Millimeter Radio Continuum Emissions as the Activity of Super Massive Black Holes in Nearby Early-Type Galaxies and Low-Luminosity Active Galactic Nuclei

TL;DR

This study uses millimeter radio observations to investigate the activity of supermassive black holes in nearby early-type galaxies and LLAGNs, revealing compact emissions, variability, and consistency with black hole activity models.

Contribution

It provides new millimeter-wave observational data on black hole activity in nearby galaxies, highlighting the presence of compact emissions and variability linked to black hole accretion processes.

Findings

Detection of flat or inverted spectrum nuclear emissions in many LLAGNs and early-type galaxies.

Observation of flux variability in three LLAGNs.

Radio luminosities align with the fundamental plane of black hole activity.

Abstract

We conducted millimeter continuum observations for samples of nearby early-type galaxies (21 sources) and nearby low-luminosity active galactic nuclei (LLAGN; 16 sources) at 100 GHz (3 mm) using the Nobeyama Millimeter Array (NMA). In addition, we performed quasi-simultaneous observations at 150 GHz (2 mm) and 100 GHz for five LLAGNs. Compact nuclear emissions showing flat or inverted spectra at centimeter-to-millimeter wavelengths were found in many LLAGNs and several early-type galaxies. Moreover, significant flux variability was detected in three LLAGNs. These radio properties are similar to Sgr A*. The observed radio luminosities are consistent with the fundamental plane of black hole activity that has suggested on the basis of samples with black hole masses ranging from 10 to 10^10 M_sun. This implies nuclear jets powered by radiatively inefficient accretion flows onto black holes.