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

TL;DR

This study maps molecular gas in the irregular galaxy CGCG 97-079 within the merging cluster Abell 1367, revealing significant gas offsets likely caused by ram pressure and tidal interactions, indicating complex environmental effects on galaxy gas dynamics.

Contribution

First detailed CO (J=2-1) mapping of an infalling galaxy in a merging cluster showing gas offsets due to ram pressure and tidal effects.

Findings

80% of CO detected within a 6.5 kpc² region offset from galaxy center

Starburst likely triggered by tidal interaction 10^8 years ago

Offsets in gas density maxima attributed to ram pressure and tidal interactions

Abstract

We report on CO (J = 2 - 1) mapping with the IRAM 30-m HERA receiver array of CGCG 97-079, an irregular galaxy in the merging galaxy cluster Abell 1367 (z = 0.022). We find that $\sim$ 80% of the detected CO (J = 2 - 1) is projected within a 16 arcsec$^{2}$ (6.5 kpc$^{2}$) region to the north and west of the optical/NIR centre, with the intensity maximum offset $\sim 10$ arcsec (4 kpc) NW of the optical/NIR centre and $\sim$ 7 arcsec (3 kpc) south-east of the HI intensity maximum. Evolutionary synthesis models indicate CGCG 97-079 experienced a burst of star formation $\sim$ 10$^8$ 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 $\sim$ 1000 km s$^{-1}$ and moderate ram pressure (P$_\mathrm{ram} \sim 10^{-11}$ dyn cm$^{-2}$). The observed offset in CGCG 97-079 of the highest density HI 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.