Research Articles (Physics)

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The 1.28 GHz MeerKAT DEEP2 Image
(2020) Asad, K; Cotton, W; Mauch, T
We 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 -
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, Sergey
The 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.
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. Förster
We 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.
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, Erik
We 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.
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, Nirupam
Measurements 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.
ALMA lensing cluster survey: Hubble space telescope and spitzer photometry of 33 lensed fields built with CHArGE
(IOP Publishing, 2022) Baker, A.J
We 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.
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, Ian
ABSTRACT 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.
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⊙.
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, A
We 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.
The altitude of sprites observed over South Africa
(Academy of Science of South Africa, 2021) Mashao, D; Kosch, MJ; Bór, J; Nnadih, O
Sprites 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.
Analysis and exploitation of landforms for improved optimisation of camera based wildfire detection systems
(Springer, 2021) Heyns, Andries M.; du Plessis, Warren; Kosch, Michael
Tower-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.
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, Christopher
The 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.
Anomalous gas in ESO 149-G003: A MeerKAT-16 view
(Oxford University Press, 2021) Jozsa, G.I.G; Thorat, K; Serylak, M
ESO 149-G003 is a close-by, isolated dwarf irregular galaxy. Previous observations with the ATCA indicated the presence of anomalous neutral hydrogen (H I) deviating from the kinematics of a regularly rotating disc. We conducted follow-up observations with the MeerKAT radio telescope during the 16-dish Early Science programme as well as with the MeerLICHT optical telescope. Our more sensitive radio observations confirm the presence of anomalous gas in ESO 149-G003, and further confirm the formerly tentative detection of an extraplanar H I component in the galaxy. Employing a simple tilted-ring model, in which the kinematics is determined with only four parameters but including morphological asymmetries, we reproduce the galaxy's morphology, which shows a high degree of asymmetry. By comparing our model with the observed H I, we find that in our model, we cannot account for a significant (but not dominant) fraction of the gas. From the differences between our model and the observed data cube, we estimate that at least 7-8 per cent of the H I in the galaxy exhibits anomalous kinematics, while we estimate a minimum mass fraction of less than 1 per cent for the morphologically confirmed extraplanar component.
Antenna beam characterization for the global 21-cm experiment LEDA and its impact on signal model parameter reconstruction
(Oxford University Press, 2022) Spinelli, Marta; Kyriakou, George A.; Bernardi, Gianni
Cosmic dawn, the onset of star formation in the early universe, can in principle be studied via the 21-cm transition of neutral hydrogen, for which a sky-averaged absorption signal, redshifted to MHz frequencies, is predicted to be O(10-100) mK. Detection requires separation of the 21-cm signal from bright chromatic foreground emission due to Galactic structure, and the characterization of how it couples to instrumental response. In this work, we present characterization of antenna gain patterns for the Large-aperture Experiment to detect the Dark Ages (LEDA) via simulations, assessing the effects of the antenna ground-plane geometries used, and measured soil properties.
Anti-lensing: the bright side of voids
(American Physical Society, 2013) Bolejko, Krzysztof; Clarkson, Chris; Maartens, Roy; Bacon, David; Meures, Nikolai; Beynon, Emma
More than half of the volume of our Universe is occupied by cosmic voids. The lensing magni ca- tion e ect from those under-dense regions is generally thought to give a small dimming contribution: objects on the far side of a void are supposed to be observed as slightly smaller than if the void were not there, which together with conservation of surface brightness implies net reduction in photons received. This is predicted by the usual weak lensing integral of the density contrast along the line of sight. We show that this standard e ect is swamped at low redshifts by a relativistic Doppler term that is typically neglected. Contrary to the usual expectation, objects on the far side of a void are brighter than they would be otherwise. Thus the local dynamics of matter in and near the void is crucial and is only captured by the full relativistic lensing convergence. There are also signi cant nonlinear corrections to the relativistic linear theory, which we show actually under-predicts the e ect. We use exact solutions to estimate that these can be more than 20% for deep voids. This remains an important source of systematic errors for weak lensing density reconstruction in galaxy surveys and for supernovae observations, and may be the cause of the reported extra scatter of eld supernovae located on the edge of voids compared to those in clusters.
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
(Institute of Physics, 2023) Liu, Daizhong; Förster Schreiber, N M; Genzel, R; Baker, Andrew J
We 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 (Re ∼ 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 (σ0,mol. ∼ 40 km s−1 and σ0,ion. ∼ 66 km s−1) that remain constant out to Re; a moderately low dark matter fraction ( fDM ∼ 0.3–0.4) within Re; and a centrally peaked Toomre Q parameter— agreeing well with the previously established σ0 versus z, fDM versus Σbaryon, and Qʼs radial trends using largesample 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.
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
(American Astronomical Society, 2023) Liu, Daizhong; Förster Schreiber, N. M.; Price, Sedona H
We 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 11 ( ) M M   ~ ) 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 (Re ∼ 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 (σ0,mol. ∼ 40 km s−1 and σ0,ion. ∼ 66 km s−1 ) that remain constant out to Re; a moderately low dark matter fraction ( fDM ∼ 0.3–0.4) within Re; and a centrally peaked Toomre Q parameter— agreeing well with the previously established σ0 versus z, fDM versus Σbaryon, and Qʼs radial trends using largesample 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.
Artist: Fast radiative transfer for large-scale simulations of the epoch of reionization
(Oxford University Press, 2019) Molaro, Margherita
We introduce the ‘Asymmetric Radiative Transfer In Shells Technique’ (ARTIST), a new method for photon propagation on large scales that explicitly conserves photons, propagates photons at the speed of light, approximately accounts for photon directionality, and closely reproduces results of more detailed radiative transfer (RT) methods. Crucially, it is computationally fast enough to evolve the large cosmological volumes required to predict the 21cm power spectrum on scales that will be probed by future experiments targeting the epoch of reionization (EoR). Most seminumerical models aimed at predicting the EoR 21cm signal on these scales use an excursion set formalism (ESF) to model the gas ionization, which achieves computational viability by making a number of approximations
An askap survey for hi absorption towards dust-obscured quasars
(Oxford Academic, 2019) Glowacki, Marcin
Obscuration of quasars by accreted gas and dust, or dusty intervening galaxies, can cause active galactic nuclei (AGN) to be missed in optically selected surveys. Radio observations can overcome this dust bias. In particular, radio surveys searching for H I absorption inform us on how the AGN can impact on the cold neutral gas medium within the host galaxy, or the population of intervening galaxies through the observed line of sight gas kinematics. We present the results of an H I absorption line survey at 0.4 < z < 1 towards 34 obscured quasars with the Australian SKA Pathfinder (ASKAP) commissioning array. We detect three H I absorption lines, with one of these systems previously unknown. Through optical follow-up for two sources, we find that in all detections the H I gas is associated with the AGN, and hence that these AGN are obscured by material within their host galaxies.
Assessing accessibility and availability of portable water supply in selected communities of Lepelle-Nkumpi local municipality, Limpopo province of South Africa
(elsevier, 2022) T, Dube; K, Mashabela; M.H.N., Mollel
In this study, we assessed the accessibility and availability of portable water supply in selected communities of the Lepelle-Nkumpi Local Municipality. A systematic random sampling method was used to select 49 households from Mashite village and 77 households from Lebowakgomo Zone F. A Global Positioning System (GPS) was used to collect absolute locations of available water taps and the reservoir in the Mashite village whereas for Lebowakgomo Zone F municipal household taps data were recorded. Data were statistically analysed and the Pearson Chi-Square test was used to test the relationship between the reuse of onsite greywater at Mashite rural area and Lebowakgomo township area. The results showed that the majority of households (38%) in Mashite village obtained their water from the rivers whereas all respondents in Lebowakgomo Zone F had access to tap water. Further, ninety-four percent (94%) of respondents in Mashite village travel less than 1 km to a water source, while 6% travel between 1 and 3 kms. Proximity to standard water pipes in Mashite village was beyond the recommended 200 m distance. Thirty-five percent (35%) of the respondents in Mashite village and 77% respondents in Lebowakgomo Zone F, respectively, indicated that the available water met their water needs although the quantity of water used per month differed between the two areas. Most of the respondents (56%) in Mashite village used 250 L of water per month while 61% use more than 6000 L in Lebowakgomo Zone F. It is, therefore, recommended that local municipalities should provide rural communities with water taps that are in close proximity of 200 m to households as recommended by the Department of Provincial and Local Government (DPLG). However, even though the DPLG recommends the proximity level of 200 m, this is still questionable as some households still struggle to have enough running water as these taps are sometimes vandalised, not functional or even situated in elevated areas were it becomes impossible for water to ascend uphill due to the pressure of the water. In addition, it is further recommend that local authorities provide household taps that are functional. Moreover, the service delivery should be improved, and water provision infrastructure maintained regularly.

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