Chandra Detection of Intra-cluster X-ray Sources in Fornax

Abstract

Based on archival {\it Chandra} observations with a total exposure of 1.3 Ms, we study X-ray point sources in the Fornax cluster of galaxies, with the primary aim of searching for intra-cluster X-ray source populations. We detect 1177 point sources out to a projected radius of $\sim$30 arcmin ($\sim$180 kpc) from the cluster center and down to a limiting 0.5--8 keV luminosity of $\sim 3\times 10^{37}\mathrm{erg}{\mathrm{s}}^{-1}$. We construct source surface density profile, after excluding sources associated with foreground stars, known globular clusters, ultra-compact dwarfs and galactic nuclei. From this profile we statistically identify $\sim$183 excess sources that are not associated with the bulk stellar content of the individual member galaxies of Fornax, nor with the cosmic X-ray background. Taking into account Poisson error and cosmic variance, the cumulative significance of this excess is at $\gtrsim 2\sigma$ level (with a maximum of 3.6\,$\sigma$) outside three effective radii of the central giant elliptical, NGC\,1399. The luminosity function of the excess sources is found to be significantly steeper than that of the GC-hosting sources (presumably low-mass X-ray binaries [LMXBs]), disfavoring the possibility that unidentified GCs are primarily responsible for the excess. We show that a large fraction of the excess can be related to the extended stellar halo of NGC\,1399 and/or the diffuse intra-cluster light, thus providing strong evidence for the presence of intra-cluster X-ray sources in Fornax, the second unambiguous case for a galaxy cluster after Virgo. Other possible origins of the excess, including supernova-kicked LMXBs and stripped nucleated dwarf galaxies are discussed.

arXiv comment29 pages, 5 figures, accepted for publication in ApJ

References in corpus (63)

• The Optical and Near-Infrared Properties of Galaxies: I. Luminosity and Stellar Mass Functions
• The USNO-B Catalog
• An Overview of the Performance and Scientific Results from the Chandra X-Ray Observatory (CXO)
• On the shape of the light profiles of early-type galaxies
• The ACS Fornax Cluster Survey. V. Measurement and Recalibration of Surface Brightness Fluctuations and a Precise Value of the Fornax--Virgo Relative Distance
• eROSITA Science Book: Mapping the Structure of the Energetic Universe
• Diffuse Light in the Virgo Cluster
• Low mass X-ray binaries as a stellar mass indicator for the host galaxy
• X-ray source populations in galaxies
• Bayesian Estimation of Hardness Ratios: Modeling and Computations
• Dwarf Elliptical Galaxies
• The ACS Virgo Cluster Survey. I. Introduction to the Survey
• A Supermassive Black Hole in an Ultracompact Dwarf Galaxy
• X-ray Luminosity Function and Total Luminosity of LMXB in Early Type Galaxies
• The Burrell Schmidt Deep Virgo Survey: Tidal Debris, Galaxy Halos, and Diffuse Intracluster Light in the Virgo Cluster
• The Fornax Deep Survey with VST. I. The extended and diffuse stellar halo of NGC~1399 out to 192 kpc
• Ultra-Compact Dwarf Galaxies in the Fornax Cluster
• The X-ray Globular Cluster Population in NGC 1399
• The ACS Fornax Cluster Survey. I. Introduction to the Survey and Data Reduction Procedures
• 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 Formation and Evolution of Intracluster Light
• A new method for determining the sensitivity of X-ray imaging observations and the X-ray number counts
• Chandra Multiwavelength Project X-ray Point Source Catalog
• The ACS Fornax Cluster Survey. VI. The Nuclei of Early-Type Galaxies in the Fornax Cluster
• Large-scale study of the NGC 1399 globular cluster system in Fornax
• The ACS Fornax Cluster Survey. II. The Central Brightness Profiles of Early-Type Galaxies: A Characteristic Radius on Nuclear Scales and the Transition from Central Luminosity Deficit to Excess
• The Quantity of Intracluster Light: Comparing Theoretical and Observational Measurement Techniques Using Simulated Clusters
• Deep ROSAT-HRI observations of the NGC 1399/NGC 1404 region: morphology and structure of the X-ray halo
• Co-evolution of BCGs and ICL using CLASH
• Intergalactic stars in the Fornax Cluster
• A Chandra Search for Coronal X Rays from the Cool White Dwarf GD 356
• Dependence of the LMXB population on stellar age
• The Black Hole in the Most Massive Ultracompact Dwarf Galaxy M59-UCD3
• A 3.5-million Solar Masses Black Hole in the Centre of the Ultracompact Dwarf Galaxy Fornax UCD3
• On Computing Upper Limits to Source Intensities
• Comparing GC and Field LMXBs in Elliptical Galaxies with deep Chandra and Hubble data
• The Next Generation Virgo Cluster Survey. X. Properties of Ultra-Compact Dwarfs in the M87, M49 and M60 Regions
• The Chandra Fornax Survey - I: The Cluster Environment
• 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
• Intra-cluster patches of baryons in the core of the Fornax cluster
• The Surface Brightness and Colour-Magnitude Relations for Fornax Cluster Galaxies
• An Ultra-deep Chandra Catalog of X-ray Point Sources in the Galactic Center Star Cluster
• VEGAS-SSS II: Comparing the globular cluster systems in NGC3115 and NGC1399 using VEGAS and FDS survey data
• Deep Chandra observations of NGC 1404: cluster plasma physics revealed by an infalling early-type galaxy
• Correction for the Flux Measurement Bias in X-ray Source Detection
• Luminosity functions of LMXBs in different stellar environments
• Radial Distribution of X-ray Point Sources near the Galactic Center
• Globular cluster clustering and tidal features around ultra compact dwarf galaxies in the halo of NGC1399
• A Catalog of Extended Clusters and Ultra-Compact Dwarf Galaxies - An Analysis of their Parameters in Early- and Late-Type Galaxies
• Tramp Novae Between Galaxies in the Fornax Cluster: Tracers of Intracluster Light
• High-precision multi-band measurements of the angular clustering of X-ray sources
• Wide-Field Multiband Photometry of Globular Cluster Systems in the Fornax Galaxy Cluster
• The radial distribution of X-ray Binaries and Globular Clusters in NGC 4649 and their relation with the local stellar mass density
• X-ray emission from the Sombrero galaxy: discrete sources
• Spatial distribution of luminous X-ray binaries in spiral galaxies
• LMXB populations in galaxy outskirts: globular clusters and supernova kicks
• Chandra Detection of Intra-cluster X-ray sources in Virgo
• Deep Chandra observations of X-ray point sources in M87
• Chandra Detection of X-ray Emission from Ultra-compact Dwarf Galaxies and Extended Star Clusters
• The Luminosity Function of Low Mass X-Ray Binaries in the Globular Cluster System of NGC 1399
• Probing the Intracluster star-light with Chandra
• An excess of low-mass X-ray binaries in the outer halo of NGC 4472

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