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Di Li

Publications and source records attributed to Di Li.

At least 19 recordsLinked to original sources
arXiv2026

Polarization and Burst Properties of the Repeating FRB~20240209A in a Quiescent Elliptical Host

We report polarimetric observations of the repeating fast radio burst (FRB) source FRB 20240209A with the Green Bank Telescope at L band and 800 MHz. This source has previously been associated with a quiescent elliptical galaxy with a mass-weighted stellar age of approximately 11 Gyr. We detected three bursts, and the brightest burst resolves into eight components that drift toward lower frequencies. The bursts have mutually consistent rotation measures (RMs), and the small extragalactic RM agrees with the low RM predicted from the small host-galaxy dispersion measure ($\mathrm{DM}_\mathrm{host}$). The linear polarization fraction decreases toward lower frequencies within the brightest burst, consistent with depolarization by an RM scatter of $σ_\mathrm{RM}\simeq3.5$ rad m$^{-2}$. This RM scatter is comparable to those of several repeaters in star-forming galaxies. Therefore, FRBs in both star-forming and old, quiescent hosts can reside in relatively complex magneto-ionic environments, which suggests that FRB sources may form through multiple channels.

astro-ph.HE↗
arXiv2026

Energy Partitioning in Dust-catalyzed $\mathrm{H_2}$ and HD Formation Revealed by Molecular Simulations Considering Nuclear Quantum Effects

Molecular hydrogen formation on interstellar dust grains is a key surface process, but the partitioning of recombination energy between the substrate and the nascent molecule remains poorly understood. Here, we use ring-polymer molecular dynamics (RPMD) with a machine-learning force field to investigate energy partitioning during H2 and HD formation on graphene at T=25 K, 50 K and 100 K, focusing on the chemisorbed-H recombination pathway previously identified as the dominant low-temperature channel on bare graphitic surfaces when nuclear quantum effects are included. The desorbing molecule retains approximately 84-87% of the effective released energy, with only weak variation across the three velocity-initialization temperatures under the present sampling protocol. Within the retained molecular energy, rovibrational motion dominates at 25 K, whereas center-of-mass translation becomes increasingly important at 100 K. H2 and HD show similar total energy retention, with modest isotope-dependent differences in their internal partitioning. The effective joint rovibrational distributions show a modest positive association between vibrational and rotational excitation. Purely radiative cascade calculations in the optically thin, collision-free limit yield formation-pumping spectra at all three temperatures. From 25 to 100 K, the rovibrational fraction of the emitted energy decreases from approximately 43% to 28% for H2 and from 41% to 28% for HD, while the strongest lines remain in similar wavelength regions. These results provide an energy-resolved microscopic picture of surface-mediated energy redistribution and formation pumping in H2/HD formation on graphene.

astro-ph.GA↗
arXiv2026

NOEMA Observations of the Center of M33: A Parsec-scale Molecular Filament and an Ordered Gas-Star-Formation Sequence

We present NOEMA CO(1-0) observations of the inner $\sim$500 pc of M33 at a resolution of $0.91''\times0.37''$ ($3.7\times1.5$ pc), resolving the compact molecular gas structures and revealing their relation to recent massive star formation. The most prominent structure is a southeastern molecular filament (SE filament) that extends 76 pc along its principal axis, is 23 pc wide, and contains three CO-bright knots. Across eight independent transverse cuts, the adjacent H$α$ ridge is displaced preferentially to one side of the principal CO ridge by a median $10.0^{+0.9}_{-1.4}$ pc. Young OB candidates are more closely associated with H$α$ than with compact CO. The filament shows little velocity change along its length but a resolved gradient across its minor axis. Its elongated morphology, transverse kinematics, and ordered CO-H$α$ distribution are consistent with locally asymmetric molecular-gas compression and subsequent massive star formation. Across the wider field, 23 well-measured compact clumps have a median radius of 2.67 pc and a median velocity dispersion of 2.15 km s$^{-1}$. Their linewidth and apparent virial-parameter distributions show no clear difference between the SE filament and the rest of the field. Although the local spiral potential and pattern speed remain unconstrained, the observations provide a resolved view of a compression-compatible molecular-to-ionized-gas sequence in the center of M33.

astro-ph.GA↗
arXiv2026

No Strong Evidence for Plasma Lensing in FRB 20240114A

FRB 20240114A is an extremely active repeating fast radio burst for which plasma lensing has been proposed to explain its burst-rate variations, spectral evolution, and apparently ``carbon-copy'' burst pairs. Using FAST data and publicly available Parkes observations, we test this interpretation with the predictions of a one-dimensional Gaussian plasma-lens model. Although the burst-rate enhancements may be fitted separately for Parkes and FAST, the corresponding magnification peaks and demagnification troughs between the two datasets are offset from each other, inconsistent with plasma lensing predictions. The enhancement peaks also do not show consistent periodicity, disfavoring a binary plasma lensing origin. The burst bandwidths are not systematically narrower during the proposed lensing interval than in other episodes. Most importantly, the burst energy distribution, which shows an intrinsic turnover peak at low energies, shows no significant shift of the turnover during the magnification interval, providing a model-independent test to the plasma-lensing interpretation. All these suggest that there is no strong evidence in favor of a plasma lensing interpretation to the source. Rather, all the burst property variations are consistent with being caused by the intrinsic variations of the FRB central engine.

astro-ph.HE↗
arXiv2026

The ALMA-QUARKS survey: A Keplerian Circumbinary Disk Candidate in the High-mass Star-forming Region IRAS 08303-4303

We present the ALMA Band 6 continuum and molecular line observations of IRAS 08303-4303, a high-mass star-forming region, with an angular resolution of $\sim 0.3''$ ($\sim 700$ au at the distance of 2.35 kpc). Six dense condensations are identified in the 1.3 mm continuum, and at least four of them are associated with molecular outflows. The estimated outflow parameters, particularly mass outflow rates $\geq 10^{-4}$ $M_{\odot}$ yr$^{-1}$, suggest that the driving sources are high-mass young stellar objects. Two of the condensations are forming a wide protobinary system with a separation of $\sim 900$ au. They reside within a single rotating structure, identified as a circumbinary disk which has a mass of about 2 $M_{\odot}$. This structure is traced by multiple molecular lines and exhibits a Keplerian rotation pattern. Based on the Keplerian rotation assumption, the enclosed mass is derived to be between 32 and 61 $M_{\odot}$: 22-43 $M_{\odot}$ for the primary and 10-18 $M_{\odot}$ for the secondary. The circumbinary disk is on the whole gravitationally stable, yet some parts with Toomre $Q < 2$ indicate potential fragmentation. Various molecular lines reveal a streamer-like structure connecting to the circumbinary disk, suggesting transfer of material from the envelope to the protobinary system through it. Despite the observational rarity of such circumbinary disks around high-mass YSOs, the high binary fraction among massive stars underscores their significance. This source, therefore, serves as a key laboratory for understanding the formation of high-mass binary systems.

astro-ph.SR↗
arXiv2026

B-fields In STar-forming Region Observations (BISTRO): Technical Foundations for Quantitative 450/850 $μ$m JCMT SCUBA-2/POL-2 Polarimetry

We present five technical validations of SCUBA-2/POL-2 polarimetry on the James Clerk Maxwell Telescope at 450 and 850 $μ$m, using 174 archival fields in 69 molecular cloud regions and subsets appropriate to each test. Extended-source calibration avoids a deterministic shift of $Δβ=-1.05$ in the dust emissivity index $β$ that would result from calibrating extended emission using peak brightness. We modeled Stokes $I$ noise with additive and signal-dependent components. The measured median ratio of surface-brightness noise at 450/850 $μ$m is 25. Independent tests of Stokes $Q,U$ noise support approximately equal additive variances and weak error correlations, providing a basis for propagating polarization uncertainties. Corrections determined for individual fields reduce additive zero-level offsets of order $1$ mJy arcsec$^{-2}$ in the 450 $μ$m Stokes $Q$ and $U$ intensities. The three-step regression leaves a median combined residual amplitude of $0.07$ mJy arcsec$^{-2}$. Independent comparisons with SOFIA/HAWC+ at 154 and 214 $μ$m support the correction in strongly affected fields. We matched the 450 $μ$m maps to the modeled 850 $μ$m beam and the common $12.6''$-$300''$ range of angular scales. We compared three reductions of the same 450 $μ$m observations across 30 sources. Taking the median angular residual relative to the final product for each source, we find that beam matching reduces the median over sources from $6.3^\circ$ to $4.7^\circ$. After matching, 29 of the 30 sources have median residuals below $10^\circ$. We also quantified how residual $Q/U$ offsets propagate in ratios of polarization fractions, differences in spectral indices, and polarization angles. These validations provide procedures and quantitative references for interpreting POL-2 measurements and combining them with polarimetry at other wavelengths.

astro-ph.GA↗
arXiv2026

B-fields In STar-forming Region Observations (BISTRO): Dual-Wavelength Constraints on Size-Dependent Grain Alignment in Star-Forming Regions

We compared 450 and 850 $μ$m POL-2 observations from the James Clerk Maxwell Telescope at $12.6''$ resolution. The median absolute difference in polarization angle between bands is $6.7^\circ$ across 21 regions. For total intensity $I\proptoν^α$ and polarized intensity $PI\proptoν^γ$, 24-27 of 35 regions have $γ<α$, allowing for $3σ$ limits on weak polarized intensities. The median $γ-α$ is $-0.51$, ranging from $-0.57$ to $-0.45$ under these limits. The ratio of polarization fractions is $P_{450}/P_{850}=0.69\pm0.02_{\rm sys}\pm0.03_{\rm stat}$, with no detected dependence on the angle difference. We suggest that the dependence of alignment on grain size offers the simplest explanation of these findings. For optically thin components sharing a polarization angle and opacity law, temperature mixing reproduces the median $-0.51$ only if the warm dust is polarized less efficiently than the cold dust. If the cold dust is at 10 K or warmer and the warm dust at 40 K or cooler, the median requires a ratio of warm to cold effective polarization efficiencies $r\lesssim0.18$. We tested mixtures with opacity index $β=2$ in four fields against Herschel dust temperatures and Green Bank Ammonia Survey kinetic temperatures. We assumed equal gas and dust temperatures, ammonia tracing cold gas, and model ranges of 3-20 K for cold dust and 25-40 K for warm dust carrying at most half the mass. Mixtures matching both temperatures cannot reproduce $γ-α$ within $1σ$ in three fields, including OMC 2 tentatively, even for $r=0$. Allowing warm dust at 10-100 K and up to 95% of the mass permits solutions only for $r\leq0.041$. To explain these three fields by temperature mixing, we need wider model ranges and a very strong contrast in polarization efficiency. The origin of this contrast remains undetermined.

astro-ph.GA↗
arXiv2026

A high-Galactic-altitude scattering screen: scintillation from Globular Cluster pulsar M53A

While known interstellar scattering screens are largely confined to the Galactic disk, the scattering properties of the circumgalactic medium (CGM) in the deep Galactic halo have remained unexplored. Using observations from the Five-hundred-meter Aperture Spherical radio Telescope (FAST), we report the first detection of scintillation arcs in the secondary spectra of the high-latitude pulsar J1312+1810A (M53A). Under the 1D anisotropic and 2D isotropic thin-screen models considered here, the inferred scintillation screen distances are $12.8_{-3.5}^{+2.6}$ and $11.7_{-3.5}^{+2.8}$\,kpc, respectively. These model-dependent estimates correspond to Galactic heights of $12.6_{-3.5}^{+2.6}$ and $11.5_{-3.5}^{+2.7}$\,kpc, placing the candidate screen among the highest-altitude scattering structures inferred to date. The strong, time-variable scintillation asymmetry suggests substantial electron-density inhomogeneity within the screen. We speculate that this screen is associated with small-scale structures near the shock boundary of the northern eROSITA bubble. These results support the presence of discrete, inhomogeneous scattering structures deep within the Galactic halo, far beyond the regions where localized stellar feedback is typically concentrated, and highlight pulsar scintillation as a promising probe of small-scale ionized structures in the CGM.

astro-ph.GA↗
arXiv2026

The ALMA-QUARKS Survey. IV. Core Mass Function and Evolutionary Trends in Core Formation Efficiency and Chemistry

The ALMA-QUARKS (Querying Underlying Mechanisms of Massive Star Formation with ALMA-Resolved Gas Kinematics and Structures) survey targets 139 massive protoclusters selected from the ATOMS survey. The targets were observed at 1.3~mm wavelength with an angular resolution of $\sim0.3^{\prime\prime}$, corresponding to $\sim10^3$~au at the sample's median distance of $\sim3.8$~kpc. Using \texttt{getsf}, we identify 3374 dense cores and classify them as starless, protostellar, hot core, or H{\sc ii} region candidates based on spectral-line diagnostics (e.g., H30$α$, CH$_3$CN, and CH$_3$OH) and CO outflow associations. The resulting catalog provides core physical properties and enables statistical investigations of dense core populations in massive protocluster environments. The derived global core mass function (CMF) after excluding H{\sc ii} region candidates, which is biased by distance effects, has a relatively flat power-law slope at the high-mass end ($\mathrm{d}N/\mathrm{d}\log M \propto M^{-γ}$, with $γ=0.98\pm0.03$). In contrast, the measured high-mass slopes in individual distance bins are approximately Salpeter-like, while their fitted lower mass limits increase with distance. We further examine the core formation efficiency (CFE) across the full sample and find that it positively correlates with the luminosity-to-mass ratio of the parental clumps, consistent with an evolutionary increase in the fraction of mass concentrated into dense cores. We also investigate the detection rates of different molecular tracers and find systematic chemical variations with evolutionary stage. Compared with the ASHES survey, we find that the detection rates of deuterated species vary significantly even for cores at the same evolutionary stages, suggesting an important environmental influence on the chemical evolution of cores.

astro-ph.GA↗
arXiv2026

Identifying the principal mechanism of star formation feedback

Feedback from massive stars regulates the formation of next-generation stars and planets and thus shapes the evolution of galaxies, yet observational evidence capable of determining which mechanism dominates the feedback process has long been lacking. Here,we present a large-scale HI survey toward Orion A$.$ With an unprecedented sensitivity and superior resolution, FAST (Five-hundred-meter Aperture Spherical radio Telescope) reveals a well-defined heart-shaped expanding HI bubble, enshrouding the well-known "Veil" bubble of ionized gas. The photoionization-driven and wind-driven gas expands at 10.9 and 13.8 kilometers per second, respectively, with a kinetic energy ratio of 1:2 assuming a spherical symmetry and a uniform HI-to-H2 ratio. This first direct comparison within a single bubble shows that radiation does not dominate the feedback process as predicted by classical theories; instead, stellar winds contribute a comparable share of the injected kinetic energy.

astro-ph.GA↗
arXiv2026

The FAST HI 21-cm Absorption Blind Survey. III. OH Absorption Search in the 21-cm Absorber Sample and Continued HI Absorption Search

We present the first blind search for OH 18-cm absorption with the Five-hundred-meter Aperture Spherical Telescope (FAST), conducted alongside the HI 21-cm absorption search. Our previous FAST blind HI absorption search identified 34 systems. In this work, we extend the search using 2024 and part of the 2025 CRAFTS and FASHI data (394.4 hr and 1622.1 deg$^{2}$) together with FATHOMER observations, yielding four known and three new HI absorbers, for a total of 41 HI absorption systems. We search for OH absorption in 19 HI absorption systems whose OH redshifted frequencies fall within the FAST band. The known OH absorber towards PKS 1413+135 was re-detected, making our survey the first blind survey to detect OH absorption. No new OH absorbers were identified. We examine the relationship between $N_{\rm{OH}}$ and $N_{\rm{HI}}$, applying survival analysis to account for upper limits. The analysis does not provide statistically significant evidence for either an $N_{\rm{OH}}$-$N_{\rm{HI}}$ correlation or redshift evolution of $N_{\rm{OH}}$/$N_{\rm{HI}}$. Finally, spectral stacking sets 3$σ$ OH column density upper limits of 4.93, 1.64, and 1.72 $T_{\rm{ex}}$/$c_{\rm{f,OH}}\times$10$^{12}$cm$^{-2}$K$^{-1}$ for associated, intervening, and combined samples, corresponding to [\rm{OH}]/[\rm{HI}] ratios of $<$1.66$\times$10$^{-8}$, $<$1.42$\times$10$^{-8}$, and $<$0.90$\times$10$^{-8}$, assuming $T_{\rm{ex}}$=10K for OH and $T_{\rm{s}}$=100K for HI. These results place the strongest constraints to date on the OH content in radio-selected HI absorbers and establish a blind-survey benchmark for future studies of molecular gas in HI-selected systems. They also demonstrate that known HI 21-cm absorbers provide an effective parent sample for systematic OH absorption searches, paving the way for future larger surveys.

astro-ph.GA↗
arXiv2026

A Unified Multi-Band Secular Framework for the Hierarchical Triple PSR J0435+3233 System

The millisecond pulsar PSR J0435+3233, discovered by FAST, exhibits an unusually large apparent spin-down rate, potentially reflecting line-of-sight acceleration from a distant companion. Recent investigations reveal a hierarchical triple consisting of an inner pulsar-helium white dwarf binary with an orbital period of ~8 days, orbited by a G-type subgiant tertiary on an eccentric ~74 yr orbit. The current timing description admits two distinct geometrical solutions. We develop a singly averaged (SA) formulation that averages over the inner orbit while retaining the instantaneous phase of the eccentric outer orbit, thereby capturing the time-dependent quadrupolar perturbations induced by the tertiary. We show how this physical three-body description can be incorporated naturally into pulsar-timing analyses and use it to forward-propagate the two currently viable configurations, Tv1 and Tv2, to forecast when their timing signatures become distinguishable with FAST. The SA evolution predicts that the two configurations will become distinguishable in the coming years, with the effective projected semi-major axis, $x_{1,\mathrm{eff}}$, providing the earliest discriminating observable. We further extend the framework to predict the tertiary's spectroscopic radial-velocity and astrometric evolution, linking FAST timing with LAMOST time-domain spectroscopy and Gaia astrometry. This multi-band framework has the potential to establish PSR J0435+3233 as an exceptionally well-constrained laboratory for three-body dynamics, compact-binary and stellar evolution, and gravitational physics.

astro-ph.HE↗
arXiv2026

Fast Radio Bursts Associated with Persistent Radio Sources Prefer Hydrogen-poor Superluminous Supernova Host Environments

A subset of repeating fast radio bursts (FRBs) is associated with compact persistent radio sources (PRSs). The FRB-PRS hosts differ dramatically from the general FRB host population: they do not follow the distribution of localized non-PRS FRB hosts, nor the SFR-weighted or mass-weighted mock host distributions expected for the general star-forming galaxy population, instead occupying the extreme low-mass, high-sSFR, and low-metallicity end of host-galaxy parameter space. We compare these hosts with well-defined samples of hydrogen-poor superluminous supernovae (SLSNe-I), hydrogen-rich superluminous supernovae (SLSNe-II), and Type II core-collapse supernovae (CCSNe). Using cumulative distribution functions and statistical tests, we find that FRB-PRSs tend to reside in dwarf galaxies with high specific star formation rates and low gas-phase metallicities, even relative to galaxies of similar stellar mass. Their hosts are most similar to those of SLSNe-I, but differ significantly from CCSN hosts, with SLSN-II hosts lying between these populations. These results suggest that FRB-PRSs do not simply trace star formation activity or the general FRB host population, but instead favor SLSN-I-like environments. This preference is consistent with young magnetars formed through low-metallicity massive-star channels, for which SLSN-I-like ejecta imply a characteristic free--free transparency time of ~29 yr at 600 MHz.

astro-ph.HE↗
arXiv2026

Supernova origin of galactic turbulence revealed by superbubbles

Supernovae (SNe) are among the leading candidates for powering galactic-scale turbulence. SNe drive expanding shells of neutral atomic hydrogen (HI) known as superbubbles. Due to the lack of a sensitive, dynamically complete, galaxy-wide census, superbubbles have not been used to quantify the galactic-scale turbulent energy budget. Here we present a combined Five-hundred-meter Aperture Spherical radio Telescope (FAST) and Jansky Very Large Array HI survey of the Andromeda galaxy (M31), the nearest giant spiral, with superior sensitivity and dynamical coverage. We identify 118 superbubbles across the entire disk of M31 with dynamical ages up to 40 Myr, consistent with the expected duration of SN activity in a star cluster and extending the age coverage well beyond previous surveys. Inferred from these superbubbles, the kinetic energy injection rates ($10^{49}$--$10^{51.5}$ erg kpc$^{-3}$ Myr$^{-1}$) from SNe closely match the turbulence dissipation rates derived independently from the same data, in both magnitude and spatial distribution. These results demonstrate that clustered SN feedback is sufficient to sustain galactic-scale turbulence, which shapes disk structure and influences galaxy evolution.

astro-ph.GA↗
arXiv2026

Local constraints on alcohol--thioalcohol analogs in G35.2N

The chemistry of sulfur-bearing complex organic molecules in dense star-forming environments remains uncertain, partly because the dominant sulfur reservoirs in dense gas and ices are poorly identified. Alcohol--thioalcohol pairs allow direct comparisons of structurally related O- and S-bearing molecules. We present ALMA Band 6 observations of CH$_3$OH/CH$_3$SH and C$_2$H$_5$OH/C$_2$H$_5$SH toward three spectral-extraction positions (MM3-pos, MM4-pos, and MM5-pos) in the MM3--MM5 region of G35.2N. Local thermodynamic equilibrium modeling yields column densities and abundance ratios. CH$_3$OH column densities were inferred from $^{13}$CH$_3$OH assuming $^{12}$C/$^{13}$C = 50 to mitigate optical-depth effects. CH$_3$OH, CH$_3$SH, and C$_2$H$_5$OH are robustly constrained at all three positions; C$_2$H$_5$SH is robustly constrained at MM3-pos and MM5-pos but remains tentative at MM4-pos. The corresponding adopted column-density ranges are $(1.8-2.7)\times10^{18}$, $(1.7-2.6)\times10^{16}$, $(5.7-8.5)\times10^{16}$, and $(2.4-4.6)\times10^{15}$ cm$^{-2}$. The CH$_3$OH/C$_2$H$_5$OH and CH$_3$OH/CH$_3$SH ratios are consistent across the positions within uncertainties, with nominal values of 31--32 and 100--110, respectively. Comparisons with chemically rich sources and warm-up chemical models show that CH$_3$OH/C$_2$H$_5$OH lies within the range measured elsewhere, whereas CH$_3$OH/CH$_3$SH exhibits greater source-to-source variation. The ethyl-level O/S comparison remains less certain because many literature C$_2$H$_5$SH measurements provide only lower limits. CH$_3$OH/CH$_3$SH is thus the best-constrained O/S alcohol--thioalcohol ratio in these data and provides an empirical probe of source-dependent sulfur-bearing organic chemistry. More sensitive C$_2$H$_5$SH observations are needed to test C$_2$H$_5$OH/C$_2$H$_5$SH.

astro-ph.GA↗
arXiv2026

Low Star Formation Efficiency in M31: Evidence for a Deficit of Bound Gas

The Andromeda galaxy (M31) exhibits a systematically low star formation efficiency (SFE) compared to other star-forming galaxies. Star formation is thought to be regulated by the mass of gravitationally bound gas. To investigate whether the low SFE in M31 originates from a scarcity of such bound gas, we analyze the dynamical state of its giant molecular cloud (GMC) population by estimating their virial parameters ($α_{\rm vir}$). Using a JCMT-SCUBA2 850 micron dust-continuum GMC catalog as the parent sample, we combine it with IRAM 30 m CO(1-0) data to define a working sample of 173 GMCs and derive their kinematic properties. Most analyzed GMCs exhibit high $α_{\rm vir}$, indicating that they are predominantly gravitationally unbound at the approximately 86 pc resolution of our observations. While no statistically significant global correlation is found between SFE and $α_{\rm vir}$ for the full cloud sample, the upper quantiles of the SFE distribution show progressively stronger negative trends with increasing $α_{\rm vir}$. This upper-tail trend may arise from the combined effects of the virial parameter limiting the upper range of SFE values accessible to the GMC population and feedback-driven disruption reducing the number of high-SFE, high-$α_{\rm vir}$ CO-bright clouds in the observed sample. The substantial scatter in the SFE-$α_{\rm vir}$ plane likely reflects the diverse evolutionary stages of GMCs, the temporal mismatch between gas and star formation tracers, and the limitations of a cloud-averaged virial parameter as a tracer of internal dynamical structure, making a simple one-to-one correspondence between $α_{\rm vir}$ and instantaneous SFE difficult to recover for individual GMCs.

astro-ph.GA↗
arXiv2026

FAST Observations of Filamentary and Compact H I Structure in a Magellanic Stream IV Field

The Magellanic Stream (MS) is believed to have formed from gas removed from the Large and Small Magellanic Clouds through tidal forces and hydrodynamic interactions with the Milky Way's gaseous halo. It provides an important laboratory for studying how stripped gas fragments, mixes, and evolves in a circumgalactic environment. In this work, we present HI observations of a $3.8^\circ\times2.2^\circ$ field in the MS IV region, using the data from the Commensal Radio Astronomy FasT Survey (CRAFTS). The total HI mass in the analyzed field is $\simeq 5.3 \times 10^{6} (d/120\,{\rm kpc})^{2}\,M_{\odot}$, where $d$ is the distance to the MS IV gas. The data resolve the emission into three coherent filamentary HI structures with related but distinct velocity trends. To characterize the HI structures and study potential multiphase gas, we adopt a Gaussian decomposition procedure to identify and reconstruct sources. Our results indicate that the field is dominated by one major filamentary HI complex, together with several smaller kinematic clump-like components. Among these identified sources, only one source likely shows multiple velocity components. Because several sources appear spatially overlapped in projection, we further examine their apparent overlap regions using position-velocity (P-V) diagrams. P-V diagrams across the apparent overlap region show no clear intermediate-velocity bridge or V-shaped structure, favoring line-of-sight projection over direct cloud-cloud collision. These results demonstrate the value of deep, high-angular-resolution HI observations for resolving faint emission, compact morphologies, and kinematic structure in the MS.

astro-ph.GA↗
arXiv2026

Fast radio bursts, magnetars and earthquakes: their "family feud"?

Fast radio bursts (FRBs) are millisecond-duration cosmic transients whose origin remains elusive. Competing models invoke either earthquake-like processes or flare-like mechanisms. To discriminate between these scenarios, we develop a novel diagnostic, the Pincus-Lyapunov diagram (PLD), to characterize the energetic transients in the stochasticity-chaos phase space. We compile burst sequences from five representative FRBs (FRB 20121102A, FRB 20190520B, FRB 20201124A, FRB 20220912A, and FRB 20240114A), together with those from magnetar flares (SGR J1550$-$5418, SGR J0501+4516, SGR 1806$-$20, SGR 1900+14, and SGR J1935+2154), pulsar glitches, solar flares, and earthquakes, and map them onto the PLD for comparative analysis. The resulting diagram shows that FRBs occupy a distinct region of the phase space. Specifically, a permutation test reveals a statistically significant difference in the distributions of magnetar flares and pulsar glitches compared to those of repeating FRBs ($p$-value $\simeq 0.05$). To examine whether temporal variations in source activity can shift a repeater's position in this phase space, we analyze the time evolution of the most prolific repeater, FRB~20240114A. For this repeating FRB, both Pincus Index and Lyapunov Exponent demonstrate statistically stable behaviour over the eight-month observation session, with Augmented Dickey--Fuller tests yielding $p \simeq 1.78\times10^{-3}$ and $9.91\times10^{-3}$, respectively. By assembling the most comprehensive dataset to date, our work indicates that the trigger mechanisms of repeating FRBs are likely to be distinct from those driving magnetar flares, pulsar glitches, solar flares, and earthquakes.

astro-ph.HE↗