Publications of the Astronomical Society of Australia最新文献

{"title":"The depletion of star-forming gas by AGN activity in radio Sources","authors":"S. J. Curran","doi":"10.1017/pasa.2024.1","DOIUrl":"https://doi.org/10.1017/pasa.2024.1","url":null,"abstract":"Cold, neutral interstellar gas, the reservoir for star formation, is traced through the absorption of the 21-centimetre continuum radiation by neutral hydrogen (H I). Although detected in one hundred cases in the host galaxies of distant radio sources, only recently have column densities approaching the maximum value observed in Lyman-a absorption systems (NHI ∼ 1022 cm−2) been found. Here we explore the implications these have for the hypothesis that the detection rate of H I absorption is dominated by ionising photon rate from the active galactic nucleus (AGN). We find, with the addition all of the current searches for H I absorption at z ≥0.1, a strong correlation between the H I absorption strength and the ionising photon rate, with the maximum value at which H I is detected (QHI = 2.9 ×1056 ionising photons s−1) remaining close to the theoretical value in which all of the neutral gas would be ionised in a large spiral galaxy. We also rule out other effects (excitation by the radio continuum and changing gas properties), as the dominant cause for the decrease in detection rate with redshift. Furthermore, from the maximum theoretical column density, we find that the five high column density systems have spin temperatures close to those of the Milky Way (Tspin ≲ 300 K), whereas, from our model of a gaseous galactic disk, the H I detection at QH I = 2.9 ×1056 s−1 yields Tspin ∼ 10 000 K, consistent with the gas being highly ionised.","PeriodicalId":20753,"journal":{"name":"Publications of the Astronomical Society of Australia","volume":"28 1","pages":""},"PeriodicalIF":6.3,"publicationDate":"2024-01-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139413391","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":"Radio continuum from the most massive early-type galaxies detected with ASKAP RACS","authors":"Michael J. I. Brown, Teagan A. Clarke, Andrew M. Hopkins, Ray P. Norris, T.H. Jarrett","doi":"10.1017/pasa.2023.62","DOIUrl":"https://doi.org/10.1017/pasa.2023.62","url":null,"abstract":"All very massive early-type galaxies contain supermassive blackholes but are these blackholes all sufficiently active to produce detectable radio continuum sources? We have used the 887.5 MHz Rapid ASKAP Continuum Survey DR1 to measure the radio emission from morphological early-type galaxies brighter than <jats:italic>K<jats:sub>S</jats:sub></jats:italic> = 9.5 selected from the 2MASS Redshift Survey, HyperLEDA and RC3. In line with previous studies, we find median radio power increases with infrared luminosity, with <jats:inline-graphic xmlns:xlink=\"http://www.w3.org/1999/xlink\" mime-subtype=\"png\" xlink:href=\"S1323358023000620_inline1.png\" /> although the scatter about this relation spans several orders of magnitude. All 40 of the <jats:italic>M<jats:sub>K</jats:sub></jats:italic> &lt; −25.7 early-type galaxies in our sample have measured radio flux densities that are more than 2<jats:italic>α</jats:italic> above the background noise, with 1.4 GHz radio powers spanning <jats:inline-graphic xmlns:xlink=\"http://www.w3.org/1999/xlink\" mime-subtype=\"png\" xlink:href=\"S1323358023000620_inline2.png\" />. Cross matching our sample with integral field spectroscopy of early-type galaxies reveals that the most powerful radio sources preferentially reside in galaxies with relatively low angular momentum (i.e. slow rotators). While the infrared colours of most galaxies in our early-type sample are consistent with passive galaxies with negligible star formation and the radio emission produced by active galactic nuclei or AGN remnants, very low levels of star formation could power the weakest radio sources with little effect on many other star formation rate tracers.","PeriodicalId":20753,"journal":{"name":"Publications of the Astronomical Society of Australia","volume":"298 1 1","pages":""},"PeriodicalIF":6.3,"publicationDate":"2023-12-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"138691634","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 Rapid ASKAP Continuum Survey V: cataloguing the sky at 1367.5 MHz and the second data release of RACS-mid","authors":"S. W. Duchesne, J. A. Grundy, George H. Heald, Emil Lenc, James K. Leung, David McConnell, Tara Murphy, Joshua Pritchard, Kovi Rose, Alec J. M. Thomson, Yuanming Wang, Ziteng Wang, Matthew T. Whiting","doi":"10.1017/pasa.2023.60","DOIUrl":"https://doi.org/10.1017/pasa.2023.60","url":null,"abstract":"The Australian SKA Pathfinder (ASKAP) has surveyed the sky at multiple frequencies as part of the Rapid ASKAP Continuum Survey (RACS). The first two RACS observing epochs, at 887.5 (RACS-low) and 1367.5 (RACS-mid) MHz, have been released (McConnell et al., 2020; Duchesne et al., 2023). A catalogue of radio sources from RACS-low has also been released, covering the sky south of declination +30° (Hale et al., 2021). With this paper, we describe and release the first set of catalogues from RACS-mid, covering the sky below declination +49°. The catalogues are created in a similar manner to the RACS-low catalogue, and we discuss this process and highlight additional changes. The general purpose primary catalogue covering 36 200 deg<jats:sup>2</jats:sup> features a variable angular resolution to maximise sensitivity and sky coverage across the catalogued area, with a median angular resolution of 11.2″ × 9.3″. The primary catalogue comprises 3 105 668 radio sources, including those in the Galactic Plane (2 861 923 excluding Galactic latitudes of |b| &lt; 5°) and we estimate the catalogue to be 95% complete for sources above 2 mJy. With the primary catalogue, we also provide two auxiliary catalogues. The first is a fixed-resolution, 25-arcsec catalogue approximately matching the sky coverage of the RACS-low catalogue. This 25-arcsec catalogue is constructed identically to the primary catalogue, except images are convolved to a less-sensitive 25-arcsec angular resolution. The second auxiliary catalogue is designed for time-domain science, and is the concatenation of source-lists from the original RACS-mid images with no additional convolution, mosaicking, or de-duplication of source entries to avoid losing time-variable signals. All three RACS-mid catalogues, and all RACS data products, are available through the CSIRO ASKAP Science Data Archive <jats:sup>a</jats:sup>.","PeriodicalId":20753,"journal":{"name":"Publications of the Astronomical Society of Australia","volume":"1 1","pages":""},"PeriodicalIF":6.3,"publicationDate":"2023-12-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"138567877","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":"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":"17 1","pages":""},"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":"135 4","pages":""},"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":"134 11","pages":""},"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":"134 3","pages":""},"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":"131 7","pages":""},"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&lt;jats:inline-formula&gt; &lt;jats:alternatives&gt; &lt;jats:inline-graphic xmlns:xlink=\"http://www.w3.org/1999/xlink\" mime-subtype=\"png\" xlink:href=\"S132335802300053X_inline1.png\" /&gt; &lt;jats:tex-math&gt; $_{3}$ &lt;/jats:tex-math&gt; &lt;/jats:alternatives&gt; &lt;/jats:inline-formula&gt;) (&lt;jats:italic&gt;J&lt;/jats:italic&gt;, &lt;jats:italic&gt;K&lt;/jats:italic&gt; = 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 &lt;jats:inline-formula&gt; &lt;jats:alternatives&gt; &lt;jats:inline-graphic xmlns:xlink=\"http://www.w3.org/1999/xlink\" mime-subtype=\"png\" xlink:href=\"S132335802300053X_inline2.png\" /&gt; &lt;jats:tex-math&gt; $sim$ &lt;/jats:tex-math&gt; &lt;/jats:alternatives&gt; &lt;/jats:inline-formula&gt; 3.7&lt;jats:sup&gt;′′&lt;/jats:sup&gt;). Our analysis indicates that the central region of the core is close-to-round in shape obtained both from NH&lt;jats:inline-formula&gt; &lt;jats:alternatives&gt; &lt;jats:inline-graphic xmlns:xlink=\"http://www.w3.org/1999/xlink\" mime-subtype=\"png\" xlink:href=\"S132335802300053X_inline3.png\" /&gt; &lt;jats:tex-math&gt; $_{3}$ &lt;/jats:tex-math&gt; &lt;/jats:alternatives&gt; &lt;/jats:inline-formula&gt; (1,1) and (2,2) emissions. Radially averaged kinetic temperature (&lt;jats:inline-formula&gt; &lt;jats:alternatives&gt; &lt;jats:inline-graphic xmlns:xlink=\"http://www.w3.org/1999/xlink\" mime-subtype=\"png\" xlink:href=\"S132335802300053X_inline4.png\" /&gt; &lt;jats:tex-math&gt; $T_{k}$ &lt;/jats:tex-math&gt; &lt;/jats:alternatives&gt; &lt;/jats:inline-formula&gt;) is almost constant with a mean value of &lt;jats:inline-formula&gt; &lt;jats:alternatives&gt; &lt;jats:inline-graphic xmlns:xlink=\"http://www.w3.org/1999/xlink\" mime-subtype=\"png\" xlink:href=\"S132335802300053X_inline5.png\" /&gt; &lt;jats:tex-math&gt; $sim$ &lt;/jats:tex-math&gt; &lt;/jats:alternatives&gt; &lt;/jats:inline-formula&gt; 9 K. A radially sharp decrease in kinetic temperature (&lt;jats:inline-formula&gt; &lt;jats:alternatives&gt; &lt;jats:inline-graphic xmlns:xlink=\"http://www.w3.org/1999/xlink\" mime-subtype=\"png\" xlink:href=\"S132335802300053X_inline6.png\" /&gt; &lt;jats:tex-math&gt; $T_{k}$ &lt;/jats:tex-math&gt; &lt;/jats:alternatives&gt; &lt;/jats:inline-formula&gt;) 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 &lt;jats:inline-formula&gt; &lt;jats:alternatives&gt; &lt;jats:inline-graphic xmlns:xlink=\"http://www.w3.org/1999/xlink\" mime-subtype=\"png\" xlink:href=\"S132335802300053X_inline7.png\" /&gt; &lt;jats:tex-math&gt; $beta$ &lt;/jats:tex-math&gt; &lt;/jats:alternatives&gt; &lt;/jats:inline-formula&gt;, which is defined as the ratio of rotational energy to gravitational potential energy and find that &lt;jats:inline-formula&gt; &lt;jats:alternatives&gt; &lt;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":"131 2","pages":""},"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":"93 5","pages":"0"},"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}