Confirming the intrinsic abundance spread in the globular cluster NGC 6273 (M 19) with calcium triplet spectroscopy

TL;DR

This study confirms a significant intrinsic metallicity spread in the globular cluster NGC 6273 using calcium triplet spectroscopy, suggesting it may be a remnant nucleus of a disrupted dwarf galaxy.

Contribution

First spectroscopic confirmation of intrinsic metallicity dispersion in NGC 6273, linking its formation to dwarf galaxy remnants.

Findings

Intrinsic [Fe/H] spread of ~1.0 dex in NGC 6273

Intrinsic abundance dispersion c[Fe/H]e = 0.17 dex

Comparison with omega Cen and M 54 suggests a similar formation mechanism.

Abstract

We present metallicities for red giant stars in the globular cluster NGC 6273 based on intermediate resolution GMOS-S spectra of the calcium triplet region. For the 42 radial velocity members with reliable calcium triplet line strength measurements, we obtain metallicities, [Fe/H], using calibrations established from standard globular clusters. We confirm the presence of an intrinsic abundance dispersion identified by Johnson et al. (2015). The total range in [Fe/H] is ~1.0 dex and after taking into account the measurement errors, the intrinsic abundance dispersion is \sigma[Fe/H] = 0.17 dex. Among the Galactic globular clusters, the abundance dispersion in NGC 6273 is only exceeded by omega Cen, which is regarded as the remnant of a disrupted dwarf galaxy, and M 54, which is the nuclear star cluster of the Sagittarius dwarf galaxy. If these three globular clusters share the same formation mechanism, then NGC 6273 may also be the remnant nucleus of a disrupted dwarf galaxy.