{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2025,10,12]],"date-time":"2025-10-12T02:48:33Z","timestamp":1760237313892,"version":"build-2065373602"},"reference-count":55,"publisher":"MDPI AG","issue":"4","license":[{"start":{"date-parts":[[2020,4,3]],"date-time":"2020-04-03T00:00:00Z","timestamp":1585872000000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Symmetry"],"abstract":"<jats:p>Many low-luminosity active galactic nuclei (AGNs) contain a compact radio core which can be observed with high angular resolution using very long baseline interferometry (VLBI). Combining arcsec-scale structural information with milliarcsec-resolution VLBI imaging is a useful way to characterise the objects and to find compact cores on parsec scales. VLBI imaging could also be employed to look for dual AGNs when the sources show kpc-scale double symmetric structure with flat or inverted radio spectra. We observed five such sources at redshifts     0.36 &lt; z &lt; 0.58     taken from an optically selected sample of Type 2 quasars with the European VLBI Network (EVN) at 1.7 and 5 GHz. Out of the five sources, only one (SDSS J1026\u20130042) shows a confidently detected compact VLBI core at both frequencies. The other four sources are marginally detected at 1.7 GHz only, indicating resolved-out radio structure and steep spectra. Using first-epoch data from the ongoing Karl G. Jansky Very Large Array Sky Survey, we confirm that indeed all four of these sources have steep radio spectra on arcsec scale, contrary to the inverted spectra reported earlier in the literature. However, the VLBI-detected source, SDSS J1026\u22120042, has a flat integrated spectrum. Radio AGNs that show kpc-scale symmetric structures with truly flat or inverted spectra could still be promising candidates of dual AGNs, to be targeted with VLBI observations in the future.<\/jats:p>","DOI":"10.3390\/sym12040527","type":"journal-article","created":{"date-parts":[[2020,4,3]],"date-time":"2020-04-03T05:55:16Z","timestamp":1585893316000},"page":"527","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":4,"title":["High-Resolution Radio Observations of Five Optically Selected Type 2 Quasars"],"prefix":"10.3390","volume":"12","author":[{"ORCID":"https:\/\/orcid.org\/0000-0002-8813-4884","authenticated-orcid":false,"given":"M\u00e1t\u00e9","family":"Krezinger","sequence":"first","affiliation":[{"name":"Department of Astronomy, E\u00f6tv\u00f6s Lor\u00e1nd University, P\u00e1zm\u00e1ny P\u00e9ter s\u00e9t\u00e1ny 1\/A, H-1117 Budapest, Hungary"},{"name":"Konkoly Observatory, Research Centre for Astronomy and Earth Sciences, Konkoly Thege Mikl\u00f3s \u00fat 15-17, H-1121 Budapest, Hungary"}]},{"ORCID":"https:\/\/orcid.org\/0000-0003-3079-1889","authenticated-orcid":false,"given":"S\u00e1ndor","family":"Frey","sequence":"additional","affiliation":[{"name":"Konkoly Observatory, Research Centre for Astronomy and Earth Sciences, Konkoly Thege Mikl\u00f3s \u00fat 15-17, H-1121 Budapest, Hungary"},{"name":"Institute of Physics, ELTE E\u00f6tv\u00f6s Lor\u00e1nd University, P\u00e1zm\u00e1ny P\u00e9ter s\u00e9t\u00e1ny 1\/A, H-1117 Budapest, Hungary"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-5195-335X","authenticated-orcid":false,"given":"Zsolt","family":"Paragi","sequence":"additional","affiliation":[{"name":"Joint Institute for VLBI ERIC, Oude Hoogeveensedijk 4, 7991 PD Dwingeloo, The Netherlands"}]},{"ORCID":"https:\/\/orcid.org\/0000-0003-1027-5043","authenticated-orcid":false,"given":"Roger","family":"Deane","sequence":"additional","affiliation":[{"name":"Department of Physics, University of Pretoria, Hatfield, Pretoria 0028, South Africa"},{"name":"Centre for Radio Astronomy Techniques and Technologies, Department of Physics and Electronics, Rhodes University, Mkhanda 6140, South Africa"}]}],"member":"1968","published-online":{"date-parts":[[2020,4,3]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","first-page":"315","DOI":"10.1086\/313041","article-title":"A Search for \u201cDwarf\u201d Seyfert Nuclei. III. Spectroscopic Parameters and Properties of the Host Galaxies","volume":"112","author":"Ho","year":"1997","journal-title":"Astrophys. J. Suppl. Ser."},{"key":"ref_2","doi-asserted-by":"crossref","first-page":"197","DOI":"10.1086\/309543","article-title":"Radio Sources in Low-Luminosity Active Galactic Nuclei. II. Very Long Baseline Interferometry Detections of Compact Radio Cores and Jets in a Sample of LINERs","volume":"542","author":"Falcke","year":"2000","journal-title":"Astrophys. J."},{"key":"ref_3","doi-asserted-by":"crossref","first-page":"53","DOI":"10.1051\/0004-6361:20020874","article-title":"Radio sources in low-luminosity active galactic nuclei. III. \u201cAGNs\u201d in a distance-limited sample of \u201cLLAGNs\u201d","volume":"392","author":"Nagar","year":"2002","journal-title":"Astron. Astrophys."},{"key":"ref_4","first-page":"49","article-title":"The jet\/disk symbiosis. III. What the radio cores in GRS 1915+105, NGC 4258, M 81 and Sgr A* tell us about accreting black holes","volume":"342","author":"Falcke","year":"1999","journal-title":"Astron. Astrophys."},{"key":"ref_5","doi-asserted-by":"crossref","first-page":"521","DOI":"10.1051\/0004-6361:20042277","article-title":"Radio sources in low-luminosity active galactic nuclei. IV. Radio luminosity function, importance of jet power, and radio properties of the complete Palomar sample","volume":"435","author":"Nagar","year":"2005","journal-title":"Astron. Astrophys."},{"key":"ref_6","doi-asserted-by":"crossref","first-page":"L2","DOI":"10.1051\/0004-6361\/201628302","article-title":"Unveiling the origin of the radio emission in radio-quiet quasars","volume":"589","author":"Middelberg","year":"2016","journal-title":"Astron. Astrophys."},{"key":"ref_7","doi-asserted-by":"crossref","first-page":"704","DOI":"10.1086\/308397","article-title":"Compact Radio Emission from Warm Infrared Galaxies","volume":"530","author":"Kewley","year":"2000","journal-title":"Astrophys. J."},{"key":"ref_8","doi-asserted-by":"crossref","first-page":"554","DOI":"10.1086\/305070","article-title":"Advection-dominated accretion model of Sagittarius A*: Evidence for a black hole at the Galactic center","volume":"492","author":"Narayan","year":"1998","journal-title":"Astron. J."},{"key":"ref_9","doi-asserted-by":"crossref","first-page":"387","DOI":"10.1038\/s41550-019-0765-4","article-title":"The origin of radio emission from radio-quiet active galactic nuclei","volume":"3","author":"Panessa","year":"2019","journal-title":"Nat. Astron."},{"key":"ref_10","doi-asserted-by":"crossref","first-page":"L133","DOI":"10.1086\/338254","article-title":"The Origin of Radio Emission in Low-Luminosity Active Galactic Nuclei: Jets, Accretion Flows, or Both?","volume":"562","author":"Ulvestad","year":"2001","journal-title":"Astrophys. J."},{"key":"ref_11","doi-asserted-by":"crossref","first-page":"1089","DOI":"10.1088\/0004-6256\/139\/3\/1089","article-title":"The Radio Properties of Type 2 Quasars","volume":"139","author":"Lal","year":"2010","journal-title":"Astron. J."},{"key":"ref_12","doi-asserted-by":"crossref","first-page":"65","DOI":"10.1086\/170407","article-title":"Compact Starbursts in Ultraluminous Infrared Galaxies","volume":"378","author":"Condon","year":"1991","journal-title":"Astron. J."},{"key":"ref_13","doi-asserted-by":"crossref","first-page":"5513","DOI":"10.1093\/mnras\/sty3098","article-title":"What drives the radio slopes in radio-quiet quasars?","volume":"482","author":"Laor","year":"2019","journal-title":"Mon. Not. R. Astron. Soc."},{"key":"ref_14","doi-asserted-by":"crossref","first-page":"L6","DOI":"10.1088\/2041-8205\/815\/1\/L6","article-title":"Binary Active Galactic Nuclei in Stripe 82: Constraints on Synchronized Black Hole Accretion in Major Mergers","volume":"815","author":"Fu","year":"2015","journal-title":"Astrophys. J. Lett."},{"key":"ref_15","doi-asserted-by":"crossref","first-page":"035001","DOI":"10.1088\/1538-3873\/ab63eb","article-title":"The Karl G. Jansky Very Large Array Sky Survey (VLASS). Science Case and Survey Design","volume":"132","author":"Lacy","year":"2020","journal-title":"Publ. Astron. Soc. Pac."},{"key":"ref_16","doi-asserted-by":"crossref","first-page":"1211","DOI":"10.1029\/2018RS006647","article-title":"VLBI studies of DAGN and SMBHB hosting galaxies","volume":"53","author":"An","year":"2018","journal-title":"Radio Sci."},{"key":"ref_17","first-page":"101525","article-title":"The Quest for Multiple Supermassive Black Holes: A Multi-Messenger View","volume":"89","author":"Vignali","year":"2019","journal-title":"New Astron. Rev."},{"key":"ref_18","doi-asserted-by":"crossref","first-page":"L271","DOI":"10.1088\/2041-8205\/714\/2\/L271","article-title":"VLBI Detection of an Active Galactic Nucleus Pair in the Binary Black Hole Candidate SDSS J1536+0441","volume":"714","author":"Bondi","year":"2010","journal-title":"Astrophys. J."},{"key":"ref_19","doi-asserted-by":"crossref","first-page":"847","DOI":"10.1111\/j.1365-2966.2008.13806.x","article-title":"On the origin of radio emission in radio-quiet quasars","volume":"390","author":"Laor","year":"2008","journal-title":"Mon. Not. R. Astron. Soc."},{"key":"ref_20","doi-asserted-by":"crossref","unstructured":"Deane, R., Paragi, Z., Jarvis, M., Coriat, M., Bernardi, G., Frey, S., Heywood, I., and Kloeckner, H.R. (2014, January 9\u201313). Multiple supermassive black hole systems: SKA\u2019s future leading role. Proceedings of the Advancing Astrophysics with the Square Kilometre Array, Proceedings of Science, Giardini Naxos, Italy.","DOI":"10.22323\/1.215.0151"},{"key":"ref_21","doi-asserted-by":"crossref","first-page":"L49","DOI":"10.1093\/mnrasl\/slx076","article-title":"Discovery of a dual active galactic nucleus with \u223c8 kpc separation","volume":"470","author":"Ellison","year":"2017","journal-title":"Mon. Not. R. Astron. Soc."},{"key":"ref_22","doi-asserted-by":"crossref","first-page":"1711","DOI":"10.1086\/510102","article-title":"A Cosmology Calculator for the World Wide Web","volume":"118","author":"Wright","year":"2006","journal-title":"Publ. Astron. Soc. Pac."},{"key":"ref_23","doi-asserted-by":"crossref","first-page":"2125","DOI":"10.1086\/378610","article-title":"Candidate Type II Quasars from the Sloan Digital Sky Survey. I. Selection and Optical Properties of a Sample at 0.3 < z < 0.83","volume":"126","author":"Zakamska","year":"2003","journal-title":"Astron. J."},{"key":"ref_24","doi-asserted-by":"crossref","first-page":"A89","DOI":"10.1051\/0004-6361\/201935270","article-title":"QSO2 outflow characterization using data obtained with OSIRIS at the Gran Telescopio Canarias","volume":"626","author":"Bellocchi","year":"2019","journal-title":"Astron. Astrophys."},{"key":"ref_25","doi-asserted-by":"crossref","first-page":"80","DOI":"10.1111\/j.1365-2966.2012.20652.x","article-title":"Mergers and interactions in Sloan Digital Sky Survey type 2 quasars at z\u223c0.3\u20130.4. SDSS J143027.66-005614.8: A case study","volume":"423","author":"Bessiere","year":"2012","journal-title":"Mon. Not. R. Astron. Soc."},{"key":"ref_26","doi-asserted-by":"crossref","first-page":"1829","DOI":"10.1093\/mnras\/sty2910","article-title":"The host galaxies of luminous type 2 AGNs at z\u223c0.3\u20130.4","volume":"483","author":"Buitrago","year":"2019","journal-title":"Mon. Not. R. Astron. Soc."},{"key":"ref_27","doi-asserted-by":"crossref","first-page":"23","DOI":"10.3847\/1538-4365\/aaf651","article-title":"The Fifteenth Data Release of the Sloan Digital Sky Surveys: First Release of MaNGA-derived Quantities, Data Visualization Tools, and Stellar Library","volume":"240","author":"Aguado","year":"2019","journal-title":"Astrophys. J. Suppl. Ser."},{"key":"ref_28","unstructured":"Gaia Collaboration, Prusti, T., de Bruijne, J.H.J., Brown, A.G.A., Vallenari, A., Babusiaux, C., Bailer-Jones, C.A.L., Bastian, U., Biermann, M., and Evans, D.W. (2016). The Gaia mission. Astron. Astrophys., 595, A1."},{"key":"ref_29","doi-asserted-by":"crossref","unstructured":"Gaia Collaboration, Brown, A.G.A., Vallenari, A., Prusti, T., de Bruijne, J.H.J., Babusiaux, C., Bailer-Jones, C.A.L., Biermann, M., Evans, D.W., and Eyer, L. (2018). Gaia Data Release 2. Summary of the contents and survey properties. Astron. Astrophys., 616, A1.","DOI":"10.1051\/0004-6361\/201832964"},{"key":"ref_30","unstructured":"Zensus, J.A., Diamond, P.J., and Napier, P.J. (1995). VLBI Phase-Referencing. Very Long Baseline Interferometry and the VLBA, Astronomical Society of the Pacific. Chapter 17."},{"key":"ref_31","doi-asserted-by":"crossref","first-page":"559","DOI":"10.1086\/176166","article-title":"The FIRST Survey: Faint Images of the Radio Sky at Twenty Centimeters","volume":"450","author":"Becker","year":"1995","journal-title":"Astron. J."},{"key":"ref_32","doi-asserted-by":"crossref","first-page":"1693","DOI":"10.1086\/300337","article-title":"The NRAO VLA Sky Survey","volume":"115","author":"Condon","year":"1998","journal-title":"Astron. J."},{"key":"ref_33","unstructured":"Villarreal Hern\u00e1ndez, A.C., and Andernach, H. (2018). A Search for Extended Radio Sources in 1.3 sr of the VLA Sky Survey (VLASS). arXiv."},{"key":"ref_34","unstructured":"Zensus, J.A., Diamond, P.J., and Napier, P.J. (1995). VLBI Data Reduction in Practice. Very Long Baseline Interferometry and the VLBA, Astronomical Society of the Pacific. Chapter 12."},{"key":"ref_35","first-page":"987","article-title":"DIFMAP: An interactive program for synthesis imaging","volume":"26","author":"Shepherd","year":"1994","journal-title":"Bull. Am. Astron. Soc."},{"key":"ref_36","unstructured":"Lacy, M., Myers, S., Kimball, A., Schinzel, F., Chandler, C., Sjouwerman, L., Marvil, J., Masters, J., Medlin, D., and Vargas, A. (2020, February 27). Pilot and Epoch 1 Quick Look Data Release. VLASS Project Memo #13. Available online: https:\/\/safe.nrao.edu\/wiki\/pub\/JVLA\/VLASS\/VLASS_Memo_013_Epoch_1_Quicklook_Data_Release.pdf."},{"key":"ref_37","doi-asserted-by":"crossref","first-page":"2473","DOI":"10.1086\/497430","article-title":"Sub-Milliarcsecond Imaging of Quasars and Active Galactic Nuclei. IV. Fine-Scale Structure","volume":"130","author":"Kovalev","year":"2005","journal-title":"Astron. J."},{"key":"ref_38","unstructured":"Taylor, G.B., Carilli, C.L., and Perley, R.A. (1999). Image Analysis. Synthesis Imaging in Radio Astronomy II, Astronomical Society of the Pacific."},{"key":"ref_39","doi-asserted-by":"crossref","first-page":"143","DOI":"10.3847\/1538-4357\/aaf650","article-title":"Dissecting the AGN Disk-Jet System with Joint VLBI-Gaia Analysis","volume":"871","author":"Plavin","year":"2019","journal-title":"Astron. J."},{"key":"ref_40","doi-asserted-by":"crossref","first-page":"L1","DOI":"10.1051\/0004-6361\/201630031","article-title":"VLBI-Gaia offsets favor parsec-scale jet direction in active galactic nuclei","volume":"598","author":"Kovalev","year":"2017","journal-title":"Astron. Astrophys."},{"key":"ref_41","doi-asserted-by":"crossref","first-page":"3775","DOI":"10.1093\/mnras\/stx1747","article-title":"Observational consequences of optical band milliarcsec-scale structure in active galactic nuclei discovered by Gaia","volume":"471","author":"Petrov","year":"2017","journal-title":"Mon. Not. R. Astron. Soc."},{"key":"ref_42","doi-asserted-by":"crossref","first-page":"102","DOI":"10.1086\/159538","article-title":"Strong radio sources in bright spiral galaxies. II. Rapid star formation and galaxy-galaxy interactions","volume":"252","author":"Condon","year":"1982","journal-title":"Astron. J."},{"key":"ref_43","doi-asserted-by":"crossref","first-page":"519","DOI":"10.1051\/0004-6361:20030198","article-title":"The infrared supernova rate in starburst galaxies","volume":"401","author":"Mannucci","year":"2003","journal-title":"Astron. Astrophys."},{"key":"ref_44","doi-asserted-by":"crossref","first-page":"A134","DOI":"10.1051\/0004-6361\/201118446","article-title":"The nuclear starburst in Arp 299-A: From the 5.0 GHz VLBI radio light-curves to its core-collapse supernova rate","volume":"539","author":"Bondi","year":"2012","journal-title":"Astron. Astrophys."},{"key":"ref_45","doi-asserted-by":"crossref","first-page":"4191","DOI":"10.1093\/mnras\/stv2571","article-title":"Star formation in quasar hosts and the origin of radio emission in radio-quiet quasars","volume":"455","author":"Zakamska","year":"2016","journal-title":"Mon. Not. R. Astron. Soc."},{"key":"ref_46","doi-asserted-by":"crossref","first-page":"L3","DOI":"10.1051\/0004-6361\/201628305","article-title":"Compact radio cores in radio-quiet active galactic nuclei","volume":"589","author":"Maini","year":"2016","journal-title":"Astron. Astrophys."},{"key":"ref_47","doi-asserted-by":"crossref","first-page":"1810","DOI":"10.1086\/342343","article-title":"Spectroscopic Target Selection in the Sloan Digital Sky Survey: The Main Galaxy Sample","volume":"124","author":"Strauss","year":"2002","journal-title":"Astron. J."},{"key":"ref_48","doi-asserted-by":"crossref","first-page":"A13","DOI":"10.1051\/0004-6361\/201321279","article-title":"Optical-radio positional offsets for active galactic nuclei","volume":"553","author":"Orosz","year":"2013","journal-title":"Astron. Astrophys."},{"key":"ref_49","doi-asserted-by":"crossref","first-page":"5179","DOI":"10.1093\/mnras\/sty114","article-title":"Spatially offset AGN candidates in the CLASS survey","volume":"475","author":"Skipper","year":"2018","journal-title":"Mon. Not. R. Astron. Soc."},{"key":"ref_50","doi-asserted-by":"crossref","first-page":"L80","DOI":"10.1111\/j.1745-3933.2006.00247.x","article-title":"A population of high-redshift type 2 quasars\u2014II. Radio properties","volume":"373","author":"Rawlings","year":"2006","journal-title":"Mon. Not. R. Astron. Soc."},{"key":"ref_51","doi-asserted-by":"crossref","first-page":"1002","DOI":"10.1086\/423220","article-title":"Candidate Type II Quasars from the Sloan Digital Sky Survey. II. From Radio to X-Rays","volume":"128","author":"Zakamska","year":"2004","journal-title":"Astron. J."},{"key":"ref_52","doi-asserted-by":"crossref","first-page":"L58","DOI":"10.1093\/mnrasl\/slt008","article-title":"Probing the nature of compact ultrasteep spectrum radio sources with the e-EVN and e-MERLIN","volume":"431","author":"Argo","year":"2013","journal-title":"Mon. Not. R. Astron. Soc."},{"key":"ref_53","doi-asserted-by":"crossref","first-page":"12","DOI":"10.3847\/1538-4357\/aa8321","article-title":"Double-peaked Emission Lines Due to a Radio Outflow in KISSR 1219","volume":"846","author":"Kharb","year":"2017","journal-title":"Astrophys. J."},{"key":"ref_54","doi-asserted-by":"crossref","first-page":"40","DOI":"10.3847\/1538-4357\/ab6a09","article-title":"The Intriguing Parsec-scale Radio Structure in the \u201cOffset AGN\u201d KISSR 102","volume":"890","author":"Kharb","year":"2020","journal-title":"Astrophys. J."},{"key":"ref_55","doi-asserted-by":"crossref","first-page":"A53","DOI":"10.1051\/0004-6361\/201014203","article-title":"Coherence loss in phase-referenced VLBI observations","volume":"515","author":"Ros","year":"2010","journal-title":"Astron. Astrophys."}],"container-title":["Symmetry"],"original-title":[],"language":"en","link":[{"URL":"https:\/\/www.mdpi.com\/2073-8994\/12\/4\/527\/pdf","content-type":"unspecified","content-version":"vor","intended-application":"similarity-checking"}],"deposited":{"date-parts":[[2025,10,11]],"date-time":"2025-10-11T09:14:58Z","timestamp":1760174098000},"score":1,"resource":{"primary":{"URL":"https:\/\/www.mdpi.com\/2073-8994\/12\/4\/527"}},"subtitle":[],"short-title":[],"issued":{"date-parts":[[2020,4,3]]},"references-count":55,"journal-issue":{"issue":"4","published-online":{"date-parts":[[2020,4]]}},"alternative-id":["sym12040527"],"URL":"https:\/\/doi.org\/10.3390\/sym12040527","relation":{},"ISSN":["2073-8994"],"issn-type":[{"type":"electronic","value":"2073-8994"}],"subject":[],"published":{"date-parts":[[2020,4,3]]}}}