DOI: 10.1017/pasa.2026.10256 ISSN: 1323-3580
Hector Galaxy Survey:
Falling in between
– infalling galaxies in the midst of the Abell 3667 merger
Oğuzhan Çakır, Matt Owers, Gabriella Quattropani, Mina Pak, Stefania Barsanti, Joss Bland-Hawthorn, Julia Bryant, Scott Croom, Pratyush Kumar Das, Caroline Foster, Madusha Gunawardhana, Hyunjin Jeong, Jong Chul Lee, Joon Hyeop Lee, Yifan Mai, Kyuseok Oh, Sree Oh, Andrei Ristea, Sarah M. Sweet, Sujeeporn Tuntipong, Gurashish Bhatia, David Brodrick, Rebecca Brown, Elton Cheng, Robert Content, Fred Crous, Tony Farrell, Peter Gillingham, Ellen Houston, Jon Lawrence, Helen McGregor, Mahesh Mohanan, Seong-sik Min, Barnaby Norris, Naveen Pai, Ayoan Sadman, Will Saunders, Sudarshan Venkatesan, Adeline Wang, Ross Zhelem, Jessica Zheng Abstract
Whether cluster mergers enhance ram pressure stripping (RPS) and accelerate the subsequent evolution of member galaxies remains an open question. In this paper, we address this question by investigating galaxy populations in the nearby merging cluster Abell 3667 (
z
≃ 0.0553) using spatially resolved data from the Hector Galaxy Survey. We define an RPS sample by combining Hector-selected galaxies with ionised gas disturbances (e.g. asymmetric tails or truncated disks) and supplementary, optically identified jellyfish galaxies lacking Hector data. The majority of the RPS sample (∼
71 Subscript negative 10 Superscript plus 7
71
−
10
+
7
${71}_{-10}^{+7}$
%; 20/28) lies within
R
200
, where the impact of the merger is greater. Most asymmetric galaxies (∼
73 Subscript negative 14 Superscript plus 8
73
−
14
+
8
$73_{-14}^{+8}$
%; 11/15), especially those with extreme RPS signatures, are concentrated towards the inner cluster regions (
R
≲ 0.6
R
200
), distributed along the merger axis between two shock-tracing radio relics. These central asymmetric galaxies present two separate spatial and kinematic concentrations: a population located at the North-West (NW) subcluster and downstream of its radio relic, a region of high-velocity intracluster medium (ICM) bulk motion, with blueshifted line-of-sight velocities, and a primarily redshifted population close to the main cluster (MC), which also shows evidence of a turbulent ICM. Despite their projected spatial association with the MC core and the NW substructure, the velocities of both samples indicate they are not bound to these merging substructures. Tail orientations provide additional insight into their orbital histories: NW tails point away from the cluster centre and are frequently aligned with the merger axis, suggestive of merger-driven stripping, while MC tails show neither pattern clearly. The tails are also broadly westward-pointing, with the MC tails closely tracing due west and the NW tails shifted towards the northwest, pointing to two distinct filamentary accretion events for the NW and MC populations. Taken together, our results indicate enhanced RPS activity in the heart of A3667, primarily driven by infalling galaxies accreted along nearby filaments and interacting with the merger-driven turbulent environment.