Distortion of globular clusters by galactic bulges

• Published in: Monthly notices of the Royal Astronomical Society 1999-04, Vol.304 (2), p.288-296
• Main Authors: Nordquist, Holly K., Klinger, Robert J., Laguna, Pablo, Charlton, Jane C.
• Format: Article
• Language: English
• Subjects: celestial mechanics; celestial mechanics, stellar dynamics; galaxies: structure; globular clusters: general; methods: numerical; stellar dynamics
• ISSN: 0035-8711; 1365-2966
• DOI: 10.1046/j.1365-8711.1999.02293.x

One of the external fields that influences the population of globular clusters is that resulting from galactic bulges. In extreme situations, at perigalactic distances rp≤ 100 pc, globular clusters could suffer total disruption in a single passage. A more common scenario is that for cluster orbits with rp≥ 200 pc. We investigate the effects of tidal forces from a bulge on the shape of globular clusters for this type of encounter. We find distortions characterized by ‘twisting isophotes’ and consider the potential for observability of this effect. In the Milky Way, a typical globular cluster must pass within several hundred pc of the centre to experience substantial distortion, and it is possible that this has happened recently to one or two present-day clusters. We estimate that this distortion could be observed even for globulars in dense fields towards the bulge. In more extreme environments such as giant ellipticals or merger products with newly formed globulars, this effect could be more common, extending out to orbits that pass within 1 kpc of the bulge centre. This would lead to a substantial shift in the eccentricity distribution of globulars in those galaxies.