We present a suite of 50 high-fidelity simulations of Coma cluster analogues constructed from BORG/MANTICORE constrained initial conditions and evolved with the IllustrisTNG galaxy formation model. Regions predicted to form massive clusters comparable to Coma in mass and environment are selected and followed through cosmic time, producing realistic galaxy populations and intracluster medium properties. The ensemble captures both cosmic variance and uncertainties in the local initial conditions, providing a statistically robust framework for interpreting Coma in a cosmological context. We focus on direct comparisons with observed thermodynamical profiles of the intracluster medium. Specifically, we extract X-ray surface brightness profiles from the simulated clusters and confront them with measurements from eROSITA, as well as compute the thermal Sunyaev--Zel'dovich effect via integrated Compton-$y$ profiles for comparison with Planck satellite data. The simulations reproduce the broad shape and normalisation of both observables, while also highlighting the range of scatter expected from environmental and assembly history differences. This enables us to assess how feedback processes, merger activity, and large-scale environment shape observable cluster properties. Our results demonstrate that combining constrained cosmological initial conditions with state-of-the-art galaxy formation physics provides an effective strategy for generating targeted, observation-driven analogues of specific clusters. The resulting dataset offers a valuable resource for testing models of intracluster medium physics, calibrating scaling relations, and interpreting upcoming joint X-ray and Sunyaev--Zel'dovich observations of nearby massive clusters.

Dust attenuation is a major source of systematic uncertainty in both SED fitting and forward modeling of galaxy populations, yet the functional form used to parameterize attenuation curves has received surprisingly little systematic scrutiny. Particular unanswered questions include: how many free parameters are genuinely needed, and which analytic expression best captures the full diversity of attenuation curve shapes in galaxies across cosmic time? Using a large library of synthetic attenuation curves from TNG50 and TNG100 galaxies post-processed with the SKIRT radiative transfer code using three dust mixtures (Milky Way, SMC, and stellar dust), we show via Information-Ordered Bottleneck analysis that exactly four parameters are needed to capture the diversity of attenuation curves. Guided by this result, we use symbolic regression to derive a new, interpretable four-parameter attenuation model that outperforms existing parameterizations in recovering both attenuation curves and emergent fluxes across all dust mixtures explored. The four parameters of this model have clear physical interpretations: UV bump strength, FUV slope, UV-bump transition curvature, and large-scale optical slope. Their correlations with galaxy properties are primarily regulated by star-formation rate surface density, metallicity, and stellar-dust geometry, and are largely preserved across dust mixtures -- except for the bump-sensitive parameters, which retain a stronger dependence on grain composition. We further provide symbolic-regression scaling relations linking all four parameters to quasi-observable galaxy properties, offering a physically motivated route to assign realistic attenuation curves in SED fitting and forward modeling without radiative-transfer calculations.

We present a new subgrid model for interstellar gas evolution in cosmological simulations of galaxy formation, based on the pressure-regulated, feedback-modulated (PRFM) theory of star formation. In contrast to the empirically pegged star formation prescriptions employed in current cosmological simulations, the PRFM model links the local star formation rate to the dynamic balance achieved in galactic interstellar gas between gravity and stellar feedback effects. With this formulation, both the star formation efficiency and the effective equation of state may be directly calibrated using numerical simulations, such as TIGRESS, which resolve physics of the interstellar medium and star formation at parsec scales. We develop, and implement in the Arepo moving-mesh code, two complementary classes of the subgrid model: a volumetric version (PRFM-vol) applicable when the gas disk scale height of a galaxy is numerically resolved in a simulation, and an integrated version (PRFM-int) that reconstructs the mid-plane density and pressure from vertical equilibrium considerations when the true gas scale height cannot be numerically resolved. Using isolated Milky-Way-like disk simulations across mass resolutions $10^5$-$10^7~{\rm M}_\odot$, we show that both implementations yield shorter gas depletion times than the IllustrisTNG prescription, especially in regions where pressure and density are large. At high resolution, PRFM-vol and PRFM-int agree closely with each other and with TIGRESS for the star formation rate; PRFM-int remains robust at all resolutions tested. These results demonstrate that PRFM-derived subgrid prescriptions provide a physically grounded and numerically stable framework for star formation across the dynamic range of galaxy formation simulations, paving the way for future cosmological applications.

Learning cosmology from galaxy surveys requires large suites of simulations spanning the cosmological and astrophysical parameter space, yet hydrodynamical simulations of galaxy formation remain prohibitively expensive. Semi-analytic models offer an inexpensive, physically grounded alternative, but still require halo merger trees from $N$-body simulations, and densely sampling cosmological parameters in sufficient volume remains expensive. We address this by extending cosmological rescaling to operate directly on merger trees and applying it in the $Ω_{\rm m}$-$σ_8$ plane, running the Santa Cruz semi-analytic model for galaxy formation on the rescaled trees to produce galaxy populations across new cosmological and astrophysical parameters at negligible additional cost. A novel halo-profile-based correction, controlled by a single free parameter, suppresses systematic bias in rescaled halo masses to below the per cent level. We apply the method to parameter estimation of $Ω_{\rm m}$ and $σ_8$ given either the stellar mass function or the two-point correlation function, finding that as few as 64, and potentially fewer, base $N$-body simulations, rescaled to $\sim1000$ training samples, match the accuracy of 750 dedicated $N$-body simulations; rescaling to 3200 realisations improves the prediction of $Ω_{\rm m}$ by $\sim25\%$. Rescaling all merger trees from a single CAMELS-SAM $N$-body simulation costs $\sim0.1$ CPUh, compared to several thousand CPUh to run the simulation itself. We demonstrate a practical route to obtaining predictions of galaxy summary statistics across cosmological and astrophysical parameters, even with a relatively small number of base $N$-body simulations.

We introduce PRFM-vol, a new subgrid model for star formation in cosmological simulations that aims to increase the physical realism of cosmological simulations by leveraging results obtained with focused ISM simulations. We deploy a modified effective equation of state and calculate the star formation rate for each gas cell as a function of the ambient densities of gas, dark matter, and stars, based on the pressure-regulated feedback-modulated (PRFM) theory of star formation. Test simulations of our model in isolated galaxies show that we match PRFM predictions and TIGRESS scaling relations remarkably well, provided sufficiently high resolution is available. In particular, we are able to clearly demonstrate the impact of the stellar potential on the star formation rate, thereby retaining an important prediction of PRFM. We then apply our new model to cosmological multizoom simulations and find, compared to our previous TIGRESS/Schmidt model, a significant increase in the stellar scale heights and a slight increase in stellar mass. We demonstrate that modifying the effective equation of state significantly affects the morphology of simulated galaxies. Pronounced stellar clumps appear if the effective pressure at low hydrogen number densities is low, and disappear for higher pressure. We show that the formation of clumps is a result of Toomre instabilities, and conclude that simulated galaxy morphologies can be used to constrain effective equation of state models. Overall, our results establish PRFM-vol as a new self-consistent, physics-motivated subgrid model for star formation in high-resolution cosmological simulations.

We present Manticore-Deep, a high-resolution Bayesian field-level inference of cosmic large-scale structure spanning a comoving volume of $(4~h^{-1}\mathrm{Gpc})^{3}$ out to $z \approx 0.7$, at ${\sim}4$~Mpc/h resolution. Building on the inference framework established in the companion Manticore-Local analysis (P1), Manticore-Deep jointly constrains five galaxy redshift surveys (2M++, 6dFGS, 2dFGRS, SDSS, and BOSS) within a single hierarchical Bayesian framework using the BORG algorithm. The method infers initial conditions that are evolved forward under gravitational dynamics, delivering a full posterior ensemble of three-dimensional density and velocity fields that causally reproduce the observed large-scale structure. A novel tiled inference strategy makes this computation feasible, extending the reconstructed volume by more than an order of magnitude beyond P1. The posterior realisations are statistically consistent with LCDM, exhibiting Gaussian, isotropic initial conditions and evolving into late-time structures that reproduce the expected $z=0$ matter power spectrum, bispectrum, and halo mass function across the resolved scales tested. We validate the physical fidelity of the reconstruction through two independent, template-free posterior-predictive tests against observations not used in the inference. Cross-correlation of the reconstructed matter field with the Planck PR3 CMB lensing map yields a conservative cumulative detection significance of 7.4$σ$, while velocity-weighted stacking of $64750$ galaxy clusters on the Planck 217~GHz map produces a kSZ detection at $3.5σ$, with a model-independent approach--recession split confirming that the inferred velocities are statistically aligned with the true cluster motions. As a case study, we show that the BOSS Great Wall is recovered as a ${\sim}3σ$ overdensity consistent with LCDM across all posterior realisations.

Massive stars die as energetic supernova explosions, but the physical processes during and before such explosions are poorly studied observationally. The first electromagnetic signals from core-collapse events are predicted to be a flash of soft X-ray and ultraviolet (UV) light, produced as a result of a shock wave breaking out of the star and its surrounding medium. Such shock breakout (SBO) events often carry essential information about the explosion energetics, the progenitor star, and its immediate environment. However, they are difficult to catch because of their very short durations and a historical lack of sensitive wide-field monitors. Only two SBO events have been detected so far in X-rays, but their emission spectra are modified from the simple thermal form by complicated physical factors, however. Here we report the discovery of a fast X-ray transient, EP260321a, followed by a broad-lined Type Ic supernova (SN Ic-BL) emerging days later, suggesting its progenitor as a Wolf-Rayet star with its hydrogen and helium envelopes stripped. Its X-ray emission is soft and best modeled by blackbody radiation, making it a bona fide SBO. The observed long duration and large total energy output of the X-ray event jointly indicate a shock breaking out from a surrounding shell at a radius of about 300 solar radii, rather than from the progenitor star's surface. This provides direct evidence of abrupt mass ejection within a month prior to core collapse, suggesting intense pre-explosion activity for a massive star. The real-time detection of SBOs yields precise timing of stellar core-collapse, allowing for efficient searches for associated neutrinos and potential gravitational-wave signals. These, together with timely multi-wavelength observations, may uncover how massive stars end their lives.

Primordial black holes (PBHs), possibly formed from the collapse of early universe perturbations, will evaporate via Hawking radiation with a lifetime comparable to the age of the universe, if their mass is $O(10^{14})$ g. Such black holes can contribute to the observed gamma-ray fluxes in the MeV and GeV range. Using the observed extragalactic gamma-ray background (EGRB) from the \textit{Fermi} Large Area Telescope, the \textit{EGRET}, and the \textit{COMPTEL} telescopes that cover gamma-ray energies from 0.5 MeV to 1 TeV, we evaluate limits on the abundance of PBHs with masses of $10^{14}$ to $10^{17}$ g. We study both monochromatic and extended mass distributions of PBHs. To model the EGRB spectrum, we calculate the contribution from extragalactic sources including blazars, star-forming galaxies and radio galaxies and also account for ultra-high-energy cosmic rays that produce gamma rays when interacting with the infrared background. Our EGRB modeling uses information from the \textit{Fermi} gamma-ray point sources catalog, from observations at X-rays, the visible spectrum, the infrared and radio waves, and also accounts for modeling uncertainties and variations on the properties within each class of these sources. Moreover, we use recent work on the modeling of the PBHs' gamma-ray emission, that includes the direct Hawking radiation, gamma rays produced in the hadronization and decay of unstable particles, final state radiation and gamma rays from pair annihilations in the interstellar medium. As the contribution of final state radiation and the annihilation of positrons enhances the low-energy part of the produced gamma-ray spectra from PBHs, we find that the EGRB observations can set the tightest limits on their abundance among all indirect dark matter probes, within the mass range of interest.[abridged]

Non-ideal magnetohydrodynamic simulations of protoplanetary disks show a plethora of complex gas structures, including winds, rings, and gaps. These affect dust transport and help form dust traps, which are essential for planetesimal formation. Although studies have explored the evolution of dust in such systems, they have done so either in 1D or without dust coagulation, and the effect of such systems on dust growth is still an active area of research. This work aims to investigate the effect of a complex gas flow architecture on global dust evolution, including dust growth and transport. We examine the timescales of different processes impacting dust evolution and discuss prospects of forming planetesimals. We post-process gas velocity output from a 2D non-ideal magnetohydrodynamic simulation using a 2D (r-z) Monte Carlo dust coagulation code to perform global simulations of dust growth and evolution. We perform three runs, one with a typical steady-state disk and two with the gas velocity from the MHD simulation, where we vary the fragmentation velocity. Our results show that the advection of small particles by the gas due to strong gas velocities can play an important role in setting the dust size distributions around protoplanetary disks. The gas flow structure has a transition region, and this region acts as a location of a dust pile-up, increasing the pebble-to-gas ratio by a factor of 2.5 when compared to the steady state disk. Lowering the fragmentation velocity improves the stability of the pile-up, but the pebble concentration is not as high. This scenario acts as a way to form a dust trap in a disk without a pressure bump. We discuss the possibilities for planetesimal formation in such a trap.

In March 2026, the Einstein Probe (EP) discovered its most nearby (z = 0.0343) Fast X-ray Transient (FXT), EP260321a, the first EP FXT to provide a strong match to expectations for X-ray ''shock breakout'' (SBO) emission. Here, we present our multi-wavelength follow-up campaign of EP260321a and its broad-line Type Ic (Ic-BL) supernova (SN) counterpart, SN 2026gzf, the first Type Ic-BL SN with a definitive X-ray SBO. We show that our radio follow-up extending over 5.8 - 54.5 days post-FXT rules out an on-axis jet counterpart of isotropic-equivalent kinetic energy $E_{K} > 10^{49}$ erg for circumburst densities $n > 10^{-2}~{\rm cm}^{-3}$ and constrains radio synchrotron emission from the fastest-moving SN ejecta. In addition, we derive the properties of SN 2026gzf and its host galaxy from our well-sampled optical data and compare them with those of optically discovered Type Ic-BL SNe, finding that SN2026gzf is well within the 90% confidence interval across all properties. We further fit SN 2026gzf's light curve with five different physical models, and determine that combined emission from both interaction with circumstellar material (CSM) and $^{56}$Ni radioactive decay provides the best fit with plausible model parameters. Finally, using the rate of Ic-BL SNe from the ZTF Bright Transient Survey and assuming all Type Ic-BL SNe produce EP260321a-like FXTs, we infer an expected rate of EP-detected SBOs of 4.4 - 16 year$^{-1}$. This is inconsistent at the 90% confidence level with current EP detection rates, potentially indicating that most Type Ic-BL SNe produce less luminous X-ray SBO signals compared to EP 260321a.

When a massive star explodes as a supernova, crucial information about its immediate environment is lost within hours. Here we report rapid optical observations from Lulin Observatory of the broad-lined Type Ic supernova SN 2026gzf, beginning 1.25 hours after Einstein Probe detected the X-ray transient EP260321a. Our data led to the discovery of the optical counterpart and showed a luminous blue first-day excess that cannot be reproduced by standard radioactive models. We find that interaction between the ejecta and $\approx 0.02$ M$_{\odot}$ of circumstellar material accounts for the early excess. Archival Panoramic Survey Telescope and Rapid Response System (Pan-STARRS) images show variability at the explosion site over the previous $\sim 12$ years, with the source brightening by a factor of $\sim 1.5$ in the final $\sim 3$ years before explosion, providing rare evidence for pre-explosion activity in a stripped-envelope progenitor system. The precursor brightening suggests enhanced eruptive mass loss during late-stage oxygen burning before core collapse, while an additional silicon-burning episode shortly before explosion may have created the compact nearby material responsible for the X-ray shock-breakout signal. SN 2026gzf therefore offers the first view of how a stripped progenitor modifies its immediate environment shortly before death, linking long-term precursor variability, circumstellar interaction and the explosion itself.

The Standard Model of particle physics contains a diverse set of particle species, motivating the possibility of a similarly complex dark sector. Here we study two-component dark matter (DM) mixtures, in which one component behaves as standard CDM while the other suppresses the formation of small-scale structure, either through an astrophysically relevant de~Broglie wavelength (fuzzy DM; FDM) or collisional damping from temperature-independent scattering (interacting DM; IDM). Using the observed population of Milky Way satellite galaxies, we derive new leading constraints on the parameter spaces of mixed FDM and of mixed IDM coupled to photons ($γ$-DM), neutrinos ($ν$-DM), or baryons ($p$-DM), for beyond-CDM fractions down to $50\%$. We require that the linear matter power spectra of allowed models remain less suppressed than a constrained reference model. The resulting $95\%$ confidence bounds on FDM mass and IDM cross section weaken systematically with decreasing fraction, following distinct power-law scalings. At $50\%$ fraction, IDM cross section bounds weaken by a factor of $\sim$2--6 and FDM mass bounds by $\sim$1.5, relative to the $100\%$ case. We forecast that idealized future satellite surveys, which adopt approximate LSST sensitivity thresholds, can improve these $100\%$ bounds by a factor of $\sim$1.6--14 for IDM and $\sim$3 for FDM. Self-consistent cosmological simulations of mixed DM scenarios will be essential to more robustly characterize the degeneracy between particle physics parameters and fractional contribution, to extend constraints to lower fractions, and to identify signatures beyond satellite abundance to further inform these models.

We have simulated Lyα, Hα, Hβ, [OII], and [OIII] intensity maps which are observable by SPHEREx during cosmic reionization. We simulate these intensity maps including all significant sources of emission for each line, and include radiative transfer for the Lyα intensity maps. We also include a simple model of dust extinction based on observations of galaxies at z<5. One of the main challenges of intensity mapping is interloping lines from galaxies at lower redshifts, which makes producing an auto-power spectrum challenging. We focus on cross-correlations between different lines, as this eliminates such foreground contamination of the signal. We have cross-correlated the simulated SPHEREx intensity maps to find the most observable cases. This includes modeling of interloping lines and masking bright interloping galaxies. Testing a range of cases motivated by observations, we find total signal-to-noise values up to 99 for the highest case of Hα cross-correlated with [OIII] at z=5 assuming no dust extinction. We also find cases which will not be detectable. We find that the dominant noise source in these intensity maps on most scales is from the instrument, except for Lyα and [OII] and then only on the largest scales the interlopers are the dominant source. We find through intensity mapping we can probe galaxies with masses $M<4x10^{10}~M_{\odot}$ which are below the necessary luminosity for a 3σ signal-to-noise direct detection of galaxies by SPHEREx. However, the majority of our observable signal is dominated by large, directly detectable galaxies, rather than the smaller, fainter galaxies. We find marginal detections of the clustering portion of the power spectrum at z=5 for Hαx[OIII]. Detections of the clustering signal from other lines or at z>6 will require more sensitive instruments, such as the Cosmic Dawn Intensity Mapper.

A long-standing question in the death of massive stars is the role of relativistic jets. While many gamma-ray bursts and some fast X-ray transients seem to be associated with broad-lined type Ic supernovae, the opposite is not true. The lack of observable jet emission in those Ic-BL SNe can be explained by invoking off-axis jets, choked jets that inject all their energy into the stellar envelope, baryon-loaded jets for which the prompt high-energy emission is strongly suppressed, or non-jetted SNe. The lack of exact explosion time in the majority of SNe presents an obstacle to distinguish between these scenarios. Here we report the properties of SN 2026gzf associated with the X-ray thermal Einstein Probe shock-breakout EP260321a at z=0.0343. The absence of compelling shocked cocoon and radio emission up to 54 days, combined with initial expansion velocities of ~30,000 km/s and a circumstellar shell of ~0.07 M$_\odot$, favour a scenario for SN 2026gzf in which a jet was choked in the circumstellar shell. Our high-spatial resolution images of the SN environment show that the progenitor was located between two highly star-forming regions with a metallicity lower than any previously known Ic-BL SN. As the first case of a Ic-BL SN associated with high-energy prompt emission without the signature of a jet, SN 2026gzf provides a unique perspective to understand the successful launch of relativistic jets during the deaths of massive stars.

A population of dense stellar systems at high redshift has recently been uncovered by the JWST. To investigate the formation of supermassive black hole (SMBH) seeds in these dense environments without invoking any \textit{ad hoc} seeding mechanisms, we present star cluster-scale simulations performed with an updated version of the hydrodynamics code \texttt{Enzo-Abyss}, which self-consistently integrates the gravity using a direct $N$-body method coupled with stellar evolution. By modeling initially dense, metal-poor gas clouds with varying turbulence, we consistently find the formation of dense clusters resembling early-stage nuclear star clusters (NSCs), as well as the formation of very massive stars (VMSs) ranging from $343\;\mathrm{M_\odot}$ to $5108\;\mathrm{M_\odot}$ via runaway collisions, irrespective of stellar wind feedback strength. Following the direct collapse of these VMSs, the resulting intermediate-mass black holes (IMBHs) grow through Eddington-limited gas accretion and tidal disruption events (TDEs). In our most optimistic model, we find a mass accretion rate of $1.64\times10^{-4}\;\mathrm{M_\odot\;yr^{-1}}$, with TDEs contributing $23\%$ of the total accretion over $\sim10\;\mathrm{Myr}$. Assuming a steady gas supply into the NSC driven by rapid structural assembly in the high-redshift environment, together with a constant TDE rate, we project that an IMBH with an initial mass of $6747\;\mathrm{M_\odot}$ at the center of the NSC can grow to $\sim62000\;\mathrm{M_\odot}$ within $100\;\mathrm{Myr}$ of its formation. Our numerical study, conducted within a single self-consistent framework that incorporates the essential physical processes, suggests that VMSs can form in dense gas clouds, collapse into IMBHs, and subsequently provide viable seeds for the SMBHs observed at high redshift.

In modern simulations that include star formation, it is common to use a universal and invariant initial mass function (IMF) to represent star populations or sample individual stars. However, stellar masses are determined by local and environmental processes that operate over a wide dynamical range and remain unresolved in simulations. We introduce a semi-deterministic (SDT) scheme for sampling individual stars from star-forming gas in numerical simulations. We represent unresolved molecular cores and protostellar disks with reservoir particles (RsvPs) and employ an on-the-fly friends-of-friends algorithm to identify star clusters. The instantaneous IMF for newly formed stars is then derived from the current cluster mass. We test the performance of this method in simulations of isolated molecular clouds and a major merger between two dwarf galaxies. Compared to existing IMF sampling methods, our SDT scheme naturally reproduces the observed $m_{\star,\text{max}}$-$M_\text{ecl}$ relation and yields numbers of massive stars consistent with optimal sampling theory. It also exhibits the smallest run-to-run variation among simulations with different random seeds. The regulated star formation results in a small ($\sim0.15$ Myr) but coherent time delay in the emergence of massive stars, reduces the large scatter arising from Poisson noise, and produces initial mass segregation within the clusters. On galactic scales, the SDT method predicts a steeper high-mass IMF slope at low star formation rates (SFRs), with the slope negatively correlated with the SFR. As the specific abundance of massive stars declines, we predict that H$α$-based SFR diagnostics will systematically underestimate the intrinsic SFR due to IMF sampling effects.

The formation histories of halos set the baseline rate at which galaxies accrete gas over cosmic time. While a number of models describe these histories and their derivative, the mass accretion rate (MAR), a simple and universal formula has remained elusive. Here we measure the median MARs and half-mass formation times of halos in dark matter-only and hydrodynamical simulations, in extremely different cosmologies ($Λ$CDM and Einstein-de Sitter), and across a wide range of redshifts ($z = 0$-$14$). We confirm that MARs increase with mass and redshift, and that they are virtually identical in hydrodynamical and dark matter-only simulations. We show that MARs are accurately described by a universal six-parameter function of three physical variables: the peak height $ν$, the slope of the linear power spectrum $n_{\rm eff}$, and the effective linear growth rate $α_{\rm eff}$. A complementary two-parameter fit for the formation redshift improves on the function of Lacey \& Cole by fixing one parameter to its physical value and adding a dependence on $n_{\rm eff}$. Our model is broadly consistent with some prescriptions from the literature but provides a larger range and higher accuracy at high redshifts and low masses. Our fitting functions are implemented in the publicly available \textsc{Colossus} toolkit.

A cosmological pseudo-scalar field provides a compelling realization of dynamical dark energy (DE). If its coupling to photons is non-negligible, the cosmic microwave background acquires a rotation of its polarization plane, known as cosmic birefringence (CB). We present an extended analysis of several pseudo-scalar DE models and derive constraints on the parameters of their potentials by combining observations of the background expansion history with measurements of CB. We find that the axion-like potential constitutes a viable model only for large values of the anomaly coefficient. Scenarios in which the pseudo-scalar field rolls down a potential with quadratic, linear, or Ratra-Peebles forms can successfully explain DE and CB, with a symmetry-breaking scale close to the GUT scale.

The explosion of a star is first marked by the shock wave breaking out of the stellar surface, producing a burst of ultraviolet and X-ray radiation. These events are observationally rare, despite likely accompanying the majority of supernovae. Here, we report on our multi-wavelength observing campaign of the closest Einstein Probe fast X-ray transient EP260321a at $z=0.0344$. The thermal ($kT=160$ eV) X-ray emission with peak luminosity $2.2\times10^{44}$ erg s$^{-1}$ points to a shock breakout origin. We demonstrate that EP260321a is accompanied by a broad-lined Type Ic supernova, SN 2026gzf. The supernova properties, including its spectral evolution, lightcurve evolution, and expansion velocities, are all typical of the energetic stripped-envelope supernovae associated with gamma-ray bursts. However, deep X-ray upper limits obtained with the \textit{Chandra X-ray Observatory} do not detect an X-ray afterglow, and instead exclude the afterglow of known gamma-ray bursts or fast X-ray transients. If the stellar explosion launched a successful relativistic jet, we require that it had both a low Lorentz factor $Γ_0$\,$<$\,$30$ and a kinetic energy $E_\textrm{kin}$\,$<$\,$10^{49}$ erg for a stellar wind density of $A_*$\,$\gtrsim$\,$1$. We propose that EP260321a originated from a mildly relativistic, weak outflow that was choked by the progenitor star. This scenario is capable of naturally explaining its low X-ray luminosity and lack of prompt gamma-ray emission. EP260321a bridges the gap between SN 2008D and low-luminosity GRBs, suggesting a greater diversity in the physical parameters of stripped stars as they undergo terminal collapse.

We analyze a large brightening event that lasted for roughly half a day in the pulsating hydrogen-atmosphere white dwarf GD 1212 during K2 Campaign 12 of the extended Kepler mission. For the other 80 days of K2 observations, GD 1212 exhibited a rich spectrum of long-period (~1100 s) pulsations that underwent rapid variations in frequency and amplitude but did not exhibit any additional outbursts. We refine previous attempts at mode identification and find a likely sequence of dipole and quadrupole splittings that reveal an overall rotation rate of roughly 17.0 hr. The outburst at Day 61 is fully resolved by the 60-second-cadence K2 data, with the entire white dwarf becoming up to 17.5% brighter overall, from an approximately 850 K increase in effective temperature, with pulsational variability during the outburst showing shorter periods and higher amplitudes. Outbursts are believed to be the result of nonlinear mode coupling via parametric instability, whereby energy stored in linearly excited parent modes is rapidly transferred to damped child modes that dissipate near the surface. Additionally, we characterize a "failed" outburst that caused correlated pulsation frequency changes, an approximately 5 microHz increase, with a small approximately 0.35% corresponding brightness increase. GD 1212 is now the eighth pulsating hydrogen-atmosphere DAV white dwarf to show outburst behavior, although it exhibited the largest outburst yet and has the longest inferred recurrence timescale. This high-signal-to-noise record tracing pulsations through both large and small temperature excursions in GD 1212 provides unique insights into parametric resonance and nonlinear mode coupling in white dwarf pulsations.

We present a systematic X-ray analysis of the narrow-line Type 1 quasar PHL 1811, which has long been regarded as the prototype of intrinsically X-ray weak quasars. A critical breakthrough came with the first detection of a bright X-ray flare from this source by the Einstein Probe (EP) in 2024. We utilize archival X-ray observations spanning 2001-2024, including the post-flare EP and Swift data. We confirm that PHL 1811 shows X-ray weakness factors $f_{\rm weak} \approx 23$-179 across all epochs before 2024. The 2024 EP flare marks the first detection of an X-ray nominal state with $f_{\rm weak} \approx 0.63$, followed by a rapid flux decline. We identify three key observational signatures that strongly support heavy obscuration: (1) a significant hard X-ray excess above $\approx5$ keV in the 2015 XMM-Newton spectrum; (2) relatively flat spectral shapes in two Swift observations; and (3) transitions between X-ray nominal and multiple X-ray weak states without corresponding optical/infrared variability, consistent with expectations from obscuration by a clumpy dust-free absorber. Fitting with a partial-covering obscuration model reproduces all multi-epoch spectra well. The observed steep spectra are dominated by a small leaked/scattered fraction of the intrinsic continuum, and variability is driven by changes in the leakage fraction and column density. Our results strongly favor the scenario where PHL 1811 is obscured by a radiatively driven accretion-disk wind from super-Eddington accretion, unifying PHL 1811 with the broader population of super-Eddington accreting AGNs under a single obscuration framework.

The formation mechanism(s) of substellar objects, such as brown dwarfs and free-floating planets, remains an ongoing puzzle in stellar and planetary physics. Recent observational and theoretical work points towards a star-like origin for brown dwarfs, though several authors posit that they could form like planets in a circumstellar disc, and then subsequently be ejected into a star-forming region or the Galactic field. Recently, JWST observations have discovered nine substellar objects in the IC348 star-forming region with a spectral absorption feature at 3.4$μ$m from an unidentified aliphatic hydrocarbon, detected for the first time in planetary atmospheres outside of the Solar System. It is unclear whether these hydrocarbon absorption features in these 'H-type' objects indicate a different formation mechanism compared to more massive brown dwarfs. We quantify the spatial distribution of these objects and find they are indistinguishable from the spatial distribution of stars and other brown dwarfs in IC348. We use N-body simulations to test whether the H-type objects could have formed as planets in circumstellar discs and then been dynamically ejected by stellar fly-bys. We show that a similar number of free-floating planets could be produced if those planets initially resided at ~5au from their host stars. However, these free-floating planets have a much more dispersed spatial distribution than the stars and brown dwarfs, inconsistent with the spatial distribution of the H-type objects in IC348. We therefore conclude that the H-type objects are unlikely to have a planetary-like origin.

We present the discovery of a compact Milky Way satellite in the constellation of Gemini. This system was discovered by cross-matching detections from two independent search algorithms applied to Blanco/DECam data from the third data release of the DECam Local Volume Exploration survey (DELVE DR3), and confirmed with deeper imaging from Gemini/GMOS-N. Based on these data, we determine that the system is an ultra-faint ($M_V = -2.1^{+0.4}_{-0.6}$), compact ($r_{1/2} = 8.6^{+1.4}_{-1.2}$ pc) system located at a heliocentric distance of $120^{+7}_{-6}$ kpc. These physical properties place the system in the regime of ambiguous, ultra-faint compact Milky Way halo satellites that cannot be confidently classified as dwarf galaxies or star clusters from morphology alone; we therefore name the system DELVE 8/Gemini I. From medium-resolution Keck/DEIMOS spectroscopy, we securely identify four members including two blue horizontal branch stars, confirming the system as a bound satellite moving at a mean radial velocity of $v_{\rm hel} = -82.7^{+3.7}_{-3.9} {\rm km\,s}^{-1}$. We also use these spectra to place an upper limit of $\rm [Fe/H] \lesssim -2.5$ on the metallicity of DELVE 8/Gemini I's brightest star, supporting the classification of the system as either an ancient star cluster or ultra-faint dwarf galaxy. The discovery of faint, distant systems similar to DELVE 8/Gemini I is expected to become more common with upcoming surveys.

Slitless spectroscopy enables efficient, large-area surveys without target pre-selection, yet it faces challenges from source blending, higher noise, and lost spatial-spectral information. We present an advanced, non-parametric, data-driven algorithm that leverages multiple dispersion angles to reconstruct three-dimensional flux distributions, providing low-resolution Integral Field Unit (IFU) capabilities from slitless data. By treating each pixel as an independent element, our method naturally handles source confusion without requiring prior assumptions regarding redshifts, templates, or model libraries. We validate the algorithm using simulated Roman Space Telescope wide-field slitless spectroscopy images that are equivalent to what is expected from the High-Latitude Time-Domain Survey. First, we demonstrate that a host-galaxy model reconstructed from multiple dispersion angles can be used to accurately subtract host light from a transient, recovering a Type Ia supernova spectrum with minimal bias. Second, we showcase a high-fidelity flux-cube reconstruction of a complex galaxy, successfully measuring the redshift and recovering continuum, emission, and absorption features. This approach highlights the potential of multi-dispersion-angle slitless data to provide spatially resolved spectral information in a non-parametric way, which is traditionally accessible only with integral field spectroscopy, opening a new window into large, unbiased, and spatially-resolved studies of galaxy evolution.

Young planets (<1 Gyr) provide opportunities to directly probe planet formation and evolution processes in action. However, due to heightened stellar activity, there is a lack of known transiting planets in adolescence (~100-500 Myr). Here we present the validation of TIC 150070085 b, a 3.6 R_E planet on a 10.47 day orbit, and report the candidate TIC 150070085 c, a 3.0 R_E planet on a 15.90 day orbit. While we are unable to validate the second signal, the proximity to mean motion resonance (3:2) and transit timing variations observed in the transits of TIC 150070085 b strongly suggest the signal is planetary. We confirm the host star as a member of Alessi 84 and combine the group's CMD, rotation, and variability properties to update the age to 135 +/- 10 Myr. We additionally use MAROON-X to observe the Rossiter-McLaughlin signal of TIC 150070085 b and measure the sky projected obliquity angle ($λ$). We find TIC 150070085 b is consistent with a near-aligned orbit with its host star (|$λ$| = 18 +/- 12$^\circ$), in line with similarly aged transiting planets with measured $λ$ values. Continued discovery and characterization of planets in this age regime are vital to link planetary infancy (<50 Myr) and maturity (>1 Gyr).

Little Red Dots (LRDs) are enigmatic, compact red sources ubiquitous in JWST deep fields whose physical nature remains elusive. As one of the most sensitive tracers of neutral hydrogen in galaxy environments, Ly$α$ is uniquely positioned to probe the gaseous structures proposed to explain LRDs' unusual properties. We present a systematic study of Ly$α$ emission in LRDs, using a sample of 110 spectroscopically confirmed LRDs at $z \geq 4$ from the A. de Graaff et al. (2025) catalog, all with NIRSpec/PRISM coverage of the Ly$α$ line. We detect Ly$α$ at signal-to-noise S/N $\geq$ 3 in 32 LRDs, finding Ly$α$ luminosities and the distribution of rest-frame equivalent widths consistent with normal star-forming galaxies at comparable redshifts. Yet the Ly$α$/H$α$ ratios fall systematically below those of star-forming galaxies, and the Ly$α$ luminosity tracks [O III] luminosity more closely than [O III] equivalent width, together suggesting that Ly$α$ is primarily associated with the host-scale component rather than the compact component responsible for the broad Balmer lines and red continuum. For 13 LRDs at $z \gtrsim 5.5$, we construct continuum-subtracted Ly$α$ maps using broadband imaging from HST/ACS or JWST/NIRCam, revealing spatially extended, asymmetric, and often offset emission relative to the rest-optical light, consistent with resonant scattering through clumpy, anisotropic gas commonly observed in high-redshift Ly$α$ emitters. These results support a two-component picture in which the compact rest-optical source is embedded within a more extended host-galaxy environment whose interstellar and circumgalactic gas shapes Ly$α$ escape and spatial redistribution. Ly$α$ opens a new window into the relation between the compact red component, the host galaxy, and the surrounding gas in LRDs.

We present a patch-level scoring architecture for unsupervised gravitational-wave glitch detection that mitigates the signal dilution limitation identified in Cirfeta (2026b). The CLS token of frozen DINOv2 (ViT-S/14) performs global average pooling over 37x37=1369 patches, systematically suppressing signals occupying less than 5% of the spectrogram grid. We replace the global CLS similarity metric with a top-$k$ order statistic over individual patch token similarities against a Vector-Quantized reference index ($K=64$ centroids per class, 19 Gravity Spy O3b morphologies, 1216 total centroids). Applied to strain-domain injections in LIGO O4a L1 data (session 20260524), we demonstrate a statistically significant distributional separation ($\text{KS}=0.963$ at optimal $k=68$) for spatially extended morphologies (SpiralBurst), while confirming the patch-size temporal resolution limit for ultra-short transients (AsymBlip). A topological saliency map constructed from spatial patch similarity against a background matrix (78 null segments) correctly localizes glitch signatures for Scattered_Light and injected SpiralBurst. The Max/Mean ratio analysis demonstrates that patch-level saliency functions as a topological visualizer rather than a binary detector, consistent with the non-isotropic geometry of DINOv2 embedding space on GW spectrograms.

Pulsar Wind Nebulae (PWNe) are among the most important sources emitting in the very-high-energy gamma-ray band. Predicting their long-term evolution is crucial for forthcoming high-energy observatories like ASTRI and CTA. In this work, We investigate the dynamical evolution of middle-aged PWNe - probably the major contributors to the Galactic TeV emission - and test the robustness of current approaches. To understand the diversity of these systems, we derive the Pulsar and Supernova Remnant (SNR) parameters governing PWN evolution. SNR evolution is set by supernova kinetic energy, ejecta mass, and ambient density, while pulsar energy injection powers the PWN expansion. Adopting standard distributions, we generate a synthetic PWN-SNR population and define a region of interest encompassing the majority of these objects. We use a semi-analytical framework for the early evolution and a 1D Lagrangian code to track their interaction with parent SNRs (the reverberation phase). Within our region of interest, we find large diversity in the late-stage evolution. Despite this, all systems converge toward a relaxed state consistent with the Sedov solution. To address 1D limitations, we perform 2D simulations - optimized to reduce computational cost while preserving physical accuracy - to study instability growth and long-term mixing. We find that instability growth depends on initial perturbations but does not significantly alter global dynamics. While effective volume evolution agrees with 1D predictions, multidimensional effects can increase the apparent size by up to 50%. For the first time, we investigated in detail the multidimensional evolution of middle-aged PWNe in the reverberation phase. By characterizing the late-time evolution across the population, our results confirm the robustness of 1D models, demonstrating that current predictions remain trustworthy.

Let $X$ be a compact Riemann surface and $G$ a connected reductive complex Lie group with centre $Z$. Consider the moduli space $M(X,G)$ of polystable $G$-Higgs bundles on $X$. The group of isomorphism classes of $Z$-bundles on $X$, which is isomorphic to $H^1(X,Z)$, acts on $M(X,G)$ via extension of structure group by the multiplication homomorphism $Z\times G\to G$. The group $\text{Aut}(G)$ also acts on $M(X,G)$ by extension of structure group, and so does the group $\text{Aut}(X)$ of holomorphic automorphisms via pullback. Finally, $\mathbb{C}^*$ acts by multiplying the Higgs field. Combining these provides an action of the semidirect product of $H^1(X,Z)$ and $(\text{Aut}(G)\times\text{Aut}(X))\times\mathbb{C}^*$ on $M(X,G)$, where $\text{Aut}(G)$ and $\text{Aut}(X)$ act on $H^1(X,Z)$ by extension of structure group and pullback, respectively. Let $H$ be such semidirect product. Let $Γ$ be a finite subgroup of $H$. The goal of this thesis is to find a Prym--Narasimhan--Ramanan-type construction to describe the fixed points of the action of $Γ$ on $M(X,G)$. More precisely, we show that fixed points correspond to twisted equivariant Higgs pairs over certain étale covers of $X$. Our results generalize García-Prada--Ramanan, where $Γ$ was considered to be cyclic, and Narasimhan--Ramanan, who only consider actions of cyclic subgroups of $H^1(X,\mathbb{C}^*)$ for $G=\text{GL}(n,\mathbb{C})$.

We study the Cauchy problem for a mixed-sign quadratic Dirac equation on a noncompact $N$-star metric graph $G$, \[ \mathrm{i}\partial_t ψ= Dψ- \mathcal N(ψ), \qquad ψ(0)=ψ_0, \] where $ψ=(ψ_1,ψ_2)^{\mathsf T}:\mathbb{R}\times G\to\mathbb{C}^2$ and $D$ denotes the self-adjoint Dirac-Kirchhoff operator on $G$. The nonlinearity acts edgewise and is given by a bilinear interaction between the positive and negative spectral parts, \[ \mathcal N(ψ)=\mathcal B\bigl(Π_+ψ,Π_-ψ\bigr), \] where $Π_\pm$ are the spectral projections of $D$ and $\mathcal B$ is a fixed bilinear map on $\mathbb{C}^2$ applied componentwise on each edge. This is a model quadratic interaction tailored to the mixed-sign Bourgain-space mechanism, rather than a general nonlinear Dirac equation on graphs. Using Bourgain-type spaces associated with the spectral resolution of $D$ and a mixed-sign bilinear estimate on $N$-star graphs, we prove local well-posedness in the operator Sobolev space $H_D^s(G)$ for \(s>-\frac18\). We also establish a blow-up alternative in $H_D^s(G)$ for the maximal forward lifespan.