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

Taylor, DJ, Mason, AC, Schiavon, RP, Horta, D, Nataf, DM, Geisler, D, Kisku, S, Phillips, SG, Cohen, RE, Fernández-Trincado, JG, Beers, TC, Bizyaev, D, García-Hernández, DA, Lane, RR, Longa-Peña, P, Minniti, D, Muñoz, C, Pan, K and Villanova, S (2022) Is Terzan 5 the remnant of a building block of the Galactic bulge?Evidence from APOGEE. Monthly Notices of the Royal Astronomical Society, 513 (3). pp. 3429-3443. ISSN 0035-8711

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Terzan5.pdf - Published Version
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 $\sim3\times10^8$ M$_\odot$ so that it was likely unable to significantly influence the mean chemistry of the bulge/inner disk, which is significantly more massive ($\sim10^{10}$ M$_\odot$). We briefly discuss existing scenarios for the nature of Terzan 5 and propose an observational test that may help elucidate its origin.