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Item The 1.28 GHz MeerKAT DEEP2 Image(2020) Asad, K; Cotton, W; Mauch, TWe present the confusion-limited 1.28 GHz MeerKAT DEEP2 image covering one qb » ¢ 68 FWHM primarybeam area with θ = 7 6 FWHM resolution and s = m - n 0.55 0.01 Jy beam 1 rms noise. Its J2000 center position α = 04h 13m 26 4, δ = −80° 00′ 00″ was selected to minimize artifacts caused by bright sources. We introduce the new 64-element MeerKAT array and describe commissioning observations to measure the primary-beam attenuation pattern, estimate telescope pointing errors, and pinpoint (u, v) coordinate errors caused by offsets in frequency or time. We constructed a 1.4 GHz differential source count by combining a power-law count fit to the DEEP2 confusion P(D) distribution from 0.25 to 10 μJy with counts of individual DEEP2 sources between 10 μJy and 2.5 mJy. Most sources fainter than S ∼ 100 μJy are distant star-forming galaxies (SFGs) obeying the far-IR/ radio correlation, and sources stronger than 0.25 μJy account for ∼93% of the radio background produced by SFGs. For the first time, the DEEP2 source count has reached the depth needed to reveal the majority of the star formation history of the universe. A pure luminosity evolution of the 1.4 GHz local luminosity function consistent with the Madau & Dickinson model for the evolution of SFGs based on UV and infrared data underpredicts our 1.4 GHz source count in the range -5 log Jy 4 [ ( )] S -Item The 2020 release of the ExoMol database: Molecular line lists for exoplanet and other hot atmospheres(Elsevier, 2020) Lynas-Gray, A.E.; Tennyson, Jonathan; Yurchenko, SergeyThe ExoMol database (www.exomol.com) provides molecular data for spectroscopic studies of hot atmospheres. While the data are intended for studies of exoplanets and other astronomical bodies, the dataset is widely applicable. The basic form of the database is extensive line lists; these are supplemented with partition functions, state lifetimes, cooling functions, Landé g-factors, temperature-dependent cross sections, opacities, pressure broadening parameters, k-coefficients and dipoles. This paper presents the latest release of the database which has been expanded to consider 80 molecules and 190 isotopologues totaling over 700 billion transitions. While the spectroscopic data are concentrated at infrared and visible wavelengths, ultraviolet transitions are being increasingly considered in response to requests from observers. The core of the database comes from the ExoMol project which primarily uses theoretical methods, albeit usually fine-tuned to reproduce laboratory spectra, to generate very extensive line lists for studies of hot bodies. The data have recently been supplemented by line lists derived from direct laboratory observations, albeit usually with the use of ab initiotransition intensities. A major push in the new release is towards accurate characterisation of transition frequencies for use in high resolution studies of exoplanets and other bodies.Item An ∼600 pc view of the strongly lensed, massive main-sequence galaxy J0901: a baryon-dominated, thick turbulent rotating disk with a clumpy cold gas ring at z = 2.259(The astrophysical journal, 2023) Baker, Andrew J.; Liu, Daizhong; Schreiber, N. M. FörsterWe present a high-resolution kinematic study of the massive main-sequence star-forming galaxy (SFG) SDSS J090122.37+181432.3 (J0901) at z = 2.259, using ∼0.″36 Atacama Large Millimeter/submillimeter Array CO(3-2) and ∼0.″1-0.″5 SINFONI/VLT Hα observations. J0901 is a rare, strongly lensed but otherwise normal massive ( log ( M ⋆ / M ⊙ ) ∼ 11 ) main-sequence SFG, offering a unique opportunity to study a typical massive SFG under the microscope of lensing. Through forward dynamical modeling incorporating lensing deflection, we fit the CO and Hα kinematics in the image plane out to about one disk effective radius (R e ∼ 4 kpc) at an ∼600 pc delensed physical resolution along the kinematic major axis. Our results show high intrinsic dispersions of the cold molecular and warm ionized gas (σ 0,mol. ∼ 40 km s−1 and σ 0,ion. ∼ 66 km s−1) that remain constant out to R e; a moderately low dark matter fraction (f DM ∼ 0.3-0.4) within R e; and a centrally peaked Toomre Q parameter—agreeing well with the previously established σ 0 versus z, f DM versus Σbaryon, and Q's radial trends using large-sample non-lensed main-sequence SFGs. Our data further reveal a high stellar mass concentration within ∼1-2 kpc with little molecular gas, and a clumpy molecular gas ring-like structure at R ∼ 2-4 kpc, in line with the inside-out quenching scenario. Our further analysis indicates that J0901 had assembled half of its stellar mass only ∼400 Myr before its observed cosmic time, and the cold gas ring and dense central stellar component are consistent with signposts of a recent wet compaction event of a highly turbulent disk found in recent simulations. © 2023. The Author(s). Published by the American Astronomical Society.Item A census of the deep radio sky with the vla. i. 10 ghz survey of the goods-n field(American Astronomical Society, 2024) Jiménez-Andrade, Eric Faustino; Taylor, Russ; Murphy, EricWe present the first high-resolution, high-frequency radio continuum survey that fully maps an extragalactic deep field: the 10 GHz survey of the Great Observatories Origins Deep Survey-North (GOODS-N) field. This is a Large Program of the Karl G. Jansky Very Large Array that allocated 380 hours of observations using the X-band (8 − 12 GHz) receivers, leading to a 10 GHz mosaic of the GOODS-field with an average rms noise σn = 671 nJy beam−1 and angular resolution θ1/2 = 0. ′′22 across 297 arcmin2 . To maximize the brightness sensitivity we also produce a low-resolution mosaic with θ1/2 = 1. ′′0 and σn = 968 nJy beam−1 , from which we derive our master catalog containing 256 radio sources detected with peak signal-to-noise ratio ≥ 5. Radio source size and flux density estimates from the high-resolution mosaic are provided in the master catalog as well. The total fraction of spurious sources in the catalog is 0.75%. Monte Carlo simulations are performed to derive completeness corrections of the catalog. We find that the 10 GHz radio source counts in the GOODS-N field agree, in general, with predictions from numerical simulations/models and expectations from 1.4 and 3 GHz radio counts.Item A classifier-based approach to multiclass anomaly detection for astronomical transients(Oxford University Press, 2025) Lochner, Michelle.; Gupta, Rithwik.; Muthukrishna, Daniel.Automating real-time anomaly detection is essential for identifying rare transients, with modern survey telescopes generating tens of thousands of alerts per night, and future telescopes, such as the Vera C. Rubin Observatory, projected to increase this number dramatically. Currently, most anomaly detection algorithms for astronomical transients rely either on hand-crafted features extracted from light curves or on features generated through unsupervised representation learning, coupled with standard anomaly detection algorithms. In this work, we introduce an alternative approach: using the penultimate layer of a neural network classifier as the latent space for anomaly detection. We then propose a novel method, Multi-Class Isolation Forests, which trains separate isolation forests for each class to derive an anomaly score for a light curve from its latent space representation. This approach significantly outperforms a standard isolation forest. We also use a simpler input method for real-time transient classifiers which circumvents the need for interpolation and helps the neural network handle irregular sampling and model inter-passband relationships. Our anomaly detection pipeline identifies rare classes including kilonovae, pair-instability supernovae, and intermediate luminosity transients shortly after trigger on simulated Zwicky Transient Facility light curves. Using a sample of our simulations matching the population of anomalies expected in nature (54 anomalies and 12 040 common transients), our method discovered anomalies (recall) after following up the top 2000 () ranked transients. Our novel method shows that classifiers can be effectively repurposed for real-time anomaly detection.Item A measurement of Galactic synchrotron emission using MWA drift scan observations(Cambridge University Press, 2025) Chatterjee, Suman; Sarkar, Shouvik; Choudhuri, SamirStudying the diffuse Galactic synchrotron emission (hereafter, DGSE) at arc-minute angular scale is important to remove the foregrounds for the cosmological 21-cm observations. Statistical measurements of the large-scale DGSE can also be used to constrain the magnetic field and the cosmic ray electron density of our Galaxy's interstellar medium (ISM). Here, we have used the Murchison Widefield Array (MWA) drift scan observations at$154.2 \, {\rm MHz}$to measure the angular power spectrum$({\cal C}_{\ell})$of the DGSE of a region of the sky from right ascension (RA)$349^{\circ}$to$70.3^{\circ}$at the fixed declination$-26.7^{\circ}$ . In this RA range, we have chosen 24 pointing centers (PCs), for which we have removed all the bright point sources above$\sim430 \, {\rm mJy}\,(3σ)$ , and applied the Tapered Gridded Estimator (TGE) on residual data to estimate the${\cal C}_{\ell}$ . We use the angular multipole range$65 \le \ell \le 650$to fit the data with a model,${\cal C}^M_{\ell}=A\times \left(\frac{1000}{\ell}\right)^β+C$ , where we interpret the model as the combination of a power law$(\propto \ell^{-β})$nature of the DGSE and a constant part due to the Poisson fluctuations of the residual point sources. We are able to fit the model${\cal C}^M_{\ell}$for six PCs centered at$α=352.5^{\circ}, 353^{\circ}, 357^{\circ}, 4.5^{\circ}, 4^{\circ}$and$1^{\circ}$ . We run the Markov Chain Monte Carlo (MCMC) ensemble sampler to get the best-fit values of the parameters$A, β$and$C$for these PCs. We see that the values of$A$vary in the range$155$to$400$mK $^{2}$ , whereas the$β$varies in the range$0.9$to$1.7$ . We find that the value of$β$is consistent at$2-σ$level with the earlier measurement of the DGSE at similar frequency and angular scalesItem A MeerKAT study of a neutral hydrogen rich grouping of galaxies with megaparsec-scale filamentary-like structure(EDP Sciences, 2025) Davé, Romeel; Lawrie, Graham; Deane, RogerContext. Environmental effects within cosmological overdensities, such as galaxy groups and clusters, have been shown to impact galaxies and their cold gas reservoirs and thereby provide constraints on galaxy evolution models. Galaxy groups foster frequent galaxy-galaxy interactions, making them rich environments in which to study galaxy transformation. Aims. In this work, we study a serendipitously discovered large overdensity of neutral hydrogen (H I) galaxies at z ∼ 0.04. The galaxies appear to lie in a filamentary-like structure of megaparsec scale. Using MeerKAT’s angular resolution and field of view, we were able to spatially resolve the H I galaxies while simultaneously probing large-scale structure. Methods. The H I and sub-arcsec Dark Energy Survey (DES) imaging have revealed a large number of both interacting and disturbed galaxies in this collective group. MeerKAT data enabled us to derive H I masses and investigate interacting galaxies. We used DES and Wide-field Infrared Survey Explorer (WISE) data to quantify the star formation rates, stellar masses, and stellar morphologies of member galaxies and compared these with field scaling relations. To place this discovery and the environmental effects in context, we used the SIMBA cosmological hydrodynamical simulation to investigate the prevalence of qualitatively similar H I overdensities and their large-scale morphological properties. This enabled us to make a prediction of how frequently such structures might be serendipitously discovered with MeerKAT and SKA-Mid H I observations in comparable observation time.Item A river runs through it: reading the text and context of a river(Routledge, 2024) Delia Marshall; Adré MarshallThis article is framed and inspired by Jacklyn Cock’s Writing the Ancestral River (Johannesburg: Wits University Press, 2018), which traces the history of the Kowie river in the Eastern Cape and its significance both in her own life and in shaping a specific geographical area. We set out to “read” the Kromme river through the lens of Cock’s “biography-of-a-river” approach, which is both an evocative personal account and a social and environmental history of a river. Like the Kowie, the story of the Kromme river raises issues of competing interests; environmental, economic, and social justice concerns; and the tension between a river viewed in instrumentalist terms or as a complex, precious wetland and estuary. We consider questions such as whether the natural world in itself has inalienable rights, and whether rivers—even minor ones such as the Kromme—should have the right to be protectedItem A study of dipolar signal in distant quasars with various observables(Springer, 2024) Kothari, Rahul; Panwar, Mohit; Singh, GurmeetWe study the signal of anisotropy in AGNs/quasars of CatWISE2020 catalogue using different observables. It has been reported earlier that this data shows a strong signal of dipole anisotropy in the source number counts. We test this claim using two independent data analysis procedures and find our number count dipole consistent with the earlier results. In addition to number counts, we test for the anisotropy signal in two other observables – mean spectral index α¯ and mean flux density S¯. We find a strong dipole signal both in the mean spectral index and the mean flux density. The dipole in mean flux density points towards the galactic center and becomes very weak after imposing a flux cut to remove sources with flux greater than 1 mJy. This can be attributed to the presence of some (∼ 26,600) bright sources. The signal in the mean spectral index, however, is relatively stable as a function of both flux and galactic cuts. The dipole in this observable points roughly opposite to the galactic center and hence most likely arises due to galactic bias. We consider a simple model of galactic extinction which nicely explains the dipole both in mean spectral index and mean flux density for a wide range of flux and galactic cuts. Hence, the signal in both these parameters does not appear to be of cosmological origin.Item Aligned metal absorbers and the ultraviolet background at the end of reionization(Oxford University Press, 2018) Doughty, Caitlin; Finlator, Kristian; Oppenheimer, Benjamin D.; Dave, Romeel; Zackrisson, ErikWe use observations of spatially-aligned C ii, C iv, Si ii, Si iv, and O i absorbers to probe the slope and intensity of the ultraviolet background (UVB) at z ∼ 6. We accom- plish this by comparing observations with predictions from a cosmological hydrody- namic simulation using three trial UVBs applied in post-processing: a spectrally soft, fluctuating UVB calculated using multi-frequency radiative transfer; a soft, spatially- uniform UVB; and a hard, spatially-uniform “quasars-only” model. When considering our paired high-ionization absorbers (Civ/Siiv), the observed statistics strongly prefer the hard, spatially-uniform UVB. This echoes recent findings that cosmological sim- ulations generically underproduce strong C iv absorbers at z > 5. A single low/high ionization pair (Si ii/Si iv), by contrast, shows a preference for the HM12 UVB, while two more (C ii/C iv and O i/C iv) show no preference for any of the three UVBs. Despite this, future observations of specific absorbers, particularly Si iv/C iv, with next-generation telescopes probing to lower column densities should yield tighter con- ts on the UVB.Item All-sky angular power spectrum – I. Estimating brightness temperature fluctuations using the 150-MHz TGSS survey(Oxford University Press, 2020) Ghosh, Abhik; Choudhuri, Samir; Roy, NirupamMeasurements of the Galactic synchrotron emission are important for the 21-cm studies of the epoch of reionization. The study of synchrotron emission is also useful for quantifying the fluctuations in the magnetic field and the cosmic-ray electron density of the turbulent interstellar medium (ISM) of our Galaxy. Here, we present the all-sky angular power spectrum (Cℓ) measurements of the diffuse synchrotron emission obtained using the TIFR GMRT Sky Survey (TGSS) at 150 MHz.Item ALMA lensing cluster survey: Hubble space telescope and spitzer photometry of 33 lensed fields built with CHArGE(IOP Publishing, 2022) Baker, A.JWe present a set of multiwavelength mosaics and photometric catalogs in the Atacama Large Millimeter/submillimeter Array (ALMA) lensing cluster survey fields. The catalogs were built by the reprocessing of archival data from the Complete Hubble Archive for Galaxy Evolution compilation, taken by the Hubble Space Telescope (HST) in the Reionization Lensing Cluster Survey, Cluster Lensing And Supernova survey with Hubble, and Hubble Frontier Fields. Additionally, we have reconstructed the Spitzer Infrared Array Camera 3.6 and 4.5 μm mosaics, by utilizing all the available archival IPAC Infrared Science Archive/Spitzer Heritage Archive exposures.Item An ALMA survey of the brightest sub-millimetre sources in the SCUBA-2–COSMOS field(Oxford University Press, 2020) An, Fang Xia; Simpson, J. M.; Smail, IanABSTRACT We present an ALMA study of the ∼180 brightest sources in the SCUBA-2 850-μm map of the COSMOS field from the S2COSMOS survey, as a pilot study for AS2COSMOS – a full survey of the ∼1000 sources in this field. In this pilot study, we have obtained 870-μm continuum maps of an essentially complete sample of the brightest 182 sub-millimetre sources (S850μm> 6.2 mJy) in COSMOS. Our ALMA maps detect 260 sub-millimetre galaxies (SMGs) spanning a range in flux density of S870μm = 0.7–19.2 mJy.Item An ALMA survey of the SCUBA-2 CLS UDS field: Physical properties of 707 sub-millimetre galaxies(Oxford University Press, 2020) An, Fang Xia; Smail, Ian; Swinbank, A. M.We analyse the physical properties of a large, homogeneously selected sample of ALMA-located sub-millimetre galaxies (SMGs). This survey, AS2UDS, identified 707 SMGs across the ∼1 deg2 field, including ∼17 per cent, which are undetected at K ≳ 25.7 mag. We interpret their ultraviolet-to-radio data using MAGPHYS and determine a median redshift of z = 2.61 ± 0.08 (1σ range of z = 1.8–3.4) with just ∼6 per cent at z > 4. Our survey provides a sample of massive dusty galaxies at z ≳ 1, with median dust and stellar masses of Md = (6.8 ± 0.3) × 108 M⊙ (thus, gas masses of ∼1011 M⊙) and M* = (1.26 ± 0.05) × 1011 M⊙.Item An ALMA/NOEMA survey of the molecular gas properties of high-redshift star-forming galaxies(Oxford University Press, 2021) An, F.X.; Birkin, J.E; Weiss, AWe have used ALMA and NOEMA to study the molecular gas reservoirs in 61 ALMA-identified submillimetre galaxies (SMGs) in the COSMOS, UDS, and ECDFS fields. We detect 12CO (Jup = 2-5) emission lines in 50 sources, and [C I](3P1 -3P0) emission in eight, at z = 1.2-4.8 and with a median redshift of 2.9±0.2. By supplementing our data with literature sources, we construct a statistical CO spectral line energy distribution and find that the 12CO line luminosities in SMGs peak at Jup ∼ 6, consistent with similar studies. We also test the correlations of the CO, [C I], and dust as tracers of the gas mass, finding the three to correlate well, although the CO and dust mass as estimated from the 3-mm continuum are preferable. We estimate that SMGs lie mostly on or just above the star-forming main sequence, with a median gas depletion timescale, tdep = Mgas/SFR, of 210±40 Myr for our sample.Item The altitude of sprites observed over South Africa(Academy of Science of South Africa, 2021) Mashao, D; Kosch, MJ; Bór, J; Nnadih, OSprites are mesospheric optical emissions that are mostly produced by large, positive cloud-to-ground lightning discharges. Sprites appear in different morphologies such as carrot, jellyfish and column, and are typically in the altitude range of ~40–100 km above the Earth’s surface. Sprites are a subset of transient luminous events and they contribute to the global electric circuit. South Africa has large convective thunderstorms, which typically occur in the summer months of every year. Peak current, time and geographical position of lightning strokes were obtained from the South African Weather Service. Sprite observations were recorded in South Africa for the first time on 11 January 2016 from Sutherland in the Northern Cape using a night-vision television camera from the South African National Space Agency’s Optical Space Research laboratory. We report the first estimates of the top altitude, and the altitude of maximum brightness, of 48 sprites over South Africa. We found that the average top altitude and the altitude of maximum brightness of sprites are approximately 84.3 km and 69 km, respectively, which is consistent with estimates made elsewhere. We also found a moderately high positive and a weak positive correlation between the top altitude and the altitude of maximum brightness, respectively, of sprites and the lightning stroke charge moment change.Item Analysis and exploitation of landforms for improved optimisation of camera based wildfire detection systems(Springer, 2021) Heyns, Andries M.; du Plessis, Warren; Kosch, MichaelTower-mounted camera-based wildfire detection systems provide an effective means of early forest fire detection. Historically, tower sites have been identified by foresters and locals with intimate knowledge of the terrain and without the aid of computational optimisation tools. When moving into vast new territories and without the aid of local knowledge, this process becomes cumbersome and daunting. In such instances, the optimisation of final site layouts may be streamlined if a suitable strategy is employed to limit the candidate sites to landforms which offer superior system visibility. A framework for the exploitation of landforms for these purposes is proposed. The landform classifications at 165 existing tower sites from wildfire detection systems in South Africa, Canada and the USA are analysed using the geomorphon technique, and it is noted that towers are located at or near certain landform types.Item Analytical gaussian process cosmography: unveiling insights into matter-energy density parameter at present(Springer Nature, 2024) Dinda, Bikash RIn this study, we introduce a novel analytical Gaussian Process (GP) cosmography methodology, leveraging the differentiable properties of GPs to derive key cosmological quantities analytically. Our approach combines cosmic chronometer (CC) Hubble parameter data with growth rate (f) observations to constrain the Ωm0 parameter, offering insights into the underlying dynamics of the Universe. By formulating a consistency relation independent of specific cosmological models, we analyze under a flat FLRW metric and first-order Newtonian perturbation theory framework. Our analytical approach simplifies the process of Gaussian Process regression (GPR), providing a more efficient means of handling large datasets while offering deeper interpretability of results. We demonstrate the effectiveness of our methodology by deriving precise constraints on Ωm0h2, revealing Ωm0h2=0.139±0.017. Moreover, leveraging H0 observations, we further constrain Ωm0, uncovering an inverse correlation between mean H0 and Ωm0. Our investigation offers a proof of concept for analytical GP cosmography, highlighting the advantages of analytical methods in cosmological parameter estimation. © The Author(s) 2024.Item Analytical gaussian process cosmography: unveiling insights into matter-energy density parameter at present(Springer Nature, 2024) Dinda, Bikash RanjanIn this study, we introduce a novel analytical Gaussian Process (GP) cosmography methodology, leveraging the differentiable properties of GPs to derive key cosmological quantities analytically. Our approach combines cosmic chronometer (CC) Hubble parameter data with growth rate (f) observations to constrain the Ωm0 parameter, offering insights into the underlying dynamics of the Universe. By formulating a consistency relation independent of specific cosmological models, we analyze under a flat FLRW metric and first-order Newtonian perturbation theory framework. Our analytical approach simplifies the process of Gaussian Process regression (GPR), providing a more efficient means of handling large datasets while offering deeper interpretability of results. We demonstrate the effectiveness of our methodology by deriving precise constraints on Ωm0h2, revealing Ωm0h2=0.139±0.017. Moreover, leveraging H0 observations, we further constrain Ωm0, uncovering an inverse correlation between mean H0 and Ωm0. Our investigation offers a proof of concept for analytical GP cosmography, highlighting the advantages of analytical methods in cosmological parameter estimation.Item Annealing effect of hybrid solar cells based on poly (3-hexylthiophene) and zinc-oxide nanostructures(Elsevier, 2013) Motaung, David; Malgas, Gerald; Ray, Suprakas S.; Arendse, ChristopherThe structural growth and optical and photovoltaic properties of the organic–inorganic hybrid structures of zinc oxide (ZnO)-nanorods/poly-3-hexylthiophene (P3HT) and two variations of organic polymer blends of ZnO/ P3HT:C60 fullerene and ZnO/P3HT:6,6]-phenyl C61 butyric acid methyl ester were studied in detail during thermal annealing. The ordering of the P3HT nanocrystals increased during annealing, which also improved hole transport in the hybrid structures. The optical constants of the ZnO/P3HT:[6,6]-phenyl C61 butyric acid methyl ester (PCBM) films elevated with annealing temperature due to the improved crystallisation induced by the formation of P3HT crystalline domains. As a result, a maximum power conversion efficiency of approximately 1.03% was achieved for the annealed ZnO/P3HT:PCBM device at 140 °C. These findings indicate that ZnO-nanorods/P3HT:PCBM films are stable at temperatures up to 160 °C.