XRISM Reveals Low Nonthermal Pressure in the Core of the Hot, Relaxed Galaxy Cluster A2029
M. Audard, Hisamitsu Awaki, Ralf Ballhausen, Aya Bamba, Ehud Behar, Rozenn Boissay-Malaquin, Laura Brenneman, G. V. Brown, Lía Corrales, E. Costantini, Renata Cumbee, María Díaz Trigo, Chris Done, Tadayasu Dotani, Ken Ebisawa, Megan E. Eckart, D. Eckert, S. Eguchi, Teruaki Enoto, Yuichiro Ezoe, Adam Foster, Ryuichi Fujimoto, Yutaka Fujita, Y. Fukazawa, Kotaro Fukushima, Akihiro Furuzawa, Luigi Gallo, Javier A. García, Liyi Gu, M. Guainazzi, Kouichi Hagino, Kenji Hamaguchi, Isamu Hatsukade, Katsuhiro Hayashi, Takayuki Hayashi, Natalie Hell, Edmund Hodges‐Kluck, A. E. Hornschemeier, Yuto Ichinohe, Manabu Ishida, Kumi Ishikawa, Yoshitaka Ishisaki, J. S. Kaastra, T. R. Kallman, Erin Kara, Satoru Katsuda, Yoshiaki Kanemaru, Richard L. Kelley, Caroline A. Kilbourne, Shunji Kitamoto, Shōgo Kobayashi, Takayoshi Kohmura, Aya Kubota, Maurice A. Leutenegger, Michael Loewenstein, Yoshitomo Maeda, Maxim Markevitch, Hironori Matsumoto, Kyoko Matsushita, D. McCammon, B. R. McNamara, François Mernier, Eric D. Miller, J. M. Mïller, Ikuyuki Mitsuishi, Misaki Mizumoto, Tsunefumi Mizuno, Koji Mori, K. Mukai, Hiroshi Murakami, R. F. Mushotzky, Hiroshi Nakajima, Kazuhiro Nakazawa, Jan‐Uwe Ness, Kumiko Nobukawa, Masayoshi Nobukawa, Hirofumi Noda, Hirokazu Odaka, Shoji Ogawa, Anna Ogorzałek, Takashi Okajima, Naomi Ota, S. Paltani, Robert Petre, Paul P. Plucinsky, F. S. Porter, K. Pottschmidt, Kosuke Sato, Toshiki Sato, Makoto Sawada, Hiromi Seta, M. Shidatsu, A. Simionescu, Randall K. Smith, Hiromasa Suzuki, Andrew E. Szymkowiak, H. Takahashi, Mai Takeo, Toru Tamagawa, Keisuke Tamura
Abstract
Abstract We present XRISM Resolve observations of the core of the hot, relaxed galaxy cluster Abell 2029 (A2029). We find that the line-of-sight bulk velocity of the intracluster medium (ICM) within the central 180 kpc is at rest with respect to the brightest cluster galaxy, with a 3 σ upper limit of ∣ v bulk ∣ < 100 km s −1 . We robustly measure the field-integrated ICM velocity dispersion to be σ v = 169 ± 10 km s −1 , obtaining similar results for both single-temperature and two-temperature plasma models to account for the cluster cool core. This result, if ascribed to isotropic turbulence, implies a subsonic ICM with Mach number <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi class="MJX-tex-calligraphic" mathvariant="script">M</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>3</mml:mn> <mml:mrow> <mml:mi mathvariant="normal">D</mml:mi> </mml:mrow> </mml:mrow> </mml:msub> <mml:mo>≈</mml:mo> <mml:mn>0.22</mml:mn> </mml:math> and a nonthermal pressure fraction of 2.6 ± 0.3%. The turbulent velocity is similar to what was measured in the core of the Perseus cluster by Hitomi, but here in a more massive cluster with an ICM temperature of 7 keV, the limit on the nonthermal pressure fraction is even more stringent. Our result is consistent with expectations from simulations of relaxed clusters, but it is on the low end of the predicted distribution, indicating that A2029 is an exceptionally relaxed cluster with no significant impacts from either a recent minor merger or active galactic nucleus activity.