Search

In terms of the variable nature of normal active galaxy nuclei (AGN) and luminous quasars, a so-called flux variation gradient (FVG) method has been widely utilized to estimate the underlying non-variable host galaxy fluxes. The FVG method assumes an invariable AGN color, but this assumption has been questioned by the intrinsic color variation of quasars and local Seyfert galaxies. Here, using an up-to-date thermal fluctuation model to simulate multi-wavelength AGN variability, we theoretically demonstrate that the FVG method generally overestimates the host galaxy flux; that is, it is more significant for brighter AGN/quasars. Furthermore, we observationally confirm that the FVG method indeed overestimates the host galaxy flux by comparing it to that estimated through other independent methods. We thus caution that applying the FVG method should be performed carefully in the era of time-domain astronomy. [ABSTRACT FROM AUTHOR]

Narrow-line Seyfert 1 (NLS1) galaxies are a peculiar subclass of active galactic nuclei (AGN). Among them, TXS 1206+549 belongs to a small group of radio-loud and γ-ray-emitting NLS1 galaxies. We focus on the radio properties of this galaxy by analysing archival, high-resolution, very long baseline interferometry (VLBI) imaging observations taken at 8 GHz frequency in six epochs between 1994 and 2018. Using the milliarcsecond-scale radio structure, we can resolve a core and a jet component whose angular separation increases by (0.055±0.006) mas yr−1. This corresponds to an apparent superluminal jet component motion of (3.5±0.4)c. From the core brightness temperature and the jet component proper motion, we determine the characteristic Doppler-boosting factor, the bulk Lorentz factor, and the jet viewing angle. We find no compelling evidence for a very closely aligned blazar-type jet. The parameters for TXS 1206+549 resemble those of radio-loud quasar jets with a moderate Lorentz factor (Γ≈4) and ϑ≈24∘ inclination to the line of sight.

Using Sloan Digital Sky Survey (SDSS) spectra, we applied an automatic method to search for outflows (OFs) in three large samples of narrow-line active galactic nuclei (AGN) at low redshifts ( z < 0.4), separated into three spectral activity classes: radio-loud galaxies (RGs), 15,793; radio-quiet Seyfert 2 AGN (Sy2), 18,585; and LINERs, 25,656. In general, the probability of detecting an OF decreases along the sequence Sy1→Sy2→LINER/RG and independently of the AGN class, the wind velocity, traced by W 80, increases with the AGN luminosity. Moreover W 80 is systematically higher in RGs or any of the other AGN classes when detected in radio. These results support the idea that there are two main modes of production of OF, the radiative mode dominant in radio-quiet AGN and the jet mode dominant in RGs, although both modes could also happen simultaneously at different levels. From the spectra and SDSS photometry, the characteristics of the AGN host galaxies and their supermassive black holes (SMBHs) were also retrieved using the stellar population synthesis code STARLIGHT. This revealed that, independently of the AGN spectral class, (1) galaxy hosts with OFs have systematically later morphological types and higher star formation rates (SFRs) than their counterparts without OF, (2) the AGN occupy different positions in the specific diagnostic diagram (specific black hole accretion rate (sBHAR) versus specific SFR), which suggests they follow different evolutionary paths congruent with the morphology of their galaxy hosts, and (3) they show no evidence of AGN quenching or triggering of star formation. These results are consistent with a scenario explaining the different AGN classes as consequences of different formation processes of galaxies: early-type galaxies (LINERs and RGs) formed bigger bulges and more massive SMBHs, exhausting their reservoir of gas more rapidly than late-type galaxies (Sy2 and Sy1), and thereby quenching their star formation and starving their SMBHs.

We introduce our project, AGNSTRONG (Active Galactic Nuclei and STaR fOrmation in Nearby Galaxies). Our research goals encompass investigating the kinematic properties of ionized and molecular gas outflows, understanding the impact of AGN feedback, and exploring the coevolution dynamics between AGN strength activity and star formation activity. We aim to conduct a thorough analysis to determine whether there is an increase or suppression in star formation rates (SFRs) among targets with and without powerful relativistic jets. Our sample consists of 35 nearby AGNs with and without powerful relativistic jet detections. Utilizing submillimeter continuum observations at 450 and 850 μ m from SCUBA-2 at the James Clerk Maxwell Telescope, we determine SFRs for our sources using spectral energy distribution (SED) fitting models. Additionally, we employ high-quality, spatially resolved spectra from UV-optical to near-infrared bands obtained with the Double Spectrograph and Triple Spectrograph mounted on the 200 inch Hale Telescope at Palomar Observatory to study their multiphase gas outflow properties. This paper presents an overview of our sample selection methodology, research strategy, and initial results of our project. We find that the SFRs determined without including the submillimeter data in the SED fitting are overestimated by ∼0.08 dex compared to those estimated with the inclusion of submillimeter data. Additionally, we compare the estimated SFRs in our work with those traced by the 4000 Å break, as provided by the Max Planck Institute for Astrophysics and Johns Hopkins University catalog. We find that our determined SFRs are systematically higher than those traced by the 4000 Å break. Finally, we outline our future research plans.

Key issues in AGN and galaxy formation are discussed. Very successful Unified Models explain much of the variety of AGN with orientation effects; the ingredients are shadowing by a dusty “torus” and relativistic beaming. A spinoff result is described which is important for the formation of massive elliptical galaxies, the most spectacular and unequivocal AGN feedback phenomenon known. This is the so-called “alignment effect” in powerful radio galaxies at z∼>1. One of them is a BAL radio galaxy! Next, I explain a very robust derivation of the reddening law for nuclear dust, which reveals a dearth of small grains on parsec scales. Then, the quasistatic thin accretion disk model, thought by many to explain the energetically dominant optical/UV continuum, is thoroughly debunked. Much of this was known when the model was proposed 35 years ago. A new argument is provided that trivially falsifies a huge superset of such models. I then show that it is possible to see the central engine spectrum with the atomic and dust emission surgically removed! Few have noticed this breakthrough work. Finally, the far IR dust emission in Cygnus A is 10% polarized; to date, high nuclear dust polarization has been seen in all radio loud objects and no radio quiet ones.

Blazars are a subclass of active galactic nuclei (AGN) having relativistic jets aligned within a few degrees of our line-of-sight and form the majority of the AGN detected in the TeV regime. The Fermi-Large Area Telescope (LAT) is a pair-conversion telescope, sensitive to photons having energies between 20 MeV and 2 TeV, and is capable of scanning the entire gamma-ray sky every three hours. Despite the remarkable success of the Fermi mission, many questions still remain unanswered, such as the site of gamma-ray production and the emission mechanisms involved. The Asteroid Terrestrial-impact Last Alert System (ATLAS) is a high cadence all sky survey system optimized to be efficient for finding potentially dangerous asteroids, as well as in tracking and searching for highly variable and transient sources, such as AGN. In this study, we investigate possible correlations between the Fermi-LAT observations in the 100 MeV–300 GeV energy band and the ATLAS optical data in the R-band, centered at 679 nm, for a sample of 18 TeV-detected northern blazars over 8 years of observations between 2015 and 2022. Under the assumption that the optical and gamma-ray flares are produced by the same outburst propagating down the jet, the strong correlations found for some sources suggest a single-zone leptonic model of emission.

The advancement of neutrino observatories has sparked a surge in multi-messenger astronomy. Multiple neutrino associations among blazars are reported while neutrino production sites are located within their central (sub)parsecs. Yet, many questions remain on the nature of those processes. The next generation Event Horizon Telescope (ngEHT) is uniquely positioned for these studies, as its high frequency and resolution can probe both the accretion disk region and the parsec-scale jet. This opens up new opportunities for connecting the two regions and unraveling the proton acceleration and neutrino production in blazars. We outline observational strategies for ngEHT and highlight what it can contribute to the multi-messenger study of blazars.

We propose the usage of an innovative method for selecting transients and variables. These sources are detected at different wavelengths across the electromagnetic spectrum spanning from radio waves to gamma-rays. We focus on radio signals and use State Space Models, which are also referred to as Dynamic Linear Models. State Space Models (and more generally parametric auto-regressive models) have been the mainstay of economic modelling for some years, but rarely they have been used in Astrophysics. The statistics currently used to identify radio variables and transients are not sophisticated enough to distinguish different types of variability. These methods simply report the overall modulation and significance of the variability, and the ordering of the data in time is insignificant. State Space Models are much more advanced and can encode not only the amount and significance of the variability but also properties, such as slope, rise or decline for a given time t. In this work, we evaluate the effectiveness of State Space Models for transient and variable detection including classification in time-series astronomy. We also propose a method for detecting a transient source hosted in a variable active galaxy, whereby the time-series of a static host galaxy and the dynamic nature of the transient in the galaxy are intertwined. Furthermore, we examine the hypothetical scenario where the target transient we want to detect is the gravitational wave source GW170817 (or similar). [ABSTRACT FROM AUTHOR]

Radio activity in AGN (Active Galactic Nuclei) produce feedback on the host galaxy via the impact of the relativistic jets on the circumnuclear gas. Although radio jets can reach up to several times the optical radius of the host galaxy, in this review we focus on the observation of the feedback deposited locally in the central region of the host galaxies, in the form of outflows due to the jet-gas interaction. We begin by discussing how galaxy mergers and interactions are the most favored scenario for triggering radio AGN after gas accretion to the nuclear supermassive black hole and star formation enhancement in the nuclear region, observed in particular in the most luminous sources. We then discuss observational signatures of the process of jet-gas coupling, in particular the resulting outflows and their effects on the host galaxy. These include the presence of shock signatures and the detection of outflows not only along the radio jet but perpendicular to it in many sources. Although most of the studies are done via the observation of ionized gas, molecular gas is also being increasingly observed in outflow, contributing to the bulk of the mass outflow rate. Even though most radio sources present outflow kinetic powers that do not reach 1%Lbol, and thus do not seem to provide an immediate impact on the host galaxy, they act to heat the ISM gas, preventing star formation, slowing the galaxy mass build-up process and limiting the stellar mass growth, in a “maintenance mode” feedback.

The results of observations of selected stars orbiting the central body of our Galaxy, which, according to the latest data, has a mass of about 4 million of solar mass, are considered. Using themethods of observation and processing of binary stars used at the Pulkovo Observatory and the published exact relative positions of the star-central body obtained with the Keck and VLT telescopes, we checked the possibility of determining the preliminary orbits of the above objects in some cases from observations covering sufficient short arc in relation to the turnover period. Examples are the stars S02 and S102 with published positions and the graphical data for S27 and S4711. We attempted to calculate the assumed relativistic effects in accordance with the orbital elements obtained by Pulkovo methods. In this case, the estimates of the O-C errors for these orbits turned out to be comparable with the O-C errors for the orbits published by the Keck and VLT observers, in some cases about several milliarcseconds. The theoretical relativistic parameters also turned out to be of the same order of value with the results of these authors. [ABSTRACT FROM AUTHOR]

We present an overview of the results obtained from the study of the resolved distribution of molecular gas around eight young (≲106yr), peaked-spectrum radio galaxies. Tracing the distribution and kinematics of the gas around these radio sources allows us to trace the interplay between the jets and the surrounding medium. For three of these sources, we present new CO(1-0) observations, obtained with the Northern Extended Millimeter Array (NOEMA) with arcsecond resolution. In two of these targets, we also detected CN lines, both in emission and absorption. Combining the new observations with already published data, we discuss the main results obtained. Although we found that a large fraction of the cold molecular gas was distributed in disc-like rotating structures, in the vast majority of the sources, high turbulence and deviations from purely quiescent gas (including outflows) were observed in the region co-spatial with the radio continuum emission. This suggests the presence of an interaction between radio plasma and cold molecular gas. In particular, we found that newly born and young radio jets, even those with low power i.e., Pjet < 1045 erg s−1), are able to drive massive outflows of cold, molecular gas. The outflows are, however, limited to the sub-kpc regions and likely short lived. On larger scales (a few kpc), we observed cases where the molecular gas appears to avoid the radio lobes and, instead, wraps around them. The results suggest the presence of an evolutionary sequence, which is consistent with previous simulations, where the type of impact of the radio plasma changes as the jet expands, going from a direct jet-cloud interaction able to drive gas outflows on sub-kpc scales to a more gentle pushing aside of the gas, increasing its turbulence and likely limiting its cooling on kpc scales. This effect can be mediated by the cocoon of shocked gas inflated by the jet–cloud interactions. Building larger samples of young and evolved radio sources for observation at a similar depth and spatial resolution to test this scenario is now needed and may be possible thanks to more data becoming available in the growing public archives.

We analyze the X-ray properties of a sample of 23 high-probability active galactic nucleus (AGN) candidates with ultraviolet variability identified in Wasleske et al. Using data from the Chandra X-ray Observatory and XMM-Newton Observatory, we that find 11/23 nuclei are X-ray detected. We use spectral energy distribution modeling to compute star formation rates and show that the X-ray luminosities are typically in excess of the X-ray emission expected from star formation by at least an order of magnitude. Interestingly, this sample shows a diversity of optical spectroscopic properties. We explore possible reasons for why some objects lack optical spectroscopic signatures of black hole activity while still being UV-variable and X-ray bright. We find that host galaxy stellar emission and obscuration from gas and dust are potential factors. We study where this sample falls on relationships such as α _OX − L _2500 and L _X − L _IR and find that some of the sample falls outside the typical scatter for these relations, indicating that they differ from the standard quasar population. With the diversity of optical spectroscopic signatures and varying impacts of dust and stellar emissions on our sample, these results emphasize the strength of variability in selecting the most complete set of AGN, regardless of other host galaxy properties.

Active galactic nuclei with their relativistic jets pointed toward the observer are a class of luminous gamma-ray sources commonly known as blazars. The study of this source class is essential to unveil the physical processes powering these extreme jets, to understand their cosmic evolution, as well as to indirectly probe the extragalactic background light. To do so, however, one needs to correctly classify and measure a redshift for a large sample of these sources. The Third Fermi–LAT Catalog of High-Energy Sources (3FHL) contains 1212 blazars detected at energies greater than 10 GeV. However, ∼25% of these sources are unclassified and ∼56% lack redshift information. To increase the optical completeness of blazars in the 3FHL catalog, we devised an optical spectroscopic follow-up campaign using 4 m and 8 m telescopes. In this paper, we present the results of the last part of this campaign, where we observed 5 blazars using the 8 m Gemini-S telescope in Chile. We report all the 5 sources to be classified as BL Lacs, a redshift lower limit for 2 sources, and featureless spectra for the remaining 3 sources. We also performed a one-zone leptonic fit to the two sources with the redshift lower limits.

Relativistic jets from nearby low-luminosity active-galactic-nuclei (LLAGN) were observed by Very-Long Baseline Interferometry (VLBI) across many orders of magnitude in space, from milliparsec to sub-parsec scales, and from the jet base in the vicinity of black holes to the jet collimation and acceleration regions. With the improved resolution for VLBI observations, resolved VLBI jet morphologies provide valuable opportunities for testing and constraining black hole jet physics. In this review, we summarize and discuss the current progress of modeling nearby LLAGN jet images from horizon scales to large scales, including the construction of jet models and the assumed emission details. Illustrative examples for jet image modeling are also given to demonstrate how jet image features may vary with the underlying physics.

The effective size of broad line region (BLR), so-called the BLR radius, in galaxies with active galactic nuclei (AGN) scales with the source luminosity. Therefore, by determining this location either observationally through reverberation mapping or theoretically, one can use AGNs as an interesting laboratory to test cosmological models. In this article we focus on the theoretical side of BLR based on the Failed Radiatively Accelerated Dusty Outflow (FRADO) model. By simulating the dynamics of matter in BLR through a realistic model of radiation of accretion disk (AD) including the shielding effect, as well as incorporating the proper values of dust opacities, we investigate how the radial extension and geometrical height of the BLR depends on the Eddington ratio [and blackhole mass], and modeling of shielding effect. We show that assuming a range of Eddington ratios and shielding we are able to explain the time-delays in a sample of reverberation-measured AGNs.

A fascinating topic in radio astronomy is how to associate the complexity of observed radio structures with their environment in order to understand their interplay and the reason for the plethora of radio structures found in surveys. In this project, we explore the distortion of the radio structure of Fanaroff–Riley (FR)-type radio sources in the VLA-COSMOS Large Project at 3 GHz and relate it to their large-scale environment. We quantify the distortion by using the angle formed between the jets/lobes of two-sided FRs, namely bent angle (BA). Our sample includes 108 objects in the redshift range 0.08

We explored the statistical properties of short-term X-ray variability using long-exposure XMM-Newton data during high X-ray variability phases of blazars S5 0716+714 and PKS 2155-304. In general, the hardness ratio shows correlated variations with the source flux state (count rate), but in a few cases, mainly the bright phases, the trend is complex with both correlation and anti-correlation, indicating spectral evolution. Stationarity tests suggest the time series are non-stationarity or have trend stationarity. Except for one, none of the histogram fits resulted in a reduced-χ2∼1 for a normal and log-normal profile but a normal profile is favored in general. On the contrary, the Anderson–Darling test favors log-normal with a test-statistic value lower for log-normal over normal for all the observations, even if out of significance limits. None of the IDs show linear RMS-flux relation. The contrary inferences from different widely used statistical methods indicate that a careful analysis is needed while the complex behavior of count rate with hardness ratio suggests spectral evolution over a few 10 s of kilo-seconds during bright phases of the sources. In these cases, the spectrum extracted from whole observation may not be meaningful for spectral studies and certainly not a true representation of the spectral state of the source.

We present a unified model for X-ray quasi-periodic oscillations (QPOs) seen in Narrow-line Seyfert 1 (NLSy1) galaxies, γ-ray and optical band QPOs that are seen in Blazars. The origin of these QPOs is attributed to the plasma motion in corona or jets of these AGN. In the case of X-ray QPOs, we applied the general relativistic precession model for the two simultaneous QPOs seen in NLSy1 1H 0707-945 and deduce orbital parameters, such the radius of the emission region, and spin parameter a for a circular orbit; we obtained the Carter’s constant Q, a, and the radius in the case of a spherical orbit solution. In other cases where only one X-ray QPO is seen, we localized the orbital parameters for NLSy1 galaxies REJ 1034+396, 2XMM J123103.2+110648, MS 2254.9-3712, Mrk 766, and MCG-06-30-15. By applying the lighthouse model, we found that a kinematic origin of the jet based γ-ray and optical QPOs, in a relativistic MHD framework, is possible. Based on the inbuilt Hamiltonian formulation with a power-law distribution in the orbital energy of the plasma consisting of only circular or spherical trajectories, we show that the resulting Fourier power spectral density (PSD) has a break corresponding to the energy at ISCO. Further, we derive connection formulae between the slopes in the PSD and that of the energy distribution. Overall, given the preliminary but promising results of these relativistic orbit models to match the observed QPO frequencies and PSD at diverse scales in the inner corona and the jet, it motivates us to build detailed models, including a transfer function for the energy spectrum in the corona and relativistic MHD jet models for plasma flow and its polarization properties.

We reviewed X-ray flux and spectral variability properties studied to date by various X-ray satellites for Mrk 421 and PKS 2155-304, which are TeV emitting blazars. Mrk 421 and PKS 2155-304 are the most X-ray luminous blazars in the northern and southern hemispheres, respectively. Blazars show flux and spectral variabilities in the complete electromagnetic spectrum on diverse timescales ranging from a few minutes to hours, days, weeks, months and even several years. The flux and spectral variability on different timescales can be used to constrain the size of the emitting region, estimate the super massive black hole mass, find the dominant emission mechanism in the close vicinity of the super massive black hole, search for quasi-periodic oscillations in time series data and several other physical parameters of blazars. Flux and spectral variability is also a dominant tool to explain jet as well as disk emission from blazars at different epochs of observations.

Magnetic field threading a black hole ergosphere is believed to play the key role in both driving the powerful relativistic jets observed in active galactic nuclei and extracting the rotational energy from a black hole via Blandford-Znajek process. The magnitude of magnetic field and the magnetic flux in the vicinity of a central black hole is predicted by theoretical models. On the other hand, the magnetic field in a jet can be estimated through measurements of either the core shift effect or the brightness temperature. In both cases the obtained magnetic field is in the radiating domain, so its direct application to the calculation of the magnetic flux needs some theoretical assumptions. In this paper we address the issue of estimating the magnetic flux contained in a jet using the measurements of a core shift effect and of a brightness temperature for the jets, directed almost at the observer. The accurate account for the jet transversal structure allow us to express the magnetic flux through the observed values and an unknown rotation rate of magnetic surfaces. If we assume the sources are in a magnetically arrested disk state, the lower limit for the rotation rate can be obtained. On the other hand, the flux estimate may be tested against the total jet power predicted by the electromagnetic energy extraction model. The resultant expression for power depends logarithmically weakly on an unknown rotation rate. We show that the total jet power estimated through the magnetic flux is in good agreement with the observed power. We also obtain the extremely slow rotation rates, which may be an indication that the majority of the sources considered are not in the magnetically arrested disk state.

Broad absorption lines (BALs) in the spectra of quasi-stellar objects (QSOs) are thought to arise from outflowing winds along our line of sight; winds, in turn, are thought to originate from the accretion disk, in the very surroundings of the central supermassive black hole (SMBH), and they likely affect the accretion process onto the SMBH, as well as galaxy evolution. BALs can exhibit variability on timescales typically ranging from months to years. We analyze such variability and, in particular, BAL disappearance, with the aim of investigating QSO physics and structure. We search for disappearing C IV BALs in the spectra of 1,319 QSOs from different programs from the Sloan Digital Sky Survey (SDSS); the analyzed time span covers 0.28–4.9 year (rest frame), and the source redshifts are in the range 1.68–4.27. This is to date the largest sample ever used for such a study. We find 67 sources (5.1-0.6+0.7% of the sample) with 73 disappearing BALs in total (3.9-0.5+0.5% of the total number of C iv BALs detected; some sources have more than one BAL that disappears). We compare the sample of disappearing BALs to the whole sample of BALs, and investigate the correlation in the variability of multiple troughs in the same spectrum. We also derive estimates of the average lifetime of a BAL trough and of the BAL phase along our line of sight.

M87 has been identified as a displaced supermassive black hole (SMBH) candidate. We investigated this possibility by a temporal analysis of 12 adaptive-optics assisted VLT and HST images spanning 20 yr. We found that the centre of the isophotal fitting to the nuclear region of M87 – assumed to mark the centre of mass of the galaxy – changes location depending on the image and size of the image analysed. In an absolute frame of reference, the change varies from 15 to 130 miliarcseconds (mas) with respect to the active galactic nucleus (AGN), which remains stable within an uncertainty of ±15 mas in both x- and y- axis. The temporal analysis of the results indicates that the major displacements measured coincide with a powerful outburst that took place between 2003 and 2007, where there was a flux increment in the nucleus and the first knot of the jet. After the outburst, the isophotal centre remains stable and is consistent with the AGN location. This suggests that the displacements are artificially caused by a flux variation in the galaxy and that the SMBH actually resides in the equilibrium position. We caution about the determination of the galaxy photocentre by isophotal fitting in cases of nuclear variability and/or presence of photometric irregularities, and advise a long-term temporal analysis of the results to confirm possible displaced SMBHs. [ABSTRACT FROM AUTHOR]

Active galactic nuclei (AGNs) are known to cover an extremely broad range of radio luminosities and the spread of their radio-loudness is very large at any value of the Eddington ratio. This implies very diverse jet production efficiencies which can result from the spread of the black hole spins and magnetic fluxes. Magnetic fluxes can be developed stochastically in the innermost zones of accretion discs, or can be advected to the central regions prior to the AGN phase. In the latter case there could be systematic differences between the properties of galaxies hosting radio-loud (RL) and radio-quiet (RQ) AGNs. In the former case the differences should be negligible for objects having the same Eddington ratio. To study the problem we decided to conduct a comparison study of host galaxy properties of RL and RQ AGNs. In this study we selected type II AGNs from SDSS spectroscopic catalogs. Our RL AGN sample consists of the AGNs appearing in the Best and Heckman (2012) catalog of radio galaxies. To compare RL and RQ galaxies that have the same AGN parameters we matched the galaxies in black hole mass, Eddington ratio and redshift. We compared several properties of the host galaxies in these two groups of objects like galaxy mass, color, concentration index, line widths, morphological type and interaction signatures. We found that in the studied group RL AGNs are preferentially hosted by elliptical galaxies while RQ ones are hosted by galaxies of later type. We also found that the fraction of interacting galaxies is the same in both groups of AGNs. These results suggest that the magnetic flux in RL AGNs is advected to the nucleus prior to the AGN phase.

We study BAL variations of SDSS J141955.28+522741.4 utilizing 32 epochs of spectroscopic observations from SDSS. We identify three individual BAL troughs for C iv and one BAL trough for Si iv. The deepest C iv BAL trough shows significant EW variations in timescales of a few 10 h. The fast component of the deepest C iv BAL presents disappearance and re-emergence preserving its initial velocity range and profile. All identified BAL troughs show coordinated variations supporting that the possible mechanism behind variations are the ionization level changes of the absorbing gas.

Several observed spectral properties of quasars are believed to be influenced by quasar orientation. In this investigation we examine the effect of orientation on the Mg ii line located at 2,798 Å in a sample of 36 radio-loud quasars, with orientation angles having been obtained in a previous study using radio observations. We find no significant relationship between orientation angle and either Mg ii line full-width at half-maximum or equivalent width. The lack of correlation with inclination angle contradicts previous studies which also use radio data as a proxy for inclination angle and suggests the Mg ii emission region does not occupy a disk-like geometry. The lack of correlation with Mg ii equivalent width, however, is reported in at least one previous study. Although the significance is not very strong (86%), there is a possible negative relationship between inclination angle and Fe ii strength which, if true, could explain the Fe ii anti-correlation with [O iii] strength associated with Eigenvector 1. Interestingly, there are objects having almost edge-on inclinations while still exhibiting broad lines. This could be explained by a torus which is either clumpy (allowing sight lines to the central engine) or mis-aligned with the accretion disk.

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.

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 present the galactic stellar age—velocity dispersion relation obtained from a semi-analytic model of galaxy formation. We divide galaxies into two populations: galaxies which have over-massive/under-massive black holes (BHs) against the best-fitting BH mass—velocity dispersion relation. We find that galaxies with larger velocity dispersion have older stellar ages. We also find that galaxies with over-massive BHs have older stellar ages. These results are consistent with observational results obtained from Martín-Navarro et al. (2016). We tested the model with weak AGN feedback and find that galaxies with larger velocity dispersion have a younger stellar age.

Polarimetry has been a standard tool to probe the active galactic nucleus (AGN) jet magnetic field. In recent years, several optical polarization monitoring programs have been carried out, bringing in many exciting new results and insights into jet dynamics and emission. This article discusses current progress in blazar optical polarimetry. The main focus is the variability of polarization signatures, which has spurred a lot of theoretical studies. These novel developments have provided unique constraints on the blazar flares and emphasized the role of the magnetic field in jet evolution. Optical polarimetry will continue to act as an essential component in the multi-messenger study of AGN jets, in particular with the upcoming high-energy polarimetry. Comparing to first-principle numerical simulations, future multi-wavelength polarimetry can shed light on jet dynamics, particle acceleration, and radiation processes.

After three years of polarimetric monitoring of blazars, the RoboPol project has uncovered several key characteristics of polarimetric rotations in the optical for these most variable sources. The most important of these is that polarization properties of the synchrotron emission in the optical appear to be directly linked with gamma-ray activity. In this paper, we discuss the evidence for this connection, as well as the broader features of polarimetric behavior in blazars that are key in making progress with theoretical modeling of blazar emission.

This review provides an overview of recent advances in multi-wavelength and multi-messenger observations of blazars, the current status of theoretical models for blazar emission, and prospects for future facilities. The discussion of observational results will focus on advances made possible through the Fermi Gamma-Ray Space Telescope and ground-based gamma-ray observatories (H.E.S.S., MAGIC, VERITAS), as well as the recent first evidence for a blazar being a source of IceCube neutrinos. The main focus of this review will be the discussion of our current theoretical understanding of blazar multi-wavelength and multi-messenger emission, in the spectral, time, and polarization domains. Future progress will be expected in particular through the development of the first X-ray polarimeter, IXPE, and the installation of the Cherenkov Telescope Array (CTA), both expected to become operational in the early to mid 2020s.

The time lag between optical and near-infrared continuum emission in active galactic nuclei (AGN) shows a tight correlation with luminosity and has been proposed as a standardizable candle for cosmology. In this paper, we explore the use of these AGN hot-dust time lags for cosmological model fitting under the constraints of the new VISTA Extragalactic Infrared Legacy Survey (VEILS). This new survey will target a 9 deg² field observed in J and Ks band with a 14-d cadence and will run for 3 yr. The same area will be covered simultaneously in the optical griz bands by the Dark Energy Survey, providing complementary time-domain optical data. We perform realistic simulations of the survey setup, showing that we expect to recover dust time lags for about 450 objects out of a total of 1350 optical type 1 AGN, spanning a redshift range of 0.1 < z < 1.2. We use the lags recovered from our simulations to calculate precise distance moduli, establish a Hubble diagram, and fit cosmological models. Assuming realistic scatter in the distribution of the dust around the AGN as well as in the normalization of the lag-luminosity relation, we are able to constrain ΩΛ in ΛCDM with similar accuracy as current supernova samples. We discuss the benefits of combining AGN and supernovae for cosmology and connect the present work to future attempts to reach out to redshifts of z > 4. [ABSTRACT FROM AUTHOR]

In this contribution we report on the study of the optical emission lines and X-ray spectra of a sample of Type 1 AGNs, collected from the SDSS database and observed by the XMM-Newton satellite. Using different instruments onboard XMM, we identify the spectral components of the soft and hard energy bands (in the range from 0.3 keV to 10 keV). The properties of the X-ray continuum and of the Fe Kα line feature are related to the optical broad emission line profiles and intensity ratios. The resulting picture of emission, absorption and reflection processes is interpreted by means of a structural model of the broad line region, developed on the basis of independent optical and radio observations.

We monitored BL Lacertae frequently during 2014–2016 when it was generally in a high state. We searched for intra-day variability for 43 nights using quasi-simultaneous measurements in the B, V, R, and I bands (totaling 143 light curves); the typical sampling interval was about eight minutes. On hour-like timescales, BL Lac exhibited significant variations during 13 nights in various optical bands. Significant spectral variations are seen during most of these nights such that the optical spectrum becomes bluer when brighter. The amplitude of variability is usually greater for longer observations but is lower when BL Lac is brighter. No evidence for periodicities or characteristic variability time-scales in the light curves was found. The color variations are mildly chromatic on long timescales.

We reviewed multi-wavelength blazars variability and detection of quasi-periodic oscillations on intra-day timescales. The variability timescale from a few minutes to up to less than a days is commonly known as intra-day variability. These fast variations are extremely useful to constrain the size of the emitting region, black hole mass estimation, etc. It is noticed that in general, blazars show intra-day variability in the complete electromagnetic spectrum. However, some classes of blazars either do not show or show very little intra-day variability in a specific band of the electromagnetic spectrum. Blazars show rarely quasi-periodic oscillations in time series data in optical and X-ray bands. Other properties and emission mechanisms of blazars are also briefly discussed.

The article offers information on the constellation of Lacerta and mysteries associated with it. Topics discussed include appearance of planetary nebula in the constellation; presence of BL Lacertae which is an active galaxy with an active galactic nucleus (AGN) in the south-east of the constellation; and the LBN 438 Lynd's Catalogue dark nebula present in southern part of the constellation.

I have reinterpreted Rucinski's line profiles (broadening functions) for the hot A-type W Ursae Majoris binary AW UMa in terms of various contact models, finding that the detached/ semidetached geometry he postulates does not fit the system's light variation or its line profiles. The highly overcontact geometry that actually fits the system's ellipsoidal light variation reproduce the total breadth of the lines but give profiles too broad tofit their shapes. The best solution to this dilemma is differential rotation of both stars in which the mid-latitudes are rotating 20-30 per cent slower than synchronously. This approach preserves the traditional light-curve solution and explains the drift of ripples seen in the line profiles. In addition, there are obviously other flows superimposed on the rotation which make the profiles asymmetrical. Fitting the line profiles is complicated by uncertainties in how the equivalent widths of the lines change with effective temperature and how much they are limb darkened. The contribution of any point on the stellar surface to the equivalent width depends only very weakly on local temperature throughout the range of W UMa binaries. The limb darkening of the lines is probably small, although the effect remains unexplored. I also speculate about the nature of hypothetical star-spots in this system. [ABSTRACT FROM AUTHOR]

We investigate active galactic nuclei (AGN) candidates within the FourStar Galaxy Evolution Survey (ZFOURGE) to determine the impact they have on star formation in their host galaxies. We first identify a population of radio, X-ray, and infrared-selected AGN by cross-matching the deep Ks-band imaging of ZFOURGE with overlapping multiwavelength data. From this, we construct a mass-complete (log(M*/M☉) ≥9.75), AGN luminosity limited sample of 235 AGN hosts over z = 0.2-3.2. We compare the rest-frame U - V versus V - J (UVJ) colours and specific star formation rates (sSFRs) of the AGN hosts to a mass-matched control sample of inactive (non-AGN) galaxies. UVJ diagnostics reveal AGN tend to be hosted in a lower fraction of quiescent galaxies and a higher fraction of dusty galaxies than the control sample. Using 160 μm Herschel PACS data, we find the mean specific star formation rate of AGN hosts to be elevated by 0.34 ± 0.07 dex with respect to the control sample across all redshifts. This offset is primarily driven by infrared-selected AGN, where the mean sSFR is found to be elevated by as much as a factor of ∼5. The remaining population, comprised predominantly of X-ray AGN hosts, is found mostly consistent with inactive galaxies, exhibiting only a marginal elevation. We discuss scenarios that may explain these findings and postulate that AGN are less likely to be a dominant mechanism for moderating galaxy growth via quenching than has previously been suggested. [ABSTRACT FROM AUTHOR]

We present the first multi-frequency VLBA study of the quasar 0850+581 which appears to have a two-sided relativistic jet. Apparent velocity in the approaching jet changes from 3.4c to 7c with the separation from the core. The jet-to-counter-jet ratio of about 5 and apparent superluminal velocities suggest that the observing angle of the inner jet is ≤ 17 ∘ . It is likely that this orientation significantly changes downstream due to an interaction of the jet with the surrounding medium; signs of this are seen in polarization. A dense inhomogeneous Faraday screen is detected in the innermost regions of this quasar. We suggest that there is a presence of ionized gas in its nucleus, which might be responsible for the free-free absorption of the synchrotron emission in the jet and counter-jet at frequencies below 8.4 GHz. The experiment makes use of slowly varying instrumental polarisation factors (polarization leakage or D-terms) in time. We report application of the “D-term connection” technique for the calibration of an absolute orientation of electric vector position angle (EVPA) observed by VLBA at 4.6, 5.0, 8.1, 8.4, 15.4, 22.3, and 43.3 GHz bands during the 2007–2011.