A Radio Detection Survey of Narrow-Line Seyfert 1 Galaxies using
  Very-Long-Baseline Interferometry at 22 GHz
  We conducted a high-sensitivity radio detection survey for forty narrow-line
Seyfert 1 (NLS1) galaxies using very-long-baseline interferometry (VLBI) at 22
GHz through phase-referencing long-time integration and using a newly
developing recorder with a data rate of 8 Gbps, which is a candidate of the
next generation VLBI data recording systems for the Japanese VLBI Network. The
baseline sensitivity was typically a few mJy. The observations resulted in a
detection rate of 12/40 for our radio-selected NLS1 sample; 11 out of the
detected 12 NLS1s showed inverted radio spectra between 1.4 and 22 GHz on the
basis of the Very Large Array flux densities and the VLBI detections. These
high fractions suggest that a compact radio core with a high brightness
temperature is frequently associated with NLS1 nuclei. On the other hand, at
least half of the sample indicated apparently steep spectra even with the
limited VLBI sensitivity. Both the inverted and steep spectrum radio sources
are included in the NLS1 population.
