Absorbed relativistic jets in radio-quiet narrow-line Seyfert 1 galaxies

¹ Finnish Centre for Astronomy with ESO (FINCA), University of Turku, Vesilinnantie 5, 20014 Turku, Finland
e-mail: marco.berton@utu.fi
² Aalto University Metsähovi Radio Observatory, Metsähovintie 114, 02540 Kylmälä, Finland
³ European Space Agency, European Space Astronomy Centre, C/ Bajo el Castillo s/n, 28692 Villanueva de la Cañada, Madrid, Spain
e-mail: ejarvela@sciops.esa.int
⁴ Dipartimento di Fisica e Astronomia “G. Galilei”, Università di Padova, Vicolo dell’Osservatorio 3, 35122 Padova, Italy
⁵ Aalto University Department of Electronics and Nanoengineering, PO Box 15500, 00076 Aalto, Finland
⁶ Las Campanas Observatory, Carnegie Institution of Washington, Colina El Pino, Casilla 601, La Serena, Chile
⁷ National Centre for Radio Astrophysics – Tata Institute of Fundamental Research, Post Bag 3, Ganeshkhind, Pune 411007, India
⁸ Center for Interdisciplinary Exploration and Research in Astrophysics CIERA, Department of Physics and Astronomy, Northwestern University, Evanston, IL 60208, USA

Received: 21 February 2020
Accepted: 5 March 2020

Abstract

Narrow-line Seyfert 1 (NLS1) galaxies are peculiar active galactic nuclei. Most of them do not show strong radio emission, but seven radio-quiet (or radio-silent) NLS1s have recently been detected flaring multiple times at 37 GHz by the Metsähovi Radio Telescope, indicating relativistic jets in these peculiar sources. We observed them with the Karl G. Jansky Very Large Array (JVLA) in A configuration at 1.6, 5.2, and 9.0 GHz. Our results show that these sources are either extremely faint or not detected in the JVLA bands. At these frequencies, the radio emission from their relativistic jet must be absorbed, either through synchrotron self-absorption as it occurs in gigahertz-peaked sources, or more likely, through free-free absorption by a screen of ionized gas associated with starburst activity or shocks. Our findings cast new shadows on the radio-loudness criterion, which seems to be increasingly frequently a misleading parameter. New high-frequency and high-resolution radio observations are essential to test our hypotheses.