An infrared and far-UV study of jet-induced star formation in the halo of Centaurus A

¹ Graduate School of Science, Nagoya University, Furo-cho, Chikusa-ku, Nagoya, Aichi 464-8602, Japan
² Subaru Telescope, National Astronomical Observatory of Japan, 650 North Aohoku Place, Hilo, HI 96720, USA
³ Institute of Liberal Arts and Sciences, Tokushima University, 1-1 Minami-Jyosanjima, Tokushima-shi, Tokushima 770-8502, Japan
⁴ Institute of Space and Astronomical Science, Japan Aerospace Exploration Agency, 3-1-1 Yoshinodai, Chuo-ku, Sagamihara Kanagawa 252-5210, Japan
⁵ Institute of Astronomy, The University of Tokyo, 2-21-1 Osawa, Mitaka, Tokyo 181-0015, Japan

^⋆ Corresponding author; r.katayama@u.phys.nagoya-u.ac.jp

Received: 5 April 2024
Accepted: 7 November 2024

Abstract

Centaurus A (Cen A) is the nearest galaxy hosting an active galactic nucleus (AGN), which produces powerful radio and X-ray jets extending to hundreds of kiloparsecs from the center. At 15 kpc northeast (NE) and 12 kpc southwest (SW) in the halo along the jet from the nucleus of Cen A, dust clouds accompanying the Hα emission are detected. For both NE and SW clouds, past studies suggested that star formation may have been induced through interactions between the AGN jet and the surrounding intergalactic media. For these clouds, we performed dust model fitting of infrared (IR) spectral energy distributions (SEDs) created from the archival data of WISE, Spitzer, and Herschel. Then we compare the IR emission properties of the dust clouds with the far-ultraviolet (UV) emission using the archival data of GALEX/FUV. As a result, we find that the interstellar radiation field intensity G₀ (and thus the dust temperature) in the NE cloud suggests star formation activity, while that in the SW cloud does not. The local far-UV intensity and G₀ in the NE region are significantly larger than those expected for the far-UV radiation originating from the central region of Cen A and its dust-scattered component, respectively. In contrast, the local far-UV intensity and G₀ in the SW region are compatible with them. The polycyclic aromatic hydrocarbon (PAH) emission is detected for both NE and SW clouds. The mass abundance ratios of PAH to dust are similar for both clouds and significantly lower than that in the central region of Cen A. We suggest that the dust clouds and the PAHs in the clouds are associated with the broken ring-like structure of H I gas which is thought to be a remnant of the past gas-rich merger and that shocks by the jet responsible for the middle lobe on the north side may have triggered the star formation in the NE cloud.