The contribution of N-rich stars to the Galactic stellar halo using APOGEE red giants

Danny Horta, J. Ted Mackereth, Ricardo P. Schiavon, Sten Hasselquist, Jo Bovy, Carlos Allende Prieto, Timothy C. Beers, Katia Cunha, D. A. Garciá-Hernández, Shobhit S. Kisku, Richard R. Lane, Steven R. Majewski, Andrew C. Mason, David M. Nataf, Alexandre Roman-Lopes, Mathias Schultheis

Research output: Contribution to journalArticlepeer-review

9 Scopus citations

Abstract

The contribution of dissolved globular clusters (GCs) to the stellar content of the Galactic halo is a key constraint on models for GC formation and destruction, and the mass assembly history of the Milky Way. Earlier results from APOGEE pointed to a large contribution of destroyed GCs to the stellar content of the inner halo, by as much as 25 percent, which is an order of magnitude larger than previous estimates for more distant regions of the halo. We set out to measure the ratio between nitrogen-rich (N-rich) and normal halo field stars, as a function of distance, by performing density modelling of halo field populations in APOGEE DR16. Our results show that at 1.5 kpc from the Galactic Centre, N-rich stars contribute a much higher 16.8+10.0-7.0, percent fraction to the total stellar halo mass budget than the 2.7 +1.0-0.8percent ratio contributed at 10 kpc. Under the assumption that N-rich stars are former GC members that now reside in the stellar halo field, and assuming the ratio between first and second population GC stars being 1:2, we estimate a total contribution from disrupted GC stars of the order of 27.5+15.4-11.5 percent at r = 1.5 kpc and 4.2+1.5-1.3 percent at r = 10 kpc. Furthermore, since our methodology requires fitting a density model to the stellar halo, we integrate such density within a spherical shell from 1.5 to 15 kpc in radius, and find a total stellar mass arising from dissolved and/or evaporated GCs of MGC,total = 9.6+4.0-2.6 × 107 M·.

Original languageEnglish (US)
Pages (from-to)5462-5478
Number of pages17
JournalMonthly Notices of the Royal Astronomical Society
Volume500
Issue number4
DOIs
StatePublished - Feb 1 2021
Externally publishedYes

Keywords

  • Galaxy: evolution
  • Galaxy: formation
  • Galaxy: halo
  • globular clusters: general

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science

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