A dust condensation instability in AGN atmospheres: failed winds and the broad line region

view Abstract Citations (35) References (111) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Gas Clouds from Tidally Disrupted Stars in Active Galactic Nuclei Roos, Nico Abstract A direct implication of the presence of massive black holes in galactic nuclei is the occasional tidal disruption of a star in the vicinity of the hole. The tidal disruption rate will be enhanced as a result of perturbations of the star cluster around the hole (for instance during the final stage of a merger with a smaller galaxy) leading to prolonged periods of activity. Recent investigations of the tidal break- up of solar-type stars near massive black holes have shown that debris gas will be distributed throughout the galactic nucleus. About half of the stellar debris mass is strongly bound to the hole and will quickly be swallowed while the rest is expelled with typical velocities of order 5000M^1/6^_6_ km s^-1^, where M_6_ = M_hole_/10^6^ M_sun_. In this paper the structure and properties of freely expanding (unbound) remnant clouds irradiated by the central continuum source of an AGN are explored. It is argued that the remnant cloud fragments into cold clumps of gas (T~10^4^K) surrounded by hot gas at the Compton temperature (T_c_~10^7-8^K) when the ionization parameter {XI} (defined as the ratio of the ionizing radiation pressure to the gas pressure) reaches the critical value {XI}_c_ ~ 10. Subsequently the fraction of hot gas slowly increases at the expense of the cold component while the ionization parameter of both components remains equal to {XI}_c_. Photoionization of cold gas in the outmoving and radially elongated remnant clouds produces a broad line region at a distance of ~10^16-17^ cm in Seyferts and ~10^17-18^ cm in quasars. The broad line region (BLR) has an outer boundary where the remnant clouds become optically thin to the ionizing radiation from the central source. The densities and column densities in the BLR are in the range ~10^9-11 cm^-3^ and ~10^24-27^ cm^-2^, respectively ({XI}~10). Bound debris orbiting at ~10^15-16^M^2/3^_6_ cm with characteristic densities >= 10^11^ cm^-3^ may contribute to the inner part of the broad line region yielding symmetric lines, whereas a relatively small number (~10-100) of large outmoving remnant clouds produces a more asymmetric and bumpy line profile. There are two potential problems with this new model for the BLR: First, a high tidal disruption rate of order >= 0.1 M_sun_ yr^-1^ seems required to replenish the gas in the BLR in Seyferts as well as in QSOs. Second, in some AGN the central continuum source may be obscured by optically thick remnant clouds along our line of site. A very attractive property of the tidal disruption model is that it offers a natural interpretation not only for the broad emission lines but for a number of other features in AGN spectra as well. Tidal disruption will provide cold, dense gas close to the central source which can reprocess the radiation from the central source and produce a thermal bump in the optical/UV as well as several characteristic X-ray features. Optically thin remnants moving along our line of site outside the BLR at about 10^18-19^ cm may produce broad absorption lines similar to those observed in broad absorption line QSOs. The radially outmoving remnants are decelerated and compressed by the interstellar medium at radii >= 10^19^ cm, where they will emit narrow forbidden lines. Publication: The Astrophysical Journal Pub Date: January 1992 DOI: 10.1086/170919 Bibcode: 1992ApJ...385..108R Keywords: Active Galactic Nuclei; Black Holes (Astronomy); Gravitational Collapse; High Temperature Gases; Interstellar Gas; Star Clusters; Gas Ionization; Gas Pressure; Perturbation Theory; Photoionization; Quasars; Seyfert Galaxies; Spectral Line Width; Tides; Astrophysics; BLACK HOLE PHYSICS; GALAXIES: KINEMATICS AND DYNAMICS; GALAXIES: NUCLEI; GALAXIES: SEYFERT; GALAXIES: QUASARS: GENERAL full text sources ADS | data products SIMBAD (3) MAST (1)

We investigate the physical cause of the great range in the ionization level seen in the spectra of narrow lined active galactic nuclei (AGN). Mean field independent component analysis identifies examples of individual SDSS galaxies whose spectra are not dominated by emission due to star formation (SF), which we designate as AGN. We assembled high S/N ratio composite spectra of a sequence of these AGN defined by the ionization level of their narrow-line regions (NLR), extending down to very low-ionization cases. We used a local optimally emitting cloud (LOC) model to fit emission-line ratios in this AGN sequence. These included the weak lines that can be measured only in the co-added spectra, providing consistency checks on strong line diagnostics. After integrating over a wide range of radii and densities our models indicate that the radial extent of the NLR is the major parameter in determining the position of high to moderate ionization AGN along our sequence, providing a physical interpretation for their systematic variation. Higher ionization AGN contain optimally emitting clouds that are more concentrated towards the central continuum source than in lower ionization AGN. Our LOC models indicate that for the objects that lie on our AGN sequence, the ionizing luminosity is anticorrelated with the NLR ionization level, and hence anticorrelated with the radial concentration and physical extent of the NLR. A possible interpretation that deserves further exploration is that the ionization sequence might be an age sequence where low ionization objects are older and have systematically cleared out their central regions by radiation pressure. We consider that our AGN sequence instead represents a mixing curve of SF and AGN spectra, but argue that while many galaxies do have this type of composite spectra, our AGN sequence appears to be a special set of objects with negligible SF excitation.

Context. The physics and demographics of high-redshift obscured active galactic nuclei (AGN) is still scarcely investigated. New samples of such objects, selected with different techniques, can provide useful insights into their physical properties.Aims. With the goal to determine the properties of the gas in the emitting region of type 2 AGN, in particular, the gas metal content, we exploit predictions from photoionization models, including new parameterizations for the distance of gas distribution from the central source and internal microturbulence in the emitting clouds, to interpret rest-frame UV spectral data.Methods. We selected a sample of 90 obscured (type 2) AGN with 1.45 ≤z≤ 3.05 from the zCOSMOS-deep galaxy sample by 5σdetection of the high-ionization C IVλ1549 narrow emission line. This feature in a galaxy spectrum is often associated with nuclear activity, and the selection effectiveness has also been confirmed by diagnostic diagrams based on utraviolet (UV) emission-line ratios. We applied the same selection technique and collected a sample of 102 unobscured (type 1) AGN. Taking advantage of the large amount of multiband data available in the COSMOS field, we investigated the properties of the C IV-selected type 2 AGN, focusing on their host galaxies, X-ray emission, and UV emission lines. Finally, we investigated the physical properties of the ionized gas in the narrow-line region (NLR) of this type 2 AGN sample by combining the analysis of strong UV emission lines with predictions from photoionization models.Results. We find that in order to successfully reproduce the relative intensity of UV emission lines of the selected high-ztype 2 AGN, two new ingredients in the photoionization models are fundamental: small inner radii of the NLR (≈90 pc forLAGN = 1045erg s−1), and the internal dissipative microturbulence of the gas-emitting clouds (withvmicr≈ 100 km s−1). With these modified models, we compute the gas-phase metallicity of the NLR, and our measurements indicate a statistically significant evolution of the metal content with redshift. Finally, we do not observe a strong relationship between the NLR gas metallicity and the stellar mass of the host galaxy in our C IV-selected type 2 AGN sample.

There is clear observational evidence that some narrow-line (type 2) active galactic nuclei (AGNs) have a hidden broad-line region (BLR) and are thus intrinsically broad-line (type 1) AGNs. Does this AGN unification apply for all type 2 AGNs? Indirect arguments suggest that some type 2 AGNs, i.e., AGNs having no obscured BLR, do exist, but it is not clear why the BLR is missing in these AGNs. Here we point out a possible natural explanation. The observed radius-luminosity relation for the BLR implies an increasing line width with decreasing luminosity for a given black hole mass (MBH). In addition, there appears to be an upper limit to the observed width of broad emission lines in AGNs of Δvmax ~ 25,000 km s-1, which may reflect a physical limit above which the BLR may not be able to survive. Thus, at a low enough luminosity the BLR radius shrinks below the Δvmax radius, leaving no region where the BLR can exist, although the AGN may remain otherwise normal. The implied minimum bolometric luminosity required to sustain a BLR with Δv < 25,000 km s-1 is Lmin ~ 1041.8(MBH/108 M☉)2. All AGNs with L < Lmin are expected to be type 2 AGNs, i.e., narrow-line AGNs without a hidden BLR. Predictions for the true nature of low-luminosity AGNs in two samples of nearby galaxies are provided. These can be used to test the above Lmin conjecture and the predictions of other models for the size and origin of the BLR.

Infrared (IR) interferometry has made significant progress over the last 10 years to a level that active galactic nuclei (AGN) are now routine targets for long-baseline interferometers. Almost 50 different objects have been studied today in the near-IR and mid-IR. This allowed for detailed characterisation of the dusty environment of the actively growing black holes . It was possible to show directly that the dust must be arranged in clumps, as had been indirectly inferred from theory and unresolved observations. The dust composition seems to undergo significant evolution from galactic scales to the AGN environment, with the hottest dust close to the sublimation front being dominated by large graphite grains. While the overall distribution of the dusty mass is quite diverse from object to object, indications have been found that the dust distribution may depend on AGN luminosity, with more powerful AGN potentially showing more compact dust structures. Arguably the most exciting discovery was the fact that the bulk of the mid-IR emission in Seyfert galaxies emerges from the polar region of the AGN, which is difficult to reconcile with classical torus models. An alternative model is currently being debated that consists of a dusty disc plus a dusty wind driven by radiation pressure from the central source. This finding has major implications for our understanding of AGN unification and will become a focus of the upcoming generation of instruments at the VLTI. More recently, an application of interferometry to cosmology was proposed to measure precise geometric distances to AGN in the Hubble flow. Further exploration of this method may open up interferometry to a new scientific community.

In active galactic nuclei (AGNs), radiation pressure is important for the dynamics of the line-emitting clouds. In SS433, the steady speed of the jets (~ 0.26 c) suggests that radiative acceleration may be responsible; but there are difficulties with this interpretation, and it is perhaps unlikely that analogous effects occur in AGNs. In the pair-dominated plasmas expected in AGNs, radiation pressure is competitive with gravity even for luminosities below the normal Eddington limit. For realistic geometries, radiation-driven pair-dominated winds may arise. The most dramatic outflow from AGNs, however, is manifested by the relativistic jets observed predominantly in the radio band. Although the plasma in these jets may be predominantly electron-positron pairs, the outflow is probably driven electromagnetically rather than radiatively: most of the energy may initially be Poynting flux, which is converted into fast particles in the “blobs” whose apparently superluminal motion is revealed by VLBI. Finally, the possibility is raised that sporadic outflow may result from tidal disruption of stars near a massive black hole: such a process may have observable conseguences in our Galactic Centre.

We examine the long-term optical/near-infrared (NIR) flux variability of a ‘changing-look’ active galactic nucleus (AGN) Mrk 590 between 1998 and 2007. Multiband multi-epoch optical/NIR photometry data from the SDSS Stripe 82 data base and the Multicolor Active Galactic Nuclei Monitoring (MAGNUM) project reveal that Mrk 590 experienced a sudden luminosity decrease during the period from 2000 to 2001. Detection of dust reverberation lag signals between V- and K-band light curves obtained by the MAGNUM project during the faint state in 2003–2007 suggests that the dust torus innermost radius Rdust of Mrk 590 had become very small [Rdust ≃ 32 light-days (lt-days)] by the year 2004 according to the aforementioned significant decrease in AGN luminosity. The Rdust in the faint state is comparable to the H β broad-line region (BLR) radius of RH β, BLR ≃ 26 lt-days measured by previous reverberation mapping observations during the bright state of Mrk 590 in 1990–1996. These observations indicate that the innermost radius of the dust torus in Mrk 590 decreased rapidly after the AGN ultraviolet-optical luminosity drop, and that the replenishment time-scale of the innermost dust distribution is less than 4 yr, which is much shorter than the free fall time-scale of BLR gas or dust clouds. We suggest that rapid replenishment of the innermost dust distribution can be accomplished either by new dust formation in radiatively cooled BLR gas clouds or by new dust formation in the disc atmosphere and subsequent vertical wind from the dusty disc as a result of radiation pressure.

The evolution of galaxy cluster counts is a powerful probe of several fundamental cosmological parameters. A number of recent studies using this probe have claimed tension with the cosmology preferred by the analysis of the Planck primary CMB data, in the sense that there are fewer clusters observed than predicted based on the primary CMB cosmology. One possible resolution to this problem is systematic errors in the absolute halo mass calibration in cluster studies, which is required to convert the standard theoretical prediction (the halo mass function) into counts as a function of the observable (e.g., X-ray luminosity, Sunyaev-Zel'dovich flux, optical richness). Here I propose an alternative strategy, which is to directly compare predicted and observed cluster counts as a function of the one-dimensional velocity dispersion of the cluster galaxies. I show that the velocity dispersion of groups/clusters can be theoretically predicted as robustly as mass but, unlike mass, it can also be directly observed, thus circumventing the main systematic bias in traditional cluster counts studies. With the aid of the BAHAMAS suite of cosmological hydrodynamical simulations, I demonstrate the potential of the velocity dispersion counts for discriminating even similar ΛCDM models. Then, I compare the abundance of groups in the GAMA survey to the predictions from BAHAMAS to constrain the values of several cosmological parameters. Additionally, I investigate the role of active galactic nuclei (AGN) in galaxy evolution. The color bimodality of galaxy populations roughly divides galaxies into two groups: blue, star-forming galaxies, and red, quiescent galaxies. One theory that explains how high-mass, red, non-star-forming galaxies maintain this condition is the duty cycle hypothesis. This hypothesis invokes AGN feedback from low luminosity radio-loud AGN (LERGs) to deposit mechanical heating into the intergalactic medium, thus preventing star formation. I test this hypothesis by comparing the half-light radii of quiescent elliptical galaxies with LERG host galaxies using a large multi-wavelength sample from two surveys, UKIDSS/UDS, and ULTRAVISTA/COSMOS. The radius distribution of the two groups are similar, thus providing evidence for the duty cycle hypothesis. I also check the star formation activity of the LERGs. For the duty cycle to hold, LERGs should reside within non-star-forming galaxies. However, I find that a subset of LERGs appear to be dusty star forming galaxies.

Active galactic nuclei (AGNs) with double-peaked [O iii] lines are suspected to be sub-kpc or kpc-scale binary AGNs. However, pure gas kinematics can produce the same double-peaked line profile in spatially integrated spectra. Here we combine integral-field spectroscopy and high-resolution imaging of 42 double-peaked [O iii] AGNs from the Sloan Digital Sky Survey to investigate the constituents of the population. We find two binary AGNs where the line splitting is driven by the orbital motion of the merging nuclei. Such objects account for only ∼2% of the double-peaked AGNs. Almost all (∼98%) of the double-peaked AGNs were selected because of gas kinematics; and half of those show spatially resolved narrow-line regions that extend 4–20 kpc from the nuclei. Serendipitously, we find two spectrally unresolved binary AGNs where gas kinematics produced the double-peaked [O iii] lines. The relatively frequent serendipitous discoveries indicate that only ∼1% of binary AGNs would appear double-peaked in Sloan spectra and 2.2+2.5−0.8% of all Sloan AGNs are binary AGNs. Therefore, the double-peaked sample does not offer much advantage over any other AGN samples in finding binary AGNs. The binary AGN fraction implies an elevated AGN duty cycle (8+8−3%), suggesting galaxy interactions enhance nuclear accretion. We illustrate that integral-field spectroscopy is crucial for identifying binary AGNs: several objects previously classified as "binary AGNs" with long-slit spectra are most likely single AGNs with extended narrow-line regions (ENLRs). The formation of ENLRs driven by radiation pressure is also discussed.

In this paper, we present an evolutionary unification scenario, involving supermassive black holes (SMBHs) and starbursts (SBs) with outflow (OF), that seems capable of explaining most of the observational properties (of at least part) of active galactic nuclei (AGN). The scenario includes a nuclear/circumnuclear SB closely associated with the AGN where the narrow-line region (NLR), broad-line region (BLR) and broad absorption line (BAL) region are produced in part by the OF process with shells and in compact supernova remnants (cSNRs). The OF process in BAL quasi-stellar objects (QSOs) with extreme infrared (IR) and Fe II emission is studied. In addition, the Fe II problem regarding the BLR of AGN is analysed. The correlations between the BAL, IR emission, Fe II intensity and the intrinsic properties of the AGN are not clearly understood. We suggest here that the behaviour of the BAL, IR and Fe II emission in AGN can be understood within an evolutionary and composite model for AGN. In our model, strong BAL systems and Fe II emission are present (and intense) in young IR objects. Parameters like the BALs, IR emission, Fe II/Hβ intensity ratio, Fe II equivalent width (EW), broad-line width, [O III] λ5007-A intensity and width, NLR size, X-ray spectral slope in radio quiet (RQ) AGN plus lobe separation, and lobe to core intensity ratio in radio loud (RL) AGN are proposed to be fundamentally time-dependent variables inside time-scales of the order of 10 8 yr. Orientation/obscuration effects take the role of a second parameter providing the segregation between Seyfert 1/Seyfert 2 galaxies (Sy1/Sy2) and broad-/narrow-line radio galaxies (BLRG/NLRG).

We present a catalog of the millimeter-wave (mm-wave) continuum properties of 98 nearby (z < 0.05) active galactic nuclei (AGNs) selected from the 70 month Swift/BAT hard-X-ray catalog that have precisely determined X-ray spectral properties and subarcsecond-resolution Atacama Large Millimeter/submillimeter Array Band 6 (211–275 GHz) observations as of 2021 April. Due to the hard-X-ray (>10 keV) selection, the sample is nearly unbiased for obscured systems at least up to Compton-thick-level obscuration, and provides the largest number of AGNs with high-physical-resolution mm-wave data (≲100–200 pc). Our catalog reports emission peak coordinates, spectral indices, and peak fluxes and luminosities at 1.3 mm (230 GHz). Additionally, high-resolution mm-wave images are provided. Using the images and creating radial surface brightness profiles of mm-wave emission, we identify emission extending from the central sources and isolated blob-like emission. Flags indicating the presence of these emission features are tabulated. Among 90 AGNs with significant detections of nuclear emission, 37 AGNs (≈41%) appear to have both or one of extended or blob-like components. We, in particular, investigate AGNs that show well-resolved mm-wave components and find that these seem to have a variety of origins (i.e., a jet, radio lobes, a secondary AGN, stellar clusters, a narrow-line region, galaxy disk, active star formation regions, or AGN-driven outflows), and some components have currently unclear origins.

Context. The size and geometry of the broad-line region (BLR) in active galactic nuclei (AGNs) are among the main ingredients in determining the mass of the accreting black hole. Size and geometry can be constrained by determining the delay between the optical continuum and the flux reprocessed by the BLR, in particular, through the emission lines. Aims. We propose here that the delay between polarized and unpolarized light can also be used in much the same way to constrain the size of the BLR; we verify that meaningful results can be expected from observations using this technique. Methods. We used our code STOKES to simulate polarized radiative transfer. We determined the response of the environment of the central source (BLR, dust torus, and polar wind) to randomly generated fluctuations in the central source. We then calculated the cross correlation between the simulated polarized flux and the total flux to estimate the time delay that would be provided by observations using the same method. Results. The BLR is the main contributor to the delay between the polarized flux and the total flux. This delay is independent of the observation wavelength. Conclusions. This validates the use of polarized radiation in the optical/UV band to estimate the geometrical properties of the BLR in type I AGNs, in which the viewing angle is close to pole-on and the BLR is not obscured by the dust torus.

Spectroscopy with theJames WebbSpace Telescope has opened the possibility of identifying moderate-luminosity active galactic nuclei (AGNs) in the early Universe, at and beyond the epoch of re-ionisation, complementing previous surveys of much more luminous (and much rarer) quasars. We present 12 new AGNs at 4 &lt; z &lt; 7 in the JADES survey (in addition to the previously identified AGN in GN-z11 at z = 10.6) revealed through the detection of a broad-line region (BLR) seen in the Balmer emission lines. The depth of JADES, together with the use of three different spectral resolutions, enables us to probe a lower-mass regime relative to previous studies. In a few cases, we find evidence for two broad components of Hα, which suggests that these could be candidate merging black holes (BHs), although a complex BLR geometry cannot be excluded. The inferred BH masses range from 8 × 107 M⊙down to 4 × 105 M⊙, interestingly probing the regime expected for direct collapse BHs. The inferred AGN bolometric luminosities (∼1044 − 1045erg/s) imply accretion rates that are &lt; 0.5 times the Eddington rate in most cases. However, small BHs, with MBH∼ 106M⊙, tend to accrete at Eddington or super-Eddington rates. These BHs at z ∼ 4–11 are over-massive relative to their host galaxies’ stellar masses when compared to the local MBH− Mstarrelation, even approaching MBH∼ Mstar, as was expected from heavy BH seeds and/or super-Eddington accretion scenarios. However, we find that these early BHs tend to be more consistent with the local relation between MBHand velocity dispersion, as well as between MBHand dynamical mass, suggesting that these are more fundamental and universal relations. On the classical, optical narrow-line excitation-diagnostic diagrams, these AGNs are located in the region that is locally occupied by star-forming galaxies, implying that they would be missed by the standard classification techniques if they did not display broad lines. Their location on the diagram is consistent with what is expected for AGNs hosted in metal-poor galaxies (Z ∼ 0.1 − 0.2 Z⊙). The fraction of broad-line AGNs withLAGN&gt; 1044erg/s among galaxies in the redshift range of 4 &lt; z &lt; 6 is about 10%, suggesting that the contribution of AGNs and their hosts to the re-ionisation of the Universe is &gt; 10%.

We present an analysis of the first two XRISM/Resolve spectra of the well-known Seyfert-1.5 active galactic nucleus (AGN) in NGC 4151, obtained in 2023 December. Our work focuses on the nature of the narrow Fe K α emission line at 6.4 keV, the strongest and most common X-ray line observed in AGN. The total line is found to consist of three components. Even the narrowest component of the line is resolved with evident Fe K α,1 (6.404 keV) and K α,2 (6.391 keV) contributions in a 2:1 flux ratio, fully consistent with neutral gas with negligible bulk velocity. Subject to the limitations of our models, the narrowest and intermediate-width components are consistent with emission from optically thin gas, suggesting that they arise in a disk atmosphere and/or wind. Modeling the three line components in terms of Keplerian broadening, they are readily associated with (1) the inner wall of the “torus,” (2) the innermost optical “broad-line region” (or “X-ray BLR”), and (3) a region with a radius of r ≃ 100 GM/c 2 that may signal a warp in the accretion disk. Viable alternative explanations of the broadest component include a fast-wind component and/or scattering; however, we find evidence of variability in the narrow Fe K α line complex on timescales consistent with small radii. The best-fit models are statistically superior to simple Voigt functions, but when fit with Voigt profiles the time-averaged lines are consistent with a projected velocity broadening of FWHM =1600−200+400kms−1 . Overall, the resolution and sensitivity of XRISM show that the narrow Fe K line in AGN is an effective probe of all key parts of the accretion flow, as it is currently understood. We discuss the implications of these findings for our understanding of AGN accretion, future studies with XRISM, and X-ray-based black hole mass measurements.

view Abstract Citations (10) References (33) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Two-phase accretion model for emission-line regions in quasars and active galactic nuclei Wandel, A. ; Milgrom, M. ; Yahil, A. Abstract A model is constructed for the broad-line region of quasars and active galactic nuclei. A two-phase medium, made of cool photoionized filaments embedded in a hot gas, and assumed to be in a quasi-spherical infall, is producing the line emission, as well as supplying the mass needed to power the central continuum sources. Taking into account conduction and radiative cooling in the filaments, an asymptotic solution is found, in which the ionization parameter in the clouds is almost independent of the distance from the central source. This can reproduce the observed feature that lines of different excitation levels have similar profiles. A new relation is found between the efficiency of the central source and the dimensionless accretion rate, and the efficiency is expressed in terms of observable quantities. The observational data on the emission lines imply high central masses, 10 to the 7th-10 to the 10th solar masses; 0.3 - 1000 solar masses per year; and low efficiencies, e approximately equal to or less than 0.001. Publication: The Astrophysical Journal Pub Date: May 1985 DOI: 10.1086/163148 Bibcode: 1985ApJ...292..206W Keywords: Active Galactic Nuclei; Black Holes (Astronomy); Quasars; Stellar Mass Accretion; Astronomical Models; Asymptotic Methods; Interstellar Gas; Mach Number; Photoionization; Astrophysics full text sources ADS |