Surface Brightness Research Articles

Euclid: Early Release Observations of diffuse stellar structures and globular clusters as probes of the mass assembly of galaxies in the Dorado group

Deep surveys have helped to unveil the history of past and present galaxy mergers, and, in particular, uncovering their tidal debris and co-located globular clusters (GCs). Euclid's unique combination of capabilities (spatial resolution, depth, and wide sky coverage) will make it a groundbreaking tool for galactic archaeology in the Local Universe, bringing low-surface-brightness (LSB) science into the era of large-scale astronomical surveys. Euclid's Early Release Observations (ERO) demonstrate this potential with a field of view that includes several galaxies in the Dorado group. In this paper, we aim to derive from this image a mass assembly scenario for its main galaxies: NGC,1549, NGC,1553, and NGC,1546. We detected their internal and external diffuse structures, and identified candidate GCs. By analysing the colours and distributions of the diffuse structures and candidate GCs, we can place constraints on the galaxies' mass assembly and merger histories. The results demonstrate that feature morphology, surface brightness, colours, and GC density profiles are consistent with galaxies that have undergone different merger scenarios. We classify NGC,1549 as a pure elliptical galaxy that has undergone a major merger. NGC,1553 appears to have recently transitioned from a late-type galaxy to early type, after a series of radial minor to intermediate mergers. NGC,1546 is a rare specimen of galaxy with an undisturbed disk and a prominent diffuse stellar halo, which we infer has been fed by minor mergers and then disturbed by the tidal effect from NGC,1553. Finally, we identify limitations specific to the observing conditions of this ERO, in particular, stray light in the visible and persistence in the near-infrared bands. Once these issues are addressed and the extended emission from LSB objects is preserved by the data-processing pipeline, the Euclid Wide Survey will allow for studies of the Local Universe to be extended to statistical ensembles over a large part of the extragalactic sky.

Calcium in a supernova remnant as a fingerprint of a sub-Chandrasekhar-mass explosion

Abstract Type Ia supernovae play a fundamental role as cosmological probes of dark energy and produce more than half of the iron in our Galaxy. Despite their central importance, a comprehensive understanding of their progenitor systems and triggering mechanism is still a long-standing fundamental problem. Here we present high-resolution integral field spectroscopic observations of the young supernova remnant SNR 0509-67.5 in the Large Magellanic Cloud. We uncover a double-shell morphology of highly ionized calcium [Ca XV] and a single shell of sulphur [S XII], observed in the reverse shocked ejecta. Our analysis reveals that the outer calcium shell originates from the helium detonation at the base of the outer envelope, while the inner shell is associated with the carbon–oxygen core detonation. This morphological distribution of intermediate-mass elements agrees qualitatively with the predicted signature of the double detonation of a sub-Chandrasekhar-mass white dwarf from a hydrodynamical explosion simulation. Our observations reveal two distinct, spatially separated peaks in surface brightness of [Ca XV] from the supernova remnant phase, providing substantial evidence that sub-Chandrasekhar-mass explosions through the double-detonation mechanism could occur in nature. They also highlight the importance of remnant tomography in understanding explosion mechanisms from the remnant phase.

The TRGB−SBF Project. III. Refining the HST Surface Brightness Fluctuation Distance Scale Calibration with JWST

Abstract The TRGB−SBF Project team is developing an independent distance ladder using a geometrical calibration of the tip of the red giant branch (TRGB) method in elliptical galaxies that can, in turn, be used to set the surface brightness fluctuation (SBF) distance scale independent of Cepheid variables and Type Ia supernovae. The purpose of this project is to measure the local expansion rate of the Universe independently of the methods that are most at odds with the theoretically predicted value of the Hubble–Lemaître constant H 0, and therefore isolate the influence of potential systematic observational errors. In this paper, we use JWST TRGB distances calibrated using the megamaser galaxy NGC 4258 to determine a new Cepheid-independent SBF zero-point with the Hubble Space Telescope. This new calibration, along with improved optical color measurements from Pan-STARRS and DECam, gives an updated value of H 0 = 73.8 ± 0.7 (statistical) ±2.3 (systematic) km s−1 Mpc−1 that is virtually identical to the SBF Hubble–Lemaître constant measured by J. P. Blakeslee et al.

The ALMA-CRISTAL survey: Gas, dust, and stars in star-forming galaxies when the Universe was ∼1 Gyr old

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

Cosmic Rays Masquerading as Hot CGM Gas: An Inverse-Compton Origin for Diffuse X-ray Emission in the Circumgalactic Medium

Observations from ROSAT and eROSITA have argued that Milky Way (MW), Andromeda, and lower-mass galaxies exhibit extended soft X-ray ( 1keV) diffuse halos out to radii R≳100kpc in the circumgalactic medium (CGM). If interpreted as thermal emission from hot gas, the surprisingly shallow surface brightness profiles SX∝R−1 of this emission are difficult to explain, and contradict other observations. We show that such halos instead arise from inverse Compton (IC) scattering of CMB photons with GeV cosmic ray (CR) electrons. GeV electrons have long ( ∼,Gyr) lifetimes and escape the galaxy, forming a shallow extended radial profile out to R≳100kpc, where IC off the CMB dominates their losses and should produce soft, thermal-like X-ray spectra peaked at ∼1keV. The observed keV halo luminosities and brightness profiles agree well with those expected for CRs observed in the local interstellar medium (LISM) escaping the galaxy, with energetics consistent with known CRs from SNe and/or AGN, around galaxies with stellar masses M*≲2×1011M⊙. At higher masses observed X-ray luminosities are larger than predicted from IC and should be dominated by hot gas. In the MW+M31, the same models of escaping CRs reproduce {} γ-ray observations if we assume an LISM-like proton-to-electron ratio and CR-pressure-dominated halo. In all other halos, the associated non-thermal radio and γ-ray brightness is far below detectable limits. If we have indeed detected the expected IC X-ray halos, the observations provide qualitatively new and stringent constraints on the properties of the CGM and CR physics: the observed X-ray brightness {} traces the CR lepton energy density in the CGM (without any degenerate parameters). The implied agrees well with LISM values at radii R≲10kpc, while following the profile predicted by simple steady state models of escaping CRs at larger radii. The inferred CR pressure is a major part of the total pressure budget in the CGM of Milky Way-mass galaxies, suggesting that models of thermally dominated halos at Milky Way mass may need to be revised. The measurement of X-ray surface brightness and total luminosity allows one to further determine the effective CGM diffusivity/CR streaming speed at radii ∼10−1000kpc. We show these also agree with LISM values at small radii but the inferred diffusivity increases significantly at larger radii, consistent with independent CGM constraints from UV absorption at ∼100kpc.

Anisotropic Diffusion of e± in Pulsar Halos over Multiple Coherence of Magnetic Fields

Abstract The slow particle diffusion in pulsar halos, inferred from TeV gamma-ray surface brightness profiles (SBPs), is attributed to cross-field diffusion under the anisotropic diffusion model. This model assumes sub-Alfvénic interstellar turbulence in the medium surrounding the pulsar and a rough alignment of the line of sight of observers toward the pulsar with the local mean magnetic field direction in the halo. In this model, the expected morphology of a pulsar halo is highly dependent on the properties of the interstellar magnetic field. We investigate the anisotropic diffusion of electron–positron pairs across multiple coherence of magnetic fields in pulsar halos in this work. We focus particularly on their influence on the predicted gamma-ray SBP and the asymmetry of the halo’s morphology, as well as the observational expectations of the Large High Altitude Air Shower Observatory. Our results indicate that the requirement of a specific magnetic field geometry can be alleviated when accounting for a limited (and realistic) coherence length of the magnetic field in the model. Also, the halo’s morphology may appear less asymmetric, especially after being smoothed by the point-spread function of instruments. This largely relaxes the tension between the asymmetric morphology of halos predicted by the model and the lack of apparent asymmetric halos detected so far. Our findings demonstrate the important influence of the coherence length of the interstellar magnetic field on the distribution of particles around their accelerators, and the consequence for the measured source morphology.

ASKAP–EMU radio continuum detection of planetary nebula NGC 5189: the “Infinity” nebula

Abstract We report the radio continuum detection of well known Galactic Planetary Nebula (PN) NGC5189, observed at 943MHz during the Australian Square Kilometre Array Pathfinder (ASKAP) Evolutionary Map of the Universe (EMU) survey. Two detections of NGC5189 have been made during the survey, of better resolution than previous radio surveys. Both measurements of the integrated flux density are consistent with each other, at S943 MHz = 0.33 ± 0.03 Jy, and the spectral luminosity is L943 MHz = 8.89 × 1013 W m–2 Hz–1. Using available flux density measurements for radio-detections of NGC5189, we calculate a radio surface brightness at 1GHz and measure Σ1 GHz = 6.0 × 10–21 W m–2 Hz–1 sr–1, which is in the expected range for Galactic PNe. We measure an apparent size of 3.′4×2.′2 corresponding to physical diameters of 1.48 pc × 0.96 pc, and combine available radio observations of NGC5189 to estimate a spectral index of α = 0.12 ± 0.05. Hence, we agree with previous findings that NGC5189 is a thermal (free–free) emitting nebula. Additional measurements of the optical depth (τ = 0.00246) and electron density (N e = 138 cm–3) support our findings that NGC5189 is optically thin at 943 MHz. Furthermore, the radio contours from the ASKAP–EMU image have been overlaid onto a Hubble Space Telescope (HST) Wide Field Camera 3 image, demonstrating that the radio morphology closely traces the optical. Notably, the contour alignment for the innermost region highlights the two envelopes of gas previously reported to be low-ionisation structures, which is considered a defining feature of post common–envelope PNe that surround a central Wolf-Rayet star.

DAWN JWST Archive: Morphology from profile fitting of over 340,000 galaxies in major JWST fields. Morphology evolution with redshift and galaxy type

Understanding how galaxies assemble their structure and evolve morphologically over cosmic time is a central goal of galaxy evolution studies. In particular, the morphological evolution of quiescent and star-forming galaxies provides key insights into the mechanisms that regulate star formation and quenching. We present a new catalog of morphological measurements for more than 340,000 sources spanning $0 < z < 12$, derived from deep NIRCam imaging across four major extragalactic fields (CEERS, PRIMER–UDS, PRIMER–COSMOS, GOODS) compiled in the DAWN Archive (DJA). We performed two-dimensional surface brightness fitting for all galaxies in a uniform, flux-limited sample. Each galaxy was modeled with both a Sérsic profile and a two-component (bulge and disk) decomposition, yielding consistent structural parameters, including effective radius, Sérsic index (n_S), axis ratio, and bulge-to-total ratio (B/T). To demonstrate the scientific application of our morphology catalogs, we combined these measurements with DJA photometric redshifts, physical parameters and rest-frame colors, and investigated the relation between total, bulge, and disk sizes, n_S , star formation activity, and redshift. Bulge-dominated galaxies (high n_S and B/T) predominantly occupy the quiescent region of the UVJ diagram, while disk-dominated galaxies are mostly star-forming. A significant bimodality persists, with quiescent disks and compact, bulge-dominated star-forming galaxies observed out to z > 3. Quiescent galaxies also show significantly higher stellar mass surface densities, nearly an order of magnitude greater at z ∼ 4 than at z ∼ 1. Our results confirm a strong and evolving link between morphology and star formation activity and support a scenario in which bulge growth and quenching are closely connected. This work is a highly valuable addition to the DJA, adding a morphological dimension to this rich dataset and thus enabling a wider scientific application.

The vertical structure of the stellar disk in NGC 551

This paper aims to self-consistently determine the 3D density distribution of the stellar disk in NGC 551 and to utilize it to study the observational signatures of two-component stellar disks (thin and thick) in galaxies. Assuming that the baryonic disks are in hydrostatic equilibrium, we solved the Poisson-Boltzmann equation to estimate the 3D density distribution in the stellar disk of NGC 551. Unlike in previous studies, we used integral-field spectroscopic observations to estimate the stellar velocity dispersion. A 3D dynamical model of the stellar disk was built using these density solutions and the observed rotation curve. Using this model, we generated simulated surface brightness maps and compared them with observations to verify the consistency of our modeling. Furthermore, the dynamical model was inclined to $90^∘$ to produce an edge-on surface density map of the galaxy. We further investigated this map by fitting different 2D functions and plotting vertical cuts in a logarithmic scale to infer observational signatures of two-component disks in galaxies. We estimated the vertical stellar velocity dispersion in NGC 551 using an iterative method and obtained results consistent with the formalism employed in the Disk Mass Survey. Through dynamical modeling of the stellar disk in NGC 551, we produced moment maps, which reasonably matched the observations, indicating consistent modeling. We examined the simulated edge-on model by taking vertical cuts and decomposing them into multiple Gaussian components. We find that an artificial double Gaussian component arises due to the line-of-sight integration effect, even for a single-component disk. This indicates that decomposing vertical intensity cuts into multiple Gaussian components is an unreliable method for identifying multicomponent disks. Instead, an up-bending break, visible in the plot of the vertical cuts in the logarithmic scale for a two-component disk, serves as a more reliable indicator, which is absent in the case of a single-component disk. We performed 2D fitting on the edge-on surface density map using the product of a scaled modified Bessel function (for the radial profile) and a rm sech^2 function (for the vertical profile) to estimate the stellar disk’s structural parameters. We find that these traditional methods systematically underestimate the scale length and flattening ratio of the stellar disk. Therefore, we suggest using detailed modeling to accurately deduce the structural parameters of stellar disks in galaxies.

Testing the asteroseismic estimates of stellar radii with surface brightness--colour relations and Gaia DR3 parallaxes. III. Main-sequence stars

Expanding upon a recent investigation devoted to giant stars, we compare the radii derived from the asteroseismic scaling relations with those from surface brightness--colour relations (SBCRs) combined with the Gaia DR3 parallaxes for main-sequence (MS) stars. The atmospheric and asteroseismic parameters were sourced from the recently released KEYSTONE catalogue and matched to Gaia DR3 and TESS Input Catalog v8.2 to obtain precise parallaxes, V- and K_S-band magnitudes, and colour excesses, E(B- V). We computed SBCR-based radii using two different SBCRs, and estimated their relative differences with respect to radius estimates from asteroseismic grid-based methods. We find a good agreement between SBCR and asteroseismic radii, with mean relative differences in radii (E_g) in the range 2% to 3% and a standard deviation of about 3%, consistent with the expected variability of SBCRs. We find no dependence on parallax, and a mild dependence on Fe/H for one of the SBCRs tested. The relative difference in the estimated radii decreases as the mass increases, leading to a negative correlation between E_g and the estimated stellar mass, with a slope varying from -0.051±0.016 to -0.039±0.014 per solar mass, depending on the chosen SBCR. This change in slope led to a roughly 1.5% larger discrepancy in the E_g estimates for stars with masses below 1.0 M_ This larger discrepancy at the low-mass end supports conclusions drawn from giant star studies. This result is independently corroborated by the LEGACY sample, which uses Kepler photometry processed with the same pipeline as KEYSTONE. For the LEGACY sample we measure a mean relative offset in E_g of -1.4% with a standard deviation of 2.3%, and a dependence of E_g on mass with a slope of -0.052±0.011 per mass unit, both fully consistent with the KEYSTONE analysis. The analysis reveals a strong agreement between SBCR-based and asteroseismic radii for MS stars, but the apparent mass dependence still requires closer examination. This result is reassuring as it demonstrates the great accuracy and reliability of the radius estimates obtained through SBCRs, which, moreover, offer the significant advantage of being applicable to a large sample of stars with substantially lower time and costs compared to what is required by asteroseismology.

LIGHTS. The extended point spread functions of the LIGHTS survey at the LBT

With the arrival of the next generation of ultra-deep optical imaging surveys reaching μV ∼ 30 mag/arcsec 2 (3 σ; 10′′ × 10′′), the removal of scattered light due to the point spread function (PSF) effect remains a critical step for the scientific exploitation of the low surface brightness information contained in these data. Because virtually all pixels in the ground-based images are affected by an unwanted screen of light with a brightness greater than μV ∼ 29 mag/arcsec 2, the characterization of the extended PSF (R > 5 arcmin) is mandatory. We describe the procedure used to construct the extended PSFs of the LIGHTS survey in the g- and r-band images taken with the Large Binocular Cameras (LBCs) of the Large Binocular Telescope (LBT). We produce PSFs with a radial extension of 6.5 arcmins. These are later extended to 30 arcmins following an empirically motivated power-law extrapolation of their behaviour in their outermost regions. As an example of the application of our methodology, we subtract the scattered light around the galaxy NGC3198. The result of this subtraction clearly shows the outermost parts of the galaxy’s disc, which have been obscured by the influence of nearby bright stars. We make all the PSF (compact and extended) models publicly available.

A New Shock in the Premerging Cluster Pair 1E2215-2216

Abstract The galaxy cluster pair 1E2216.0-0401 and 1E2215.7-0404 represents a major cluster merger in its early stages, a phase that has been scarcely explored in previous studies. Within this system, both axial and equatorial merger shocks have been identified. Recent XMM-Newton observations of the southern region of the cluster pair have increased the total exposure time to approximately 300 ks, enhancing the sensitivity to detect faint shock features in the cluster outskirts. Through a combined analysis of XMM-Newton and Chandra data, including both imaging and spectral techniques, a new shock front has been identified at approximately 2 . ′ 3 south of the X-ray brightness peak of 1E2215. This shock front exhibits a surface brightness ratio of 1.33 ± 0.07 and a temperature ratio of 1.2 2 − 0.14 + 0.13 in XMM-Newton, consistent with Chandra results. The Mach number, independently calculated from both the temperature and surface brightness discontinuities, yields consistent values of M ≈ 1.2 . The age, velocity, and spatial distribution of this shock suggest that it shares a common physical origin with the previously identified equatorial shock.

Spatiotemporally tunable dark/bright and weak/strong mode coupling in all-dielectric DBR-metasurface-DBR structures

We report spatiotemporally tunable mode coupling between Fabry-Pérot (F-P) resonances and dark or bright modes in the weak- or strong-coupling regime in an all-dielectric coupled system, which consists of an F-P microcavity formed by two distributed Bragg reflectors (DBR) and a metasurface made of periodic nanocavities. Simulation results show that F-P resonances can be tuned to be coupled to dark waveguide modes or a bright electric dipole Mie surface lattice resonance, depending on the microcavity height, and that the coupling strength can be manipulated between the weak- and strong-coupling regimes by varying the photon lifetime, or equivalently the quality factors (Q-factors) of F-P resonances, which can be realized by changing the number of DBR layers. We also show that the slow-light effect associated with the electromagnetically induced reflection-like window in the weak-coupling regime can also be regulated through the Q-factor. With all these findings, our study provides an alternative for manipulating light-matter interactions in coupled micro-/nano-cavities that are promising for various applications.

Four ages of rotating stars in the rotation--activity relationship and gyrochronology

Gyrochronology and the rotation--activity relationship are standard techniques used to determine the evolution phase and dynamo process of low-mass stars based on their slowing down. Gyrochronology identifies two tracks in color--period diagrams: the convective (C) phase (younger, faster rotating) and the interface (I) phase (older, slower rotating). These phases are separated by a transition, or ``gap'' (g phase), and there is no precise estimate of its duration. The rotation--activity relation also identifies two stages: the saturated regime (faster, with higher activity) and unsaturated regime (slower, with declining activity). The mismatch in the definition of the evolutionary phases has so far raised many issues in physics and mathematics and has hampered the understanding of how the internal dynamo processes affect the observable properties. To address this problem, we seek a unified scheme that shows a one-to-one mapping from gyrochronology to the rotation--activity relationship. We combined LAMOST spectra, the Kepler mission, and two open clusters to obtain the chromospheric activity R'_ HK of 6846 stars and their rotation periods. We used R'_ HK and the rotation period to investigate the rotation--activity relationship. Instead of the traditional two-interval model, we applied a three-interval model to fit the rotation--activity relationship in the range of the Rossby number Ro$<0.7$. We also used the X-ray data to verify our new model. We find that the rotation--activity relationship is best fit by three intervals in the rang of Ro$<0.7$. We associate those intervals with the convective, gap, and interface phases of gyrochronology. The mean Ro of the C-to-g and g-to-I transition is ≈ 0.022 and ≈ 0.15, respectively. The g-to-I transition is on the edge of the intermediate period gap, indicating that the transition of surface brightness from being spot dominated to facula dominated can be associated with the transition from the gap to the I sequence. Furthermore, based on previous studies, we suggest an additional epoch at late times of the I phase (Ro $>0.7$; weakened magnetic breaking phase) from the perspective of activity. We further used the three-interval models to fit the period--activity relationship in temperature bins and determine the duration of the transition phase as a function of effective temperature. By comparing the critical temperature and period of the g-to-I transition with the slowly rotating sequence of ten young open clusters whose ages range from 1 Myr to 2.5 Gyr, we conclude that our new model finds the pure I sequence without fast rotating outliers, which defines the zero-age I sequence (ZAIS). We propose that there is an ambiguous consensus on when the I sequence begins. This ambiguity is from the visually convergent sequence of the color--period diagrams in open clusters. This visually convergent sequence is younger than the ZAIS and is actually the pre-I sequence that can be associated with the stall of the spin-down. Our results unify the rotation--activity relationship and gyrochronology for the stellar evolution of low-mass stars, which we denote as the ``CgIW" scenario.

Are compact groups of galaxies special?

It is often believed that isolated compact groups (CGs) of galaxies are special systems, but only a few studies have compared CGs to regular groups. We study the global properties and internal correlations of a volume- and luminosity-complete subsample of 78 groups of four members ( s) within the HMCG Hickson-like sample of compact groups. We compared these CGs to those of a similarly built subsample (including the three-magnitude range of s ) of the Lim regular groups. The latter were split into three control samples: one with the four brightest members ( s), one with the four closest members to the brightest group galaxy (BGG; s), and one with exactly four members ( s). The vast majority of the s are located within regular groups, and a large preponderance of the BGGs of these s are the same as those of their host groups. The s are smaller than the groups of all other samples and more luminous than s. Both results are a consequence of their selection as high surface brightness systems. However, the s (especially those split among several regular groups) have luminosities similar to s. The s also have higher velocity dispersions, probably because of a too-permissive redshift accordance criterion. The BGGs of the s are not any more dominant in luminosity than those of s, but they are significantly more offset relative to the group size because the Lim groups are built around their BGGs. In summary, the compact groups have similar properties to the regular groups of four galaxies and to the cores of regular groups once the selection criteria of CGs are considered. A large fraction of the CGs are the cores of regular groups, which are isolated on the sky by construction but rarely isolated in real space (from simulations), indicating that they are often plagued by chance alignments of host group galaxies along the line of sight.

Radio-loud AGN morphology and host-galaxy properties in the LOFAR Two-Metre Sky Survey Data Release 2

Abstract Radio-loud active galaxies (RLAGN) can exhibit various morphologies. The Fanaroff-Riley (FR) classifications, which are defined by the locations of peaks in surface brightness, have been applied to many catalogues of RLAGN. The FR classifications were initially found to correlate with radio luminosity. However, recent surveys have demonstrated that radio luminosity alone does not reliably predict radio morphology. We have devised a new-semi automated method involving ridgeline characterisations to compile the largest known classified catalogue of RLAGN to date with data from the second data release of the LOFAR Two-Metre Sky Survey (LoTSS DR2). We reassess the FR divide and its cause by examining the physical and host galaxy properties of 3590 FRIIs and 2354 FRIs (at $z$ ≤ 0.8). We find that RLAGN near the FR divide with 1025 ≤ L144 ≤ 1026 WHz−1 are more likely to show FRI over FRII morphology if they occupy more massive host galaxies. We find no correlation, when considering selection effects, between the FR break luminosity and stellar mass or host-galaxy rest-frame absolute magnitude. Overall, we find the cause of different radio morphologies in this sample to be complex. Considering sources near the FR divide with 1025 ≤ L144 ≤ 1026 WHz−1, we find evidence to support inner environment having a role in determining jet disruption. We make available a public catalogue of morphologies for our sample, which will be of use for future investigations of RLAGN and their impact on their surroundings.

Detecting low-mass haloes with strong gravitational lensing. II: Constraints on the density profiles of two detected subhaloes

Strong gravitational lensing can detect the presence of low-mass haloes and subhaloes through their effect on the surface brightness of lensed arcs. We carry out an extended analysis of the density profiles and mass distributions of two detected subhaloes, with the intention of determining whether their properties are consistent with the predictions of the cold dark matter (CDM) model. We analysed two gravitational lensing systems in which the presence of a low-mass subhalo has previously been reported: SDSSJ0946+1006 and JVASB1938+66. We modelled these detections by assuming four different models for their density profiles and compared our results with predictions from the TNG50 simulation. We find that the detected subhaloes are well modelled by steep inner density slopes, close to or steeper than isothermal. The Navarro-Frenk-White (NFW) profile thus needs extremely high concentrations to reproduce the observed properties, which are outliers of the CDM predictions. We also find a characteristic radius within which the best-fitting density profiles predict the same enclosed mass. We conclude that the lens modelling can constrain this quantity more robustly than the inner slope. We find that the diversity of subhalo profiles in TNG50, consistent with tidally stripping and baryonic effects, is able to match the observed steep inner slopes, somewhat alleviating the tension reported by previous works even if the detections are not well fitted by the typical subhalo. However, while we find simulated analogues of the detection in B1938+666, the stellar content required by simulations to explain the central density of the detection in J0946+1006 is in tension with the upper limit in luminosity estimated from the observations. New detections will increase our statistical sample and help us reveal more about the density profiles of these objects and the dark matter content of the Universe.

Finding Massive Double-exponential Disk Galaxies with Extended Low Surface Brightness Stellar Disk: An IllustrisTNG Exploration

Abstract We study massive disk galaxies (stellar mass > = 1011 M ⊙) at z = 0 from IllustrisTNG simulation to detect galaxies that contain two exponential stellar disks—a central high surface brightness (HSB) disk surrounded by an extended low surface brightness (LSB) envelope. This is motivated by the observation of several giant LSB galaxies (Malin 1, UGC 1378, UGC 1382 etc), reported in the literature, showing such complex morphology. Studying such systems can help us to understand the mass assembly process and growth of stellar disks in massive galaxies, and thus can shed light on massive galaxy formation and evolution scenarios. We use the high-resolution IllustrisTNG50 data and perform Sérsic plus exponential profile modeling on the idealized, synthetic Sloan Digital Sky Survey g- and r-band images of the massive disk galaxies using GALFIT. We identify seven disk galaxies (12% of the parent sample of disk galaxies) that are best represented by a central Sérsic plus a central HSB disk surrounded by an extended LSB disk. The radial scale lengths of the LSB disk lie in the range of ∼9.7–31.7 kpc, in agreement with that found in the literature. We study the star formation properties of these simulated double-disk galaxies to understand the distribution of these from blue star-forming to red-quenched region. Some of these double-disk galaxies display a characteristic minima in their (g − r) color radial profiles. The double-disk galaxies are found to lie within ∼1.5σ region of the Baryonic Tully–Fisher relation from observation.

The Polarisation Sky Survey of the Universe’s Magnetism (POSSUM): Science Goals and Survey Description

Abstract The Australian SKA Pathfinder (ASKAP) offers powerful new capabilities for studying the polarised and magnetised Universe at radio wavelengths. In this paper, we introduce the Polarisation Sky Survey of the Universe’s Magnetism (POSSUM), a groundbreaking survey with three primary objectives: (1) to create a comprehensive Faraday rotation measure (RM) grid of up to one million compact extragalactic sources across the southern ∼ 50 per cent of the sky (20,630 deg2); (2) to map the intrinsic polarisation and RM properties of a wide range of discrete extragalactic and Galactic objects over the same area; and (3) to contribute interferometric data with excellent surface brightness sensitivity, which can be combined with single-dish data to study the diffuse Galactic interstellar medium. Observations for the full POSSUM survey commenced in May 2023 and are expected to conclude by mid-2028. POSSUM will achieve an RM grid density of around 30–50 RMs per square degree with a median measurement uncertainty of ∼1 rad m−2. The survey operates primarily over a frequency range of 800–1088 MHz, with an angular resolution of 20″ and a typical RMS sensitivity in Stokes Q or U of 18 μJy beam−1. Additionally, the survey will be supplemented by similar observations covering 1296–1440 MHz over 38 per cent of the sky. POSSUM will enable the discovery and detailed investigation of magnetized phenomena in a wide range of cosmic environments, including the intergalactic medium and cosmic web, galaxy clusters and groups, active galactic nuclei and radio galaxies, the Magellanic System and other nearby galaxies, galaxy halos and the circumgalactic medium, and the magnetic structure of the Milky Way across a very wide range of scales, as well as the interplay between these components. This paper reviews the current science case developed by the POSSUM Collaboration and provides an overview of POSSUM’s observations, data processing, outputs, and its complementarity with other radio and multi-wavelength surveys, including future work with the SKA.

Kohler-Polarization Sensor for Glint Removal in Water-Leaving Radiance Measurement

High-precision hyperspectral remote sensing reflectance measurement of water bodies serves as the fundamental technical basis for accurately retrieving spatiotemporal distribution characteristics of water quality parameters, providing critical data support for dynamic monitoring of aquatic ecosystems and pollution source tracing. To address the critical issue of water surface glint interference significantly affecting measurement accuracy in aquatic remote sensing, this study innovatively developed a novel sensor system based on multi-field-of-view Kohler-polarization technology. The system incorporates three Kohler illumination lenses with exceptional surface uniformity exceeding 98.2%, effectively eliminating measurement errors caused by water surface brightness inhomogeneity. By integrating three core technologies—multi-field polarization measurement, skylight blocking, and high-precision radiometric calibration—into a single spectral measurement unit, the system achieves radiation measurement accuracy better than 3%, overcoming the limitations of traditional single-method glint suppression approaches. A glint removal efficiency (GRE) calculation model was established based on a skylight-blocked approach (SBA) and dual-band power function fitting to systematically evaluate glint suppression performance. Experimental results show that the system achieves GRE values of 93.1%, 84.9%, and 78.1% at ±3°, ±7°, and ±12° field-of-view angles, respectively, demonstrating that the ±3° configuration provides a 9.2% performance improvement over the ±7° configuration. Comparative analysis with dual-band power-law fitting reveals a GRE difference of 2.1% (93.1% vs. 95.2%) at ±3° field-of-view, while maintaining excellent consistency (ΔGRE < 3.2%) and goodness-of-fit (R2 > 0.96) across all configurations. Shipborne experiments verified the system’s advantages in glint suppression (9.2%~15% improvement) and data reliability. This research provides crucial technical support for developing an integrated water remote sensing reflectance monitoring system combining in situ measurements, UAV platforms, and satellite observations, significantly enhancing the accuracy and reliability of ocean color remote sensing data.