Search

The Eigenvector 1 schema, or the main sequence of quasars, was introduced as an analogous scheme to the HR diagram that would allow us to understand the more complex, extended sources -active galactic nuclei (AGNs) that harbor accreting supermassive black holes. The study has spanned more than three decades and has advanced our knowledge of the diversity of Type-1 AGNs from both observational and theoretical aspects. The quasar main sequence, in its simplest form, is the plane between the FWHM of the broad Hβ emission line and the strength of the optical Fe II emission to the Hβ. While the former allows the estimation of the black hole mass, the latter enables direct measurement of the metal content and traces the accretion rate of the AGN. Together, they allow us to track the evolution of AGN in terms of the activity of the central nuclei, its effect on the line-emitting regions surrounding the AGN, and their diversity making them suitable distance indicators to study the expansion of our Universe. This mini-reviewaims to provide (i) a brief history leading up to the present day in the study of the quasar main sequence, (ii) introduce us to the many possibilities to study AGNs with the main sequence as a guiding tool, and (iii) highlight some recent, exciting lines of researches at the frontier of this ever-growing field. [ABSTRACT FROM AUTHOR]

The Eigenvector 1 schema, or the main sequence of quasars, was introduced as an analogous scheme to the HR diagram that would allow us to understand the more complex, extended sources - active galactic nuclei (AGNs) that harbor accreting supermassive black holes. The study has spanned more than three decades and has advanced our knowledge of the diversity of Type-1 AGNs from both observational and theoretical aspects. The quasar main sequence, in its simplest form, is the plane between the FWHM of the broad Hβ emission line and the strength of the optical Fe ii emission to the Hβ. While the former allows the estimation of the black hole mass, the latter enables direct measurement of the metal content and traces the accretion rate of the AGN. Together, they allow us to track the evolution of AGN in terms of the activity of the central nuclei, its effect on the line-emitting regions surrounding the AGN, and their diversity making them suitable distance indicators to study the expansion of our Universe. This mini-review aims to provide (i) a brief history leading up to the present day in the study of the quasar main sequence, (ii) introduce us to the many possibilities to study AGNs with the main sequence as a guiding tool, and (iii) highlight some recent, exciting lines of researches at the frontier of this ever-growing field.

Constraining the physical conditions of the ionized media in the vicinity of an active supermassive black hole (SMBH) is crucial to understanding how these complex systems operate. Metal emission lines such as iron (Fe) are useful probes to trace the gaseous media’s abundance, activity, and evolution in these accreting systems. Among these, the Feii emission has been the focus of many prior studies to investigate the energetics, kinematics, and composition of the broad-emission line region (BELR) from where these emission lines are produced. In this paper, we present the first simultaneous Feii modeling in the optical and near-infrared (NIR) regions. We use cloudy photoionization code to simulate both spectral regions in the wavelength interval 4000–12,000 Å. We compare our model predictions with the observed line flux ratios for I Zw (Zwicky) 1—a prototypical strong Feii-emitting active galactic nuclei (AGNs). This allows setting constraints on the BLR cloud density and metal content that is optimal for the production of the Feii emission, which can be extended to I Zw 1-like sources by examining a broad parameter space. We demonstrate the salient and distinct features of the Feii pseudo-continuum in the optical and NIR, giving special attention to the effect of micro-turbulence on the intensity of the Feii emission.

We present the first measurement of H i mass of star-forming galaxies in different large scale structure environments from a blind survey at z ∼ 0.37. In particular, we carry out a spectral line stacking analysis considering 2875 spectra of colour-selected star-forming galaxies undetected in H i at 0.23 < z < 0.49 in the COSMOS field, extracted from the MIGHTEE-H i Early Science data cubes, acquired with the MeerKAT radio telescope. We stack galaxies belonging to different subsamples depending on three different definitions of large-scale structure environment: local galaxy overdensity, position inside the host dark matter halo (central, satellite, or isolated), and cosmic web type (field, filament, or knot). We first stack the full star-forming galaxy sample and find a robust H i detection yielding an average galaxy H i mass of |$M_{\rm H \, {\small I}}=(8.12\pm 0.75)\times 10^9\, {\rm M}_\odot$| at ∼11.8σ. Next, we investigate the different subsamples finding a negligible difference in M H i as a function of the galaxy overdensity. We report an H i excess compared to the full sample in satellite galaxies (M H i  = (11.31 ± 1.22) × 109, at ∼10.2σ) and in filaments (M H i  = (11.62 ± 0.90) × 109. Conversely, we report non-detections for the central and knot galaxies subsamples, which appear to be H i -deficient. We find the same qualitative results also when stacking in units of H i fraction (f H i ). We conclude that the H i amount in star-forming galaxies at the studied redshifts correlates with the large-scale structure environment. [ABSTRACT FROM AUTHOR]

Constraining the physical conditions of the ionized media in the vicinity of an active supermassive black hole (SMBH) is crucial to understanding how these complex systems operate. Metal emission lines such as iron (Fe) are useful probes to trace the gaseous media's abundance, activity, and evolution in these accreting systems. Among these, the Feii emission has been the focus of many prior studies to investigate the energetics, kinematics, and composition of the broad-emission line region (BELR) from where these emission lines are produced. In this paper, we present the first simultaneous Feii modeling in the optical and near-infrared (NIR) regions. We use cloudy photoionization code to simulate both spectral regions in the wavelength interval 4000–12,000 Å. We compare our model predictions with the observed line flux ratios for I Zw (Zwicky) 1—a prototypical strong Feii-emitting active galactic nuclei (AGNs). This allows setting constraints on the BLR cloud density and metal content that is optimal for the production of the Feii emission, which can be extended to I Zw 1-like sources by examining a broad parameter space. We demonstrate the salient and distinct features of the Feii pseudo-continuum in the optical and NIR, giving special attention to the effect of micro-turbulence on the intensity of the Feii emission. [ABSTRACT FROM AUTHOR]

Properties of the broad line region (BLR) in active galactic nuclei (AGNs) are commonly used to estimate the mass of the supermassive black hole (SMBH) that powers an AGN. However, the understanding of the physics behind the BLR remains incomplete. The AGNs exhibit strong optical variability, observed in the change of the profiles and fluxes of broad emission lines. Utilizing this variability provides an opportunity to constrain the physics of the BLR, and understand the interplay of the BLR with SMBH and surrounding regions. Here, we present the long-term monitoring campaign of a sample of the known broad-line AGNs (identified as LoTerm AGN). The aim of this study is to show the importance of sustained and dedicated campaigns that continually collect spectroscopic data of the known AGNs over extended timescales, providing unique insight into the origin and structure of the BLR. LoTerm AGN is a collaborative network of seven moderate-size telescopes equipped for spectroscopy. We focus on the recent spectral data of the known changing-look AGN, NGC 3516. Specifically, we examine the broad hydrogen Balmer H α line observed in the period 2020–2023, demonstrating that this AGN remains active with the BLR signatures observed in the spectra. No significant change in the broad line profile of H α line is observed during this recent period. [ABSTRACT FROM AUTHOR]

Properties of the broad line region (BLR) in active galactic nuclei (AGNs) are commonly used to estimate the mass of the supermassive black hole (SMBH) that powers an AGN. However, the understanding of the physics behind the BLR remains incomplete. The AGNs exhibit strong optical variability, observed in the change of the profiles and fluxes of broad emission lines. Utilizing this variability provides an opportunity to constrain the physics of the BLR, and understand the interplay of the BLR with SMBH and surrounding regions. Here, we present the long-term monitoring campaign of a sample of the known broad-line AGNs (identified as LoTerm AGN). The aim of this study is to show the importance of sustained and dedicated campaigns that continually collect spectroscopic data of the known AGNs over extended timescales, providing unique insight into the origin and structure of the BLR. LoTerm AGN is a collaborative network of seven moderate-size telescopes equipped for spectroscopy. We focus on the recent spectral data of the known changing-look AGN, NGC 3516. Specifically, we examine the broad hydrogen Balmer Hα line observed in the period 2020–2023, demonstrating that this AGN remains active with the BLR signatures observed in the spectra. No significant change in the broad line profile of Hα line is observed during this recent period.

Conditional Neural Process (QNPy) has shown to be a good tool for modeling quasar light curves. However, given the complex nature of the source and hence the data represented by light curves, processing could be time-consuming. In some cases, accuracy is not good enough for further analysis. In an attempt to upgrade QNPy, we examine the effect of the prepossessing quasar light curves via the Self-Organizing Map (SOM) algorithm on modeling a large number of quasar light curves. After applying SOM on the SWIFT/BAT data and modeling curves from several clusters, results show the Conditional Neural Process performs better after the SOM clustering. We conclude that the SOM clustering of quasar light curves could be a beneficial prepossessing method for QNPy. [ABSTRACT FROM AUTHOR]

We present a review of the topics of X‐ray stellar tidal disruption events (TDEs) and changing‐look active galactic nuclei (AGN). Stars approaching a supermassive black hole (SMBH) can be tidally disrupted and accreted. TDEs were first discovered in the X‐ray regime and appear as luminous, giant‐amplitude flares from inactive galaxies. The early X‐ray observations with ROSAT also established the extreme X‐ray spectral softness of these events with temperatures of order 50–100 eV that continues to be seen in the majority of more recently identified events. While the majority of X‐ray TDEs has been identified from inactive galaxies and some showed the highest amplitudes of variability recorded from galaxy cores (amplitudes exceeding factors of 1000–6000), a small fraction of AGN has been found to be highly variable as well. In AGN, this so‐called changing‐look phenomenon often comes with a strong change in the optical broad emission lines, leading to Seyfert‐type changes between class 1 and class 2. These two forms of activity represent the extremes of variability among active and quiescent galaxies, and have opened up a new window to understanding accretion physics under extreme conditions. Finally, we introduce the term "frozen‐look AGN" to describe systems that show constant line emission despite dramatic changes in the observed ionizing continuum. These systems are best explained by strong changes of absorption along our line‐of‐sight. [ABSTRACT FROM AUTHOR]

Results of spectral studies of fifteen Seyfert galaxies at red wavelengths based on long-term observations are presented. In this range there are lines of hydrogen Hα, [NII], [OI], and [SII]. Data on the absolute emission fluxes in the emission lines and in the continuum at the wavelength of λ = 6400 Å are presented. In order to objectively compare the examined galaxies with one another, the values of their luminosities were calculated in absolute units with the distances to these objects taken into account. [ABSTRACT FROM AUTHOR]

We discuss the polarization of broad emission lines in the type 1 active galactic nuclei (AGN). The polarization depends on the geometry of the broad line region (BLR), and also on the polarization mechanism, or distribution of the scattering material. Therefore, the polarization measurements can indicate the geometry of the BLR and the mechanism of polarization (equatorial or polar scattering). In addition, the polarization angle (PA) shape across the line profile can be used to measure the supermassive black hole (SMBH) mass, and constrain the BLR characteristics. We give an overview of ours and other recent investigations of the polarization in broad lines from both aspects: theoretical and observational. [ABSTRACT FROM AUTHOR]

Several powerful outbursts have been observed during many years of observations of the symbiotic object MWC 560. The last active stage began in the autumn of 2018 and continues to the present. Observations of this event began at the Fesenkov Astrophysical Institute at the beginning of 2019. In our previous article we published the results obtained in early 2019. A light curve of the object and emission line profiles are presented; it is noted that a broad absorption band formed in a high velocity collimated jet vanishes. In this article we present the results of further spectral and photometric observations of MWC 560. It is to be noted that in 2021 the brightness of this object is sustained at a high level exceeding that obtained during the previous outbursts. In addition, at the end of 2020 a tendency toward a gradual weakening of the radiative fluxes in the emission lines was remarked. The profiles of all the lines have absorption components shifted to the "blue" by 52±5 km/s. It may be assumed that during this outburst there was partial (or complete) destruction of the accretion disk, so that the source of the high velocity collimated jet vanished. The gradual reduction in the radiative fluxes in the emission lines may be caused by a drop in the power of ionizing radiation. [ABSTRACT FROM AUTHOR]

Broad Emission Lines are the most characteristic features of Active Galaxies, but the mechanism of creating a medium able to emit these intense lines is not quite clear. Observations clearly indicate that the motion of the material is predominantly Keplerian, with traces of inflow and clear signatures of outflow, but this still does not point out whether the lines partially come from the disk surface, or exclusively from the circumnuclear material, and whether this material originates from the disk as a wind, or comes, at least partially, from outside. I review the basic scenarios for the formation of the Broad Line Region (BLR), and the recent progress in modelling the physical conditions in he emitting medium. The current state is the outer radius of the BLR is fixed by the dust sublimation temperature in the medium exposed to the irradiation from the central source, the inner radius is likely fixed by the dust sublimation temperature in the atmosphere of the non-illuminated accretion disk, and the local cloud density is a universal number fixed by the radiation pressure confinement. The time-dependent aspects of the BLR formation, however, still wait for serious modelling effort matching the quality of the observational data.

Aditya-L1 is India’s first solar mission with the Visible Emission Line Coronagraph (VELC), which consists of three spectral channels taking high-resolution spectroscopic observations of the inner corona up to 1.5 Rʘ at 5,303, 7,892, and 10,747 Å. In this work, we present a strategy for the slit width optimization of the VELC using synthetic line profiles by taking into account the instrument characteristics and coronal conditions for log(T) varying from 6 to 6.5. The synthetic profiles are convolved with simulated instrumental scattered light and noise to estimate the signal-to-noise ratio (SNR), which will be crucial to designing the future observation plans. We find that the optimum slit width for VELC turns out to be 50 μm, providing sufficient SNR for observations in different solar conditions. We also analyzed the effect of plasma temperature on the SNR at different heights in the VELC field of view for the optimized slit width. We also studied the expected effect of the presence of a CME on the spectral channel observations. This analysis will help to plan the scientific observations of VELC in different solar conditions.

This is a theoretical study of changes in several characteristics of the spectra of early-type supergiants owing to scattering of continuum radiation. Thomson scattering on free electrons is treated as the scattering mechanism, although the approach used here is quite general. The reason for changes in the spectral class of a star with constant bolometric luminosity and surface temperature is elucidated and the necessary conditions for their realization are introduced. The effect of scattering in the continuum on the magnitude of the intensity jumps in the hydrogen spectrum depending on the degree of ionization is studied. The conditions under which the Schuster mechanism for formation of emission lines sets in are clarified both for an isothermal atmosphere and for an atmosphere with a temperature gradient. [ABSTRACT FROM AUTHOR]

We carried out photometric and spectroscopic observations of the well-studied broad-line radio galaxy 3C 120 with the Las Cumbres Observatory (LCO) global robotic telescope network from 2016 December to 2018 April as part of the LCO AGN Key Project on Reverberation Mapping of Accretion Flows. Here, we present both spectroscopic and photometric reverberation mapping results. We used the interpolated cross-correlation function to perform multiple-line lag measurements in 3C 120. We find the H γ, He  ii λ4686, H β, and He  i λ5876 lags of |$\tau _{\text{cen}} = 18.8_{-1.0}^{+1.3}$|⁠ , |$2.7_{-0.8}^{+0.7}$|⁠ , |$21.2_{-1.0}^{+1.6}$|⁠ , and |$16.9_{-1.1}^{+0.9}$| d, respectively, relative to the V -band continuum. Using the measured lag and rms velocity width of the H β emission line, we determine the mass of the black hole for 3C 120 to be |$M=(6.3^{+0.5}_{-0.3})\times 10^7\, (f/5.5)$|  M⊙. Our black hole mass measurement is consistent with similar previous studies on 3C 120, but with small uncertainties. In addition, velocity-resolved lags in 3C 120 show a symmetric pattern across the H β line, 25 d at line centre decreasing to 17 d in the line wings at ±4000 km s−1. We also investigate the inter-band continuum lags in 3C 120 and find that they are generally consistent with τ ∝ λ4/3 as predicted from a geometrically thin, optically thick accretion disc. From the continuum lags, we measure the best-fitting value τ0 = 3.5 ± 0.2 d at |$\lambda _{\rm 0} = 5477\, \mathring{\rm A}$|⁠. It implies a disc size a factor of 1.6 times larger than prediction from the standard disc model with L / L Edd = 0.4. This is consistent with previous studies in which larger than expected disc sizes were measured. [ABSTRACT FROM AUTHOR]

This is a study of spectral and photometric observations of the binary system with an X-ray component V725 Tauri=A0535+262. It consists of a giant star HDE 245770 of spectral class O9.7 and the pulsar A0535+26 with a pulsation period of ~103 s. Active stages of this object, accompanied by "giant" X-ray outbursts, have been observed repeatedly. The last events occurred during 2009-2011. Our studies in 2017-2020 yielded the following data: over the last three years the B and V band brightness of the object has remained at a high level and began to decrease at the end of 2019. Here, beginning in 2016 a gradual increase in the radiative fluxes in the Hβ and Hα emission lines has been observed. At present the equivalent widths of these lines exceed the values recorded during the time of the gigan X-ray outburst of 2011. Previous studies have shown that a similar combination of the characteristics of this object, specifically an increase in emission line fluxes as the brightness decreases. is detected just before the onset of an active stage. [ABSTRACT FROM AUTHOR]

Spectroscopic mapping of planetary nebulae (PNe) is particularly useful to capture the richness in terms of physical and chemical properties that exist in these objects. The advent of the multi-unit spectroscopic explorer (MUSE), a large integral field unit mounted on the ESO Very Large Telescope, allow us to obtain this information over the whole face of galactic PNe in a reasonable amount of time. This in turn reveals a wealth of information that can bring insight into this structural complexity. Here we discuss new results from commissioning data for the physical properties of IC 418 and succinctly review recently published results on two additional targets (NGC 3132 and NGC 7009). For the newly-analysed PN, electron densities are high with ne([S ii]) displaying a completely different structure than ne([Cl iii]). The electron temperature was relatively uniform, but somewhat higher at the rim as measured by two of the three used diagnostics ([S iii] 6312/9069, and [Ar iii] 5192/7136). The joint results for the three PNe amply illustrate the potential of MUSE for the study of galactic PNe.

Quasars accreting matter at very high rates (known as extreme Population A [xA] quasars, possibly associated with super-Eddington accreting massive black holes) may provide a new class of distance indicators covering cosmic epochs from present day up to less than 1 Gyr from the Big Bang. At a more fundamental level, xA quasars are of special interest in studies of the physics of AGNs and host galaxy evolution. However, their observational properties are largely unknown. xA quasars can be identified in relatively large numbers from major optical surveys over a broad range of redshifts, and efficiently separated from other type-1 quasars thanks to selection criteria defined from the systematically-changing properties along the quasars main sequence. It has been possible to build a sample of ~250 quasars at low and intermediate redshift, and larger samples can be easily selected from the latest data releases of the Sloan Digital Sky Survey. A large sample can clarify the main properties of xA quasars which are expected—unlike the general population of quasars—to radiate at an extreme, well-defined Eddington ratio with small scatter. As a result of the small scatter in Eddington ratio shown by xA quasars, we propose a method to derive the main cosmological parameters based on redshift-independent “virial luminosity” estimates from measurements of emission line widths, roughly equivalent to the luminosity estimates based from line width in early and late type galaxies. A major issue related to the cosmological application of the xA quasar luminosity estimates from line widths is the identification of proper emission lines whose broadening is predominantly virial over a wide range of redshift and luminosity. We report on preliminary developments using the AlIIIλ1860 intermediate ionization line and the Hydrogen Balmer line Hβ as virial broadening estimators, and we briefly discuss the perspective of the method based on xA quasars.

The character of the interaction of two gaseous components which are a structural feature of the nucleus of the Seyfert galaxy NGC 1275 is established during the epoch of a minimum in its activity. A bank of emission line profiles (Hβ and O[III] λ5007Å) obtained from observations on the 1.5-m Russian-Turkish telescope (RTT-150) in January 2012 is used. The physical characteristics (Te, ne) of the emission region of the nebular line [OIII] are calculated for this observation epoch and are compared with other published data. The changes in an important spectral characteristic of the emission from the galaxy nucleus (Ewλ, the equivalent with of the Hβ and O[III] λ5007Å lines) are tracked during individual nights and from night-to-night. These studies show that the two "interpenetrating" gaseous components retain a high level of interaction over a long period of time. [ABSTRACT FROM AUTHOR]

It is very important to make the spectrographic observations of the outer emission corona in number of emission lines simultaneously in view of the results of the observations made in [Fe x] 6374 Å, [Fe xi] 7892 Å, [Fe xiv] 5303 Å and [Fe xiii] 10,747 Å coronal emission lines with the 25 cm coronagraph at Norikura Observatory in Japan. At ground based observatories, availability of number of hours of clear sky for coronagraphic observations is limited due to aerosols scattering and scattering from the internal coronagraph reflections. A space based coronagraph Visible Emission Line Coronagraph (VELC) on board ADITYA-L1 has been planned to perform spectroscopy in 3 out of the 4 emission lines mentioned above. Here, we discuss the various requirements for the parameters of the payload, given the specifications of the satellite, to observe the outer emission corona reliably with good Signal to Noise Ratio (SNR), realize the projected scientific goals and make the mission a great success. [ABSTRACT FROM AUTHOR]

The Multi-Unit Spectroscopic Explorer (MUSE) is a large integral field unit mounted on the ESO Very Large Telescope. Its spatial (60 arcsecond field) and wavelength (4800–9300Å) coverage is well suited to detailed imaging spectroscopy of extended planetary nebulae, such as in the Galaxy. An overview of the capabilities of MUSE applied to Planetary Nebulae (PNe) is provided together with the specific advantages and disadvantages. Some examples of archival MUSE observations of PNe are provided. MUSE datacubes for two targets (NGC 3132 and NGC 7009) are analyzed in detail, and they are used to show the advances achievable for planetary nebula studies. Prospects for further MUSE observations of PNe and a broader analysis of existing datasets are outlined.

Here we investigate the connection of broad emission line shapes and continuum light curve variability time scales of type-1 Active Galactic Nuclei (AGN). We developed a new model to describe optical broad emission lines as an accretion disk model of a line profile with additional ring emission. We connect ring radii with orbital time scales derived from optical light curves, and using Kepler's third law, we calculate mass of central supermassive black hole (SMBH). The obtained results for central black hole masses are in a good agreement with other methods. This indicates that the variability time scales of AGN may not be stochastic, but rather connected to the orbital time scales which depend on the central SMBH mass.

The last 25 years saw a major step forward in the analysis of optical and UV spectroscopic data of large quasar samples. Multivariate statistical approaches have led to the definition of systematic trends in observational properties that are the basis of physical and dynamical modeling of quasar structure. We discuss the empirical correlates of the so-called “main sequence” associated with the quasar Eigenvector 1, its governing physical parameters and several implications on our view of the quasar structure, as well as some luminosity effects associated with the virialized component of the line emitting regions. We also briefly discuss quasars in a segment of the main sequence that includes the strongest FeII emitters. These sources show a small dispersion around a well-defined Eddington ratio value, a property which makes them potential Eddington standard candles.

The symbiotic object EG And consists of a giant star (M4III) and a white dwarf. Numerous studies of this object show that its light curve has two minima. There are different hypotheses regarding the source of the secondary minimum, but the problem has not yet been solved. In this paper we present data from photometric and spectral observations of EG And during 2009-2018: B, V, and R magnitudes in the Johnson system and fluxes in the Hβ and Hα emission lines. An analysis of these data showed that the emission fluxes correlate with the orbital phase. The highest fluxes are observed near the secondary minimum. At the same time, emission fluxes are still observed in the primary minimum but attenuated by roughly a factor of 7-10. This indicates that the size of the ionized zone exceeds that of the giant star. On the whole, the light curve for 2009-2018 is consistent with previous photometric data. Rapid (over a few minutes) fluctuations in the brightness of this object are detected in the V and R bands with amplitudes of ~0m.15 and 0m.35, respectively. [ABSTRACT FROM AUTHOR]

We present a detailed study of the kinematic, chemical and excitation properties of the giant Ly α emitting nebula and the giant HI absorber associated with the z = 2.92 radio galaxy MRC 0943-242, using spectroscopic observations from Very Large Telescope (VLT)/Multi Unit Spectroscopic Explorer (MUSE), VLT/X-SHOOTER and other instruments. Together, these data provide a wide range of rest-frame wavelength (765-6378 Å at z = 2.92) and 2D spatial information. We find clear evidence for jet gas interactions affecting the kinematic properties of the nebula, with evidence for both outflows and inflows being induced by radiomode feedback. We suggest that the regions of relatively lower ionization level, spatially correlated with the radio hotspots, may be due to localized compression of photoionized gas by the expanding radio source, thereby lowering the ionization parameter, or due to a contribution from shock-heating. We find that photoionization of supersolar metallicity gas (Z/Z☉ = 2.1) by an active galactic nuclei-like continuum (α =-1.0) at a moderate ionization parameter (U = 0.018) gives the best overall fit to the complete X-SHOOTER emission-line spectrum. We identify a strong degeneracy between column density and Doppler parameter such that it is possible to obtain a reasonable fit to the HI absorption feature across the range log N(H I/cm-2 ) = 15.20 and 19.63, with the two best fitting occurring near the extreme ends of this range. The extended HI absorber is blueshifted relative to the emission-line gas, but shows a systematic decrease in blueshift towards larger radii, consistent with a large-scale expanding shell. [ABSTRACT FROM AUTHOR]

We explore the origin of fast molecular outflows that have been observed in active galactic nuclei (AGNs). Previous numerical studies have shown that it is difficult to create such an outflow by accelerating existing molecular clouds in the host galaxy, as the clouds will be destroyed before they can reach the high velocities that are observed. In this work, we consider an alternative scenario where molecules form in situ within the AGN outflow. We present a series of hydro-chemical simulations of an isotropic AGN wind interacting with a uniform medium. We follow the time-dependent chemistry of 157 species, including 20 molecules, to determine whether molecules can form rapidly enough to produce the observed molecular outflows. We find H2 outflow rates up to 140M☉ yr-1, which is sensitive to density, AGN luminosity, and metallicity.We compute emission and absorption lines of CO, OH, andwarm (a few hundred K) H2 from the simulations in post-processing. The CO-derived outflow rates and OH absorption strengths at solar metallicity agree with observations, although the maximum line-of-sight velocities from the model CO spectra are a factor ≈2 lower than is observed. We derive a CO (1-0) to H2 conversion factor of αCO(1-0) = 0.13M☉ (K km s-1 pc2)-1, 6 times lower than is commonly assumed in observations of such systems. We find strong emission from the mid-infrared lines of H2. The mass of H2 traced by this infrared emission is within a few per cent of the total H2 mass. This H2 emission may be observable by JamesWebbSpaceTelescope. [ABSTRACT FROM AUTHOR]

UV and optically selected candidates for stellar tidal disruption events (TDEs) often exhibit broad spectral features (He II emission, Hα emission, or absorption lines) on a blackbody-like continuum (104 K ≲ T ≲ 105 K). The lines presumably emit from TDE debris or circumnuclear clouds photoionized by the flare. Line velocities however are much lower than expected from a stellar disruption by supermassive black hole (SMBH), and are somewhat faster than expected for the broad line region (BLR) clouds of a persistently active galactic nucleus (AGN). The distinctive spectral states are not strongly related to observed luminosity and velocity, nor to SMBH mass estimates. We use exhaustive photoionization modelling to map the domain of fluxes and cloud properties that yield (e.g.) an He-overbright state where a large He II(4686 Å)/H α line ratio creates an illusion of helium enrichment. Although observed line ratios occur in a plausible minority of cases, AGN-like illumination cannot reproduce the observed equivalent widths. We therefore propose to explain these properties by a light-echo photoionization model: the initial flash of a hot blackbody (detonation) excites BLR clouds, which are then seen superimposed on continuum from a later, expanded, cooled stage of the luminous source. The implied cloud mass is substellar, which may be inconsistent with a TDE. Given these and other inconsistencies with TDE models (e.g. host-galaxies distribution) we suggest to also consider alternative origins for these nuclear flares, which we briefly discuss (e.g. nuclear supernovae and starved/subluminous AGNs). [ABSTRACT FROM AUTHOR]

Spectroscopic studies of active galactic nuclei (AGN) are powerful means of probing the physical properties of the ionized gas within them. In particular, near future observational facilities, such as the James Webb Space Telescope (JWST), will allow detailed statistical studies of rest-frame ultraviolet and optical spectral features of the very distant AGN with unprecedented accuracy. In this proceedings, we discuss the various ways of exploiting new dedicated photoionization models of the narrow-line emitting regions (NLR) of AGN for the interpretation of forthcoming revolutionary datasets.

We present our recent results about the extended narrow-line region (ENLR) of two nearby Seyfert 2 galaxies (IC 5063 and NGC 7212) obtained by modeling the observed line profiles and spectra with composite models (photoionization+shocks) in the different regions surrounding the AGN. Then, we compare the Seyfert 2 ENLRs with the very extended one recently discovered in the narrow-line Seyfert 1 (NLS1) galaxy Mrk 783. We have found several evidences of interaction between the ISM of the galaxies and their radio jets, such as (a) the contribution of shocks in ionizing the high velocity gas, (b) the complex kinematics showed by the profile of the emission lines, (c) the high fragmentation of matter, etc. The results suggest that the ENLR of IC 5063 have a hollow bi-conical shape, with one edge aligned to the galaxy disk, which may cause some kind of dependence on velocity of the ionization parameter. Regarding the Mrk 783 properties, it is found that the extension of the optical emission is almost twice the size of the radio one and it seems due to the AGN activity, although there is contamination by star formation around 12 arcsec from the nucleus. Diagnostic diagrams excluded the contribution of star formation in IC 5063 and NGC 7212, while the shock contribution was used to explain the spectra emitted by their high velocity gas.

In this paper we explore the intermediate line region (ILR) by using the photoionisation simulations of the gas clouds present at different radial distances from the center, corresponding to the locations from BLR out to NLR in four types of AGNs. We let for the presence of dust whenever conditions allow for dust existence. All spectral shapes are taken from the recent multi-wavelength campaigns. The cloud density decreases with distance as a power law. We found that the slope of the power law density profile does not affect the line emissivity radial profiles of major emission lines: Hβ, He II, Mg II, C III, and O III. When the density of the cloud at the sublimation radius is as high as 1011.5 cm−3, the ILR should clearly be seen in the observations independently of the shape of the illuminating radiation. Moreover, our result is valid for low ionization nuclear emission regions of active galaxies.

We develop a self-consistent description of the Broad Line Region based on the concept of a failed wind powered by radiation pressure acting on a dusty accretion disk atmosphere in Keplerian motion. The material raised high above the disk is illuminated, dust evaporates, and the matter falls back toward the disk. This material is the source of emission lines. The model predicts the inner and outer radius of the region, the cloud dynamics under the dust radiation pressure and, subsequently, the gravitational field of the central black hole, which results in asymmetry between the rise and fall. Knowledge of the dynamics allows us to predict the shapes of the emission lines as functions of the basic parameters of an active nucleus: black hole mass, accretion rate, black hole spin (or accretion efficiency) and the viewing angle with respect to the symmetry axis. Here we show preliminary results based on analytical approximations to the cloud motion.

Recently, an unknown emission line at E ~3.5 keV from several astrophysical objects has been detected. The line is suggested to be originating from decaying dark matter particles. The results have drawn great attention from the astrophysics and particle physics community. Since the detected line is significantly weak there has also been a long debate over the origin of this mysterious signal. The most accepted scenario is a radiatively decaying sterile neutrino of 7.1 keV in mass producing a monochromatic 3.5 keV line, which is observable in X-ray energy ranges. The problem has not been settled and further observations from more objects are needed to verify the detection in order to constrain the physical properties and the nature of the signal. In this paper, we present the current situation and provide further insights into the subject. [ABSTRACT FROM AUTHOR]

Data from long-term spectral observations of two young planetary nebulae are presented. A significant enhancement of the radiation fluxes in all emission lines and a higher degree of ionization of the gas are detected in the spectrum of M1-46. The opposite effect is observed in the spectrum of M1-65. Over 10 years (2005-2015) the radiative fluxes in the emission lines fell by a factor of 2-3, after which they began to increase. The cause of the observed variability may be a change in the temperature of the central star or a change in the inhomogeneous structure of the nebula through which the ionizing radiation passes. [ABSTRACT FROM AUTHOR]

This contribution, presented at the 2016 conference on Atomic Spectra and Oscillator Strengths for Astrophysical and Laboratory Plasmas (ASOS12), shows how atomic physics contributes to the interpretation of emission-line spectra observed in astronomical nebulae, and discusses a few unsolved issues where atomic physics may play a role, although other possible explanations are indeed possible. It is limited to the determinations of chemical abundances, the most sought-after information derived from emission lines. [ABSTRACT FROM AUTHOR]

The results of spectral and photometric observations of the emission object CH Cyg are presented. The active stage of CH Cyg during 2014-2015 showed up as an increase in the brightnesses to B~7.8 and V~6.8, intensification of the continuum, and increased fluxes in emission lines. A rapid, within days, variability in the emission line profiles was observed. The velocities of individual absorption components were as high as ~3000 km/s. [ABSTRACT FROM AUTHOR]

Based on the gravitational red shift, which is a prediction of Einstein's general relativity theory, of broad optical emission lines in active galactic nuclei (AGNs), a new method is proposed to estimate the virial factors f in measuring black hole masses MRM by the reverberation mapping of AGNs. The factors f can be measured based on two physical quantities, i.e. the gravitational red shifts zg and the full widths at half maxima vFWHM of broad lines. In the past, it has been difficult to determine the factors f for individual AGNs. We apply this new method to several reverberation-mapped type 1 Seyfert galaxies. There is a correlation between f and the radius of the broad-line region (BLR) rBLR, f = 5.4r0.3BLR, for the gravitationally red-shifted broad lines He II, HeI, Hβ and Hα in the narrow-line type 1 Seyfert galaxy (NLS1) Mrk 110. This correlation results from the influence of the radiation pressure of the accretion disc on the BLR clouds. This influence seems to be more important than usually thought so in AGNs. Mrk 110 has f ≈ 8-16, distinctly larger than the mean f ≈1 usually used to estimate MRM for vFWHM. NGC 4593 and NLS1 Mrk 486 have f ≈3 and f ≈9, respectively. Higher f values of several tens are derived for three other NLS1s. There is a correlation between f and accretion rate Mf=1, f = 6.8M0.4 f=1 for five objects, where Mf=1 = M•/LEddc -2 as f = 1 is assumed when estimating MRM used in the Eddington luminosity LEdd, M• is the mass accretion rate, and c is the speed of light. These larger f values will produce higher MRM values and lower Eddington ratios. [ABSTRACT FROM AUTHOR]

The results of the observations and studies of the comet C/2007 N3 (Lulin) on the optical spectra of medium resolution. Spectra were obtained using 23-25.02.2009, the 2nd telescope Zeiss (F_1=6.3 m; F_2=16 m) at high mountain astronomical station “Terskol” Main Astronomical Observatory, National Academy of Sciences of Ukraine and the Institute of Astronomy of the RAS. With a resolution of λ/Δ λ = 3500 (echelle) obtained 7 spectra of the comet (3780–7600 ÅÅ) with exposure to T=3600 s. The comet was at heliocentric distance r=1.38 AU and geocentric – Δ=0.41 AU had the integral magnitude equal to m_1 = 6^m, the phase angle was S-O-T=10°, elongation angle S-O-T=165°, position angle α=292°. Identified on the spectral emission lines. The spectra were examined for the presence luminescent continuum. Determined some physical parameters of luminescent continuum and some other physical parameters of the neutral coma of the comet. The dependence of the change in albedo on wavelength was obtained.

Six middle-resolution optical spectra of comet C/2009 K5 (McNaught) were obtained from 27 March to 2 April 2010 with the help of the 2-m Zeiss reflector and echelle-spectrograph of the High-mountain astronomical station “Terskol” of Institute of Astronomy of Russian Academy of Sciences and Main Astronomical Observatory of National Academy of Sciences of Ukraine. The comet was at heliocentric distance 1.5 A.U. and geocentric one 1.4 A.U. and had the integral magnitude equal to T≈11^m. We present the energy distribution in the spectra of comet С/2009 К5 and the energy distribution of comet emissions along the slit of the spectrograph. Some physical parameters of the neutral coma of comet were calculated with the help of Haser's models. The detailed identification of the spectral emission lines in these spectra were obtained. Presence of luminescent continuum in the spectra of comet С/2009 К5 is discussed and some physical parameters of luminescent continuum were calculated.

Seventeen middle-resolution optical spectra of comet 103Р/Hartley 2 were obtained on 26–28 October 2010 with the help of the 2-m Zeiss reflector and echelle-spectrograph of the High-mountain astronomical station of Institute of Astronomy of Russian Academy of Sciences and Main Astronomical Observatory of National Academy of Sciences of Ukraine at Peak Terskol. The comet was at heliocentric distance 1.06 A.U. and geocentric one 0.13 A.U. and had the integral magnitude equal to m_1=9.1^m. We built the energy distribution in the spectra of comet 103P and made the detailed identification of the spectral emission lines in these spectra. Also in the spectra of comet we found out luminescent continuum in and determined some physical parameters of luminescent continuum. Short period comet 103Р/Hartley 2 of Jupiter’s comet family was the target of the space mission “EPOXI” in 2010.