Swayamtrupta Panda

We present the largest statistical spectroscopic sample of radio quasars at 4.7 ≤ z ≤ 6.7 to date. These have been selected from a dedicated Dark Energy Spectroscopic Instrument target program and provide a robust sample to study the influence of radio jets on early quasar evolution. Using low-frequency radio data from the LOFAR Two Metre Sky Survey Data Release 3 at 144 MHz, we identify 83 high- z radio quasars, 26 of which are classified as radio-loud (5%–15% of 646 confirmed high- z quasars, defined as R = F _5GHz / F _4400Å > 10). With radio luminosities of ∼10 ²⁵⁻²⁸ W Hz ⁻¹ , the radio emission in all 83 quasars is expected to be jet dominated rather than powered by star formation. Analysis of their rest-frame ultraviolet spectra reveals broadly similar composite spectral properties and C iv velocity shifts compared to radio-nondetected quasars. The radio-detected and radio-loud quasars exhibit slightly smaller Ly α and C iv equivalent widths on average; however, we find no significant evidence (∼1.3 σ ) for a higher fraction of weak-line quasars (∼10% ± 4% versus ∼4% ± 1% for radio-nondetected quasars). We further find that the broad absorption line (BAL) quasars are predominantly radio-quiet, and no correlation is observed between absorption index and radio-loudness, suggesting that radio emission is not produced by the BAL outflows themselves and is a physically distinct phenomenon. Our results demonstrate that powerful radio jets were already well established by z ∼ 5.

Circumnuclear structures in active galactic nuclei (AGN) respond to accretion variability over different spatial and temporal scales, but whether compact narrow-line gas responds on decade timescales has not been systematically established. We use repeat Sloan Digital Sky Survey and Dark Energy Spectroscopic Instrument spectroscopy of 473 variability-selected galactic nuclei with evidence for recent nuclear brightening. We identify 19 sources whose narrow [O III ] λ 5007 flux increased by more than a factor of 2 over rest-frame baselines of 12.0–20.4 yr, which we term narrow-line ionization echoes (NIEs). In equal-weight stacked spectra, [O III ] increased by 229% ± 22%, while lower-ionization lines remained nearly unchanged or declined, indicating an ionization-dependent response rather than uniform spectral rescaling. The NIE hosts also moved coherently toward higher excitation in optical diagnostic diagrams, with mean increases of 0.46 ± 0.18 dex in log ( [ O III ] / H β ) and 0.58 ± 0.13 dex in log ( [ O III ] / [ O II ] ) . Photoionization models reproduce this evolution with a higher ionization parameter and a harder AGN-like ionizing spectrum at fixed gas abundance. For 13 sources with well-defined mid-infrared (MIR) outbursts, the integrated W1+W2 excess energy correlates strongly with the absolute [O III ] luminosity change ( r = 0.87), linking the dust and narrow-line responses to the same nuclear event. The MIR timescale and spectroscopic baseline constrain the variable [O III ]-emitting gas to characteristic scales of 1.5–5.2 pc. Compact narrow-line gas therefore appears to form an intermediate, decade-scale response layer between the infrared dust echo and the long-lived extended narrow-line region.

Head–tail radio sources are jetted active galactic nuclei (AGN) moving through the dense intracluster medium of galaxy clusters. They are extremely rare in the γ -ray sky, likely because they are usually observed at large viewing angles. Therefore, every new γ -ray detection of head–tail radio galaxies allows us to probe the origin of the high-energy emission in this unique class of AGN. Here we report, for the first time, the association of ESO 0137−G007 ( z = 0.016), a head–tail radio galaxy located at the outskirts of the merging cluster A3627, with the γ -ray source FL16Y J1615.5−6034. The motion of the galaxy through the dense cluster environment and subsequent ram pressure and/or intracluster medium turbulence have led to the formation of a >500 kpc long jet exhibiting a twisted, wiggly radio morphology. Its optical spectrum, obtained with the 4.1 m SOAR telescope, is devoid of emission lines, indicating that the underlying accretion activity is radiatively inefficient. From the measured line-of-sight stellar velocity dispersion, we estimate the mass of the central supermassive black hole to be (3.36 ± 1.32) × 10 ⁹ M _⊙ . We briefly discuss several radiative models to explain the observed broadband spectral energy distribution of ESO 0137−G007. We conclude that deeper multiwavelength observations of this unique γ -ray-emitting head–tail radio galaxy will enable us to better understand the interaction of the jet with the hot cluster environment, thus setting the stage for the research of this class of AGN with the upcoming Square Kilometre Array.

We present the first direct comparison between accretion-disk (AD) and broad-line region (BLR) sizes in quasars at z > 2. The comparison was possible because we combined continuum reverberation mapping with interferometric BLR constraints from GRAVITY and GRAVITY+. Using medium-band photometric monitoring with the MPG/ESO 2.2 m telescope, we measured interband continuum lags in two quasars: SDSS J092034.17+065718.0 at z = 2.33 (J0920) and SMSS J052915.80–435152.0 at z = 3.96 (J0529). These are two of the most luminous quasars known ( L _bol ~ 10 ⁴⁸ erg s ⁻¹ ) and currently the only two quasars at z > 2 with spatially resolved BLRs and dynamical black hole masses measured via interferometry, making this comparison uniquely possible. We detect significant con-tinuum lags in both quasars that increase monotonically with wavelength. The inferred UV disk sizes are R _AD = 4.35 _−0.91 ^+0.78 light-days for J0529 and R _AD = 3.15 _−0.48 ^+0.50 light-days for J0920. For J0920, which accretes at λ _Edd ~ 7–20, the disk size is consistent with standard thin-disk expectations, a surprising result given that the standard thin-disk approximation is not expected to hold in this super-Eddington regime. For J0529, the disk size is consistent with thin-disk predictions under the single-epoch black hole mass but would imply disk inflation by a factor of a few if the GRAVITY+ dynamical mass – which is an order of magnitude lower – is adopted instead. This tension illustrates that UV continuum disk sizes provide an independent physical scale that any self-consistent model of the black hole mass and accretion rate must satisfy. This provides an addition way of studying objects where BLR kinematics are dominated by outflows rather than virial motion. A comparison with the interferometric BLR sizes reveals pronounced radial hierarchies, with R _BLR / R _AD ~ 270 for J0529 (H β ) and ~ 115 for J0920 (H α ). The successful detection of lags in both quasars at L _bol ~ 10 ⁴⁸ erg s ⁻¹ demonstrates that continuum reverberation mapping remains feasible even at the low-amplitude variability end expected for the most luminous systems, opening a path toward extending AD size measurements to larger samples with wide-field surveys such as the Vera C. Rubin Observatory’s LSST.

Using the first spectroscopic data release from the Dark Energy Spectroscopic Instrument (DESI DR1), we conduct the largest systematic search for active galactic nuclei (AGN) signatures in ≈1.7 million low-redshift (0.001 ≤ z ≤ 0.45) line-emitting galaxies. Based on the [N ii ]/H α versus [O iii ]/H β emission-line ratio diagnostic, we identify AGN in 314,245/1,211,573 (25.9%) high-mass ( log ( M ⋆ / M ⊙ ) > 9.5 ) and 9648/467,214 (2.1%) dwarf ( log ( M ⋆ / M ⊙ ) ≤ 9.5 ) galaxies. The AGN fraction in line-emitting galaxies increases monotonically with stellar mass, from ∼1.4% at the low-mass end to ∼93.3% at the high-mass end. Among these AGN, 17,949 exhibit broad H α emission (BL-AGN), which we use to estimate their black hole (BH) masses via single-epoch virial methods. Leveraging this large BL-AGN sample, we extend the M _BH − M _⋆ scaling relation down to log ( M ⋆ / M ⊙ ) ≈ 7.8 and log ( M BH / M ⊙ ) ≈ 4.4 . We find a bimodal distribution of galaxies in this space, characterized by two distinct empirical relations. The relation for galaxies with high stellar and BH masses extrapolates to overlap with the high-redshift overmassive BH candidates. Our results suggest at least two broad evolutionary pathways for these overmassive BHs and their host galaxies across cosmic time. With this paper, we release the EmFit value-added catalog, containing emission-line flux and width measurements for ∼7.4 million galaxies, the largest catalog with emission-line decomposition into narrow, broad, and outflow components to date. This work significantly expands upon the early DESI results and provides a statistical sample for probing the galaxy−BH connection in the low-mass galaxy regime.

At cosmic noon ( z ≈ 2–3), both star formation and active galactic nucleus (AGN) activity peaked, each playing a significant role in ionizing interstellar gas on galaxy-wide scales. The spatial distribution of this ionized gas provides a direct probe of how AGN and stellar ionization influence the gaseous reservoirs of their host galaxies. Using JWST/NIRCam imaging from the JWST Extragalactic Medium-band Survey (JEMS), we spatially map two complementary tracers of ionized gas, [O iii ]+H β and Pa β , in ∼200 galaxies at 2.5 < z < 2.9. We apply multiwavelength AGN diagnostics to divide the sample into AGN hosts (33 galaxies), Pa β -detected systems (32 galaxies), and control objects (175 galaxies). We measure the [O iii ]+H β and Pa β spatial extents in each population and relate them to AGN and host properties derived from spectral energy distribution (SED) modeling. Both tracers exhibit systematically larger maximum radial extents in AGN hosts than in control galaxies (by ∼0.3 dex), with [O iii ]+H β emission modestly more extended than Pa β by ∼0.1 dex. With this statistically robust AGN sample, we measure the [O iii ]+H β radial extent–AGN luminosity relation at z ∼ 3 and derive a slope of ∼0.2, consistent with the shallow end of values reported at low redshift. The larger ionized gas extents among AGN hosts relative to the control sample, combined with the strong correlation between [O iii ]+H β extent and AGN luminosity, suggest that AGN activity may dominate gas ionization in galaxies with mixed AGN and star-forming activity at cosmic noon, although stellar processes can still contribute significantly on kiloparsec scales.

Context. The growing volume of spectroscopic data in modern surveys motivates the development of data-driven approaches that complement traditional emission-line diagnostics for the identification of active galactic nuclei (AGNs). Aims. We develop and validate a machine-learning (ML) framework for galaxy and AGN classification that exploits the full optical spectrum, using unsupervised learning to capture spectral features within a semi-supervised classification framework that complements classical approaches. Methods. We adapted the SPENDER autoencoder architecture to compress galaxy spectra obtained with the Dark Energy Spectroscopic Instrument (DESI) into a low-dimensional latent space that encodes physically meaningful label-agnostic information. We introduced a quantitative classification method via a k-d tree nearest-neighbor search in latent space. The model was trained on 50 222 spectra from the DESI main survey, corresponding to the internal Guadalupe dataset, released as part of data release 1 (DR1), and restricted to z ≤ 0.5. We validated the performance using labels derived from the FastSpecFit emission line measurements defining seven galaxy classes: AGN, broad-line (BL), composite, star-forming, passive, retired, and other. Results. The model achieves a high performance in identifying AGN and BL sources, with accuracies of 0.952 and 0.965, respectively. The model reliably recovers AGN and BL sources even in spectra with a low signal-to-noise ratio and identifies AGNs missed by single-diagnostic standard methods. Our classification metrics are benchmarked against traditional diagnostics, and we show that they represent lower limits of the true model performance. The latent space learned by the autoencoder not only separates AGN and non-AGN galaxies, but also correlates with key physical properties such as stellar mass and star formation rate, demonstrating that the method captures astrophysical meaningful features. Conclusions. This work demonstrates that unsupervised spectral representation learning implemented within a semi-supervised classification framework offers a powerful and scalable pathway toward more complete and reliable AGN catalogs for current and upcoming large spectroscopic surveys.

We present a study of the evolution of type 1 quasars at 1.0 < z < 3.5, covering the peak epoch of quasar activity. The quasar evolution has been extensively explored by a variety of previous works and the derived quasar luminosity functions (QLFs) are not very consistent with each other, presumably due to the complexities introduced by different quasar selection techniques and associated completeness corrections. We use a new strategy to construct QLFs based on a library of all known quasars. We focus on a wide region of ∼1700 deg ² and a deep field of ∼265 deg ² that have rich spectroscopic data primarily from the Sloan Digital Sky Survey and DESI. We then apply traditional color cuts in the rest-frame UV–optical to select quasar candidates and use the quasar library to identify them. Our final sample consists of 62,426 quasars at 1.0 < z < 3.5, with a high completeness (∼96%) and a high purity (∼93%) in the color selection. Simple color cuts can potentially minimize selection biases for the study of quasar evolution. We derive binned QLFs and characterize them using a double power-law model. Sample incompleteness and contamination are considered as part of the uncertainties in the calculation. Compared to previous results, our QLFs are slightly higher at the faint end, and also higher at the bright end at 2.5 < z < 3.5. The QLFs suggest that the quasar evolution at 1.0 < z < 2.5 can be well described by the pure luminosity evolution model, while at 2.5 < z < 3.5, it can be described by either the pure luminosity evolution or the pure density evolution model.

We present the fifth data release (DR5) of the Southern Photometric Local Universe Survey (S-PLUS), covering 4592 deg ² across 2491 fields. Observations were conducted with the T80-South, a Brazilian robotic telescope equipped with the Javalambre 12-filter system, containing five broadband and seven narrowband filters. Data products feature FITS images and extensive catalogs containing fluxes, magnitudes, and shape parameters for over 113 million detections. In addition, several value-added catalogs are provided, offering photometric redshifts (photo- zs ), object classifications, masks, and extinction coefficients. For the first time, this release includes coverage of 110 deg ² along the Galactic disk, facilitating new research into Galactic structure and stellar populations. The release also provides full coverage of the Hydra Supercluster and numerous other nearby clusters with improved data reduction and calibration, enhancing photo- z accuracy, which is vital for large-scale structure studies. A preliminary analysis of the Hydra and Antlia galaxy clusters up to 5 × R ₂₀₀ yields an updated catalog of 1706 cluster members based on both spectroscopic and high-quality photo- zs . Our photometric data shows that both clusters have a similar proportion of galaxies with an H α excess relative to their clustercentric distance, though Hydra has a higher fraction near its center. Additionally, the spatial distribution of all objects in our sample highlights a bridge connecting both clusters. We verify that S-PLUS DR5 provides a solid foundation for future scientific investigations, ranging from solar system studies to cosmology.