Research Articles (Physics)
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Item Euclid preparation: LXXII. three-dimensional galaxy clustering in configuration space: two-point correlation function estimation(EDP Sciences, 2025) Karagiannis, Dionysios; De La Torre, Sylvain; Marulli, FedericoThe two-point correlation function of the galaxy spatial distribution is a major cosmological observable that enables constraints on the dynamics and geometry of the Universe. The Euclid mission is aimed at performing an extensive spectroscopic survey of approximately 20 30 million Hα-emitting galaxies up to a redshift of about 2. This ambitious project seeks to elucidate the nature of dark energy by mapping the three-dimensional clustering of galaxies over a significant portion of the sky. This paper presents the methodology and software developed for estimating the three-dimensional two-point correlation function within the Euclid Science Ground Segment. The software is designed to overcome the significant challenges posed by the large and complex Euclid dataset, which involves millions of galaxies. The key challenges include efficient pair counting, managing computational resources, and ensuring the accuracy of the correlation function estimation. The software leverages advanced algorithms, including k-d tree, octree, and linked-list data partitioning strategies, to optimise the pair-counting process. These methods are crucial for handling the massive volume of data efficiently. The implementation also includes parallel processing capabilities using shared-memory open multi-processing to further enhance performance and reduce computation times. Extensive validation and performance testing of the software are presented. Those have been performed by using various mock galaxy catalogues to ensure that it meets the stringent accuracy requirement of the Euclid mission. The results indicate that the software is robust and can reliably estimate the two-point correlation function, which is essential for deriving cosmological parameters with high precision. Furthermore, the paper discusses the expected performance of the software during different stages of Euclid Wide Survey observations and forecasts how the precision of the correlation function measurements will improve over the mission's timeline, highlighting the software's capability to handle large datasets efficiently.Item The role of ion beams in the propagation of linear and nonlinear ion-acoustic waves in space plasmas(American Institute of Physics, 2025) Maxengana, Mihlali; Bharuthram, Ramesh; Maharaj, ShimulA detailed theoretical investigation of ion beam effects on linear and nonlinear ion-acoustic waves is conducted for a model with two adiabatic ion components and Boltzmann electrons for plasma models with a single ion beam and two counterstreaming ion beams. The linear analysis confirms that the slow ion-acoustic modes, which emerge in models with at least one ion beam, coexist with the fast modes, which occur in both beam and beamless plasma models. For increasing beam speed in the model with single or asymmetric counterstreaming beams, the backward propagating slow mode changes direction and couples with the forward propagating slow mode. One mode becomes unstable to the ion beam instability, and the other is damped for intermediate values of the beam speed. Both slow mode waves change propagation directions in the model with symmetric counterstreaming beams. There are two groups of beam ion-acoustic solitons, which are supported above a minimum threshold value of the beam speed of which one or both are subsonic for plasma beam configurations, which are, respectively, asymmetric or symmetric. While the propagation of the beam ion-acoustic solitons is continuous over the entire range of speeds between the pair of critical acoustic speeds for small deviations of the beam speed above a minimum threshold value, soliton propagation is discontinuous for higher beam speeds yielding a stopband region in soliton speed. Our results could be applied to various regions in the terrestrial magnetosphere where electrostatic solitary waves have been observed in conjunction with ion beams.Item MIGHTEE: a first look at MIGHTEE quasars(Oxford University Press, 2025) Whittam, Imogen; White, Sarah; Delvecchio, IvanIn this work, we study a robust, Ks-band complete, spectroscopically confirmed sample of 104 unobscured (Type-1) quasars within the COSMOS and XMM–LSS fields of the MeerKAT International GHz Tiered Extragalactic Exploration (MIGHTEE) Survey, at 0.60 < zspec < 3.41. The quasars are selected via gJKs colour-space and, with 1.3-GHz flux-densities reaching rms ≈ 3.0 μJy beam−1, we find a radio-loudness fraction of 5 per cent. Thanks to the deep, multiwavelength data sets that are available over these fields, the properties of radio-loud and radio-quiet quasars can be studied in a statistically robust way, with the emphasis of this work being on the active-galactic-nuclei (AGNs)-related and star-formation-related contributions to the total radio emission. We employ multiple star-formation-rate estimates for the analysis so that our results can be compared more easily with others in the literature, and find that the fraction of sources that have their radio emission dominated by the AGN crucially depends on the SFR estimate that is derived from the radio luminosity. When redshift dependence is not taken into account, a larger fraction of sources is classed as having their radio emission dominated by the AGN. When redshift dependence is considered, a larger fraction of our sample is tentatively classed as ‘starbursts’. We also find that the fraction of (possible) starbursts increases with redshift, and provide multiple suggestions for this trend.Item Squeezing information from radio surveys to probe the primordial universe(Institute of Physics, 2025) Karagiannis, Dionysios; Fonseca, José; Camera, Stefano; Clarkson, ChrisA major goal of cosmology is to understand the nature of the field(s) which drove primordial Inflation. Through future observations, the statistics of large-scale structure will allow us to probe primordial non-Gaussianity of the curvature perturbation at the end of Inflation. We show how a new correlation statistic can significantly improve these constraints over conventional methods. Next-generation radio telescope arrays are under construction which will map the density field of neutral hydrogen to high redshifts. These telescopes can operate as an interferometer, able to probe small scales, or as a collection of single dishes, combining signals to map the large scales. We show how to fuse these operating modes in order to measure the squeezed bispectrum with higher precision and greater economy. This leads to constraints on primordial non-Gaussianity that will improve on measurements by Planck, and out-perform other surveys such as Euclid. We forecast that σ(f NLloc)∼ 3, achieved by using a small subset, O(102 - 103), of the total number of accessible triangles. The proposed method identifies a low instrumental noise, systematic-free scale regime, enabling clean squeezed bispectrum measurements. This provides a pristine window into local primordial non-Gaussianity, allowing tight constraints not only on primordial non-Gaussianity, but on any observable that peaks in squeezed configurations.Item Improved null tests of ΛCDM and FLRW in light of DESI DR2(Institute of Physics, 2025) Dinda, Bikash; Maartens, Roy; Clarkson, ChrisThe DESI DR2 BAO data, in combination with CMB and different SNIa datasets, exclude the flat ΛCDM model at more than 2.5σ when analyzed through the w 0 w aCDM parametrization for evolving dark energy. This simple parametrization may not accurately capture the behavior of the entire redshift range at late times, which may introduce bias in the results. We use null tests that probe for deviations from flat ΛCDM at late times, independent of any specific dark energy parametrization. We provide several diagnostics for null tests and discuss their advantages and disadvantages. In particular, we derive diagnostics that improve on previous ones, such as the popular O m diagnostic. The diagnostics are derived from both background and perturbed quantities. Using the combination of DESI DR2 BAO and supernova data, with or without CMB data, we find that deviations from flat ΛCDM are at ∼1σ confidence level in most of the redshift range (more than 1σ for a few small redshift intervals in a few cases). When considering SDSS BAO data instead of DESI BAO data, in combination with PantheonPlus, with or without CMB data, we find even smaller deviations. Since spatial curvature can potentially modify the results, we also test for curvature in the general ΛCDM model and the general FLRW model. While there is slight evidence for nonzero cosmic curvature at lower redshifts in a general ΛCDM model, there is no statistically significant evidence in a general FLRW model.Item H I intensity mapping with the MIGHTEE Survey: first results of the H I power spectrum(Oxford University Press, 2025) Taylor, Russ; Santos, Mario G.; Townsend, Junaid; Taylor, RussWe present the first results of the H I intensity mapping power spectrum analysis with the MeerKAT International GigaHertz Tiered Extragalactic Exploration (MIGHTEE) survey. We use data covering ∼ 4 square degrees in the COSMOS field using a frequency range of 962.5–1008.42 MHz, equivalent to H I emission in 0.4 < z < 0.48. The data consist of 15 pointings with a total of 94.2 h on-source. We verify the suitability of the MIGHTEE data for H I intensity mapping by testing for residual systematics across frequency, baselines, and pointings. We also vary the window used for H I signal measurements and find no significant improvement using stringent Fourier mode cuts. We compute the H I power spectrum at scales 0.5 Mpc−1 ≾ k ≾ 10 Mpc−1 in autocorrelation as well as cross-correlation between observational scans using power spectrum domain averaging for pointings. We report consistent upper limits of 29.8 mK2 Mpc3 from the 2σ cross-correlation measurements and 25.82 mK2 Mpc3 from autocorrelation at k ∼2 Mpc−1.The low signal-to-noise ratio in this data potentially limits our ability to identify residual systematics, which will be addressed in the future by incorporating more data in the analysis.Item Large quadrupole deformation in 20Ne challenges rotor model and modern theory(American Physical Society, 2025) Mehl, Craig Vernon; Orce, José Nicolás; Ngwetsheni, CeboThe spectroscopic quadrupole moment of the first excited state, QS (2+1 ), at 1.634 MeV in 20Ne was determined from sensitive reorientation-effect Coulomb-excitation measurements using a heavy target and safe energies well below the Coulomb barrier. Particle-γ coincidence measurements were collected at iThemba LABS with a digital data-acquisition system using the AFRODITE array coupled to an annular, doubled-sided silicon detector. A precise value of QS (2+1 ) = −0.22(2) eb was determined at backward angles in agreement with the only safe energy measurement prior to this work, QS (2+1 ) = −0.23(8) eb. This result adopts 1 ¯hω shell-model calculations of the nuclear dipole polarizability of the 2+1 state that contributes to the effective quadrupole interaction and determination of QS (2+1 ). It disagrees, however, with the ideal rotor model for axially symmetric nuclei by almost 3σ. Larger discrepancies are computed by modern state-of-the-art calculations performed in this and prior work, including ab initio shell model with chiral effective interactions and the multireference relativistic energy density functional (MR-EDF) model. The intrinsic nucleon density of the 2+1 state in 20Ne calculated with the MR-EDF model illustrates the presence of α clustering, which explains the largest discrepancy with the rotor model found in the nuclear chart and motivates the explicit inclusion of α clustering for full convergence of E2 collective properties.Item Investigating mutual coupling in the hydrogen epoch of reionization array and mitigating its effects on the 21-cm power spectrum(Oxford University Press, 2025) Ghosh, Amitav; Kittiwisit, Piyanat; Santos, MarioInterferometric experiments designed to detect the highly redshifted 21-cm signal from neutral hydrogen are producing increasingly stringent constraints on the 21-cm power spectrum, but some k-modes remain systematics-dominated. Mutual coupling is a major systematic that must be o v ercome in order to detect the 21-cm signal, and simulations that reproduce effects seen in the data can guide strategies for mitigating mutual coupling. In this paper, we analyse 12 nights of data from the Hydrogen Epoch of Reionization Array and compare the data against simulations that include a computationally efficient and physically moti v ated semi-analytic treatment of mutual coupling. We find that simulated coupling features qualitatively agree with coupling features in the data; ho we ver, coupling features in the data are brighter than the simulated features, indicating the presence of additional coupling mechanisms not captured by our model. We explore the use of fringe-rate filters as mutual coupling mitigation tools and use our simulations to investigate the effects of mutual coupling on a simulated cosmological 21-cm power spectrum in a ‘worst case’ scenario where the foregrounds are particularly bright. We find that mutual coupling contaminates a large portion of the ‘EoR Window’, and the contamination is several orders-of-magnitude larger than our simulated cosmic signal across a wide range of cosmological Fourier modes. While our fiducial fringe-rate filtering strategy reduces mutual coupling by roughly a factor of 100 in power, a non-negligible amount of coupling cannot be excised with fringe-rate filters, so more sophisticated mitigation strategies are required.Item Searching for Axion Dark Matter Gegenschein of the Vela Supernova remnant with FAST(Institute of Physics, 2025) Hu, Wenkai; Yang, Wenxiu; Sun, YitianAxions are one of the leading dark matter candidates. If we are embedded in a Milky Way dark matter halo comprised of axions, their stimulated decay would enable us to observe a counterimage (“axion gegenschein”) with a frequency equal to half the axion mass in the opposite direction of a bright radio source. This spectral line emission will be broadened to Δν/ν ∼ σd/c ∼ 10−3 due to the velocity dispersion of dark matter, σd. In this pilot study, we perform the first search for the expected axion gegenschein image of Vela supernova remnant with 26.4 hr of effective ON–OFF data from the Five-hundred-meter Aperture Spherical radio Telescope (FAST) Lband (1.0–1.5 GHz) 19 beam receiver. Our null detection limits the axion–photon coupling strength to be gaγγ ≲ 2 × 10−10 GeV−1 in the mass ranges of 8.7 μeV � ma � 9.44 μeV and 10.85 μeV � ma � 12.01 μeV. These results provide a stronger constraint on gaγγ in this axion mass range than the current limits obtained by the direct search of an axion decay signal from a dwarf galaxy that uses FAST observations, but are a factor of ∼3 times weaker than the current CERN Axion Solar Telescope limit. Based on our observation strategy, data processing methods, and results, the expected sensitivity will reach ∼10−11 GeV−1 with ∼2000 hr of observation in the future.Item Physical versus phantom dark energy after DESI: thawing quintessence in a curved background(Oxford University Press, 2025) Dinda, Bikash; Maartens, RoyRecent data from Dark Energy Spectroscopic Instrument, in combination with other data, provide moderate evidence of dynamical dark energy, w = −1. In the w 0 , w a parametrization of w, there is a preference for a phantom crossing, w < −1, at redshift z ∼ 0 . 5. In general relativity, the phantom equation of state is unphysical. Thus, it is important to check whether phantom crossing is present in other physically self-consistent models of dark energy that have equi v alent e vidence to the w 0 , w a parametrization. We find that thawing quintessence with non-zero cosmic curvature can fit the recent data as well as w 0 , w a in a flat background, based on both parametric and realistic scalar field evolutions. Although the realistic model does not allow w < −1, the parametrizations do allow it. However even if we allow w < −1 the data do not enforce phantom crossing. Thus, the phantom crossing is an artefact of a parametrization that is not based on a physical model.Item MIGHTEE-HI: the radial acceleration relation with resolved stellar mass measurements(Oxford University Press, 2025) Jarvis, Matt; Ponomareva, Anastasia; Vărăşteanu, AndreeaThe radial acceleration relation (RAR) is a fundamental relation linking baryonic and dark matter in galaxies by relating the observed acceleration derived from dynamics to the one estimated from the baryonic mass. This relation exhibits small scatter, thus providing key constraints for models of galaxy formation and evolution – allowing us to map the distribution of dark matter in galaxies – as well as models of modified dynamics. However, it has only been extensively studied in the very local Universe with largely heterogeneous samples. We present a new measurement of the RAR, utilizing a homogeneous sample of 19 H i-selected galaxies out to $z=0.08$. We introduce a novel approach of measuring resolved stellar masses using spectral energy distribution fitting across 10 photometric bands to determine the resolved mass-to-light ratio, which we show is essential for measuring the acceleration due to baryons in the low-acceleration regime. Our results reveal a tight RAR with a low-acceleration power-law slope of $\sim 0.5$, consistent with previous studies. Adopting a spatially varying mass-to-light ratio yields the tightest RAR with an intrinsic scatter of only $0.045 \pm 0.022$ dex, highlighting the importance of resolved stellar mass measurements in accurately characterizing the gravitational contribution of the baryons in low-mass, gas-rich galaxies. We also find the first tentative evidence for redshift evolution in the acceleration scale, but more data will be required to confirm this. Adopting a more general MOND interpolating function, we find that our results ameliorate the tension between previous RAR analyses, the Solar System quadrupole, and wide-binary test.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 Effect of calcination on morphology of zinc oxide nanoparticles(Taylor and Francis Ltd., 2025) Mahapatro, Ajit Kumar; Tandona, Ram Pal; Kumara, SubodhZinc oxide (ZnO) nanoparticles are synthesized using the sol-gel method by considering zinc acetate dihydrate as a precursor, and the morphology and crystalline structure of the as-synthesized ZnO nanoparticles are understood using materials characterization techniques. The effect of calcination temperature and time on the morphology of ZnO powder is studied thoroughly and systematically. The recipe for preparing highly pure ZnO powders is optimized at minimal calcination temperature and time. The powder X-ray diffraction analysis reveals a wurtzite crystal structure for ZnO nanoparticles (ZnO-NPs). From the diffraction patterns, it is evident that the powders calcined at 700 °C for 3 h closely match the JCPDS standard for minimal calcination temperature and time. The peak at 364.48 cm−1 in the Fourier transform infrared spectroscopy provides information about the bonding interaction between Zn and O in ZnO-NPs. The UV-Visible absorption spectra of ZnO-NPs indicate a shifting of peak from 374.37 to 378.49 nm, and the corresponding Tauc plot estimates a change in band gap from 2.461 eV to 2.847 eV for ZnO prepared with calcined at 700 °C for 3 h and 6 h, respectively, due to change in morphology and particle size. The field emission scanning electron microscopy (FESEM) images indicate the formation of spherical-shaped nanoparticles with smooth surfaces and EDAX spectra reveal compositions of zinc and oxygen-only ZnO-NPs. Noticeable changes in the particle size and morphology are observed with increasing calcination temperature. The Raman spectra of the ZnO-NPs recorded using a 514 nm excitation wavelength indicate E2(high) mode at 437.5 cm−1 in Zno-NPs prepared by calcining at 700 °C for 3 h. The optimal condition for achieving high pure ZnO-NPs with well-defined morphology is concluded by calcining the ZnO powder at 700 °C for a duration of 3 h.Item Outshining by recent star formation prevents the accurate measurement of high-z galaxy stellar masses(Institute of Physics, 2024) Romeel, Davé; Desika, Narayanan; Sidney, LowerWe demonstrate that the inference of galaxy stellar masses via spectral energy distribution (SED) fitting techniques for galaxies formed in the first billion years after the Big Bang carries fundamental uncertainties owing to the loss of star formation history (SFH) information from the very first episodes of star formation in the integrated spectra of galaxies. While this early star formation can contribute substantially to the total stellar mass of high-redshift systems, ongoing star formation at the time of detection outshines the residual light from earlier bursts, hampering the determination of accurate stellar masses. As a result, order-of-magnitude uncertainties in stellar masses can be expected. We demonstrate this potential problem via direct numerical simulation of galaxy formation in a cosmological context. In detail, we carry out two cosmological simulations with significantly different stellar feedback models, which span a significant range in SFH burstiness. We compute the mock SEDs for these model galaxies at z = 7 via calculations of 3D dust radiative transfer, and then backward fit these SEDs with PROSPECTOR SED fitting software. The uncertainties in derived stellar masses that we find for z>7 galaxies motivate the development of new techniques and/or priors for SFH to model star formation in the early Universe.Item Euclid preparation: XXXIII. characterization of convolutional neural networks for the identification of galaxy-galaxy strong-lensing events(EDP Sciences, 2024) Lochner, Michelle; Leuzzi, Luca; Meneghetti, MassimoForthcoming imaging surveys will increase the number of known galaxy-scale strong lenses by several orders of magnitude. For this to happen, images of billions of galaxies will have to be inspected to identify potential candidates. In this context, deep-learning techniques are particularly suitable for finding patterns in large data sets, and convolutional neural networks (CNNs) in particular can efficiently process large volumes of images. We assess and compare the performance of three network architectures in the classification of strong-lensing systems on the basis of their morphological characteristics. In particular, we implemented a classical CNN architecture, an inception network, and a residual network. We trained and tested our networks on different subsamples of a data set of 40 000 mock images whose characteristics were similar to those expected in the wide survey planned with the ESA mission Euclid, gradually including larger fractions of faint lenses. We also evaluated the importance of adding information about the color difference between the lens and source galaxies by repeating the same training on single- and multiband images. Our models find samples of clear lenses with ≳90% precision and completeness. Nevertheless, when lenses with fainter arcs are included in the training set, the performance of the three models deteriorates with accuracy values of ~0.87 to ~0.75, depending on the model. Specifically, the classical CNN and the inception network perform similarly in most of our tests, while the residual network generally produces worse results. Our analysis focuses on the application of CNNs to high-resolution space-like images, such as those that the Euclid telescope will deliver. Moreover, we investigated the optimal training strategy for this specific survey to fully exploit the scientific potential of the upcoming observations. We suggest that training the networks separately on lenses with different morphology might be needed to identify the faint arcs. We also tested the relevance of the color information for the detection of these systems, and we find that it does not yield a significant improvement. The accuracy ranges from ~0.89 to ~0.78 for the different models. The reason might be that the resolution of the Euclid telescope in the infrared bands is lower than that of the images in the visual band.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 Physics-informed neural networks in the recreation of hydrodynamic simulations from dark matter(Oxford University Press, 2024) Dai, Zhenyu; Davé, RomeelPhysics-informed neural networks have emerged as a coherent framework for building predictive models that combine statistical patterns with domain knowledge. The underlying notion is to enrich the optimization loss function with known relationships to constrain the space of possible solutions. Hydrodynamic simulations are a core constituent of modern cosmology, while the required computations are both expensive and time-consuming. At the same time, the comparatively fast simulation of dark matter requires fewer resources, which has led to the emergence of machine learning algorithms for baryon inpainting as an active area of research; here, recreating the scatter found in hydrodynamic simulations is an ongoing challenge. This paper presents the first application of physics-informed neural networks to baryon inpainting by combining advances in neural network architectures with physical constraints, injecting theory on baryon conversion efficiency into the model loss function. We also introduce a punitive prediction comparison based on the Kullback-Leibler divergence, which enforces scatter reproduction. By simultaneously extracting the complete set of baryonic properties for the simba suite of cosmological simulations, our results demonstrate improved accuracy of baryonic predictions based on dark matter halo properties and successful recovery of the fundamental metallicity relation, and retrieve scatter that traces the target simulation's distribution.Item Decoupling local primordial non-Gaussianity from relativistic effects in the galaxy bispectrum(Institute of Physics, 2025) Maartens, Roy; Clarkson, Chris; Camera, StefanoUpcoming galaxy surveys aim to map the Universe with unprecedented precision, depth and sky coverage. The galaxy bispectrum is a prime source of information as it allows us to probe primordial non-Gaussianity (PNG), a key factor in differentiating various models of inflation. On the scales where local PNG is strongest, Doppler and other relativistic effects become important and need to be included. Unlike for the single-tracer power spectrum, the leading order imaginary Doppler term does not cancel out in the bispectrum, leaving a smoking gun imaginary dipole signal. We investigate the detectability and importance of relativistic and local PNG contributions in the galaxy bispectrum. We compute the signal-to-noise ratio for the detection of lightcone projection effects in the bispectrum. Furthermore, we perform information matrix forecasts on the local PNG parameter, fNL, and on the parametrised amplitudes of the relativistic corrections. Finally, we quantify the bias on the measurement of fNL that arises from neglecting relativistic effects. Our results show that detections of both first- and second-order relativistic effects are promising with forthcoming spectroscopic survey specifications and are largely unaffected by the uncertainty in fNL. Conversely, we show for the first time that neglecting relativistic corrections in the galaxy bispectrum can lead to a shift >1.5σ(fNL) on the detected value of fNL, highlighting the importance of including relativistic effects in our modelling.Item Mitigating the effect of 1/f noise on the detection of the H I intensity mapping power spectrum from single-dish measurements(Oxford University Press, 2024) Irfan, Melis O; Santos, Mario G; Bull, Philip; Wang, JingyingWe present and compare several methods to mitigate time-correlated (1/f) noise within the H I intensity mapping component of the MeerKAT Large Area Synoptic Survey (MeerKLASS). By simulating scan strategies, the H I signal, foreground emissions, white and correlated noise, we assess the ability of various data-processing pipelines to recover the power spectrum of H I brightness temperature fluctuations. We use MeerKAT pilot data to assess the level of 1/f noise expected for the MeerKLASS survey and use these measurements to create realistic levels of time-correlated noise for our simulations. We find the time-correlated noise component within the pilot data to be between 10 and 20 times higher than the white noise level at the scale of k = 0.04 Mpc−1. Having determined that the MeerKAT 1/f noise is partially correlated across all the frequency channels, we employ Singular Value Decomposition (SVD) as a technique to remove both the 1/f noise and Galactic foregrounds but find that over-cleaning results in the removal of H I power at large (angular and radial) scales; a power loss of 40 per cent is seen for a 3-mode SVD clean at the scale of k = 0.04 Mpc−1. We compare the impact of map-making using weighting by the full noise covariance (i.e. including a 1/f component), as opposed to just a simple unweighted binning, finding that including the time-correlated noise information reduces the excess power added by 1/f noise by up to 30 per cent.Item Mightee: Multi-wavelength counterparts in the Comos field(Oxford University Press, 2024) Imogen H. Whittam; Prescott Matthew; Jarvis M.J; An, Fangxia; Glowacki M.; Adams N.J.In this paper, we combine the early science radio continuum data from the MeerKAT International GHz Tiered Extragalactic Exploration (MIGHTEE) Survey, with optical and near-infrared data and release the cross-matched catalogues. The radio data used in this work covers 0.86 deg2 of the COSMOS field, reaches a thermal noise of 1.7 μJy beam-1 and contains 6102 radio components. We visually inspect and cross-match the radio sample with optical and near-infrared data from the hyper suprime-cam (HSC) and UltraVISTA surveys. This allows the properties of active galactic nuclei and star-forming populations of galaxies to be probed out to z ≈ 5. Additionally, we use the likelihood ratio method to automatically cross-match the radio and optical catalogues and compare this to the visually cross-matched catalogue. We find that 94 per cent of our radio source catalogue can be matched with this method, with a reliability of 95 per cent. We proceed to show that visual classification will still remain an essential process for the cross-matching of complex and extended radio sources. In the near future, the MIGHTEE survey will be expanded in area to cover a total of ∼20 deg2; thus the combination of automated and visual identification will be critical. We compare the redshift distribution of SFG and AGN to the SKADS and T-RECS simulations and find more AGN than predicted at z ∼1.