BASS

XLIV. Morphological preferences of local hard X-ray selected AGNs

¹ Instituto de Astrofísica, Facultad de Física, Pontificia Universidad Católica de Chile, Casilla 306, Santiago 22, Chile
² Instituto de Alta Investigación, Universidad de Tarapacá, Casilla 7D, Arica, Chile
³ Dipartimento di Fisica “Ettore Pancini”, Università di Napoli Federico II, via Cinthia 9, 80126 Napoli, Italy
⁴ INAF - Osservatorio Astronomico di Capodimonte, Salita Moiariello 16, 80131 Napoli, Italy
⁵ Millennium Institute of Astrophysics, MAS, Monseñor Nuncio Sótero Sanz 100, Providencia, Santiago de Chile, Chile
⁶ Eureka Scientific, 2452 Delmer Street Suite 100, Oakland, CA 94602-3017, USA
⁷ Department of Astronomy, Yonsei University, 50 Yonsei-ro, Seodaemun-gu, Seoul 03722, Korea
⁸ Korea Astronomy and Space Science Institute, Daedeokdae-ro 776, Yuseong-gu, Daejeon 34055, Republic of Korea
⁹ STAR Institute, Liège Université, Quartier Agora - Allée du six Août, 19c B-4000 Liège, Belgium
¹⁰ Sterrenkundig Observatorium, Universiteit Gent, Krijgslaan 281 S9, B-9000 Gent, Belgium
¹¹ Departamento de Física, Universidad Técnica Federico Santa María, Vicuña Mackenna 3939, San Joaquín, Santiago de Chile, Chile
¹² Instituto de Estudios Astrofísicos, Facultad de Ingeniería y Ciencias, Universidad Diego Portales, Av. Ejército Libertador 441, Santiago, Chile
¹³ Kavli Institute for Astronomy and Astrophysics, Peking University, Beijing 100871, People’s Republic of China
¹⁴ Dipartimento di Matematica e Fisica, Università degli Studi Roma Tre, Via della Vasca Navale 84, I-00146 Roma, Italy
¹⁵ INAF – Osservatorio Astronomico di Roma, via Frascati 33, 00040 Monteporzio Catone, Italy
¹⁶ George P. and Cynthia Woods Mitchell Institute for Fundamental Physics and Astronomy, Texas A&M University, College Station, TX 77845, USA
¹⁷ Leiden Observatory, PO Box 9513 2300 RA, Leiden, The Netherlands
¹⁸ Cahill Center for Astronomy and Astrophysics, California Institute of Technology, Pasadena, CA 91125, USA
¹⁹ Leibniz-Institut für Astrophysik Potsdam (AIP), An der Sternwarte 16, 14482 Potsdam, Germany
²⁰ Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, MS 169-224 Pasadena CA 91109, USA
²¹ School of Physics and Astronomy, Tel Aviv University, Tel Aviv 69978, Israel
²² Yale Center for Astronomy & Astrophysics and Department of Physics, Yale University, P.O. Box 208120 New Haven, CT 06520-8120, USA
²³ Department of Physics, Yale University P.O. Box 208120 New Haven CT 06520, USA

^⋆ Corresponding author: mgparra@uc.cl

Received: 1 April 2025
Accepted: 12 June 2025

Abstract

We present detailed morphological classifications for the hosts of 1189 hard X-ray selected (14–195 keV) active galactic nuclei (AGNs) from the Swift-BAT 105-month catalog as part of the BAT AGN Spectroscopic Survey (BASS). BASS provides a powerful all-sky census of nearby AGNs, minimizing obscuration biases and providing a robust dataset for studying AGN-host galaxy connections. Classifications are based on a volunteer-based visual inspection workflow on the Zooniverse platform, adapted from the Galaxy Zoo DECaLS (GZD) project. Dual-contrast grz color composite images, generated from public surveys (e.g., NOAO Legacy Survey, Pan-STARRS, SDSS) and dedicated observations enabled key morphological features to be identified. Our analysis reveals that, with respect to a control sample of inactive galaxies, BASS AGN hosts show a deficiency of smooth elliptical galaxies (∼70%) and spiral galaxies with prominent arms (∼80%), while displaying an excess of mergers or disturbed systems (∼400%), and disk galaxies without a spiral structure (∼300%). These trends are found after controlling for redshift and i-band magnitude, which suggests a preference for AGN activity in gas-rich, dynamically disturbed environments or transitional disk systems. We also find a higher bar fraction among AGN hosts than in a control sample (∼50% vs. ∼30%). We further explore the relationships between AGN properties (e.g., X-ray luminosity, black hole mass, and Eddington ratio) and host morphology, and find that high-luminosity and high-accretion AGNs preferentially reside in smooth or point-like hosts. At the same time, lower-luminosity AGNs are more common in disk galaxies. These results underscore the importance of morphological studies in understanding the fueling and feedback mechanisms that drive AGN activity and their role in galaxy evolution. Our dataset provides a valuable benchmark for future multiwavelength surveys (e.g. LSST, Roman, and Euclid) and automated morphological classification efforts.