# 2MASX J17201001+2637317

2MASX J17201001+2637317 also known as PGC 1782937, is a massive type-cD elliptical galaxy located in the constellation of Hercules. With redshift of 0.16, the galaxy is located 2.4 billion light-years from Earth and the brightest cluster galaxy in the galaxy cluster, RX J1720.1+2638.

## Characteristics

2MASX J17201001+2637317 is classified as an optically luminous galaxy according to Sloan Digital Sky Survey. It has a luminosity value of 10L$_*$ (L$_*$ = 1.0 × 10$^{10}$ h$^2$ L, with a radio source found embedded inside its host with elliptical morphology. The galaxy also has an X-ray bright, radio-loud active galactic nucleus (L $_{1.4GHz}$ > 10$^{23}$ W Hz$^{−1}$), suggesting it contributes to energy distribution into the intergroup medium. According to ROSAT and Green Bank Telescope, 2MASX J17201001+2637317 is classified as a low-excitation narrow-line radio galaxy with a weak-line and also a LINER galaxy with radio power high as 10$^{23}$ - 10$^{26}$ W Hz$^{−1}$ at 5 GHz, making it among the strongest radio emitting LINERs known so far.
2MASX J17201001+2637317 is a fossil group galaxy with an estimated space density of n = (1.0 ± 0.6) × 10$^{−6}$ h Mpc$^{−3}$. The galaxy has a central velocity dispersion between the range Ỽ ~ 300–400 km s$^{−1}$ and an extended stellar envelope of excessive light with the light profile being described by a de Vaucouleurs surface brightness law, μ(r) ә r$^{1/4}$, over a large range in radius. It has been theorized the galaxy might have been formed from multiple galaxy mergers possibly made up of separate disk galaxies. As they collided, combined efforts of dynamic friction and tidal forces redistribute the kinetic energy into random form of energy. This allows the galaxies to merge into a one amorphous, triaxial system resembling an elliptical galaxy in the case of 2MASX J17201001+2637317.
MASX J17201001+2637317 is known to have significant ongoing star formation. Researchers who identified at least 120 early-type galaxies between redshifts of 0.1 < z < 0.4, found out the galaxy contains strong emission lines in its optical spectra, with both Hα and [O II]λ3727 line emission present.

## Observations of 2MASX J17201001+2637317

Researchers who investigated a connection between its star formation, the active galactic nucleus (AGN) and intracluster medium, found the sharp threshold for the star formation during the central cooling time of the hot atmosphere, is below ~5 × 10$^8$ yr or equivalent to ~30 keV cm$^2$. This results showed the AGN feedback in 2MASX J17201001+2637317 into its hot intracluster medium is largely responsible for regulating cooling and star formation in the cores of its parent cluster, leading to the significant growth of the galaxy's supermassive black hole found to actively powering an astrophysical jet.
2MASX J17201001+2637317 was also observed by Spitzer Space Telescope along with 62 other brightest cluster galaxies. Through the results presented by researchers, they found the galaxy has an infrared luminosity greater than 10$^{11}$ L⊙. This makes it as a luminous infrared galaxy (LIRG) showing one sign of infrared excess and a 24/8 μm flux ratio above 1.0.

## RX J1720.1+2638

The cluster where 2MASX J17201001+2637317 is residing, is found to be a cool-core 'relaxed-appearing' galaxy cluster and a non-fossil system. It has a mini halo detected up to 8.4 GHz and confined by X-ray-detected cold fronts with its spectrum consistent with a single power law up to 18 GHz. Moreover, the cluster has a luminosity of 6.20$^{+0.04}$$_{-0.02}${×}10$^{44}$ observed in 2-10 keV band mass profile of M$_{500}$ in the range of (5–7)× 10$^{14}$ M⊙. It actually displays a cool core profile, but there is evidence the galaxy cluster might have undergone a merger.
According to researchers who used the caustic technique to measure cluster mass profiles from galaxy redshifts that is obtained with the Hectospec Cluster Survey (HeCS), the halo mass in RX J1720.1+2638 is estimated to be (1.99 ± 0.11)M $_{200.}$ They noted it as a new observational cosmological test in essential agreement with the simulations.
RX J1720.1+2638 is known to have a strong gravitational lens containing a lognormal distribution of Einstein radius, with a peak and 1σ width of <log10θE(z = 2)> = 1.16 +/- 0.28. Researchers who presented the results from Keck Telescope detected an X-ray/lensing mass discrepancy of <M$_{SL}$/M$_X$> = 1.3 at 3σ significance showing cluster-cluster mergers do play a prominent role in shaping the properties of the cluster core, specifically causing departures from hydrostatic equilibrium, and possibly disturbing the cool core in RX J1720.1+2638.