Highly perturbed molecular gas in infalling cluster galaxies : the case of CGCG97-079

Abstract

We report on CO (J = 2 → 1) mapping with the IRAM 30-m HEtrodyne Receiver Array (HERA) of CGCG 97-079, an irregular galaxy in the merging galaxy cluster Abell 1367 (z = 0.022). We find that ˜80 per cent of the detected CO (J = 2 → 1) is projected within a 16 arcsec2 (6.5 kpc2) region to the north and west of the optical/NIR centre, with the intensity maximum offset ˜10 arcsec (4 kpc) NW of the optical/NIR centre and ˜7 arcsec (3 kpc) south-east of the H I intensity maximum. Evolutionary synthesis models indicate CGCG 97-079 experienced a burst of star formation ˜108 yr ago, most likely triggered by a tidal interaction with CGCG 97-073. For CGCG 97-079 we deduce an infall velocity to the cluster of ˜1000 km s-1 and moderate ram pressure (Pram ≈ 10-11 dyne cm-2). The observed offset in CGCG 97-079 of the highest density H I and CO (J = 2 → 1) from the stellar components has not previously been observed in galaxies currently undergoing ram pressure stripping, although previous detailed studies of gas morphology and kinematics during ram pressure stripping were restricted to significantly more massive galaxies with deeper gravitational potential wells. We conclude the observed cold gas density maxima offsets are most likely the result of ram pressure and/or the high-speed tidal interaction with CGCG 97-073. However ram pressure stripping is likely to be playing a major role in the perturbation of lower density gas.