This paper presents the twentieth data release (DR20) from the Sloan Digital Sky Survey, the third data release of its fifth generation (SDSS-V). SDSS-V is a panoptic spectroscopy survey that is mapping the stars, gas, and galaxies through three scientific programs: the Milky Way Mapper (MWM), the Local Volume Mapper (LVM), and the Black Hole Mapper (BHM). DR20 presents the first optical (BOSS) SDSS-V spectra from southern hemisphere for the MWM and BHM surveys; new optical MWM and BHM data from the northern hemisphere are also available, for a total over 3 million spectra of 1.5 million stars and half a million galaxies and quasars, with galactic and extragalactic x-ray targets coordinate with eROSITA DR2. DR20 includes integral field spectroscopy maps from LVM of six targets and 169 tiles, spanning Galactic HII regions, planetary nebulae, and nearby galaxies. Additionally, eighteen value added catalogs are also released with DR20, based on SDSS-V MWM and BHM data, and we present a new LVM visualization tool including an RGB HiPS map as a value added product.

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 <= z <= 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 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 Heii A1640 line luminosity and define the slopes between this and the 2500 & Aring; monochromatic luminosity ( L-2500 ) and L-2 keV (alpha(ouv )and alpha(uvx), respectively) in a similar manner to the familiar alpha ox parameter, which tracks the spectral slope between L2500 and L2 keV. The quantity alpha(ouv )is more strongly correlated with wind strength in our sample than alpha(ox). We show that the correlation between alpha 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.

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 Mg ii lambda 2798 emission line observed in the spectra demonstrates that the majority of these sources cannot be driven by variable obscuration. Our CL-AGNs roughly follow the MBH-sigma* and MBH-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.

Red quasars (rQSOs) have been recognized as a short-lived, early stage in the evolutionary cycle of Active Galactic Nuclei (AGN), with fundamental differences in their intrinsic properties compared to blue quasars (bQSOs). In this work, we present the first large X-ray sample of 380 rQSOs, selected from the eROSITA/SDSS-V collaboration, providing uniform X-ray detection with optical spectroscopy accros half the sky, in the German hemisphere of eROSITA. We combine X-ray imaging, optical spectroscopy, and multi-wavelength photometry to fully probe the accretion, absorption and host properties of rQSOs. Independent Component Analysis is used to reconstruct optical spectra in a data-driven and non-parametric approach, while accounting for dust reddening and host contamination. rQSOs are intrinsically X-ray weak compared to bQSOs, with a higher fraction found at low X-ray luminosities (over 50% of the rQSO sample have L_X < 10^43.5 erg s^-1). We investigate the relative X-ray strength of rQSOs by measuring the spectral slope indicator α_OX. Despite their suppressed X-ray emission, rQSOs are not optically faint, but show low α_OX values, indicating weak X-ray emission relative to their bright optical continua. X-ray spectral measurements reveal large gas column densities relative to optical reddening due to dust, implying that X-ray absorption could arise from dust-free gas close to the supermassive Black Hole (BH) rather than a classical dusty torus, while the dust responsible for optical reddening likely resides on larger host-galaxy scales or is associated with dusty gas carried in disc winds. rQSOs trace a phase of suppressed BH assembly relative to stellar mass growth, suggesting that they represent a distinct evolutionary stage where BH accretion is suppressed while the host galaxy continues to grow.

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.

The automated spectroscopic pipeline of the Sloan Digital Sky Survey (SDSS) systematically assigns Galactic star, galaxy, or typical quasar classifications to jet-dominated blazars, owing to the absence of a non-thermal jet continuum component in its template library. In this study, we present a new, physically motivated, multi-component spectral fitting pipeline that we apply to 746 optical counterparts of Fermi/4FGL-DR4 γ-ray sources in the SDSS-V Data Release 20 spectroscopic database, yielding 707 well-fitted blazar candidates dominated by Power-law+Galaxy (59.4

The Sloan Digital Sky Survey V (SDSS-V) is pioneering panoptic spectroscopy: it is the first all-sky, multiepoch, optical-to-infrared spectroscopic survey. SDSS-V is mapping the sky with multiobject spectroscopy (MOS) at telescopes in both hemispheres (the 2.5 m Sloan Foundation Telescope at Apache Point Observatory and the 100-inch du Pont Telescope at Las Campanas Observatory), where 500 zonal robotic fiber positioners feed light from a wide-field focal plane to an optical (R similar to 2000, 500 fibers) and a near-infrared (R similar to 22,000, 300 fibers) spectrograph. In addition to these MOS capabilities, the survey is pioneering ultra-wide-field (similar to 4000 deg(2)) integral field spectroscopy enabled by a new dedicated facility (LVM-I) at Las Campanas Observatory, where an integral field spectrograph (IFS) with 1801 lenslet-coupled fibers arranged in a 0 degrees.5-diameter hexagon feeds multiple R similar to 4000 optical spectrographs that cover 3600-9800 angstrom. SDSS-V's hardware and multiyear survey strategy are designed to decode the chemodynamical history of the Milky Way and tackle fundamental open issues in stellar physics in its Milky Way Mapper program, trace the growth physics of supermassive black holes in its Black Hole Mapper program, and understand the self-regulation mechanisms and the chemical enrichment of galactic ecosystems at the energy injection scale in its Local Volume Mapper program. The survey is well timed to multiply the scientific output from major all-sky space missions. The SDSS-V MOS programs began robotic operations in 2021; IFS observations began in 2023 with the completion of the LVM-I facility. SDSS-V builds on decades of heritage of SDSS's pioneering advances in data analysis, collaboration spirit, infrastructure, and product deliverables in astronomy.

Supermassive black holes (SMBHs) are observed in diverse galaxy populations across time yet a clear understanding of how they coevolve with their hosts has not been reached. Physically-motivated models of SMBH accretion and feedback vary widely between galaxy formation simulations due to the difficulty of modeling the range of scales important for galactic and SMBH processes. Here we use observational data to build an empirical model for SMBH growth. We apply observed specific accretion rate probability distributions as a function of galaxy star formation rate between z = 0-2 to the UniverseMachine galaxy formation model to determine SMBH accretion rates based on galaxy properties. We use observed z = 0 SMBH-stellar mass relations for the quiescent and star-forming populations to provide the local boundary conditions for SMBH growth histories. We then track the coevolutionary histories of galaxy stellar mass and their SMBHs backwards in time to z = 2. We find that the most massive SMBHs at z = 0 have grown very little of their total mass between z = 0-2, indicating early SMBH mass assembly for these systems. Conversely, lower mass SMBHs at z = 0 assembled their mass gradually across z = 0-2. This results in substantial evolution of the SMBH-stellar mass relation, shifting to higher normalization and shallower slope with increasing redshift. We find that the substantial scatter observed in the z = 0 SMBH-stellar mass relation results in the diversity of growth pathways found in our model, with some galaxies assembling their stellar mass before their SMBHs and others doing the opposite.

Understanding the AGN-galaxy co-evolution, feedback processes, and the evolution of Black Hole Accretion rate Density (BHAD) requires accurately estimating the contribution of obscured Active Galactic Nuclei (AGN). However, detecting these sources is challenging due to significant extinction at the wavelengths typically used to trace their emission. We evaluate the capabilities of the proposed far-infrared observatory PRIMA and its synergies with the X-ray observatory NewAthena in detecting AGN and in measuring the BHAD. Starting from X-ray background synthesis models, we simulate the performance of NewAthena and of PRIMA in Deep and Wide surveys. Our results show that the combination of these facilities is a powerful tool for selecting and characterising all types of AGN. While NewAthena is particularly effective at detecting the most luminous, the unobscured, and the moderately obscured AGN, PRIMA excels at identifying heavily obscured sources, including Compton-thick AGN (of which we expect 7500 detections per deg^2). We find that PRIMA will detect 60 times more sources than Herschel over the same area and will allow us to accurately measure the BHAD evolution up to z=8, better than any current IR or X-ray survey, finally revealing the true contribution of Compton-thick AGN to the BHAD evolution.

We present new methods to quantify the active galactic nucleus (AGN) population in terms of a multidimensional luminosity function that describes the space density of sources as a function of both X-ray and radio luminosity. We compile a sample of 1538 radio and X-ray detected extragalactic sources from the Bootes and COSMOS fields. First, we investigate the X-ray-radio luminosity correlation in the sample and find that an apparent correlation is introduced due to the sensitivity limits of the surveys; when considering individual redshift bins we find a wide range of radio luminosities associated with a given X-ray luminosity, and vice versa, indicating little direct connection between the emission processes. We then measure the X-ray luminosity function, radio luminosity function and multidimensional X-ray-radio luminosity function across redshift (0 < z < 6). We apply luminosity thresholds in X-ray and radio to restrict our sample to those in the AGN-dominated regime and explore how the fraction of radio-selected AGNs within the overall X-ray sample varies with increasing X-ray luminosity (and vice versa). We find that towards the highest X-ray and radio luminosities the fraction of sources with both an X-ray and radio detection increases towards 100 per cent, indicating that at the highest luminosities we are more likely to obtain a detection in both bands, though the source will not necessarily be bright in both bands. Thus, the most luminous accretion events are more likely to be associated with the production of a jet, despite the distinct physical structures that produce the emission and likely persist over very different time-scales.

We used a supervised machine learning algorithm (probabilistic random forest) to classify similar to 130 million sources in the VISTA Survey of the Magellanic Clouds (VMC). We used multiwavelength photometry from optical to far-infrared as features to be trained on, and spectra of active galactic nuclei (AGNs), galaxies and a range of stellar classes including from new observations with the Southern African Large Telescope (SALT) and South African Astronomical Observatory (SAAO) 1.9-m telescope. We also retain a label for sources that remain unknown. This yielded average classifier accuracies of similar to 79 per cent [Small Magellanic Cloud (SMC)] and similar to 87 per cent [Large Magellanic Cloud (LMC)]. Restricting to the 56 696 719 sources with class probabilities (P-class) > 80 per cent yields accuracies of similar to 90 per cent (SMC) and similar to 98 per cent (LMC). After removing sources classed as 'Unknown', we classify a total of 707 939 (SMC) and 397 899 (LMC) sources, including >77 600 extragalactic sources behind the Magellanic Clouds. The extragalactic sources are distributed evenly across the field, whereas the Magellanic sources concentrate at the centres of the Clouds, and both concentrate in optical/IR colour-colour/magnitude diagrams as expected. We also test these classifications using independent data sets, finding that, as expected, the majority of X-ray sources are classified as AGN (554/883) and the majority of radio sources are classed as AGN (1756/2694) or galaxies (659/2694), where the relative AGN-galaxy proportions vary substantially with radio flux density. We have found >49 500 hitherto unknown AGN candidates, likely including more AGN dust dominated sources which are in a critical phase of their evolution; >26 500 new galaxy candidates and >2800 new young stellar object (YSO) candidates.

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 <= z <= 3 . 5. This observed BAL fraction of approximate to 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(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 the redshift evolution of quasar luminosity functions (QLFs) decomposed by halo mass, galaxy mass, supermassive black hole (SMBH) mass, and Eddington ratio, as well as SMBH/radiative energy output ratios from trinity, a flexible empirical model that self-consistently infers the halo–galaxy–SMBH connection that match observational data. Key findings include: (1) The normalization of quasar luminosity function increases by ∼3–4 dex from z ∼ 10 to z ∼ 4, due to the fast mass build-up of different SMBH populations; (2) From z ∼ 4 to z ∼ 1, less massive galaxies and SMBHs make up bigger and bigger fractions of QLFs, due to the active galactic nuclei (AGNs) downsizing effect; (3) At z ∼ 0, massive haloes/galaxies/SMBHs are responsible for most bright quasars due to low Eddington ratios among all SMBHs; (4) The bright ends of QLFs are dominated by SMBHs that are at least 0.3 dex overmassive relative to the median SMBH mass–galaxy mass relation; (5) QLFs at z ∼ 6–7 are dominated by SMBHs accreting at Eddington ratios 0.1 < ηrad < 1, but super-Eddington AGNs contribute more significantly to QLFs towards z ∼ 9–10.

ABSTRACT In active galactic nuclei, the relationship between UV and X-ray luminosity is well studied (often characterised by αox) but often with heterogeneous samples. We have parametrized the intrinsic distribution of X-ray luminosity, LX, for the optically selected sample of SDSS quasars in the Stripe 82 and XXL fields across redshifts 0.5–3.5. We make use of the available XMM observations and a custom pipeline to produce Bayesian sensitivity curves that are used to derive the intrinsic X-ray distribution in a hierarchical Bayesian framework. We find that the X-ray luminosity distribution is well described by a Gaussian function in log10 LX space with a mean that is dependent on the monochromatic 2500 Å UV luminosity, L2500. We also observe some redshift dependence of the distribution. The mean of the LX distribution increases with redshift while the width decreases. This weak but significant redshift dependence leads to L2500–LX and L2500–αox relations that evolve with redshift, and we produce a redshift- and L2500-dependent αox equation. Neither black hole mass nor Eddington ratio appear to be potential drivers of the redshift evolution.

ABSTRACT We adopt a Bayesian X-ray spectral approach to investigate the accretion properties of unobscured ($20\lt \log (N_{\rm H}/{\rm cm}^{-2}\lt 22$) and obscured ($22\lt \log (N_{\rm H}/{\rm cm}^{-2}\lt 24$) active galactic nuclei (AGNs) to shed light on the orientation versus evolution scenarios for the origin of the obscuring material. For a sample of 3882 X-ray-selected AGN from the Chandra COSMOS Legacy, AEGIS, and CDFS extragalactic surveys, we constrain their stellar masses, $M_\star$, intrinsic X-ray luminosities, $L_{\rm X}$, obscuring column densities, $N_{\rm H}$, and specific accretion rates $\lambda \propto L_{\rm X}/M_\star$. By combining these observables within a Bayesian non-parametric approach, we infer, for the first time, the specific accretion rate distribution (SARD) of obscured and unobscured AGN to $z\approx 3$, i.e. the probability of a galaxy with mass $M_\star$ at redshift z hosting an AGN with column density $N_{\rm H}$ and specific accretion rate $\lambda$. Our findings indicate that (1) both obscured and unobscured SARDs share similar shapes, shifting towards higher accretion rates with redshift, (2) unobscured SARDs exhibit a systematic offset towards higher $\lambda$ compared to obscured SARD for all redshift intervals, (3) the obscured AGN fraction declines sharply at $\log \lambda _{\rm break} \sim -2$ for $z \lt 0.5$, but shifts to higher $\lambda$ values with increasing redshift, (4) the incidence of AGN within the theoretically unstable blow-out region of the $\lambda -N_{\rm H}$ plane increases with redshift. These observations provide compelling evidence for AGN ‘downsizing’ and radiation-regulated nuclear-scale obscuration with an increasing host galaxy contribution towards higher redshifts.

Supermassive black holes (BHs) are known to efficiently grow through gas accretion, but even sustained and intense mass build-up through this mechanism struggles to explain the assembly of the most massive BHs observed in the local Universe. Using the Chandra Deep-Wide Field Survey (CDFWS) in the Bo & ouml;tes field, we measure BH-galaxy assembly in massive galaxies (M star greater than or similar to 10(10)M(circle dot)) through the active galactic nucleus (AGN) fraction and specific black hole accretion rate (sBHAR) distribution as a function of redshift and stellar mass. We determine stellar masses and star formation rates for a parent sample of optically selected galaxies as well as those with X-ray detections indicating the presence of an AGN through spectral energy distribution (SED) fitting. We derive a redshift-dependent mass completeness limit and extract X-ray information for every galaxy as to provide a comprehensive picture of the AGN population in massive galaxies. While X-ray AGN samples are dominated by moderately massive host galaxies of M star >= 10(10)M(circle dot), we do not find a strong stellar mass dependence in AGN fraction (to limits in sBHAR), indicating a bias towards massive galaxies in the observed samples. We derive BH-galaxy growth tracks over time, which reveal that while most BH mass has been accumulated since z=4 for lower mass BHs, the assembly of the most massive BHs is more complex, with little to no relative mass gain since z=4, implying that rapid and intense growth episodes prior to z=4 were necessary to form these massive BHs.

We present a catalog of hard X-ray serendipitous sources detected in the first 80 months of observations by the Nuclear Spectroscopic Telescope Array (NuSTAR). The NuSTAR serendipitous survey 80 month (NSS80) catalog has an unprecedented ∼62 Ms of effective exposure time over 894 unique fields (a factor of 3 increase over the 40 month catalog, NSS40), with an areal coverage of ∼36 deg 2 , larger than all NuSTAR extragalactic surveys. NSS80 provides 1274 hard X-ray sources in the 3−24 keV band (822 new detections compared to the previous NSS40). Approximately 76% of the NuSTAR sources have lower-energy (<10 keV) X-ray counterparts from Chandra, XMM-Newton, and Swift-XRT. We have undertaken an extensive campaign of ground-based spectroscopic follow-up to obtain new source redshifts and classifications for 427 sources. Combining these with existing archival spectroscopy provides redshifts for 550 NSS80 sources, of which 547 are classified. The sample is primarily composed of active galactic nuclei (AGNs), detected over a large range in redshift ( z = 0.012–3.43), but also includes 58 spectroscopically confirmed Galactic sources. In addition, five AGN–galaxy pairs, one dual AGN system, one BL Lac candidate, and a hotspot of 4C 74.26 (radio quasar) have been identified. The median rest-frame 10−40 keV luminosity and redshift of NSS80 are 〈 L 10−40 keV 〉 = 1.2 × 10 44 erg s −1 and 〈 z 〉 = 0.56. We investigate the optical properties and construct composite optical spectra to search for subtle signatures not present in the individual spectra, finding an excess of redder BL AGNs compared to optical quasar surveys, predominantly due to the presence of the host galaxy and, at least in part, due to dust obscuration.

ABSTRACT We present predictions for the high-redshift halo–galaxy–supermassive black hole (SMBH) connection from the Trinity model. Matching a comprehensive compilation of galaxy (0 ≤ z ≤ 13) and SMBH data sets (0 ≤ z ≤ 6.5), Trinity finds: (1) The number of SMBHs with M• > 109 M⊙ in the observable Universe increases by five orders of magnitude from z ∼ 10 to z ∼ 2, and by another factor of ∼3 from z ∼ 2 to z = 0; (2) The M• > 109 and 1010 M⊙ SMBHs at z ∼ 6 live in haloes with ∼(2 − 3) and (3 − 5) × 1012 M⊙; (3) the newly discovered JWST AGN candidates at 7 ≲ z ≲ 11 are overmassive compared to the intrinsic SMBH mass–galaxy mass relation from Trinity, but they are still broadly consistent with Trinity predictions for flux limited AGN samples with Lauer bias. This bias favours the detection for overmassive SMBHs due to higher luminosities at a fixed Eddington ratio. However UHZ1’s M•/M* ratio is still some 1 dex higher than Trinity AGNs, indicating a discrepancy; (4) Trinity underpredicts the number densities of GN-z11 and CEERS_1019 analogues. But given the strong constraints from existing data in Trinity, the extra constraint from GN-z11 and CEERS_1019 does not significantly change trinity model results. (5) z = 6–10 quasar luminosity functions will reduce uncertainties in the trinity prediction of the z = 6–10 SMBH mass–galaxy mass relation by up to ∼0.5 dex. These luminosity functions will be available with future telescopes, such as Roman and Euclid.

Large X-ray observatories such as Chandra and XMM-Newton have been delivering scientific breakthroughs in research fields as diverse as our Solar System, the astrophysics of stars, stellar explosions and compact objects, accreting supermassive black holes, and large-scale structures traced by the hot plasma permeating and surrounding galaxy groups and clusters. The recently launched X-Ray Imaging and Spectroscopy Mission observatory is opening in earnest the new observational window of non-dispersive high-resolution spectroscopy. However, several questions remain open, such as the effect of the stellar radiation field on the habitability of nearby planets, the equation of state regulating matter in neutron stars, the origin and distribution of metals in the Universe, the processes driving the cosmological evolution of the baryons locked in the gravitational potential of dark matter and the impact of supermassive black hole growth on galaxy evolution, to mention just a few. Furthermore, X-ray astronomy has a key part to play in multimessenger astrophysics. Addressing these questions experimentally requires an order-of-magnitude leap in sensitivity, spectroscopy and survey capabilities with respect to existing X-ray observatories. This article succinctly summarizes the main areas where high-energy astrophysics is expected to contribute to our understanding of the Universe in the next decade and describes a new mission concept under study by the European Space Agency, the scientific community worldwide and two international partners (JAXA and NASA), designed to enable transformational discoveries: NewAthena. This concept inherits its basic payload design from a previous study carried out until 2022, Athena. This Perspective looks forwards to the next decade of X-ray astronomy, explaining how it will contribute to better understanding of the high-energy Universe. In this context, the authors describe the NewAthena mission, a concept led by the European Space Agency.

Much of the baryonic matter in the Universe, including the most active and luminous sources, are best studied in the X-ray band. Key advances in X-ray optics and detectors have paved the way for the Advanced X-ray Imaging Satellite (AXIS), a Probe-class mission that is a major improvement over Chandra, which has generated a steady stream of important discoveries for the past 2 decades. AXIS can be launched in the late 2020s and will transform our understanding in several major areas of astrophysics, including the growth and fueling of supermassive black holes, galaxy formation and evolution, the microphysics of cosmic plasmas, the time-variable universe, and a wide variety of cutting-edge studies. Relative to Chandra, the AXIS PSF is nearly twice as sharp on-axis; its field of view for subarcsecond imaging 70 times larger by area; its effective area at 1 keV is 10 times larger. The low-Earth orbit ensures a low and stable detector background, resulting in 50 times greater sensitivity than Chandra for extended sources. AXIS has a rapid repointing response with operations similar to Swift, but is 100 times more sensitive for time-domain science. These capabilities open up a vast discovery space and complement the next generation of astronomical observatories. A high-spectral-resolution mission (Athena) operating at the same time as a high-angular-resolution mission (AXIS) greatly increases the range of scientific discovery. AXIS will use lightweight X-ray optics made of thin single-crystal silicon mirrors developed at NASA Goddard. The detector array builds on a long legacy of X-ray CCD and provides improved photon localization, much faster readout time, and broader energy band. The estimated mission costs are consistent with the $1B Probe mission cost guideline.