The Phoenix Cluster (SPT-CL J2344-4243) is a massive, Abell class type I galaxy cluster located at its namesake, southern constellation of Phoenix. It was initially detected in 2010 during a 2,500 square degree survey of the southern sky using the Sunyaev–Zeldovich effect by the South Pole Telescope collaboration. It is one of the most massive galaxy clusters known, with the mass on the order of 2 , and is the most luminous X-ray cluster discovered, producing more X-rays than any other known massive cluster. It is located at a comoving distance of from Earth. About 42 member galaxies were identified and currently listed in the SIMBAD Astronomical Database, though the real number may be as high as 1,000.
Discovery
The Phoenix Cluster was first reported in a paper by R. Williamson and colleagues during a survey by the South Pole Telescope in Antarctica, being one of the 26 galaxy clusters identified by the survey. The detection has been conducted at frequencies between 95, 150, and 220 GHz, with 14 of the galaxy clusters detected have been previously identified, while 12 – including Phoenix Cluster, being new discoveries. The would-be named Phoenix Cluster (still identified by its numerical catalogue entry SPT-CL J2344–4243) has been remarked to be having "the largest X-ray luminosity of any cluster" described by the survey. A bright, type-2 Seyfert galaxy has also been pronounced lying 19 arcseconds from the apparent center of the cluster that has been identified as 2MASX J23444387-4243124, which would later be named Phoenix A, the cluster's central galaxy.
Characteristics
Owing to its extreme properties, the Phoenix Cluster has been extensively studied and is considered one of the most important class of objects of its type. A multiwavelength observational study by M. McDonald and colleagues show that it has an extremely strong cooling flow rate (roughly 3,280 per annum), described as a runaway cooling flow. This measurement is one of the highest ever seen in the middle of a galaxy cluster. The very strong cooling flow, in contrast to other galaxy clusters, has been a suggested result of the feedback mechanism to prevent a runaway cooling flow which may not yet be established yet in the Phoenix Cluster; the heating mechanism expected to be produced by the central black hole being inadequate to create a feedback (in contrast to the Perseus and Virgo clusters). This is further supported by the high starburst activity of the central galaxy Phoenix A, where stars are formed at 740 per annum (compared to the Milky Way's 1 per annum of star production); the central active galactic nucleus attested to not have been producing sufficient energy to ionize the galaxy's gas and prevent starburst activity.
Components
Central galaxy
The central elliptical cD galaxy of this cluster, Phoenix A (RBS 2043, 2MASX J23444387-4243124), hosts an active galactic nucleus that has been described as sharing both the properties of being a quasar and a type 2 Seyfert galaxy, which is powered by a central supermassive black hole. The galaxy has yet an uncertain morphology. Based on the "total" aperture at the K-band, Phoenix A has an angular diameter of 16.20 arcseconds, corresponding to a large isophotal diameter of , making it one of largest known galaxies discovered from Earth.
Phoenix A also contains vast amounts of hot gas. More normal matter is present there than the total of all the other galaxies in the cluster. Data from observations indicate that hot gas is cooling in the central regions at a rate of 3,820 solar masses per year, the highest ever recorded.
It is also undergoing a massive starburst, the highest recorded in the middle of a galaxy cluster, although other galaxies at higher redshifts have a higher starburst rate. (see Baby Boom Galaxy)
Observations by a variety of telescopes including the GALEX and Herschel space telescopes shows that it has been converting the material to stars at an exceptionally high rate of 740 per year. This is considerably higher than that of NGC 1275 A, the central galaxy of the Perseus Cluster, where stars are formed at a rate around 20 times lower, or the one per year rate of star formation in the Milky Way.