* Astronomy

Title: 65 kpc of ionised gas trailing behind NGC 4848 during its first crossing of the Coma cluster
Authors: Matteo Fossati, Giuseppe Gavazzi, Alessandro Boselli, Michele Fumagalli

In a 5 hour H{\alpha} exposure of the N-W region of the Coma cluster with the 2.1m telescope at SPM (Mx) we discovered a 65 kpc cometary emission of ionised gas trailing behind the SBab galaxy NGC 4848. The tail points in the opposite direction of the cluster center, in the same direction where stripped HI has been detected in previous observations. The galaxy shows bright HII regions in an inner ring-like pattern, where the star formation takes place at the prodigious rate of 8.6 Msun/yr. From the morphology of the galaxy and of the trailing material, we infer that the galaxy is suffering from ram pressure due to its high velocity motion through the cluster IGM. We estimate that 4 x 10^9 Msun of gas is swept out from the galaxy forming the tail. Given the ambient conditions in the Coma cluster ({rho}0 = 6.3 x 10^-27 g/cm^3; {\sigma}vel = 940 km/s) simulations predict that the ram pressure mechanism is able to remove such an amount of gas in less than 200 Myr. This, combined with the geometry of the interaction, indicating radial infall into the cluster, leads to the conclusion that NGC 4848 is caught in its first passage through the dense cluster environment.

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