Astronomy & Astrophysics最新文献

{"title":"ZTF SN Ia DR2: High-velocity components in the Si IIλ6355","authors":"L. Harvey, K. Maguire, U. Burgaz, G. Dimitriadis, J. Sollerman, A. Goobar, J. Johansson, J. Nordin, M. Rigault, M. Smith, M. Aubert, R. Cartier, P. Chen, M. Deckers, S. Dhawan, L. Galbany, M. Ginolin, W. D. Kenworthy, Y.-L. Kim, C. Liu, A. A. Miller, P. Rosnet, R. Senzel, J. H. Terwel, L. Tomasella, M. Kasliwal, R. R. Laher, J. Purdum, B. Rusholme, R. Smith","doi":"10.1051/0004-6361/202449746","DOIUrl":"https://doi.org/10.1051/0004-6361/202449746","url":null,"abstract":"The Zwicky Transient Facility SN Ia Data Release 2 provides a perfect opportunity to perform a thorough search for and subsequent analysis of Si II<i>λ<i/>6355 high-velocity features (HVFs) in the pre-peak regime. The source of such features remains unclear, but potential origins include circumstellar material, as well as enhancements to the abundances or densities intrinsic to the supernova (SN) ejecta. Therefore, they may provide clues to the elusive progenitor and explosion scenarios of Type Ia SNe (SNe Ia). We employed a Markov chain Monte Carlo fitting method followed by Bayesian information criterion testing to classify single and double Si II<i>λ<i/>6355 components in the DR2. The detection efficiency of our classification method was investigated through the fitting of simulated features, which allowed us to place cuts on the spectral quality required for reliable classification. These simulations were also used to perform an analysis of the recovered parameter uncertainties and potential biases in the measurements. Within the 329 spectra sample we investigated, we identified 85 spectra exhibiting Si II<i>λ<i/>6355 HVFs. We find that HVFs decrease in strength with phase relative to their photospheric counterparts; however, this decrease can occur at different phases for different objects. HVFs with larger velocity separations from the photosphere were observed to fade earlier, leaving only the double components with smaller separations as we moved towards maximum light. Our findings suggest that around three quarters of SN Ia spectra before −11 d show high-velocity components in the Si II<i>λ<i/>6355, with this dropping to around one third in the six days before maximum light. We observed no difference between the populations of SNe Ia that do and do not form Si II<i>λ<i/>6355 HVFs in terms of the SALT2 light curve parameter <i>x<i/><sub>1<sub/>, peak magnitude, decline rate, host mass, or host colour, supporting the idea that these features are ubiquitous across the SN Ia population.","PeriodicalId":8571,"journal":{"name":"Astronomy & Astrophysics","volume":"29 1","pages":""},"PeriodicalIF":6.5,"publicationDate":"2025-03-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143703051","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":"Kinetic tomography of the Galactic plane within 1.25 kiloparsecs from the Sun","authors":"J. D. Soler, S. Molinari, S. C. O. Glover, R. J. Smith, R. S. Klessen, R. A. Benjamin, P. Hennebelle, J. E. G. Peek, H. Beuther, G. Edenhofer, E. Zari, C. Swiggum, C. Zucker","doi":"10.1051/0004-6361/202453022","DOIUrl":"https://doi.org/10.1051/0004-6361/202453022","url":null,"abstract":"We present a reconstruction of the line-of-sight motions of the local interstellar medium (ISM) based on the combination of a model of the three-dimensional dust density distribution within 1.25 kpc from the Sun and the H I and CO line emission within Galactic latitudes |<i>b<i/>| ≤ 5°. We used the histogram of oriented gradient (HOG) method, a computer vision technique for evaluating the morphological correlation between images, to match the plane-of-the-sky dust distribution across distances with the atomic and molecular line emission. We identified a significant correlation between the 3D dust model and the line emission. We employed this correlation to assign line-of-sight velocities to the dust across density channels and produce a face-on map of the local ISM radial motions with respect to the local standard of rest (LSR). We find that most of the material in the 3D dust model follows the large-scale pattern of Galactic rotation; however, we also report local departures from the rotation pattern with standard deviations of 10.8 and 6.6 km s<sup>−1<sup/> for the H I and CO line emission, respectively. The mean kinetic energy densities corresponding to these streaming motions are around 0.11 and 0.04 eV/cm<sup>3<sup/> from either gas tracer. Assuming homogeneity and isotropy in the velocity field, these values are within a factor of a few of the total kinetic energy density. These kinetic energy values are roughly comparable to other energy densities, thus confirming the near-equipartition in the local ISM. Yet, we identify energy and momentum overdensities of around a factor of ten concentrated in the Radcliffe Wave, the Split, and other local density structures. Although we do not find evidence of the local spiral arm’s impact on these energy overdensities, their distribution suggests the influence of large-scale effects that, in addition to supernova feedback, shape the energy distribution and dynamics in the solar neighborhood.","PeriodicalId":8571,"journal":{"name":"Astronomy & Astrophysics","volume":"57 1","pages":""},"PeriodicalIF":6.5,"publicationDate":"2025-03-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143702985","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":"Wandering and escaping: Recoiling massive black holes in cosmological simulations","authors":"Chi An Dong-Páez, Marta Volonteri, Yohan Dubois, Ricarda S. Beckmann, Maxime Trebitsch","doi":"10.1051/0004-6361/202453070","DOIUrl":"https://doi.org/10.1051/0004-6361/202453070","url":null,"abstract":"After a merger of two massive black holes (MBHs), the remnant receives a gravitational wave (GW) recoil kick that can have a strong effect on its future evolution. The magnitude of the kick (<i>v<i/><sub>recoil<sub/>) depends on the mass ratio and the alignment of the spins and orbital angular momenta, and therefore on the previous evolution of the MBHs. We investigate the cosmic effect of GW recoil by running for the first time a high-resolution cosmological simulation including on-the-fly GW recoil that depends on the MBH spins (evolved through accretion and mergers), masses and dynamics which are also all evolved directly in the simulation. We also run a twin simulation without GW recoil. The simulations are zoom-in type of simulations run down to <i>z<i/> = 4.4. We find that GW recoil reduces the growth of merger remnants, and can have a significant effect on the MBH-galaxy correlations and the merger rate. We find large recoil kicks across all galaxy masses in the simulation, up to a few 10<sup>11<sup/> <i>M<i/><sub>⊙<sub/>. The effect of recoil can be significant even if the MBHs are embedded in a rotationally supported gaseous structure. We investigate the dynamics of recoiling MBHs and find that MBHs remain in the centre of the host galaxy for low <i>v<i/><sub>recoil<sub/>/<i>v<i/><sub>esc<sub/> and escape rapidly for high <i>v<i/><sub>recoil<sub/>/<i>v<i/><sub>esc<sub/>. Only if <i>v<i/><sub>recoil<sub/> is comparable to <i>v<i/><sub>esc<sub/> the MBHs escape the central region of the galaxy but might remain as wandering MBHs until the end of the simulation. Recoiling MBHs are a significant fraction of the wandering MBH population. Although the dynamics of recoiling MBHs can be complex, some retain their initial radial orbits but are difficult to discern from other wandering MBHs on radial orbits. Others scatter with the halo substructure or circularise in the asymmetric potential. Our work highlights the importance of including GW recoil in cosmological simulation models.","PeriodicalId":8571,"journal":{"name":"Astronomy & Astrophysics","volume":"61 1","pages":""},"PeriodicalIF":6.5,"publicationDate":"2025-03-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143677461","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":"Growth of ex situ diffuse intragroup light in simulated galaxy groups","authors":"B. Bilata-Woldeyes, J. D. Perea, J. M. Solanes","doi":"10.1051/0004-6361/202452917","DOIUrl":"https://doi.org/10.1051/0004-6361/202452917","url":null,"abstract":"<i>Context.<i/> Deep surface photometry has revealed the presence of a faint and diffuse baryonic component permeating the intragroup space in a significant fraction of galaxy groups. This intragroup light (IGL) is primarily formed by stars that are removed from their host galaxies through gravitational interactions and now drift freely, unbound to any particular galaxy.<i>Aims.<i/> We conducted a detailed analysis to investigate how various physical parameters of galaxy groups influence the formation of ex situ IGL during the earliest stages of group assembly, and to explore their correlations with the mass and fractional abundance of this component. Additionally, we evaluated the potential of the IGL as a luminous tracer of the total mass distribution in galaxy groups, with a particular focus on systems that are far from dynamically relaxed.<i>Methods.<i/> We used controlled numerical simulations of 100 low-mass galaxy groups spanning a range of masses and numbers of constituent galaxies to track the formation and evolution of IGL during the earliest pre-virialization stages of these systems.<i>Results.<i/> We show that the IGL typically begins to form in significant amounts after the turnaround epoch, which in our simulated groups occurs at a median redshift ( ) of ∼0.85, increasing steadily thereafter. We observe a sub-linear relationship between the masses of this component and the brightest group galaxy, which indicates intertwined formation histories but differing growth rates. This suggests that other group members may also significantly contribute to the diffuse light. Additionally, we observe indications that IGL formation is enhanced in groups with lower internal velocity dispersions, which suggests that gravitational interactions between member galaxies become more efficient when their relative velocities are reduced. For two-thirds of our groups, the radial surface density profiles of the total and IGL mass are significantly aligned, with fractional discrepancies below 25%. This supports the notion that this diffuse and faint baryonic component serves as a reliable tracer of the total gravitational potential in galaxy aggregations, regardless of their dynamical state. However, the results also indicate that the degree of similarity depends on the viewing direction.","PeriodicalId":8571,"journal":{"name":"Astronomy & Astrophysics","volume":"183 1","pages":""},"PeriodicalIF":6.5,"publicationDate":"2025-03-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143677772","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":"Evolution of the near-core rotation frequency of 2497 intermediate-mass stars from their dominant gravito-inertial mode","authors":"Conny Aerts, Timothy Van Reeth, Joey S. G. Mombarg, Daniel Hey","doi":"10.1051/0004-6361/202452691","DOIUrl":"https://doi.org/10.1051/0004-6361/202452691","url":null,"abstract":"<i>Context.<i/> The sparsely sampled time-series photometry from <i>Gaia<i/> Data Release 3 (DR3) led to the discovery of more than 100 000 main-sequence non-radial pulsators. The majority of these were further scrutinised by uninterrupted high-cadence space photometry assembled by the Transiting Exoplanet Survey Satellite (TESS).<i>Aims.<i/> We combined <i>Gaia<i/> DR3 and TESS photometric light curves to estimate the internal physical properties of 2497 gravity-mode pulsators. We performed asteroseismic analyses with two major aims: (1) to measure the near-core rotation frequency and its evolution during the main sequence and (2) to estimate the mass, radius, evolutionary stage, and convective core mass from stellar modelling.<i>Methods.<i/> We relied on asteroseismic properties of <i>Kepler<i/> <i>γ<i/> Doradus and slowly pulsating B stars to derive the cyclic near-core rotation frequency, <i>f<i/><sub>rot<sub/>, of the <i>Gaia<i/>-discovered pulsators from their dominant prograde dipole gravito-inertial pulsation mode. Further, we investigated the impact of adding <i>f<i/><sub>rot<sub/> as an extra asteroseismic observable apart from the luminosity and effective temperature on the outcome of grid-based modelling from rotating stellar models.<i>Results.<i/> We offer a recipe based on linear regression to deduce <i>f<i/><sub>rot<sub/> from the dominant gravito-inertial mode frequency. It is applicable to prograde dipole modes with an amplitude above 4 mmag and occurring in the sub-inertial regime. By applying it to 2497 pulsators with such a mode, we have increased the sample of intermediate-mass dwarfs with such an asteroseismic observable by a factor of four. We used the estimate of <i>f<i/><sub>rot<sub/> to deduce spin parameters between two and six, while the sample’s near-core rotation rates range from 0.7% to 25% of the critical Keplerian rate. We used <i>f<i/><sub>rot<sub/>, along with the <i>Gaia<i/> effective temperature and luminosity to deduce the (convective core) mass, radius, and evolutionary stage from grid modelling based on rotating stellar models. We derived a decline of <i>f<i/><sub>rot<sub/> with a factor of two during the main-sequence evolution for this population of field stars, which covers a mass range from 1.3 M<sub>⊙<sub/> to 7 M<sub>⊙<sub/>. We found observational evidence for an increase in the radial order of excited gravity modes as the stars evolve. For 969 pulsators, we derived an upper limit of the radial differential rotation between the convective core boundary and the surface from <i>Gaia<i/>’s vbroad measurement and found values up to 5.4.<i>Conclusions.<i/> Our recipe to deduce the near-core rotation frequency from the dominant prograde dipole gravito-inertial mode detected in the independent <i>Gaia<i/> and TESS light curves is easy to use, facilitates applications to large samples of pulsators, and allows to map their angular momentum and evolutionary stage in the Milky Way.","PeriodicalId":8571,"journal":{"name":"Astronomy & Astrophysics","volume":"57 1","pages":""},"PeriodicalIF":6.5,"publicationDate":"2025-03-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143677468","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":"JWST Observations of Starbursts: Relations between PAH features and CO clouds in the starburst galaxy M 82","authors":"V. Villanueva, A. D. Bolatto, R. Herrera-Camus, A. Leroy, D. B. Fisher, R. C. Levy, T. Böker, L. Boogaard, S. A. Cronin, D. A. Dale, K. Emig, I. De Looze, G. P. Donnelly, T. S.-Y. Lai, L. Lenkic, L. A. Lopez, S. Lopez, D. S. Meier, J. Ott, M. Relano, J. D. Smith, E. Tarantino, S. Veilleux, F. Walter, P. van der Werf","doi":"10.1051/0004-6361/202553891","DOIUrl":"https://doi.org/10.1051/0004-6361/202553891","url":null,"abstract":"We present a study of new 7.7–11.3 μm data obtained with the <i>James Webb<i/> Space Telescope Mid-InfraRed Instrument in the starburst galaxy M 82. In particular, we focus on the dependency of the integrated CO(1–0) line intensity on the MIRI-F770W and MIRI-F1130W filter intensities to investigate the correlation between H<sub>2<sub/> content and the 7.7 and 11.3 μm features from polycyclic aromatic hydrocarbons (PAH) in M 82’s outflows. To perform our analysis, we identify CO clouds using the archival <sup>12<sup/>CO(<i>J<i/> = 1 − 0) NOEMA moment 0 map within 2 kpc from the center of M 82, with sizes ranging between ∼21 and 270 pc; then, we compute the CO-to-PAH relations for the 306 validated CO clouds. On average, the power-law slopes for the two relations in M 82 are lower than what is seen in local main-sequence spirals. In addition, there is a moderate correlation between <i>I<i/><sub>CO(1 − 0)<sub/> − <i>I<i/><sub>7.7 μm<sub/>/<i>I<i/><sub>11.3 μm<sub/> for some of the CO cloud groups analyzed in this work. Our results suggest that the extreme conditions in M 82 translate into CO not tracing the full budget of molecular gas in smaller clouds, perhaps as a consequence of photoionization and/or emission suppression of CO molecules due to hard radiation fields from the central starburst.","PeriodicalId":8571,"journal":{"name":"Astronomy & Astrophysics","volume":"41 1","pages":""},"PeriodicalIF":6.5,"publicationDate":"2025-03-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143677526","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":"Insights from the first flaring activity of a high synchrotron peaked blazar with X-ray polarization and VHE gamma rays","authors":"K. Abe, S. Abe, J. Abhir, A. Abhishek, V. A. Acciari, A. Aguasca-Cabot, I. Agudo, T. Aniello, S. Ansoldi, L. A. Antonelli, A. Arbet Engels, C. Arcaro, K. Asano, A. Babić, U. Barres de Almeida, J. A. Barrio, L. Barrios-Jiménez, I. Batković, J. Baxter, J. Becerra González, W. Bednarek, E. Bernardini, J. Bernete, A. Berti, J. Besenrieder, C. Bigongiari, A. Biland, O. Blanch, G. Bonnoli, Ž Bošnjak, E. Bronzini, I. Burelli, A. Campoy-Ordaz, A. Carosi, R. Carosi, M. Carretero-Castrillo, A. J. Castro-Tirado, D. Cerasole, G. Ceribella, Y. Chai, A. Chilingarian, A. Cifuentes, E. Colombo, J. L. Contreras, J. Cortina, S. Covino, F. D’Ammando, G. D’Amico, P. Da Vela, F. Dazzi, A. De Angelis, B. De Lotto, R. de Menezes, M. Delfino, J. Delgado, C. Delgado Mendez, F. Di Pierro, R. Di Tria, L. Di Venere, A. Dinesh, D. Dominis Prester, A. Donini, D. Dorner, M. Doro, L. Eisenberger, D. Elsaesser, J. Escudero, L. Fariña, L. Foffano, L. Font, S. Fröse, Y. Fukazawa, R. J. García López, M. Garczarczyk, S. Gasparyan, M. Gaug, J. G. Giesbrecht Paiva, N. Giglietto, F. Giordano, P. Gliwny, N. Godinović, T. Gradetzke, R. Grau, D. Green, J. G. Green, P. Günther, D. Hadasch, A. Hahn, T. Hassan, L. Heckmann, J. Herrera Llorente, D. Hrupec, R. Imazawa, D. Israyelyan, T. Itokawa, I. Jiménez Martínez, J. Jiménez Quiles, J. Jormanainen, S. Kankkunen, T. Kayanoki, D. Kerszberg, M. Khachatryan, G. W. Kluge, Y. Kobayashi, J. Konrad, P. M. Kouch, H. Kubo, J. Kushida, M. Láinez, A. Lamastra, E. Lindfors, S. Lombardi, F. Longo, R. López-Coto, M. López-Moya, A. López-Oramas, S. Loporchio, A. Lorini, E. Lyard, P. Majumdar, M. Makariev, G. Maneva, M. Manganaro, S. Mangano, K. Mannheim, M. Mariotti, M. Martínez, P. Maruševec, A. Mas-Aguilar, D. Mazin, S. Menchiari, S. Mender, D. Miceli, J. M. Miranda, R. Mirzoyan, M. Molero González, E. Molina, H. A. Mondal, A. Moralejo, T. Nakamori, C. Nanci, V. Neustroev, L. Nickel, M. Nievas Rosillo, C. Nigro, L. Nikolić, K. Nilsson, K. Nishijima, T. Njoh Ekoume, K. Noda, S. Nozaki, A. Okumura, S. Paiano, D. Paneque, R. Paoletti, J. M. Paredes, M. Peresano, M. Persic, M. Pihet, G. Pirola, F. Podobnik, P. G. Prada Moroni, E. Prandini, G. Principe, W. Rhode, M. Ribó, J. Rico, C. Righi, N. Sahakyan, T. Saito, F. G. Saturni, F. Schmuckermaier, J. L. Schubert, A. Sciaccaluga, G. Silvestri, J. Sitarek, V. Sliusar, D. Sobczynska, A. Stamerra, J. Strišković, D. Strom, M. Strzys, Y. Suda, H. Tajima, M. Takahashi, R. Takeishi, P. Temnikov, K. Terauchi, T. Terzić, M. Teshima, S. Truzzi, A. Tutone, S. Ubach, J. van Scherpenberg, S. Ventura, G. Verna, I. Viale, A. Vigliano, C. F. Vigorito, V. Vitale, I. Vovk, R. Walter, F. Wersig, M. Will, T. Yamamoto, P. K. H. Yeung, I. Liodakis, R. Middei, S. Kiehlmann, L. D. Gesu, D. E. Kim, S. R. Ehlert, M. L. Saade, P. Kaaret, W. P. Maksym, C. T. Chen, I. De La Calle Pérez, M. Perri, F. Verrecchia, O. Domann, S. Dürr, M. Feige, M. Heidemann, O. Koppitz, G. Manhalter, D. Reinhart, R. Steineke, C. Lorey, C. McCall, H. E. Jermak, I. A. Steele, V. Fallah Ramazani, J. Otero-Santos, D. Morcuende, F. J. Aceituno, V. Casanova, A. Sota, S. G. Jorstad, A. P. Marscher, C. Pauley, M. Sasada, K. S. Kawabata, M. Uemura, T. Mizuno, T. Nakaoka, H. Akitaya, I. Myserlis, M. Gurwell, G. K. Keating, R. Rao, E. Angelakis, A. Kraus","doi":"10.1051/0004-6361/202452785","DOIUrl":"https://doi.org/10.1051/0004-6361/202452785","url":null,"abstract":"&lt;i&gt;Context.&lt;i/&gt; Blazars exhibit strong variability across the entire electromagnetic spectrum, including periods of high-flux states commonly known as flares. The physical mechanisms in blazar jets responsible for flares remain poorly understood to date.&lt;i&gt;Aims.&lt;i/&gt; Our aim is to better understand the emission mechanisms during blazar flares using X-ray polarimetry and broadband observations from the archetypical TeV blazar Mrk 421, which can be studied with higher accuracy than other blazars that are dimmer and/or located farther away.&lt;i&gt;Methods.&lt;i/&gt; We studied a flaring activity from December 2023 that was characterized from radio to very high-energy (VHE; &lt;i&gt;E&lt;i/&gt; &gt; 0.1 TeV) gamma rays with MAGIC, &lt;i&gt;Fermi&lt;i/&gt;-LAT, &lt;i&gt;Swift&lt;i/&gt;, &lt;i&gt;XMM-Newton&lt;i/&gt;, and several optical and radio telescopes. These observations included, for the first time for a gamma-ray flare of a blazar, simultaneous X-ray polarization measurements with IXPE, in addition to optical and radio polarimetry data. We quantify the variability and correlations among the multi-band flux and polarization measurements, and describe the varying broadband emission within a theoretical scenario constrained by the polarization data.&lt;i&gt;Results.&lt;i/&gt; We find substantial variability in both X-rays and VHE gamma rays throughout the campaign, with the highest VHE flux above 0.2 TeV occurring during the IXPE observing window, and exceeding twice the flux of the Crab Nebula. However, the VHE and X-ray spectra are on average softer, and the correlation between these two bands is weaker than those reported in the previous flares of Mrk 421. IXPE reveals an X-ray polarization degree significantly higher than that at radio and optical frequencies, similar to previous results for Mrk 421 and other high synchrotron peaked blazars. Differently to past observations, the X-ray polarization angle varies by ∼100° on timescales of days, and the polarization degree changes by more than a factor of 4. The highest X-ray polarization degree, analyzed in 12 h time intervals, reaches 26 ± 2%, around which an X-ray counter-clockwise hysteresis loop is measured with &lt;i&gt;XMM-Newton&lt;i/&gt;. It suggests that the X-ray emission comes from particles close to the high-energy cutoff, hence possibly probing an extreme case of the Turbulent Extreme Multi-Zone model for which the chromatic trend in the polarization may be more pronounced than theoretically predicted. We model the broadband emission with a simplified stratified jet model throughout the flare. The polarization measurements imply an electron distribution in the X-ray emitting region with a very high minimum Lorentz factor ( ), which is expected in electron-ion plasma, as well as a variation of the emitting region size of up to a factor of 3 during the flaring activity. We find no correlation between the fluxes and the evolution of the model parameters, which indicates a stochastic nature of the underlying physical mechanism that likely explains the lack of a tight X-ra","PeriodicalId":8571,"journal":{"name":"Astronomy & Astrophysics","volume":"25 1","pages":""},"PeriodicalIF":6.5,"publicationDate":"2025-03-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143677525","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":"Photometric versus dynamical stellar masses and their impact on scaling relations in nearby disc galaxies","authors":"A. Marasco, S. M. Fall, E. M. Di Teodoro, P. E. Mancera Piña","doi":"10.1051/0004-6361/202553925","DOIUrl":"https://doi.org/10.1051/0004-6361/202553925","url":null,"abstract":"The study of scaling relations of disc galaxies and their evolution across cosmic time requires accurate estimates of galaxy stellar masses, <i>M<i/><sub>⋆<sub/>, over broad redshift ranges. While photometric <i>M<i/><sub>⋆<sub/> estimates (<i>M<i/><sub>phot<sub/>) based on spectral energy distribution (SED) modelling methods are employed routinely at high-<i>z<i/>, it is unclear to what extent these are compatible with dynamical <i>M<i/><sub>⋆<sub/> estimates (<i>M<i/><sub>dyn<sub/>), available for nearby galaxies. Here, we compare newly determined, SED-model-based <i>M<i/><sub>phot<sub/> with previously obtained <i>M<i/><sub>dyn<sub/> inferred via rotation curve decomposition techniques in a sample of ∼100 nearby galaxies from the SPARC database. We find that the two mass estimates show a systematic agreement at the ∼12% (0.05 dex) level and a ∼55% (0.22 dex) scatter across almost 5 dex in <i>M<i/><sub>⋆<sub/>. Our <i>M<i/><sub>phot<sub/> estimates correspond to mass-to-light ratios in the 3.6 μm band that increase gradually with 3.6 μm luminosity, as a consequence of the earlier (later) assembly history of high-mass (low-mass) disc galaxies. The choice of using either <i>M<i/><sub>dyn<sub/> or <i>M<i/><sub>phot<sub/> has only a marginal impact on the slope and zero-point of the Tully-Fisher and Fall relations: the observed orthogonal scatter in both relations is virtually the same for the two methods, and indistinguishable from that derived using a constant mass-to-light ratio in the 3.6 μm band. <i>M<i/><sub>⋆<sub/> estimates based on the assumption that discs are marginally stable lead to the largest scatter in the scaling relations.","PeriodicalId":8571,"journal":{"name":"Astronomy & Astrophysics","volume":"18 1","pages":""},"PeriodicalIF":6.5,"publicationDate":"2025-03-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143677768","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":"X-Shooting ULLYSES: Massive stars at low metallicity","authors":"J. M. Bestenlehner, P. A. Crowther, C. Hawcroft, H. Sana, F. Tramper, J. S. Vink, S. A. Brands, A. A. C. Sander","doi":"10.1051/0004-6361/202452491","DOIUrl":"https://doi.org/10.1051/0004-6361/202452491","url":null,"abstract":"<i>Context<i/>. The proximity and low dust extinction of the Magellanic Clouds provides an ideal environment for metal-poor massive stars to be studied in detail. The <i>Hubble Space Telescope<i/> ULLYSES initiative has provided exquisite ultraviolet spectroscopy of a large sample of OB stars in the Magellanic Clouds, and its legacy value has been enhanced through the acquisition of optical VLT/XShooter spectroscopy (XShootU).<i>Aims<i/>. We aim to determine the spectral types and physical properties of 122 LMC and 103 SMC OB stars observed via XShootU. Physical parameters are required for these to serve as templates in spectral libraries of metal-poor massive stars. We also aim to identify double-lined binaries and OeBe stars for which analysis requires non-standard treatment.<i>Methods<i/>. We have applied a pipeline designed to analyse large spectroscopic samples of hot luminous stars to XShootU spectroscopic datasets, together with grids of synthetic model spectra computed with the non-Local Thermodynamic Equilibrium atmospheric code FASTWIND at LMC and SMC metallicities.<i>Results<i/>. We have determined physical and wind properties of 97 LMC and 77 SMC massive stars, ranging from O2 to B9 subtypes, representing the majority of the XShootU OB sample (OeBe and candidate SB2 systems are excluded). Results are broadly in agreement with previous optical spectroscopic studies, with evolutionary masses spanning 12–117 <i>M<i/><sub>⊙<sub/> in the LMC and 11–74 <i>M<i/><sub>⊙<sub/> in the SMC. We have determined a revised <i>T<i/><sub>eff<sub/>-spectral type calibration for Magellanic Cloud stars, identified stars with peculiar radial velocities, and compared wind properties of high luminosity O stars with dense winds, revealing ∼ 0.27 dex higher wind momenta of LMC stars with respect to SMC counterparts. Incorporating the recent empirical metallicity dependence of <i>Z<i/><sup>0.22<sup/> for wind velocities, this suggests a mass-loss dependence of <i>Z<i/><sup>0.5<sup/> for luminous O stars. Studies incorporating ultraviolet mass-loss diagnostics are required for OB stars with weak winds and/or low luminosities.","PeriodicalId":8571,"journal":{"name":"Astronomy & Astrophysics","volume":"49 1","pages":""},"PeriodicalIF":6.5,"publicationDate":"2025-03-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143677530","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 Galactic bulge exploration","authors":"Z. Prudil, A. Kunder, L. Beraldo e Silva, S. Gough-Kelly, M. Rejkuba, S. R. Anderson, V. P. Debattista, O. Gerhard, R. M. Rich, D. M. Nataf, A. J. Koch-Hansen, A. Savino, I. Dékány","doi":"10.1051/0004-6361/202450620","DOIUrl":"https://doi.org/10.1051/0004-6361/202450620","url":null,"abstract":"RR Lyrae stars toward the Galactic bulge are used to investigate whether this old stellar population traces the Galactic bar. Although the bar is known to dominate the mass in the inner Galaxy, there is no consensus on whether the RR Lyrae star population, which constitutes some of the most ancient stars in the bulge and thus traces the earliest epochs of star formation, contributes to the barred bulge. We create new reddening maps and derive new extinction laws from visual to near-infrared passbands using improved RR Lyrae period-absolute magnitude-metallicity relations, enabling distance estimates for individual bulge RR Lyrae variables. The extinction law is most uniform in and and the distances to individual RR Lyrae based on these colors are determined with an accuracy of 6 and 4%, respectively. Using only the near-infrared passbands for distance estimation, we infer the distance to the Galactic center equal to pc after geometrical correction. We show that variations in the extinction law toward the Galactic bulge can mimic a barred spatial distribution in the bulge RR Lyrae star population in visual passbands. This arises from a gradient in extinction differences along Galactic longitudes and latitudes, which can create the perception of the Galactic bar, particularly when using visual passband-based distances. A barred angle in the RR Lyrae spatial distribution disappears when near-infrared passband-based distances are used, as well as when reddening law variations are incorporated in visual passband-based distances. The prominence of the bar, traced by RR Lyrae stars, depends on their metallicity, with metal-poor RR Lyrae stars ([Fe/H] < −1.0 dex) showing little to no tilt with respect to the bar. Metal-rich ([Fe/H] > −1.0 dex) RR Lyrae stars do show a barred bulge signature in spatial properties derived using near-infrared distances, with an angle of <i>ι<i/> = 18 ± 5 deg, consistent with previous bar measurements from the literature. This also hints at a younger age for this RR Lyrae subgroup. The 5D kinematic analysis, primarily based on transverse velocities, indicates a rotational lag in RR Lyrae stars compared to red clump giants. Despite variations in the extinction law, our kinematic conclusions are robust across different distance estimation methods.","PeriodicalId":8571,"journal":{"name":"Astronomy & Astrophysics","volume":"6 1","pages":""},"PeriodicalIF":6.5,"publicationDate":"2025-03-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143677590","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}