A Universal Entropy Profile for the Hot Atmospheres of Galaxies and Clusters within R2500

• Published in: The Astrophysical journal Vol. 862; no. 1
• Main Authors: Babyk, Iu. V., McNamara, B. R., Nulsen, P. E. J., Russell, H. R., Vantyghem, A. N., Hogan, M. T., Pulido, F. A.
• Format: Journal Article
• Language: English
• Published: Philadelphia The American Astronomical Society 20.07.2018; IOP Publishing
• Subjects: Active galactic nuclei; Astrophysics; Atmosphere; Atmospheres; Cooling; Elliptical galaxies; Entropy; galaxies: clusters: general; galaxies: clusters: intracluster medium; Gravitational collapse; Heating; Radio jets (astronomy); Space telescopes; Spiral galaxies; Spirals; Star & galaxy formation; Star formation; Stars & galaxies
• ISSN: 0004-637X; 1538-4357
• DOI: 10.3847/1538-4357/aacce5

We present atmospheric gas entropy profiles for 40 early-type galaxies and 110 clusters spanning several decades of halo mass, atmospheric gas mass, radio jet power, and galaxy type. We show that within ∼0.1R2500 the entropy profiles of low-mass systems, including ellipticals, brightest cluster galaxies, and spiral galaxies, scale approximately as K ∝ R2/3. Beyond ∼0.1R2500 entropy profiles are slightly shallower than the K ∝ R1.1 profile expected from gravitational collapse alone, indicating that heating by active galactic nuclei (AGN) feedback extends well beyond the central galaxy. We show that the K ∝ R2/3 entropy profile shape indicates that thermally unstable cooling is balanced by heating where the inner cooling and free-fall timescales approach a constant ratio. Hot atmospheres of elliptical galaxies have a higher rate of heating per gas particle compared to those of central cluster galaxies. This excess heating may explain why some central cluster galaxies are forming stars while most early-type galaxies have experienced no significant star formation for billions of years. We show that the entropy profiles of six lenticular and spiral galaxies follow the R2/3 form. The continuity between central galaxies in clusters, giant ellipticals, and spirals suggests perhaps that processes heating the atmospheres of elliptical and brightest cluster galaxies are also active in spiral galaxies.