A comprehensive analysis of the nucleus of the radio source 3C 84 with VLBI

Jets powered by active galactic nuclei (AGN) are some of most powerful phenomena of the cosmos. Understanding the underlying physical mechanisms is necessary to enhance our knowledge of the universe. The focus of this thesis lies on the innermost region of the radio source 3C 84, harboured in the radio galaxy NGC 1275, which exhibits such energetic jets. Perhaps connected to this jet activity is a perpendicularly to the bulk jet flow oriented structure, which was recently revealed in a RadioAstron space very-long-baseline interferometry (VLBI) image. Interpreting this structure and its implications to jet physics is one of the main motivations of this thesis. It is accomplished by utilising millimetre-VLBI observations of 3C 84 at the highest resolution, with the available data covering a period of more than twenty years and at different frequencies. The thesis is organised as follows: in Sect. 1 an overview of the astrophysical background required to interpret the data is introduced. This includes brief descriptions of the radiation received by the telescopes, of black holes and AGN, as well as of astrophysical jets. AGN classification schemes and the relevant details of jet physics are also discussed. Section 2 offers a review of the technical background, including the basics of the technique of interferometry and VLBI arrays, calibrating a VLBI data set and imaging it. In Sect. 3 we utilise quasi-simultaneous observations at 15, 43, and 86 GHz and create the highest resolution spectral index images of 3C 84 to date. Our analysis reveals the existence of a spectral index gradient in the north-south direction, with values between $\alpha_{43−86} \sim 2$ upstream of the 86 GHz VLBI core and $\alpha_{43−86} \sim -2$ downstream. In this context, we discuss the spectral index distribution. We determine the location of the jet apex to be 400 − 1500 Rs (Schwarzschild radii) upstream of the 86 GHz VLBI core, by means of two-dimensional cross-correlation analysis. In that region, the magnetic field appears to be a mix between poloidal and toroidal, with a strength of 2 − 4 G. Section 4 presents an alternative approach for pinpointing the jet apex of 3C 84, by directly imaging the core region. The temporal stacking of a number of 86 GHz data sets at different epochs confirms the existence of a double component structure present in the core region, concurring the RadioAstron result. Both a conical and a parabolic jet expansion profile are then fit to the data to determine the shape of the expansion. This constrains the position of the jet apex to 200 − 3000 Rs upstream of the 86 GHz VLBI core. Our analysis also reveals a possible change of viewing angle along the jet flow (perhaps indicative of jet bending) and sets an upper limit for the viewing angle of 35 degrees for the inner jet. Section 5 showcases a comprehensive study of the evolution and jet kinematics of 3C 84 over more than twenty years. Our analysis reveals the ejection of numerous components from the core region, which seem to move at subluminal speeds, with newer components being faster. We also checked for possible differences between the velocities of the 43 and 86 GHz components individually but only found marginal evidence of faster motion at 86 GHz. The jet width appears frequency dependent, with the jet width decreasing with in- creasing frequency, which might be explained by stratification in the context of the spine-sheath jet stratification scenario. We also produced spectral in- dex maps at 43 − 86 GHz, which show that the orientation of the spectral index gradient position angle is time variable. This further indicates that the black hole is positioned off-centred from the total intensity maximum and that the jet axis is changing with time. Finally, in Sect. 6 our analysis and results are summarised and in Sect. 7 an outlook for the future is provided

Μελέτη της διέγερσης του μοριακού αερίου σε τυπικές συνθήκες του μεσοαστρικού χώρου

Στην εργασία αυτήν εξετάζουμε το ραδιογαλαξία OQ 208 με σκοπό να μελετήσουμε τις ιδιότητες του μοριακού αερίου στο μεσοαστρικό χώρο. Ο γαλαξίας αυτός παρου- σιάζει πίδακες από τον ενεργό πυρήνα του, οι οποίοι πιθανόν να επηρεάζουν το υπό μελέτη αέριο. Για το λόγο αυτό εξετάζουμε τη διέγερση του μονοξειδίου του άνθρακα χρησιμοποιώντας τρεις γραμμές εκπομπής του, τις CO J = 1 → 0, 2 → 1 και 3 → 2. Εξετάζουμε την όψη του γαλαξία στις τρεις μεταβάσεις και βρίσκουμε ότι αποτελείται από ένα δίσκο, τρεις σπειροειδείς/παλιρροϊκές δομές, μια δομή εκτός δυναμικής ισορ- ροπίας και διάσπαρτα νέφη που υποδεικνύουν πως ο γαλαξίας προήλθε από σύγκρουση άλλων γαλαξιών, των οποίων οι πυρήνες φαίνονται στο οπτικό. ́Ολα αυτά μαζί εμπε- ριέχουν μάζα 1.22 ± 0.2 × 10^10 M⊙. Κατόπιν, μελετούμε τη διέγερση του μοριακού αερίου με βάση το μοντέλο Radex που προβλέπει την ένταση ροής των φασματικών γραμμών ανάλογα με τη θερμοκρασία, την αριθμητική πυκνότητα και την πυκνότητα κολόνας του αερίου. Βρίσκουμε ότι κατά μέση τιμή το αέριο είναι στους 16 ± 2 K. Είναι υψηλότερα διεγερμένο στον πυρήνα από ό,τι στις εξωτερικές περιοχές. Η θερμο- κρασία είναι στους 15 ± 5 K για τα εσωτερικά 0.5” του δίσκου, ενώ είναι 10 ± 5 K σε όλες τις υπόλοιπες περιοχές. Είναι αβέβαιο αν αυτή η υψηλή διέγερση οφείλεται αποκλειστικά στον πίδακα ή τον ενεργό πυρήνα, καθώς στην ίδια περιοχή ανεμένεται έντονη αστρογέννηση. Χρησιμοποιώντας κυρίως επικουρικά δεδομένα, μοντελοποιούμε την εκπομπή της σκόνης με πολλαπλά modified black bodies και βλέπουμε πως έχει θερμοκρασία 20 ± 5 K. Με βάση τα δεδομένα μας η εκπομπή της σκόνης προέρχεται από το εσωτερικό 1” του πυρήνα. Συνεπώς, οι θερμοκρασίες σκόνης και αερίου είναι συνολικά συνεπείς μεταξύ τους.In this thesis we study the radiogalaxy OQ 208, aiming to examine the properties of the molecular gas in the interstellar medium. This galaxy exhibits jets originat- ing from its active nucleus, which could disturb the molecular gas in question. For this reason we study the excitation of the first three transitions of carbon monoxide molecules: CO J = 1 → 0, 2 → 1 and 3 → 2. We examine different views of the galaxy for the aforementioned transitions and discover that it consists of a disk, spiral/tidal structures, one structure out of dynamical equilibrium, and scattered molecular clouds, from which we deduce that it must have experienced a merging event. The nuclei of the merging galaxies are visible in optical wavelengths. The components listed above add up to 1.22 ± 0.2 × 10^10 M⊙. We analyse the excitation of the molecular gas using the model Radex, which estimates the spectral line en- ergy distribution of the CO based on the temperature, column density, and volume density of the said gas. We find an average temperature of 16 ± 2 K for the bulk of the gas. The latter is more highly excited at the nucleus than at outer regions. The temperature is at 15±5 K for the inner 0.5” of the disk, and at 10±5 K for the gas in all other components. It is unclear if this high excitation is entirely due to the jet or to the active nucleus, as increased star formation is expected in the same region. Based on primarily ancillary data, the spectral energy distribution yields a dust temperature of 20 ± 5 K, if modeled with multiply modified black bodies. Based on our data the dust emission originates mainly from the inner 1”. The dust and gas temperatures are, thus, overall consistent

Spatially resolved excitation study of CO molecules in active galactic nuclei

Η δραστηριότητα πιδάκων και οι αλληλεπιδράσεις τους με το διαστρικό μέσο, όπως συγκρούσεις πίδακα- μοριακού νέφους, όπως και διάχυση ενέργειας του πίδακα στο διαστρικό μέσο μπορούν να μελετηθούν μέσω χωρικά ανειλημμένων παρατηρήσεων της διέγερσης του μορίου του μονοξειδίου του άνθρακα (CO). Σε αυτήν τη διπλωματική εργασία στοχεύομε να μελετήσουμε την αλληλεπίδραση μεταξύ πιδάκων, προερχόμενων από μελανές οπές και του περιβάλλοντος, μοριακού αερίου κα του διαστρικού μέσου. Για να το κάνουμε αυτό, μελετούμε 3 ραδιογαλαξίες τους OQ208, 4C12.50 και IC5063, κάνοντας χρήση των παρατηρήσεων από τις συστοιχίες ραδιοτηλεσκοπίων ALMA, SMA και Plateau de Bure. Δημιουργούμε χάρτες της κινητικής θερμοκρασίας και της θερμοκρασίας διέγερσης, της αριθμητικής πυκνότητας, πυκνότητας κολόνας, πίεσης καθώς και οπτικού βάθους συγκρίνοντας τη ροή του εκάστοτε μεμονομένου pixel με τις θεωρητικές ροές υπολογισμένες με τον κώδικα RADEX. Στον πρώτο γαλαξία, OQ208, παρατηρείται βαθμίδα θερμοκρασίας τάξης 10Κ μεταξύ του πυρήνα και του υπόλοιπου αερίου. Αυτό το αποτέλεσμα είναι τυπικό για σπειροειδή γαλαξία, αλλά όχι ιδιαίτερα ενδεικτικό για δράση jet. Στο γαλαξία 4C12.50 έχει παρατηρηθεί άνεμος CO. Στοχεύουμε να αντιστοιχίσουμε την υψηλή διέγερση του αερίου γύρω από τον πυρήνα, που συμπίπτει και με την περιοχή δράσης ανέμου, σε κινητική θερμοκρασία. Ο τελευταίος κατά σειρά γαλαξίας που μελετήσαμε είναι ο IC5063, ένα τυπικό παράδειγμα γαλαξία για τον οποίο έχει προηγηθεί αναλυτική, χωρικά ανειλημμένη μελέτη και έχει αποδειχθεί ότι περιοχές επίδρασης πιδάκων χαρακτηρίζονται από υψηλές κινητικές θερμοκρασίες, τάξης ~200Κ. Επιβεβαιώνουμε αυτό το αποτέλεσμα, ανεξάρτητως υπόθεσης αν το αέριο βρίσκεται σε τοπική θερμοδυναμική ισορροπία ή όχι. Συνολικά βρίσκουμε ότι οι πίδακες μπορούν να επηρεάσουν το περιβάλλων διαστρικό μέσο, αυξάνοντας τη θερμοκρασία ακόμα και κατά μια τάξη μεγέθους. Αυτή η διαφορά στη θερμοκρασία μπορεί να έχει επίδραση στην ανίχνευση των ανέμων, καθώς και στη μάζα που περικλείουν, καθώς αλλάζει ο παράγοντας μετατροπής CO σε H2 αCO.Jet activity and interactions with the ISM, like jet-cloud collisions, as well as energy deposition of the jet into the ambient ISM can be studied using spatially resolved observations of the CO excitation. In this thesis we aim to study this interaction between jets, originating from black holes, and the ambient, molecular gas and ISM. To do this we study three radio galaxies: OQ 208, 4C 12.50 and IC 5063, using observations from ALMA, SMA and the Plateau de Bure. We create maps of the kinetic and excitation temperatures, number density, column density, pressure and optical depth by comparing the fluxes of each individual pixel to the theoretical fluxes calculated by the RADEX code. Our first target, galaxy OQ 208, exhibits a temperature gradient of 10K between the nucleus and the rest of the gas. This result is typical for a spiral galaxy but not particularly indicative of jet activity. Our second target is galaxy 4C12.50 for which a CO wind has been observed. We aimed to translate the high excitation of the circumnuclear gas, that coincides with a wind location, into a temperature. Our last target is galaxy IC 5063, a primary example for which analytical calculations have been carried out in a spatially resolved manner and have shown that the jet impacted regions reach a kinetic temperature of ∼200K. We confirm this result, whether the gas is presumed to be in LTE or not. Overall we find that jets can indeed impact the ambient ISM, causing the temperature to rise as a high as a whole order of magnitude. This difference in temperature can have an impact in the detectability of winds but also in their mass content, as it can affect the αCO CO to H2 conversion factor

A persistent double nuclear structure in 3C 84

3C 84 (NGC 1275) is the radio source at the centre of the Perseus cluster and exhibits a bright radio jet. We observed the source with the Global Millimeter VLBI Array (GMVA) between 2008 and 2015, with a typical angular resolution of ∼50 μas. The observations revealed a consistent double nuclear structure separated by ∼770 gravitational radii assuming a black hole mass of 3.2 × 108 M⊙. The region is likely too broad and bright to be the true jet base anchored in the accretion disc or black hole ergosphere. A cone and parabola were fit to the stacked (time averaged) image of the nuclear region. The data did not strongly prefer either fit, but combined with a jet/counter-jet ratio analysis, an upper limit on the viewing angle to the inner jet region of ≤35° was found. This provides evidence for a variation of the viewing angle along the jet (and therefore a bent jet) within ∼0.5 pc of the jet launching region. In the case of a conical jet, the apex is located ∼2400 gravitational radii upstream of the bright nuclear region and up to ∼600 gravitational radii upstream in the parabolic case. We found a possible correlation between the brightness temperature and relative position angle of the double nuclear components, which may indicate rotation within the jet. © 2021 The Author(s).This research was supported by Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education (NRF-2021R1A6A3A01086420). JAH was supported by Korea Research Fellowship Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Science and ICT, South Korea (2018H1D3A1A02032824) and the research grant (2021R1C1C1009973). S-SL was supported by the National Research Foundation of Korea (NRF) grant funded by the Korea government (MIST) (2020R1A2C2009003). J-YK is supported for this research by the International Max-Planck Research School (IMPRS) for Astronomy and Astrophysics at the University of Bonn and Cologne. This research was supported by an appointment to the NASA Postdoctoral Program at the Goddard Space Flight Center, administered by Universities Space Research Association through a contract with NASA. RL acknowledges the support of the Spanish Ministerio de Economía y Competitividad (grant PID2019-108995GB-C21), the Consejería de Economía, Conocimiento, Empresas y Universidad, Junta de Andalucía (grant P18-FR-1769), and the Consejo Superior de Investigaciones Científicas (grant 2019AEP112). GFP is supported for this research by the International Max-Planck Research School (IMPRS) for Astronomy and Astrophysics at the University of Bonn and Cologne. ST and MK acknowledge support via NRF grant 2019R1F1A1059721. This research has made use of data obtained with the Global Millimeter VLBI Array (GMVA), which consists of telescopes operated by the MPIfR, IRAM, Onsala, Metsahovi, Yebes, the Korean VLBI Network, the Green Bank Observatory, and the Very Long Baseline Array (VLBA). The VLBA is an instrument of the NRAO, which is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc. The data were correlated at the correlator of the Max Planck Institute for Radioastronomy (MPIfR) in Bonn, Germany. This work made use of the Swinburne University of Technology software correlator, developed as part of the Australian Major National Research Facilities Programme and operated under licence.With funding from the Spanish government through the Severo Ochoa Centre of Excellence accreditation SEV-2017-0709.Peer reviewe

A Universal Power-law Prescription for Variability from Synthetic Images of Black Hole Accretion Flows

We present a framework for characterizing the spatiotemporal power spectrum of the variability expected from the horizon-scale emission structure around supermassive black holes, and we apply this framework to a library of general relativistic magnetohydrodynamic (GRMHD) simulations and associated general relativistic ray-traced images relevant for Event Horizon Telescope (EHT) observations of Sgr A*. We find that the variability power spectrum is generically a red-noise process in both the temporal and spatial dimensions, with the peak in power occurring on the longest timescales and largest spatial scales. When both the time-averaged source structure and the spatially integrated light-curve variability are removed, the residual power spectrum exhibits a universal broken power-law behavior. On small spatial frequencies, the residual power spectrum rises as the square of the spatial frequency and is proportional to the variance in the centroid of emission. Beyond some peak in variability power, the residual power spectrum falls as that of the time-averaged source structure, which is similar across simulations; this behavior can be naturally explained if the variability arises from a multiplicative random field that has a steeper high-frequency power-law index than that of the time-averaged source structure. We briefly explore the ability of power spectral variability studies to constrain physical parameters relevant for the GRMHD simulations, which can be scaled to provide predictions for black holes in a range of systems in the optically thin regime. We present specific expectations for the behavior of the M87* and Sgr A* accretion flows as observed by the EHT

The Changing Landscape for Stroke\ua0Prevention in AF: Findings From the GLORIA-AF Registry Phase 2

Background GLORIA-AF (Global Registry on Long-Term Oral Antithrombotic Treatment in Patients with Atrial Fibrillation) is a prospective, global registry program describing antithrombotic treatment patterns in patients with newly diagnosed nonvalvular atrial fibrillation at risk of stroke. Phase 2 began when dabigatran, the first non\u2013vitamin K antagonist oral anticoagulant (NOAC), became available. Objectives This study sought to describe phase 2 baseline data and compare these with the pre-NOAC era collected during phase 1. Methods During phase 2, 15,641 consenting patients were enrolled (November 2011 to December 2014); 15,092 were eligible. This pre-specified cross-sectional analysis describes eligible patients\u2019 baseline characteristics. Atrial fibrillation disease characteristics, medical outcomes, and concomitant diseases and medications were collected. Data were analyzed using descriptive statistics. Results Of the total patients, 45.5% were female; median age was 71 (interquartile range: 64, 78) years. Patients were from Europe (47.1%), North America (22.5%), Asia (20.3%), Latin America (6.0%), and the Middle East/Africa (4.0%). Most had high stroke risk (CHA2DS2-VASc [Congestive heart failure, Hypertension, Age  6575 years, Diabetes mellitus, previous Stroke, Vascular disease, Age 65 to 74 years, Sex category] score  652; 86.1%); 13.9% had moderate risk (CHA2DS2-VASc = 1). Overall, 79.9% received oral anticoagulants, of whom 47.6% received NOAC and 32.3% vitamin K antagonists (VKA); 12.1% received antiplatelet agents; 7.8% received no antithrombotic treatment. For comparison, the proportion of phase 1 patients (of N = 1,063 all eligible) prescribed VKA was 32.8%, acetylsalicylic acid 41.7%, and no therapy 20.2%. In Europe in phase 2, treatment with NOAC was more common than VKA (52.3% and 37.8%, respectively); 6.0% of patients received antiplatelet treatment; and 3.8% received no antithrombotic treatment. In North America, 52.1%, 26.2%, and 14.0% of patients received NOAC, VKA, and antiplatelet drugs, respectively; 7.5% received no antithrombotic treatment. NOAC use was less common in Asia (27.7%), where 27.5% of patients received VKA, 25.0% antiplatelet drugs, and 19.8% no antithrombotic treatment. Conclusions The baseline data from GLORIA-AF phase 2 demonstrate that in newly diagnosed nonvalvular atrial fibrillation patients, NOAC have been highly adopted into practice, becoming more frequently prescribed than VKA in Europe and North America. Worldwide, however, a large proportion of patients remain undertreated, particularly in Asia and North America. (Global Registry on Long-Term Oral Antithrombotic Treatment in Patients With Atrial Fibrillation [GLORIA-AF]; NCT01468701

First Sagittarius A* Event Horizon Telescope Results. IV. Variability, Morphology, and Black Hole Mass

In this paper we quantify the temporal variability and image morphology of the horizon-scale emission from Sgr A*, as observed by the EHT in 2017 April at a wavelength of 1.3 mm. We find that the Sgr A* data exhibit variability that exceeds what can be explained by the uncertainties in the data or by the effects of interstellar scattering. The magnitude of this variability can be a substantial fraction of the correlated flux density, reaching ∼100% on some baselines. Through an exploration of simple geometric source models, we demonstrate that ring-like morphologies provide better fits to the Sgr A* data than do other morphologies with comparable complexity. We develop two strategies for fitting static geometric ring models to the time-variable Sgr A* data; one strategy fits models to short segments of data over which the source is static and averages these independent fits, while the other fits models to the full data set using a parametric model for the structural variability power spectrum around the average source structure. Both geometric modeling and image-domain feature extraction techniques determine the ring diameter to be 51.8 ± 2.3 μas (68% credible intervals), with the ring thickness constrained to have an FWHM between ∼30% and 50% of the ring diameter. To bring the diameter measurements to a common physical scale, we calibrate them using synthetic data generated from GRMHD simulations. This calibration constrains the angular size of the gravitational radius to be 4.8−0.7+1.4 μas, which we combine with an independent distance measurement from maser parallaxes to determine the mass of Sgr A* to be 4.0−0.6+1.1×106 M ⊙

Characterizing and Mitigating Intraday Variability: Reconstructing Source Structure in Accreting Black Holes with mm-VLBI

The extraordinary physical resolution afforded by the Event Horizon Telescope has opened a window onto the astrophysical phenomena unfolding on horizon scales in two known black holes, M87* and Sgr A*. However, with this leap in resolution has come a new set of practical complications. Sgr A* exhibits intraday variability that violates the assumptions underlying Earth aperture synthesis, limiting traditional image reconstruction methods to short timescales and data sets with very sparse (u, v) coverage. We present a new set of tools to detect and mitigate this variability. We develop a data-driven, model-agnostic procedure to detect and characterize the spatial structure of intraday variability. This method is calibrated against a large set of mock data sets, producing an empirical estimator of the spatial power spectrum of the brightness fluctuations. We present a novel Bayesian noise modeling algorithm that simultaneously reconstructs an average image and statistical measure of the fluctuations about it using a parameterized form for the excess variance in the complex visibilities not otherwise explained by the statistical errors. These methods are validated using a variety of simulated data, including general relativistic magnetohydrodynamic simulations appropriate for Sgr A* and M87*. We find that the reconstructed source structure and variability are robust to changes in the underlying image model. We apply these methods to the 2017 EHT observations of M87*, finding evidence for variability across the EHT observing campaign. The variability mitigation strategies presented are widely applicable to very long baseline interferometry observations of variable sources generally, for which they provide a data-informed averaging procedure and natural characterization of inter-epoch image consistency

The Event Horizon Telescope Image of the Quasar NRAO 530

We report on the observations of the quasar NRAO 530 with the Event Horizon Telescope (EHT) on 2017 April 5−7, when NRAO 530 was used as a calibrator for the EHT observations of Sagittarius A*. At z = 0.902, this is the most distant object imaged by the EHT so far. We reconstruct the first images of the source at 230 GHz, at an unprecedented angular resolution of ∼20 μas, both in total intensity and in linear polarization (LP). We do not detect source variability, allowing us to represent the whole data set with static images. The images reveal a bright feature located on the southern end of the jet, which we associate with the core. The feature is linearly polarized, with a fractional polarization of ∼5%–8%, and it has a substructure consisting of two components. Their observed brightness temperature suggests that the energy density of the jet is dominated by the magnetic field. The jet extends over 60 μas along a position angle ∼ −28°. It includes two features with orthogonal directions of polarization (electric vector position angle), parallel and perpendicular to the jet axis, consistent with a helical structure of the magnetic field in the jet. The outermost feature has a particularly high degree of LP, suggestive of a nearly uniform magnetic field. Future EHT observations will probe the variability of the jet structure on microarcsecond scales, while simultaneous multiwavelength monitoring will provide insight into the high-energy emission origin

First Sagittarius A* Event Horizon Telescope Results. VI. Testing the Black Hole Metric

Astrophysical black holes are expected to be described by the Kerr metric. This is the only stationary, vacuum, axisymmetric metric, without electromagnetic charge, that satisfies Einstein’s equations and does not have pathologies outside of the event horizon. We present new constraints on potential deviations from the Kerr prediction based on 2017 EHT observations of Sagittarius A* (Sgr A*). We calibrate the relationship between the geometrically defined black hole shadow and the observed size of the ring-like images using a library that includes both Kerr and non-Kerr simulations. We use the exquisite prior constraints on the mass-to-distance ratio for Sgr A* to show that the observed image size is within ∼10% of the Kerr predictions. We use these bounds to constrain metrics that are parametrically different from Kerr, as well as the charges of several known spacetimes. To consider alternatives to the presence of an event horizon, we explore the possibility that Sgr A* is a compact object with a surface that either absorbs and thermally reemits incident radiation or partially reflects it. Using the observed image size and the broadband spectrum of Sgr A*, we conclude that a thermal surface can be ruled out and a fully reflective one is unlikely. We compare our results to the broader landscape of gravitational tests. Together with the bounds found for stellar-mass black holes and the M87 black hole, our observations provide further support that the external spacetimes of all black holes are described by the Kerr metric, independent of their mass