Research Articles (Physics)
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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.Item Period variability in the pulsating extreme helium stars V652 Her and BX Cir(Oxford University Press, 2024) Kilkenny ,DavidEighteen new timings of maxima of the radially pulsating Extreme Helium star, V652 Her, obtained during 2010-2023 are reported, together with 26 new timings of the very similar star, BX Cir, during 2014-2023. New ephemerides are derived from baselines which are now substantially longer than previously published. Both ephemerides are thus refined and, in the case of BX Cir, we find for the first time evidence of a cubic term (the period change rate is decreasing). BX Cir data from the Transiting Exoplanet Survey Satellite (TESS) reveals a previously unreported frequency near 65 μHz (period ∼0.179 d) with amplitude ∼0.002 mag.Item Annealing influence on the magnetic and thermal stability of FeNi3 nanoparticles for magnetic hyperthermia applications(Elsevier Ltd, 2025) Mahapatro, Ajit Kumar; Kadian, Ankit; Dev, KapilMetallic magnetic nanoparticles having excellent magnetic properties are potential candidate for biomedical applications like magnetic hyperthermia and drug delivery, however their long-term stability remains a critical challenge, limiting their utility for such applications. Monodisperse spherical FeNi3 permalloy nanoparticles (NPs) were synthesized by surfactant free polyol method and their magnetic and thermal stability was tested for magnetic hyperthermia. The synthesized NPs possessed FCC phase and spherical morphology with average diameter of ∼155 nm. The structural ordering and morphology were improved upon annealing treatment at 300 ˚C resulting in enhanced magnetic properties where the saturation magnetization increased from 54 emu/g to 78 emu/g. The magnetic properties were retained over a long period in ambient conditions. Further, the thermogravimetric measurements in ambient conditions established the thermal stability of the nanoparticles up to 350 ˚C. Transmission electron microscopy revealed a protective amorphous coating all over the NP surface, which shield them from corrosion in ambient conditions. These highly stable NPs showed excellent magnetic hyperthermia response in water as well as ethylene glycol medium. The specific absorption rate of the NPs was improved upon annealing from 268 W/g to 299 W/g in water. The long-term magnetic and thermal stability of these NPs and their excellent SAR values makes them a suitable candidate for magnetic hyperthermia-based cancer therapy.Item On the existence of a tight planar relation between stellar specific angular momentum, mass, and effective surface brightness for ALFALFA galaxies(Oxford University Press, 2024) Elson EdMeasurements of the dependence of stellar specific angular momentum (j∗) on stellar mass (M∗) are presented for large samples of galaxies from the Arecibo Legacy Fast ALFA (ALFALFA) survey, spanning the stellar mass range ∼108–1011 M☉. Accurate estimates of j∗ are generated using measurements of I-band effective radius and velocity width of the H I line profile. While the full sample (N = 3607) of galaxies yields a j∗–M∗ relation with power-law index α = 0.404 ± 0.03, it is shown that various subsamples have indices that are very similar to the best literature results, yet with comparatively lower intrinsic scatters. A galaxy’s mean I-band surface brightness within its effective radius (<μeff>) is shown to significantly correlate with j∗–M∗ scatter. A 3D plane fit to all N = 3607 galaxies in log10j∗–log10M∗–<μeff> space yields j∗ ∝ M0.589 ± 0.002 <μeff>0.193 ± 0.002 with scatter σ = 0.089 dex. <μeff>-selected subsamples of size up to N = 1450 yield power-law j∗–M∗ relations mostly consistent with α = 0.55 ± 0.02 from the literature and with intrinsic scatter ranging from 0.083 to 0.129 dex. Thus, this paper presents new, highly accurate measurements of the j∗–M∗ relation that can be used to better understand the important roles played by angular momentum in the formation and evolution of galaxies.Item Feedback-driven anisotropy in the circumgalactic medium for quenching galaxies in the simba simulations(Oxford University Press, 2024) Yang, Tianyi; Davé, RomeelWe use the simba galaxy formation simulation suite to explore anisotropies in the properties of circumgalactic gas that result from accretion and feedback processes. We particularly focus on the impact of bipolar active galactic nuclei (AGNs) jet feedback as implemented in simba, which quenches galaxies and has a dramatic effect on large-scale gas properties. We show that jet feedback at low redshifts is most common in the stellar mass range (1-5) × 1010 MȮ, so we focus on galaxies with active jets in this mass range. In comparison to runs without jet feedback, jets cause lower densities and higher temperatures along the galaxy minor axis (simba jet direction) at radii and beyond. This effect is less apparent at higher or lower stellar masses, and is strongest within green valley galaxies. The metallicity also shows strong anisotropy out to large scales, driven by star formation feedback. We find substantially stronger anisotropy at, but this also exists in runs with no explicit feedback, suggesting that it is due to anisotropic accretion. Finally, we explore anisotropy in the bulk radial motion of the gas, finding that both star formation and AGN wind feedback contribute to pushing the gas outwards along the minor axis at Mpc, but AGN jet feedback further causes bulk outflow along the minor axis out to several Mpc, which drives quenching via gas starvation. These results provide observational signatures for the operation of AGN feedback in galaxy quenching.Item Relationship between semiotic representations and student performance in the context of refraction(American Physical Society, 2024) Linder, CedricSocial semiotic discussions about the role played by representations in effective teaching and learning in areas such as physics have led to theoretical proposals that have a strong common thread: in order to acquire an appropriate understanding of a particular object of learning, access to the disciplinary relevance aspects in the representations used calls for the attainment of representational competence across a particular critical constellation of systematically used semiotic resources (which are referred to as modes, see more on this later). However, an affirming empirical investigation into the relationship between a particular object of learning and different representational formulations, particularly with large numbers of students, is missing in the literature, especially in the context of university-level physics education. To start to address, this research shortfall the positioning for this article is that such studies need to embrace the complexities of student thinking and application of knowledge. To achieve this, both factor and network analyses were used. Even though both approaches are grounded in different frameworks, for the task at hand, both approaches are useful for analyzing clustering dynamics within the responses of a large number of participants. Both also facilitate an exploration of how such clusters may relate to the semiotic resource formulation of a representation. The data were obtained from a questionnaire given to 1368 students drawn from 12 universities across 7 countries. The questionnaire deals with the refraction of light in introductory-level physics and involves asking students to give their best prediction of the relative visual positioning of images and objects in different semiotically constituted situations. The results of both approaches revealed no one-to-one relationship between a particular representational formulation and a particular cluster of student responses. The factor analysis used correct answer responses to reveal clusters that brought to the fore three different complexity levels in relation to representation formulation. The network analysis used all responses (correct and incorrect) to reveal three structural patterns. What is evident from the results of both analyses is that they confirm two broad conclusions that have emerged from social semiotic explorations dealing with representations in relation to attempting to optimize teaching and learning. The first, which is linked to a facilitating-awareness perspective, is that any given disciplinary visual representation can be expected to evoke a dispersed set of knowledge structures, which is referred to as their relevance structure. Thus, the network analysis results can be seen as presenting a unique starting point for studies aiming to identify such relevance structure. The second broad conclusion is that disciplinary visual representation can and often does contain more disciplinary-relevant aspects than what may be directly visible in a given representation. These are referred to as the appresent aspects that need to become part of the total awareness needed by someone to constitute an intended meaning. The results of the factor analysis can then also be seen to be a way of capturing all the disciplinary-relevant aspects (both present and appresent). Educational implications are discussed.Item Circumnuclear dust in luminous Early-type galaxies. i. sample properties and stellar luminosity models(American Astronomical Society, 2024) Davidson, Jared R; Baker, Andrew J; Boizelle, Benjamin DDusty circumnuclear disks (CNDs) in luminous early-type galaxies (ETGs) show regular, dynamically cold molecular gas kinematics. For a growing number of ETGs, Atacama Large Millimeter/sub-millimeter Array (ALMA) CO imaging and detailed gas-dynamical modeling facilitate moderate-to-high precision black hole (BH) mass (MBH) determinations. From the ALMA archive, we identified a subset of 26 ETGs with estimated MBH/Me 108 to a few × 109 and clean CO kinematics but that previously did not have sufficiently high-angularresolution near-IR observations to mitigate dust obscuration when constructing stellar luminosity models. We present new optical and near-IR Hubble Space Telescope (HST) images of this sample to supplement the archival HST data, detailing the sample properties and data-analysis techniques. After masking the most apparent dust features, we measure stellar surface-brightness profiles and model the luminosities using the multi-Gaussian expansion (MGE) formalism. Some of these MGEs have already been used in CO dynamical modeling efforts to secure quality MBH determinations, and the remaining ETG targets here are expected to significantly improve the high-mass end of the current BH census, facilitating new scrutiny of local BH mass–host galaxy scaling relationships. We also explore stellar isophotal behavior and general dust properties, finding these CNDs generally become optically thick in the near-IR (AH 1 mag). These CNDs are typically well aligned with the larger-scale stellar photometric axes, with a few notable exceptions. Uncertain dust impact on the MGE often dominates the BH mass error budget, so extensions of this work will focus on constraining CND dust attenuation.Item Solar variability in the mg ii h and k lines(Institute of Physics, 2025) Snow,Martin; Krishnamurthy, Sowmya; Chatzistergos, TheodosiosSolar irradiance and its variations in the ultraviolet (UV) control the photochemistry in Earth's atmosphere and influence Earth's climate. The variability in the Mg ii h and k core-to-wing ratio, also known as the Mg ii index, is highly correlated with the solar UV irradiance variability. Because of this, the Mg ii index is routinely used as a proxy for solar UV irradiance variability, which can help to get insights into the influence of solar UV irradiance variability on Earth's climate. Measurements of the Mg ii index, however, have only been carried out since 1978 and do not cover climate-relevant timescales longer than a few decades. Here we present a model to calculate the Mg ii index and its variability based on the well-established Spectral And Total Irradiance REconstruction (SATIRE) model. We demonstrate that our model calculations yield an excellent agreement with the observed Mg ii index variations, both on the solar activity cycle and on the solar rotation timescales. Using this model, we synthesize the Mg ii index time series on climate-relevant timescales of decades and longer. Here we present the time series of the Mg ii index spanning nearly three centuries.Item Towards cosmological inference on unlabeled out-of-distribution hi observational data(Springer Science and Business Media B.V., 2025) Andrianomena, Sambatra; Hassan, SultanWe present an approach that can be utilized in order to account for the covariate shift between two datasets of the same observable with different distributions. This helps improve the generalizability of a neural network model trained on in-distribution samples (IDs) when inferring cosmology at the field level on out-of-distribution samples (OODs) of unknown labels. We make use of HI maps from the two simulation suites in CAMELS, IllustrisTNG and SIMBA. We consider two different techniques, namely adversarial approach and optimal transport, to adapt a target network whose initial weights are those of a source network pre-trained on a labeled dataset. Results show that after adaptation, salient features that are extracted by source and target encoders are well aligned in the embedding space. This indicates that the target encoder has learned the representations of the target domain via the adversarial training and optimal transport. Furthermore, in all scenarios considered in our analyses, the target encoder, which does not have access to any labels (Ωm) during adaptation phase, is able to retrieve the underlying Ωm from out-of-distribution maps to a great accuracy of R2 score ≥ 0.9, comparable to the performance of the source encoder trained in a supervised learning setup. We further test the viability of the techniques when only a few out-of-distribution instances are available for training and find that the target encoder still reasonably recovers the matter density. Our approach is critical in extracting information from upcoming large scale surveys.Item Metallicity dependence of pressure-regulated feedback-modulated star formation in the tigress-ncr simulation suite(American Astronomical Society, 2024) Kim, Chang-Goo; Hassan, Sultan; Ostriker, Eve CWe present a new suite of numerical simulations of the star-forming interstellar medium (ISM) in galactic disks using the TIGRESS-NCR framework. Distinctive aspects of our simulation suite are: (1) sophisticated and comprehensive numerical treatments of essential physical processes including magnetohydrodynamics, self-gravity, and galactic differential rotation, as well as photochemistry, cooling, and heating coupled with direct ray-tracing UV radiation transfer and resolved supernova feedback and (2) wide parameter coverage including variation in metallicity over Z ′ ≡ Z/Z⊙ ∼ 0.1 − 3, gas surface density Σgas ∼ 5−150 M⊙ pc−2 , and stellar surface density Σstar ∼ 1−50 M⊙ pc−2 . The range of emergent star formation rate (SFR) surface density range is ΣSFR ∼ 10−4 − 0.5 M⊙ kpc−2 yr−1 and ISM total midplane pressure is Ptot/kB = 103 − 106 cm−3 K, with Ptot equal to the ISM weight W. For given Σgas and Σstar, we find ΣSFR ∝ Z ′0.3 . We provide an interpretation based on the pressureregulated feedback-modulated (PRFM) star formation theory. The total midplane pressure consists of thermal, turbulent, and magnetic stresses. We characterize feedback modulation in terms of the yield Υ, defined as the ratio of each stress to ΣSFR. The thermal feedback yield varies sensitively with both weight and metallicity as Υth ∝ W−0.46Z ′−0.53, while the combined turbulent and magnetic feedback yield shows weaker dependence Υturb+mag ∝ W−0.22Z ′−0.18. The reduction in ΣSFR at low metallicity is due mainly to enhanced thermal feedback yield, resulting from reduced attenuation of UV radiation. With the metallicity-dependent calibrations we provide, PRFM theory can be used for a new subgrid star formation prescription in cosmological simulations where the ISM is unresolved.Item First observation of rotational bands in the nucleus 231U(Springer, 2024) Roux D.G.; Lawrie E.A.; Kheswa B.V.; Khumalo N.A; Noncolela S.P.; Ndayishimye J.; Sharpey-Schafer J.F.This work reports the first rotational bands observed in the neutron-deficient nucleus 231U. Excited states were populated in the 232Th(α,5n) reaction at a beam energy of 52 mev. Coincident decay γ-rays were measured with the high-purity germanium detectors of the afrodite spectrometer array, in conjunction with a recoil detector to discriminate against the fission background. The bands are interpreted as the ground-state band ν[633]5/2+, yrast band ν[752]5/2-, and an excited band ν[631]3/2+. Configuration assignments are supported by Cranked Shell Model and B(M1)/B(E2) calculations. The excitation energy of the ν[752]5/2- bandhead is suggested to be 113.0 kev. © The Author(s) 2024.