New density profile and structural parameters of the complex stellar system Terzan 5

TL;DR

This study re-evaluates the structural parameters of Terzan 5, revealing it is less concentrated and more massive than previously thought, which impacts understanding of its millisecond pulsar population.

Contribution

The paper provides a new analysis of Terzan 5's structure using combined high-resolution and wide-field data, updating its parameters and implications for stellar evolution.

Findings

Terzan 5 is less concentrated than previously believed.

It is more massive, with a high collision rate.

Findings influence the understanding of its millisecond pulsar population.

Abstract

Terzan 5 is a globular cluster-like stellar system in the Galactic Bulge which has been recently found to harbor two stellar populations with different iron content and probably different ages (Ferraro et al. 2009). This discovery suggests that Terzan 5 may be the relic of a primordial building block which contributed to the formation of the Galactic Bulge. Here we present a re-determination of the structural parameters (center of gravity, density and surface brightness profiles, total luminosity and mass) of Terzan 5, as obtained from the combination of high-resolution (ESO-MAD and HST ACS-WFC) and wide-field (ESO-WFI) observations. We find that Terzan 5 is significantly less concentrated and more massive than previously thought. Still it has the largest collision rate of any stellar aggregate in the Galaxy. We discuss the impact of these findings on the exceptional population of millisecond pulsars harbored in this stellar system.