Abstract
Abstract We present measurements of the thermal Sunyaev–Zel’dovich effect (SZE) toward SPT-CL J2334-4243 (the Phoenix galaxy cluster) at $z=0.597$ by the Atacama Large Millimeter/submillimeter Array (ALMA) in Band 3. The SZE is imaged at $5^{\prime \prime }$ resolution (corresponding to the physical scale of $23\:h^{-1}\:$kpc) within $200\:h^{-1}\:$kpc from the central galaxy, with the peak signal-to-noise ratio exceeding 11. Combined with the Chandra X-ray image, the ALMA SZE data further allow for non-parametric deprojection of electron temperature, density, and entropy. Our method can minimize contamination by the central active galactic nucleus and the X-ray absorbing gas within the cluster, both of which greatly affect the X-ray spectrum. We find no significant asymmetry or disturbance in the SZE image within the current measurement errors. The detected SZE signal shows much higher central concentration than other distant galaxy clusters and agrees well with the average pressure profile of local cool-core clusters. Unlike in typical clusters at any redshift, the gas temperature drops by at least a factor of 5 toward the center. We identify $\sim\!\! 6 \times 10^{11}\, M_\odot$ cool gas with temperature $\sim\!\! 3\:$keV in the inner $20\:h^{-1}\:$kpc. Taken together, our results imply that the gas is indeed cooling efficiently and nearly isobarically down to this radius in the Phoenix cluster.
Highlights
It has long been argued that the density of thermal gas particles in cores of galaxy clusters is large enough for these particles to cool radiatively, leading to a runaway “cooling flow” toward the cluster center (e.g., Fabian 1994 for review)
We report on measurements of the thermal Sunyaev-Zel’dovich effect (SZE: Sunyaev & Zel’dovich 1970; Sunyaev & Zel’dovich 1972) toward the Phoenix cluster by the Atacama Large Millimeter/submillimeter Array (ALMA)
We have presented the SZE image of the Phoenix galaxy cluster at z = 0.597 taken by ALMA in Band 3
Summary
It has long been argued that the density of thermal gas particles in cores of galaxy clusters is large enough for these particles to cool radiatively, leading to a runaway “cooling flow” toward the cluster center (e.g., Fabian 1994 for review). The Phoenix galaxy cluster, SPT-CL J2344-4243, at redshift z = 0.597 possibly provides a unique counter example to suppressed gas cooling mentioned above It is the most X-ray luminous galaxy cluster known to date with exceptionally high concentration of thermal gas within the central 100 kpc; the predicted cooling (or mass deposition) rate amounts to Mcool = 2000 − 4000 M⊙ yr−1 (McDonald et al 2012; McDonald et al 2013; Ueda et al 2013). We use the dimensionless Hubble constant h ≡ H0/(100km/s/Mpc); given controversial results on the value of h (e.g., Verde, Treu & Riess 2019) we do not fix it unless otherwise stated In this cosmology, the angular size of 1′′ corresponds to the physical size of 4.67 h−1kpc at the source redshift z = 0.597. Array Date Total on-source time [hr] Number of execution blocks Number of antennas Flux calibrator Phase calibrator Bandpass calibrator Central frequency [GHz] Band widths [GHz] Baseline coverage [kλ] Primary beam FWHM at the central frequency [arcsec] Number of pointings
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