Is Terzan 5 the remnant of a building block of the Galactic bulge? Evidence from APOGEE

Abstract

It has been proposed that the globular cluster-like system Terzan 5 is the surviving remnant of a primordial building block of the Milky Way bulge, mainly due to the age/metallicity spread and the distribution of its stars in the $\alpha$-Fe plane. We employ Sloan Digital Sky Survey (SDSS-IV) data from the Apache Point Observatory Galactic Evolution Experiment (APOGEE 2) to test this hypothesis. Adopting a random sampling technique, we contrast the abundances of 10 elements in Terzan 5 stars with those of their bulge field counterparts with comparable atmospheric parameters, finding that they differ at statistically significant levels. Abundances between the two groups differ by more than 1$\sigma$ in Ca, Mn, C, O, and Al, and more than 2$\sigma$ in Si and Mg. Terzan 5 stars have lower [$\alpha$/Fe] and higher [Mn/Fe] than their bulge counterparts. Given those differences, we conclude that Terzan 5 is not the remnant of a $major$ building block of the bulge. We also estimate the stellar mass of the Terzan 5 progenitor based on predictions by the Evolution and Assembly of GaLaxies and their Environments (EAGLE) suite of cosmological numerical simulations, concluding that it may have been as low as $\sim 3\times 10^8$ M${}_{\odot }$ so that it was likely unable to significantly influence the mean chemistry of the bulge/inner disk, which is significantly more massive ($\sim 10^{10}$ M${}_{\odot }$). We briefly discuss existing scenarios for the nature of Terzan 5 and propose an observational test that may help elucidate its origin.

15 pages, 10 figures, accepted for publication by MNRAS

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• A 34 Yr Timing Solution of the Redback Millisecond Pulsar Terzan 5A
• On the manifest link between Terzan 5 and the Galactic bulge
• Bulge Fossil Fragments as a new population of factories of gravitational wave sources in the Galaxy
• CAPOS: The bulge Cluster APOgee Survey VIII. Final ASPCAP results for all clusters
• Probing populations of dark stellar remnants in the globular clusters 47 Tuc and Terzan 5 using pulsar timing
• Digging deeper into the dense Galactic globular cluster Terzan 5 with Electron-Multiplying CCDs. Variable star detection and new discoveries