Journal Article

Head–tail Galaxies: beacons of high-density regions in clusters

Minnie Y. Mao, Melanie Johnston-Hollitt, Jamie B. Stevens and Simon J. Wotherspoon

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 392, issue 3, pages 1070-1079
Published in print January 2009 | ISSN: 0035-8711
Published online January 2009 | e-ISSN: 1365-2966 | DOI:
Head–tail Galaxies: beacons of high-density regions in clusters

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Using radio data at 1.4 GHz from the Australia Telescope Compact Array (ATCA), we identify five head–tail (HT) galaxies in the central region of the Horologium–Reticulum Supercluster (HRS). Physical parameters of the HT galaxies were determined along with substructure in the HRS to probe the relationship between environment and radio properties. Using a density enhancement technique applied to 582 spectroscopic measurements in the 2°× 2° region about A3125/A3128, we find all five HT galaxies reside in regions of extremely high density (>100 galaxies Mpc−3). In fact, the environments surrounding HT galaxies are statistically denser than those environments surrounding non-HT galaxies and among the densest environments in a cluster. Additionally, the HT galaxies are found in regions of enhanced X-ray emission and we show that the enhanced density continues out to substructure groups of 10 members. We propose that it is the high densities that allow ram pressure to bend the HT galaxies as opposed to previously proposed mechanisms relying on exceptionally high peculiar velocities.

Keywords: galaxies: clusters: general; radio continuum: galaxies; galaxies: clusters: individual: A3125; galaxies: clusters: individual: A3128

Journal Article.  6803 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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