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A landmark of accretion processes in active galactic nuclei (AGN) is the continuum originating from a complex structure, i.e., an accretion disk and a corona around a supermassive black hole. Modelling the broad-band spectral energy distribution (SED) effectively ionizing the gas-rich broad emission line region (BLR) is key to understanding the various radiative processes at play and their importance that eventually leads to the emission from diverse physical conditions. Photoionization codes are a useful tool to investigate two aspects, the importance of the shape of the spectral energy distribution, and the physical conditions in the broad emission line region. In this work, we critically review long-standing issues pertaining to the spectral energy distribution shape and the anisotropic continuum radiation from the central regions around the accreting supermassive black holes (a few 10-100 gravitational radii), with a focus on black holes accreting at high rates, possibly much above the Eddington limit. The anisotropic emission is a direct consequence of the development of a geometrically and optically thick structure at regions very close to the black hole due to a marked increase in the accretion rates. The analysis presented in this paper took advantage of the look at the diversity of the type-1 active galactic nuclei provided by the main sequence of quasars. The main sequence permitted us to assess the importance of the Eddington ratio and hence to locate the super Eddington sources in observational parameter space, as well as to constrain the distinctive physical conditions of their line-emitting BLR. This feat is posing the basis for the exploitation of quasars as cosmological distance indicators, hopefully allowing us to use the fascinating super Eddington quasars up to unprecedented distances., Comment: Identical to the published version in Frontiers in Astronomy and Space Sciences (09-05-2023). 31 pages, 8 figures, 2 tables, based on the invited talk presented at the SPIG - 31st Summer School and International Symposium on the Physics of Ionized Gases, held between 05th - 09th September 2022

Optical and UV properties of radio-quiet (RQ) and radio-loud (RL, relativistically "jetted") active galactic nuclei (AGN) are known to differ markedly; however, it is still unclear what is due to a sample selection and what is associated with intrinsic differences in the inner workings of their emitting regions. Chemical composition is an important parameter related to the trends of the quasar main sequence. Recent works suggest that in addition to physical properties such as density, column density, and ionization level, strong FeII emitters require very high metal content. Little is known, however, about the chemical composition of jetted radio-loud sources. In this short note, we present a pilot analysis of the chemical composition of low-z radio-loud and radio-quiet quasars. Optical and UV spectra from ground and space were combined to allow for precise measurements of metallicity-sensitive diagnostic ratios. The comparison between radio-quiet and radio-loud was carried out for sources in the same domain of the Eigenvector 1 / main sequence parameter space. Arrays of dedicated photoionization simulations with the input of appropriate spectral energy distributions indicate that metallicity is sub-solar for RL AGN, and slightly sub-solar or around solar for RQ AGN. The metal content of the broad line emitting region likely reflects a similar enrichment story for both classes of AGN not involving recent circum-nuclear or nuclear starbursts., 14 pages, 5 figures, to appear in Galaxies

The Vera Rubin Observatory will provide an unprecedented set of time-dependent observations of the sky. The planned Legacy Survey of Space and Time (LSST) operating for 10 years will provide dense lightcurves for thousands of active galactic nuclei (AGN) in Deep Drilling Fields (DDFs) and less dense lightcurves for millions of AGN. We model the prospects for measuring time delays for emission lines with respect to the continuum, using these data. We model the artificial lightcurves using Timmer-Koenig algorithm, we use the exemplary cadence to sample them, we supplement lightcurves with the expected contamination by the strong emission lines (Hbeta, Mg II and CIV as well as with Fe II pseudo-continuum and the starlight). We choose the suitable photometric bands appropriate for the redshift and compare the assumed line time delay with the recovered time delay for 100 statistical realizations of the light curves. We show that time delays for emission lines can be well measured from the Main Survey for the bright tail of the quasar distribution (about 15% of all sources) with the accuracy within 1 sigma error, for DDFs results for fainter quasars are also reliable when all 10 years of data are used. There are also some prospects to measure the time delays for the faintest quasars at the smallest redshifts from the first two years of data, and eventually even from the first season. The entire quasar population will allow obtaining results of apparently high accuracy but in our simulations, we see a systematic offset between the assumed and recovered time delay depending on the redshift and source luminosity which will not disappear even in the case of large statistics. Such a problem might affect the slope of the radius-luminosity relation and cosmological applications of quasars if simulations correcting for such effects are not performed., Astronomy & Astrophysics in press

A sample of X-ray detected reverberation-mapped quasars provides a unique opportunity to compare cosmological constraints inferred using two well-established relations - the X-ray/UV luminosity ($L_{X}-L_{UV}$) relation and the broad-line region radius-UV monochromatic luminosity ($R-L$) relation. $L_{X}-L_{UV}$ and $R-L$ luminosity distances to the same quasars exhibit a distribution of their differences that is generally positively skewed for the six cosmological models we consider. This behaviour can be interpreted qualitatively to arise as a result of the dust extinction of UV/X-ray quasar emission. We show that the extinction always contributes to the non-zero difference between $L_{X}-L_{UV}$-based and $R-L$-based luminosity distances and we derive a linear relationship between the X-ray/UV colour index $E_{X-UV}$ and the median/mean value of the luminosity-distance difference, which also depends on the value of the $L_{X}-L_{UV}$ relation slope. Taking into account the prevailing positive values of the luminosity-distance difference median, we estimate an average X-ray/UV colour index of $\overline{E}_{X-UV}=0.089 \pm 0.019$ mag, while the value based on the positive mean values of the difference is $\overline{E}_{X-UV}=0.050\pm 0.013$ mag. We demonstrate that this amount of extinction is typical for the majority of quasars since it originates in the circumnuclear and interstellar media of host galaxies. It can only be slightly alleviated by the standard hard X-ray and far-UV extinction cuts used by Lusso et al. (2020). Consequently, the $L_{X}-L_{UV}$ relation QSO data compilation of Lusso et al. (2020) cannot be used for cosmological purposes., Comment: 12 pages, 7 figures, 3 tables; submitted to the MNRAS Main Journal, comments welcome

Development of the Rubin Observatory Legacy Survey of Space and Time (LSST) includes a series of Data Challenges (DC) arranged by various LSST Scientific Collaborations (SC) that are taking place during the projects preoperational phase. The AGN Science Collaboration Data Challenge (AGNSCDC) is a partial prototype of the expected LSST AGN data, aimed at validating machine learning approaches for AGN selection and characterization in large surveys like LSST. The AGNSC-DC took part in 2021 focusing on accuracy, robustness, and scalability. The training and the blinded datasets were constructed to mimic the future LSST release catalogs using the data from the Sloan Digital Sky Survey Stripe 82 region and the XMM-Newton Large Scale Structure Survey region. Data features were divided into astrometry, photometry, color, morphology, redshift and class label with the addition of variability features and images. We present the results of four DC submitted solutions using both classical and machine learning methods. We systematically test the performance of supervised (support vector machine, random forest, extreme gradient boosting, artificial neural network, convolutional neural network) and unsupervised (deep embedding clustering) models when applied to the problem of classifying/clustering sources as stars, galaxies or AGNs. We obtained classification accuracy 97.5% for supervised and clustering accuracy 96.0% for unsupervised models and 95.0% with a classic approach for a blinded dataset. We find that variability features significantly improve the accuracy of the trained models and correlation analysis among different bands enables a fast and inexpensive first order selection of quasar candidates, Comment: Accepted by ApJ. 21 pages, 14 figures, 5 tables

We test a scenario claiming that the broad absorption line (BAL) phenomenon in quasars (QSOs) is not a temporary stage of their life. In this scenario, we see the BAL effect only if the line of sight is within a spatially limited and collimated massive outflow cone covering only a fraction of sky from the point of view of the nucleus. The aim is to understand the theoretical mechanism behind the massive outflow in BAL QSOs which is important for modelling the impact of quasars onto the star formation rate in the host galaxy, and, subsequently, onto the galaxy evolution. We apply the specific theoretical model of dust-driven wind. The model has considerable predictive power. The 2.5D version of FRADO model of Czerny & Hryniewicz gives rise to the formation of fast funnel-shaped outflow from the disk for a certain range of black hole masses, Eddington ratios and metallicities. We now interpret BAL QSO as sources viewed along the outflowing stream and we calculate the probabilities of seeing the BAL phenomenon as functions of these global parameters, and we compare these probabilities to those seen in the observational data. We include considerations on the presence/absence of obscuring torus. Comparing our theoretical results with observational data for a sample consisting of two sub-populations of BAL and non-BAL QSOs we found that both in the model and in the data the BAL phenomenon mostly happens for sources with black hole masses larger than 10^{8} solar mass, the effect get stronger with accretion rate, and also high metallicities are more likely in QSOs showing BAL features if the presence of torus is taken into account. The consistency of the model with the data provides support for the interpretation of the BAL phenomenon as the result of the orientation of the source. It also supports the underlying theoretical model although more consistency checks should be done in the future., 15 pages, 13 figures, 3 tables, Accepted for publication in the Journal of Astronomy and Astrophysics (A&A)

This paper is the first in a series of preparing and analyzing spectral and other properties for a database of already discovered Changing-Look Active Galactic Nuclei (CL AGNs). Here, we focus on the spectral fitting and analysis of broad emission lines in an exhaustive sample of 112 CL AGNs available in the literature with existing SDSS/BOSS/eBOSS spectroscopy. Additionally, we have gathered older/newer spectral epochs from all the available SDSS data releases to make the database more complete. We use PyQSOFit and perform a homogeneous spectral decomposition of all of our SDSS spectra and tabulate the AGN continuum and emission-line properties per epoch per source, chronologically. This further allows us to categorize the sources in our sample as Turn-On or Turn-Off and subsequently check for repeated occurrences of such phases. We then estimate the black hole mass (M$_{\rm BH}$) and the Eddington ratio ($\lambda_{\rm Edd}$) per epoch per source where the required parameters are available and well-estimated. We realize the movement of the source in the M$_{\rm BH}$-$\lambda_{\rm Edd}$ plane allowing us to check for systematic changes in the source's fundamental properties. We then track their transition along the optical plane of the Eigenvector 1 (EV1) schema and categorize sources that either stay within the same Population (A or B) or make an inter-population movement as a function of spectral epoch. We also test the Balmer decrement (H$\alpha$/H$\beta$) of a subset of our sample of CL AGNs as a function of time and AGN luminosity., Comment: 65 pages, 20 figures, 4 tables, submitted to AAS journals, comments welcome! arXiv admin note: text overlap with arXiv:2201.09123 by other authors

Narrow Line Seyfert 1 (NLSy1) galaxies have been shown to have high Eddington ratios and relatively small black hole masses. The measurement of the black hole masses is based on the virial relation which is dependent on the distribution of the line-emitting gas and the viewing angle to the source. Spectropolarimetry enables us to probe the geometry of this line-emitting gas and allows us to estimate independently the viewing angle of the source by comparing the spectrum viewed under natural light and in the polarized light. We performed spectropolarimetric observations of three NLSy1 - Mrk 1044, SDSS J080101.41+184840.7, and IRAS 04416+1215 using the European Southern Observatory's Very Large Telescope. We use ESO Reflex workflow to perform standard data reduction and extract the natural and polarized spectra. We estimate the Stokes parameters and the viewing angles of the three sources. We model the Stokes parameters and infer the properties of the scattering media - located in the equatorial and polar regions, and simulate the spectra observed both in natural light and in polarized light using the polarization radiative transfer code STOKES. We confirm that all three sources are high Eddington ratio objects. We are successful in recovering the observed H$\alpha$ line profile both in the natural and polarized light using the STOKES modelling. We recover the polarization fractions of the order of 0.2-0.5% for the three sources. Our principal component analysis shows that the sample of the 25 sources including our sources, Fairall 9 from Jiang et al. (2021), and sources from Capetti et al. (2021) are mainly driven by the black hole mass and Eddington ratio. We re-affirm the connection of the strength of the optical FeII emission with the Eddington ratio. But, the dependence on the viewing angle is moderate, more like a secondary effect., Comment: 20 pages, 17 figures, 10 tables, submitted to Astronomy & Astrophysics. Comments welcome!

The study of the broad-line region (BLR) using reverberation mapping has allowed us to establish an empirical relation between the size of this line emitting region and the continuum luminosity that drives the line emission (i.e. the R$_{\rm BLR}$-L$_{\rm 5100}$ relation). To realize its full potential, the intrinsic scatter in the R$_{\rm BLR}$-L$_{\rm 5100}$ relation needs to be understood better. The Eddington ratio plays a key role in addressing this problem. On the other hand, the Eigenvector 1 schema has helped to reveal an almost clear connection between the Eddington ratio and the strength of the optical FeII emission which has its origin from the BLR. This paper aims to reveal the connection between theoretical entities, like, the ionization parameter (U) and cloud mean density (n$_{\rm H}$) of the BLR, with physical observables obtained directly from the spectra, such as optical FeII strength (R$_{\rm FeII}$) that has immense potential to trace the accretion rate. We utilize the photoionization code CLOUDY and perform a suite of models to reveal the BLR in the U-n parameter space and estimate RFeII. We compare the SEDs for a prototypical Population A and Population B source, I Zw 1 and NGC 5548, respectively, in this study. The results from the photoionization modelling are combined with existing reverberation mapped sources with observed R$_{\rm FeII}$ estimates, allowing us to provide an analytical formulation to tie together the aforementioned quantities. We utilize the comparison of the modelled equivalent widths for the low-ionization emission lines to their observed values to identify the optimal (U,n$_{\rm H}$). The recovery of the correct physical conditions in the BLR suggests that the BLR `sees' a different, filtered ionizing continuum with only a very small fraction (~1-10%) that leads to the line emission in the dustless, low-ionization BLR., 33 pages, 12 figures, 4 tables, accepted for publication in `Frontiers in Astronomy and Space Sciences: Rising Stars' Issue

We report preliminary results on the analysis of the continuum and H$��$ light curves of the type-1 active galactic nucleus (AGN) NGC 5548. We notice a clear signature of shallowing in the trend between the H$��$ and the continuum luminosities. We attempt the recovery of this observed H$��$ emission trend as a response to large continuum flux increase using CLOUDY photoionization simulations. We explore a wide range in the physical parameters space for modelling the H$��$ emission from the broad-line region (BLR) appropriate for this source. We employ a constant density, single cloud model approach in this study and successfully recover the observed shallowing of the H$��$ emission with respect to the rising AGN continuum. With our modelling, we are able to provide constraints on the local BLR cloud density and recover the BLR distances (from the continuum source) consistent with the H$��$ reverberation mapping estimates. We further discuss the implications of the BLR covering factor and their sizes on recovering the observed trend., 10 pages, 7 figures, accepted version after proofs in Astronomische Nachrichten (Special Issue, 13th Serbian Conference on Spectral Line Shapes in Astrophysics)

Broad-band spectra of active galaxies contain a wide range of information that help reveal the nature and activity of the central continuum source and their immediate surroundings. Understanding the evolution of metals in the spectra of Active Galactic Nuclei (AGN) and linking them with the various fundamental black hole (BH) parameters, for example, BH mass, the bolometric luminosity of the source, its accreting power, can help address the connection between the growth of the BH across cosmic time. We investigate the role of selected metallicity indicators utilizing the rich spectroscopic database of emission lines covering a wide range in redshift in the recent spectroscopic data release of Sloan Digital Sky Survey (SDSS). We make careful filtering of the parent sample to prepare a pair of high-quality, redshift-dependent sub-samples and present the first results of the analysis here. To validate our findings from the simple correlations, we execute and evaluate the performance of a linear dimensionality reduction technique - principal component analysis (PCA), over our sub-samples and present the projection maps highlighting the primary drivers of the observed correlations. The projection maps also allow us to isolate peculiar sources of potential interest., Comment: 3 pages, 2 figures, submitted to the Proceedings of the 40th Polish Astronomical Society Meeting, 13-17 September 2021, Szczecin, Poland

Using bonafide black hole (BH) mass estimates from reverberation mapping and the line ratio [Si VI]1.963$\mu$m/Br$\gamma_{\rm broad}$ as tracer of the Active Galactic Nuclei (AGN) ionizing continuum, we find a novel BH-mass scaling relation of the form log($M_{\rm BH}) = (6.40\pm 0.17) - (1.99\pm 0.37) \times$ log ([Si VI]/Br$\gamma_{\rm broad})$, over the BH mass interval, $10^6 - 10^8$ M$_{\odot}$. The current sample consists of 21 Type-1 AGNs with the overall dispersion in our scaling relation at 0.47 dex, one that emulates the well-established M-$\sigma$ relation which shows a dispersion $\sim$0.44 dex. The new scaling offers an economic, and physically motivated alternative for BH estimate using single epoch spectra, avoiding large telescope time (reverberation mapping) or absolute flux calibration (the continuum luminosity method). With the advent of big surveys in the infrared in the near future, we aim to reduce the scatter in the relation by supplementing with more sources., Comment: 3 pages, 1 figure, submitted to the Proceedings of the 40th Polish Astronomical Society Meeting, 13-17 September 2021, Szczecin, Poland

The CaFe Project involves the study of the properties of the low ionization emission lines (LILs) pertaining to the broad-line region (BLR) in active galaxies. These emission lines, especially the singly-ionized iron (Fe II) in the optical and the corresponding singly-ionized calcium (Ca II) in the near-infrared (NIR) are found to show a strong correlation in their emission strengths, i.e., with respect to the broad H$\beta$ emission line, the latter also belonging to the same category of LILs. We outline the progress made in the past years that has developed our understanding of the location and the efficient production of these emission lines. We have yet to realize the full potential of Ca II emission and its connection to the black hole and the BLR parameters which can be useful in - (1) the classification of Type-1 active galactic nuclei (AGNs) in the context of the main sequence of quasars, (2) to realize an updated radius-luminosity relation wherein the inclusion of the strength of this emission line with respect to H$\beta$ can be an effective tracer of the accretion rate of the AGN, and, (3) the close connection of Ca II to Fe II can allow us to use the ratio of the two species to quantify the chemical evolution in these active galaxies across cosmic time. In this paper, we use our current sample and utilize a non-linear dimensionality reduction technique - t-distributed Stochastic Neighbour Embedding (tSNE), to understand the clustering in our dataset based on direct observables., Comment: 6 pages, 3 figures, submitted to the Proceedings of the 40th Polish Astronomical Society Meeting, 13-17 September 2021, Szczecin, Poland

Getting insights on the shape and nature of the ionizing continuum in astronomical objects is often done via indirect methods as high energy photons are absorbed by our Galaxy. This work explores the ionization continuum of active galactic nuclei (AGN) using the ubiquitous coronal lines. Using bona-fide BH mass estimates from reverberation mapping and the line ratio [Si VI] 1.963 micron/Br$\gamma_{\rm broad}$ as tracer of the AGN ionizing continuum, a novel BH-mass scaling relation of the form log($M_{\rm BH}) = (6.40\pm 0.17) - (1.99\pm 0.37) \times$ log ([Si VI]/Br$\gamma_{\rm broad})$, over the BH mass interval, $10^6 - 10^8$ M$_{\odot}$ with dispersion 0.47 dex is found. Following on the thin accretion disc approximation and after surveying a basic parameter space for coronal lines production, we believe that a key parameter driving this anti-correlation is the effective temperature of the accretion disc, this being effectively sampled by the coronal line gas. Accordingly, the observed anti-correlation becomes formally in line with the thin accretion disc prediction $T_{\rm{disc}} \propto {M_{\rm BH}}^{-1/4}$., Comment: 16 pages, 6 figures. Submitted to ApJ

In the near future, the arrival of new surveys promises a significant increment in the number of quasars (QSO) at large redshift ranges. This will help to constrain the dark energy models using quasars. The Large Synoptic Survey Telescope (LSST) will cover over 10 million QSO in six photometric bands during its 10-year run. QSO will be monitored and subsequently analysed using the photometric reverberation mapping technique. Oncoming LSST data will decrease the uncertainties in the dark energy determination using reverberating--mapped sources, particularly at high redshifts. We present the first steps in modelling of light curves for H$\beta$ and MgII and discuss the quasar selection in the context of photometric reverberation mapping with LSST. With the onset of the LSST era, we expect a huge rise in the overall quasar counts and redshift range covered ($z\leq7.0$), which will provide a better constraint of AGN properties with cosmological purposes., Comment: 3 pages, 1 figure, contribution to the Proceedings of the XXXIX Polish Astronomical Society Meeting (09-12 September 2019, Olsztyn, Poland)

Broad-line regions (BLR) are one of the main components that constitute the phenomenological picture of active galaxies near the vicinity of the accreting supermassive black holes. Both theoretical and observational studies have shown that the BLR is made of dense, ionized gas clumps that have a strong virialized distribution at parsec-scale distances from the nuclei. Using a theoretically motivated photoionized gas model, I constrain the ionisation parameter (U) and cloud density (n$_{\rm{H}}$) as a function of the strength of the FeII emission. Recent observations in the reverberation mapping studies have contested the standard radius-luminosity relation showing increased dispersion in the relation, in particular, after the inclusion of highly accreting quasars. I incorporate the departure coefficient that accounts for this dispersion. This departure term in terms of the dimensionless accretion rate ($\dot{\mathcal{M}}$) and Eddington ratio ($L\mathrm{_{bol}}/L\mathrm{_{Edd}}$), also includes the virial factor that accounts for the BLR geometry. I then combine the fundamental plane relation for the BLR to connect the FeII strength (R$_{\rm{FeII}}$) in terms of U and n$_{\rm{H}}$ using selected values for the shape of the broad H$\beta$ profile., Comment: 6 pages, 3 figures, contribution to the Proceedings of the XXXIX Polish Astronomical Society Meeting (09-12 September 2019, Olsztyn, Poland)

Eigenvector 1 (EV1) was found to be the dominant component behind the significant correlations for the measured parameters in quasar spectra (Boroson & Green, 1992). The parameter R$_{\mathrm{FeII}}$, which strongly correlates to the EV1, is the ${\mathrm{FeII}}$ strength, defined to be the ratio of the equivalent width of ${\mathrm{FeII}}$ to the equivalent width of ${\mathrm{H\beta}}$. This allows to construct a quasar main sequence analogous to the stellar properties driven HR diagram (Sulentic et al. 2001). We try to find the main driver behind the EV1 among the basic (theoretically motivated) parameters of an active nucleus (Eddington ratio, black hole mass, accretion rate, spin, and viewing angle). Based on theoretical modeling using the photoionization code CLOUDY (Ferland et al. 2013), we test the hypothesis that the physical driver of EV1 is the maximum of the accretion disk temperature ($\mathrm{T_{BBB}}$), reflected in the shape of the spectral energy distribution (SED). We have assumed that both H$\mathrm{\beta}$ and Fe${\mathrm{II}}$ emission come from the Broad Line Region represented as a constant density cloud in a plane-parallel geometry. We test the effect of changing Eddington ratio on the $\mathrm{R_{FeII} - T_{BBB}}$ trends with varying mean hydrogen densities. We also test the effect of adding microturbulence that affect the line intensities on the overall $\mathrm{R_{FeII} - T_{BBB}}$ picture., Comment: 4 pages, 4 figures, to be published in the proceedings of the 3rd Cosmology School (Polish Astronomical Society), 10-23 July 2017, Krak\'ow, Poland