Pub Date : 2025-01-10DOI: 10.1051/0004-6361/202451040
S. Zarattini, J. M. Rodríguez-Espinosa, C. Muñoz-Tuñón, J. M. Mas-Hesse, P. Arrabal Haro
Aims. We report the discovery and characterisation of a Lyman α (Lyα) blob close to a galaxy at redshift z = 3.49. We present the analysis we performed to check whether the companion galaxy could be the source of the ionised photons responsible for the Lyα emission from the blob.Methods. We used images obtained from the 10.4 m Gran Telescopio Canarias (GTC) telescope that are part of the Survey of High-z Absorption Red and Dead Sources (SHARDS) project. The blob is only visible in the F551W17 filter, centred around the Lyα line at the redshift of the galaxy. We measured the luminosity of the blob with a two-step procedure. Here, we start with a description of the radial surface-brightness (SB) profile of the galaxy, using a Sérsic function. We then removed this model from the SB profile of the blob and measured the luminosity of the blob alone. We also estimated the Lyα continuum of the galaxy using an Advanced Camera for Surveys (ACS) image from the Hubble Space Telescope (HST) in the F606W filter, which is wider than the SHARDS one and centred at about the same wavelength. In this image, the galaxy is visible, but the blob is not detected, since its Lyα emission is diluted in the larger wavelength range of the F606W filter.Results. We find that the Lyα luminosity of the blob is 1.0 × 1043 erg s−1, in agreement with other Lyα blobs reported in the literature. The luminosity of the galaxy in the same filter is 2.9 × 1042 erg s−1. The luminosity within the HST/ACS image that we used to estimate the Lyα continuum emission is Lcont = 1.1 × 1043 erg s−1. With these values, we have been able to estimate the Lyα equivalent width (EW), found to be 111 Å (rest-frame). This value is in good agreement with the literature and suggests that a super-cluster of massive (1 − 2 × 107 M⊙) and young (2 − 4 Myr) stars could be responsible for the ionisation of the blob. We also used two other methods to estimate the luminosity of the galaxy and the blob to assess the robustness of our results. We find a reasonable agreement that supports our conclusions. It is worth noting that the Lyα blob is spatially decoupled from the galaxy by 3 GTC/SHARDS pixels, corresponding to 5.7 kpc at the redshift of the objects. This misalignment could suggest the presence of an ionised cone of material escaping from the galaxy, as found in nearby galaxies such as M 82.
{"title":"Discovery of a Lyα blob photo-ionised by a super-cluster of massive stars associated with a z = 3.49 galaxy","authors":"S. Zarattini, J. M. Rodríguez-Espinosa, C. Muñoz-Tuñón, J. M. Mas-Hesse, P. Arrabal Haro","doi":"10.1051/0004-6361/202451040","DOIUrl":"https://doi.org/10.1051/0004-6361/202451040","url":null,"abstract":"<i>Aims.<i/> We report the discovery and characterisation of a Lyman <i>α<i/> (Ly<i>α<i/>) blob close to a galaxy at redshift <i>z<i/> = 3.49. We present the analysis we performed to check whether the companion galaxy could be the source of the ionised photons responsible for the Ly<i>α<i/> emission from the blob.<i>Methods.<i/> We used images obtained from the 10.4 m Gran Telescopio Canarias (GTC) telescope that are part of the Survey of High-<i>z<i/> Absorption Red and Dead Sources (SHARDS) project. The blob is only visible in the F551W17 filter, centred around the Ly<i>α<i/> line at the redshift of the galaxy. We measured the luminosity of the blob with a two-step procedure. Here, we start with a description of the radial surface-brightness (SB) profile of the galaxy, using a Sérsic function. We then removed this model from the SB profile of the blob and measured the luminosity of the blob alone. We also estimated the Ly<i>α<i/> continuum of the galaxy using an Advanced Camera for Surveys (ACS) image from the Hubble Space Telescope (HST) in the F606W filter, which is wider than the SHARDS one and centred at about the same wavelength. In this image, the galaxy is visible, but the blob is not detected, since its Ly<i>α<i/> emission is diluted in the larger wavelength range of the F606W filter.<i>Results.<i/> We find that the Ly<i>α<i/> luminosity of the blob is 1.0 × 10<sup>43<sup/> erg s<sup>−1<sup/>, in agreement with other Ly<i>α<i/> blobs reported in the literature. The luminosity of the galaxy in the same filter is 2.9 × 10<sup>42<sup/> erg s<sup>−1<sup/>. The luminosity within the HST/ACS image that we used to estimate the Ly<i>α<i/> continuum emission is <i>L<i/><sub>cont<sub/> = 1.1 × 10<sup>43<sup/> erg s<sup>−1<sup/>. With these values, we have been able to estimate the Ly<i>α<i/> equivalent width (EW), found to be 111 Å (rest-frame). This value is in good agreement with the literature and suggests that a super-cluster of massive (1 − 2 × 10<sup>7<sup/> M<sub>⊙<sub/>) and young (2 − 4 Myr) stars could be responsible for the ionisation of the blob. We also used two other methods to estimate the luminosity of the galaxy and the blob to assess the robustness of our results. We find a reasonable agreement that supports our conclusions. It is worth noting that the Ly<i>α<i/> blob is spatially decoupled from the galaxy by 3 GTC/SHARDS pixels, corresponding to 5.7 kpc at the redshift of the objects. This misalignment could suggest the presence of an ionised cone of material escaping from the galaxy, as found in nearby galaxies such as M 82.","PeriodicalId":8571,"journal":{"name":"Astronomy & Astrophysics","volume":"24 1","pages":""},"PeriodicalIF":6.5,"publicationDate":"2025-01-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142967961","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 : 2025-01-09DOI: 10.1051/0004-6361/202450152
M. Prucker, M. Sasaki, E. Schlegel, J. Knies, P. Weber, I. Kreykenbohm, J. Wilms
The historical supernova (SN) S Andromedae (S And or SN1885A) in the Andromeda Galaxy (M31) was discovered in August 1885 and since then has been studied extensively in multi-wavelength observations. Although the remnant of S And could be detected in optical images, so far no X-ray source has been reported at the position of S And. In this work we report the first detection of X-ray emission from the remnant of SN1885A with a significance of σ = 3.43 using Chandra High-Resolution Camera (HRC) data taken in the imaging (I) mode. A total of 45 Chandra HRC-I observations were analysed, which corresponds to ~940 ks of exposure time. A faint X-ray source could be detected at the reported position of the supernova remnant (SNR) 1885 and the corresponding X-ray luminosity in the 0.1–10 keV band was obtained. The resulting value from merging all 45 observations amounts to L0.1 − 10 keV = (6−3+4) × 1033 erg s−1. To contextualise the results, the luminosity was compared to the X-ray luminosities of four of the oldest known X-ray SNe, some younger Galactic remnants, some SNRs in M31, and to theoretical predictions. The X-ray luminosity of SNR1885 is three to four orders of magnitude lower compared to the other examined remnants. A comparison to theoretical models shows that such low X-ray luminosities can only be produced if the ejecta is still expanding freely into a low-density interstellar medium (ISM). On the other hand, strong absorption by a high-density medium surrounding the freely expanding ejecta could also account for the lack of X-ray emission. Furthermore, the extremely low emission in X-rays could be an indication that the X-ray luminosity decreases faster towards the end of the ejecta-dominated (ED) phase in the evolution of SNRs than in the beginning.
{"title":"X-Ray emission from SN1885A","authors":"M. Prucker, M. Sasaki, E. Schlegel, J. Knies, P. Weber, I. Kreykenbohm, J. Wilms","doi":"10.1051/0004-6361/202450152","DOIUrl":"https://doi.org/10.1051/0004-6361/202450152","url":null,"abstract":"The historical supernova (SN) S Andromedae (S And or SN1885A) in the Andromeda Galaxy (M31) was discovered in August 1885 and since then has been studied extensively in multi-wavelength observations. Although the remnant of S And could be detected in optical images, so far no X-ray source has been reported at the position of S And. In this work we report the first detection of X-ray emission from the remnant of SN1885A with a significance of <i>σ<i/> = 3.43 using Chandra High-Resolution Camera (HRC) data taken in the imaging (I) mode. A total of 45 Chandra HRC-I observations were analysed, which corresponds to ~940 ks of exposure time. A faint X-ray source could be detected at the reported position of the supernova remnant (SNR) 1885 and the corresponding X-ray luminosity in the 0.1–10 keV band was obtained. The resulting value from merging all 45 observations amounts to <i>L<i/><sub>0.1 − 10 keV<sub/> = (6<sub>−3<sub/><sup>+4<sup/>) × 10<sup>33<sup/> erg s<sup>−1<sup/>. To contextualise the results, the luminosity was compared to the X-ray luminosities of four of the oldest known X-ray SNe, some younger Galactic remnants, some SNRs in M31, and to theoretical predictions. The X-ray luminosity of SNR1885 is three to four orders of magnitude lower compared to the other examined remnants. A comparison to theoretical models shows that such low X-ray luminosities can only be produced if the ejecta is still expanding freely into a low-density interstellar medium (ISM). On the other hand, strong absorption by a high-density medium surrounding the freely expanding ejecta could also account for the lack of X-ray emission. Furthermore, the extremely low emission in X-rays could be an indication that the X-ray luminosity decreases faster towards the end of the ejecta-dominated (ED) phase in the evolution of SNRs than in the beginning.","PeriodicalId":8571,"journal":{"name":"Astronomy & Astrophysics","volume":"14 1","pages":""},"PeriodicalIF":6.5,"publicationDate":"2025-01-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142940232","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}
The latest ALMA and JWST observations provide new information on the birth and evolution of galaxies in the early Universe at the epoch of reionization. Measurements at redshift z > 5 of their cold-gas budget are particularly important because this budget is known to be the main fuel for star formation. A powerful tool for probing the physics characterising galaxies at high redshift is the [C II] 158 μm emission line. Due to its low excitation potential, [C II] emission can be produced in photodissociation regions, neutral atomic gas, and molecular clouds. To properly capture the cold-gas processes taking place in these environments (molecule formation, self-shielding, dust grain catalysis, and photoelectric and cosmic-ray heating), we made use of a new set of dedicated hydrodynamic simulations (COLDSIM) including time-dependent non-equilibrium chemistry, star formation, stellar evolution, metal spreading, and feedback mechanisms. We were able to accurately track the evolution of H I, H II and H2 in a cosmological context and predict the contribution of each gas phase to [C II] luminosity. We provide formulas that can be used to estimate the mass of molecular and atomic gas from [C II] detections. Furthermore, we analysed the evolution of conversion factors with galactic properties, such as stellar metallicity, star formation rate, and stellar mass. We demonstrate that [C II] emission is dominated by H I gas and that most of the [C II] luminosity is generated in warm, dense, star-forming regions. We conclude that although [C II] predominantly traces atomic rather than molecular gas, the [C II] luminosity remains a robust indicator of the H2 mass.
{"title":"Atomic and molecular gas as traced by [C II] emission","authors":"Benedetta Casavecchia, Umberto Maio, Céline Péroux, Benedetta Ciardi","doi":"10.1051/0004-6361/202452282","DOIUrl":"https://doi.org/10.1051/0004-6361/202452282","url":null,"abstract":"The latest ALMA and JWST observations provide new information on the birth and evolution of galaxies in the early Universe at the epoch of reionization. Measurements at redshift <i>z<i/> > 5 of their cold-gas budget are particularly important because this budget is known to be the main fuel for star formation. A powerful tool for probing the physics characterising galaxies at high redshift is the [C II] 158 μm emission line. Due to its low excitation potential, [C II] emission can be produced in photodissociation regions, neutral atomic gas, and molecular clouds. To properly capture the cold-gas processes taking place in these environments (molecule formation, self-shielding, dust grain catalysis, and photoelectric and cosmic-ray heating), we made use of a new set of dedicated hydrodynamic simulations (COLDSIM) including time-dependent non-equilibrium chemistry, star formation, stellar evolution, metal spreading, and feedback mechanisms. We were able to accurately track the evolution of H I, H II and H<sub>2<sub/> in a cosmological context and predict the contribution of each gas phase to [C II] luminosity. We provide formulas that can be used to estimate the mass of molecular and atomic gas from [C II] detections. Furthermore, we analysed the evolution of conversion factors with galactic properties, such as stellar metallicity, star formation rate, and stellar mass. We demonstrate that [C II] emission is dominated by H I gas and that most of the [C II] luminosity is generated in warm, dense, star-forming regions. We conclude that although [C II] predominantly traces atomic rather than molecular gas, the [C II] luminosity remains a robust indicator of the H<sub>2<sub/> mass.","PeriodicalId":8571,"journal":{"name":"Astronomy & Astrophysics","volume":"48 1","pages":""},"PeriodicalIF":6.5,"publicationDate":"2025-01-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142940242","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 : 2025-01-09DOI: 10.1051/0004-6361/202348581
Yating Liu, Lulu Fan, Lei Hu, Junqiang Lu, Yan Lu, Zelin Xu, Jiazheng Zhu, Haochen Wang, Xu Kong
<i>Context<i/>. The mounting data stream of large time-domain surveys renders the visual inspections of a huge set of transient candidates impractical. Techniques based on deep learning-based are popular solutions for minimizing human intervention in the time domain community. The classification of real and bogus transients is a fundamental component in real-time data processing systems and is critical to enabling rapid follow-up observations. Most existing methods (supervised learning) require sufficiently large training samples with corresponding labels, which involve costly human labeling and are challenging in the early stages of a time-domain survey. One method that can make use of training samples with access to only a limited amount of labels is highly desirable for future large time-domain surveys. These include the forthcoming 2.5-meter Wide-Field Survey Telescope (WFST) six-year survey and the Vera C. Rubin Observatory Legacy Survey of Space and Time (LSST).<i>Aims<i/>. Deep-learning-based methods have been favored in astrophysics owing to their adaptability and remarkable performance. They have been applied to the task of the classification of real and bogus transients. Unlike most existing approaches, which necessitate massive and expensive annotated data, we aim to leverage training samples with only 1000 labels and discover real sources that vary in brightness over time in the early stages of the WFST six-year survey.<i>Methods<i/>. We present a novel deep learning method that combines active learning and semi-supervised learning to construct a competitive real-bogus classifier. Our method incorporates an active learning stage, where we actively select the most informative or uncertain samples for annotation. This stage aims to achieve higher model performance by leveraging fewer labeled samples, thus reducing annotation costs and improving the overall learning process efficiency. Furthermore, our approach involves a semi-supervised learning stage that exploits the unlabeled data to enhance the model’s performance and achieve superior results, compared to using only the limited labeled data.<i>Results<i/>. Our proposed methodology capitalizes on the potential of active learning and semi-supervised learning. To demonstrate the efficacy of our approach, we constructed three newly compiled datasets from the Zwicky Transient Facility, achieving average accuracies of 98.8, 98.8, and 98.6% across these three datasets. It is important to note that our newly compiled datasets only work in terms of testing our deep learning methodology and there may be a potential bias between our datasets and the complete data stream. Therefore, the observed performance on these datasets cannot be assumed to directly translate to the general alert stream for general transient detection in actual scenarios. The algorithm will be integrated into the WFST pipeline, enabling an efficient and effective classification of transients in the early period of a time-d
{"title":"Classification of real and bogus transients using active learning and semi-supervised learning","authors":"Yating Liu, Lulu Fan, Lei Hu, Junqiang Lu, Yan Lu, Zelin Xu, Jiazheng Zhu, Haochen Wang, Xu Kong","doi":"10.1051/0004-6361/202348581","DOIUrl":"https://doi.org/10.1051/0004-6361/202348581","url":null,"abstract":"<i>Context<i/>. The mounting data stream of large time-domain surveys renders the visual inspections of a huge set of transient candidates impractical. Techniques based on deep learning-based are popular solutions for minimizing human intervention in the time domain community. The classification of real and bogus transients is a fundamental component in real-time data processing systems and is critical to enabling rapid follow-up observations. Most existing methods (supervised learning) require sufficiently large training samples with corresponding labels, which involve costly human labeling and are challenging in the early stages of a time-domain survey. One method that can make use of training samples with access to only a limited amount of labels is highly desirable for future large time-domain surveys. These include the forthcoming 2.5-meter Wide-Field Survey Telescope (WFST) six-year survey and the Vera C. Rubin Observatory Legacy Survey of Space and Time (LSST).<i>Aims<i/>. Deep-learning-based methods have been favored in astrophysics owing to their adaptability and remarkable performance. They have been applied to the task of the classification of real and bogus transients. Unlike most existing approaches, which necessitate massive and expensive annotated data, we aim to leverage training samples with only 1000 labels and discover real sources that vary in brightness over time in the early stages of the WFST six-year survey.<i>Methods<i/>. We present a novel deep learning method that combines active learning and semi-supervised learning to construct a competitive real-bogus classifier. Our method incorporates an active learning stage, where we actively select the most informative or uncertain samples for annotation. This stage aims to achieve higher model performance by leveraging fewer labeled samples, thus reducing annotation costs and improving the overall learning process efficiency. Furthermore, our approach involves a semi-supervised learning stage that exploits the unlabeled data to enhance the model’s performance and achieve superior results, compared to using only the limited labeled data.<i>Results<i/>. Our proposed methodology capitalizes on the potential of active learning and semi-supervised learning. To demonstrate the efficacy of our approach, we constructed three newly compiled datasets from the Zwicky Transient Facility, achieving average accuracies of 98.8, 98.8, and 98.6% across these three datasets. It is important to note that our newly compiled datasets only work in terms of testing our deep learning methodology and there may be a potential bias between our datasets and the complete data stream. Therefore, the observed performance on these datasets cannot be assumed to directly translate to the general alert stream for general transient detection in actual scenarios. The algorithm will be integrated into the WFST pipeline, enabling an efficient and effective classification of transients in the early period of a time-d","PeriodicalId":8571,"journal":{"name":"Astronomy & Astrophysics","volume":"13 1","pages":""},"PeriodicalIF":6.5,"publicationDate":"2025-01-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142940426","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 : 2025-01-09DOI: 10.1051/0004-6361/202451411
Ruijie He, Xiangcun Meng, Zhenxin Lei, Huahui Yan, Shunyi Lan
<i>Context.<i/> It is generally thought that hot subdwarfs are helium-core- or helium-shell-burning objects with extremely thin hydrogen envelopes and that binary interactions are always needed in their formation. Different types of hot subdwarfs may have different origins, which will cause them to present different radial velocity (RV) variability properties.<i>Aims.<i/> We plan to study the RV-variability fractions of different types of hot subdwarfs, as well as their distributions in the <i>T<i/><sub>eff<sub/> − log <i>g<i/> diagram. This provides insights into the formation of hot subdwarfs.<i>Methods.<i/> The cross-correlation function method was adopted to measure RV variations in 434 hot subdwarfs based on spectra obtained with the Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST). Light curves from the Transiting Exoplanet Survey were also used to search for short-period binary hot subdwarfs.<i>Results.<i/> Only 6 ± 4% of our single-lined He-rich hot subdwarfs that only show spectroscopic features of hot subdwarfs are found to be RV variable, which is lower than the fraction of single-lined He-poor sdB stars (31 ± 3%). Single-lined sdB stars with effective temperatures (<i>T<i/><sub>eff<sub/>) ∼ 25 000–33 000 K show an RV-variability fraction of 34 ± 5%, while lower RV-variability fractions are observed for single-lined sdB stars cooler than about 25 000 K (11 ± 4%), single-lined sdB/OB stars with <i>T<i/><sub>eff<sub/> ∼ 33 000–40 000 K and surface gravities ∼ 5.7–6.0 (13 ± 3%), as well as single-lined sdO/B stars with <i>T<i/><sub>eff<sub/> ∼ 45 000–70 000 K (10 ± 7%). Single-lined hot subdwarfs with <i>T<i/><sub>eff<sub/> ∼ 35 000–45 000 K located above the extreme horizontal branch (EHB) show a similar RV-variability fraction of 34 ± 9% as single-lined sdB stars at about 25 000–33 000 K. The largest RV-variability fraction of 51 ± 8% is found in single-lined hot subdwarfs below the canonical EHB. The detected RV-variability fraction of our composite hot subdwarfs with an infrared excess in their spectral energy distributions is 9 ± 3%, which is lower than that fraction of single-lined hot subdwarfs. Since the average RV uncertainty we measured in the LAMOST spectra is about 7.0 km/s, the lower detected RV-variability fraction for composite hot subdwarfs is expected because the RV amplitudes associated with long-period systems are lower.<i>Conclusions.<i/> The results here are generally consistent with the canonical binary evolution channels for forming hot subdwarfs. Most single-lined He-rich hot subdwarfs may form through merger channels, while the stable Roche-lobe overflow channel could play an important role in the formation of composite hot subdwarfs. Single-lined hot subdwarfs with <i>T<i/><sub>eff<sub/> ∼ 35 000–45 000 K located above the EHB may have an evolutionary connection to the sdB stars at about 25 000–33 000 K. The different detected RV-variability fractions for the different subclasses of single-lined
{"title":"Radial velocity variability fractions of different types of hot subdwarf stars","authors":"Ruijie He, Xiangcun Meng, Zhenxin Lei, Huahui Yan, Shunyi Lan","doi":"10.1051/0004-6361/202451411","DOIUrl":"https://doi.org/10.1051/0004-6361/202451411","url":null,"abstract":"<i>Context.<i/> It is generally thought that hot subdwarfs are helium-core- or helium-shell-burning objects with extremely thin hydrogen envelopes and that binary interactions are always needed in their formation. Different types of hot subdwarfs may have different origins, which will cause them to present different radial velocity (RV) variability properties.<i>Aims.<i/> We plan to study the RV-variability fractions of different types of hot subdwarfs, as well as their distributions in the <i>T<i/><sub>eff<sub/> − log <i>g<i/> diagram. This provides insights into the formation of hot subdwarfs.<i>Methods.<i/> The cross-correlation function method was adopted to measure RV variations in 434 hot subdwarfs based on spectra obtained with the Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST). Light curves from the Transiting Exoplanet Survey were also used to search for short-period binary hot subdwarfs.<i>Results.<i/> Only 6 ± 4% of our single-lined He-rich hot subdwarfs that only show spectroscopic features of hot subdwarfs are found to be RV variable, which is lower than the fraction of single-lined He-poor sdB stars (31 ± 3%). Single-lined sdB stars with effective temperatures (<i>T<i/><sub>eff<sub/>) ∼ 25 000–33 000 K show an RV-variability fraction of 34 ± 5%, while lower RV-variability fractions are observed for single-lined sdB stars cooler than about 25 000 K (11 ± 4%), single-lined sdB/OB stars with <i>T<i/><sub>eff<sub/> ∼ 33 000–40 000 K and surface gravities ∼ 5.7–6.0 (13 ± 3%), as well as single-lined sdO/B stars with <i>T<i/><sub>eff<sub/> ∼ 45 000–70 000 K (10 ± 7%). Single-lined hot subdwarfs with <i>T<i/><sub>eff<sub/> ∼ 35 000–45 000 K located above the extreme horizontal branch (EHB) show a similar RV-variability fraction of 34 ± 9% as single-lined sdB stars at about 25 000–33 000 K. The largest RV-variability fraction of 51 ± 8% is found in single-lined hot subdwarfs below the canonical EHB. The detected RV-variability fraction of our composite hot subdwarfs with an infrared excess in their spectral energy distributions is 9 ± 3%, which is lower than that fraction of single-lined hot subdwarfs. Since the average RV uncertainty we measured in the LAMOST spectra is about 7.0 km/s, the lower detected RV-variability fraction for composite hot subdwarfs is expected because the RV amplitudes associated with long-period systems are lower.<i>Conclusions.<i/> The results here are generally consistent with the canonical binary evolution channels for forming hot subdwarfs. Most single-lined He-rich hot subdwarfs may form through merger channels, while the stable Roche-lobe overflow channel could play an important role in the formation of composite hot subdwarfs. Single-lined hot subdwarfs with <i>T<i/><sub>eff<sub/> ∼ 35 000–45 000 K located above the EHB may have an evolutionary connection to the sdB stars at about 25 000–33 000 K. The different detected RV-variability fractions for the different subclasses of single-lined","PeriodicalId":8571,"journal":{"name":"Astronomy & Astrophysics","volume":"21 1","pages":""},"PeriodicalIF":6.5,"publicationDate":"2025-01-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142940240","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 : 2025-01-09DOI: 10.1051/0004-6361/202451153
Armin Nabizadeh, Erik Zackrisson, Emma Lundqvist, Massimo Ricotti, Seyong Park, Brian Welch, Jose M. Diego
Observations of gravitationally lensed, high-mass stars at redshifts ≳1 occasionally reveal spectral energy distributions that contain two components with different effective temperatures. Given that two separate stars are involved, this suggests that both stars have simultaneously reached very high magnification, as expected for two stars in a binary system close to the caustic curve of the foreground galaxy-cluster lens. The inferred effective temperatures and luminosities of these stars are, however, difficult to reconcile with known binaries, or even with isolated stars of the same age. Here, we explore three alternative explanations for these cases: circumstellar dust around the cooler of the two stars, age differences of a few million years among stars in the same star cluster, and a scenario in which the stars originate in two separate star clusters of different age along the lensing caustic. While all of these scenarios are deemed plausible in principle, dust solutions would require more circumstellar extinction than seen in local observations of the relevant supergiant and hypergiant stars. Hence, we argue that age differences between the two stars are the most likely scenario, given the current data.
{"title":"Explanations for the two-component spectral energy distributions of gravitationally lensed stars at high redshifts","authors":"Armin Nabizadeh, Erik Zackrisson, Emma Lundqvist, Massimo Ricotti, Seyong Park, Brian Welch, Jose M. Diego","doi":"10.1051/0004-6361/202451153","DOIUrl":"https://doi.org/10.1051/0004-6361/202451153","url":null,"abstract":"Observations of gravitationally lensed, high-mass stars at redshifts ≳1 occasionally reveal spectral energy distributions that contain two components with different effective temperatures. Given that two separate stars are involved, this suggests that both stars have simultaneously reached very high magnification, as expected for two stars in a binary system close to the caustic curve of the foreground galaxy-cluster lens. The inferred effective temperatures and luminosities of these stars are, however, difficult to reconcile with known binaries, or even with isolated stars of the same age. Here, we explore three alternative explanations for these cases: circumstellar dust around the cooler of the two stars, age differences of a few million years among stars in the same star cluster, and a scenario in which the stars originate in two separate star clusters of different age along the lensing caustic. While all of these scenarios are deemed plausible in principle, dust solutions would require more circumstellar extinction than seen in local observations of the relevant supergiant and hypergiant stars. Hence, we argue that age differences between the two stars are the most likely scenario, given the current data.","PeriodicalId":8571,"journal":{"name":"Astronomy & Astrophysics","volume":"67 1","pages":""},"PeriodicalIF":6.5,"publicationDate":"2025-01-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142940241","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 : 2025-01-09DOI: 10.1051/0004-6361/202451217
Jiaqi Zhao, Craig O. Heinke, Su Fu
Context. Diffuse X-ray emission has been detected from a few Galactic globular clusters (GCs), but its nature remains largely unclear. The GC Terzan 5 was previously found to show a significant diffuse thermal X-ray excess from its field, likely contributed by the Galactic background, and a nonthermal component described by a power-law model with photon index Γ ~ 1.Aims. With over 16 times the accumulated Chandra exposure time compared to a prior study, we reexamined and verified the diffuse X-ray emission from the field of Terzan 5, which enabled us to place constraints on its nature.Methods. We analyzed all available useful Chandra observations of Terzan 5, including 18 observations over a span of 13 years, with a total exposure time of 641.6 ks. To study the diffuse X-ray emission, we focused on four annular regions with an equal width of 0.72 arcmin centered on Terzan 5 (0.72–3.60 arcmin), from which we extracted and analyzed the X-ray spectra after removing point sources and instrumental backgrounds.Results. We confirm a significant diffuse X-ray excess from the field of Terzan 5 in the band 0.8–3 keV. After constraining the contribution from the local X-ray background, we find a diffuse X-ray component that is genuinely associated with Terzan 5 and can be well described by a power-law model. More interestingly, the fitted photon indices show a significant increase from Γ = 1.96 ± 0.18 in the inner region to Γ = 3.48 ± 0.71 in the outer region. The diffuse X-rays are also well fit by a thermal bremsstrahlung model, with plasma temperatures declining from kT ∼ 3 keV to kT ∼ 1 keV.Conclusions. We suggest that synchrotron radiation from the combined pulsar winds of Terzan 5’s millisecond pulsar population is a possible origin of the observed diffuse X-ray emission but that the sharp steepening in the spectra cannot be produced solely by synchrotron cooling. Other radiation processes, like thermal bremsstrahlung, may also contribute to the diffuse X-rays.
{"title":"A deep Chandra study confirms diffuse nonthermal X-ray emission from the globular cluster Terzan 5","authors":"Jiaqi Zhao, Craig O. Heinke, Su Fu","doi":"10.1051/0004-6361/202451217","DOIUrl":"https://doi.org/10.1051/0004-6361/202451217","url":null,"abstract":"<i>Context<i/>. Diffuse X-ray emission has been detected from a few Galactic globular clusters (GCs), but its nature remains largely unclear. The GC Terzan 5 was previously found to show a significant diffuse thermal X-ray excess from its field, likely contributed by the Galactic background, and a nonthermal component described by a power-law model with photon index Γ ~ 1.<i>Aims<i/>. With over 16 times the accumulated <i>Chandra<i/> exposure time compared to a prior study, we reexamined and verified the diffuse X-ray emission from the field of Terzan 5, which enabled us to place constraints on its nature.<i>Methods<i/>. We analyzed all available useful <i>Chandra<i/> observations of Terzan 5, including 18 observations over a span of 13 years, with a total exposure time of 641.6 ks. To study the diffuse X-ray emission, we focused on four annular regions with an equal width of 0.72 arcmin centered on Terzan 5 (0.72–3.60 arcmin), from which we extracted and analyzed the X-ray spectra after removing point sources and instrumental backgrounds.<i>Results<i/>. We confirm a significant diffuse X-ray excess from the field of Terzan 5 in the band 0.8–3 keV. After constraining the contribution from the local X-ray background, we find a diffuse X-ray component that is genuinely associated with Terzan 5 and can be well described by a power-law model. More interestingly, the fitted photon indices show a significant increase from Γ = 1.96 ± 0.18 in the inner region to Γ = 3.48 ± 0.71 in the outer region. The diffuse X-rays are also well fit by a thermal bremsstrahlung model, with plasma temperatures declining from <i>kT<i/> ∼ 3 keV to <i>kT<i/> ∼ 1 keV.<i>Conclusions<i/>. We suggest that synchrotron radiation from the combined pulsar winds of Terzan 5’s millisecond pulsar population is a possible origin of the observed diffuse X-ray emission but that the sharp steepening in the spectra cannot be produced solely by synchrotron cooling. Other radiation processes, like thermal bremsstrahlung, may also contribute to the diffuse X-rays.","PeriodicalId":8571,"journal":{"name":"Astronomy & Astrophysics","volume":"81 1","pages":""},"PeriodicalIF":6.5,"publicationDate":"2025-01-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142940233","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 : 2025-01-09DOI: 10.1051/0004-6361/202451702
V. Busillo, C. Tortora, G. Covone, L. V. E. Koopmans, M. Silvestrini, N. R. Napolitano
Physical processes can influence the formation and evolution of galaxies in diverse ways. It is essential to validate their incorporation into cosmological simulations by testing them against real data encompassing various types of galaxies and spanning a broad spectrum of masses and galaxy properties. For these reasons, in this second paper of the CASCO series, we compare the structural properties and dark matter content of early-type galaxies taken from the CAMELS IllustrisTNG cosmological simulations to three different observational datasets (SPIDER, ATLAS3D, and MaNGA DynPop), to constrain the value of cosmological and astrophysical feedback parameters, and we compare the results with those obtained comparing the simulation expectations with late-type galaxies. We consider the size-mass, internal DM fraction-mass, and internal DM mass-stellar mass relations for all the simulations, and search for the best-fit simulation for each set of observations. For SPIDER, we find values for the cosmological parameters in line with both the literature and the results obtained from the comparison between simulations and late-type galaxies; results for the supernovae feedback parameters are instead opposite with respect to the previous results based on late-type galaxies. For ATLAS3D, we find similar values as from SPIDER for the cosmological parameters, but we find values for the supernovae feedback parameters more in line with what we found for late-type galaxies. From MaNGA DynPop, we find extreme values for the cosmological parameters, while the supernovae feedback parameters are consistent with ATLAS3D results. When considering the full MaNGA DynPop sample, including both late- and early-type galaxies, no single simulation can reproduce the full variety in the observational datasets. The constraints depend strongly on the specific properties of each observational trend, making it difficult to find a simulation matching all galaxy types, indicating the existence of limitations in the ability of simulations in reproducing the observations.
{"title":"CASCO: Cosmological and AStrophysical parameters from Cosmological simulations and Observations","authors":"V. Busillo, C. Tortora, G. Covone, L. V. E. Koopmans, M. Silvestrini, N. R. Napolitano","doi":"10.1051/0004-6361/202451702","DOIUrl":"https://doi.org/10.1051/0004-6361/202451702","url":null,"abstract":"Physical processes can influence the formation and evolution of galaxies in diverse ways. It is essential to validate their incorporation into cosmological simulations by testing them against real data encompassing various types of galaxies and spanning a broad spectrum of masses and galaxy properties. For these reasons, in this second paper of the CASCO series, we compare the structural properties and dark matter content of early-type galaxies taken from the CAMELS IllustrisTNG cosmological simulations to three different observational datasets (SPIDER, ATLAS<sup>3D<sup/>, and MaNGA DynPop), to constrain the value of cosmological and astrophysical feedback parameters, and we compare the results with those obtained comparing the simulation expectations with late-type galaxies. We consider the size-mass, internal DM fraction-mass, and internal DM mass-stellar mass relations for all the simulations, and search for the best-fit simulation for each set of observations. For SPIDER, we find values for the cosmological parameters in line with both the literature and the results obtained from the comparison between simulations and late-type galaxies; results for the supernovae feedback parameters are instead opposite with respect to the previous results based on late-type galaxies. For ATLAS<sup>3D<sup/>, we find similar values as from SPIDER for the cosmological parameters, but we find values for the supernovae feedback parameters more in line with what we found for late-type galaxies. From MaNGA DynPop, we find extreme values for the cosmological parameters, while the supernovae feedback parameters are consistent with ATLAS<sup>3D<sup/> results. When considering the full MaNGA DynPop sample, including both late- and early-type galaxies, no single simulation can reproduce the full variety in the observational datasets. The constraints depend strongly on the specific properties of each observational trend, making it difficult to find a simulation matching all galaxy types, indicating the existence of limitations in the ability of simulations in reproducing the observations.","PeriodicalId":8571,"journal":{"name":"Astronomy & Astrophysics","volume":"89 3 1","pages":""},"PeriodicalIF":6.5,"publicationDate":"2025-01-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142940427","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 : 2025-01-08DOI: 10.1051/0004-6361/202452296
D. Zakharova, S. McGee, B. Vulcani, G. De Lucia
Galaxies within groups exhibit characteristics different from those of galaxies that reside in regions of average density (the field). Galaxy properties also depend on their location within the host structure and orientation with respect to the central galaxy: galaxies in the inner regions that are aligned to the major axis of the central galaxy tend to be more quenched and redder than galaxies in the outskirts and with random orientation. This phenomenon, called anisotropic satellite galaxy quenching (ASGQ), can be explained in two different ways: invoking either external influences (large-scale distribution of matter) or internal factors (black hole activity of the central galaxy). In this work, we study the impact of filaments in shaping the ASGQ in the local Universe, exploiting the magneto-hydrodynamic (MHD) simulation IllustrisTNG. We separated all surviving satellites into young and old populations depending on their infall times. We show that only young satellites contribute to the observed ASGQ. These satellites preferentially infall along the major axis of the central galaxy, which tends to have the same direction of the filament feeding the groups. We demonstrate that old satellites were quenched inside their hosts and do not exhibit signatures of ASGQ. We show that the ASGQ emerges at the time of the infall of the young satellites and is also visible outside R200. In contrast, there is no sign of anisotropic distribution in the inner regions (R < 0.5R200). We argue that our results support a scenario in which a large-scale structure is imprinted on the ASGQ.
{"title":"The impact of large-scale structure on the anisotropic quenching of satellites","authors":"D. Zakharova, S. McGee, B. Vulcani, G. De Lucia","doi":"10.1051/0004-6361/202452296","DOIUrl":"https://doi.org/10.1051/0004-6361/202452296","url":null,"abstract":"Galaxies within groups exhibit characteristics different from those of galaxies that reside in regions of average density (the field). Galaxy properties also depend on their location within the host structure and orientation with respect to the central galaxy: galaxies in the inner regions that are aligned to the major axis of the central galaxy tend to be more quenched and redder than galaxies in the outskirts and with random orientation. This phenomenon, called anisotropic satellite galaxy quenching (ASGQ), can be explained in two different ways: invoking either external influences (large-scale distribution of matter) or internal factors (black hole activity of the central galaxy). In this work, we study the impact of filaments in shaping the ASGQ in the local Universe, exploiting the magneto-hydrodynamic (MHD) simulation IllustrisTNG. We separated all surviving satellites into young and old populations depending on their infall times. We show that only young satellites contribute to the observed ASGQ. These satellites preferentially infall along the major axis of the central galaxy, which tends to have the same direction of the filament feeding the groups. We demonstrate that old satellites were quenched inside their hosts and do not exhibit signatures of ASGQ. We show that the ASGQ emerges at the time of the infall of the young satellites and is also visible outside <i>R<i/><sub>200<sub/>. In contrast, there is no sign of anisotropic distribution in the inner regions (<i>R<i/> < 0.5<i>R<i/><sub>200<sub/>). We argue that our results support a scenario in which a large-scale structure is imprinted on the ASGQ.","PeriodicalId":8571,"journal":{"name":"Astronomy & Astrophysics","volume":"28 1","pages":""},"PeriodicalIF":6.5,"publicationDate":"2025-01-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142936850","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 : 2025-01-08DOI: 10.1051/0004-6361/202452622
C. Martínez-Sebastián, S. Simón-Díaz, H. Jin, Z. Keszthelyi, G. Holgado, N. Langer, J. Puls
There is increasing evidence that single-star evolutionary models are unable to reproduce all of the observational properties of massive stars. Binary interaction has emerged as a key factor in the evolution of a significant fraction of massive stars. In this study, we investigate the helium (YHe) and nitrogen (ϵN) surface abundances in a comprehensive sample of 180 Galactic O-type stars with projected rotational velocities of ≤150 km s−1. We found a subsample (∼20% of the total, and ∼80% of the stars with YHe ≥ 0.12) with a YHe and ϵN combined pattern that is unexplainable by single-star evolution. We argue that the stars with anomalous surface abundance patterns are binary interaction products.
{"title":"The IACOB project","authors":"C. Martínez-Sebastián, S. Simón-Díaz, H. Jin, Z. Keszthelyi, G. Holgado, N. Langer, J. Puls","doi":"10.1051/0004-6361/202452622","DOIUrl":"https://doi.org/10.1051/0004-6361/202452622","url":null,"abstract":"There is increasing evidence that single-star evolutionary models are unable to reproduce all of the observational properties of massive stars. Binary interaction has emerged as a key factor in the evolution of a significant fraction of massive stars. In this study, we investigate the helium (Y<sub>He<sub/>) and nitrogen (<i>ϵ<i/><sub>N<sub/>) surface abundances in a comprehensive sample of 180 Galactic O-type stars with projected rotational velocities of ≤150 km s<sup>−1<sup/>. We found a subsample (∼20% of the total, and ∼80% of the stars with Y<sub>He<sub/> ≥ 0.12) with a Y<sub>He<sub/> and <i>ϵ<i/><sub>N<sub/> combined pattern that is unexplainable by single-star evolution. We argue that the stars with anomalous surface abundance patterns are binary interaction products.","PeriodicalId":8571,"journal":{"name":"Astronomy & Astrophysics","volume":"118 1","pages":""},"PeriodicalIF":6.5,"publicationDate":"2025-01-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142936848","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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