Search

Context. Ultra-fast outflows (UFOs) have been revealed in a large number of active galactic nuclei (AGN) in the past two decades. Their extreme velocities and high ionization states make them a promising candidate for AGN feedback on the evolution of the host galaxy. However, their exact underlying driving mechanism is not yet fully understood. Aims. Given that the variability of UFOs may be used to distinguish among different launching mechanisms, we aim to search for and characterize the responses of the UFO properties to the variable irradiating luminosity. Methods. We perform a high-resolution time- and flux-resolved spectroscopy of archival XMM-Newton observations on six highly accreting narrow-line Seyfert 1 (NLS1) galaxies, selected by UFO detection and sufficient exposure times. The state-of-the-art methods of the blind Gaussian line scan and photoionization model scan are used to identify UFO solutions. We search for ionized winds and investigate the structure of ionized winds and their responses to the luminosity variations. The location, density, and kinetic energy of UFOs are estimated as well. Results. The powerful photoionization model scan reveals three previously unreported UFOs in RE J1034+396, PG 1244+026 and I ZW 1 with a detection significance above 3σ, and two new warm absorbers (WAs) in RE J1034+396. Five out of six (83%) AGN in our sample host multi-phase ionized winds, where outflows in I ZW 1 are energy-conserved. The relatively low-ionization entrained UFOs are discovered in four (66%) AGN of our sample, supporting the shocked outflow interpretation for ionized winds in AGN. We notice that two out of seven (28%) UFOs in our sample seem to respond to the radiation field and three (43%) UFOs hint at a radiatively accelerated nature, requiring further observations. Combined with published works, we do not find any correlations between UFO responses and AGN properties except for a tentative (∼1.8σ) anti-correlation between the UFO acceleration and the Eddington ratio, to be confirmed by further observations and an enlarged sample. The kinetic energy of UFOs, mostly detected in soft X-rays, is found to have a large uncertainty. We, therefore, cannot conclude whether soft X-ray UFOs have sufficient energy to drive the AGN feedback, although they are very promising based on some reasonable assumptions. The primary UFO in I ZW 1 (detected in the hard X-ray) is the only case in our sample to possess conclusively sufficient energy to affect the host galaxy. [ABSTRACT FROM AUTHOR]

We present a selection technique to detect Compton-thick (CT) active galactic nuclei (AGNs) in the 3XMM/SDSS-DR7 cross-correlation. A subsample of 3481 X-ray sources that are detected in the hard band (2–8 keV) and have photometric redshifts constitute our parent sample. We first applied an automated spectral-fitting procedure to select highly absorbed sources (N H > 1023 cm−2). We found 184 highly absorbed candidates. Then, we performed the Bayesian Monte Carlo Markov chains (MCMCs) selection technique to find CT AGNs. We also tested the MCMC selection technique by applying Monte Carlo simulations. We found that the method is accurate at 90 per cent independently of the nature of the underlying source. Our sample contains 52 bona fide CT AGNs. The CT AGNs were selected to have a range >0.75 of probability of being CT when either fitting with the two models Torus and MYTorus. About 75 per cent of CT AGNs in our sample had probabilities >90 per cent. From the spectral analysis, we significantly found an anticorrelation between the equivalent width of the neutral Fe K α line and the X-ray luminosity at 2–10 keV, the so-called X-ray Baldwin effect. [ABSTRACT FROM AUTHOR]

We present hydrodynamic simulations of the interstellar medium (ISM) within the circumnuclear disc (CND) of a typical active galactic nucleus (AGN)-dominated galaxy influenced by mechanical feedback from an AGN. The simulations are coupled with the CHIMES non-equilibrium chemistry network to treat the radiative-cooling and AGN-heating. A focus is placed on the central 100 pc scale where AGN outflows are coupled to the ISM and constrained by observational Seyfert-2 galaxies. AGN-feedback models are implemented with different wind-velocity and mass-loading factors. We post-process the simulation snapshots with a radiative-transfer code to obtain the molecular emission lines. We find that the inclusion of an AGN promotes the formation of CO in clumpy and dense regions surrounding supermassive black holes (SMBHs). The CO(1-0) intensity maps (<6 Myr) in the CND seem to match well with observations of NGC 1068 with a best match for a model with 5000 km s−1 wind-velocity and a high mass-loading factor. We attempt to discern between competing explanations for the apparent counter-rotating gas disc in the NGC 1068 through an analysis of kinematic maps of the CO line emission. We suggest that mechanical AGN-feedback could explain the alignment-stability of position-angle across the different CND radii around the SMBH through momentum and energy loading of the wind. It is the wind-velocity that drives the disc out of alignment on a 100 pc scale for a long period of time. The position–velocity diagrams are in broad agreement with the predicted Keplerian rotation-curve in the model without AGN, but the AGN models exhibit a larger degree of scatter, in better agreement with NGC 1068 observations. [ABSTRACT FROM AUTHOR]

Ultrafast outflows (UFOs) have been revealed in a large number of active galactic nuclei (AGN) and are regarded as promising candidates for AGN feedback on the host galaxy. The nature and launching mechanism of UFOs are not yet fully understood. Here we perform a time- and flux-resolved X-ray spectroscopy on four XMM–Newton observations of a highly accreting narrow-line Seyfert 1 (NLS1) galaxy, Mrk 1044, to study the dependence of the outflow properties on the source luminosity. We find that the UFO in Mrk 1044 responds to the source variability quickly and its velocity increases with the X-ray flux, suggesting a high-density (⁠|$10^{9}\!-\!4.5\times 10^{12}\, \mathrm{cm}^{-3}$|⁠) and radiatively driven outflow, launched from the region within a distance of |$98\!-\!6600\, R_\mathrm{g}$| from the black hole. The kinetic energy of the UFO is conservatively estimated (⁠|$L_\mathrm{UFO}\sim 4.4~{{\ \rm per\ cent}}\, L_\mathrm{Edd}$|⁠), reaching the theoretical criterion to affect the evolution of the host galaxy. We also find that emission lines, from a large-scale region, have a blueshift of 2700–4500 km s−1 in the spectra of Mrk 1044, which is rarely observed in AGN. By comparing with other sources, we propose a correlation between the blueshift of emission lines and the source accretion rate, which can be verified by a future sample study. [ABSTRACT FROM AUTHOR]

Compact symmetric objects (CSOs) show radio features such as jets, lobes, and hot spots, which are contained within their host galaxies, and likely represent a recent radio activity. A subpopulation of CSOs with high intrinsic X-ray column densities has been inferred from shallow, soft X-ray band exposures, and observed to cluster in the linear radio size versus 5 GHz radio power plane, which suggests that a dense circumnuclear medium may dramatically influence the growth of compact radio structures. Here, we report on the first detection of two CSOs, 2021+614 and J1511+0518, at energies above 10 keV with NuSTAR. We model the NuSTAR data jointly with the new XMM-Newton data of J1511+0518, and with the archival XMM-Newton data of 2021+614. A toroidal reprocessor model fits the data well and allows us to robustly confirm the X-ray properties of the CSO absorbers and continuum. In both sources, we find intrinsic X-ray absorbing column densities in excess of 1023 cm−2, hard photon indices of the primary emission, Γ ∼ 1.4–1.7, Fe K α line emission, and variability of the intrinsic X-ray flux density on the timescale of years. The studied X-ray continua are dominated by the primary power-law emission at energies above 3 keV, and by the scattered component at energies below 3 keV. An additional soft X-ray component, modeled with a hot, collisionally ionized plasma with temperature kT ∼ 1 keV, is required by the XMM-Newton data in J1511+0518, which is corroborated by the tentative evidence for the extension in the archival Chandra image of the source. [ABSTRACT FROM AUTHOR]

We present a study of optically selected dual Active Galactic Nuclei (AGN) with projected separations of 3–97 kpc. Using multiwavelength (MWL) information (optical, X-ray, mid-IR), we characterized the intrinsic nuclear properties of this sample and compared them with those of isolated systems. Among the 124 X-ray-detected AGN candidates, 52 appear in pairs and 72 as single X-ray sources. Through MWL analysis, we confirmed the presence of the AGN in >80 per cent of the detected targets in pairs (42 out of 52). X-ray spectral analysis confirms the trend of increasing AGN luminosity with decreasing separation, suggesting that mergers may have contributed to triggering more luminous AGN. Through X-ray/mid-IR ratio versus X-ray colours, we estimated a fraction of Compton-thin AGN (with 1022 cm−2 < N H < 1024 cm−2) of about 80 per cent, while about 16 per cent are Compton-thick sources (with N H > 1024 cm−2). These fractions of obscured sources are larger than those found in samples of isolated AGN, confirming that pairs of AGN show higher obscuration. This trend is further confirmed by comparing the de-reddened [O  iii ] emission with the observed X-ray luminosity. However, the derived fraction of Compton-thick sources in this sample at the early stages of merging is lower than that reported for late-merging dual-AGN samples. Comparing N H from X-rays with that derived from E (B − V) from narrow-line regions, we found that the absorbing material is likely to be associated with the torus or broad-line regions. We also explored the X-ray detection efficiency of dual-AGN candidates, finding that, when observed properly (at on-axis positions and with long exposures), X-ray data represent a powerful way to confirm and investigate dual-AGN systems. [ABSTRACT FROM AUTHOR]

While theory and simulations indicate that galaxy mergers play an important role in the cosmological evolution of accreting black holes and their host galaxies, samples of active galactic nuclei (AGNs) in galaxies at close separations are still small. In order to increase the sample of AGN pairs, we undertook an archival project to investigate the X-ray properties of an SDSS-selected sample of 32 galaxy pairs with separations ≤150 kpc containing one optically identified AGN, which were serendipitously observed by XMM–Newton. We discovered only one X-ray counterpart among the optically classified non-active galaxies, with a weak X-ray luminosity (≃ 5 × 1041 erg s−1). 59 per cent (19 out of 32) of the AGNs in our galaxy pair sample exhibit an X-ray counterpart, covering a wide range in absorption-corrected X-ray luminosity (5 × 1041–2 × 1044 erg s−1). More than 79 per cent of these AGNs are obscured (column density N H > 1022 cm−2), with more than half thereof (i.e. about 47 per cent of the total AGN sample) being Compton-thick. AGN/no-AGN pairs are therefore more frequently X-ray obscured (by a factor ≃1.5) than isolated AGNs. When compared to a luminosity and redshift-matched sample of bona fide dual AGN, AGN/no-AGN pairs exhibit one order-of-magnitude lower X-ray column density in the same separation range (>10 kpc). A small sample (4 objects) of AGN/no-AGN pairs with sub-pc separation is all heavily obscured, driving a formal anticorrelation between the X-ray column density and the galaxy pair separation in these systems. These findings suggest that the galactic environment has a key influence on the triggering of nuclear activity in merging galaxies. [ABSTRACT FROM AUTHOR]

We have investigated the nature and origin of the Fe K emission lines in Mrk 205 using observations with Suzaku and XMM–Newton , aiming to resolve the ambiguity between a broad emission line and multiple unresolved lines of higher ionization. We detect the presence of a narrow Fe K α emission line along with a broad-band Compton reflection hump at energies |$E\gt 10\rm \, \, {\rm keV}$|⁠. These are consistent with reflected emission of hard X-ray photons off a Compton-thick material of |$N_{\rm H}\ge 2.15\times 10^{24}\rm \, \, {\rm cm^{-2}}$|⁠. In addition we detect a partially covering ionized absorption with ionization parameter |$\log (\xi /\rm \, erg\, cm\, s^{-1})=1.9_{-0.5}^{+0.1}$|⁠ , column density |$N_{\rm H}=(5.6_{-1.9}^{+2.0})\times 10^{22}\rm \, \, {\rm cm^{-2}}$|⁠ , and a covering factor of |$0.22_{-0.06}^{+0.09}$|⁠. We detect the presence of emission arising out of ionized disc reflection contributing in the soft and hard X-rays consistently in all the observations. We however, could not definitely ascertain the presence of a relativistically broadened Fe line in the X-ray spectra. Using relativistic reflection models, we found that the data are unable to statistically distinguish between the scenarios when the supermassive black hole is non-rotating and when it is maximally spinning. Using the disc reflection model we also find that the accretion disc of the active galactic nucleus may be truncated at a distance 6 R G < R < 12 R G, which may suggest why there may not be any broad Fe line. The Eddington rate of the source is low (λEdd = 0.03), which points to an inefficient accretion, possibly due to a truncated disc. [ABSTRACT FROM AUTHOR]

The observed spatial and kinematic overlap between soft X-ray emission and the narrow-line region (NLR) in obscured active galactic nuclei (AGNs) yields compelling evidence that relatively low-density gas co-exists with higher density gas on scales as large as 100 s of pc. This is commonly interpreted as evidence for a constant gas pressure multiphase medium, likely produced by thermal instability. Alternatively, radiation pressure compression (RPC) also leads to a density distribution, since a gas pressure (and hence density) gradient must arise within each cloud to counteract the incident ionizing radiation pressure. RPC leads to a well-defined ionization distribution, and a differential emission measure (DEM) distribution with a universal slope of ∼−0.9, weakly dependent on the gas properties and the illuminating radiation field. In contrast, a multiphase medium does not predict the form of the DEM. The observed DEMs of obscured AGN with XMM – Newton Reflection Grating Spectrometer spectra (the CHRESOS sample) are in striking agreement with the predicted RPC DEM, providing a clear signature that RPC is the dominant mechanism for the observed range of densities in the X-ray NLR. In contrast with the constant gas pressure multiphase medium, RPC further predicts an increasing gas pressure with decreasing ionization, which can be tested with future X-ray missions using density diagnostics. [ABSTRACT FROM AUTHOR]

Context. High-resolution X-ray spectroscopy has advanced our understanding of the hot Universe by revealing physical properties like kinematics, temperature, and abundances of the astrophysical plasmas. Despite technical and scientific achievements, the lack of scientific products at a level higher than count spectra is hampering complete scientific exploitation of high-quality data. This paper introduces the Catalog of Ionized Emission Lines Observed by the Reflection Grating Spectrometer (CIELO-RGS) onboard the XMM-Newton space observatory. Aims. The CIELO-RGS catalog aims to facilitate the exploitation of emission features in the public RGS spectra archive. In particular, we aim to analyze the relationship between X-ray spectral diagnostics parameters and measurements at other wavelengths. This paper focuses on the methodology of catalog generation, describing the automated line-detection algorithm. Methods. A moderate sample (∼2400 observations) of high-quality RGS spectra available at XMM-Newton Science Archive is used as our starting point. A list of potential emission lines is selected based on a multi-scale peak-detection algorithm in a uniform and automated way without prior assumption on the underlying astrophysical model. The candidate line list is validated via spectral fitting with simple continuum and line profile models. We also compare the catalog content with published literature results on a small number of exemplary sources. Results. We generate a catalog of emission lines (1.2 × 104) detected in ∼1600 observations toward stars, X-ray binaries, supernovae remnants, active galactic nuclei, and groups and clusters of galaxies. For each line, we report the observed wavelength, broadening, energy and photon flux, equivalent width, and so on. [ABSTRACT FROM AUTHOR]

We report on an optical (SDSS) and X-ray (XMM- Newton) study of an optically selected sample of four dual AGN systems at projected separations of 30–60 kpc. All sources are detected in the X-ray band (0.3–10keV); seven objects are optically identified as Seyfert, while one source, optically classified as a low-ionization nuclear emission-line region (LINER), is likely powered by accretion in virtue of its relatively high X-ray luminosity (1.2 × 1041 erg s−1). Six of the eight objects are obscured in X-rays with N H ≥ 1023 cm−2; three of these, whose X-ray spectrum is dominated by a reflection component, are likely Compton-thick (N H ≥ 1024 cm−2). This finding is in agreement with the hypothesis that galaxy encounters are effective in driving gas inflow toward the nuclear region, thus increasing the obscuration. We compare the absorption properties in our dual AGN with those in larger samples observed in X-rays but selected in different ways (optical, IR, and hard X-rays). We find that the obscured (N H ≥ 1022 cm−2) AGN fraction within the larger sample is 84 ± 4 per cent (taking into account the 90 per cent error on the N H measure) up to large pair separations (∼100 kpc). This is statistically higher than the fraction of obscured AGN in isolated galaxies found in X-ray surveys. [ABSTRACT FROM AUTHOR]

We have carried out a systematic X-ray spectral analysis of a sample of low-luminosity quasars (LLQSO) to investigate the nature of the central engines of these sources. The optically selected LLQSO sample consists of close, known bright active galactic nuclei (AGN) which serves as an important link between the powerful quasars at higher redshift and local Seyfert galaxies. We find that although the bolometric luminosities of the LLQSOs are lower than those of the higher redshift quasars by almost an order of magnitude, their distribution of the Eddington rate $$\lambda _{\rm \, Edd}$$ is similar. We detect a strong anticorrelation between αOX and $$L_{2500 \mathring{\rm A}}$$, as has also been detected in several other quasar studies with large sample sizes, indicating that as the UV luminosity of the source increases, the X-ray luminosity decreases. We do not detect any significant neutral obscuration ($$N_{\rm H}\ge 10^{22}\rm \, \, {\rm cm^{-2}}$$) in the X-ray spectra of the LLQSOs, and hence rule out obscuration as a possible cause for their lower luminosity. We conclude that the central engines of the LLQSOs function similarly to those of the higher redshift quasars, and the difference is possibly because of the fact that the LLQSOs have lower black hole masses. We do not find any correlation between the molecular gas in the host galaxies and accretion states of the AGN. This indicates that the presence of molecular gas in the host galaxies of the LLQSOs does not significantly influence the instantaneous accretion rates of their SMBHs. [ABSTRACT FROM AUTHOR]

We present a multi-epoch X-ray spectroscopy analysis of the nearby narrow-line Seyfert I galaxy NGC 5506. For the first time, spectra taken by Chandra, XMM–Newton, Suzaku, and NuSTAR– covering the 2000–2014 time span – are analysed simultaneously, using state-of-the-art models to describe reprocessing of the primary continuum by optical thick matter in the active galactic nucleus environment. The main goal of our study is determining the spin of the supermassive black hole (SMBH). The nuclear X-ray spectrum is photoelectrically absorbed by matter with column density ≃ 3 × 1022 cm−2. A soft excess is present at energies lower than the photoelectric cut-off. Both photoionized and collisionally ionized components are required to fit it. This component is constant over the time-scales probed by our data. The spectrum at energies higher than 2 keV is variable. We propose that its evolution could be driven by flux-dependent changes in the geometry of the innermost regions of the accretion disc. The black hole spin in NGC 5506 is constrained to be 0.93 $\pm _{ 0.04 }^{0.04}$ at 90 per cent confidence level for one interesting parameter. [ABSTRACT FROM AUTHOR]

I briefly review in this paper the main observational properties of relativistically broadened X-ray spectral lines in Galactic Black Holes and Active Galactic Nuclei, and the (scanty) estimates of their frequency in the corresponding parent populations. The available measurements allow us to derive some constraints on the black hole spin and mass, and on the accretion disk geometry and illumination. [ABSTRACT FROM AUTHOR]

Examines the formerly X-ray reflection-dominated Seyfert 2 galaxy NGC 6300. Class of transient active galactic nucleus; Nature of the X-ray absorbers in the galaxy; Association of the bulk of the iron line observed in the galaxy with Compton-thick matter.

The quest for binary and dual supermassive black holes (SMBHs) at the dawn of the multi-messenger era is compelling. Detecting dual active galactic nuclei (AGN) – active SMBHs at projected separations larger than several parsecs – and binary AGN – probing the scale where SMBHs are bound in a Keplerian binary – is an observational challenge. The study of AGN pairs (either dual or binary) also represents an overarching theoretical problem in cosmology and astrophysics. The AGN triggering calls for detailed knowledge of the hydrodynamical conditions of gas in the imminent surroundings of the SMBHs and, at the same time, their duality calls for detailed knowledge on how galaxies assemble through major and minor mergers and grow fed by matter along the filaments of the cosmic web. This review describes the techniques used across the electromagnetic spectrum to detect dual and binary AGN candidates and proposes new avenues for their search. The current observational status is compared with the state-of-the-art numerical simulations and models for formation of dual and binary AGN. Binary SMBHs are among the loudest sources of gravitational waves (GWs) in the Universe. The search for a background of GWs at nHz frequencies from inspiralling SMBHs at low redshifts, and the direct detection of signals from their coalescence by the Laser Interferometer Space Antenna in the next decade, make this a theme of major interest for multi-messenger astrophysics. This review discusses the future facilities and observational strategies that are likely to significantly advance this fascinating field. [ABSTRACT FROM AUTHOR]