Manda Banerji

Context . Active galactic nuclei (AGNs) play a crucial role in galaxy evolution, but they are a minority of extragalactic sources with diverse spectral energy distributions (SEDs), which depend on their means of selection. Upcoming large-scale surveys such as LSST will identify many AGNs, but analysis tools are not optimized for them. The limited number of photometric bands in these surveys impacts the calculation of photometric redshifts for AGNs, which are essential for scientific advancement. Aims . We use LePHARE to demonstrate the impact that a limited number of bands and erroneous assumptions have on the determination of the photometric redshifts of AGNs. We conducted tests on six AGN samples selected using X-ray, radio, infrared, variability, color, and spectroscopic criteria in the COSMOS field, using photometry from HSC-CLAUDS, which is closest in depth and wavelength coverage to LSST. Methods . We present the LSST pipeline for LePHARE within the redshift assessment infrastructure layers (RAIL), facilitating comparison between SED fitting and machine-learning algorithms. Results . AGNs that appear as point-like sources in optical data are assigned highly unreliable photometric redshifts if they are processed using galaxy templates. Additionally, shallow all-sky surveys (such as eROSITA, WISE, and ZTF) miss many AGNs. As a result, these “hidden” AGNs are often misidentified as galaxies in public survey data, leading to incorrect photometric redshifts. Conclusions . We provide the configurations that are suggested for each type of AGN alongside measures of expected performance as a function of redshift, magnitude, and selection. To facilitate studies with a panchromatic view of AGNs, we also released photometric redshifts and posterior distributions for all AGN sources identified in the COSMOS field using the six criteria, based on 28-band photometry.

Heavily reddened quasars (HRQs) are luminous, dust-obscured broad-line quasars thought to trace a short-lived phase of intense black hole growth and feedback. Previous studies have been limited by small sample sizes, which restricted robust statistical analyses of their properties. We expand the census of the most luminous HRQs to enable population-level studies, aiming to connect their spectral energy distributions (SEDs) to other luminous quasar populations and place them in the context of an evolutionary sequence for massive galaxy and black hole formation. We assembled multi-wavelength broadband photometry for the brightest (K_ ̊m AB $1.6. We employed -Gaia (Quaia) quasars, as well as luminous hot dust-obscured galaxies (hot DOGs). spectrophotometry to confirm the HRQs and determine redshifts. Detailed SED fitting allowed us to compare these HRQs to other luminous quasar populations, including a control sample of hyper-luminous, unobscured unWISE We confirm 76 new HRQs with redshifts of 1.53. A UV excess consistent with scattered quasar emission is detected in 76 per cent of HRQs. We conclusively demonstrate that HRQs are hot-dust poor compared to blue quasars of similar luminosities and redshifts. We find that the 6μ m continuum luminosities of HRQs are systematically lower at fixed 3000Å, continuum luminosity relative to blue Quaia quasars, suggesting that HRQs are deficient in both hot and warm dust components. This combination of depleted torus-scale dust reservoirs and higher luminosities compared to hot DOGs and blue quasars supports a scenario in which HRQs represent a blow-out phase, when strong feedback has begun to clear the central regions of obscuring material.

The slitless spectroscopy mode of the on board the Euclid telescope has enabled efficient spectroscopy of objects within a large field of view. Nevertheless, the relatively low spectral resolution, overlapping spectra, and contamination pose challenges to source classification and redshift determination using the spectra alone. In this work, we present a large and homogeneous sample of bright quasars identified from the Euclid Quick Data Release (Q1), constructed by combining high-purity candidate selections from to wavelengths without telluric lines, which will be pivotal to quasar spectral analysis. We obtained an empirical spectroscopic depth of JE łesssim 21.5 and ̋E łesssim 21.3 at the sensitivity of the Wide Field Survey, beyond which the number of securely identified quasars declines sharply. Accordingly, the sample presented in this paper comprises spectroscopically confirmed quasars brighter than these limits. We analysed morphological parameters from the Visible Camera (VIS) using Sérsic and model-independent (CAS) metrics, and a deep-learning point spread function fraction to track nuclear dominance. The VIS morphologies show a clear redshift dependence: at low redshift (z<0.5), obvious host structures are common and a single Sérsic model fits about half of the sources; at intermediate redshift (0.5<z<2), the nuclear component dominates, with 90% of the Sérsic fits saturating at the upper index limit. In this intermediate redshift regime, f_ nisp nisp and WISE with the new spectroscopic capabilities of Euclid. Through visual inspection of the Euclid spectra of these quasar candidates, we identify approximately 3500 quasars and determine reliable redshifts in the range of 0< z łesssim4.8. Of these, 2686 are new spectroscopic identifications relative to existing public compilations. We generated the first Euclid composite spectrum of quasars covering rest-frame nuv nir nir PSF is available, and we use it as a more reliable compactness measure than the single-Sérsic and CAS parameters to quantify nuclear versus host emission. We also explore the novel Euclid colour space and discuss the role of these quasars in refining active galactic nucleus selection techniques for future Euclid data releases. nir

We present a spectroscopic follow-up program targeting closely-separated dual quasar candidates selected from imaging of SDSS quasars with the Subaru Hyper Suprime-Cam Subaru Strategic Program (HSC-SSP). Using two-dimensional image decomposition, our selection identifies PSF-like companions within 0″.6–4″separation (≲ 30 kpc) around the SDSS quasar. We newly confirm six broad-line dual quasars and eleven offset quasars (quasar-galaxy pairs), spanning 1.5 < z < 3.3 for the duals and predominantly z < 0.6 for the offset systems. No obvious lensed quasars were discovered from this program. We obtained 99 spectra of these candidates from NTT/EFOSC2, Gemini/GMOS-N, Keck/NIRES, and Subaru/FOCAS. From the spectra, we measure the emission-line properties of these dual black holes (BH). At z > 1.5, the confirmed duals exhibit high black hole mass (M_BH =10^8.5–10¹⁰M_⊙) with high bolometric luminosities (L_bol =10^45.5–10^47.5 erg s⁻¹), yet accrete at moderate Eddington ratios (λ_Edd =0.01–0.4). From the spectroscopically-confirmed samples, we estimate the dual fraction of SDSS quasars with separations of 0.6″–4″ to be 0.2 %-1.2 % at z < 0.8, 0.08 %-0.24 % at 0.8 < z < 1.5, and 0.06 % at 1.5 < z < 3.3. These values are broadly consistent with other recent optical studies, but lower than theoretical expectations of a rising dual fraction at cosmic noon. However, we note that these fractions, especially at high z, still need a more accurate assessment of selection and observation effects.

We present a rest-ultraviolet to infrared spectral energy distribution (SED) analysis of 63 heavily reddened quasars (HRQs) at redshifts z=0.7-2.7 and with dust extinctions E(B-V)=0.4-1.8. Our analysis demonstrates that SEDs with red optical and blue UV continua are very common in HRQs, with more than 82 per cent of the sample showing a UV-excess relative to the reddened quasar continuum. We model the SEDs by combining a reddened quasar and an unobscured scattered light component, though contributions from a star-forming host galaxy cannot be ruled out. The average scattering fraction is small (0.3 per cent). Higher scattering fractions are ruled out by the (i-K)=2.5 colour-cut used to select HRQs which pre-dates the discovery of the JWST "Little Red Dot" (LRD) population. Hence, LRDs generally have bluer UV continua. Nevertheless, four HRQs satisfy the LRD UV/optical continuum slope selections and are therefore massive, cosmic noon analogues of LRDs. Analysis of the near-infrared SEDs of HRQs reveals a deficit of hot dust relative to blue quasars, similar to what is observed in LRDs. This suggests HRQs trace a phase where strong AGN feedback processes eject dust from the inner torus. The UV scattering fraction of HRQs is weakly correlated with the amount of hot dust emission and anti-correlated with the line-of-sight extinction, E(B-V). This is consistent with the hot dust acting as the scattering medium, and the line-of-sight extinction being dominated by dust on interstellar medium scales in the host galaxy.

Near-infrared imaging is a powerful technique in observational astronomy, but the bright background – primarily from the Earth’s atmosphere – makes the detection of faint features particularly challenging. To recover low surface brightness (LSB) structures in such data, we present NASIM (Near-infrared Automated low Surface brightness reduction In Maneage), a fully automated and reproducible data reduction pipeline optimised for VISTA/VIRCAM observations. NASIM builds on advanced techniques from the GNU Astronomy Utilities (Gnuastro) to effectively remove large-scale instrumental artefacts and detector patterns while preserving faint, diffuse emission crucial for LSB science. As a key science application, we focus on the deep K_s-band observations of the Euclid Deep Field South (KEDFS), one of the deepest VISTA/VIRCAM datasets and a high-priority field for synergy with current and future facilities, including Euclid, JWST, LSST, Roman, Spitzer, and ALMA. Situated near the South Ecliptic Pole, KEDFS offers favourable conditions for deep extragalactic observations due to minimal Galactic foreground contamination. With VIRCAM no longer operational, it now stands as a unique and irreplaceable legacy dataset for near-infrared astronomy. We release selected tiles from the KEDFS survey and highlight representative science cases – including galaxy outskirts, LSB galaxies, and intracluster light – that demonstrate NASIM’s ability to recover diffuse structures. Our reduction reaches a surface brightness limit of ∼27.7 mag arcsec^-2 (3σ over 100 arcsec²) in the K_s band, approximately 67 times deeper than 2MASS and 11 times deeper than VISTA Hemisphere Survey (VHS). A direct comparison with conventional VISTA data reduction pipelines demonstrates the advantages of NASIM in preserving diffuse emission without compromising compact source detection. All quantitative results presented in this paper are fully reproducible with Maneage (commit a02b40dd).

We present a study of the molecular gas in five closely-separated (R⊥ < 20 kpc) dual quasars (Lbol ≳ 1044 erg s−1) at redshifts 0.4 < z < 0.8 with the Atacama Large Millimeter/submillimeter Array. The dual quasar phase represents a distinctive stage during the interaction between two galaxies for investigating quasar fueling and feedback effects on the gas reservoir. The dual quasars were selected from the Sloan Digital Sky Survey and Subaru/Hyper Suprime-Cam Subaru Strategic Program, with confirmatory spectroscopic validation. Based on the detection of the CO J=2–1 emission line with Band 4, we derive key properties including CO luminosities, line widths, and molecular gas masses for these systems. Eight quasars, of the ten in pairs, have line detections exceeding 5σ that result in molecular gas masses (Mmolgas) between 109.7 − 10.7 M⊙. The molecular gas-to-stellar mass ratios (μmolgas) of these dual quasars are between 18-50% with the exception of 301%, which are similar to the single quasars in mergers and inactive star-forming galaxies. The results indicate no clear evidence of molecular gas depletion attributed to dual quasar activities on global scale. However, intriguing gas features in certain systems appear to show possible signatures of AGN feedback effect.