X-Ray Luminosity Function and Total Luminosity of Low-Mass X-Ray Binaries in Early-Type Galaxies

By Dong-Woo Kim, G. Fabbiano. 2003

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We have derived bias-corrected X-ray luminosity functions (XLFs) of sources detected in a uniformly selected sample of 14 E and S0 galaxies observed with Chandra ACIS-S3. The entire sample yields 985 pointlike X-ray sources, with typical detections of 30-140 sources per galaxy. After correcting for incompleteness, the individual XLFs are statistically consistent with a single power law of a (differential) XLF slope β = 1.8-2.2 (with a typical error of 0.2-0.3). A break at or near LX,Edd, as reported in the literature for some of these galaxies, is not required in any case. Given the uniform XLF shape, we have generated a combined, higher statistics XLF, representative of X-ray sources in elliptical galaxies. Although the combined XLF is marginally consistent with a single power law (with β = 2.1 ± 0.1), a broken power law gives an improved fit. The best-fit slope is β = 1.8 ± 0.2 in the low-luminosity range LX = a few × 1037 to 5 × 1038 ergs s-1. At higher luminosities, the slope is steeper, β = 2.8 ± 0.6. The break luminosity is (5 ± 1.6) × 1038 ergs s-1 (with an error at 90%), which may be consistent with the Eddington luminosity of neutron stars with the largest possible mass (3 M☉), He-enriched neutron star binaries, or low-mass stellar-mass black holes. If the change in XLF slope at high luminosities is real and does not mask a step in the XLF, our result would imply a different population of high-luminosity sources, instead of a beaming effect. This high-luminosity portion of the XLF must reflect the mass function of black holes in these galaxies. We note that this high-luminosity population does not resemble that of the ultraluminous X-ray sources detected in star-forming galaxies, where no break in the XLF is present and the XLF is much flatter than in the older stellar system we are studying here. We use our results to derive the integrated X-ray luminosity of accreting low-mass X-ray binaries (LMXBs) in each sample galaxy. We confirm that the total X-ray luminosity of LMXBs is correlated with the optical and more tightly with the near-IR luminosities, but in both cases the scatter exceeds that expected from measurement errors. We find that the scatter in LX(LMXB)/LK is marginally correlated with the specific frequency of globular clusters.

Subfields: Astronomy and Astrophysics, Nuclear and High Energy Physics

View Paper: https://www.semanticscholar.org/paper/d118d6c78d90faed093a88b3e9d73c2fd2b4aa59

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Citations in the corpus

The SAURON project - XVI. On the sources of ionization for the gas in elliptical and lenticular galaxies (2009, background): “…exquisite spatial resolution of the Chandra X-ray observatory has recently allowed to detect LMXBs in nearby ellipticals, enabling thederivation of their luminosity function and, most important in thepresent context, their total X-ray luminosity (in the 0.3-8 keV range; e.g. Kim & Fabbiano 2004).”
CHANDRA STUDIES OF THE X-RAY GAS PROPERTIES OF GALAXY GROUPS (2008, methodology): “The total LMXB luminosity is fixed from the LX − LKs relation derived in Kim & Fabbiano (2004), where LKs is the total Ks band luminosity of the cD from 2MASS.”
The Assembly History of Field Spheroidals: Evolution of Mass-to-Light Ratios and Signatures of Recent Star Formation (2005, methodology): “Using the relation from Kim & Fabbiano (2004), LX(LMXB) ¼ (0:9 0:5) ;1030 ergs s 1 LB/LB; , and our measured LB, we find that for our sample14 the median contribution of LMXBs to the total X-ray emission is 16% 9%.”
Populations of X-Ray Sources in Galaxies (2006, methodology): “In the case of Chandra the detection efficiency is also affected by the radial dependence of the degradation of the mirror resolution off-axis (see Kim & Fabbiano 2003, 2004; Gilfanov 2004).”
REVISITING WITH CHANDRA THE SCALING RELATIONS OF THE X-RAY EMISSION COMPONENTS (BINARIES, NUCLEI, AND HOT GAS) OF EARLY-TYPE GALAXIES (2010, methodology): “These relations have been the basis for much discussion and modeling of the physical evolution of the hot halos in past studies (see Canizares et al. 1987; Eskridge et al. 1995a, 1995b; O’Sullivan et al. 2003; Ciotti et al. 1991; Kim & Fabbiano 2004; David et al. 2006).”
ASASSN-15oi: a rapidly evolving, luminous tidal disruption event at 216 Mpc (2016, methodology): “Based on the correlations of Kim & Fabbiano (2004) between the K-band luminosities of galaxies and the integrated X-ray emission by their LMXBs, however, this contribution should only be of order 1040 ergs s−1, well below the observed luminosity.”
THE FERMI HAZE: A GAMMA-RAY COUNTERPART TO THE MICROWAVE HAZE (2009, unknown): “…power laws with α ∼ 2.5 have been observed in flat spectrum radio quasars, and at low luminosities very shallow power laws with α ∼ 1.2 have been measured in LMXB populations (Grimm et al. 2003; Gilfanov 2004; Kim & Fabbiano 2004; Voss & Gilfanov 2006; Padovani et al. 2007; Abdo et al. 2009a).”
Compact Object Modeling with the StarTrack Population Synthesis Code (2005, background): “…may also result in an independent diagnostic of star formation rates for nearby galaxies, since both the numbers and properties of XRBs are directly connected to the star formation history (see, e.g., Grimm et al. 2003; Gilfanov 2004; Kim & Fabbiano 2004; K. Belczynski et al. 2008, in preparation).”