XRISM forecast for the Coma cluster: stormy, with a steep power spectrum
Abstract
The XRISM Resolve microcalorimeter array measured the velocities of hot intracluster gas at two positions in the Coma galaxy cluster: 3'x3' squares at the center and at 6' (170 kpc) to the south. We find the line-of-sight velocity dispersions in those regions to be sigma_z=208+-12 km/s and 202+-24 km/s, respectively. The central value corresponds to a 3D Mach number of M=0.24+-0.015 and the ratio of the kinetic pressure of small-scale motions to thermal pressure in the intracluster plasma of only 3.1+-0.4%, at the lower end of predictions from cosmological simulations for merging clusters like Coma, and similar to that observed in the cool core of the relaxed cluster A2029. Meanwhile, the gas in both regions exhibits high line-of-sight velocity differences from the mean velocity of the cluster galaxies, Delta v_z=450+-15 km/s and 730+-30 km/s, respectively. A small contribution from an additional gas velocity component, consistent with the cluster optical mean, is detected along a sightline near the cluster center. The combination of the observed velocity dispersions and bulk velocities is not described by a Kolmogorov velocity power spectrum of steady-state turbulence; instead, the data imply a much steeper effective slope (i.e., relatively more power at larger linear scales). This may indicate either a very large dissipation scale resulting in the suppression of small-scale motions, or a transient dynamic state of the cluster, where large-scale gas flows generated by an ongoing merger have not yet cascaded down to small scales.
Cite
@article{arxiv.2504.20928,
title = {XRISM forecast for the Coma cluster: stormy, with a steep power spectrum},
author = {XRISM Collaboration and Marc Audard and Hisamitsu Awaki and Ralf Ballhausen and Aya Bamba and Ehud Behar and Rozenn Boissay-Malaquin and Laura Brenneman and Gregory V. Brown and Lia Corrales and Elisa Costantini and Renata Cumbee and Maria Diaz Trigo and Chris Done and Tadayasu Dotani and Ken Ebisawa and Megan E. Eckart and Dominique Eckert and Satoshi Eguchi and Teruaki Enoto and Yuichiro Ezoe and Adam Foster and Ryuichi Fujimoto and Yutaka Fujita and Yasushi Fukazawa and Kotaro Fukushima and Akihiro Furuzawa and Luigi Gallo and Javier A. Garcia and Liyi Gu and Matteo Guainazzi and Kouichi Hagino and Kenji Hamaguchi and Isamu Hatsukade and Katsuhiro Hayashi and Takayuki Hayashi and Natalie Hell and Edmund Hodges-Kluck and Ann Hornschemeier and Yuto Ichinohe and Daiki Ishi and Manabu Ishida and Kumi Ishikawa and Yoshitaka Ishisaki and Jelle Kaastra and Timothy Kallman and Erin Kara and Satoru Katsuda and Yoshiaki Kanemaru and Richard Kelley and Caroline Kilbourne and Shunji Kitamoto and Shogo Kobayashi and Takayoshi Kohmura and Aya Kubota and Maurice Leutenegger and Michael Loewenstein and Yoshitomo Maeda and Maxim Markevitch and Hironori Matsumoto and Kyoko Matsushita and Dan McCammon and Brian McNamara and Francois Mernier and Eric D. Miller and Jon M. Miller and Ikuyuki Mitsuishi and Misaki Mizumoto and Tsunefumi Mizuno and Koji Mori and Koji Mukai and Hiroshi Murakami and Richard Mushotzky and Hiroshi Nakajima and Kazuhiro Nakazawa and Jan-Uwe Ness and Kumiko Nobukawa and Masayoshi Nobukawa and Hirofumi Noda and Hirokazu Odaka and Shoji Ogawa and Anna Ogorzalek and Takashi Okajima and Naomi Ota and Stephane Paltani and Robert Petre and Paul Plucinsky and Frederick S. Porter and Katja Pottschmidt and Kosuke Sato and Toshiki Sato and Makoto Sawada and Hiromi Seta and Megumi Shidatsu and Aurora Simionescu and Randall Smith and Hiromasa Suzuki and Andrew Szymkowiak and Hiromitsu Takahashi and Mai Takeo and Toru Tamagawa and Keisuke Tamura and Takaaki Tanaka and Atsushi Tanimoto and Makoto Tashiro and Yukikatsu Terada and Yuichi Terashima and Yohko Tsuboi and Masahiro Tsujimoto and Hiroshi Tsunemi and Takeshi Tsuru and Aysegul Tumer and Hiroyuki Uchida and Nagomi Uchida and Yuusuke Uchida and Hideki Uchiyama and Shutaro Ueda and Yoshihiro Ueda and Shinichiro Uno and Jacco Vink and Shin Watanabe and Brian J. Williams and Satoshi Yamada and Shinya Yamada and Hiroya Yamaguchi and Kazutaka Yamaoka and Noriko Yamasaki and Makoto Yamauchi and Shigeo Yamauchi and Tahir Yaqoob and Tomokage Yoneyama and Tessei Yoshida and Mihoko Yukita and Irina Zhuravleva and Andrew Fabian and Dylan Nelson and Nobuhiro Okabe and Annalisa Pillepich and Cicely Potter and Manon Regamey and Kosei Sakai and Mona Shishido and Nhut Truong and Daniel R. Wik and John ZuHone},
journal= {arXiv preprint arXiv:2504.20928},
year = {2025}
}
Comments
ApJ Letters in press. 14 pages, 8 figures