Formation of the Galactic globular clusters with He-rich stars in low-mass halos virialized at high redshift

Abstract

Recent observations have reported that the Galactic globular clusters (GCs) with unusually extended horizontal-branch (EHB) morphologies show a significantly lower velocity dispersion compared with that of the entire Galactic GC system. We consider that the observed distinctive kinematics of GCs with EHB has valuable information on the formation epochs of GCs and accordingly discuss this observational result based on cosmological N-body simulations with a model of GC formation. We assume that GCs in galaxies were initially formed in low-mass halos at high redshifts and we investigate final kinematics of GCs in their host halos at $z=0$. We find that GCs formed in halos virialized at z>10 show lower velocity dispersions on average than those formed at z>6 for halos with GCs at z=0. We thus suggest that the origin of the observed lower velocity dispersion for the Galactic GCs with EHBs is closely associated with earlier formation epochs (z>10) of halos initially hosting the GCs in the course of the Galaxy formation. Considering that the origin of EHBs can be due to the presence of helium-enhanced second-generation stars in GCs, we discuss the longstanding second parameter problem of GCs in the context of different degrees of chemical pollution in GC-forming gas clouds within low-mass halos virialized at different redshifts.

5 pages, 3 figures, accepted by MNRAS Letters

References in corpus (10)

• Kinematic Decoupling of Globular Clusters with Extended Horizontal-Branch
• Origin of Abundance Inhomogeneity in Globular Clusters
• The Chemical Evolution of Helium in Globular Clusters: Implications for the Self-Pollution Scenario
• The presence of intermediate-mass black holes in globular clusters and their connection with extreme horizontal branch stars
• UV Bright Globular Clusters in M87: More Evidence for Super-helium-rich Stellar Populations?
• On spatial distributions of old globular clusters in clusters of galaxies
• Massive stars and globular cluster formation
• On the Origin of Mass--Metallicity Relations, Blue Tilts, and Scaling Relations for Metal-poor Globular Cluster Systems
• First stars as a possible origin for the helium-rich population in omega Centauri
• Origin of lower velocity dispersions of ultra-compact dwarf galaxy populations in clusters of galaxies