The dynamically hot stellar halo around NGC 3311: a small cluster-dominated central galaxy

TL;DR

This study reveals that NGC 3311 has a dynamically hot stellar halo with high velocity dispersion, indicating dominance by intracluster stars and providing insights into galaxy cluster core dynamics.

Contribution

It presents detailed kinematic measurements of NGC 3311's halo, showing a transition from galaxy-bound to intracluster stars, highlighting the influence of the cluster environment.

Findings

Velocity dispersion increases steeply from 150 km/s to 450 km/s within 12 kpc.

Beyond 12 kpc, velocity dispersion remains constant at ~450 km/s.

Dark matter and intracluster stars dominate the galaxy's outer halo.

Abstract

An important open question is the relation between intracluster light and the halos of central galaxies in galaxy clusters. Here we report results from an on going project with the aim to characterize the dynamical state in the core of the Hydra I (Abell 1060) cluster around NGC 3311. Methods: We analyze deep long-slit absorption line spectra reaching out to ~25 kpc in the halo of NGC 3311. Results: We find a very steep increase in the velocity dispersion profile from a central sigma_0=150 km/s to sigma_out ~450 km/s at R ~ 12 kpc. Farther out, to ~25 kpc, sigma appears to be constant at this value, which is ~60% of the velocity dispersion of the Hydra I galaxies. With its dynamically hot halo kinematics, NGC 3311 is unlike other normal early-type galaxies. Conclusions: These results and the large amount of dark matter inferred from X-rays around NGC 3311 suggest that the stellar halo of this galaxy is dominated by the central intracluster stars of the cluster, and that the transition from predominantly galaxy-bound stars to cluster stars occurs in the radial range 4 to 12 kpc from the center of NGC 3311. We comment on the wide range of halo kinematics observed in cluster central galaxies, depending on the evolutionary state of their host clusters.