Rationale
Program

List of Abstracts



Name : Sonia ANTON

Title : Chasing offset supermassive black holes

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Name : Roberto ASSEF

Title : Quasars in the Infrared

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Name : Christophe BARACHE

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Name : Ciprian BERGHEA

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Name : Anirban BHATTACHARJEE

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Name : Laura BLECHA

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Name : Ian BROWNE

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Name : Neven CAPLAR

Title : Characterizing short and long term AGN variability properties

Abstract : The rise of large surveys with high cadence has enabled us to study in detail the properties of AGN variability. In addition to studying short term variability, through comparison of data with earlier surveys we can now place constraints on AGN flux changes on decadal timescales. The photometric quality of GAIA data and large sky coverage makes it a perfect probe for AGN variability. I will show results of our recent work on the comparison of AGN fluxes between the SDSS and Hyper Supreme Cam Survey - these show that AGN selected in SDSS are, on average, dimmer when observed today compared to cca 20 years ago. I will briefly demonstrate how we can use these results to discriminate between different models and put constraints on the parameters of variability. I will discuss how GAIA will be able to complement these data and how it will help us to break various degeneracies in the current datasets.

Name : Nico CAPPELLUTI

Title : BLACKBASE, a machine learning oriented Quasar and AGN database

Abstract : Most galaxies host massive black holes at their centers, which grow over billions of years, often hidden from view by thick columns of gas and dust along the line of sight. In order to detect, in future surveys, AGN that are normally missed by standard selections, we developed BLACKBASE a machine learning oriented database of all the AGN and QUASARs detected so far at every wavelength. The database has been designed to exploit the enormous amount of photometric and imaging data with machine learning. So far GAIA, SSDS, WISE and Chandra/XMM/Swift catalogs are the backbones of the database. I will show interesting applications and a description of the database that will be soon released to the public.

Name : Patrick CHARLOT

Title : Exploring radio source structure with the Bordeaux VLBI Image Database

Abstract : The Bordeaux VLBI Image Database (BVID) has made VLBI images of radio reference frame sources available to the community since 2008. The database currently contains more than 6400 such images along with associated data (especially those that qualify the source structure, i.e. the compactness and structure index information) which are of interest for various applications. On the astrophysical side, the BVID data are useful to monitor the source evolution on time scales of months to years, including VLBI jet component motion, the jet direction, the total flux density,… The available images are also important to qualify the source astrometric suitability, i.e. their ability to define accurately the celestial frame. In this respect, the ultimate goal would be to account for source structure in the definition of the reference frame. The presentation will address such aspects on the basis of the BVID data.

Name : Yuting CHENG

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Name : Goran DAMLJANOVIC

Title : Optical color variations with time and against R magnitude of some QSOs important for Gaia CRF - ICRF link

Abstract : We report some results of our optical (mostly VR) photometric observations of QSOs important for Gaia CRF - ICRF link. The period of observations is from mid-2013 to the end of 2019. Mostly, optical color variations (with time, and against R magnitude) are presented.

Name : Jeremy DARLING

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Name : Aletha DE WITT

Title : The Status and Direction of the ICRF

Abstract : High precision astrometric VLBI measurements of positions of extra-galactic radio sources are used to define and maintain the International Celestial Reference Frame (ICRF). The extra-galactic radio reference sources selected for the ICRF are mainly radio-loud quasars; quasars being at great distances (median z ~ 1) do not exhibit any measurable proper motion or parallax, making them ideal reference sources. A new realization of the frame, the ICRF3, was adopted by the IAU during its XXXth General Assembly in August 2018, and has replaced it predecessor, the ICRF2, on 1 January 2019. The ICRF3 is based on nearly 40 years of VLBI data at the standard 2.3 and 8.4 GHz (S/X-band) frequencies, along with observations at 24 GHz (K-band) and at 8.4 and 32 GHz (X/Ka-band), making it the first multi-frequency frame ever realized. The ICRF3 contains source positions for a total of 4536 sources at X-band, supplemented with independently estimated positions for 824 sources at K-band and 678 at Ka-band. The noise floor in the individual source coordinates is at a level of 30 μas, with a median position error of 127 μas in right ascension and 218 μas in declination, a factor of more than 3 improvement over the ICRF2. Comparison between the ICRF3 S/X frame and the recently released Gaia celestial reference frame (Gaia-CRF2) shows no relative deformations at the level of the ICRF3 noise floor. Looking to the future, the international reference frame community is developing a road map for continued improvement of the ICRF. This work is motivated by the IAU's call to maintain and improve the ICRF3. In particular, special effort should be made to strengthen the celestial frame in the far south. It is a well known fact that radio reference frames, including the ICRF, are much weaker in the far south, in both density and precision. It is also important that the ICRF sources be imaged on a regular basis in order to track potential source structure changes. Such structure can introduce significant errors in the VLBI measurements thereby degrading the accuracy of the estimated source positions. Finally, there are also plans for a fully integrated multi-frequency realization of the ICRF, incorporating also the optical Gaia celestial reference frame data.

Name : Ludovic DELCHAMBRE

Title : Discovering multiply-imaged quasars with Gaia

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Name : Chengyu DING

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Name : Bryan DORLAND

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Name : Christine DUCOURANT

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Name : Thomas Marshall EUBANKS

Title : Anchored in Shadows: Tying the Celestial Reference Frame Directly to Black Hole Event Horizons

Abstract : The International Celestial Reference Frame (ICRF) is based on observations of Super Massive Black Holes (SMBH) jets produced by active galactic nuclei and quasars. These jets are inherently subject to change and will appear different at different observing frequencies. Recently, the Event Horizon Telescope (EHT), a mm wave Very Long Baseline Interferometry (VLBI) array, has observed the 40 microas diameter shadow of the SMBH in M87 at 1.3 mm, showing that the emitting region is smaller than the black-hole shadow. General Relativity predicts that inside the bright emission ring will be ``photon rings,'' narrow arcs representing photons escaping after one or more orbits around the event horizon. These photon rings will be stable features tied to the mass and spin rate of the host SMBH, and thus will be the ultimate reference points for Celestial Reference Frames at any frequencies. Anchoring the Celestial Reference Frame (CRF) in black hole shadows could improve the accuracy and stability of the CRF by two orders of magnitude, allowing for new tests of fundamental physics and astrometric cosmology, and providing a profound improvement in our understanding of the kinematics and dynamics of active galactic nuclei.

Name : Justin FINKE

Title : The Properties of Parsec-Scale Blazar Jets

Abstract : By assuming a standard Blandford-Konigl jet, it is possible to determine the bulk Lorentz factor and angle to the line of sight of self-similar parsec-scale blazar jets by using five measured quantities: redshift, core radio flux, extended radio flux, magnitude of the core shift between two frequencies, and apparent jet opening angle. From the bulk Lorentz factor and angle computed with this method, one can compute other jet properties such as the Doppler factor, magnetic field strength, and intrinsic opening angle. I use data taken from the literature and marginalize over nuisance parameters associated with the electron distribution and equipartition to compute these quantities, although the errors are large. Results are generally consistent with constraints from other methods. Primary sources of uncertainty are the errors on the core shift measurements and the uncertainty in the electron spectral index.

Name : Travis FISCHER

Title : FRAMEx: Initial Results and Implications

Abstract : We present initial observations for the Fundamental Reference AGN Monitoring Experiment (FRAMEx), an observational campaign dedicated to understanding the physical processes that affect the apparent positions and morphologies of AGNs. We find that a comparison between simultaneous X-ray (Swift XRT) and radio (VLBA) observations of a volume-complete sample of nearby AGN often place targets in our sample below the established fundamental plane, relating X-ray and radio luminosity and black hole mass. These findings suggest that previous radio observations may have been overestimated when attributing emission to the nucleus versus the surrounding medium and that this contamination may be due to larger interactions between the AGN and its host disk. We also present a deeper look at the extended structure in VLBA observations of NGC 1068 and compare observations over 20 years in difference. We find that the bright, resolved knots of emission largely are static, or travel at velocities of the order of ~100s km/s. As these radio structures can also be mapped to existing optical structures as observed with the Hubble Space Telescope, these findings further suggest that the extranuclear radio emission observed in radio-quiet AGN can be a byproduct of AGN winds versus emission from a radio jet.

Name : Helene FLOHIC

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Name : Eilat GLIKMAN

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Name : Andy GOULDING

Title : Discovering close-separation binary quasars and implications for low-frequency Gravitational Waves

Abstract : Supermassive black hole binaries are expected to dominate the contribution to the as-yet undetected gravitational wave background (GWB) signal at the nanohertz frequencies accessible to Pulsar Timing Arrays (PTA). However, we currently lack firm empirical constraints on the GWB amplitude due to the dearth of confirmed SMBH binaries with ~10^8-10^9 Msun. I will present our recent discovery of a z∼0.2 merger remnant hosting a quasar pair separated by only 0.13'' (430pc), where each BH has mass >4x10^8 Msun. I will discuss the implications of this quasar pair, expectations for the identification of the full population of close separation quasar pairs through the use of GAIA and sensitive ground-based surveys, and their predicted contribution to a stochastic GWB that should be detected by PTA in the next several years.

Name : Gregory HENNESSY

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Name : Lucas HUNT

Title : VLBA Investigations of Positional Offsets in International Celestial Reference Frame Sources

Abstract : We present results from an imaging study of objects in the International Celestial Reference Frame which have ambiguities in their position estimate. We investigate 8 objects that show a positional offset between ICRF2 and ICRF3. We also investigate 28 objects from the list of ICRF2 defining sources that had a positional offset between ICRF2 and Gaia DR1. We briefly discuss how the positions of these sources have changed as updates to both the ICRF and Gaia have been released and what the images reveal about these offsets.

Name : Nan JIANG

Title : Discussing the axis stability of the ICRF S/X frame using coordinate time series from VLBI observations

Abstract : The International Celestial Reference Frame (ICRF) is based on a set of precise coordinates of compact exragalactic radio sources observed by Very Long Basline Interferometry (VLBI). However, the structure of extragalactic radio sources, mainly AGNs, is changing over time, which may cause jitter of their observed positions, and bring a negative impact on the axis stability of the ICRF. Latest study (Gattano et al. 2018) also suggests that almost no source exhibited "idealized" position stability in a long observation time. That indicates the axis stability of ICRF may get worse over time, and it's necessary to reassess it. In this work, we provide an analysis of the position stability of extragalactic radio sources using statistic tools like the Allan variance for coordinate time series, and lead a further discussion on the axis stability of the ICRF.

Name : Megan JOHNSON

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Name : Maria KARBON

Title : ICRFc: A multifrequency reference frame in the Gaia-era – a geodetic perspective

Abstract : We present a celestial reference frame (CRF) based on the combination of independent, multifrequency radio source position catalogs using nearly 40 years of very long baseline interferometry observations at the standard geodetic frequencies at SX band and about 15 years of observations at higher frequencies (K and XKa). The final catalog contains 4617 sources. Until recently there were no means to have an independent comparison and validation of a radio CRF, as all CRFs, for instance galactic or optical, heavily depend on the ICRF or were not accurate enough. With the Gaia mission, this changed. A crucial point when combining and comparing catalogs at different frequencies is the the so-called core-shift. That is an offset between the positions in the different frequencies, as the apparent position of the jet base (core) in radio-loud active galactic nuclei changes with frequency due to synchrotron self-absorption. In our study we tackle this issue using statistical tools on the totality of sources and take a closer look at a smaller sample. Further, we explore the nature of the VLBI CRFs, and their role in the definition of the origin of the Gaia-CRF. We will show, that an independent comparison with Gaia-CRF proves difficult, as Gaia-CRF is not completely independent, nor consistent. Nonetheless, we can confirm the presence significant deformations. Their origin, however, remains unclear.

Name : Amy KIMBALL

Title : Constraining the contribution of AGN jet emission in radio-quiet quasi-stellar objects (QSOs)

Abstract : One of the puzzling aspects of optically-luminous AGNs is the physical origin of their radio emission. For radio-loud objects, it's clear that the dominant origin is the AGN radio-jet. But for radio-quiet objects, there is an ongoing controversy in the literature. Potential sources of radio emission include (scaled-down) AGN jets, shocks from AGN driven winds, and host galaxy star formation. In reality, all of these may contribute, but the question remains as to which one (if any) is the dominant origin over different sources among the radio-quiet QSO population. I will present new results from my work to constrain the AGN-jet emission in radio-quiet QSOs, and probe the contribution from star formation in the host galaxy, using high-resolution VLBI observations along with lower-resolution observations from the Very Large Array.

Name : Allison KIRKPATRICK

Title : Cold Quasars: AGN and Stellar Co-evolution in Extreme Objects

Abstract : Quasars are the most luminous of active galactic nuclei (AGN), and are perhaps responsible for quenching star formation in their hosts. The Stripe 82X catalog spans 15.6 deg2 covered with XMM-Newton that is also covered by Herschel/SPIRE. We have 2500 X-ray detected sources with multi-wavelength counterparts, and 30% of these are unobscured quasars. We define a new population of quasars which are unobscured, have X-ray luminosities in excess of 10^44 erg/s, have broad emission lines, and yet are also bright in the far-infrared. We refer to these Herschel-detected, unobscured quasars as ``Cold Quasars''. A mere 4% (23) of the X-ray- and optically-selected unobscured quasars in Stripe 82X are detected at 250 microns. These Cold Quasars lie at z=1-3, have Mdust =10^8-10^9 Msun and have star formation rates of 200-2000 Msun/yr. Crucially, Cold Quasars have 4-7x as much star formation as the unobscured quasar population at similar redshifts. This phase is likely short-lived, as the central engine and immense star formation consume the gas reservoir. Cold Quasars are type-1 blue quasars that reside in starburst galaxies.

Name : Sergei KLIONER

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Name : Hana KRASNA

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Name : Sébastien LAMBERT

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Name : Mikhail LISAKOV

Title : Moving apparent cores in active galactic nuclei

Abstract : Future improvement of the astrometric accuracy when observing active galactic nuclei requires detailed knowledge of the sources' structure and evolution. One of the issues to be addressed is a violation of the assumption that the position of the apparent beginning of the jet is fixed. We have developed a method to measure any movement of the apparent core based on the position of bright features in the jet. A hundred of densely monitored sources from the MOJAVE sample revealed that their cores can move back and forth along the jet by several hundred microarcseconds from their average position. We present this result together with our finding of a connection between the position of the apparent core in a jet and its other properties, e.g. flux density, compactness, etc.

Name : Niu LIU

Title : Measure the radio-to-optical offset from simultaneous VLBI and Gaia observations

Abstract : We measure the radio-to-optical offsets for 1264 ICRF sources from a special VLBI solution and the Gaia-CRF2 subset. The VLBI observations are limited to those made at 8 GHz during the observing windows of the Gaia Data Release 2, which makes our measurements free of large uncertainty in the historical VLBI data and apparent motion of radio positions. We found that large radio-to-optical offsets tend to occur to sources with poor VLBI observations (thus large VLBI positional error ) and optically faint sources (thus large Gaia positional error). Removing sources observed in less than three VLBI sessions, only a few sources yield a significant VLBI/Gaia offset with respective to the combined formal uncertainty. Our results complement recent works on the same topic, such as Petrov et al 2019.

Name : Valeri MAKAROV

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Name : Zinovy MALKIN

Title : To the accuracy assessment of the orientation parameters between the CRF realizations

Abstract : Comparison of the astrometric source position catalogs is a necessary step in solving various astrometric problems, such as comparison of different VLBI-based celestial reference frame (CRF) realizations, mutual alignment of radio and optical frames, and constructing of the future multi-waveband CRF. In this work, an analysis is performed of several factors that may affect the accuracy of computation of the orientation parameters between astrometric position catalogs.

Name : Zinovy MALKIN

Title : Using ground-based photometry data for verification of the Gaia-ICRF cross-identification

Abstract : Comparison of the positions of the same objects as determined from the VLBI observations at radio waves and optical observations of the Gaia mission plays a very important role in many studies related to both constructing celestial reference system and frame, and physics of the celestial bodies. Obviously, the accuracy of scientific conclusions derived from such studies depends on the correct cross-identification of the objects in the VLBI and Gaia catalogs. Currently, this cross-identification is based of the distance between two positions, sometimes with additional criteria, such as an analysis of the position quality. In this work, a comparison was made between the optical magnitudes provided by the Gaia and magnitudes obtained from ground-based observations. The OCARS catalog is used for this purpose. This comparison showed that the Gaia and ground-based measurements are not always in good agreement, which my suggest mistakes in the cross-identification. Such an analysis can serve as a supplement criterium for cross-identification between the Gaia and ICRF.

Name : Francois MIGNARD

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Name : Boyko MIHOV

Title : The VLBI-to-Gaia offsets: the radio galaxy 3C 382

Abstract : The position angles of the VLBI-to-Gaia offsets for AGNs reveal a strong correlation with the jet direction. For the bulk of the sources, the offsets occur downstream the jet which could be generally due to the presence of a strong optical jet. The majority of the rest show upstream offsets possibly related to the accretion disk, the core-shift effect, etc. We have initiated a study on a sample of sources with position angles of the VLBI-to-Gaia offsets roughly perpendicular the jet direction. Analysed are the innermost regions and the possible aligment between the optical and radio morphology. We report the results for 3C 382, a broad-line radio galaxy. The 2-D decomposition residual image reveals an irregular ring-like structure with three filaments emerging out of it. The radio morphology displays a significant match with the filaments. Lifetime arguments favour a scenario, in which the filaments precede the jet. We suggest the filaments deflect the jet and cause the offset of the opposite lobe. We discuss the position angle of the VLBI-to-Gaia offset relative to the jet in the framework of the host galaxy.

Name : Kristina NYLAND

Title : Compact Radio AGN Identified in the VLA Sky Survey:

Abstract : Recent studies have shown that the slow transient radio sky is dominated by emission from AGN, the majority of which are likely associated with variability. Although common, the physical origin of radio AGN variability, as well as its dependence on cosmic epoch and host galaxy properties, is not well understood. As part of an on-going study of transients in the Epoch 1 (2017-2019) of the VLA Sky Survey (VLASS), we have discovered a population of radio sources with up to 10X flux increases in VLASS compared to FIRST (1993-2011). These previously unknown radio sources are co-located with powerful AGN identified in SDSS and WISE at 0.2 < z < 3.2. The large variability amplitudes, variability timescale constraints (> a few months), and high radio luminosities favor an intrinsic variability scenario. Quasi-simultaneous 2019 VLA/A-config data from 1-18 GHz have revealed sources with compact (<0.1”) emission and curved radio SEDs indicative of absorption, possibly associated with young, recently-triggered jets identified for the first time. Here, we discuss implications for our understanding of radio jet lifecycles and triggering from our multi-band VLA observations as well as our forthcoming VLBA follow-up campaign.

Name : Eric PERLMAN

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Name : Leonid PETROV

Title : NASA program of charting the sky with VLBI

Abstract : We witnessed an explosive growth in radioastrometry in the last decade. There were two dozens dedicated program of VLBI astrometry that resulted in an increase of the number of accumulated visibilities collected by a factor of 50, and in an increase of the number of new sources with milliarcsecond level of accuracy by a factor of 5. Over 96% the sources at declinations above -40deg were imaged. The objectives of the programs: support of Fermi mission, providing a dense grid of phase calibrators for radioastronomy, providing reference sources for space navigation, and overall improvement in accuracy. The main directions of the observing programs were densification of the grid of sources with known precise coordinates, reaching completeness of the catalogue, elimination of the hemisphere bias, finding associations with gamma-ray sources, improvement in accuracy. Impressive improvement of the astrometric catalogues both in terms of accuracy and in terms of the growth of the number of sources resulted in important discoveries. Among them, is discovery of the presence of optical jets at milliarcsecond level by a purely astrometric method, discovery of variability of core shifts, and discovery of significant contribution of source structure in the weak regime. I will provide the overview of development in radioastrometry focusing on observational campaign, interpretation of results, its broader impact on astronomy and astrophysics, and the role of NASA in these activities.

Name : François-Xavier PINEAU

Title : Cross-match algorithms and tools

Abstract : Cross-matches are widely used in astronomy whether it be for astrometric purposes (calibration, proper motion estimation, ...), to generate time-series from multi-epoch observations or to build multi-wavelength datasets. Basic cross-matches are quite easy to implement, even as single SQL/TAP queries. But they are getting more complicated when the data volume increases, when a cross-match involves more than two catalogues, when one wants to account for positional errors or wants to quantify the probability each match has of being spurious. We will review the capabilities and limitations of a few cross-match tools that are available for the community. We will also remind some theoretical aspects of statistical (multi-catalogue) cross-matches together with examples of results accounting for photometric information.

Name : Alexander PLAVIN

Title : AGN jet launching: VLBI and Gaia outlook

Abstract : The most accurate reference frames are currently based on Active Galactic Nuclei observed by VLBI and Gaia. These instruments utilize very different principles and operate at frequencies separated by many orders of magnitude. As a result, they see emission of a different nature and from different parts of an AGN. Understanding the physics of emission processes of AGNs is thus crucial to figure out the possibilities and limitations of astrometric measurements, and to find ways of further improvements. In this talk we discuss opacity effects close to the jet origin, complex geometry of the jet formation and collimation zone and downstream, as well as intricate jet-disk-dust interplay seen in the AGN emission. We show how these are strongly tied to reference frame accuracy, temporal stability, and consistency between multiple bands. We conclude the talk presenting some ideas on how to overcome or reduce such adverse effects.

Name : Brigitte ROCCA VOLMERANGE

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Name : Jacques ROLAND

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Name : Henrique SCHMITT

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Name : Nathan SECREST

Title : opening remarks

Abstract : (general notes about the conference before Keynote)

Name : Yue SHEN

Title : Variability-induced astrometric jitter in sub-kpc dual and off-center AGN

Abstract : Gaia’s precision astrometry allows systematic identification of optically selected sub-kiloparsec dual active galactic nuclei (AGNs), off-nucleus AGNs, and small-scale lensed quasars by “varstrometry” -- where variability-induced astrometric jitter, i.e., temporal displacements of photocenter in unresolved sources, can be reasonably well detected or constrained. This approach extends systematic searches for small-scale (>~mas) dual and off-nucleus AGNs to the poorly explored regime between ~10 pc and ~1 kpc, with Gaia’s full sky coverage and depth to G ~ 21. I will introduce this method, and discuss its implications on using quasars as reference for future high-precision astrometry missions.

Name : Chris SKIPPER

Title : Hunting for spatially-offset-AGN candidates in the Gaia Era

Abstract : The presence of an offset between the position of a compact radio source, and the optical centroid of its host galaxy, may indicate that the galaxy harbours an offset AGN, which could either be part of a dual/binary AGN system, or else a 'kicked' SMHB that has become dislodged following the merger of a dual AGN system. Our recent study of offsets between JVLA/eMERLIN and SDSS positions placed an upper limit of 17% on the fraction of nearby (z < 0.2) galaxies with offset AGN, highlighting some already-known sources along with a number of new and interesting offset-AGN candidates. Here I discuss how the much greater precision of Gaia and VLBI imaging can help reveal smaller offsets at much larger redshifts, and greatly increase the pool of offset-AGN candidates for follow-up study.

Name : Elena SKURIKHINA

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Name : Jean SOUCHAY

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Name : François TARIS

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Name : Oleg TITOV

Title : Optical spectroscopy of reference radio source

Abstract : In the dedicated spectroscopic program, spectra of about 350 reference radio sources were observed at large optical facilities (the 3.58m European Southern Observatory New Technology Telescope, the 2.5m Nordic Optical Telescope, and the two 8.2m Gemini telescopes in Hawaii and Chile). Redshifts of more than 250 quasars and radio galaxies were obtained. While most of the targets are powerful quasars, a significant fraction of radio galaxies is also included from the list of non-defining ICRF radio sources. Several features found in the optical spectra (the Mg II absorption lines, both associated and intervening, and the CIV emission line blue shift), may be linked to the radio characteristics of the geodetic VLBI sources.

Name : Junfeng WANG

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Name : Stephen WILLIAMS

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Name : Minghui XU

Title : Source structure effects in the broadband VLBI Global Observing System

Abstract : With 21 broadband VLBI sessions so far public released, we made quality assessments for two kinds of observables from VGOS, group delay and differential total electron content (δTEC). Our study reveals that the random measurement noises of VGOS group delays are below the level of three picoseconds (ps), while the contributions from other systematic error sources, mainly source structure related, are at the level of 20 ps. Due to the significant improvement in measurement noise, source structure effects with relatively small magnitudes that are not overwhelming in the S/X VLBI system are clearly visible in VGOS observations. The structure effects on broadband VLBI observations are studied based on multi-frequency VLBI images for several sources.

Name : Norbert ZACHARIAS

Title : Status of Deep South Telescope (DST) Observations

Abstract : A fully robotic 1-meter telescope, the Deep South Telescope (DST), is operated by the U.S. Naval Observatory (USNO) at Cerro Tololo Interamerican Observatory (CTIO) since August 2019. A list of about 200 selected VLBI optical counterparts are being observed through B,V,R,I filters. Experience with this new telescope, calibration efforts and first results will be reported.