A survey for dwarf galaxy remnants around fourteen globular clusters in the outer halo

TL;DR

This survey investigates the outer halo of the Milky Way to find remnants of satellite galaxies around globular clusters, finding minimal evidence of such structures, consistent with hierarchical galaxy formation models.

Contribution

It provides the first systematic deep photometric survey of fourteen outer halo globular clusters searching for satellite remnants, with results supporting hierarchical accretion theories.

Findings

Only two clusters show extended stellar populations.

Most clusters lack detectable substructures.

Results align with cosmological simulation predictions.

Abstract

We report the results of a systematic photometric survey of the peripheral regions of a sample of fourteen globular clusters in the outer halo of the Milky Way at distances d_GC>25 kpc from the Galactic centre. The survey is aimed at searching for the remnants of the host satellite galaxies where these clusters could originally have been formed before being accreted onto the Galactic halo. The limiting surface brightness varies within our sample, but reaches muV_lim=30-32 mag arcsec^-2. For only two globular clusters (NGC 7492 and Whiting 1; already suggested to be associated with the Sagittarius galaxy) we detect extended stellar populations that cannot be associated with either the clusters themselves or with the surrounding Galactic field population. We show that the lack of substructures around globular clusters at these Galactocentric distances is still compatible with the predictions of cosmological simulations whereby in the outer halo the Galactic globular cluster system is built up through hierarchical accretion at early epochs.