New time series photometry of the short period (P<0.2 d) binary stars ZTF J032906.36+070408.3 (ZTF 0329) and ATO J090.7238+00.5996 (ATL 0602) is presented. The primary (hotter) stars in both systems are white dwarfs, while the cooler stars are M dwarfs. Archival photometry and new and archival spectra are used to derive the temperatures of the components in the two binaries. Both are single-lined binaries. Velocity curves are fitted to radial velocity measurements of the red dwarfs and used to place lower limits on the masses of the white dwarfs. New and archival time series photometry show evolution in the shapes of the light curves of both stars. Spectra of ZTF 0329 show an excess of radiation in the R_C band which is ascribed to electron cyclotron radiation, suggesting that the star is a low accretion rate polar. Satisfactory model fits to the multi-filter light curves of ATL 0602 require the presence of cool spots on the red component of the binary. The latter star exhibits a variety of velocities associated with Balmer and Ca II emission lines within individual spectra.
I consider recent observations of the Little Dots (LDs) observed in high–redshift (z∼ 7) galaxies. I have suggested that the central black holes in these objects are probably fed mass at very super–Eddington (factors ∼ 50) rates. In physical terms, this idea makes them supermassive analogues of the (stellar–mass) ultraluminous X–ray sources (ULXs), whose hard X–ray emission is strongly anisotropic (`beamed'). In this paper I argue that the recent discovery of extended rest–frame hard X–ray ionization cones from an LD gives strong quantitative support to this view, as its geometry is what one would expect from a ULX–like object viewed not along one of its X–ray beams, but instead `from the side', very similar to the extreme Galactic system SS433. This in turn agrees in quantitative terms with recent suggestions that LDs resemble supermassive versions of SS433–like systems. I emphasize that in contrast, the rest–frame soft X–ray emission from LDs must be roughly isotropic, and presumably power the torus emission observed from these galaxies.
Abstract High-redshift radio galaxies (HzRGs) are among the earliest and most massive galaxies whose powerful radio emission allows us to probe the large-scale structure, galaxy evolution, and the epoch of reionisation. We present a new sample of HzRG candidates constructed using the 1.28 GHz data from the MeerKAT Galaxy Cluster Legacy Survey (MGCLS) Data Release 1 (DR1). We select a subsample of MGCLS fields with good dynamic range, astrometric accuracy, and full optical and near-infrared coverage from the Dark Energy Spectroscopic Instrument Legacy Imaging Surveys (LS) Data Release 10.1 and the All-sky Wide Infrared Survey Explorer (AllWISE), respectively. We use the likelihood ratio method to cross-match the unresolved radio sources against LS and AllWISE. For radio sources lacking optical and near-infrared counterparts, we apply an ultra-steep spectrum (USS) selection criterion of α < −1.0, and a 5σ signal-to-noise ratio cut, resulting in a total of 1,819 HzRG candidates, spread over a non-contiguous sky area of ~43 deg2, with 824 USS sources and 995 faint sources (0.036 mJy < S1.28 GHz < 0.278 mJy) lacking sufficient spectral data as potential candidates. We achieve complete spectral coverage above ~0.28 mJy and reliable in-band spectral index measurements down to 44 μJy, making this the faintest HzRG candidate search at GHz frequencies to date. Confirming the nature and redshifts of these candidates will require dedicated spectroscopic and deep near-infrared follow-up observations.
We present MeerKAT HI observations of galaxies in the nearby Virgo III filament. At a median distance of ∼30 Mpc, the filament extends over ≈16 Mpc across ∼56 deg^2. Our survey comprises 15 targeted MeerKAT pointings centred on HI deficient galaxies. Multi-resolution HI imaging at 8-90 arcsec with an rms of ∼0.3 mJy beam^-1 reaches column densities of ∼4×10^20 to ∼4×10^18 atoms cm^-2. This probes HI in galaxy discs at ∼1.2 kpc resolution and their outskirts at ∼13.5 kpc. We detect HI emission from 80 sources within the 500-3000 km/s range; most are optically detected galaxies, while 10 per cent lack confirmed counterparts. We also identify three HI clouds without optical counterparts near an interacting system, possibly displaced during the interaction. Galaxies in the filament lie below the field HI gas-fraction scaling relations at fixed stellar mass. Crucially, ∼40 per cent of galaxies not selected for HI deficiency fall more than 1σ below these relations, with an even greater fraction lying under the mean relation itself, indicating that the low HI gas fractions are widespread in the filament rather than confined to the pre-selected deficient population. Quantifying HI morphologies using an asymmetry parameter, we find a wide range of disturbances without a clear trend with projected distance to the filament spine or local density, suggesting a combination of local interactions and the filament itself. This paper presents the survey description, catalogue, and HI atlas enabling investigations of gas removal mechanisms in Virgo III galaxies.
Abstract Young massive stellar clusters have been recognized as a significant population of cosmic ray accelerators and gamma-ray sources. We report the detection of extended gamma-ray emission toward the young massive star cluster Berkeley 87 using 18 years of Fermi-LAT data. The emission has an angular extension of 0.36 degree and a photon index of 2.68. To investigate the ambient gas target, we combine CO, EBHIS and Planck data. The total gas mass within the region is ~21.61 × 102M⊙, with an average proton density of $\sim 368\ \rm cm^{-3}$. The hadronic scenario is favored given the dense gas and the cluster’s strong stellar winds. The kinetic energy injection rate from stellar winds in Berkeley 87 exceeds $1.0 \times 10^{36}\ \rm erg \ s^{-1}$. Considering a CR acceleration efficiency 10−2.0 to 10−2.5, the cluster can supply sufficient energy to power the observed gamma-ray emission. A nearby pulsar, PSR J2021+3651, associated with the Dragonfly pulsar wind nebula and the 4HWC source 4HWC J2021+3650, lies in the same field of view. We also discuss the maximum accelerated proton energy and electron energy density of this pulsar.
A detailed study using abundance tomography of SN 2012dn, a peculiar Type Ia supernova, is presented. Despite exhibiting a normal peak luminosity, it retains early-phase super-Chandrasekhar (03fg-like) characteristics: weak Fe III, narrow intermediate-mass element (IME), persistent carbon, and the absence of high-velocity Ca II features. Its nebular spectrum is unusually faint due to grey dimming beginning ∼60 days after maximum and shows [O I] emission, rare in SNe Ia. While a Chandrasekhar-mass density profile reproduces the photospheric phase, it fails at late times. The [O I] emission requires additional low-velocity mass, implying a total ejecta mass of 1.66 M_⊙, including 0.33 M_⊙ of oxygen (with 0.1 M_⊙ in the core). The ^56Ni mass is estimated to be 0.45–0.49 M_⊙, a range set by uncertainties in the grey-extinction correction applied at the nebular phase, and is insufficient on its own to account for the peak luminosity. Stable iron is confined to intermediate layers and absent from both the core and outer ejecta, the latter indicating sub-solar progenitor metallicity. Silicon and sulfur span the full ejecta, while carbon extends down to v ∼ 6000 km,s^-1. These properties favour a double-degenerate CO–CO white dwarf merger scenario. The remaining luminosity deficit may be explained by additional energy input from a weak interaction with a low-mass, carbon-rich circumstellar shell.
The extragalactic background light (EBL), ranging from the infrared to the ultraviolet bands, is the second most intense photon field in the universe, surpassed only by the cosmic microwave background (CMB). It is primarily generated by starlight in galaxies, either directly or through absorption by dust and re-emission at longer wavelengths. Very high energy (VHE, E > 100GeV) photons can be absorbed via γγ interactions with the EBL during their propagation across cosmological distances, providing an indirect method to probe the EBL by studying its impact on the energy spectra of distant VHE sources. This paper examines the robustness of EBL constraints derived from gamma-ray data, critically assessing the assumptions made in previous studies about the intrinsic source spectra, the uncertainties of the observations and the validity of the analysis tools. We find that earlier studies likely underestimated the uncertainties in the EBL intensity constraints, underscoring the need to account for systematic uncertainties comprehensively. By employing a Monte Carlo (MC) simulation and a plausible model for unknown systematic errors, we compute more realistic uncertainties. Additionally, we discuss possible alternatives to set EBL constraints, relaxing the assumptions on the intrinsic spectra of gamma-ray sources, with the goal of achieving more robust constraints.
ABSTRACT We investigate magnetospheric accretion in disc-fed X-ray pulsars assuming that the neutron star spin axis is not perpendicular to the disc plane. We focus on X-ray pulsars, where a geometrically thin disc is truncated far from the stellar surface; the channelled part of the accretion flow is expected to be guided by the large-scale dipolar magnetic field after coupling to it near the disc–magnetosphere boundary. Using numerical simulations of plasma motion from the inner disc edge to the neutron star surface, we show that a finite inclination between the disc normal and the stellar spin axis leads to periodic modulation of the mass accretion rate onto the magnetic poles even for a steady mass supply through the disc. This purely geometrical effect arises because stellar rotation changes the orientation of the magnetosphere relative to the disc, producing phase-dependent mass loading of magnetic field lines. The amplitude and shape of the modulation are determined by the system geometry and by the ratio of the stellar spin period to the flow time through the magnetosphere. The resulting variability affects the structure and luminosity of emitting regions near the neutron star surface and leads to asymmetric X-ray pulse profiles. Even without intrinsic asymmetries of the emission regions, this mechanism breaks the time-reversal symmetry expected for stationary accretion and naturally contributes to the observed asymmetry of pulse profiles and phase-resolved spectral features. The effect may also be relevant for ULX pulsars, where intrinsic accretion rate modulation can help preserve strong pulsations in the presence of geometric beaming.
Hints of planet formation have been independently reported within the gap of the disc around 2MASS J16120668-301027 from millimetre continuum, infrared, and H-alpha observations. In this work, we present new evidence for ongoing planet formation based on Atacama Large Millimeter/submillimeter Array (ALMA) Band 7 observations, detecting 0.87 mm dust continuum emission together with 12CO (J=3-2) and 13CO (J=3-2) line emission. Visibility modelling of the continuum data reveals an inner disc and two dust rings peaking at 23 and 75 au. The continuum morphology is better reproduced by an eccentric disc model (e approximately 0.1) than by an axisymmetric disc. We further investigate the gas kinematics through modelling of the 12CO channel maps. The residual line-width map shows a localised increase in velocity dispersion at the position of a previously reported circumplanetary disc candidate (deprojected radius approximately 32 au, position angle approximately 170 degrees) and along its orbit. This signal is spatially coincident with kink-like features and a transition from sub-Keplerian to super-Keplerian velocities. In addition, the velocity residual map exhibits an arc-like structure extending outward from the planet candidate, while the gas kinematics, despite substantial uncertainties, is consistent with inflow towards the candidate's orbital radius. The observed increase in velocity dispersion agrees with predictions from planet-disc interaction simulations, which produce enhanced turbulence both at the planet location and along its orbital path. Taken together, the continuum morphology and gas kinematic signatures provide compelling new evidence for ongoing planet formation within the disc gap.
Abstract It is still debating on whether the disc is magnetically arrested in M87. We assume that a weak external magnetic field is dragged inwards by the accretion disc, which is substantially enhanced to drive strong jets near the black hole horizon via Blandford-Znajek mechanism. The jet power of M87 has been well constrained with the observational data, while the accretion rate in the inner region of the accretion flow in M87 is estimated by fitting the multi-waveband continuum spectrum and the data of the Faraday rotation measurement, with which the surface density of the disc is derived. Our calculations show that, in order to produce the observed jet power $P_{\rm jet}=3.2\times 10^{43}~\rm erg~s^{-1}$, an external field with several hundred $\mu \rm G$ at the outer edge of the disc is required to be amplified in the disc to hundreds G at the BH horizon, and the accretion flow in M87 must be magnetically arrested. A standard and normal evolution (SANE) disc is allowed in M87, only if the jet power is significantly lower than $\sim 1.75 \times 10^{43} \rm erg~ s^{-1}$,
Abstract While long-term radial velocity (RV) monitoring has successfully mapped blue straggler star (BSS) multiplicity in nearby, unreddened open clusters, such spectroscopic surveys are observationally prohibitive for distant (d > 2 kpc) and moderately reddened Galactic clusters. To bypass this limitation, we present a general statistical framework that combines an empirical colour–magnitude diagram (CMD) displacement parameter (ηbinary) with Gaia astrometric noise (renormalised unit-weight error, RUWE) to diagnose BSS multiplicity on a population level. We apply this methodology to the intermediate-age open cluster Haffner 10 (d ≃ 3.5 kpc, AV ≃ 1.2 mag) as a representative test-bed. Out of 52 identified BSS candidates, the population is strongly redward-dominated (47 stars, fred ≃ 0.90). After correcting for differential reddening, we find a non-negligible residual main-sequence colour dispersion (σΔC = 0.105 mag), showing that individual CMD positions are insufficient to identify formation channels. However, a Spearman rank test reveals a positive correlation between the continuous CMD displacement ηbinary and RUWE (ρS = 0.35, p = 0.011), indicating that redward-displaced BSS candidates tend to show enhanced astrometric residuals. We compare our results with a literature sample of well-studied open clusters (M67, NGC 188, Melotte 66, and NGC 7789) to discuss how observational limitations and dynamical states shape the observed BSS configurations. Our approach offers a highly cost-effective template for characterizing BSS origins in distant open clusters where spectroscopy is currently unavailable.
Abstract Self-interacting dark matter (SIDM) influences halo structure through collisional heat transport and offers potential solutions for a range of small-scale puzzles in structure formation. SIDM creates thermalized cores in low-mass haloes, which may account for the observed cored dwarf galaxies. In the meantime, during the late-time gravothermal core collapse, SIDM can produce dense low-mass DM haloes and substructures that have been detected through perturbations to cold stellar streams and strong gravitational lenses. In this work, we present a new Monte-Carlo SIDM implementation in the moving-mesh code arepo-2, designed for efficiency, scalability, and extensibility. The central feature of the implementation is a dedicated DM-only neighbour-search tree that decouples the scattering solver from gravity. This preserves compatibility with the hierarchical time integration used by arepo-2 while leaving the optimized gravity solver unconstrained. A pairwise communication scheme between MPI tasks allows tracking multiple scattering events in a single timestep while conserving momentum and energy and maintaining parallel consistency by construction. This is complemented by a per-pair timestep criterion that significantly reduces unnecessary timestep restrictions. The implementation natively supports velocity-dependent cross-sections and inelastic interactions, while a compact interface is designed for additional SIDM physics to be implemented without knowledge of the parallelization layer. We validate the implementation for isotropic, elastic scattering using a suite of idealized and cosmological tests. We assess performance and scalability in isolated core-collapse simulations and in cosmological boxes, both DM-only and with baryons. Except during the late stages of gravothermal collapse, SIDM simulations incur only modest overhead relative to the corresponding CDM runs and are substantially faster than the previous SIDM implementation in arepo-1.
ABSTRACT We detect the kinetic Sunyaev–Zeldovich imprint of peculiar motions of galaxy groups and clusters, using the photometric Dark Energy Spectroscopic Instrument Legacy Surveys together with cosmic microwave background (CMB) maps from the Atacama Cosmology Telescope (ACT). We develop a comprehensive forward model based on the AbacusSummit cosmological simulations: Mock galaxy group catalogues and synthetic kinetic Sunyaev–Zeldovich (kSZ) maps are generated, together with a reconstructed peculiar velocity field that allows for photo-z errors, redshift-space distortions, and survey masks. We investigate possible contamination from the cosmic infrared background (CIB), finding that CIB effects are subdominant to the kSZ signal in the relevant ACT frequency channel. We then predict the kSZ signal expected when stacking CMB temperature maps around groups, taking account of their estimated radial velocities. Comparing the model with observations, we are able to constrain the total baryon fraction within haloes, as well as their internal gas profiles. We find evidence for mass dependence of the halo baryon fraction within the virial radius. The gas fraction in massive groups is consistent with the universal baryon fraction, but low-mass groups ($10^{12.5} \lesssim M\, /\, h^{-1}\, \mathrm{M}_\odot \lesssim 10^{14}$) are depleted to $0.38 \pm 0.11$ times the universal baryon fraction. We find this low virial baryon fraction to be consistent with an extended gas profile, for which the total baryon content reaches the universal value well beyond the virial radius. This conclusion is consistent with previous analyses using X-ray, kSZ, and weak lensing, and plausibly reflects energetic feedback processes from the galaxies in these haloes.
The properties of stellar bars play a crucial role in determining the bar-driven secular evolution in disc galaxies. However, a systematic observational study of the evolution of several bar properties (such as strength and length) across cosmic time is largely missing. In this paper, using a sample of 625 barred galaxies, taken from SDSS, HST COSMOS, and JWST CEERS surveys, we systematically investigate the evolution of bar properties over redshifts (0.02 ≲ z < 3) by making a novel usage of dark gap (preferential light deficit along the bar minor axis) properties as a proxy for bar properties. We show that the dark gap strength (Δμ_ max) exhibits a weak evolution, increasing from higher redshifts (z ∼ 2.5) and slightly declining towards lower redshifts (z < 0.05). Conversely, the extent of dark gaps (R_ DG, R_ dark; normalised by bar length) decreases moderately from z ≥ 1.4 and remains constant thereafter. Our results suggest that bar formation and the initial rapid growth phase occur before z ∼ 3, followed by mild growth towards lower redshifts. We also find R_ dark to be a better proxy (as compared to R_ DG) for estimating bar length, supporting earlier theoretical studies. Furthermore, the Δμ_ max shows a weak but statistically significant correlation with bar-to-total light ratio (Bar/T) and bar ellipticity (ε_ bar). Studies of the redshift evolution of bar properties over such an extensive redshift range as done here are instrumental in constraining the bar-driven evolution at early cosmic times.
ABSTRACT We provide the first analytical and numerical calculations of the joint onset/termination rate–duration relationship for stochastic Babcock–Leighton dynamo models, and compare them with the recently reported relation from seven Holocene grand minima ($R^{2}_{\rm onset} = 0.76$ and $R^{2}_{\rm term} = 0.95$). We employ the standard amplitude-equation truncation of the stochastic dynamo near its Hopf bifurcation – a 1D Langevin equation for the cycle-amplitude envelope with multiplicative noise. By fixing the single-free parameter via simultaneous calibration against four independent Holocene observables, we integrate $\sim 3.3 \times 10^{6}$ yr of Monte Carlo realizations. Two main results follow. First, the population rate–duration relation is a power law with slope $-0.55 \pm 0.01$ for both phases, with a small structural asymmetry in goodness of fit $\Delta R^{2}_{\rm pop} = 0.08 \pm 0.02$; both are derived analytically from the Ornstein–Uhlenbeck escape statistics of the underlying Langevin equation and are insensitive to the model parameters. Second, the apparent asymmetry $\Delta R^{2} \approx 0.19$ between onset and termination in the observed sample is dominated by small-sample statistical noise of a single-mechanism null at $N=7$, of which only $\sim 0.08$ is structural; both observed values lie within the predicted bootstrap distribution ($p_{\rm onset} \approx 0.34$ and $p_{\rm term} \approx 0.05$, broadly robust to detector parameters and observational uncertainty). We predict that the apparent gap will relax toward $\sim 0.08$ as the high-resolution $^{14}$C catalogue is extended, and that $N \approx 15$ well-resolved terminations would suffice to distinguish the minimal stochastic null from a state-dependent threshold mechanism. The result supports the view that grand minima are stochastically forced excursions of a weakly non-linear dynamo near criticality.
Relativistic jets are observed in both stellar-mass black hole X-ray binaries (BHXRBs) and active galactic nuclei (AGNs), yet their bulk Lorentz factors differ systematically—those in black hole X-ray binaries are typically below ∼2, whereas AGN jets can reach ∼50. The origin of this discrepancy remains unclear. Searching the literature, we compile a sample of 333 AGNs with well-measured jet component motions, consisting of 270 quasars, 47 BL Lac objects, 10 FR I, and 6 FR II galaxies. We find that quasars/FR IIs exhibit minimal bulk Lorentz factors ranging from ∼1.0 to 41.5, with a mean of 11.5 (median 9.5). In contrast, BL Lac objects/FR Is show Γ_ jet∼1.0–21.9, averaging 4.2 (median 1.5). These values, particularly the median, closely resemble those of BHXRBs, implying a strong correlation between jet speed and accretion mode. The Lorentz factor of a magnetically driven jet is mainly determined by the ratio of the magnetic pressure to rest mass energy density at the jet base. In BL Lacs/FRIs/BHXRBs, the field is maintained by the advection-dominated accretion flow (ADAF), and the gas at the ADAF surface is magnetically driven into the jets. In quasars/FRIIs, the field is maintained by the disc, while the jet base is connected to the corona. Our model calculations show that the disc field is always much stronger than that of the ADAF, and therefore leads to a larger Γ_ jet, which can explain the systematic difference in Γ_ jet between these two types of sources.
Massive, star-forming clumps are regions of intensive star-formation that are commonly observed in high-redshift (z > 1) galaxies. Observations of low-redshift clumpy galaxy analogues are rare but the availability of wide-field galaxy survey data makes the detection of large clumpy galaxy samples much more feasible. We present a population of 12,790 star-forming clumps detected in a mass-complete sample of 5,395 star-forming galaxies (SFGs) at redshifts z≤0.32, located in the XMM-LSS, E-COSMOS and DEEP2-3 fields observed by the Hyper Suprime-Cam Subaru Strategic Survey (HSC-SSP) and CFHT Large Area U-band Deep Survey (CLAUDS). The clumps were detected using an improved version of our Deep Learning (DL)-based object detection framework which uses the ZOOBOT foundation DL-model as a 'backbone' feature extractor. We determined the fraction of star-forming galaxies hosting at least one off-centre clump (f_clumpy) based on a clump definition that requires a clump-galaxy flux ratio in the CLAUDS u-band of ≥8%. We estimate f_clumpy to decrease from ∼31% at z∼0.3 to ∼23% at z ∼ 0.1, which aligns well with a low-redshift extrapolation of the clumpy fraction that is measured using high-redshift observations. At fixed redshift, f_clumpy is negatively correlated with the stellar mass and positively correlated with the specific star-formation rate (sSFR) of the host galaxies. When the clump definition is changed to include only clumps with a stellar mass of M_cl≥ 10^7 M_⊙, we observe a highly increased clumpy fraction of ∼60% that tends to increase with the stellar mass of the host galaxies but does not show a dependence on the sSFR of the host galaxies.
Large-scale spectroscopic surveys will need suitable benchmark stars that can be used to verify the performance of automatic pipelines. A promising type of object for this purpose is the detached eclipsing binary (DEB) containing an FG-star and a low temperature companion. For flux ratios ≲1 per cent, the spectra obtained for the binary will be almost identical to a single star. As the methods for obtaining accurate parameters for binaries are well established, they would be excellent benchmark candidates. We analyse a group of DEBs with M-dwarf companions using TESS light curves and high resolution spectroscopy from NIRPS and HARPS on the ESO 3.6-m telescope. We obtain accurate fundamental parameters for the stellar components. The secondary component is visible with cross-correlation, allowing them to be characterised as well. With the stellar parameters obtained from the analysis, we can measure precise effective temperatures from Gaia parallaxes and archival magnitude data. Chemical compositions of the primary stars are also extracted from the stellar spectra. In this analysis, the secondary components have minimal impact on determined spectroscopic parameters. Our radii and masses are characterised to within sub per cent precision as well as our primary effective temperatures. Beyond a new set of stellar benchmarks, the secondary components analysed in this work represent a well characterised sample of M-dwarf stars which will be useful to improve our understanding of low mass structure and evolution.
Strong gravitational lenses (SGLs) are rare systems whose discovery currently relies primarily on supervised machine learning methods trained on large simulated datasets. We present the first application of Astronomaly:PROTEGE to SGL discovery, demonstrating that a human-in-the-loop active learning framework can efficiently identify lenses in large imaging surveys without the need for simulated training data. We consider a sample of 3.7 million bright galaxies from the Kilo-Degree Survey (KiDS) DR4. Feature representations are extracted using a convolutional neural network pre-trained on the ImageNet dataset and subsequently fine-tuned on KiDS data using the self-supervised Bootstrap Your Own Latent (BYOL) framework. Within the embedding of these representations, the active learning loop of Astronomaly iteratively selects the most informative systems for expert inspection. A total of 3,000 objects are inspected across multiple rounds, yielding 34 high-quality (grade A/B) SGL candidates. On the basis that these systems occupy similar regions in the learned feature space, we expand this sample through nearest-neighbour similarity analysis. Including the active learning discoveries, we identify a total of 140 grade A/B candidates and more than 1,000 additional lower-confidence systems (grade C). Among the A/B candidates, 81 are newly identified, while approximately 22
H I gas traces the large-scale structure and provides the primary fuel for star formation. High-z protoclusters are ideal laboratories to study how H I gas is accreted and consumed during the formation of the most massive structures in the Universe. However, much remains unknown about the distribution and physical state of their H I gas. We examine a rare configuration in which a protocluster candidate is located in front of a quasar at z=3.09. Our spectroscopic campaign confirms a protocluster at z=3.079: however, no corresponding strong H I absorption is found in the background quasar spectrum. Instead, we serendipitously discover a prominent H I absorption feature at z∼ 3.01, offset by ∼ 60 cMpc from the centre of the protocluster. Spanning an exceptionally broad velocity range of ∼ 2000 km s^-1 (∼ 40 cMpc), this absorption is decoupled from the confirmed member galaxies. Detailed kinematic modelling reveals this absorption comprises five distinct components rather than a single cloud. Moreover, one of these components exhibits a super-solar metallicity ([O/H] = +1.19^+0.91_-0.78). We propose two physical scenarios for this unique system: (1) an additional, hidden massive protocluster along the line of sight, and/or (2) metal-rich outflows and metal-poor inflows driven by a single massive galaxy. The discovery highlights that while protoclusters are not universally associated with strong H I absorption, targeting the strong H I absorbers may serve as a beacon for uncovering massive, metal-rich protoclusters or complex gas kinematics in the early Universe.
