Properties of intra-cluster low-mass X-ray binaries in Fornax globular clusters

Abstract

We present a study of the intra-cluster population of low-mass X-ray binaries (LMXB) residing in globular clusters (GC) in the central 1 $de{g}^2$ of the Fornax galaxy cluster. Differently from previous studies, which were restricted to the innermost regions of individual galaxies, this work is aimed at comparing the properties of the intra-cluster population of GC-LMXBs with those of the host galaxy. We use VLT Survey Telescope (VST) and Chandra observations. We identify 168 LMXBs residing in GCs and divide it into host-galaxy and intra-cluster objects based on their distance from the nearest galaxy in terms of effective radius. We found 82 intra-cluster GC-LMXBs and 86 objects that are hosted in galaxies. We perform a Gaussian mixture model to divide the population into red and blue GCs. As has been found for the innermost regions of galaxies, LMXBs tend to form in red and bright GCs in intra-cluster space as well. We find, however, that the likelihood of a red GC to host an LMXB decreases with galactocentric distance, but it remains approximately constant for the blue GC population. Investigating the X-ray properties of the LMXBs residing in GCs, we find a difference in the X-ray luminosity function between the intra-cluster and host-galaxy sample: both follow a power-law down to $\sim 8.5\times 10^{37}$ erg s${}^{-1}$, which is consistent with field LMXBs for the intra-cluster sample, while the latter agree with previous estimates for LMXBs in GCs. We detect a tentative difference in the hardness ratio of two populations, where the intra-cluster GC-LMXBs appear to have harder spectra than the host-galaxy objects. We find the same trend when we compare red and blue GC-LMXBs: the spectra of the blue sample are harder spectra than those of the red sample. This result could suggest a relation between the spectral properties of LMXBs and the host GC colour and therefore its metallicity.

arXiv commentAccepted by A&A

References in corpus (35)

• Power laws, Pareto distributions and Zipf's law
• The COSMOS2015 Catalog: Exploring the 1<z<6 Universe with half a million galaxies
• The ACS Fornax Cluster Survey. V. Measurement and Recalibration of Surface Brightness Fluctuations and a Precise Value of the Fornax--Virgo Relative Distance
• The Chandra COSMOS Legacy survey: overview and point source catalog
• X-ray source populations in galaxies
• Modeling the Metallicity Distribution of Globular Clusters
• X-ray Luminosity Function and Total Luminosity of LMXB in Early Type Galaxies
• The globular cluster system of NGC 1399 V. dynamics of the cluster system out to 80 kpc
• The Fornax Deep Survey with VST. I. The extended and diffuse stellar halo of NGC~1399 out to 192 kpc
• The ACS Fornax Cluster Survey. VIII. The Luminosity Function of Globular Clusters in Virgo and Fornax Early-Type Galaxies and its Use as a Distance Indicator
• The Next Generation Virgo Cluster Survey. VIII. The Spatial Distribution of Globular Clusters in the Virgo Cluster
• The ACS Virgo Cluster Survey III. Chandra and HST Observations of Low-Mass X-Ray Binaries and Globular Clusters in M87
• VEGAS: A VST Early-type GAlaxy Survey. I. Presentation, wide-field surface photometry, and substructures in NGC 4472
• The Fornax Deep Survey with VST. II. Fornax A: a two-phase assembly caught on act
• Low Mass X-ray Binaries in 6 Elliptical Galaxies: Connection to Globular Clusters
• The Fornax Deep Survey (FDS) with VST. VI. Optical properties of the dwarf galaxies in the Fornax cluster
• Halo mass estimates from the Globular Cluster populations of 175 Low Surface Brightness Galaxies in the Fornax Cluster
• The SLUGGS Survey: The globular cluster systems of three early-type galaxies using wide-field imaging
• The Fornax Deep Survey with VST. V. Exploring the faintest regions of the bright early-type galaxies inside the virial radius
• Comparing GC and Field LMXBs in Elliptical Galaxies with deep Chandra and Hubble data
• Trends in the Globular Cluster Luminosity Function of Early-Type Galaxies
• The Low Mass X-ray Binary-Globular Cluster Connection II: NGC 4472 X-ray Source Properties and Source Catalogs
• The Extended Spatial Distribution of Globular Clusters in the Core of the Fornax Cluster
• Probing the GC-LMXB connection in NGC 1399: a wide-field study with HST and Chandra
• VEGAS-SSS II: Comparing the globular cluster systems in NGC3115 and NGC1399 using VEGAS and FDS survey data
• How large are the globular cluster systems of early-type galaxies and do they scale with galaxy halo properties?
• Wide-Field Hubble Space Telescope Observations of the Globular Cluster System in NGC1399
• The Fornax Cluster VLT Spectroscopic Survey. I - VIMOS spectroscopy of compact stellar systems in the Fornax core region
• An explanation for metallicity effects on X-ray Binary properties
• The Fornax Deep Survey with VST. IX. The catalog of sources in the FDS area, with an example study for globular clusters and background galaxies
• Metallicity Effect on LMXB Formation in Globular Clusters
• Scaling relations for globular cluster systems in early-type galaxies
• The Luminosity Function of Low Mass X-Ray Binaries in the Globular Cluster System of NGC 1399
• Chandra Detection of Intra-cluster X-ray Sources in Fornax
• Globular Cluster Scale Sizes in Giant Galaxies: Orbital Anisotropy and Tidally Under-filling Clusters in M87, NGC 1399, and NGC 5128

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