The Ultraluminous X-Ray Source Population from the Chandra Archive of Galaxies

By D. Swartz, K. Ghosh, A. Tennant, Kinwah Wu. 2004

276 citations recorded by the source corpus.

One hundred fifty-four discrete non-nuclear ultraluminous X-ray (ULX) sources, with spectroscopically determined intrinsic X-ray luminosities greater than 1039 ergs s-1, are identified in 82 galaxies observed with Chandra's Advanced CCD Imaging Spectrometer. Source positions, X-ray luminosities, and spectral and timing characteristics are tabulated. Statistical comparisons between these X-ray properties and those of the weaker discrete sources in the same fields (mainly neutron star and stellar-mass black hole binaries) are made. Sources above ∼1038 ergs s-1 display similar spatial, spectral, color, and variability distributions. In particular, there is no compelling evidence in the sample for a new and distinct class of X-ray object such as the intermediate-mass black holes. Eighty-three percent of ULX candidates have spectra that can be described as absorbed power laws with index 〈Γ〉 = 1.74 and column density 〈NH〉 = 2.24 × 1021 cm-2, or ∼5 times the average Galactic column. About 20% of the ULXs have much steeper indices indicative of a soft, and likely thermal, spectrum. The locations of ULXs in their host galaxies are strongly peaked toward their galaxy centers. The deprojected radial distribution of the ULX candidates is somewhat steeper than an exponential disk, indistinguishable from that of the weaker sources. About 5%-15% of ULX candidates are variable during the Chandra observations (which average 39.5 ks). Comparison of the cumulative X-ray luminosity functions of the ULXs to Chandra Deep Field results suggests ∼25% of the sources may be background objects, including 14% of the ULX candidates in the sample of spiral galaxies and 44% of those in elliptical galaxies, implying the elliptical galaxy ULX population is severely compromised by background active galactic nuclei. Correlations with host galaxy properties confirm the number and total X-ray luminosity of the ULXs are associated with recent star formation and with galaxy merging and interactions. The preponderance of ULXs in star-forming galaxies as well as their similarities to less-luminous sources suggest they originate in a young but short-lived population such as the high-mass X-ray binaries with a smaller contribution (based on spectral slope) from recent supernovae. The number of ULXs in elliptical galaxies scales with host galaxy mass and can be explained most simply as the high-luminosity end of the low-mass X-ray binary population.

Subfields: Astronomy and Astrophysics, Nuclear and High Energy Physics

View Paper: https://www.semanticscholar.org/paper/9df48a5af7c9b7aac93ae8c231199b714ff3d970

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In Astronomy and Astrophysics

1. W. N. Brandt
2. H. Feng
3. R. Soria
4. D. M. Alexander
5. B. Lehmer
6. T. Roberts
7. G. Fabbiano
8. A. Zezas

In Nuclear and High Energy Physics

1. W. N. Brandt
2. B. Lehmer
3. G. Fabbiano
4. S. Mineo
5. R. Sunyaev
6. M. Gilfanov
7. S. Vaughan
8. H. Feng

Citations in the corpus

• Ultraluminous X-ray sources in the Chandra and XMM-Newton era (2011, methodology): “AChandra catalog with 154 sources in 82 galaxies was produced by Swartz et al. (2004), and 226 objects were included in the catalog by Liu & Mirabel (2005), compiled from mixed literature sources.”
• THE EFFECT OF STARBURST METALLICITY ON BRIGHT X-RAY BINARY FORMATION PATHWAYS (2010, background): “…a subpopulation of ultra-luminous X-ray sources (ULX; defined here as LX > 1 x 10 39 erg s−1, the Eddington limit for a ≃ 7 M⊙ black hole), the exact nature of which is not well understood (Fabbiano et al. 1997; Makishima et al. 2000; Fabbiano et al. 2001; Mushotzky 2004; Swartz et al. 2004).”
• X-ray emission from star-forming galaxies – I. High-mass X-ray binaries (2011, background): “This choice was moti- vated by the value of the centroid of the power law photon index distribution of the luminous compact X-ray sources in star-forming galaxies measured by Swartz et al. (2004), Γ = 1.97 ± 0.11.”
• A CHANDRA PERSPECTIVE ON GALAXY-WIDE X-RAY BINARY EMISSION AND ITS CORRELATION WITH STAR FORMATION RATE AND STELLAR MASS: NEW RESULTS FROM LUMINOUS INFRARED GALAXIES (2010, background): “Using simple polynomial fitting techniques, 10 However, see Grimm et al. (2003), Gilfanov et al. (2004a), and Gilfanov (2004) for different scalings depending onM⋆ and SFR regimes. we find for galaxies with SFR<∼ 5 M⊙ yr −1, M⋆ and SFR are nearly linearly correlated (M⋆ ∝ SFR 1.10); however, for gal”
• XMM–Newton observations of the brightest ultraluminous X-ray sources (2006, background): “10 A near identical cut-off is found from a large sample of ULXs studied by Swartz et al. (2004).”
• Populations of X-Ray Sources in Galaxies (2006, background): “Swartz et al. (2004) find that the number of ULXs in early-type galaxies scales with galaxy mass and can be explained with the high luminosity end of the XLF (see Gilfanov 2004 and discussion in Section 3.3).”
• The ultraluminous state revisited: fractional variability and spectral shape as diagnostics of super-Eddington accretion (2013, background): “…in excess of 5 × 10−13 erg cm−2 s−1 in the ROSAT High Resolution Imager (HRI) observed sample of Liu & Bregman (2005) and the Chandra archival sample of Swartz et al. (2004) as these are likely candidates for having reasonable quality XMM–Newton data, if they have been detected in previous…”
• The Ultraluminous State (2009, methodology): “Simple, single component models have been used rather succes - fully to describe the featureless spectra of ULXs in the low-t - moderate quality data regime for some years (e.g. Humphrey et al. 2003; Swartz et al. 2004; Feng & Kaaret 2005; Winter, Mushotzky & Reynolds 2006).”