MaNGA AGN dwarf galaxies (MAD)

IV. Revealing hidden AGN in dwarf galaxies with radio observations

¹ Donostia International Physics Center (DIPC), Manuel Lardizabal Ibilbidea, 4, 20018 Donostia-San Sebastian, Spain
² Institute of Space Sciences (ICE, CSIC), Campus UAB, Carrer de Magrans, 08193 Barcelona, Spain
³ Institut d’Estudis Espacials de Catalunya (IEEC), Edifici RDIT, Campus UPC, 08860 Castelldefels, Barcelona, Spain

^★ Corresponding author: irene.valderrama@dipc.org

Received: 16 July 2025
Accepted: 9 October 2025

Abstract

Context. Low-mass black holes hosted by dwarf galaxies offer valuable insights into galaxy formation and the growth of the more massive black holes found in massive galaxies. Their detection as active galactic nuclei (AGNs) is challenging due to their low luminosity and compact size. This can be circumvented by employing multi-wavelength observational strategies, such as combining optical and radio observations, which enables the detection of AGN features that may be hidden in single-wavelength analyses.

Aims. We aim to detect any jet-like emission that is indicative of the presence of an AGN. We draw from a sample of four dwarf galaxies with AGN signatures based on spatially resolved emission line diagnostic diagrams with SDSS Mapping Nearby Galaxies at APO (MaNGA) optical integral-field unit (IFU) spectroscopy. Confirming the presence of an AGN will prove IFU spectroscopy to be a useful tool for identifying hidden or switched-off AGN.

Methods. Using Karl G. Jansky Very Large Array (VLA) radio observations, we imaged the radio emission of the four dwarf galaxies and derived their integrated radio flux and luminosity. We compared these to that expected from star formation processes to determine the origin of the radio emission and probed whether it is consistent with the results of the emission line diagnostic diagrams.

Results. We find that one out of the four galaxies shows AGN radio emission that is consistent with the analysis of the MaNGA IFU data. The kinetic jet power of this source is Q_jet ∼ 10⁴² erg s⁻¹, which indicates that dwarf galaxies can host radio jets as powerful as those of massive radio galaxies, whose jet mechanical feedback can strongly affect the star formation in the host galaxy. Furthermore, this galaxy exhibits an AGN outflow that is able to escape the gravitational bound produced by the dark matter halo, along with a decrease in the star formation rate of the central region. This suggests the presence of negative feedback from the AGN, which could be suppressing star formation. The other three galaxies exhibit regions of radio emission that are consistent with a stellar origin and overlapping with the star-forming regions found in the IFU spectroscopy.