Publication details

Ram-pressure stripped radio tail and two ULXs in the spiral galaxy HCG 97b


HU Dan ZAJAČEK Michal WERNER Norbert GROSSOVÁ Romana JÁCHYM Pavel ROBERTS Ian D IGNESTI Alessandro KENNEY D P Kenney PLŠEK Tomáš RIFFALD SOUZA BREUER Jean-Paul Bernhard SHIMWELL Timothy TASSE Cyril ZHU Zhenghao WU Linhui

Year of publication 2024
Type Article in Periodical
Magazine / Source Monthly Notices of the Royal Astronomical Society
MU Faculty or unit

Faculty of Science

Keywords galaxies: individual: HCG 97b; galaxies: interactions; radio continuum: galaxies
Description We report LOFAR and VLA detections of extended radio emission in the spiral galaxy HCG 97b, hosted by an X-ray bright galaxy group. The extended radio emission detected at 144 MHz, 1.4 GHz and 4.86 GHz is elongated along the optical disk and has a tail that extends 27 kpc in projection towards the centre of the group at GHz frequencies or 60 kpc at 144 MHz. Chandra X-ray data show two off-nuclear ultra-luminous X-ray sources (ULXs), with the farther one being a plausible candidate for an accreting intermediate-mass black hole (IMBH). The asymmetry observed in both CO emission morphology and kinematics indicates that HCG 97b is undergoing ram-pressure stripping, with the leading side at the southeastern edge of the disk. Moreover, the VLA 4.86 GHz image reveals two bright radio blobs near one ULX, aligning with the disk and tail, respectively. The spectral indices in the disk and tail are comparable and flat (?>-1), suggesting the presence of recent outflows potentially linked to ULX feedback. This hypothesis gains support from estimates showing that the bulk velocity of the relativistic electrons needed for transport from the disk to the tail is approximately ~1300 km s-1. This velocity is much higher than those observed in ram-pressure stripped galaxies (100-600 km s-1), implying an alternative mechanism aiding the stripping process. Therefore, we conclude that HCG 97b is subject to ram pressure, with the formation of its stripped radio tail likely influenced by the putative IMBH activities.
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