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Abstract Changing-look active galactic nuclei (CL-AGNs) exhibit dramatic spectral variability on unexpectedly short timescales, challenging standard accretion flow models. Despite growing samples, the physical drivers of this extreme variability, and the potential link to host-galaxy properties, remain unknown. Regardless of the underlying mechanism, the transition between AGN-dominated and host-dominated spectra offers a unique opportunity to study relations between AGNs and their hosts within the same objects. We present intermediate-resolution spectroscopy of 23 CL-AGNs identified by the Sloan Digital Sky Survey V (SDSS-V), obtained with the Very Large Telescope/X-shooter and Gemini-N/GMOS. An analysis of the Mgiiλ2798 emission line observed in the spectra demonstrates that the majority of these sources cannot be driven by variable obscuration. Our CL-AGNs roughly follow theM_BH–σ_*andM_BH–M_*relations of inactive galaxies, with a median black hole-to-stellar mass ratio of 0.38 %. We find no evidence that the stellar population properties of our CL-AGNs, including stellar mass, age, young stellar fraction, and star formation rate, differ from those of type 2 AGNs in SDSS. These results suggest that CL-AGNs reside in typical AGN host galaxies and that their extreme variability is likely unrelated to host-galaxy environment, supporting the idea that CL-AGNs are not a distinct population, but rather represent a phase of normal AGN activity. This result, in turn, implies that CL-AGNs can serve as useful probes of the AGN-host connection, providing access to both AGN-dominated and host-dominated spectra of the same systems. 

ABSTRACT Broad absorption line (BAL) quasars are often considered X-ray weak relative to their optical/UV luminosity, whether intrinsically (i.e. the coronal emission is fainter) or due to large column densities of absorbing material. The SDSS-V is providing optical spectroscopy for samples of quasar candidates identified by eROSITA as well as Chandra, XMM, or Swift, making the resulting data sets ideal for characterizing the BAL quasar population within an X-ray selected sample. We use the Balnicity Index (BI) to identify the BAL quasars based on absorption of the C iv$$\lambda \, 1549$$ emission line in the optical spectra, finding 143 BAL quasars in our sample of 2317 X-ray selected quasars within $$1.5\le z \le 3.5$$. This observed BAL fraction of $$\approx$$ 6 per cent is comparable to that found in optically selected samples. We also identify absorption systems via the Absorption Index (AI) which includes mini-BALs and NALs, finding 954 quasars with AI $>0$. We consider the C iv emission space (equivalent width versus blueshift) to study the BAL outflows within the context of the radiatively driven accretion disc–wind model. X-ray selection excludes the highest outflow velocities in emission but includes the full range of absorption velocities which we suggest is consistent with the BAL gas being located further from the X-ray corona than the emitting gas. We observe both X-ray weak and X-ray strong BALs (via the optical-to-X-ray spectral slope, $$\alpha _\text{ox}$$) and detect little evidence for differing column densities between the BAL and non-BAL quasars, suggesting the BALs and non-BALs have the same shielding gas and intrinsic X-ray emission. 

ABSTRACT We present an investigation of the rest-frame optical/UV and X-ray properties for a sample of 3027 X-ray selected quasars between $$1.5 \le z \le 3.5$$ detected in the deepest Spectrum Roentgen Gamma/eROSITA data available and observed by the fifth iteration of the Sloan Digital Sky Survey (SDSS-V). We parametrize the C iv $$\lambda 1549$$ emission line to infer the strength of accretion disc winds and perform X-ray spectral fitting. The X-ray spectral properties – namely, the 2 keV monochromatic luminosity ($$L_{2\, \text{keV}}$$) and spectral slope – are not strongly correlated with wind strength. Despite this result, the X-ray selected sample is shifted towards lower C iv blueshifts and higher equivalent widths than the optically selected sample observed in previous SDSS surveys, and matching in optical luminosity, redshift, and Eddington ratio does not reduce these differences. We estimate the far-UV luminosity using the He ii $$\lambda 1640$$ line luminosity and define the slopes between this and the 2500 Å monochromatic luminosity ($$L_{2500}$$) and $$L_{2\, \text{keV}}$$ ($$\alpha _\text{ouv}$$ and $$\alpha _\text{uvx}$$, respectively) in a similar manner to the familiar $$\alpha _\text{ox}$$ parameter, which tracks the spectral slope between $$L_{2500}$$ and $$L_{2\, \text{keV}}$$. The quantity $$\alpha _\text{ouv}$$ is more strongly correlated with wind strength in our sample than $$\alpha _\text{ox}$$. We show that the correlation between $$\alpha _\text{ox}$$ and wind strength is driven by the relationship between the optical luminosity and wind strength. Our results are consistent with a radiation line-driven wind, whereby the ionizing far-UV photons must not over-ionize the gas. The hard X-ray photons are few enough in number to have a negligible effect on the ionization state of the material. 

We present and discuss optical emission line properties obtained from the analysis of spectra obtained in the Sloan Digital Sky Survey (SDSS) for an X-ray-selected sample of 3684 galaxies (0.002 < z < 0.55) that were drawn from the eRASS1 catalog. We modeled the SDSS-V DR19 spectra using the NBURSTSfull spectrum-fitting technique with E-MILES simple stellar population models and emission line templates to decompose the broad and narrow emission line components for a correlation with the X-ray properties. We placed the galaxies on the Baldwin-Phillips-Terlevich (BPT) diagram to diagnose their dominant excitation mechanism. We show that the consistent use of the narrow component fluxes shifts most galaxies systematically and significantly upward to the active galactic nucleus (AGN) region in the BPT diagram. On this basis, we confirm the dependence of the position of a galaxy in the BPT diagram on its (0.2 − 2.3 keV) X-ray/Hαflux ratio. We also verified the correlation between the X-ray luminosity and the emission line luminosities of the narrow [O III]λ5007 and broad Hαcomponent and the relations between the supermassive black hole mass, the X-ray luminosity, and the velocity dispersion of the stellar component (σ_*) on the base of the unique sample of optical spectroscopic follow-up of X-ray sources detected by eROSITA. These results highlight the importance of emission line decomposition in the AGN classification and refine the connection between X-ray emission and optical emission line properties in galaxies. 

Which galaxies in the general population turn into active galactic nuclei (AGNs) is a keystone of galaxy formation and evolution. Thanks to SRG/eROSITA’s contiguous 140 square degree pilot survey field, we constructed a large, complete, and unbiased soft X-ray flux-limited ( F X  > 6.5 × 10 −15 erg s −1 cm −2 ) AGN sample at low redshift, 0.05 <  z  < 0.55. Two summary statistics, the clustering using spectra from SDSS-V and galaxy-galaxy lensing with imaging from HSC, are measured and interpreted with halo occupation distribution and abundance matching models. Both models successfully account for the observations. We obtain an exceptionally complete view of the AGN halo occupation distribution. The population of AGNs is broadly distributed among halos with a mean mass of 3.9 −2.4 +2.0  × 10 12   M ⊙ . This corresponds to a large-scale halo bias of b ( z  = 0.34) = 0.99 −0.10 +0.08 . The central occupation has a large transition parameter, σ log 10 ( M )  = 1.28 ± 0.2. The satellite occupation distribution is characterized by a shallow slope, α sat  = 0.73 ± 0.38. We find that AGNs in satellites are rare, with f sat  < 20%. Most soft X-ray-selected AGNs are hosted by central galaxies in their dark matter halo. A weak correlation between soft X-ray luminosity and large-scale halo bias is confirmed (3.3 σ ). We discuss the implications of environmental-dependent AGN triggering. This study paves the way toward fully charting, in the coming decade, the coevolution of X-ray AGNs, their host galaxies, and dark matter halos by combining eROSITA with SDSS-V, 4MOST, DESI, LSST, and Euclid data. 

Abstract We present the COSMOS Spectroscopic Redshift Compilation encompassing ∼20 yr of spectroscopic redshifts within a 10 deg²area centered on the 2 deg²COSMOS legacy field. This compilation contains 487,666 redshifts of 266,284 unique objects from 138 individual programs up toz ∼ 8 with median stellar mass ∼10^8.4–10¹⁰M_⊙(redshift dependent). Rest-frameNUVrJcolors and star formation rate–stellar mass correlations show that the compilation primarily contains low-to-intermediate-mass star-forming and massive, quiescent galaxies atz < 1.25 and mostly low-mass bursty star-forming galaxies atz > 2. Sources in the compilation cover a diverse range of environments, including protoclusters such as “Hyperion.” The full compilation is 50% spectroscopically complete byi ∼ 23.4 mag andK_s ∼ 21.6 mag; however, this is redshift dependent. Spatially, the compilation is >50% (>30%) complete within the central (outer) region limited toi < 24 mag andK_s < 22.5 mag, separately. We demonstrate how the compilation can be used to validate photometric redshifts and investigate calibration metrics. By training self-organizing maps on COSMOS2020/Classic and projecting the compilation onto it, we find key subpopulations currently lacking spectroscopic coverage, includingz < 1 intermediate-mass quiescent and low-/intermediate-mass bursty star-forming galaxies,z ∼ 2 massive quiescent galaxies, andz > 3 massive star-forming galaxies. This highlights how combining self-organizing maps with our compilation can provide guidance for future spectroscopic observations to get a complete spectroscopic view of galaxy populations. Lastly, the compilation will undergo periodic data releases incorporating new spectroscopic redshifts and providing a lasting legacy resource for the community. 

Abstract High-quality Extragalactic Legacy-field Monitoring (HELM) is a long-term observing program that photometrically monitors several well-studied extragalactic legacy fields with the Dark Energy Camera (DECam) imager on the CTIO 4 m Blanco telescope. Since 2019 February, HELM has been monitoring regions within COSMOS, XMM-LSS, CDF-S, S-CVZ, ELAIS-S1, and SDSS Stripe 82 with few-day cadences in the (u)gri(z) bands, over a collective sky area of ∼38 deg². The main science goal of HELM is to provide high-quality optical light curves for a large sample of active galactic nuclei (AGNs), and to build decades-long time baselines when combining past and future optical light curves in these legacy fields. These optical images and light curves will facilitate the measurements of AGN reverberation mapping lags, as well as studies of AGN variability and its dependencies on accretion properties. In addition, the time-resolved and coadded DECam photometry will enable a broad range of science applications from galaxy evolution to time-domain science. We describe the design and implementation of the program and present the first data release that includes source catalogs and the first ∼3.5 yr of light curves during 2019A–2022A. 

Abstract Mapping the local and distant Universe is key to our understanding of it. For decades, the Sloan Digital Sky Survey (SDSS) has made a concerted effort to map millions of celestial objects to constrain the physical processes that govern our Universe. The most recent and fifth generation of SDSS (SDSS-V) is organized into three scientific “mappers”: the Milky Way Mapper, which aims to chart the various components of the Milky Way and constrain its formation and assembly; the Black Hole Mapper, which focuses on understanding supermassive black holes in distant galaxies across the Universe; and the Local Volume Mapper, which uses integral field spectroscopy to map the ionized interstellar medium in the Local Group. This paper describes the scope and content for the nineteenth data release (DR19) of SDSS, which is the most substantial to date in SDSS-V. DR19 is the first to contain data from all three mappers. Additionally, we also describe nine value-added catalogs that enhance the science that can be conducted with the SDSS-V data. Finally, we discuss how to access SDSS DR19 and provide illustrative examples and tutorials.