A Brightest Cluster Galaxy with an Extremely Large Flat Core
Marc Postman, Tod R. Lauer, Megan Donahue, Genevieve Graves, Dan Coe,, John Moustakas, Anton Koekemoer, Larry Bradley, Holland C. Ford, Claudio, Grillo, Adi Zitrin, Doron Lemze, Tom Broadhurst, Leonidas Moustakas, Begona, Ascaso, Elinor Medezinski, Daniel Kelson

TL;DR
This paper reports the discovery of the largest and most unusual flat-core galaxy in a cluster, suggesting a supermassive black hole and possible black hole ejection processes have shaped its core structure.
Contribution
It presents the first detailed analysis of an extremely large flat-core brightest cluster galaxy, highlighting its unique core morphology and implications for black hole interactions.
Findings
Largest core detected in any galaxy to date.
Core size exceeds typical values by a factor of two.
Evidence suggests black hole ejection may have influenced core structure.
Abstract
Hubble Space Telescope images of the galaxy cluster Abell 2261, obtained as part of the Cluster Lensing And Supernova survey with Hubble, show that the brightest galaxy in the cluster, A2261-BCG, has the largest core yet detected in any galaxy. The cusp radius of A2261-BCG is 3.2 kpc, twice as big as the next largest core known, and ~3x bigger than those typically seen in the most luminous BCGs. The morphology of the core in A2261-BCG is also unusual, having a flat or even slightly-depressed interior surface brightness profile, rather than the typical shallow cusp. This implies that the galaxy has a core with constant or even centrally decreasing stellar density. Interpretation of the core as an end product of the "scouring" action of a binary supermassive black hole implies a total black hole mass ~1E+10 M_sun from the extrapolation of most relationships between core structure and…
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