LeMMINGs

V. Nuclear activity and bulge properties: A detailed multi-component decomposition of e-MERLIN Palomar galaxies with HST^⋆

¹ Departamento de Física de la Tierra y Astrofísica, IPARCOS (Instituto de Física de Partículas y del Cosmos), Universidad Complutense de Madrid, 28040 Madrid, Spain
e-mail: bdullo@ucm.es
² Instituto de Astrofísica de Canarias, Vía Láctea S/N, 38205 La Laguna, Tenerife, Spain
³ Departamento de Astrofísica, Universidad de La Laguna, 38206 La Laguna, Tenerife, Spain
⁴ Jodrell Bank Centre for Astrophysics, School of Physics and Astronomy, The University of Manchester, Alan Turing Building, Oxford Road, M13 9PL Manchester, UK
⁵ Istituto di Radioastronomia – INAF, Via P. Gobetti 101, 40129 Bologna, Italy
⁶ School of Physics and Astronomy, University of Southampton, Southampton SO17 1BJ, UK
⁷ Department of Astronomy, University of Wisconsin-Madison, Madison, WI, USA
⁸ Department of Space, Earth and Environment, Chalmers University of Technology, 412 96 Göteborg, Sweden
⁹ Jeremiah Horrocks Institute, University of Central Lancashire, Preston, Lancashire PR1 2HE, UK
¹⁰ Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany
¹¹ Real Academia de Ciencias, C/ Valverde 22, 28004 Madrid, Spain
¹² Department of Physics, University of Bath, Claverton Down, Bath BA2 7AY, UK
¹³ Technical University of Kenya, PO box 52428-00200 Nairobi, Kenya
¹⁴ Center for Astro, Particle and Planetary Physics (CAP 3), New York University Abu Dhabi, PO Box 129188 Abu Dhabi, UAE

Received: 16 January 2023
Accepted: 19 March 2023

Abstract

We used high-resolution HST imaging and e-MERLIN 1.5-GHz observations of galaxy cores from the LeMMINGs survey to investigate the relation between optical structural properties and nuclear radio emission for a large sample of galaxies. We performed accurate, multi-component decompositions of new surface brightness profiles extracted from HST images for 163 LeMMINGs galaxies and fitted up to six galaxy components (e.g. bulges, discs, AGN, bars, rings, spiral arms, and nuclear star clusters) simultaneously with Sérsic and/or core-Sérsic models. By adding such decomposition data for ten LeMMINGs galaxies from our past work, the final sample of 173 nearby galaxies (102 Ss, 42 S0s, 23 Es, plus six Irr) with a typical bulge stellar mass of M_∗,bulge ∼ 10⁶ − 10^12.5 M_⊙ encompasses all optical spectral classes: low-ionisation nuclear emission-line region (LINER), Seyfert, Absorption Line Galaxy (ALG), and H II. We show that the bulge mass can be significantly overestimated in many galaxies when components such as bars, rings, and spirals are not included in the fits. We additionally implemented a Monte Carlo method to determine errors on the bulge, disc, and other fitted structural parameters. Moving (in the opposite direction) across the Hubble sequence, that is from the irregular to elliptical galaxies, we confirm that bulges become larger, more prominent, and round. Such bulge dominance is associated with a brighter radio core luminosity. We also find that the radio detection fraction increases with bulge mass. At M_∗,bulge ≥ 10¹¹ M_⊙, the radio detection fraction is 77%, declining to 24% for M_∗,bulge < 10¹⁰ M_⊙. Furthermore, we observe that core-Sérsic bulges tend to be systematically round and to possess high radio core luminosities and boxy-distorted or pure elliptical isophotes. However, there is no evidence for the previously alleged strong tendency of galaxies’ central structures (i.e. a sharp Sérsic, core-Sérsic dichotomy) with their radio loudness, isophote shape, and flattening.