Ubiquitous ram pressure stripping in the Coma cluster of galaxies

We report the detection of Hα trails behind three new intermediate-mass irregular galaxies in the NW outskirts of the nearby cluster of galaxies Abell 1656 (Coma). Hints that these galaxies possess an extended component were found in earlier, deeper Hα observations carried out with the Subaru telescope. However the lack of a simultaneous r-band exposure, together with the presence of strong stellar ghosts in the Subaru images, prevented us from quantifying the detections. We therefore devoted one full night of Hα observation to each of the three galaxies using the San Pedro Martir 2.1 m telescope. One-sided tails of Hα emission of 10-20 kpc projected size were detected, suggesting an ongoing ram pressure stripping event. We added these 3 new sources of extended ionized gas to the 12 previously found, NGC 4848, and NGC 4921 whose ram pressure stripping is certified by HI asymmetry. This brings the number sources with Hα trails to 17 gaseous tails out of 27 (63%) late-type galaxies (LTG) members of the Coma cluster with direct evidence of ram pressure stripping. The 27 LTG galaxies, among these the 17 with extended Hα tails, have kinematic properties that are different from the rest of the early-type galaxy population of the core of the Coma cluster, as they deviate in the phase-space diagram |ΔV|/σ versus r/R₂₀₀.

Based on observations taken at the San Pedro Martir telescope belonging to the Mexican National Observatory (OAN).The reduced Hα images (FITS) are only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/618/A130