Detection of a diffuse extended halo-like structure around 47 Tuc

TL;DR

This study presents the first detailed stellar density profile of 47 Tuc extending beyond its tidal radius, revealing a nearly constant low-density halo-like structure rather than tidal tails or a steep fall-off.

Contribution

It provides the first high-quality deep photometric analysis showing a halo-like structure around 47 Tuc beyond its tidal radius, challenging previous theoretical and observational expectations.

Findings

Density profile reaches a constant value beyond 1.7 times the tidal radius

No evidence of tidal tails or clumpy structures at large distances

The envelope is a halo-like, nearly constant low-density structure

Abstract

We constructed for the first time a stellar density profile of 47 Tucanae (47 Tuc) out of $\sim$ 5.5 times its tidal radius ($r_t$) using high-quality deep $BV$ photometry. After carefully considering the influence of photometric errors, and Milky Way and Small Magellanic Cloud composite stellar population contamination, we found that the cluster stellar density profile reaches a nearly constant value from $\sim$ 1.7$r_t$ outwards, which does not depend on the direction from the cluster's center considered. These results visibly contrast with recent distinct theoretical predictions on the existence of tidal tails or on a density profile that falls as $r^{-4}$ at large distances, and with observational outcomes of a clumpy structure as well. Our results suggest that the envelope of 47 Tuc is a halo- like nearly constant low density structure.