arXiv subjects

J. Li

Publications and source records attributed to J. Li.

At least 55 records · Page 3Linked to original sources

arXiv2025

The PHANGS-MUSE/HST-Halpha Nebulae Catalogue

We present the PHANGS-MUSE/HST-Halpha nebulae catalogue, comprising 5177 spatially resolved nebulae across 19 nearby star-forming galaxies (< 20 Mpc), based on high-resolution Halpha imaging from HST, homogenised to a fixed 10 pc resolution and sensitivity. Combined with MUSE spectroscopy, this enables robust classification of 4882 H II regions and separation of planetary nebulae and supernova remnants. Electron densities for 2544 H II regions are derived using [S II] diagnostics, and nebular sizes measured via circularised radii and second moments yield a median of 20 pc, extending to sub-parsec scales. A structural complexity score traces substructure, showing that about a third of regions are H II complexes, with a higher fraction in galaxy centres. A luminosity-size relation calibrated from the HST sample is applied to 30,790 MUSE nebulae, recovering sizes down to 1 pc. Observed sizes exceed classical Stromgren radii, implying typical volume filling factors of 0.22. We associate 3349 H II regions with stellar populations from PHANGS-HST, finding median ages of 3 Myr and masses of 4-5 log(Msun). The dataset provides a detailed, spatially resolved link between nebular structure and ionising sources, serving as a benchmark for future studies of feedback, diffuse ionised gas, and star formation regulation in the interstellar medium. The full catalogue is made publicly available in machine-readable format.

astro-ph.GA↗

arXiv2025

Resonance density range of absolute two-plasmon decay instability

We present a new insight into absolute two-plasmon decay (TPD) instability in nonuniform plasmas by identifying the resonance density range as the key parameter governing the growth of the resonant absolute modes. This range is defined as the density interval within which these resonant modes still exhibit growth in homogeneous plasmas. This range properly characterizes the spatial growth region of the resonant absolute modes in a series of linear fluid simulations across broad parameter spaces. Building on this insight, we investigate the absolute growth of TPD modes driven by laser pulses with intensity modulations, a common feature in broadband lasers used to suppress laser plasma instabilities. We establish the relationship between the resonance density range and the threshold time interval between intensity peaks, beyond which absolute growth is suppressed.

physics.plasm-ph↗

arXiv2025

Combined dark matter search towards dwarf spheroidal galaxies with Fermi-LAT, HAWC, H.E.S.S., MAGIC, and VERITAS

Dwarf spheroidal galaxies (dSphs) are excellent targets for indirect dark matter (DM) searches using gamma-ray telescopes because they are thought to have high DM content and a low astrophysical background. The sensitivity of these searches is improved by combining the observations of dSphs made by different gamma-ray telescopes. We present the results of a combined search by the most sensitive currently operating gamma-ray telescopes, namely: the satellite-borne Fermi-LAT telescope; the ground-based imaging atmospheric Cherenkov telescope arrays H.E.S.S., MAGIC, and VERITAS; and the HAWC water Cherenkov detector. Individual datasets were analyzed using a common statistical approach. Results were subsequently combined via a global joint likelihood analysis. We obtain constraints on the velocity-weighted cross section $\langle σ\mathit{v} \rangle$ for DM self-annihilation as a function of the DM particle mass. This five-instrument combination allows the derivation of up to 2-3 times more constraining upper limits on $\langle σ\mathit{v} \rangle$ than the individual results over a wide mass range spanning from 5 GeV to 100 TeV. Depending on the DM content modeling, the 95% confidence level observed limits reach $1.5\times$10$^{-24}$ cm$^3$s$^{-1}$ and $3.2\times$10$^{-25}$ cm$^3$s$^{-1}$, respectively, in the $τ^+τ^-$ annihilation channel for a DM mass of 2 TeV.

astro-ph.HE↗

arXiv2025

The ALPINE-CRISTAL-JWST survey: spatially resolved star formation relations at $z\sim5$

Star formation governs galaxy evolution, shaping stellar mass assembly and gas consumption across cosmic time. The Kennicutt-Schmidt (KS) relation, linking star formation rate (SFR) and gas surface densities, is fundamental to understand star formation regulation, yet remains poorly constrained at $z > 2$ due to observational limitations and uncertainties in locally calibrated gas tracers. The [CII] $158 {\rm μm}$ line has recently emerged as a key probe of the cold ISM and star formation in the early Universe. We investigate whether the resolved [CII]-SFR and KS relations established at low redshift remain valid at $4 < z < 6$ by analysing 13 main-sequence galaxies from the ALPINE and CRISTAL surveys, using multi-wavelength data (HST, JWST, ALMA) at $\sim2$ kpc resolution. We perform pixel-by-pixel spectral energy distribution (SED) modelling with CIGALE on resolution-homogenised images. We develop a statistical framework to fit the [CII]-SFR relation that accounts for pixel covariance and compare our results to classical fitting methods. We test two [CII]-to-gas conversion prescriptions to assess their impact on inferred gas surface densities and depletion times. We find a resolved [CII]-SFR relation with a slope of $0.87 \pm 0.15$ and intrinsic scatter of $0.19 \pm 0.03$ dex, which is shallower and tighter than previous studies at $z\sim5$. The resolved KS relation is highly sensitive to the [CII]-to-gas conversion factor: using a fixed global $α_{\rm [CII]}$ yields depletion times of $0.5$-$1$ Gyr, while a surface brightness-dependent $W_{\rm [CII]}$, places some galaxies with high gas density in the starburst regime ($<0.1$ Gyr). Future inputs from both simulations and observations are required to better understand how the [CII]-to-gas conversion factor depends on local ISM properties. We need to break this fundamental limit to properly study the KS relation at $z\gtrsim4$.

astro-ph.GA↗

arXiv2025

The charge radii of calcium isotopes within relativistic density functional theory: nucleon's finite-size and quadrupole shape fluctuation effects

The anomaly in the charge radii of Ca isotopes has been puzzling for nuclear theory for decades. We present the first self-consistent solution to this puzzle within the density functional theory without resorting to local parameter adjustment. By taking into account both the intrinsic electromagnetic structure of nucleons and the zero-point motions of nuclear shape, which have been often neglected in previous studies, the similar charge radii of $^{40}$Ca and $^{48}$Ca as well as an inverted parabolic behavior between them are reproduced. It is found that these effects also play crucial roles in the description of the isotonic shift between the charge radii of Sn and Cd isotopes.

nucl-th↗

arXiv2025

Magnetic excitations and absence of charge order in the van der Waals ferromagnet Fe$_{4.75}$GeTe$_2$

Understanding the ground state of van der Waals (vdW) magnets is crucial for designing devices leveraging these platforms. Here, we investigate the magnetic excitations and charge order in Fe$_{4.75}$GeTe$_2$, a vdW ferromagnet with $\approx$ 315 K Curie temperature. Using Fe $L_3 - $edge resonant inelastic x-ray scattering, we observe a dual nature of magnetic excitations, comprising a coherent magnon and a broad non-dispersive continuum extending up to 150 meV, 50$\%$ higher than in Fe$_{2.72}$GeTe$_2$. The continuum intensity is sinusoidally modulated along the stacking direction $L$, with a period matching the inter-slab distance. Our results indicate that while the dual character of the magnetic excitations is generic to Fe-Ge-Te vdW magnets, Fe$_{4.75}$GeTe$_2$ exhibits a longer out-of-plane magnetic correlation length, suggesting enhanced 3D magnetic character. Furthermore, resonant x-ray diffraction reveals that previously reported $\pm$(1/3, 1/3, $L$) peaks originate from crystal structure rather than from charge order.

cond-mat.str-el↗

arXiv2025

Decadal evolution of a repeating fast radio burst source

The origin of fast radio bursts (FRBs), the brightest cosmic radio explosions, is still unknown. Bearing critical clues to FRBs' origin, the long-term evolution of FRBs has yet to be confirmed, since the field is still young and most FRBs were seen only once. Here we report clear evidence of decadal evolution of FRB~20121102A, the first precisely localized repeater. In conjunction with archival data, our FAST and GBT monitoring campaign since 2020 reveals a significant 7% decline of local dispersion measure (DM). The rotation measure (RM) of 30,755$\pm$16 $\mathrm{rad\,m^{-2}}$ detected in the last epoch represents a 70% decrease compared to that from December 2016. The $σ_{RM}$ parameter, which describes the complexity of the magneto-ionic environment surrounding the source, was shown to have decreased by 13%. These general trends reveal an evolving FRB environment, which could originate from an early-phase supernova associated with an enhanced pair wind from the FRB central engine.

astro-ph.HE↗

arXiv2025

Puzzling Variation of Gamma Rays from the Sun over the Solar Cycle Revealed with Fermi-LAT

The steady-state gamma-ray emission from the Sun is thought to consist of two emission components due to interactions with Galactic cosmic rays: (1) a hadronic disk component, and (2) a leptonic extended component peaking at the solar edge and extending into the heliosphere. The flux of these components is expected to vary with the 11-year solar cycle, being highest during solar minimum and lowest during solar maximum, as it varies with the cosmic-ray flux. No study has yet analyzed the flux variation of each component over solar cycles. In this work, we measure the temporal variations of the flux of each component over 15 years of Fermi Large Area Telescope observations and compare them with the sunspot number and Galactic cosmic-ray flux from AMS-02 near Earth. We find that the flux variation of the disk anticorrelates with the sunspot number and correlates with cosmic-ray protons, as expected, confirming its emission mechanism. In contrast, the extended component exhibits a more complex variation: despite an initial anticorrelation with the sunspot number, we find neither anticorrelation with the sunspot number nor correlation with cosmic-ray electrons over the full 15-year period. This most likely suggests that cosmic-ray transport and modulation in the inner heliosphere are unexpectedly complex and may differ for electrons and protons or, alternatively, that there is an additional, unknown component of gamma rays or cosmic rays. These findings impact space weather research and emphasize the need for close monitoring of Cycle 25 and the ongoing polarity reversal.

astro-ph.HE↗

arXiv2025

Revealing electron-electron interactions in graphene at room temperature with the quantum twisting microscope

The Quantum Twisting Microscope (QTM) is a groundbreaking instrument that enables energy- and momentum-resolved measurements of quantum phases via tunneling spectroscopy across twistable van der Waals heterostructures. In this work, we significantly enhance the QTMs resolution and extend its measurement capabilities to higher energies and twist angles by incorporating hexagonal boron nitride (hBN) as a tunneling dielectric. This advancement unveils previously inaccessible signatures of the dispersion in the tunneling between two monolayer graphene (MLG) sheets, features consistent with a logarithmic correction to the linear Dirac dispersion arising from electron-electron (e-e) interactions with a fine-structure constant of alpha = 0.32. Remarkably, we find that this effect, for the first time, can be resolved even at room temperature, where these corrections are extremely faint. Our results underscore the exceptional resolution of the QTM, which, through interferometric interlayer tunneling, can amplify even subtle modifications to the electronic band structure of two-dimensional materials. Our findings reveal that strong e-e interactions persist even in symmetric, nonordered graphene states and emphasize the QTMs unique ability to probe spectral functions and their excitations of strongly correlated ground states across a broad range of twisted and untwisted systems.

cond-mat.mes-hall↗

arXiv2025

Direct Observation of k-Gaps in Dynamically Modulated Phononic Time Crystal

Floquet time crystals, characterized by momentum gaps (k-gaps), have sparked intense interest across various branches of physics due to their intriguing dynamics and promising applications. Despite growing theoretical efforts, the realization and observation of phononic time crystals, especially for airborne sound, remain significant experimental challenges. In this work, we demonstrate a phononic time crystal by integrating discrete resonant meta-atoms into a one-dimensional acoustic waveguide, effectively creating a homogeneous, time-varying metamaterial. By dynamically modulating the effective compressibility, we experimentally observe exponential acoustic wave amplification, offering clear evidence of k-gap formation. Furthermore, we showcase the versatility of our platform by inducing momentum band folding and double k-gap phenomena via quasi-periodic temporal modulation. This flexible and reconfigurable approach not only enables the design of tailor-made resonant responses but also opens new avenues for realizing higher-dimensional phononic time crystals and exploring nontrivial topological dynamics in time-modulated media.

physics.app-ph↗

arXiv2025

Resonance density range governs two-plasmon decay saturation and enables hot-electron prediction in inertial confinement fusion

The saturation level of parametric instabilities critically determines their impact on fusion plasmas. We identify the resonance density range of two-plasmon decay as the critical parameter governing nonlinear saturation of ion density fluctuations and Langmuir waves, which drive hot-electron generation. Using this insight, we develop a predictive scaling model for the hot-electron energy fraction f_{hot} that depends only on the laser intensity I, with plasma conditions encoded via plasma ablation theory. The model can work for various experimental configurations-requiring only two (I, f_{hot}) data points to calibrate coefficients-and successfully reproduces results from prior OMEGA and OMEGA-EP experiments.

physics.plasm-ph↗

arXiv2025

The ALMA-CRISTAL survey: Gas, dust, and stars in star-forming galaxies when the Universe was ~1 Gyr old I. Survey overview and case studies

We present the ALMA-CRISTAL survey, an ALMA Cycle 8 Large Program designed to investigate the physical properties of star-forming galaxies at $4 \lesssim z \lesssim 6$ through spatially resolved, multi-wavelength observations. This survey targets 19 star-forming main-sequence galaxies selected from the ALPINE survey, using ALMA Band 7 observations to study [CII] 158 $μ$m line emission and dust continuum, complemented by JWST/NIRCam and HST imaging to map stellar and UV emission. The CRISTAL sample expanded to 39 after including newly detected galaxies in the CRISTAL fields, archival data, and pilot study targets. The resulting dataset provides a detailed view of gas, dust, and stellar structures on kiloparsec scales at the end of the era of reionization. The survey reveals diverse morphologies and kinematics, including rotating disks, merging systems, [CII] emission tails from potential interactions, and clumpy star formation. Notably, the [CII] emission in many cases extends beyond the stellar light seen in HST and JWST imaging. Scientific highlights include CRISTAL-10, exhibiting an extreme [CII] deficit similar to Arp 220; and CRISTAL-13, where feedback from young star-forming clumps likely causes an offset between the stellar clumps and the peaks of [CII] emission. CRISTAL galaxies exhibit global [CII]/FIR ratios that decrease with increasing FIR luminosity, similar to trends seen in local galaxies but shifted to higher luminosities, likely due to their higher molecular gas content. CRISTAL galaxies also span a previously unexplored range of global FIR surface brightness at high-redshift, showing that high-redshift galaxies can have elevated [CII]/FIR ratios. These elevated ratios are likely influenced by factors such as lower metallicity gas, the presence of significant extraplanar gas, and contributions from shock-excited gas.

astro-ph.GA↗

arXiv2025

In-poor IGZO: superior resilience to hydrogen in forming gas anneal and PBTI

Integrating In-Ga-Zn-oxide (IGZO) channel transistors in silicon-based ecosystems requires the resilience of the channel material to hydrogen treatment. Standard IGZO, containing 40% In (metal ratio) suffers from degradation under forming gas anneal (FGA) and hydrogen (H) driven positive bias temperature instability (PBTI). We demonstrate scaled top-gated ALD transistors with an In-poor (In $\le$ 17%) IGZO channel that show superior resilience to hydrogen compared to the In-rich (In=40%) counterpart. The devices, fabricated with a 300-mm FAB process with dimensions down to $W_\mathrm{CH} \times L_\mathrm{TG} = 80 \times 40 \mathrm{nm}^2$, show excellent stability in 2-hour 420$^\circ$C forming gas anneal ($0.06 \le \left| ΔV_{\mathrm{TH}} \right| \le 0.33\mathrm{V}$) and improved resilience to H in PBTI at 125$^\circ$C (down to no detectable H-induced $V_{\mathrm{TH}}$ shift) compared to In-rich devices. We demonstrate that the device degradation by H in the FGA is different from the H-induced VTH instability in PBTI, namely oxygen scavenging by H and H release from a gate-dielectric into the channel, respectively, and that resilience to H in one process does not automatically translate to resilience to H in the other one. This significant improvement in IGZO resilience to H enables the use of FGA treatments during fabrication needed for silicon technology compatibility, as well as further scaling and 3D integration, bringing IGZO-based technologies closer to mass production.

cond-mat.mtrl-sci↗

arXiv2025

Dark Matter Annual Modulation Analysis with Combined Nuclear and Electron Recoil Channels

After decades of experimental efforts, the DAMA/LIBRA(DL) annual modulation (AM) analysis on the $χN$ (WIMP Dark Matter interactions on nucleus) channel remains the only one which can be interpreted as positive signatures. This has been refuted by numerous time-integrated (TI) and AM analysis. It has been shown that $χe$ (WIMP interactions with electrons) alone is not compatible with the DL AM data. We expand the investigations by performing an AM analysis with the addition of $χe$ long-range and short-range interactions to $χN$, derived using the Frozen Core Approximation method. Two scenarios are considered, where the $χN$ and $χe$ processes are due to a single $χ$ ($Γ^{1 χ}_{tot}$) or two different $χ$'s ($Γ^{2 χ}_{tot}$). The combined fits with $χN$ and $χe$ provide stronger significance to the DL AM data which are compatible with the presence of additional physical effects beyond $χN$ alone. This is the first analysis which explores how $χe$ AM can play a role in DL AM. The revised allowed regions as well as the exclusion contours from the other null AM experiments are presented. All DL AM allowed parameter spaces in $χN$ and $χe$ channels under both $Γ^{1 χ}_{tot}$ and $Γ^{2 χ}_{tot}$ are excluded at the 90\% confidence level by the combined null AM results. It can be projected that DL-allowed parameter spaces from generic models with interactions induced by two-WIMPs are ruled out.

hep-ex↗

arXiv2025

JWST PRIMER: A lack of outshining in four normal z =4-6 galaxies from the ALMA-CRISTAL Survey

We present a spatially resolved analysis of four star-forming galaxies at $z = 4.44-5.64$ using data from the JWST PRIMER and ALMA-CRISTAL surveys to probe the stellar and inter-stellar medium properties on the sub-kpc scale. In the $1-5\,μ{\rm m}$ JWST NIRCam imaging we find that the galaxies are composed of multiple clumps (between $2$ and $\sim 8$) separated by $\simeq 5\,{\rm kpc}$, with comparable morphologies and sizes in the rest-frame UV and optical. Using BAGPIPES to perform pixel-by-pixel SED fitting to the JWST data we show that the SFR ($\simeq 25\,{\rm M}_{\odot}/{\rm yr}$) and stellar mass (${\rm log}_{10}(M_{\star}/{\rm M}_{\odot}) \simeq 9.5$) derived from the resolved analysis are in close ($ \lesssim 0.3\,{\rm dex}$) agreement with those obtained by fitting the integrated photometry. In contrast to studies of lower-mass sources, we thus find a reduced impact of outshining of the older (more massive) stellar populations in these normal $z \simeq 5$ galaxies. Our JWST analysis recovers bluer rest-frame UV slopes ($β\simeq -2.1$) and younger ages ($\simeq 100\,{\rm Myr}$) than archival values. We find that the dust continuum from ALMA-CRISTAL seen in two of these galaxies correlates, as expected, with regions of redder rest-frame UV slopes and the SED-derived $A_{\rm V}$, as well as the peak in the stellar mass map. We compute the resolved IRX-$β$ relation, showing that the IRX is consistent with the local starburst attenuation curve and further demonstrating the presence of an inhomogeneous dust distribution within the galaxies. A comparison of the CRISTAL sources to those from the FirstLight zoom-in simulation of galaxies with the same $M_{\star}$ and SFR reveals similar age and colour gradients, suggesting that major mergers may be important in the formation of clumpy galaxies at this epoch.

astro-ph.GA↗

arXiv2025

New Limits on Coherent Neutrino Nucleus Elastic Scattering Cross Section at the Kuo-Sheng Reactor Neutrino Laboratory

Neutrino nucleus elastic scattering (νAel) with reactor neutrinos is an interaction under full quantum-mechanical coherence. It has not yet been experimentally observed. We present new results on the studies of νAel cross section with an electro-cooled p-type point-contact germanium detector at the Kuo-Sheng Reactor Neutrino laboratory. A total of (242)357 kg-days of Reactor ON(OFF) data at a detector threshold of 200 eVee in electron equivalent unit are analyzed. The Lindhard model parametrized by a single variable k which characterizes the quenching function was used. Limits at 90% confidence level are derived on the ratio ρ relative to standard model (SM) cross section of ρ<4.7 at the predicted value of k=0.162, while k<0.285 at the SM-value of ρ=1. Prospects on future positive measurements are discussed.

nucl-ex↗

arXiv2025

Convective Nature of the Stimulated Raman Side Scattering in Inertial Confinement Fusion

The absolute growth of Stimulated Raman side scattering (SRSS) predicted by previous theories appeared to be surprisingly absent in the recent ignition-scale direct-drive experiments with the absence attributed to different reasons. We present evidence from simulations that the linear SRSS modes are naturally all convective (i.e., absolute SRSS does not exist at all) in an experimentally relevant regime where a finite-beam-width laser is incident into a non-uniform low-density plasma below a quarter of the critical density. The convective gain demonstrated by our newly proposed formula via numerical fitting monotonically increases with the beam width without saturation, which is significantly different from the prediction of previous convective SRSS theories.

physics.plasm-ph↗

arXiv2025

Making the unmodulated pyramid wavefront sensor smart II. First on-sky demonstration of extreme adaptive optics with deep learning

Pyramid wavefront sensors (PWFSs) are the preferred choice for current and future extreme adaptive optics (XAO) systems. Almost all instruments use the PWFS in its modulated form to mitigate its limited linearity range. However, this modulation comes at the cost of a reduction in sensitivity, a blindness to petal-piston modes, and a limit to the sensor's ability to operate at high speeds. Therefore, there is strong interest to use the PWFS without modulation, which can be enabled with nonlinear reconstructors. Here, we present the first on-sky demonstration of XAO with an unmodulated PWFS using a nonlinear reconstructor based on convolutional neural networks. We discuss the real-time implementation on the Magellan Adaptive Optics eXtreme (MagAO-X) instrument using the optimized TensorRT framework and show that inference is fast enough to run the control loop at >2 kHz frequencies. Our on-sky results demonstrate a successful closed-loop operation using a model calibrated with internal source data that delivers stable and robust correction under varying conditions. Performance analysis reveals that our smart PWFS achieves nearly the same Strehl ratio as the highly optimized modulated PWFS under favorable conditions on bright stars. Notably, we observe an improvement in performance on a fainter star under the influence of strong winds. These findings confirm the feasibility of using the PWFS in its unmodulated form and highlight its potential for next-generation instruments. Future efforts will focus on achieving even higher control loop frequencies (>3 kHz), optimizing the calibration procedures, and testing its performance on fainter stars, where more gain is expected for the unmodulated PWFS compared to its modulated counterpart.

astro-ph.IM↗