Absorbed relativistic jets in radio-quiet narrow-line Seyfert 1 galaxies
  Narrow-line Seyfert 1 (NLS1) galaxies are peculiar active galactic nuclei
(AGN). Most of them do not show strong radio emission, but recently seven
radio-quiet (or -silent) NLS1s have been detected flaring multiple times at 37
GHz by the Mets\"ahovi Radio Telescope, indicating the presence of 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 those frequencies, the radio emission from their relativistic jet
must be absorbed, either via synchrotron self-absorption as it occurs in
gigahertz-peaked sources or, more likely, via 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 more and more
frequently a misleading parameter. New high-frequency and high-resolution radio
observations are essential to test our hypotheses.
