TY - JOUR
T1 - The Milky Way without X
T2 - An alternative interpretation of the double red clump in the Galactic bulge
AU - Lee, Young Wook
AU - Joo, Seok Joo
AU - Chung, Chul
N1 - Publisher Copyright:
© 2015 The Authors.
Copyright:
Copyright 2016 Elsevier B.V., All rights reserved.
PY - 2015/11/11
Y1 - 2015/11/11
N2 - The presence of two red clumps (RCs) in high-latitude fields of the Milky Way bulge is interpreted as evidence for an X-shaped structure originated from the bar instability. Here we show, however, that this double RC phenomenon is more likely to be another manifestation of multiple populations observed in globular clusters (GCs) in the metal-rich regime. As in the bulge GC Terzan 5, the helium enhanced second-generation stars in the classical bulge component of the Milky Way are placed on the bright RC, which is about 0.5 mag brighter than the normal RC originated from the first-generation stars, producing the observed double RC. In a composite bulge, where a classical bulge can coexist with a boxy pseudo bulge, our models can also reproduce key observations, such as the dependence of the double RC feature on metallicity and Galactic latitude and longitude. If confirmed by Gaia trigonometric parallax distances, this would indicate that the Milky Way bar is not sufficiently buckled to form the X-shaped structure in the bulge, and suggest that the early-type galaxies would be similarly prevailed by super-helium-rich subpopulation.
AB - The presence of two red clumps (RCs) in high-latitude fields of the Milky Way bulge is interpreted as evidence for an X-shaped structure originated from the bar instability. Here we show, however, that this double RC phenomenon is more likely to be another manifestation of multiple populations observed in globular clusters (GCs) in the metal-rich regime. As in the bulge GC Terzan 5, the helium enhanced second-generation stars in the classical bulge component of the Milky Way are placed on the bright RC, which is about 0.5 mag brighter than the normal RC originated from the first-generation stars, producing the observed double RC. In a composite bulge, where a classical bulge can coexist with a boxy pseudo bulge, our models can also reproduce key observations, such as the dependence of the double RC feature on metallicity and Galactic latitude and longitude. If confirmed by Gaia trigonometric parallax distances, this would indicate that the Milky Way bar is not sufficiently buckled to form the X-shaped structure in the bulge, and suggest that the early-type galaxies would be similarly prevailed by super-helium-rich subpopulation.
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U2 - 10.1093/mnras/stv1980
DO - 10.1093/mnras/stv1980
M3 - Article
AN - SCOPUS:84946611258
VL - 453
SP - 3906
EP - 3911
JO - Monthly Notices of the Royal Astronomical Society
JF - Monthly Notices of the Royal Astronomical Society
SN - 0035-8711
IS - 4
ER -