CyberSec Research

Using NIRSpec on JWST, we studied a sample of 15 intermediate-mass (1.8-4.1 Msun) young stellar objects (YSOs) previously identified with MIRI photometry in the low-metallicity NGC 346 star-forming cluster in the Small Magellanic Cloud (SMC). All objects, observed in the 1.7-5.3 micron range, show strong hydrogen recombination lines in the Paschen, Brackett, Pfund, and Humphreys series, confirming their very young ages. The spectra of 11 YSOs show prominent absorption bands from the three most important ice species (H2O, CO2, CO), marking the first detection of these ices in intermediate-mass YSOs beyond our Galaxy. In three YSOs, water ice appears to be in crystalline form. In some objects, we also detect 13CO2 and OCS ices -- never before observed beyond the Milky Way (MW) -- and methanol ice in at least one star. We compared the column densities of H2O, CO2, and CO ices with those measured in more and less massive protostars in the MW and Large Magellanic Cloud, finding that in NGC 346 ice column densities reach values nearly an order of magnitude lower than in more massive objects (~1x10^{17} cm-2 for water and ~1x10^{16} cm-2 for CO2 and CO). However, the relative proportions of the ice species abundances do not differ from those in massive MW YSOs. This suggests that metallicity may not significantly affect ice chemistry in protoplanetary discs and that, shielded by the protostellar envelope or deep in the midplane, circumstellar material is likely impervious to the radiation environment.

The Vera C. Rubin Observatory LSST is expected to discover tens of millions of new Active Galactic Nuclei (AGNs). The survey's exceptional cadence and sensitivity will enable UV/optical/NIR monitoring of a significant fraction of these objects. The unprecedented number of sources makes spectroscopic follow-up for the vast majority of them unfeasible in the near future, so most studies will have to rely on photometric redshifts estimates which are traditionally much less reliable for AGN than for inactive galaxies. This work presents a novel methodology to constrain the photometric redshift of AGNs that leverages the effects of cosmological time dilation, and of the luminosity and wavelength dependence of AGN variability. Specifically, we assume that the variability can be modeled as a damped random walk (DRW) process, and adopt a parametric model to characterize the DRW timescale ($\tau$) and asymptotic amplitude of the variability (SF$_\infty$) based on the redshift, the rest-frame wavelength, and the AGN luminosity. We construct variability-based photo-$z$ priors by modeling the observed variability using the expected DRW parameters at a given redshift. These variability-based photometric redshift (VAR-PZ) priors are then combined with traditional SED fitting to improve the redshift estimates from SED fitting. Validation is performed using observational data from the SDSS, demonstrating significant reduction in catastrophic outliers by more than 10% in comparison with SED fitting techniques and improvements in redshift precision. The simulated light curves with both SDSS and LSST-like cadences and baselines confirm that, VAR-PZ will be able to constrain the photometric redshifts of SDSS-like AGNs by bringing the outlier fractions down to below 7% from 32% (SED-alone) at the end of the survey.

Boxy/peanut and X-shaped (BP/X) bulges are prominent features in edge-on disk galaxies and are believed to be vertically thickened bars. Despite their relevance in bar evolution, a statistically robust census of these structures in large surveys has been lacking. We aim to provide the largest catalog of BP/X structures in edge-on galaxies to date, and to investigate their properties and role in shaping galaxy scaling relations. We selected a sample of 6684 edge-on galaxies from SDSS DR8 using Galaxy Zoo classifications, requiring a high edge-on probability ($> 0.9$) and a minimum of 10 independent votes. Two-dimensional image decomposition is performed using GALFIT to obtain structural parameters. Residual images are visually inspected to classify BP/X features into four categories: strong both-sided, both-sided, one-sided, and control (no BP/X). We also estimated stellar mass, distance, and physical size for each galaxy. Out of 6653 classified galaxies, we identified 1675 ($\sim$25%) with both-sided BP/X features-545 ($\sim$8%) strong and 1130 ($\sim$17%) faint-as well as 1108 ($\sim$17%) one-sided structures, making up a total of 2783 BP/X-hosting galaxies ($\sim$42%). One-sided structures, likely signatures of ongoing buckling, are more frequent than strong both-sided bulges across all stellar masses. The fraction of BP/X bulges increases with stellar surface mass density, indicating a connection with bar formation in dense disks. We also find that galaxies with strong BP/X bulges contribute to increased scatter in the stellar mass-size and stellar mass-surface density relations, particularly at higher masses.

Local Universe dwarf galaxies are both cosmological and mass assembly probes. Deep surveys have enabled the study of these objects down to the low surface brightness (LSB) regime. In this paper, we estimate Euclid's dwarf detection capabilities as well as limits of its MERge processing function (MER pipeline), responsible for producing the stacked mosaics and final catalogues. To do this, we inject mock dwarf galaxies in a real Euclid Wide Survey (EWS) field in the VIS band and compare the input catalogue to the final MER catalogue. The mock dwarf galaxies are generated with simple S\'ersic models and structural parameters extracted from observed dwarf galaxy property catalogues. To characterize the detected dwarfs, we use the mean surface brightness inside the effective radius SBe (in mag arcsec-2). The final MER catalogues achieve completenesses of 91 % for SBe in [21, 24], and 54 % for SBe in [24, 28]. These numbers do not take into account possible contaminants, including confusion with background galaxies at the location of the dwarfs. After taking into account those effects, they become respectively 86 % and 38 %. The MER pipeline performs a final local background subtraction with small mesh size, leading to a flux loss for galaxies with Re > 10". By using the final MER mosaics and reinjecting this local background, we obtain an image in which we recover reliable photometric properties for objects under the arcminute scale. This background-reinjected product is thus suitable for the study of Local Universe dwarf galaxies. Euclid's data reduction pipeline serves as a test bed for other deep surveys, particularly regarding background subtraction methods, a key issue in LSB science.

Intensity interferometry (II) offers a powerful means to observe stellar objects with a high resolution. In this work, we demonstrate that II can also probe internal stellar kinematics by revealing a time-asymmetric Hanbury Brown and Twiss (HBT) effect, causing a measurable shift in the temporal correlation peak away from zero delay. We develop numerical models to simulate this effect for two distinct astrophysical scenarios: an emission-line circumstellar disk and an absorption-line binary system. Our simulations reveal a clear sensitivity of this temporal asymmetry to the system's inclination angle, velocity symmetry, and internal dynamics. This suggests that, with sufficiently high time resolution, II can be used to extract quantitative information about internal kinematics, offering a new observational window on stellar dynamics.

The nature and evolution of hydrocarbonaceous grains within interstellar and circumstellar media is still far from resolved, perhaps owing to the rather complex nature of their seemingly simple binary atomic compositions. This work explores the fine details of amorphous hydrocarbon nanoparticle, a-C(:H), composition and the evolution of the inherent sub-structures under extreme conditions, focusing on the characteristic CH$_n$ bands in the 3-4 micron wavelength region. Particular attention is paid to the role of dehydrogenation and its effects on the sp^3 and sp^2 hybridisations, leading to an extensive conjugated domain functionalisation of the contiguous structural network within a-C(:H) nanoparticles. Qualitatively this approach is able to explain the origin and evolution, including the appearance and disappearance, of emission bands observed in the 3-4 micron wavelength regime without a significant aromatic moiety content within the structures. A diatomic a-C(:H) phase is likely at the heart of the observed dust evolution in the interstellar medium, and circumstellar and photodissociation regions, as observed at short wavelengths. It appears that we have some way to go in fully understanding these complex materials. Much laboratory work will be required in order to elucidate their chemical and structural evolution at nanoparticle sizes under extreme conditions.

In cold, dense astrophysical environments dust grains are mixed with molecular ices. Chemistry in those dust/ice mixtures is determined by diffusion and reaction of molecules and radicals. However, investigations of diffusion of astrophysically relevant radicals and molecules across the surface and through the pores of cosmic dust grains and of surface reactions consequent to such diffusion is largely uncharted territory. This paper presents results of a study of a solid-state reaction of two molecular species, CO2 and NH3, separated by a layer of porous silicate grain aggregates, analogues of cosmic dust. The experiments demonstrate that the presence of the dust layer was necessary for a pure thermal CO2 + 2NH3 reaction to proceed, leading to the formation of ammonium carbamate (NH4+NH2COO-), an ionic solid containing a complex organic moiety of prebiotic interest recently detected in a protoplanetary disk. This result speaks for: (i) efficient diffusion of molecules on/within cosmic dust, (ii) an underestimated role for surface catalysis in the astrochemistry of cosmic dust, and (iii) potentially efficient dust-promoted chemistry in warm cosmic environments, such as protostellar envelopes and protoplanetary disks.

We investigate how stellar disks sustain their ultrathin structure throughout their evolution. We follow the evolution of ultrathin stellar disks with varying dark matter (DM) halo concentration ($c$) using collisionless $N$-body simulations with \texttt{AREPO}. We test models embedded in steep ($c = 12$), shallow ($c = 2$), and intermediate ($c = 6$) DM concentrations. Our models match the observed structural properties of the stellar disk in the low surface brightness (LSB) ultrathin galaxy FGC~2366, specifically its surface brightness, disk scalelength, and vertical thinness ($h_{z}/R_{D} = 0.1$), while excluding gas, allowing us to isolate the effects of DM. The internal disk heating mechanism driven by bars is suppressed in the LSB ultrathin stellar disks regardless of the DM concentration. The ratio of disk thickness ($h_z$) to scalelength ($R_D$) remains constant at $\leq 0.1$ throughout their evolution. To clearly establish that the LSB nature of stellar disks is the key to preventing disk thickening, we construct the initial conditions by increasing the stellar mass fraction from $f_{s} \sim 0.01$ to $0.02$ and $0.04$, respectively, while keeping the total mass equal to $10^{11} M_\odot$ and $h_z/R_D \leq 0.1$ unchanged. We find that models with a higher stellar mass fraction embedded in a shallow DM potential ($c = 2$) form bars and undergo significant disk thickening ($h_{z}/R_{D} \gg 0.1$) concurrent with the bar growth. We conclude that if the LSB disks are thin to begin with, they remain so throughout their evolution in isolation, regardless of the concentration of the DM halo.

We present a new determination of the evolving far-infrared galaxy luminosity function (FIR LF) and the resulting inferred evolution of dust-obscured star-formation rate density (SFRD) out to redshift z~6. To establish the evolving co-moving number density of FIR-bright objects, we make use of the high-resolution ALMA follow-up study (AS2UDS), of the JCMT SCUBA-2 Cosmology Legacy Survey (S2CLS) sub-mm imaging in the UKIDSS UDS survey field. In order to estimate the contributions of faint/low-mass sources we implement a method in which the faint-end of the IR LF is inferred by stacking (in stellar mass and redshift bins) the optical/near-infrared samples of star-forming galaxies into the appropriate FIR Herschel and sub-mm JCMT maps. Using this information we determine the faint-end slope of the FIR LF in two intermediate redshift bins (where it can be robustly established) and then adopt this result at all other redshifts. The evolution of the characteristic luminosity of the galaxy FIR LF, L*, is found to be increase monotonically with redshift, evolving as z^1.38+-0.07, while the characteristic number density is well fitted by double power-law function, constant at z<2.24 and declining as z^-4.95+-0.73 at higher redshifts. The evolution of the corresponding dust-obscured star-formation rate density was then calculated and is here compared with the results from a number of recent studies in the literature. Our analysis confirms that dust-obscured star-formation activity dominates SFRD at cosmic noon, but then becomes progressively less important with increasing redshift: while dusty star-forming galaxies are still found out to the highest redshifts explored here, UV-visible star formation dominates at z>4, and dust-obscured activity contributes <25% of SFRD by z~6.

We determined HI parameters for eleven nearby late-type dwarf galaxies using FASHI data cubes, despite the fact that the first version of the FASHI catalog does not list any radio sources that could correspond to these galaxies. Four of them are probable peripheral satellites of the bright spiral galaxies: NGC 3556, NGC 4258, NGC 4274, NGC 4490, while others are isolated objects. The considered sample has the following median parameters: a heliocentric velocity of $V_\mathrm{h} = 542 \ km/s$, an HI-line width of $W_\mathrm{50} = 28 \ km/s$, an hydrogen mass of $\log (M_{HI} / M_\odot) = 6.83$, a stellar mass of $\log (M_\star / M_\odot) = 7.19$, and a specific star formation rate of $\mathrm{sSFR} = -10.17 \ yr^{-1}$.

Context. The radiation field consisting of hydrogen recombination lines and continuum emission might significantly affect the hydrogen-level populations in ultra- and hypercompact (U/HC) H II regions. The escape probability approximation was used to estimate the effect of the radiation field in previous models for calculating hydrogen-level populations. The reliability of this approximation has not been systematically studied, however. Aims. We investigate the appropriate ranges of previous models with the escape probability approximation and without the effects of the radiation field. We create a new model for simulating the integrated characteristics and the spatially resolved diagnostics of the hydrogen recombination lines throughout H II regions. Methods. We developed a new nl model with a full radiative transfer treatment of the radiation field causd by hydrogen recombination lines and continuum emission to calculate the hydrogen-level populations and hydrogen recombination lines. We then compared the level populations and the corresponding hydrogen recombination line intensities simulated by the new model and previous models. Results. We studied the applicability and the valid parameter ranges of previous models. Radiation fields exhibit negligible effects on the level populations in classical and UC H II regions. With the modified escape probability, the model with the escape probability approximation is suitable for most HC H II regions. The improved new model performs better in the HC H II region with an extremely high emission measure. To address the high computational costs inherent in numerical models, we trained a precise machine-learning model to enable a rapid estimation of hydrogen-level populations and the associated hydrogen recombination lines.

The thermodynamic properties of the intracluster medium (ICM) at the outskirts of galaxy clusters provide valuable insights into the growth of the dark matter halo and the heating of the ICM. Considering the results of the soft X-ray background study of non-cluster Suzaku fields, we revisit 65 Suzaku pointing observations of the Perseus cluster in eight azimuthal directions beyond 1 Mpc (0.8 $r_{500}$). A possible foreground component, whose spectrum is modeled as a 1 keV collisional ionization equilibrium plasma, significantly affects the temperature and density measurements of the ICM in cluster outskirts. The emission measures in the six arms are similar, showing that the radial slopes of temperature and density follow $r^{-0.67\pm0.25}$ and $r^{-2.21\pm 0.06}$, respectively. The radial pressure profile is close to the average profile measured by the Planck satellite. The resulting entropy slope is $\propto r^{0.81\pm 0.25}$, consistent with the theoretical slope of 1.1. The integrated gas fraction, the ratio of the integrated gas mass to the hydrostatic mass, is estimated to be 0.13$\pm$0.01 and 0.18$\pm$0.02 at $r_{500}$ and $r_{200}$, respectively, consistent with the cosmic baryon fraction. These results suggest that the ICM at the cluster outskirts is quite regular and close to hydrostatic equilibrium. The remaining two arms show that the emission measure is higher by a factor of 1.5-2, possibly due to accretion from filaments from the large-scale structure. A sudden drop in the emission measure also occurs in a direction toward one of the filaments.

Using the PMO 13.7m telescope, we present large-field and high-sensitivity CO(1-0) line observations toward the Crab Nebula, in order to better understand the interstellar gas environment of this well-known historical supernova remnant. The CO observations show molecular clouds toward the Crab Nebula at a velocity range from about 0 to 16 km/s. After checking the CO spectra, we find shocked signatures in the clouds extending at a velocity of roughly [5, 11] km/s. These shocked molecular clouds, with an angular distance of about 0.4-0.5 degree toward the Crab Nebula, are located at the shell of a bubble discovered in the GALFA-HI (and HI4PI) images at the same velocity range. The dimension of the bubble is roughly 2.3$\times$2.6 degree and the expansion velocity is about 5 km/s. The kinetic energy referred from the shocked molecular clouds (roughly 3.5$\times$10$^{51}$ erg), together with the HI bubble, support the picture that the Crab Nebula belongs to a typical core-collapse supernova remnant. Nevertheless, due to the large uncertainty in the distance measurement, further observations are needed to verify the physical association between the shocked molecular clouds and the Crab Nebula.

At high metallicity, a majority of massive stars have at least one close stellar companion. The evolution of such binaries is subject to strong interaction processes, heavily impacting the characteristics of their life-ending supernova and compact remnants. For the low-metallicity environments of high-redshift galaxies constraints on the multiplicity properties of massive stars over the separation range leading to binary interaction are crucially missing. Here we show that the presence of massive stars in close binaries is ubiquitous, even at low metallicity. Using the Very Large Telescope, we obtained multi-epoch radial velocity measurements of a representative sample of 139 massive O-type stars across the Small Magellanic Cloud, which has a metal content of about one fifth of the solar value. We find that 45% of them show radial velocity variations which demonstrate that they are members of close binary systems, and predominantly have orbital periods shorter than one year. Correcting for observational biases indicates that at least 70[+11:-6]% of the O stars in our sample are in close binaries, and that at least 68[+7:-8]% of all O stars interact with a companion star during their lifetime. We found no evidence supporting a statistically significant trend of the multiplicity properties with metallicity. Our results indicate that multiplicity and binary interactions govern the evolution of massive stars and determine their cosmic feedback and explosive fates.

Stellar collisions in dense galactic nuclei might play an important role in fueling supermassive black holes (SMBHs) and shaping their environments. The gas released during these collisions can contribute to SMBH accretion, influencing phenomena such as active galactic nuclei and tidal disruption events of the remnants. We address the challenge of rapidly and accurately predicting the outcomes of stellar collisionsincluding remnant masses and unbound gasacross a broad parameter space of initial conditions. Existing smoothed-particle-hydrodynamic (SPH) simulation techniques, while detailed, are too resource-intensive for exploratory studies or real-time applications. We develop a machine learning framework trained on a dataset of $\sim 16,000$ SPH simulations of main-sequence star collisions. By extracting physically meaningful parameters (e.g., masses, radii, impact parameters, and virial ratios) and employing gradient-boosted regression trees with Huber loss, we create a model that balances accuracy and computational efficiency. The method includes logarithmic transforms to handle dynamic ranges and regularization to ensure physical plausibility. The model achieves predictions of collision outcomes (remnant masses, and unbound mass) with very low mean absolute errors respect to the typical mass scale. It operates in fractions of a second, enabling large-scale parameter studies and real-time applications. Parameter importance analysis reveals that the impact parameter and the relative velocity dominate outcomes, aligning with theoretical expectations. Our approach provides a scalable tool for studying stellar collisions in galactic nuclei. The rapid predictions facilitate investigations into gas supply for SMBH accretion and the cumulative effects of collisions over cosmic time, particularly relevant to address the growth of SMBHs.

The formation mechanism of Brown Dwarfs (BDs), whether akin to stars or ejected planetary-mass objects, remains debated. We present the first 3D radiation-MHD simulations of magnetized, turbulent, gravitationally unstable low-mass cores ($0.05-0.1\ \mathrm{M_{\odot}}$) collapsing into proto-BDs. Using the {\ttfamily RAMSES} code with adaptive mesh refinement, we model the full dynamical range ($10^{5}~-10^{22}\ \mathrm{cm^{-3}}$), including radiative transfer (flux limited diffusion) and non-ideal MHD (ambipolar diffusion). Our simulations self-consistently follow the isothermal collapse, first hydrostatic core formation, H$_{2}$ dissociation, and BD birth. The resulting BDs have initial radii $\approx 0.75\ \mathrm{R_{\odot}}$ and masses $\approx 0.8\ \mathrm{M_{Jup}}$, growing via accretion as we follow the early evolution of the object. Crucially, we find that BDs may form similarly to low-mass stars but with a prolonged first-core phase, supporting a star-like formation scenario.

We present Py2DJPAS, a Python-based tool to automate the analysis of spatially resolved galaxies in the \textbf{miniJPAS} survey, a 1~deg$^2$ precursor of the J-PAS survey, using the same filter system, telescope, and Pathfinder camera. Py2DJPAS streamlines the entire workflow: downloading scientific images and catalogs, performing PSF homogenization, masking, aperture definition, SED fitting, and estimating optical emission line equivalent widths via an artificial neural network. We validate Py2DJPAS on a sample of resolved miniJPAS galaxies, recovering magnitudes in all bands consistent with the catalog ($\sim 10$~\% precision using SExtractor). Local background estimation improves results for faint galaxies and apertures. PSF homogenization enables consistent multi-band photometry in inner apertures, allowing pseudo-spectra generation without artifacts. SED fitting across annular apertures yields residuals $<10$~\%, with no significant wavelength-dependent bias for regions with $S/N>5$. We demonstrate the IFU-like capability of J-PAS by analyzing the spatially resolved properties of galaxy 2470-10239 at $z = 0.078$, comparing them to MaNGA data within 1 half-light radius (HLR). We find excellent agreement in photometric vs. spectroscopic measurements and stellar mass surface density profiles. Our analysis extends to 4 HLR (S/N~$\sim$~5), showing that J-PAS can probe galaxy outskirts, enabling the study of evolutionary processes at large galactocentric distances.

Recent Pulsar Timing Arrays (PTAs) results provided strong evidence for a stochastic gravitational wave background (sGWB), consistent with a population of merging massive black holes (MBHs) at $z<1$. Meanwhile, JWST observations at $z>5$ suggest a higher number density of accreting MBHs than previously estimated. Together with constraints from local MBHs and high-$z$ quasars, these findings offer a unique opportunity to test MBH seeding and early growth models. We explore this using ${\tt L-Galaxies}\textit{BH}$, a new extension of the galaxy formation model ${\tt L-Galaxies}$, developed to explicitly model all stages of MBH evolution, including seeding, accretion, and binary dynamics. To take advantage of both the high resolution of the ${\tt MillenniumII}$ and the large volume of the ${\tt Millennium}$ simulations, we run ${\tt L-Galaxies}\textit{BH}$ on the former and use its outputs as initial conditions for the latter, via our $\textit{grafting}$ method. We find that reproducing the number density of high-$z$ active MBHs observed by JWST requires either a heavy seed formation rate significantly higher than that predicted by current models ($\gtrsim 0.01 Mpc^{-3}$ at $z \sim 10$), or widespread formation of light seeds undergoing multiple phases of super-Eddington accretion. Furthermore, matching the amplitude of the PTA sGWB signal requires nearly all galaxies with stellar masses $M_{*}> 10^9 M_\odot$ to host central MBHs by $z\sim0$. Given the extreme heavy seed densities required to satisfy both PTA and JWST constraints, our results favor a scenario in which MBHs originate from light seeds that grow rapidly and efficiently in the early universe. This work demonstrates the power of combining multi-messenger data with physical models to probe the origins and evolution of MBHs across cosmic time.