Astronomy & Astrophysics最新文献

{"title":"Combining summary statistics with simulation-based inference for the 21 cm signal from the Epoch of Reionisation","authors":"B. Semelin, R. Mériot, A. Mishra, D. Cornu","doi":"10.1051/0004-6361/202453115","DOIUrl":"https://doi.org/10.1051/0004-6361/202453115","url":null,"abstract":"The 21 cm signal from the Epoch of Reionisation will be observed with the upcoming Square Kilometer Array (SKA). We expect it to yield a full tomography of the signal, which opens up the possibility to explore its non-Gaussian properties. This raises the question of how can we extract the maximum information from tomography and derive the tightest constraint on the signal. In this work, instead of looking for the most informative summary statistics, we investigate how to combine the information from two sets of summary statistics using simulation-based inference. To this end, we trained neural density estimators (NDE) to fit the implicit likelihood of our model, the LICORICE code, using the Loreli II database. We trained three different NDEs: one to perform Bayesian inference on the power spectrum, one to perform it on the linear moments of the pixel distribution function (PDF), and one to work with the combination of the two. We performed ∼900 inferences at different points in our parameter space and used them to assess both the validity of our posteriors with a simulation-based calibration (SBC) and the typical gain obtained by combining summary statistics. We find that our posteriors are biased by no more than ∼20% of their standard deviation and under-confident by no more than ∼15%. Then, we established that combining summary statistics produces a contraction of the 4D volume of the posterior (derived from the generalised variance) in 91.5% of our cases, and in 70–80% of the cases for the marginalised 1D posteriors. The median volume variation is a contraction of a factor of a few for the 4D posteriors and a contraction of 20–30% in the case of the marginalised 1D posteriors. This shows that our approach is a possible alternative to looking for so-called sufficient statistics in the theoretical sense.","PeriodicalId":8571,"journal":{"name":"Astronomy & Astrophysics","volume":"24 1","pages":""},"PeriodicalIF":6.5,"publicationDate":"2025-05-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144137220","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}

{"title":"Zooming into the neutrino-associated blazar candidate J1718+4239","authors":"K. Perger, S. Frey, K. É. Gabányi, E. Kun","doi":"10.1051/0004-6361/202555177","DOIUrl":"https://doi.org/10.1051/0004-6361/202555177","url":null,"abstract":"The radio quasar NVSS J171822+423948 (J1718+4239) was proposed to be the counterpart of the IceCube neutrino event IC-201221A. To reveal the nature of the source, we conducted new very long baseline interferometry observations of this blazar candidate with the Very Long Baseline Array. The observations were carried out in dual-band mode between 4 and 7 GHz. Archival radio data from the literature were also collected for comparison. Our analysis revealed highly variable Doppler-boosted radio emission of the source, with a compact structure at kiloparsec and parsec scales, a slightly inverted spectrum, and a maximum jet inclination angle of <i>θ<i/> ≤ 5°. These results confirm that J1718+4239 is a blazar-type object.","PeriodicalId":8571,"journal":{"name":"Astronomy & Astrophysics","volume":"81 1","pages":""},"PeriodicalIF":6.5,"publicationDate":"2025-05-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144137218","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}

{"title":"Rotation and dispersion measure evolution of repeating fast radio bursts propagating through a magnetar’s flare ejecta","authors":"Di Xiao","doi":"10.1051/0004-6361/202554550","DOIUrl":"https://doi.org/10.1051/0004-6361/202554550","url":null,"abstract":"Rotation measure (RM) and dispersion measure (DM) are characteristic properties of fast radio bursts (FRBs) that contain important information of their source environment. The time evolution of the RM and DM is more inclined to be ascribed to local plasma in the host galaxy, rather than the intergalactic medium or free electrons in the Milky Way. A sudden, drastic RM change was recently reported for an active repeating FRB 20220529, implying that some kind of mass ejection happened near the source. In this work, I suggest that magnetar flare ejecta could play this role and give rise to the significant RM change. I introduce a toy structured ejecta model and calculate the contribution to RM and DM by a typical flare event. I find that this model could aptly reproduce the RM behavior of FRB 20220529 under reasonable parameters and similar sudden changes are expected for as long as this source maintains its activity.","PeriodicalId":8571,"journal":{"name":"Astronomy & Astrophysics","volume":"35 1","pages":""},"PeriodicalIF":6.5,"publicationDate":"2025-05-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144137247","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}

{"title":"Comprehensive UV and optical spectral analysis of Cygnus X-1","authors":"V. Ramachandran, A. A. C. Sander, L. M. Oskinova, E. C. Schösser, D. Pauli, W.-R. Hamann, L. Mahy, M. Bernini-Peron, M. Brigitte, B. Kubátová","doi":"10.1051/0004-6361/202554184","DOIUrl":"https://doi.org/10.1051/0004-6361/202554184","url":null,"abstract":"&lt;i&gt;Context&lt;i/&gt;. Cygnus X-1 contains the only dynamically confirmed black hole in a persistent high-mass X-ray binary in the Milky Way. Previous studies have suggested that the black hole in Cyg X-1 is one of the most massive stellar-mass black holes known in an X-ray binary, despite its high-metallicity environment. While the source has been actively investigated, a comprehensive UV and optical spectral analysis of the donor using modern stellar atmosphere models incorporating stellar winds and X-ray ionization has been lacking.&lt;i&gt;Aims&lt;i/&gt;. We aim to determine the stellar parameters, chemical abundances, and wind parameters of the donor star in Cyg X-1 along with the mass of the black hole. We also aim to investigate the system's current evolutionary state and its future evolution toward a binary black hole system, exploring its potential as a gravitational wave source.&lt;i&gt;Methods&lt;i/&gt;. We used archival high-resolution UV and optical spectra of Cyg X-1 taken at multiple orbital phases and X-ray states. We employed state-of-the-art, non-local thermodynamic equilibrium (non-LTE), Potsdam Wolf-Rayet (PoWR) atmosphere models that account for stellar winds, X-ray photoionization, metal line blanketing, and wind clumping. We performed a simultaneous analysis of UV and optical spectra. We further used the stellar evolution code MESA to model the further evolution of the system.&lt;i&gt;Results&lt;i/&gt;. Our analysis yields notably lower masses for both the donor ( approx 29 &lt;i&gt;M&lt;i/&gt;&lt;sub&gt;⊙&lt;sub/&gt;) and the black hole ( 12.7 to 17.8 &lt;i&gt;M&lt;i/&gt;&lt;sub&gt;⊙&lt;sub/&gt;), depending on inclination), and confirms that the donor's radius is close to reaching the inner Lagrangian point. We find super-solar Fe, Si, and Mg abundances (1.3-1.8 times solar) at the surface of the donor star, while the total CNO abundance remains solar despite evidence of CNO processing (N enrichment, O depletion) and He enrichment. This abundance pattern is distinct from the surrounding Cyg OB3 association. We observed a clear difference in wind parameters between X-ray states: &lt;i&gt;v&lt;i/&gt;&lt;sub&gt;∞&lt;sub/&gt; ≈ 1200 km s&lt;sup&gt;-1&lt;sup/&gt; and &lt;i&gt;Ṁ&lt;i/&gt; ≈ 3 ⨯ 10&lt;sup&gt;−7&lt;sup/&gt; &lt;i&gt;M&lt;i/&gt;&lt;sub&gt;⊙&lt;sub/&gt; yr&lt;sup&gt;−1&lt;sup/&gt;in the high-soft state, increasing to &lt;i&gt;v&lt;i/&gt;&lt;sub&gt;∞&lt;sub/&gt; ≲ 1800 km s&lt;sup&gt;−1&lt;sup/&gt; and &lt;i&gt;Ṁ&lt;i/&gt; ≲ 5 ⨯ 10&lt;sup&gt;−7&lt;sup/&gt; &lt;i&gt;M&lt;i/&gt;&lt;sub&gt;⊙&lt;sub/&gt; yr&lt;sup&gt;−1&lt;sup/&gt; in the low-hard state. The observed X-ray luminosity is consistent with wind-fed accretion. Evolutionary models show that Cyg X-1 will undergo Roche-lobe overflow in the near future. Under a fully conservative mass accretion scenario, our models predict a future binary black hole merger for Cyg X-1 within ∼ 5 Gyr.&lt;i&gt;Conclusions&lt;i/&gt;. Our comprehensive analysis provides refined stellar and wind parameters of the donor star in Cyg X-1, highlighting the importance of using advanced atmospheric models and considering X-ray ionization and wind clumping. The observed abundances suggest a complex formation history involving a high initial metallicity. The potential for a future ","PeriodicalId":8571,"journal":{"name":"Astronomy & Astrophysics","volume":"45 1","pages":""},"PeriodicalIF":6.5,"publicationDate":"2025-05-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144137255","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}

{"title":"Radio study of the colliding-wind binary HD 93129A near periastron and its surroundings","authors":"P. Benaglia, S. del Palacio, J. Saponara, A. B. Blanco, M. De Becker, B. Marcote","doi":"10.1051/0004-6361/202453422","DOIUrl":"https://doi.org/10.1051/0004-6361/202453422","url":null,"abstract":"<i>Context.<i/> HD 93129A is an O+O stellar system whose colliding-wind region (CWR) has been mapped by high angular resolution observations at centimetre wavelengths. The synchrotron nature of the radio emission confirms its particle accelerator status. Astrometric measurements since 1996 indicate that the system has an orbital period of ~120 yr and recently went through its periastron passage.<i>Aims.<i/> We attempted to characterise the radio emission during the epoch of the periastron passage, when the particle density and the local magnetic energy density in the CWR increase.<i>Methods.<i/> We monitored HD 93129A and its surroundings in bands centred at 2.1, 5.5, and 9.0 GHz, with the Australia Telescope Compact Array (ATCA) over a time span of 17 months, with an approximate 2-month cadence. Previous ATCA data at similar frequencies and data collected using other radio observatories were also included.<i>Results.<i/> We obtained radio light curves in sub-bands for each band and epoch. The flux densities show an average increase of a factor of four between 2003 and 2018, though the 2009–2017 time-lapse lacks data, followed by a similar-magnitude decay between 2018 and 2020. We fit the spectral energy distribution (SED) of quasi-simultaneous data at three epochs and find that the magnetic-to-thermal pressure ratio <i>η<sub>B<sub/><i/> does not remain constant along the orbit, possibly suggesting magnetic-field amplification close to periastron. In the 2019 epoch, we estimate a magnetic field strength of ≈1.1 G in the apex of the CWR (corresponding to <i>η<sub>B<sub/><i/> ≈ 0.085). The evolution of the SED and spectral index along several epochs in 2019–2020 is also presented. By combining images from the ATCA and the Australian Square Kilometre Array Pathfinder telescope, a spectral index map was obtained in an area of 30′ size, including the surroundings of Eta Car, revealing positive and negative spectral indices. The radio emission in the direction of other massive binary systems in the fields of view (WR 22, WR 25, and HD 93250) was measured and briefly discussed.<i>Conclusions.<i/> Intensive radio monitoring of a colliding-wind binary during key orbital phases allows us to track the evolution of physical conditions in the shocks. The general trend of decreasing emission of HD 93129A in the high-frequency bands in 2019–2020 suggests that the system is at post-periastron, consistent with model predictions.","PeriodicalId":8571,"journal":{"name":"Astronomy & Astrophysics","volume":"176 1","pages":""},"PeriodicalIF":6.5,"publicationDate":"2025-05-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144137254","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}

{"title":"Exploring the halo-galaxy connection with probabilistic approaches","authors":"Natália V. N. Rodrigues, Natalí S. M. de Santi, Raul Abramo, Antonio D. Montero-Dorta","doi":"10.1051/0004-6361/202453284","DOIUrl":"https://doi.org/10.1051/0004-6361/202453284","url":null,"abstract":"<i>Context.<i/> The connection between galaxies and their host dark matter halos encompasses a range of intricate and interrelated processes, playing a pivotal role in our understanding of galaxy formation and evolution. Traditionally, this link has been established through physical or empirical models. On the other hand, machine learning techniques are adaptable tools capable of handling high-dimensional data and grasping associations between numerous attributes. In particular, probabilistic models in machine learning capture the stochasticity inherent to these highly complex processes and relations.<i>Aims.<i/> We compare different probabilistic machine learning methods to model the uncertainty in the halo-galaxy connection and efficiently generate galaxy catalogs that faithfully resemble the reference sample by predicting joint distributions of central galaxy properties, namely stellar mass, color, specific star formation rate, and radius, conditioned to their host halo features.<i>Methods.<i/> The analysis is based on the IllustrisTNG300 magnetohydrodynamical simulation. The machine learning methods model the distributions in different ways. We compare a multilayer perceptron that predicts the parameters of a multivariate Gaussian distribution, a multilayer perceptron classifier, and the method of normalizing flows. The classifier predicts the parameters of a categorical distribution, which are defined in a high-dimensional parameter space through a Voronoi cell-based hierarchical scheme. The results are validated with metrics designed to test probability density distributions and the predictive power of the methods.<i>Results.<i/> We evaluate the model’s performances under various sample selections based on halo properties. The three methods exhibit comparable results, with normalizing flows showing the best performance in most scenarios. The models not only reproduce the main features of galaxy properties distributions with high-fidelity, but can also be used to reproduce the results obtained with traditional, deterministic, estimators. Our results also indicate that different halos and galaxy populations are subject to varying degrees of stochasticity, which has relevant implications for studies of large-scale structure.","PeriodicalId":8571,"journal":{"name":"Astronomy & Astrophysics","volume":"33 1","pages":""},"PeriodicalIF":6.5,"publicationDate":"2025-05-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144137253","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}

{"title":"Ray-tracing GR-MHD-generated outflows from AGNs hosting thin accretion disks","authors":"Bidisha Bandyopadhyay, Christian Fendt, Dominik R. G. Schleicher, Neil M. Nagar, Felipe Agurto-Sepúlveda, Javier Pedreros","doi":"10.1051/0004-6361/202450145","DOIUrl":"https://doi.org/10.1051/0004-6361/202450145","url":null,"abstract":"<i>Context.<i/> Active galactic nuclei (AGNs) exhibit a wide range of black hole masses and inflow/outflow properties. It is now possible to probe regions close to the event horizons of nearby supermassive black holes (SMBHs) using very long baseline interferometry (VLBI) with earth-sized baselines, as performed by the Event Horizon Telescope (EHT).<i>Aims.<i/> This study explores the emission properties of accretion and outflows near the event horizon of both low-mass and high-mass SMBHs. Using resistive general relativistic magnetohydrodynamic (GR-MHD) simulations, we model AGNs with thin Keplerian disks. This contrasts with widely studied models featuring thick disks, such as magnetically arrested disks (MADs) or the standard and normal evolution (SANE) scenario.<i>Methods.<i/> Our GR-MHD models serve as simplified representations to study disk-jet-wind structures. These simulations are postprocessed and ray-traced, using constraints of black hole mass and observed spectral energy distributions (SEDs). Thermal synchrotron emission generated near the event horizon is used to create emission maps, which are analysed by separating accretion and outflow components to determine their contributions to the total intensity.<i>Results.<i/> Whether the emission appears optically thick or thin at a given frequency depends on its position relative to the synchrotron SED peak. At 230 GHz, low-mass SMBHs appear optically thicker than high-mass ones, even at lower accretion rates. Doppler beaming affects the brightness of emission from outflows with changing viewing angles in low-mass systems.<i>Conclusions.<i/> Eddington ratios from our models align with those inferred by the EHTC for M87 and SgrA* using thicker MAD/SANE models. Although thin disks are optically thicker, their spectral properties make high-mass systems appear optically thinner at 230 GHz-ideal for probing GR effects like photon rings. In contrast, low-mass systems remain optically thicker at these frequencies because of synchrotron self-absorption, making outflow emissions near the horizon more pronounced. However, distinguishing these features remains challenging with current EHT resolution.","PeriodicalId":8571,"journal":{"name":"Astronomy & Astrophysics","volume":"18 1","pages":""},"PeriodicalIF":6.5,"publicationDate":"2025-05-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144137219","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}

{"title":"Unraveling the origin of giant exoplanets","authors":"H. Knierim, R. Helled","doi":"10.1051/0004-6361/202554506","DOIUrl":"https://doi.org/10.1051/0004-6361/202554506","url":null,"abstract":"The connection between the atmospheric composition of giant planets and their origin remains elusive. In this study, we explore how convective mixing can link the primordial planetary state to its atmospheric composition. We simulate the long-term evolution of gas giants with masses between 0.3 and 3 M<sub>J<sub/>, considering various composition profiles and primordial entropies (assuming no entropy-mass dependence). Our results show that when convective mixing is considered, the atmospheric metallicity increases with time and that this time evolution encodes information about the primordial planetary structure. Additionally, the degree of compositional mixing affects the planetary radius, altering its evolution in a measurable way. By applying mock observations, we demonstrate that combining radius and atmospheric composition can help to constrain the planetary formation history. Young systems emerge as prime targets for such characterization, with lower-mass gas giants (approaching Saturn’s mass) being particularly susceptible to mixing-induced changes. Our findings highlight convective mixing as a key mechanism for probing the primordial state of giant planets, offering new constraints on formation models and demonstrating that the conditions inside giant planets shortly after their formation are not necessarily erased over billions of years and can leave a lasting imprint on their evolution.","PeriodicalId":8571,"journal":{"name":"Astronomy & Astrophysics","volume":"3 1","pages":""},"PeriodicalIF":6.5,"publicationDate":"2025-05-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144137223","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}

{"title":"The stellar corona-chromosphere connection","authors":"S. Freund, S. Czesla, B. Fuhrmeister, P. Predehl, J. Robrade, P. C. Schneider, J. H. M. M. Schmitt","doi":"10.1051/0004-6361/202451421","DOIUrl":"https://doi.org/10.1051/0004-6361/202451421","url":null,"abstract":"Stellar activity can be observed at different wavelengths in a variety of different activity indicators. We investigated the correlation between coronal and chromospheric emissions by combining X-ray data from stars detected in the <i>eROSITA<i/> all-sky surveys (eRASS1 and eRASS:5) with Ca II infrared triplet (IRT) activity indices as published in the third <i>Gaia<i/> data release (<i>Gaia<i/> DR3). We specifically studied 24 300 and 43 200 stellar sources with reliable Ca II IRT measurement and X-ray detection in eRASS1 and eRASS:5, which is by far the largest stellar sample available so far. The largest detection fraction is obtained for highly active sources and stars of a late spectral type, while F-type and less active stars (as measured in the Ca II IRT) remain mostly undetected in X-rays. Also, the correlation is the strongest for late-type sources, while F-type stars show a rather weak correlation between the X-ray to bolometric flux ratio and the Ca II IRT activity index. The relation between the X-ray and Ca II IRT surface fluxes changes with the fractional X-ray flux without showing two separated branches as described in previous studies. For fast rotators, both activity indicators saturate at a similar Rossby number and the X-ray to bolometric flux ratio decreases faster than the IRT index for slower rotating stars. As a consequence, the ratio between X-ray and IRT fluxes is constant in the saturation regime and decreases for slow rotators.","PeriodicalId":8571,"journal":{"name":"Astronomy & Astrophysics","volume":"32 1","pages":""},"PeriodicalIF":6.5,"publicationDate":"2025-05-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144123020","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}

{"title":"The quest for high-redshift radio galaxies","authors":"Alessandro Capetti, Barbara Balmaverde, Miguel Coloma Puga, Bruno Vizzone, Ana Jimenez-Gallardo, Abigail García-Pérez, Giacomo Venturi","doi":"10.1051/0004-6361/202553967","DOIUrl":"https://doi.org/10.1051/0004-6361/202553967","url":null,"abstract":"The population of high-redshift radio galaxies (HzRGs) is still poorly studied because only a few of these objects are currently known. We here present the results of a pilot project of spectroscopic identification of HzRG candidates. The candidates are selected by combining low-frequency radio and optical surveys that cover a total of ∼2000 deg<sup>2<sup/> using the dropout technique, that is, the presence of a redshifted Lyman break in their photometric data. We focused on 39 <i>g<i/>-dropout sources, which is about one -third of the selected sources, that are expected to be at 3.0 < <i>z<i/> < 4.5. We considered single and double radio sources separately and searched for <i>g<i/>-dropout sources at the location of the midpoint of the radio structure for the latter. The host galaxy is expected to be located there. We confirm only one out of 29 candidate HzRG associated with an extended radio source. For the compact radio sources, we instead reach a success rate of 30% by confirming 3 out of 10 HzRG targets. The four newly discovered HzRGs show a wide range of spectral radio slopes. This supports the idea that not all HzRGs are ultrasteep radio sources (USSs). The criterion for USSs is most commonly used to find HzRGs, but this method only selects a subpopulation. We discuss various contamination sources for the objects that are selected with the Lyman-break method and conclude that they are likely mainly HzRGs, but with a Ly<i>α<i/> line that is underluminous with respect to expectations.","PeriodicalId":8571,"journal":{"name":"Astronomy & Astrophysics","volume":"92 1","pages":""},"PeriodicalIF":6.5,"publicationDate":"2025-05-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144123054","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}