A Radio Detection Survey of Narrow-Line Seyfert 1 Galaxies using Very-Long-Baseline Interferometry at 22 GHz

TL;DR

This study used advanced VLBI techniques at 22 GHz to detect and analyze the radio properties of 40 narrow-line Seyfert 1 galaxies, revealing a high prevalence of compact cores with diverse spectral characteristics.

Contribution

It presents the first high-sensitivity VLBI survey of NLS1 galaxies at 22 GHz using a new high-data-rate recorder, demonstrating a significant detection rate and diverse radio spectral features.

Findings

12 out of 40 NLS1s detected in radio

Majority show inverted spectra indicating compact cores

Half of the sample exhibits steep spectra despite VLBI sensitivity limits

Abstract

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.