Research Articles (Physics)

Permanent URI for this collectionhttps://hdl.handle.net/10566/726

Browse

Now showing 1 - 20 of 710

A spatially resolved spectral analysis of giant radio galaxies with Meerkat
(Oxford University Press, 2025) Jarvis, Matthew J.; An, Fangxia; Whittam, Imogen Helen
In this study we report the spatially resolved, wideband spectral properties of three giant radio galaxies (GRGs) in the COSMOS field: MGTC J095959.63+024608.6, MGTC J100016.84+015133.0, and MGTC J100022.85+031520.4. One of these galaxies, MGTC J100022.85+031520.4, is reported here for the first time, with a projected linear size of 1.29 Mpc at a redshift of 0.1034. Unlike the other two, it is associated with a brightest cluster galaxy (BCG), making it one of the few GRGs known to inhabit cluster environments. We examine the spectral age distributions of the three GRGs using new MeerKAT UHF-band (544–1088 MHz) observations, and L-band (900–1670 MHz) data from the MeerKAT International GHz Tiered Extragalactic Exploration (MIGHTEE) survey. We test two models of spectral ageing, the Jaffe–Perola and Tribble models, using the Broadband Radio Astronomy Tools (brats) software, and find that they agree well with each other. We estimate the Tribble spectral age for MGTC J095959.63+024608.6 as 68 Myr, for MGTC J100016.84+015133.0 as 47 Myr, and for MGTC J100022.85+031520.4 as 67 Myr. We find significant disagreements between these spectral age estimates and the estimates of the dynamical ages of these GRGs, modelled in cluster and group environments. Our results highlight the need for additional processes that are not accounted for in either the dynamic age or the spectral age estimations. © 2024 The Author(s). Published by Oxford University Press on behalf of Royal Astronomical Society.
Long-term eclipse time variations in white dwarf binaries
(Oxford University Press, 2026) Kilkenny, D; Yates, Amalie; Parsons, S G
The overwhelming majority of eclipsing white dwarf (WD) binary systems show quasi-periodic variations in eclipse timings on many year time-scales. Currently, the mechanism behind these eclipse time variations (ETVs) is not known, with the main competing theories being the planetary hypothesis and the Applegate/Lanza mechanisms. Here, we present a comprehensive study of 43 WD binary systems, the vast majority of which have more than a decade of eclipse timing measurements, analysing their global properties to determine which driving force is the likely origin of the observed ETVs. Long-term, high-speed photometry data obtained with ULTRACAM, ULTRASPEC, and HiPERCAM have allowed us to track the evolution of the ETVs in these systems, and analyse any previously unseen trends. From this analysis, we find a clear difference in the level of observed ETVs past the fully convective boundary, where systems with partially radiative companion stars consistently showing high levels of variation. While some systems may be affected by the presence of an unknown planet, the results from this study strongly indicates that an Applegate- or Lanza-like mechanism is the most likely driving force for the timing variations seen in the majority of systems in this sample. However, as found in previous studies, the Applegate/Lanza mechanisms are still not able to reproduce the large and rapid timing variations seen in the vast majority of systems, with the companion star to the WD unable to provide sufficient energy on these short time-scales.
Optimisation of acoustic emission sensor- waveguide assembly for soil slope instability measurement
(Taylor & Francis Ltd, 2025) Mahapatro, Ajit; Kumar, Deepak; Singh, Sushi
Acoustic emission technology (AET) based soil slope monitoring is one of the most innovative and economically viable method that exhibits immense potential in the framework of a landslide early warning system (LEWS). Essential components of AET are AE sensor for soil originated AE signal detection and capturing, active wave-guide to tackle with high AE signal attenuation of soil media, and data acquisition and analysis system (DAAS) for AE parameter extraction, signal conditioning and data storage. AE signal parameters can be exploited to assess and evaluate the soil slope instability. The magnitude, rate, and acceleration of soil slope deformation are direct measures of slope instability. Research articles oriented around AET based soil slope monitoring are prominently focussed on the correlation between slope deformations and its AE behaviour, leaving the AE sensor and waveguide assembly effects unattended. The sensitivity of AET based LEWS is reliant on the performance of the AE sensor and active waveguide, since these are the components responsible solely for collecting relevant AE data from the slope. We have experimented with variety of active waveguide materials and designs, and optimised it for better performance with respect to soil slope deformation parameters. In the studies, two kinds of AE sensors are utilised: one resonant AE sensor and one broadband AE sensor. Steel and aluminium are used as waveguide material. Different grades of high-density polyethylene pipes are used as flexible membrane of the active waveguide. The experimental design and results are described in this article. For simulating real-time landslide slope conditions, a tilt trolley set-up is used for testing the optimised AE sensor-waveguide set-up. Futuristic aspects of the set-up in context of design and development of a LEWS are also discussed.
Phase evolution of electrodeposited manganese oxide for supercapacitor applications
(Springer Science and Business Media Deutschland GmbH, 2025) Iwuoha, Emmanuel Iheanyichukwu; Nwanya, Assumpta Chinwe; Iheme, Chidozie W.
Energy is of paramount importance in our everyday lives and energy storage technologies are needed to solve the global energy problems largely. In this work, manganese oxide (MnxOy) films were electrodeposited chronoamperometrically on stainless steel (ss) and fluorine doped tin oxide (FTO) substrates at different step potentials. The effect of the deposition potential and temperature treatment on the phase and supercapacitive properties of the MnxOy were studied. At a step potential of less than 1.2 V no deposition was achieved while at 1.2 V, the as deposited oxide showed a bit of amorphousness with vestiges of Mn(OH)2 as evident from the x-ray diffraction (XRD) studies. At higher potentials (1.4 and 1.6 V), the as-deposited oxide appeared as the MnO2 phase. However, higher temperature treatment (600 °C) of all the deposits obtained at the various potentials resulted to Mn2O3 phase. The scanning electron microscopy (SEM) of the films showed that the as-deposited and the 400 °C annealed electrodes are porous while they become more compact and cemented at 600 °C. The obtained bandgap energies ranged from 1.26–2.65 eV for the films deposited at differing potentials and heat treatments. The electrochemical analysis shows the highest specific capacitance of 455 F g−1 for the 1.2 V@400 °C electrode while the Mn2O3 electrodes are more stable. The electrodes exhibited good potentials for supercapacitor application. © The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature 2025.
Electronic conduction in hot-pressed calcium manganese oxide ceramics
(Elsevier Ltd, 2025) Mahapatro, Ajit; Pant, Megha
The basic concepts of electronic charge transport in materials are crucial for understanding and improving device performances. The electronic conduction is investigated through perfectly dense calcium manganese oxide (CaMnO3) ceramics prepared with simultaneous application of pressure (64 MPa) and temperature (1073 K) using hot-press technique. A proposed model, comprising of grain boundary assisted hopping and trap assisted transport mechanisms agrees well with the acquired current – voltage characteristics in the temperature range of 133–373 K. The estimated decrease in trap charge density with increasing temperature from 1015 cm 3 at 133 K to 109 cm􀀀 3 at 373 K is attributed to the temperature assisted detrapping of the highly localized trap charge carriers, resulting in lesser availability of trapped charges with increasing temperature. An energy band diagram is demonstrated by implementing the broadening and shifting of energetic trap distribution towards deep into the energy gap with increasing temperature observed in the capacitance-frequency measurements and leads to merging of trap states with the conduction band
Stabilizing metal halide perovskite films via chemical vapor deposition and cryogenic electron beam patterning
(John Wiley and Sons Inc, 2025) Arendse, Christopher Joseph; Burns, Randy; Chiaro, Dylan
Halide perovskites are hailed as semiconductors of the 21st century. Chemical vapor deposition (CVD), a solvent-free method, allows versatility in the growth of thin films of 3- and 2D organic–inorganic halide perovskites. Using CVD grown methylammonium lead iodide (MAPbI3) films as a prototype, the impact of electron beam dosage under cryogenic conditions is evaluated. With 5 kV accelerating voltage, the dosage is varied between 50 and 50000 µC cm−2. An optimum dosage of 35 000 µC cm−2 results in a significant blue shift and enhancement of the photoluminescence peak. Concomitantly, a strong increase in the photocurrent is observed. A similar electron beam treatment on chlorine incorporated MAPbI3, where chlorine is known to passivate defects, shows a blue shift in the photoluminescence without improving the photocurrent properties. Low electron beam dosage under cryogenic conditions is found to damage CVD grown 2D phenylethlyammoinum lead iodide films. Monte Carlo simulations reveal differences in electron beam interaction with 3- and 2D halide perovskite films. © 2024 Wiley-VCH GmbH.
Giant dielectric constant in calcium manganese oxide ceramics
(Elsevier Ltd, 2025) Mahapatro,, Ajit; Pant, Megha
Giant dielectric constant (GDC) materials have been promising for their potential utilization in multifunctional devices, including high-performance energy storage and development of efficient electronic elements. The preliminary charge transport study of ceramics possessing GDC would provide insight for utilization in world-wide applications. GDC of ~106 is realized in the temperature range of 133–593 K through perfectly dense calcium manganese oxide (CaMnO3) ceramics prepared using hot-press technique. The dc-conductivity and dielectric relaxation spectra exhibit Mott-variable range hopping in the temperature range of 133–393 K and small polaron hopping above 493 K. The Nyquist plot provides an equivalent model with series combination of two sets of parallelly connected circuits comprising of resistance and constant phase element, attributed to the contributions from grains and grain boundaries. The ac-conductivity suggests the presence of non-overlapping small polaron tunneling in temperature range of 133–333 K and overlapping large polaron tunneling above 333 K. An electronpolaron band located at 0.27 eV below the conduction band edge is demonstrated with consideration of polaron hopping and band gap energy. Scaling procedure employed to the ac-conductivity universality evidences the corrected Summerfield model and presence of Coulomb interaction between the charge carriers. The in-depth study of the frequency and temperature dependent electric and dielectric properties demonstrates GDC over a wide frequency range of 1 Hz ̶10 MHz, and low loss tangent above 10 kHz in the currently prepared perfectly dense CaMnO3 ceramics and suggests its suitability for engineering charge storage devices in the radio frequency region.
The S4G-wise view of global star formation in the nearby universe
(Institute of Physics, 2025) Cluver, Michelle E.; Jarrett, Thomas H.; Dale, Daniel A.
In this work, we present source-tailored Wide-field Infrared Survey Explorer (WISE) mid-infrared photometry (at 3.4, 4.6, 12, and 23 μm) of 2812 galaxies in the extended Spitzer Survey of Stellar Structure in Galaxies sample, and characterize the mid-infrared colors and dust properties of this legacy nearby galaxy data set. Informed by the relative emission between W3 (12 μm) and W4 (23 μm), we rederive star formation rate (SFR) scaling relations calibrated to L TIR, which results in improved agreement between the two tracers. By inverse-variance weighting the W3 and W4-derived SFRs, we generate a combined mid-infrared SFR that is a broadly robust measure of star formation activity in dusty, star-forming galaxies in the nearby Universe. In addition, we investigate the use of a W3-derived dust density metric, Σ12 μm (L ⊙/kpc2), to estimate the SFR deficit of low mass, low dust galaxies. This is achieved by combining WISE with existing Galaxy Evolution Explorer ultraviolet (UV) photometry, which we further use to explore the relationship between dust and UV emission as a function of morphology. Finally, we use our derived SFR prescriptions to examine the location of galaxies in the log SFR-log M stellar plane, as a function of morphological type, which underscores the complexity of dust-derived properties seen in galaxies of progressively earlier type.
The radio spectral energy distribution and star formation calibration in MIGHTEECOSMOS highly star-forming galaxies at 1.5
(Institute of Physics, 2025) Jarvis, Matt; Taylor, Russ; Whittam, Imogen H; An, Fangxia; Vaccari, Mattia
Studying the radio spectral energy distribution (SED) of distant galaxies is essential for understanding their assembly and evolution over cosmic time. We present rest-frame radio SEDs of a sample of 160 star-forming galaxies at 1.5 < z < 3.5 in the Cosmic Evolution Survey field as part of the MeerKAT International GHz Tiered Extragalactic Exploration project. MeerKAT observations combined with archival Very Large Array and Giant Metrewave Radio Telescope data allow us to determine the integrated mid-radio (ν = 1–10 GHz) continuum (MRC) luminosity and magnetic field strength. A Bayesian method is used to model the SEDs and to separate the free–free and synchrotron emission. We also calibrate the star formation rate (SFR) in radio both directly through SED analysis and indirectly through the infrared–radio correlation (IRRC). With a mean value of αnt ≃ 0.7, the synchrotron spectral index flattens with both redshift and specific SFR, indicating that cosmic rays are more energetic in the early Universe due to higher star formation activity. The magnetic field strength increases with redshift, B ∝ (1 + z) (0.7±0.1) , and SFR as B ∝ SFR0.3, suggesting a small-scale dynamo acting as its main amplification mechanism. Taking into account the evolution of the SEDs, the IRRC is redshift invariant, and it does not change with stellar mass at 1.5 < z < 3.5, although the correlation deviates from linearity. Similarly, we show that the SFR traced using the integrated MRC luminosity is redshift invariant.
The study of 110Cd with the (n,n′γ) reaction revisited
(Springer, 2026) Garrett, Paul; Bangay J; Jolie, Jan
Data from a previous study of 110Cd with the (n,n′γ) reaction with monoenergetic neutrons have been reanalysed with the aim of identifying additional low-intensity γ-ray transitions. The data set included excitation functions measured with neutron energies between 1.94 and 3.34 MeV, and γ-ray angular distributions performed at neutron energies of 2.6, 2.9, and 3.2 MeV. A total of 162 γ rays were placed in a level scheme comprising 69 levels (of which 58 γ-ray assignments and 10 levels are newly established) up to 3.3 MeV in excitation energy. Lifetimes, or limits, were established for many levels using the Doppler-shift attenuation technique allowing for the determination of an extended set of transition rates.
Isospin mixing in 64,66Ga reexamined via total absorption spectroscopy
(American Physical Society, 2025) Orce, José Nicolás; Parra, Selene; Nacher, Enrique
New measurements of the β decay of 64Ga and 66Ga have been carried out using total absorption spectroscopy at CERN-ISOLDE. The purpose of the study was to determine whether systemic effects such as Pandemonium have affected previous measurements and also determine the degree of isospin mixing in these proton-rich nuclei. Our results show that the β strength distribution of 64Ga was previously underestimated, while that of 66Ga agrees well with previous high-resolution measurements. The results allowed us to determine the amount of isospin mixing in the 0+ → 0+ transitions to the ground states of the daughter nuclei. From the extracted log ft values, we determined the isospin mixing parameter α for the two cases. They were found to be consistent with values for similar transitions in other nuclei. 64Ga exhibits the largest amount of isospin mixing in such nuclei. These findings improve our understanding of beta decay and have implications for nuclear structure models and medical applications of 66Ga in PET imaging.
Foreground removal in HI 21 cm intensity mapping under frequency-dependent beam distortions
(EDP Sciences, 2026) Spinelli, Marta; Gkogkou, Athanasia; Bonjean, Victor
Context. Neutral hydrogen (HI) intensity mapping with single-dish experiments is a powerful approach for probing cosmology in the post-reionization epoch. It is challenging to extract it, however, because of the bright foregrounds, which are stronger than the HI signal by more than four orders of magnitude. While all methods perform well when a Gaussian beam is assumed that is degraded to the lowest resolution, most methods degrade significantly in a more realistic beam model. Aims. The complexity introduced by frequency-dependent beam effects means that we need methods that explicitly account for the instrument response. We investigate the performance of SDecGMCA. This method extends DecGMCA to spherical data by combining sparse component separation with beam deconvolution. Our goal is to evaluate this method in comparison with established foreground removal techniques by assessing its ability to recover the cosmological HI signal from single-dish intensity mapping observations under varying beam conditions. Methods. We used simulated HI signals and foregrounds informed by existing observational and theoretical models that cover the frequency ranges relevant to MeerKAT and SKA-Mid. The foreground removal techniques we tested fall into two main categories: model-fitting methods (polynomial and parametric), and blind source separation methods (PCA, ICA, GMCA, and SDecGMCA). Their effectiveness was evaluated based on the recovery of the HI angular and frequency power spectra under progressively more realistic beam conditions. Results. While all methods performed adequately under a uniform degraded beam, SDecGMCA remained robust when frequency-dependent beam distortions were introduced. For an oscillating beam, SDecGMCA suppressed the spurious spectral peak at kν-0.3 and achieved an accuracy of 5% at intermediate angular scales (10-<-<-200); it outperformed other methods. Furthermore, the masking of bright Galactic regions significantly improved the recovery of the HI signal, in particular, for SDecGMCA, which benefited most when contaminated lines of sight were excluded. The beam inversion, however, remained intrinsically unstable beyond 200. This sets a practical limit on the method. Conclusions. Our findings highlight the limitations of simple fitting and standard blind source separation methods for realistic beam effects, and they establish SDecGMCA as a particularly promising approach for future single-dish intensity mapping surveys. Its robustness for various beam models, combined with the improvements that can be achieved through masking strategies and forthcoming refinements to its thresholding scheme, suggest that SDecGMCA might provide reliable spherical harmonics reconstructions of the HI power spectrum in upcoming experiments.
The cosmos-web ring: spectroscopic confirmation of the background source at z = 5.1
(EDP Sciences, 2025) Vaccari, Mattia; Shuntov, Marko; Jin, Shuowen
We report the spectroscopic confirmation of the background source of the most distant Einstein ring known to date, the COSMOS-Web ring. This system consists of a complete Einstein ring at z = 5.1, which is lensed by a massive early-type galaxy at z ∼ 2. The redshift z = 5.1043 ± 0.0004 is unambiguously identified with our NOEMA and Keck/MOSFIRE spectroscopy; the NOEMA observations reveal the CO(4–3) and CO(5–4) lines at >8σ, and the MOSFIRE data detect [O ii] at ∼6σ. Using multiwavelength photometry spanning near-infrared to radio bands, we find that the lensed galaxy is a dust-obscured starburst (M? ∼ 1.8 × 1010 M, SFRIR ∼ 60 M yr−1) with a high star formation efficiency (gas depletion time τdep < 100 Myr), as indicated by the [C i](1–0) non-detection. The redshift confirmation re-validates that the total lens mass budget within the Einstein radius is fully accounted for by the stellar and dark matter components, without the need of modifying the initial mass function or dark matter distribution profile. This work paves the way for detailed studies and future follow-ups of this unique lensing system, which is an ideal laboratory for studying mass distribution at z ∼ 2 and physical conditions of star formation at z ∼ 5. © The Authors 2025.
Redshift drift in relativistic n-body simulations
(National University of Ireland Maynooth, 2025) Clarkson, Chris; Oestreicher, Alexander; Adamek, Julian
The cosmological redshift drift promises to be the first observable directly measuring the evolution of the cosmic expansion rate and should be detectable with upcoming surveys by the Square Kilometre Array and the Extremely Large Telescope. To prepare for these upcoming measurements we study the redshift drift in detail using the relativistic N-body code gevolution, focusing on inhomogeneity-induced fluctuations. Using a ray-tracer, we calculate the redshift drift directly from the light cone at two different time steps. To investigate observer-dependent biases we consider 10 different observers. We find that inhomogeneity-induced fluctuations in the redshift drift can in extreme cases be of the same order as the cosmic signal for z ≲ 0.15. By comparing our results to first-order perturbation theory, we find that the extreme outliers are due to peculiar motion in over-densities and can be described by first-order perturbation theory to percent precision. We calculate angular power spectra that fit very well with our predictions based on perturbation theory at linear scales and show a surprisingly large non-linear signal. This shows that redshift drift not only has the power to measure the background expansion, but could also deliver information about the velocity and acceleration fields in clusters.
Revealing cosmological fluctuations in 21 cm intensity maps with MeerKLASS: from maps to power spectra
(Springer Science and Business Media BV, 2026) Fonseca, José; Santos, Mario G.; Spinelli, Marta; Wang, Jingying
Mapping the integrated 21 cm emission line from dark matter-tracing neutral hydrogen gas is the primary science goal for MeerKLASS (MeerKAT’s Large Area Synoptic Survey). Prior to the arrival of MeerKAT, this intensity mapping technique had only been tested on a couple of pre-existing single-dish radio telescopes with a handful of observational hours with which to make early pioneering detections. The 64-dish MeerKAT array, precursor to the SKA Observatory (SKAO), can scan the sky in auto-correlation (or single-dish) mode and perform intensity mapping across large sky areas, presenting the exciting potential for a wide area (≳10,000deg2) spectroscopic survey across redshift 0.4
Bayesian recalibration of flux scale factors in diffuse radio maps using low-resolution absolute radiometers
(Oxford University Press, 2025) Bull, Philip; Nasirudin, Ainulnabilah
The Haslam 408 MHz all-sky map is widely used as a template to model the diffuse Galactic synchrotron emission at radio and microwave frequencies. Recent studies have suggested that there are large uncorrected flux scale errors in this map, however. We investigate the possibility of statistically recalibrating the Haslam map using absolutely calibrated (but low angular resolution) radio experiments designed to measure the 21cm global signal at low frequencies. We construct a Gibbs sampling scheme to recover the full joint posterior distribution of ∼50 000 parameters, representing the true sky brightness temperature field, as-yet uncorrected flux scale factors, and synchrotron power-law spectral indices. With the idealized full-sky simulated data, we perform a joint analysis of a resolution diffuse map at 408 MHz and multiband 21cm global signal data with resolution under different assumptions about (1) noise levels in the maps, (2) sky coverage, and (3) synchrotron spectral index information. For our fiducial scenario in which the global signal experiment has a 50 mK noise rms per coarse pixel in each of 20 frequency bins between 50 and 150 MHz - the typical range for a global signal experiment, we find that the notional Haslam flux scale factors can be recovered in most (but not all) sub-regions of the sky to an accuracy of. In all cases we are able to rectify the sky map to within ∼5 K of the true brightness temperature. Our method can be used to correct the Haslam map once maps obtained from global experiments are available.
Transverse velocities in real-time cosmology: position drift in relativistic n-body simulations
(National University of Ireland Maynooth, 2025) Clarkson, Chris; Oestreicher, Alexander; Adamek, Julian
The era of real-time cosmology has begun. It is now possible to directly measure the apparent drift of high-redshift astronomical sources across the sky in real time. This so-called position drift provides a valuable probe of the peculiar velocity field and cosmic structure formation by giving direct access to the transverse velocity, which is notoriously difficult to measure and is typically inferred statistically from the density field in a model-dependent way. To fully exploit this new window into the Universe, it is essential to understand how cosmological structures affect position drift measurements. Here we present the first position drift study based on the general relativistic N-body simulation code gevolution. We calculate the position drift directly from the past light cone for ten different observers and compare the results to predictions from linear perturbation theory. At linear order, the position drift is directly proportional to the transverse velocity on the sky. This linear approximation reproduces our non-linear simulation results to within about 5%. We calculate power spectra for the position drift, splitting the signal into an E-and B-mode and compare the former to linear expectations, finding good agreement. The B-mode is suppressed on linear scales, but has similar amplitude as the E-mode on non-linear scales. We further demonstrate that light-cone inhomogeneities induce biases in the dipole of the drift, introducing redshift dependence of both the amplitude and direction. Although our analysis is not yet sufficient for a firm conclusion, our results suggest that these effects alone cannot explain the possible redshift-dependent dipole in Gaia DR3 data reported in the literature.
The fast hi 21cm absorption blind survey. II. statistical exploration for associated and intervening systems
(American Astronomical Society, 2025) Hu, Wenkai; Wang, Yougang; Li, Yichao
We present an extragalactic H I 21 cm absorption lines catalog from a blind search at z ≤ 0.35, using drift-scan data collected in 1325.6 hr by the ongoing Commensal Radio Astronomy Fast Survey and FAST All Sky H I Survey, which spans a sky area of 6072.0 deg2 and covers 84,533 radio sources with a flux density greater than 12 mJy. Fourteen previously identified H I absorbers and 20 newly discovered H I absorbers were detected, comprising 15 associated systems, 10 intervening systems, and nine systems with undetermined classifications. Through spectral stacking, the mean peak optical path, mean velocity-integrated optical path, mean FWHM, and mean H I column density are measured to be 0.47 and 0.30; 27.19 and 4.36 km s−1; 42.61 and 9.33 km s−1; 0.49 and 0.08 Ts × 1020 cm−2 K−1, for the associated and intervening samples, respectively. Statistical analysis also reveals that associated systems tend to be hosted by red (g − r > 0.7) galaxies at lower redshifts, whereas galaxies hosting intervening H I absorption are typically found at higher redshifts and are of a bluer (g − r ≤ 0.7) type. A noticeable difference is observed in the positions of foregrounds, backgrounds of intervening systems, and high-redshift and low-redshift associated systems on the Wide-field Infrared Survey Explorer color–color diagram. All identified foreground sources in our sample have W1 – W2 magnitudes below 0.8, suggesting no active galactic nuclei (AGNs). In contrast, backgrounds of intervening systems tend to have W1 – W2 magnitudes above 0.8, indicating AGN presence. For associated absorption, most low-redshift (z ≤ 0.5) systems show W1 – W2 values below 0.8, while higher-redshift associated absorption (z > 0.5) displays a broader range of W1 − W2 values.
The fast hi 21cm absorption blind survey. ii. statistical exploration for associated and intervening systems
(American Astronomical Society, 2025) Hu, Wenkai; Wang, Yougang; Li, Yichao
We present an extragalactic H I 21 cm absorption lines catalog from a blind search at z ≤ 0.35, using drift-scan data collected in 1325.6 hr by the ongoing Commensal Radio Astronomy Fast Survey and FAST All Sky H I Survey, which spans a sky area of 6072.0 deg2 and covers 84,533 radio sources with a flux density greater than 12 mJy. Fourteen previously identified H I absorbers and 20 newly discovered H I absorbers were detected, comprising 15 associated systems, 10 intervening systems, and nine systems with undetermined classifications. Through spectral stacking, the mean peak optical path, mean velocity-integrated optical path, mean FWHM, and mean H I column density are measured to be 0.47 and 0.30; 27.19 and 4.36 km s−1; 42.61 and 9.33 km s−1; 0.49 and 0.08 Ts × 1020 cm−2 K−1, for the associated and intervening samples, respectively. Statistical analysis also reveals that associated systems tend to be hosted by red (g − r > 0.7) galaxies at lower redshifts, whereas galaxies hosting intervening H I absorption are typically found at higher redshifts and are of a bluer (g − r ≤ 0.7) type. A noticeable difference is observed in the positions of foregrounds, backgrounds of intervening systems, and high-redshift and low-redshift associated systems on the Wide-field Infrared Survey Explorer color–color diagram. All identified foreground sources in our sample have W1 – W2 magnitudes below 0.8, suggesting no active galactic nuclei (AGNs). In contrast, backgrounds of intervening systems tend to have W1 – W2 magnitudes above 0.8, indicating AGN presence. For associated absorption, most low-redshift (z ≤ 0.5) systems show W1 – W2 values below 0.8, while higher-redshift associated absorption (z > 0.5) displays a broader range of W1 − W2 values.
Isomer depletion of Mo 93m triggered by inelastic nuclear scattering rather than nuclear excitation by electron capture
(American Physical Society, 2026) Lawrie, Elena Atanassova; Ding, Bing; Jia, Chenxu
Isomer depletion serves as a prerequisite for a variety of important applications. Several mechanisms are proposed to trigger the isomer depletion. In the previous work [Chiara et al., Nature (London) 554, 216 (2018).NATUAS0028-083610.1038/nature25483], isomer depletion with an exceptionally high probability in Mo93m was reported and attributed to nuclear excitation by electron capture (NEEC). However, contradictory probability values were subsequently reported from both experimental and theoretical aspects. This Letter reports a new and more precise measurement of the isomer depletion of high-energy Mo93m ions during the slowing-down processes in lead and carbon foils via a low-background beam-based experimental approach. By employing a purified isomer beam, the depletion probabilities are determined to be 2.0(2)×10-5 in lead and 4.7(13)×10-6 in carbon, agreeing well with the inelastic nuclear scattering calculations. We conclude that the observed isomer depletion in Mo93m arises from inelastic nuclear scattering rather than the previously proposed NEEC mechanism.

Browse

Recent Submissions