The atlas^3DProject – XXXI. Nuclear radio emission in nearby early-type galaxies

Abstract

We present the results of a high-resolution, 5 GHz, Karl G. Jansky Very Large Array study of the nuclear radio emission in a representative subset of the ATLAS 3D survey of early-type galaxies (ETGs). We find that 51 ± 4% of the ETGs in our sample contain nuclear radio emission with luminosities as low as 10 18 W Hz −1 . Most of the nuclear radio sources have compact ( 25 − 110 pc) morphologies, although ∼10% display multi-component core+jet or extended jet/lobe structures. Based on the radio continuum properties, as well as optical emission line diagnostics and the nuclear X-ray properties, we conclude that the majority of the central 5 GHz sources detected in the ATLAS 3D galaxies are associated with the presence of an active galactic nucleus (AGN). However, even at sub-arcsecond spatial resolution, the nuclear radio emission in some cases appears to arise from low-level nuclear star formation rather than an AGN, particularly when molecular gas and a young central stellar population is present. This is in contrast to popular assumptions in the literature that the presence of a compact, unresolved, nuclear radio continuum source universally signifies the presence of an AGN. Additionally, we examine the relationships between the 5 GHz luminosity and various galaxy properties including the molecular gas mass and -for the first time -the global kinematic state. We discuss implications for the growth, triggering, and fueling of radio AGNs, as well as AGN-driven feedback in the continued evolution of nearby ETGs.

WISDOM Project – II. Molecular gas measurement of the supermassive black hole mass in NGC 4697

“…We note that radio emission from AGN typically has a flatter spectral index, that would not agree with these data (e.g. Nyland et al 2016). …”

A star formation study of the ATLAS3Dearly-type galaxies with the AKARI all-sky survey

“…Most COdetected galaxies again show a significant excess above the correlation of non-CO-detected galaxies, and their excess luminosities is not correlated with their K s -band luminosities (R = −0.18 and p = 0.32). The 18 µm emission of CO-detected galaxies is thus likely due to interstellar dust heated by relatively young stellar populations or AGN activity (see Nyland et al 2016 for a study of nuclear radio emission in ATLAS 3D ETGs). The 9 and 18 µm luminosities thus strongly suggest that ETGs with detectable molecular gas also contain significant interstellar dust.…”

A rare example of low surface-brightness radio lobes in a gas-rich early-type galaxy: the story of NGC 3998

“…Despite their low power, they can impact the ISM of the host galaxy as shown in a number of cases, e.g. NGC 1266 (Alatalo et al 2011Nyland et al 2013Nyland et al , 2016, NGC 1433 (Combes et al 2013) and IC 5063 (Morganti et al 2015). It is therefore important that we study this population in more detail.…”

“…It is therefore important that we study this population in more detail. Compared to powerful radio galaxies, low power radio sources tend to be more core dominated and have smaller spatial extents Baldi & Capetti 2010;Baldi et al 2015a;Nyland et al 2016). Although still poorly understood, the brightness, morphology and scale of the radio emission may be related to a lower, or inefficient, supply of fresh gas or to weak/poorly collimated jets likely due to lower flow velocities and, therefore, are more subject to instabilities and entrainment Laing et al 2011;Baldi et al 2015a).…”