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On the origin of the metallicity dependence in dynamically formed extragalactic low-mass X-ray binaries

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Author(s)
Ivanova, Natalia
Fragos, Tassos
Kim, Dong-Woo
Fabbiano, Guiseppina
Avendano Nandez, Jose Luis
Lombardi, James C., Jr. (Jamie)
Sivakoff, Gregory R.
Voss, Rasmus
Jordán, Andrés
Date Issued
December 1, 2012
Abstract
Globular clusters (GCs) effectively produce dynamically formed low-mass X-ray binaries (LMXBs). Observers detect ~100 times more LMXBs per stellar mass in GCs compared to stars in the fields of galaxies. Observationally, metal-rich GCs are about three times more likely to contain an X-ray source than their metal-poor counterparts. Recent observations have shown that this ratio holds in extragalactic GCs for all bright X-ray sources with L X between 2 × 1037 and 5 × 1038 erg s–1. In this Letter, we propose that the observed metallicity dependence of LMXBs in extragalactic GCs can be explained by the differences in the number densities and average masses of red giants in populations of different metallicities. Red giants serve as seeds for the dynamical production of bright LMXBs via two channels—binary exchanges and physical collisions—and the increase of the number densities and masses of red giants boost LMXB production, leading to the observed difference. We also discuss a possible effect of the age difference in stellar populations of different metallicities.
Journal
The Astrophysical Journal
Department
Physics
Citation
Ivanova, N., et al. (2012). On the origin of the metallicity dependence in dynamically formed extragalactic low-mass X-ray binaries. The Astrophysical Journal 760(L24): 1-4. doi: 10.1088/2041-8205/760/2/L24
Publisher
Institute of Physics
Version of Article
Published article
DOI
10.1088/2041-8205/760/2/L24
ISSN
0004-637X
e1538-4357
Rights
This article has been accepted for publication in the Astrophysical Journal © 2012 Ivanova, et al. Published by Institute of Physics. All rights reserved.
Subjects

binaries: close

globular clusters: ge...

X-rays: binaries

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