AGN feedback in the Phoenix cluster

Abstract

Active galactic nuclei (AGN) release a huge amount of energy into the intracluster medium (ICM) with the consequence of offsetting cooling and star formation (AGN feedback) in the centers of cool core clusters. The Phoenix cluster is among the most massive clusters of galaxies known in the Universe. It hosts a powerful starburst of several hundreds of Solar masses per year and a large amount of molecular gas in the center. In this work we use the high-resolution Reflection Grating Spectrometer (RGS) on board XMM-Newton to study the X-ray emitting cool gas in the Phoenix cluster and heating-cooling balance. We detect for the first time evidence of O VIII and Fe XXI-XXII emission lines, the latter demonstrating the presence of gas below 2 keV. We find a cooling rate of 350 ± 250 200 M yr −1 below 2 keV (at the 90% confidence level), which is consistent with the star formation rate in this object. This cooling rate is high enough to produce the molecular gas found in the filaments via instabilities during the buoyant rising time. The line broadening indicates that the turbulence (∼ 300 km s −1 or less) is below the level required to produce and propagate the heat throughout the cool core. This provides a natural explanation for the coexistence of large amounts of cool gas, star formation and a powerful AGN in the core. The AGN activity may be either at a young stage or in a different feedback mode, due to a high accretion rate.

Lessons learned from 19 years of high‐resolution X‐ray spectroscopy of galaxy clusters with the reflection grating spectrometer on board XMM‐Newton

“…However, they also showed that the cooling rates may still be high enough to explain the H α luminosity and the star formation rates measured with the Hubble Space Telescope and WISE. Pinto et al () have shown that the cooling rate of 350 ± 130 M ⊙ yr −1 below 2 keV measured with RGS in the Phoenix cluster is consistent with the star formation rate in this object and is high enough to produce the molecular gas found with ALMA in the filaments via instabilities during the buoyant rising time (Russell et al ).…”

“…This indicates that turbulence contributes to the total energy for less than ∼5% and is consistent with the measurements of Hitomi for Perseus (Hitomi Collaboration ). Bambic et al () and Pinto et al () expanded this argument and showed that the propagation velocity is too low to achieve a balance between gas cooling and heating via dissipation of turbulence (Figure ), previously invoked by Zhuravleva et al () using surface brightness fluctuations. An additional source of heating may be sound waves (Fabian et al ).…”

Anatomy of a Cooling Flow: The Feedback Response to Pure Cooling in the Core of the Phoenix Cluster

“…At small radii (r < 10 kpc), the profile dips down to ∼800 M yr −1 , which is a relatively small change compared to the 2-3 orders of magnitude that most clusters decline at similar radii. We compare this profile to estimates of the cooling rate from XMM RGS spectroscopy (Pinto et al 2018). Based on Figure 8, we estimate that the cooling from 2 → 0 keV is localized to r < 12 kpc, and that the gas cooling from 4 → 2 keV is in a shell at 12 < r < 20 kpc.…”

“…Red points and the shaded red curve show the cooling rate profile for the Phoenix cluster, which is significantly flatter than the median cool core profile, with a central cooling rate elevated by a factor of ∼10 3 above the typical low-z cluster. Blue shaded regions show the XMM-RGS spectroscopic cooling rates from Pinto et al (2018), where we have converted temperature bins into radial bins using the three-dimensional temperature profile from Figure 8. These data further support the picture in which cooling is proceeding with relatively little impedance at the center of the Phoenix cluster.…”

The Athena space X‐ray observatory and the astrophysics of hot plasma†

“…Simulations of the X‐ray spectrum of the Phoenix cluster ( z = 0.59) based on XMM‐Newton RGS (Pinto et al ) for the X‐ray integral field unit and Resolve spectrometers. The integration time is 25 and 250 ks, respectively.…”