A Chandra Study of The Stellar X-ray Emissivity of Globular Clusters in M\,31 Bulge

Abstract

The X-ray emissivity (i.e., luminosity per unit stellar mass) of globular clusters are an important indicator of their dynamical evolution history. Based on deep archival \textit{Chandra} observations, we report a stacking analysis of 44 globular clusters (GCs) with 0.5-8 keV luminosities $L_{\mathrm{X}}\lesssim 10^{35}\mathrm{erg}{\mathrm{s}}^{-1}$ in the M\,31 bulge, which are supposed to be dominated by cataclysmic variables (CVs) and coronally active binaries (ABs). We obtain a significant detection at $5\sigma$ level in 0.5-8 keV band. The average X-ray luminosity per GC and the average X-ray emissivity are determined to be $5.3\pm 1.6\times 10^{33}\mathrm{erg}{\mathrm{s}}^{-1}$ and $13.2\pm 4.3\times 10^{27}\mathrm{erg}{\mathrm{s}}^{-1}{\mathrm{M}}_{\odot }^{-1}$, respectively. Both of these values are consistent with those of MW GCs. What's more, the measured emissivity of M31 GCs is also consistent with that of the MW field stars. Massive GCs have X-ray luminosities which are marginally higher with less massive ones. Massive GCs also show a lower emissivity ($4.5\pm 2.4\times 10^{27}\mathrm{erg}{\mathrm{s}}^{-1}{\mathrm{M}}_{\odot }^{-1}$) than less massive ones ($15.0\pm 7.8\times 10^{27}\mathrm{erg}{\mathrm{s}}^{-1}{\mathrm{M}}_{\odot }^{-1}$), which is consistent with the scenario that the (progenitors of) CVs and ABs were more efficiently destructed via stellar encounters in the more massive GCs. No dependence of the X-ray emissivity on GC color or on the projected galactocentric distance of GCs were found.

15 pages, 4 figures, accepted in ApJ

References in corpus (10)

• Formation and evolution of compact binaries in globular clusters: II. Binaries with neutron stars
• Dynamical Formation of Close Binaries in Globular Clusters II: Cataclysmic Variables
• The core binary fractions of star clusters from realistic simulations
• PHAT Stellar Cluster Survey I. Year 1 Catalog and Integrated Photometry
• X-ray emissivity of old stellar populations: a local group census
• X-Rays Beware: The Deepest Chandra Catalogue of Point Sources in M31
• The Luminosity Function of Low Mass X-Ray Binaries in the Globular Cluster System of NGC 1399
• Spectral Energy Distributions and Masses of 304 M31 Old Star Clusters
• X-ray stacking of Lyman break galaxies in the 4\,Ms CDF-S - X-ray luminosities and star formation rates across cosmic time
• Faint X-ray Binaries and Their Optical Counterparts in M31

Cited by in corpus (1)

• A Chandra Survey of Milky Way Globular Clusters II: Testing the Hills-Heggie Law