BASS

LI. Cool gas supply of HI-massive local Seyfert galaxies

¹ Department of Astronomy, Yonsei University, 50 Yonsei-ro, Seodaemun-gu, Seoul, 03722, Republic of Korea
² National Radio Astronomy Observatory, 1011 Lopezville Rd, Socorro, NM, 87801, USA
³ ATNF, CSIRO, Space and Astronomy, PO Box 1130, Bentley, WA, 6102, Australia
⁴ ICRAR, University of Western Australia, 35 Stirling Highway, Crawley, WA, 6009, Australia
⁵ Korea Astronomy and Space Science Institute, 776 Daedeok-daero, Yuseong-gu, Daejeon, 34055, Republic of Korea
⁶ Australian SKA Regional Centre, University of Western Australia, 35 Stirling Highway, Crawley, WA, 6009, Australia
⁷ Eureka Scientific, 2452 Delmer Street, Suite 100, Oakland, CA, 94602-3017, USA
⁸ Instituto de Alta Investigación, Universidad de Tarapacá, Casilla 7D, Arica, Chile
⁹ Department of Astronomy, University of Geneva, Chemin Pegasi 51, 1290, Versoix, Switzerland
¹⁰ Instituto de Estudios Astrofísicos, Facultad de Ingeniería y Ciencias, Universidad Diego Portales, Av. Ejército Libertador 441, Santiago, Chile
¹¹ Frontier Research Institute for Interdisciplinary Sciences, Tohoku University, Sendai, Miyagi, 980-8578, Japan
¹² Astronomical Institute, Tohoku University, Aramaki, Aoba-ku, Sendai, Miyagi, 980-8578, Japan
¹³ Centre for Astrophysics Research, Department of Physics, Astronomy and Mathematics, University of Hertfordshire, Hatfield, AL10 9AB, UK
¹⁴ Department of Astronomy and Atmospheric Sciences, Kyungpook National University, Daegu, 41566, Republic of Korea
¹⁵ George P. and Cynthia Woods Mitchell Institute for Fundamental Physics and Astronomy, Texas A&M University, College Station, TX, 77845, USA
¹⁶ Instituto de Astrofísica, Facultad de Física, Pontificia Universidad Católica de Chile, Casilla 306, Santiago 22, Chile
¹⁷ Department of Astronomy, University of Maryland, College Park, MD, 20742, USA
¹⁸ Department of Physics, Yale University, P.O. Box 208120, New Haven, CT, 06520, USA
¹⁹ Department of Astronomy, University of Geneva, ch. d’Ecogia 16, 1290, Versoix, Switzerland
²⁰ Kavli Institute for Astronomy and Astrophysics, Peking University, Beijing, 100871, China
²¹ Dipartimento di Matematica e Fisica, Università degli Studi di Roma 3, Via della Vasca Navale, 84, 00146, Roma, Italy
²² INAF – Osservatorio Astrofisico di Arcetri, Largo Enrico Fermi 5, I-50125, Firenze, Italy
²³ European Space Agency (ESA), ESTEC, Keplerlaan 1, 2201 AZ, Noordwijk, The Netherlands
²⁴ School of Physics and Astronomy, Tel Aviv University, Tel Aviv, 69978, Israel
²⁵ SNU Astronomy Research Center, Seoul National University, 1 Gwanak-ro, Gwanak-gu, Seoul, 08826, Republic of Korea

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Received: 19 August 2025
Accepted: 24 February 2026

Abstract

We present neutral atomic hydrogen (H I) imaging observations of 22 H I-rich (M_HI ≳ 10^9.7 M_⊙), hard X-ray-selected local Seyferts to explore how cool gas is supplied to active galactic nuclei (AGN) hosts. The sample predominantly resides in group-like, gas-rich environments. About 80% (18/22) of the galaxies have H I-detected neighbors, 61% (11/18) of which clearly exhibit strong lopsidedness, one-sided gas tails, and/or gas structures connecting to nearby companion galaxies, suggesting gas exchange histories. We examine the H I size-mass relation and star formation properties of these H I-rich AGN hosts, finding no systematic deviations from known scaling relations. In most cases, our samples are the most massive systems within their respective groups, implying that our sample is more likely to acquire gas rather than lose it. Interestingly, galaxies with more extended H I disks show stronger AGN activity. Considering that extended H I is often associated with external processes, this finding suggests that environmentally accreted gas – through galaxy interactions and gas exchange with neighboring systems – may have played a role in supplying additional fuel to the AGNs in our sample. Notably, the H I extent–AGN activity correlation becomes even tighter for those AGN hosts whose neighboring galaxies are gas poor or lack H I, further supporting externally supplied gas as a fuel source.