup/> = 14.9 μJy and a dust extent <i>r<i/><sub><i>d<i/><sub/> = 1.4 kpc. If the galaxy is very dust rich (<i>ξ<i/><sub><i>d<i/><sub/> = 1/40), <i>F<i/><sub>88<sub/><sup>max<sup/> = 40.1 μJy. These values are lower (<i>F<i/><sub>88<sub/><sup>fid<sup/> = 9.5 μJy) if the dust is predominantly made of large grains such as those that form in supernova ejecta. Forthcoming ALMA observations might come very close to constraining the fiducial predictions of the outflow-based attenuation-free model. Other super-early galaxies are predicted to be fainter at 88 μm, mostly because their star formation rate is lower than that of GS-z14-0, with fiducial fluxes in the range 2 − 5.2 μJy.","PeriodicalId":8571,"journal":{"name":"Astronomy & Astrophysics","volume":"36 1","pages":""},"PeriodicalIF":6.5,"publicationDate":"2025-02-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143435770","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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