IGR J20084+3221 is a previously unclassified Galactic source first detected by INTEGRAL. Chandra observations led to possible classifications of either a magnetic Cataclysmic Variable (mCV) or high mass X-ray binary (HMXB) based on the hardness of its spectrum. Here, we report follow-up observations taken by XMM-Newton, NuSTAR, and the Hale Telescope at Palomar Observatory. Based on these observations, we conclude that IGR J20084+3221 is most likely an Intermediate Polar (IP) type mCV. Timing analysis of the X-ray data found a significant peak period of P=635.0±0.4 s, which we interpret to be the spin period of the white dwarf (WD). The X-ray spectrum is well fit to an absorbed Bremsstrahlung model with components accounting for partial covering, reflection, and a fluorescent Fe-line, all typical for an IP. The optical spectrum shows clear emission lines, consistent with emission dominated by an accretion disk. We find counterparts to the source across the optical and infrared (IR) bands, and, despite uncertainties in the distance and extinction, we estimate that the source is too faint in the IR to be an HMXB. Given the evidence pointing towards an IP classification, we fit the X-ray spectrum to a post-shock region model where we find a WD mass of M=1.09^+0.12_-0.11M_⊙, larger than the average mass for a WD in an mCV.

X-ray variability is a well-established characteristic of active galactic nuclei (AGN), known to correlate inversely with both the supermassive black hole mass and luminosity, although the degree of each remains a topic of debate. The potential of X-ray variability as a proxy for MBH or for intrinsic LX has led to proposals to use AGN as standard candles to test cosmological models. However, the large intrinsic dispersion in these relations has limited their practical applications. In this work, we investigate the dependence of X-ray variability on AGN physical properties using a sample of 134 Seyfert 1 galaxies from the BAT AGN Spectroscopic Survey (BASS), which is the largest sample to date, more than three times larger than those used in previous studies. Contrary to earlier findings, we observe that X-ray variability correlates with luminosity just as strongly as with MBH. Furthermore, we still do not find evidence for the expected anti-correlation between variability and Eddington ratio, even when using refined bolometric luminosities from SED fitting to compute the Eddington ratio. From a cosmological perspective, the increased sample size reduces the scatter in the log(L)-log(exvar) relation to 0.63 dex - a significant improvement over previous results, but still too large to serve as competitive standard candles, when compared to SNIa (uncertainties on distances of 5-10

ASASSN-24fw, monitored by the All-Sky Automated Survey for SuperNovae, underwent a rapid and deep dimming event beginning in late 2024 and lasting until 2025 June. The pre-dimming spectral energy distribution indicates that ASASSN-24fw is an F-type main-sequence star with a persistent infrared excess, corresponding to a fractional luminosity of about 10 per cent. Public survey light curves show that the star is otherwise photometrically stable, implying that the dimming was caused by an external occulter. While long-duration stellar dimming events have become increasingly common in recent years, ASASSN-24fw is distinguished by a pronounced flat-bottomed light curve lasting nearly 200 d. We analyse this event using available photometric and spectroscopic data obtained during the dimming phase. Two independent light-curve models are applied. The first characterizes the multiple phases of the ingress structure, while the second model suggests that the occulter is a gas-giant companion, likely a brown dwarf, with a minimum mass of 3.42 M$_{\rm {J}}$ and an extended ring system with a radial extent of approximately 0.17 au. Near-infrared spectra obtained during dimming show enhanced infrared excess and are consistent with an M8-type brown dwarf companion. Optical spectra reveal variable H$_{\alpha }$ emission during the event. Post-dimming spectra show no evidence for ongoing accretion, suggesting that the H$\alpha$ variability is associated with the occulter rather than the host star. We conclude that ASASSN-24fw represents a rare and unusual system, and that further observations are required to better constrain its stellar properties, circumstellar environment, and evolutionary history.

X-ray variability is a well-established characteristic of active galactic nuclei (AGNs) known to correlate inversely with both the supermassive black hole mass (M-BH) and luminosity, although the degree of each remains a topic of debate. The potential of X-ray variability as a proxy for M-BH or for intrinsic L-X has led to proposals to use AGNs as standard candles to test cosmological models. However, the large intrinsic dispersion in these relations has limited their practical applications. In this work, we investigate the dependence of X-ray variability on physical properties of AGNs using a sample of 134 Seyfert 1 galaxies from the BAT AGN Spectroscopic Survey (BASS), which is the largest sample to date (it is more than three times larger than samples used in previous studies). Contrary to earlier findings, we observed that X-ray variability correlates with luminosity just as strongly as with M-BH. Furthermore, we still find no evidence of the expected anti-correlation between variability and the Eddington ratio, even when using refined bolometric luminosities from Spectral Energy Distribution (SED) fitting to compute the Eddington ratio. From a cosmological perspective, the increased sample size reduces the scatter in the log L-log sigma(2)(NXS) relation to similar to 0.63 dex - a significant improvement over previous results, but still too large to serve as competitive standard candles, when compared to Supernovae Ia (uncertainties on distances of similar to 5-10%) or the L-X - L-UV relation in quasars (uncertainties of 10-12%). We tested including the width of broad emission lines as additional parameters, but we found that this does not significantly lower the observed dispersion, contrary to previous studies on smaller samples. Finally, we discuss how future X-ray missions such as AXIS and NewAthena will improve this scenario by enabling precise variability measurements for thousands of AGNs up to redshift z similar to 3.

We present Chandra X-ray Observatory and Hubble Space Telescope (HST) follow-up observations of 12 dwarf galaxies from A. E. Reines et al. that are potential hosts of radio-selected active galactic nuclei (AGNs), eight of which are nonnuclear and possible “wandering” black holes (BHs). Our multiwavelength analysis indicates a heterogeneous sample with five radio sources detected at both X-ray and optical wavelengths within the positional uncertainties and nondetections for the remaining objects. Of the radio objects detected in the X-ray and optical, three have multiwavelength evidence for hosting nuclear massive BHs and one object is consistent with an extreme compact starburst. Only one of the off-nuclear radio sources has a significant optical counterpart and we present Palomar spectroscopy that identifies this object as a background AGN. We cannot definitively determine if the seven remaining off-nuclear radio sources are wandering massive BHs in the target dwarf galaxies or background AGNs, although the three sources with the largest offsets have compact radio cores detected with the Very Long Baseline Array and are consistent with expectations for background AGNs. Our HST sensitivity limits also allow for wandering massive BHs in the target dwarf galaxies that are hosted by stellar clusters with masses ≲ 10 ^6 M _⊙ .

In the course of our ongoing survey of faint planetary-nebula nuclei (PNNi), we obtained optical spectroscopy of the central star of the little-studied PN Kohoutek 1-9 (K 1-9). Its spectrum is found to be that of a G-type dwarf with strong absorption features of carbon molecules and s-process elements such as Sr and Ba-a dwarf barium star. K 1-9 thus joins a very small group of PNe with barium-star nuclei. Their likely progenitors are wide binaries in which the primary star reached the thermally pulsing asymptotic-giant-branch (AGB) phase, dredged up C and s-process elements from its interior, and transferred enriched material to the companion through a dense stellar wind. The remnant core is now a hot, optically inconspicuous (pre-)white dwarf, responsible for ionizing the AGB ejecta, and leaving the optical spectrum dominated by the cool barium star. We present deep narrow-band images of K 1-9, obtained by accumulating long exposure times using amateur telescopes. The PN shows a thin-ring morphology, remarkably similar to the "wedding-ring" shapes seen around other members of this class of binary PNNi. The thin ring probably represents material preferentially ejected into the orbital plane of the binary; we note that the PNN is slightly off-center within the ring, as has been predicted theoretically. We suggest several follow-up studies, including precision photometry to search for periodic variations due to starspots on the rotating barium star, and high-resolution spectroscopy to determine atmospheric parameters of the star, chemical abundances, and its rotation velocity.

We present first results from a systematic study of extreme mid-infrared variability of active galaxies across the >10-year baseline of the Wide-field Infrared Survey Explorer (WISE) mission. WISE, which observed the full sky with a six-month cadence, is sensitive to transient events in both unobscured and obscured galaxies. This paper focuses on extreme flares in active galactic nuclei (AGNs). Previous studies identified flares such as tidal disruption events (TDEs) in inactive galaxies, typically from optical or X-ray surveys. However, flares are also expected in AGN and optical/X-ray searches are insensitive to events in dust-enshrouded AGN. In this pilot study, we present flares in two AGN identified from extreme mid-infrared color variability. One flare was also detected at optical wavelengths. While both events showed broadened Hα emission several years after the flare peak, more recent spectroscopy reveals continued broadened emission only from the source with the optical flare. After considering several potential physical causes of the flares, including supernovae and micro-lensing, we suggest both events are TDEs in AGN. Intriguingly, the optical flare decays much faster than the expected t^-5/3 fallback rate expected for TDEs in quiescent galaxies, suggesting either a partial disruption or the tidal disruption of a star by an intermediate mass black hole embedded in the accretion disk of an AGN. This work demonstrates the power of WISE to identify the full census of TDEs, including events in dust-obscured AGN. Mid-infrared data probes the nature of the event and provides a bolometric measure of the flare energetics.

The Massive and Distant Clusters of Wide-field Infrared Survey Explorer (WISE) Survey 2 (MaDCoWS2) is a WISE-selected catalog of galaxy clusters at 0.1 < z < 2 covering an effective area of >6000 deg(2). In this paper, we derive splashback radii for this cluster ensemble from galaxy density profiles and constrain the mass threshold of the survey as a function of redshift. We use MaDCoWS2 cluster candidates at 0.4 <= z <= 1.65 divided into subsamples with different Poissonian signal-to-noise ratios (S/N(P)s) and redshifts, cross correlated with galaxies from the CatWISE2020 catalog, to obtain average surface density profiles. We perform a Markov Chain Monte Carlo analysis to derive parameter estimates for theoretical models consisting of orbiting and infalling terms. A distinct splashback feature is detected in all subsamples. The measured splashback radii span from 0.89(-0.02)(+0.02)h(-1) cMpc ( 0.61(-0.02)(+0.02)h(-1) pMpc) at z & strns;=0.45 to 1.27(-0.05)(+0.05)h(-1) cMpc ( 0.53(-0.04)(+0.04)h(-1) pMpc) at z & strns;=1.54 . We also find that the splashback radii increase with S/N-P at fixed redshift. The resultant splashback radii constrain the redshift dependence of the mass of MaDCoWS2 clusters at fixed S/N-P. We calculate M-200m from the radii using a relation based on a cosmological simulation. MaDCoWS2 M-200m values derived from the simulation-based relation are lower than the expected values based on weak-lensing observations. More robust mass constraints will come from calibrating splashback radii derived from galaxy density profiles with weak-lensing shear profiles from facilities such as Euclid, the Vera C. Rubin Observatory, and the Nancy Grace Roman Space Telescope.

ABSTRACT IGR J20084+3221 is a previously unclassified Galactic source first detected by the International Gamma-Ray Astrophysics Laboratory (INTEGRAL). Chandra observations led to possible classifications of either a magnetic cataclysmic variable (mCV) or a high-mass X-ray binary (HMXB) based on the hardness of its spectrum. Here, we report follow-up observations taken by XMM–Newton, NuSTAR, and the Hale Telescope at Palomar Observatory. Based on these observations, we conclude that IGR J20084+3221 is most likely an intermediate polar (IP) type mCV. Timing analysis of the X-ray data found a significant peak period of $P=635.0\pm 0.4$ s, which we interpret to be the spin period of the white dwarf (WD). The X-ray spectrum is well fit to an absorbed bremsstrahlung model with components accounting for partial covering, reflection, and a fluorescent Fe-line, all typical for an IP. The optical spectrum shows clear emission lines, consistent with emission dominated by an accretion disc. We find counterparts to the source across the optical and infrared (IR) bands, and, despite uncertainties in the distance and extinction, we estimate that the source is too faint in the IR to be an HMXB. Given the evidence pointing towards an IP classification, we fit the X-ray spectrum to a post-shock region model where we find a WD mass of $M=1.09^{+0.12}_{-0.11}$ ${\rm M}_{\odot }$, larger than the average mass for a WD in an mCV.

Photometric selection of luminous high-redshift (z≳4) quasars is plagued by contamination from numerous low-mass Galactic stars, reddened lower-redshift quasars, as well as compact luminous red galaxies. Confirmation of these rare objects thus requires extensive spectroscopic campaigns on 4 and 8-meter-class telescopes with relatively low success rates. Here we demonstrate the utility of SPHEREx spectrophotometric survey data for quasar confirmation with no ground-based follow-up required, "from the couch," applied to candidates from a purposefully simplistic photometric and astrometric Gaia+WISE selection down to low Galactic latitudes (|b|≥8^∘). Primarily from the detection of their strong broad Hα emission lines, we discover 87 new luminous 4.0 < z < 5.7 quasars with median M_1450 = -27.5, including 19 quasars at z>5, and recover 219 previously published quasars at z>4. We validate our SPHEREx selection with a 100

The Active Galactic Nuclei (AGN) glossary is vast and complex. Depending on selection method, observing wavelength, and brightness, AGNs are assigned distinct labels, yet the relationship between different selection methods and the diversity of time-domain behavior within and across classes remains difficult to characterize in a unified framework. Changing-look AGNs (CLAGNs), which transition between classifications over time, further complicate this picture. In this work, we learn a data-driven, low-dimensional representation of multi-wavelength photometric light curves of AGNs, in which the structure of the projected manifold correlates with AGN class and independent spectroscopic properties. Using the NASA Fornax Science Platform, we assemble light curves from ZTF, Pan-STARRS, Gaia, and WISE/NEOWISE for two samples: (1) a heterogeneous set of ∼2000 AGNs spanning z ≲ 1, including SDSS quasars, variability-selected sources, and CLAGNs; and (2) a homogeneous sample of ∼65000 narrow-line AGNs at z ≈ 0.1 with well-characterized optical emission-line measurements. Without using class labels during training, the learned manifolds organize variability-selected AGNs into coherent regions of the low-dimensional space, distinguish between turn-on and turn-off CLAGNs, and place tidal disruption events in distinct regions. Manifold coordinates correlate with key spectroscopic and host-galaxy properties, including stellar mass, [OIII] luminosity, and D_n(4000), demonstrating that heterogeneous multi-band variability can be combined in a purely data-driven manner to recover correlations with independent physical diagnostics, without requiring explicit physical modeling. These results show that manifold learning offers a practical, assumption-light approach for integrating time-domain surveys and prioritizing spectroscopic follow-up.

Spectroscopic observations of the quasar J0950+5128 spanning 22 yr reveal monotonic radial velocity variations in its broad H beta emission line. Moreover, the line profile becomes broader over time, necessitating careful measurements. We present robust H beta velocity shift measurements obtained via cross correlation, applied to both the full spectra and to isolated broad H beta components derived from spectral decomposition. We also examine the light curves for variability consistent with the spectroscopic trends. Using Lomb-Scargle periodogram analysis, we find no significant periodic signal. We consider several interpretations for the observed changes, including a binary supermassive black hole, dust-cloud obscuration, outflows, a recoiling black hole, and a single perturbed, disk-like broad-line region (BLR). We deem the binary and perturbed BLR scenarios to be physically plausible. The binary interpretation is the only one for which we can immediately compare a physical model to the available data. Thus, we incorporate radial velocity "jitter" to emulate typical quasar variability and fit the radial velocity curve with a Keplerian model to examine whether it can reproduce the observations. In this context, the available observations trace only a segment of the putative orbit. The fit yields a period of 33 yr (observed frame) and an eccentricity of 0.65, with lower limits on the semimajor axis and black hole mass of 10-2 pc and 107 M circle dot, respectively. Thus, J0950+5128 is a binary candidate deserving further study. The single, perturbed BLR interpretation remains viable but requires additional observations and modeling for further evaluation. Continued monitoring is, therefore, essential.

Context. The identification of high-redshift quasars (z > 4.5) is critical for studying the early Universe, supermassive-black-hole growth, and cosmic reionization. Most known high-redshift quasars are located in the northern hemisphere, leaving the southern sky largely unexplored. Aims. As part of the 4-meter Multi-Object Spectroscopic Telescope (4MOST) and Chilean AGN/Galaxy Extragalactic Survey (ChANGES) S1604 survey, we aim to create a large catalog of high-redshift quasar candidates in the southern hemisphere using multiwavelength photometry and spectral-energy-distribution (SED) fitting, with the goal of spectroscopic follow-up with 4MOST. Methods. We constructed a multiband photometric catalog by combining optical data from the Dark Energy Camera Local Volume Exploration Survey (DELVE DR2) and Dark Energy Camera Legacy Survey (DECaLS DR10), near-infrared data from the VISTA Hemisphere Survey (VHS DR5) with an additional field of the VISTA Kilo-degree Infrared Galaxy Public Survey (VIKING), mid-infrared data from the Wide-field Infrared Survey Explorer (AllWISE), and optical astrometry from Gaia DR3. After applying morphological and color-based cuts to remove contaminants such as brown dwarfs and red galaxies, we performed a custom-made SED fitting using quasar and brown-dwarf templates. Statistical outputs including χ2, the Bayesian information criterion (BIC), and Ftest were used to rank and select candidates. Results. Our final catalog contains 6104 high-redshift quasar candidates within the redshift range of 4.5 < z < 7. These sources have detections in seven or more photometric bands and satisfy our SED-based statistical selection criteria (e.g., BIC > 0 and Ftest > 10). Initial spectroscopic validation using the New Technology Telescope (NTT) with the ESO Faint Object Spectrograph and Camera v.2 (EFOSC2) and the Palomar Observatory Hale Telescope with the Next Generation Palomar Spectrograph (NGPS) confirmed three high-redshift quasars at z > 5 out of six observed candidates.

The active galactic nuclei (AGNs) glossary is vast and complex. Depending on the selection method, observing wavelength, and brightness, AGNs are assigned distinct labels, yet the relationship between different selection methods and the diversity of time-domain behavior within and across classes remains difficult to characterize in a unified framework. Changing-look AGNs (CLAGNs), which transition between classifications over time, further complicate this picture. In this work, we learn a data-driven, low-dimensional representation of multiwavelength photometric light curves of AGNs, in which the structure of the projected manifold correlates with AGN class and independent spectroscopic properties. Using the NASA Fornax Science Platform, we assemble light curves from Zwicky Transient Facility, Pan-STARRS, Gaia, and Wide-field Infrared Survey Explorer/NEOWISE for two samples: (1) a heterogeneous set of ∼2000 AGNs spanning z ≲ 1, including Sloan Digital Sky Survey quasars, variability-selected sources, and CLAGNs; and (2) a homogeneous sample of ∼65,000 narrow-line AGNs at z ≈ 0.1 with well-characterized optical emission-line measurements. Without using class labels during training, the learned manifolds organize variability-selected AGNs into coherent regions of the low-dimensional space, distinguish between turn-on and turn-off CLAGNs, and place tidal disruption events in distinct regions. Manifold coordinates correlate with key spectroscopic and host-galaxy properties—including stellar mass, [O III ] luminosity, and D _n (4000)—demonstrating that heterogeneous multiband variability can be combined in a purely data-driven manner to recover correlations with independent physical diagnostics, without requiring explicit physical modeling. These results show that manifold learning offers a practical, assumption-light approach for integrating time-domain surveys and prioritizing spectroscopic follow-up.

Lensed quasars are key to many areas of study in astronomy, offering a unique probe into the intermediate and far universe. However, finding lensed quasars has proved difficult despite significant efforts from large collaborations. These challenges have limited catalogues of confirmed lensed quasars to the hundreds, despite theoretical predictions that they should be many times more numerous. We train machine learning classifiers to discover lensed quasar candidates. By using semi-supervised learning techniques we leverage the large number of potential candidates as unlabelled training data alongside the small number of known objects, greatly improving model performance. We present our two most successful models: (1) a variational autoencoder trained on millions of quasars to reduce the dimensionality of images for input to a dense neural network classifier that can make accurate predictions and (2) a convolutional neural network trained on a mix of labelled and unlabelled data via virtual adversarial training. These models are both capable of producing high-quality candidates, as evidenced by our discovery of GRALJ140833.73+042229.98. The success of our classifier, which uses only multi-band images, is particularly exciting as it can be combined with existing classifiers, which use other data than images, to improve the classifications of both models and discover more lensed quasars.

The X-ray emission of active galactic nuclei (AGN) is generally attributed to inverse Compton scattering of accretion-disk photons by hot electrons in a compact corona. In local AGN, directly constraining coronal properties is challenging because the high-energy cutoff often lies beyond the NuSTAR bandpass. High-redshift, luminous quasars enable systematic constraints on the high-energy cutoff, as cosmological redshift shifts the spectal cutoff into the observable hard X-ray band. We present first results from the “Probing the AGN Coronae with High-redshift AGN” (PACHA) project, based on quasi-simultaneous NuSTAR and XMM-Newton observations of 13 radio-quiet AGN at z>1. We constrain the high-energy cutoff and coronal temperature at 90% confidence level for 10 and 9 sources, respectively. The sample exhibits a mean cutoff energy of E_ cut=80.8±8.1 keV and a mean coronal temperature of kT_ e=18.4±1.6 keV, both significantly lower than those measured in local Swift-BAT AGN, while the mean optical depth (τ=4.8±0.3) is significantly higher. The uncertainties are at 1 σ. Combining our high-redshift sample with local AGN, we find a potential anti-correlation between cutoff energy and both X-ray luminosity and black hole mass, with no significant dependence on Eddington ratio. Within a hybrid coronal framework, the inferred temperatures lie well below the pair-production limits for purely thermal coronae, indicating a substantial efficient Compton cooling and/or non-thermal electron component. The detection of low coronal temperatures in high-luminosity AGN is broadly consistent with predictions from recent radiation MHD simulations that consider purely thermal electron populations, implying that non-thermal electrons may not be the primary drivers of the observed coronal properties in these systems.

Theoretical studies predict that dual AGNs are a critical stage of galaxy merger-driven supermassive black hole growth. Systematic searches for dual AGNs typically target late-stage mergers (≤10 kpc nuclear separations) and select AGNs based on optical diagnostics. Yet, simulations predict that obscuration can occur early in the merger sequence, and that a significant fraction of dual AGNs can be found beyond 10 kpc. Here, we report on a new sample of 157 spatially resolved mid-IR dual AGNs candidates selected based upon their mid-IR W1-W2 colors from the Wide-Field Infrared Survey Explorer and optically classified as galaxy merger candidates using imaging from the Dark Energy Camera Legacy Survey. Spectroscopic results are presented for approximately 2/3 of the sample. 76 candidates have been confirmed to reside in galaxy mergers; among these, 13 have been confirmed as bona fide mid-IR dual AGNs, while 63 represent strong dual AGN candidates that require further examination. 46 candidates have been rejected as non-merger contaminants (foreground-background AGNs, separations inconsistent with interacting galaxies, etc.). 35 candidates still await spectroscopic coverage. The confirmed and high confidence dual AGN candidates exhibit separations of 14.5-129 kpc; >50

The growth of galaxies in the early Universe is thought to be dominated by compact, intensely star-forming systems, yet the corresponding growth of supermassive black holes (SMBHs) within such environments remains poorly constrained. Green Pea galaxies are nearby analogs of rapidly assembling galaxies in the early Universe owing to their compact morphologies, intense star formation, low metallicities, and extreme ionization conditions. Although galaxy interactions are thought to trigger episodes of rapid SMBH growth, direct observations of simultaneous accretion onto multiple SMBHs in compact, intensely star-forming galaxies are lacking. Here we report the discovery of the first confirmed dual active galactic nucleus (AGN) in a Green Pea system, SDSS J162209.41+352107.5. Chandra imaging resolves two luminous hard X-ray sources separated by 8.4 kpc in projection, demonstrating simultaneous accretion onto two SMBHs. Follow-up Keck spectroscopy confirms that the two optical nuclei share a common redshift and independently exhibit broad Balmer emission and high-ionization AGN emission lines. Unlike most known dual AGN, which are typically found in massive mergers, J162209.41+352107.5 is a compact low-mass system analogous to galaxies thought to dominate early phases of galaxy assembly. These findings demonstrate that efficient growth of multiple SMBHs can occur in such environments and establish Green Pea galaxies as nearby laboratories for investigating the interplay between galaxy interactions, star formation, and black-hole growth under conditions analogous to those prevalent in the young Universe.

The Massive and Distant Clusters of WISE Survey 2 (MaDCoWS2) is a WISE-selected catalog of galaxy clusters at 0.16000 deg^2. In this paper, we derive splashback radii for this cluster ensemble from galaxy density profiles and constrain the mass threshold of the survey as a function of redshift. We use MaDCoWS2 cluster candidates at 0.4≤ z ≤ 1.65 divided into subsamples with different signal-to-noise (S/N_ P) and redshifts, cross-correlated with galaxies from the CatWISE2020 catalog, to obtain average surface density profiles. We perform a Markov Chain Monte Carlo analysis to derive parameter estimates for theoretical models consisting of orbiting and infalling terms. A distinct splashback feature is detected in all subsamples. The measured splashback radii span from 0.89^+0.02_-0.02h^-1 comoving Mpc/cMpc (0.61^+0.02_-0.02h^-1 proper Mpc/pMpc) at z=0.45 to 1.27^+0.05_-0.05h^-1 cMpc (0.53^+0.04_-0.04h^-1 pMpc) at z=1.54. We also find that splashback radii increase with S/N_ P at fixed redshift. The resultant splashback radii constrain the redshift dependence of the mass of MaDCoWS2 clusters at fixed S/N_ P. We calculate M_ 200m from the radii using a relation based on a cosmological simulation. MaDCoWS2 M_ 200m values derived from the simulation-based relation are lower than the expected values based on weak-lensing observations. More robust mass constraints will come from calibrating splashback radii derived from galaxy density profiles with weak lensing shear profiles from facilities such as Euclid, Rubin, and Roman.

Luminous quasars at z > 6 are key probes of early supermassive black hole (SMBH) growth, massive galaxy evolution, and intergalactic medium properties during cosmic reionization. However, their discovery is very challenging due to their scarcity and overwhelming contamination. Foreground ultracool dwarfs (UCDs) outnumber z > 6 quasars by 2–4 orders of magnitude. In this work, we leveraged the extensive coverage of DESI Legacy Survey DR10 to conduct a self-supervised search for quasars at z > 6, directly analyzing multiband optical images and minimizing the biases of the traditional catalog-driven color-color selection criteria. By applying a contrastive learning (CL) method followed by spectral energy distribution (SED) fitting prioritization, we identified 1139 high-priority quasar candidates, for which we expect a competitive 1:1 quasar-to-UCD ratio based on the literature samples. We spectroscopically confirm 16 new quasars at z = 5.94 − 6.45, achieving a 45% success rate. Remarkably, all 16 objects are relatively bright (M1450 < −25.5) quasars, including several with unusual properties such as narrow Ly[[INLINE10]] emission (FWHM ≲ 2600 km s−1), strong Ly[[INLINE13]]+N V emission with an equivalent width > 100 Å, and a mild observed-frame red near-infrared (NIR) continua (z − J > 0.4). Notably, three of them would have been missed by traditional color–color selections. These results highlight the power of self-supervised machine learning, combined with SED fitting prioritization, to uncover rare, distant sources beyond the limitations of conventional techniques. Our approach offers a scalable and robust framework for data mining and can be readily extended to forthcoming wide-field surveys such as Rubin/LSST, 4MOST, Euclid, and Roman. These applications will advance the census of high-redshift quasars, potentially extend the redshift frontier, and improve constraints on SMBH formation and evolution in the first billion years of the Universe.