Publications of the Astronomical Society of Australia最新文献

{"title":"RadioGalaxyNET: Dataset and Novel Computer Vision Algorithms for the Detection of Extended Radio Galaxies and Infrared Hosts","authors":"Nikhel Gupta, Zeeshan Hayder, Ray P. Norris, Minh Huynh, Lars Petersson","doi":"10.1017/pasa.2023.64","DOIUrl":"https://doi.org/10.1017/pasa.2023.64","url":null,"abstract":"Creating radio galaxy catalogues from next-generation deep surveys requires automated identification of associated components of extended sources and their corresponding infrared hosts. In this paper, we introduce RadioGalaxyNET, a multimodal dataset, and a suite of novel computer vision algorithms designed to automate the detection and localization of multi-component extended radio galaxies and their corresponding infrared hosts. The dataset comprises 4,155 instances of galaxies in 2,800 images with both radio and infrared channels. Each instance provides information about the extended radio galaxy class, its corresponding bounding box encompassing all components, the pixel-level segmentation mask, and the keypoint position of its corresponding infrared host galaxy. RadioGalaxyNET is the first dataset to include images from the highly sensitive Australian Square Kilometre Array Pathfinder (ASKAP) radio telescope, corresponding infrared images, and instance-level annotations for galaxy detection.We benchmark several object detection algorithms on the dataset and propose a novel multimodal approach to simultaneously detect radio galaxies and the positions of infrared hosts.","PeriodicalId":20753,"journal":{"name":"Publications of the Astronomical Society of Australia","volume":null,"pages":null},"PeriodicalIF":6.3,"publicationDate":"2023-12-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"138567428","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"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 magnetic field and flows of solar active regions with persistent magnetic bipoles before emergence","authors":"C.S. Alley, H. Schunker","doi":"10.1017/pasa.2023.52","DOIUrl":"https://doi.org/10.1017/pasa.2023.52","url":null,"abstract":"Magnetic active regions on the Sun are harbingers of space weather. Understanding the physics of how they form and evolve will improve space weather forecasting. Our aim is to characterise the surface magnetic field and flows for a sample of active regions with persistent magnetic bipoles prior to emergence. We identified 42 emerging active regions (EARs), in the Solar Dynamics Observatory Helioseismic Emerging Active Region survey (Schunker et al. 2016, A&amp;A. 595, A107), associated with small magnetic bipoles at least one day before the time of emergence. We then identified a contrasting sample of 42 EARs that emerge more abruptly without bipoles before emergence. We computed the supergranulation-scale surface flows using helioseismic holography. We averaged the flow maps and magnetic field maps over all active regions in each sample at each time interval from 2 d before emergence to 1 d after. We found that EARs associated with a persistent pre-emergence bipole evolve to be, on average, lower flux active regions than EARs that emerge more abruptly. Further, we found that the EARs that emerge more abruptly do so with a diverging flow of <jats:inline-formula> <jats:alternatives> <jats:inline-graphic xmlns:xlink=\"http://www.w3.org/1999/xlink\" mime-subtype=\"png\" xlink:href=\"S1323358023000528_inline1.png\" /> <jats:tex-math> $(3pm 0.6) times 10^{-6}$ </jats:tex-math> </jats:alternatives> </jats:inline-formula> s<jats:inline-formula> <jats:alternatives> <jats:inline-graphic xmlns:xlink=\"http://www.w3.org/1999/xlink\" mime-subtype=\"png\" xlink:href=\"S1323358023000528_inline2.png\" /> <jats:tex-math> $^{-1}$ </jats:tex-math> </jats:alternatives> </jats:inline-formula> on the order of 50–100 ms<jats:inline-formula> <jats:alternatives> <jats:inline-graphic xmlns:xlink=\"http://www.w3.org/1999/xlink\" mime-subtype=\"png\" xlink:href=\"S1323358023000528_inline3.png\" /> <jats:tex-math> $^{-1}$ </jats:tex-math> </jats:alternatives> </jats:inline-formula>. Our results show that there is a statistical dependence of the surface flow signature throughout the emergence process on the maximum magnetic flux of the active region.","PeriodicalId":20753,"journal":{"name":"Publications of the Astronomical Society of Australia","volume":null,"pages":null},"PeriodicalIF":6.3,"publicationDate":"2023-12-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"138507239","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"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":"Lyman-α at Cosmic Noon II: The relationship between kinematics and Lyman-α in z ∼ 2–3 Lyman Break Galaxies","authors":"Garry Foran, Jeff Cooke, Emily Wisnioski, Naveen Reddy, Charles Steidel","doi":"10.1017/pasa.2023.61","DOIUrl":"https://doi.org/10.1017/pasa.2023.61","url":null,"abstract":"We report for the first time a relationship between galaxy kinematics and net Lyman-α equivalent width (net Lyα EW) in star forming galaxies during the epoch of peak cosmic star formation. Building on the previously reported broadband imaging segregation of Lyα-emitting and Lyα-absorbing Lyman-break galaxies (LBGs) at <jats:italic>z</jats:italic> ∼ 2 (Paper I in this series) and previously at <jats:italic>z</jats:italic> ∼ 3, we use the Lyα spectral type classification method to study the relationship between net Lyα EWand nebular emission-line kinematics in samples of <jats:italic>z</jats:italic> ∼ 2 and <jats:italic>z</jats:italic> ∼ 3 LBGs drawn from the literature, for which matching rest-frame UV photometry, consistently measured net Lyα EWs, and kinematic classifications from integral field unit spectroscopy are available. we show that <jats:italic>z</jats:italic> ∼ 2 and <jats:italic>z</jats:italic> ∼ 3 LBGs segregate in colour-magnitude space according to their kinematic properties and Lyman-α spectral type, and conclude that LBGs with Lyα dominant in absorption (aLBGs) are almost exclusively rotation-dominated (presumably disc-like) systems, and LBGs with Lyα dominant in emission (eLBGs) characteristically have dispersion-dominated kinematics. We quantify the relationship between the strength of rotational dynamic support (as measured using <jats:italic>v</jats:italic><jats:sub>obs</jats:sub>/2σ<jats:sub>int</jats:sub> and <jats:italic>v</jats:italic><jats:sub>rot</jats:sub>/σ0) and net Lyα EWfor subsets of our kinematic sample where these data are available, and demonstrate the consistency of our result with other properties that scale with net Lyα EWand kinematics. Based on these findings, we suggest a method by which large samples of rotation- and dispersion-dominated galaxies might be selected using broadband imaging in as few as three filters and/or net Lyα EWalone. If confirmed with larger samples, application of this method will enable an understanding of galaxy kinematic behaviour over large scales in datasets from current and future large-area and all-sky photometric surveys that will select hundreds of millions of LBGs in redshift ranges from <jats:italic>z</jats:italic> ∼ 2 – 6 across many hundreds to thousands of Mpc. Finally, we speculate that the combination of our result linking net Lyα EW and nebular emission-line kinematics with the known large-scale clustering behaviour of Lyα-absorbing and Lyα-emitting LBGs is evocative of an emergent bimodality of early galaxies that is consistent with a nascent morphology-density relation at <jats:italic>z</jats:italic> ∼ 2 – 3.","PeriodicalId":20753,"journal":{"name":"Publications of the Astronomical Society of Australia","volume":null,"pages":null},"PeriodicalIF":6.3,"publicationDate":"2023-11-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"138507240","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"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 MAGPI Survey: Drivers of kinematic asymmetries in the ionised gas of z ∼ 0.3 star-forming galaxies","authors":"R. S. Bagge, C. Foster, A. Battisti, S. Bellstedt, M. Mun, K. Harborne, S. Barsanti, T. Mendel, S. Brough, S.M. Croom, C.D.P. Lagos, T. Mukherjee, Y. Peng, R-S. Remus, G. Santucci, P. Sharda, S. Thater, J. van de Sande, L. M. Valenzuela, E. Wisnioski, T. Zafar, B. Ziegler","doi":"10.1017/pasa.2023.58","DOIUrl":"https://doi.org/10.1017/pasa.2023.58","url":null,"abstract":"Galaxy gas kinematics are sensitive to the physical processes that contribute to a galaxy’s evolution. It is expected that external processes will cause more significant kinematic disturbances in the outer regions, while internal processes will cause more disturbances for the inner regions. Using a subsample of 47 galaxies (0.27 &lt; <jats:italic>z</jats:italic> &lt; 0.36) from the Middle Ages Galaxy Properties with Integral Field Spectroscopy (MAGPI) survey, we conduct a study into the source of kinematic disturbances by measuring the asymmetry present in the ionised gas line-of-sight velocity maps at the 0.5<jats:italic>Re</jats:italic> (inner regions) and 1.5<jats:italic>Re</jats:italic> (outer regions) elliptical annuli. By comparing the inner and outer kinematic asymmetries, we aim to better understand what physical processes are driving the asymmetries in galaxies. We find the local environment plays a role in kinematic disturbance, in agreement with other integral field spectroscopy studies of the local universe, with most asymmetric systems being in close proximity to a more massive neighbour. We do not find evidence suggesting that hosting an Active Galactic Nucleus (AGN) contributes to asymmetry within the inner regions, with some caveats due to emission line modelling. In contrast to previous studies, we do not find evidence that processes leading to asymmetry also enhance star formation in MAGPI galaxies. Finally, we find a weak anti-correlation between stellar mass and asymmetry (ie. high stellar mass galaxies are less asymmetric). We conclude by discussing possible sources driving the asymmetry in the ionised gas, such as disturbances being present in the colder gas phase (either molecular or atomic) prior to the gas being ionised, and non-axisymmetric features (e.g., a bar) being present in the galactic disk. Our results highlight the complex interplay between ionised gas kinematic disturbances and physical processes involved in galaxy evolution.","PeriodicalId":20753,"journal":{"name":"Publications of the Astronomical Society of Australia","volume":null,"pages":null},"PeriodicalIF":6.3,"publicationDate":"2023-11-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"138507241","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"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":"Estimating Stellar Parameters and Identifying Very Metal-poor Stars for Low-resolution Spectra (R ∼ 200)","authors":"Tianmin Wu, Yude Bu, Jianhang Xie, Junchao Liang, Wei Liu, Zhenping Yi, Xiaoming Kong, Meng Liu","doi":"10.1017/pasa.2023.59","DOIUrl":"https://doi.org/10.1017/pasa.2023.59","url":null,"abstract":"Very metal-poor (VMP, [Fe/H]&lt;-2.0) stars serve as invaluable repositories of insights into the nature and evolution of the first-generation stars formed in the early galaxy. The upcoming China Space Station Telescope (CSST) will provide us with a large amount of spectral data that may contain plenty of VMP stars, and thus it is crucial to determine the stellar atmospheric parameters (<jats:italic>T</jats:italic><jats:sub>eff</jats:sub> , log g, and [Fe/H]) for low-resolution spectra similar to the CSST spectra (<jats:italic>R</jats:italic> ∼ 200). This study introduces a novel two-dimensional Convolutional Neural Network (CNN) model, comprised of three convolutional layers and two fully connected layers. The model’s proficiency is assessed in estimating stellar parameters, particularly metallicity, from low-resolution spectra (<jats:italic>R</jats:italic> ∼ 200), with a specific focus on enhancing the search for VMP stars within the CSST spectral data. We mainly use 10,008 spectra of VMP stars from LAMOST DR3, and 16,638 spectra of non-VMP stars ([Fe/H]&gt;-2.0) from LAMOST DR8 for the experiments and apply random forest and support vector machine methods to make comparisons. The resolution of all spectra is reduced to <jats:italic>R</jats:italic> ∼ 200 to match the resolution of the CSST, followed by preprocessing and transformation into two-dimensional spectra for input into the CNN model. The validation and practicality of this model are also tested on the MARCS synthetic spectra. The results show that using the CNN model constructed in this paper, we obtain Mean Absolute Error (MAE) values of 99.40 K for <jats:italic>T</jats:italic><jats:sub>eff</jats:sub> , 0.22 dex for log g, 0.14 dex for [Fe/H], and 0.26 dex for [C/Fe] on the test set. Besides, the CNN model can efficiently identify VMP stars with a precision rate of 94.77%, a recall rate of 93.73%, and an accuracy of 95.70%. This paper powerfully demonstrates the effectiveness of the proposed CNN model in estimating stellar parameters for low-resolution spectra (<jats:italic>R</jats:italic> ∼ 200) and recognizing VMP stars that are of interest for stellar population and galactic evolution work.","PeriodicalId":20753,"journal":{"name":"Publications of the Astronomical Society of Australia","volume":null,"pages":null},"PeriodicalIF":6.3,"publicationDate":"2023-11-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"138507244","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"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":"Studying the internal structures of the central region of prestellar core L1517B in Taurus molecular cloud using ammonia (NH3) (1,1) and (2,2) lines","authors":"Atanu Koley","doi":"10.1017/pasa.2023.53","DOIUrl":"https://doi.org/10.1017/pasa.2023.53","url":null,"abstract":"Measurement of internal structures in the prestellar core is essential for understanding the initial conditions prior to star formation. In this work, we study the ammonia lines (NH<jats:inline-formula> <jats:alternatives> <jats:inline-graphic xmlns:xlink=\"http://www.w3.org/1999/xlink\" mime-subtype=\"png\" xlink:href=\"S132335802300053X_inline1.png\" /> <jats:tex-math> $_{3}$ </jats:tex-math> </jats:alternatives> </jats:inline-formula>) (<jats:italic>J</jats:italic>, <jats:italic>K</jats:italic> = 1,1 and 2,2) in the central region of the prestellar core L1517B with the Karl G. Jansky Very Large Array (VLA) radio telescope (spatial resolution <jats:inline-formula> <jats:alternatives> <jats:inline-graphic xmlns:xlink=\"http://www.w3.org/1999/xlink\" mime-subtype=\"png\" xlink:href=\"S132335802300053X_inline2.png\" /> <jats:tex-math> $sim$ </jats:tex-math> </jats:alternatives> </jats:inline-formula> 3.7<jats:sup>′′</jats:sup>). Our analysis indicates that the central region of the core is close-to-round in shape obtained both from NH<jats:inline-formula> <jats:alternatives> <jats:inline-graphic xmlns:xlink=\"http://www.w3.org/1999/xlink\" mime-subtype=\"png\" xlink:href=\"S132335802300053X_inline3.png\" /> <jats:tex-math> $_{3}$ </jats:tex-math> </jats:alternatives> </jats:inline-formula> (1,1) and (2,2) emissions. Radially averaged kinetic temperature (<jats:inline-formula> <jats:alternatives> <jats:inline-graphic xmlns:xlink=\"http://www.w3.org/1999/xlink\" mime-subtype=\"png\" xlink:href=\"S132335802300053X_inline4.png\" /> <jats:tex-math> $T_{k}$ </jats:tex-math> </jats:alternatives> </jats:inline-formula>) is almost constant with a mean value of <jats:inline-formula> <jats:alternatives> <jats:inline-graphic xmlns:xlink=\"http://www.w3.org/1999/xlink\" mime-subtype=\"png\" xlink:href=\"S132335802300053X_inline5.png\" /> <jats:tex-math> $sim$ </jats:tex-math> </jats:alternatives> </jats:inline-formula> 9 K. A radially sharp decrease in kinetic temperature (<jats:inline-formula> <jats:alternatives> <jats:inline-graphic xmlns:xlink=\"http://www.w3.org/1999/xlink\" mime-subtype=\"png\" xlink:href=\"S132335802300053X_inline6.png\" /> <jats:tex-math> $T_{k}$ </jats:tex-math> </jats:alternatives> </jats:inline-formula>) has not been observed inside the central dense nucleus of this prestellar core. In addition, we also notice that there is an overall velocity gradient from north-east to south-west direction in this region, which may be indicative of the rotational motion of the core. We then calculate the parameter <jats:inline-formula> <jats:alternatives> <jats:inline-graphic xmlns:xlink=\"http://www.w3.org/1999/xlink\" mime-subtype=\"png\" xlink:href=\"S132335802300053X_inline7.png\" /> <jats:tex-math> $beta$ </jats:tex-math> </jats:alternatives> </jats:inline-formula>, which is defined as the ratio of rotational energy to gravitational potential energy and find that <jats:inline-formula> <jats:alternatives> <jats:inline-graphic xmlns:xlink=\"http://www.w3.org/1999/xlink\" mime-subtype=\"png","PeriodicalId":20753,"journal":{"name":"Publications of the Astronomical Society of Australia","volume":null,"pages":null},"PeriodicalIF":6.3,"publicationDate":"2023-11-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"138507245","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"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":"A Near-Field Treatment of Aperture Synthesis Techniques using the Murchison Widefield Array","authors":"S. Prabu, S.J. Tingay, A. Williams","doi":"10.1017/pasa.2023.56","DOIUrl":"https://doi.org/10.1017/pasa.2023.56","url":null,"abstract":"Abstract Typical radio interferometer observations are performed assuming the source of radiation to be in the far-field of the instrument, resulting in a two-dimensional Fourier relationship between the observed visibilities in the aperture plane and the sky brightness distribution (over a small field of view). When near-field objects are present in an observation, the standard approach applies far-field delays during correlation, resulting in loss of signal coherence for the signal from the near-field object. In this paper, we demonstrate near-field aperture synthesis techniques using a Murchison Widefield Array observation of the International Space Station (ISS), as it appears as a bright near-field object. We perform visibility phase corrections to restore coherence across the array for the near-field object (however not restoring coherence losses due to time and frequency averaging at the correlator). We illustrate the impact of the near-field corrections in the aperture plane and the sky plane. The aperture plane curves to match the curvature of the near-field wavefront, and in the sky plane near-field corrections manifest as fringe rotations at different rates as we bring the focal point of the array from infinity to the desired near-field distance. We also demonstrate the inverse scenario of inferring the line-of-sight range of the ISS by inverting the apparent curvature of the wavefront seen by the aperture. We conclude the paper by briefly discussing the limitations of the methods developed and the near-field science cases where our approach can be exploited.","PeriodicalId":20753,"journal":{"name":"Publications of the Astronomical Society of Australia","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2023-11-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135092061","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"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":"Measuring the global 21-cm signal with the MWA-II: improved characterisation of lunar-reflected radio frequency interference","authors":"Himanshu Tiwari, Benjamin McKinley, Cathryn M. Trott, Nithyanandan Thyagarajan","doi":"10.1017/pasa.2023.57","DOIUrl":"https://doi.org/10.1017/pasa.2023.57","url":null,"abstract":"Abstract Radio interferometers can potentially detect the sky-averaged signal from the Cosmic Dawn (CD) and the Epoch of Reionisation (EoR) by studying the Moon as a thermal block to the foreground sky. The first step is to mitigate the Earth-based RFI reflections (Earthshine) from the Moon, which significantly contaminate the FM band ≈ 88 – 110 MHz, crucial to CD-EoR science. We analysed MWA phase-I data from 72 – 180 MHz at 40 kHz resolution to understand the nature of Earthshine over three observing nights. We took two approaches to correct the Earthshine component from the Moon. In the first method, we mitigated the Earthshine using the flux density of the two components from the data, while in the second method, we used simulated flux density based on an FM catalogue to mitigate the Earthshine. Using these methods, we were able to recover the expected Galactic foreground temperature of the patch of sky obscured by the Moon. We performed a joint analysis of the Galactic foregrounds and the Moon’s intrinsic temperature ( T Moon ) while assuming that the Moon has a constant thermal temperature throughout three epochs. We found T Moon to be at 184.4±2.6 K and 173.8±2.5 K using the first and the second methods, respectively, and the best-fit values of the Galactic spectral index ( α ) to be within the 5% uncertainty level when compared with the global sky models. Compared with our previous work, these results improved constraints on the Galactic spectral index and the Moon’s intrinsic temperature. We also simulated the Earthshine atMWA between November and December 2023 to find suitable observing times less affected by the Earthshine. Such observing windows act as Earthshine avoidance and can be used to perform future global CD-EoR experiments using the Moon with the MWA.","PeriodicalId":20753,"journal":{"name":"Publications of the Astronomical Society of Australia","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2023-11-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135342275","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"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":"Inviscid protostellar disc ring formation and high density ring edges due to the ejection and subsequent infall of material onto a protostellar disc","authors":"Kurt Liffman","doi":"10.1017/pasa.2023.55","DOIUrl":"https://doi.org/10.1017/pasa.2023.55","url":null,"abstract":"Abstract Discs of gas and dust are ubiquitous around protostars. Hypothetical viscous interactions within the disc are thought to cause the gas and dust to accrete onto the star. Turbulence within the disc is theorised to be the source of this disc viscosity. However, observed protostellar disc turbulence often appears to be small and not always conducive to disc accretion. In addition, theories for disc and planet evolution have difficulty in explaining the observed disc rings/gaps which form much earlier than expected. Protostellar accretion discs are observed to contain significant quantities of dust and pebbles. Observations also show that some of this material is ejected from near the protostar, where it travels to the outer regions of the disc. Such solid infalling material has a relatively small amount of angular momentum compared to the material in the disc. This infalling material lowers the angular momentum of the disc and should drive a radial flow towards the protostar. We show that the local radial accretion speed of the disc is proportional to the mass rate of infalling material onto the disc. Higher rates of infall onto the disc implies higher radial accretion disc speeds. As such, regions with high rates of infall of gas, dust, and pebbles onto the disc will produce gaps on relatively short timescales in the disc, while regions associated with relative low rates of infalling material will produce disc rings. As such, the inner edge of a disc gap will tend to have a higher surface density, which may enhance the probability of planet formation. In addition, the outer edge of a disc gap will act as a dust trap and may also become a site for planet formation. For the early Solar System, such a process may have collected O16-poor forsterite dust from the inner regions of the protosolar disc and O16-rich CAIs and AOAs from the inner edge regions of the protosolar disc, thereby constructing a region favourable to the formation of prechondritic planetesimals.","PeriodicalId":20753,"journal":{"name":"Publications of the Astronomical Society of Australia","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2023-11-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135635347","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"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":"Dynamical aspects of Galactic habitability in N-body simulations","authors":"A. Mitrašinović, B. Vukotić, M. Micic, M. M. Ćirković","doi":"10.1017/pasa.2023.54","DOIUrl":"https://doi.org/10.1017/pasa.2023.54","url":null,"abstract":"Abstract Recent studies of Galactic evolution revealed that the dynamics of the stellar component might be one of the key factors when considering galactic habitability. We run an N-body simulation model of the Milky Way, which we evolve for 10 Gyr, to study the secular evolution of stellar orbits and the resulting galactic habitability-related properties, i.e., the density of the stellar component and close stellar encounters. The results indicate that radial migrations are not negligible, even in a simple axisymmetric model with mild levels of dynamical heating, and that the net outward diffusion of the stellar component can populate galactic outskirts with habitable systems. Habitable environment is also likely even at sub-Solar galactocentric radii, because the rate of close encounters should not significantly degrade habitability. Stars that evolve from non-circular to stable nearly-circular orbits typically migrate outwards, settling down in a broad Solar neighborhood. The region between R ≈ 3 kpc and R ≈ 12 kpc represents the zone of radial mixing, which can blur the boundaries of the Galactic Habitable Zone, as it has been conventionally understood. The present-day stable population of the stars in the Solar neighborhood originates from this radial mixing zone, with most of the stars coming from the inner regions. The Solar system can be considered as a typical Milky Way habitable system because it migrated outwards from the metal-rich inner regions of the Disk and has a circular orbit in the present epoch. We conclude that the boundaries of the Galactic Habitable Zone cannot be sharply confined for a given epoch because of the mixing caused by the stellar migrations and secular evolution of stellar orbits.","PeriodicalId":20753,"journal":{"name":"Publications of the Astronomical Society of Australia","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2023-11-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135636955","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"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}