Very Long Baseline Array Imaging of Parsec-scale Radio Emissions in Nearby Radio-quiet Narrow-line Seyfert 1 Galaxies

TL;DR

This study uses VLBA observations to reveal parsec-scale jets and nonthermal processes in radio-quiet NLS1 galaxies, challenging previous assumptions about their radio emission origins.

Contribution

First systematic VLBI imaging of the central regions of radio-quiet NLS1s, showing jet structures and high brightness temperatures similar to radio-loud AGNs.

Findings

Detection of high brightness temperature cores in 5 out of 7 galaxies.

Identification of parsec-scale jets with linear structures in some sources.

Diffuse emission dominates the nuclear radio power in these galaxies.

Abstract

We conducted Very Long Baseline Array (VLBA) observations of seven nearby narrow-line Seyfert 1 (NLS1) galaxies at 1.7 GHz (18cm) with milli-arcsecond resolution. This is the first systematic very long baseline interferometry (VLBI) study focusing on the central parsec-scale regions of radio-quiet NLS1s. Five of the seven were detected at a brightness temperature of >~5x10^6 K and contain radio cores with high brightness temperatures of >6x10^7 K, indicating a nonthermal process driven by jet-producing central engines as is observed in radio-loud NLS1s and other active galactic nucleus (AGN) classes. VLBA images of MRK 1239, MRK 705, and MRK 766 exhibit parsec-scale jets with clear linear structures. A large portion of the radio power comes from diffuse emission components that are distributed within the nuclear regions (<~300 pc), which is a common characteristic throughout the observed NLS1s. Jet kinetic powers limited by the Eddington limit may be insufficient to allow the jets escape to kiloparsec scales for these radio-quiet NLS1s with low-mass black holes of <~10^7 M_sun.