A 100 kpc ram pressure tail trailing the group galaxy NGC 2276

Abstract

We present the discovery of a $100\ kpc $ low-frequency radio tail behind the nearby group galaxy, NGC 2276. The extent of this tail is a factor of ten larger than previously reported from higher-frequency radio and X-ray imaging. The radio morphology of the galaxy disc and tail suggest that the tail was produced via ram-pressure stripping, cementing NGC 2276 as the clearest known example of ram-pressure stripping in a low-mass group. With multi-frequency imaging, we extract radio continuum spectra between $ sim MHz $ and $1.2\ GHz $ as a function of projected distance along the tail. All of the spectra are well fit by a simple model of spectral ageing due to synchrotron and inverse-Compton losses. From these fits we estimate a velocity of $870\ $ for the stripped plasma across the plane of the sky, and a three-dimensional orbital velocity of $970\ $ for NGC 2276. The orbital speed that we derive is in excellent agreement with the previous estimates from an X-ray shock analysis, despite the completely independent methodology.