钱德拉ACIS巡天观测附近星系中的X射线点源。II。X射线光度函数与超铝X射线源
Chandra ACIS Survey of X-ray Point Sources in Nearby Galaxies. II. X-ray Luminosity Functions and Ultraluminous X-ray Sources
摘要：
基于最近完成的邻近星系X射线点源的{ \it Chandra}/ACIS巡天，我们研究了不同类型星系中X射线点源的X射线光度函数（XLF）和超亮X射线源（ULX）的统计特性。统一的程序来计算检测阈值，估计前景/背景污染，并计算XLF为个别星系和星系群，导致在XLF库的343个不同类型的星系。利用大量的观测数据，我们研究了不同类型主星系的XLF和ULX特性，并通过统计证实了XLF斜率从透镜星系（$α\sim1.50\pm0.07$）到椭圆星系（$\sim1.21\pm0.02$）、螺旋星系（$\sim0.80\pm0.02$）、特殊星系（$\sim0.55\pm0.30$）和不规则星系（$\sim0.26\pm0.10$）的变化规律。中子星和黑洞双星的XLF分裂也得到了证实，尽管不同类型的星系在相当不同的亮度上。椭圆星系的XLF斜率较低，位于$D_{25}$和2 $D_{25}$之间，表明早型星系外区的XLF斜率主要由球状星团中的低质量X射线双星控制。这项研究表明，早型星系中的ULX率是$0.24\pm0.05$ ULXs每个被调查的星系，在$5σ$的置信水平。晚型星系中ULX的XLF平滑地延伸，直到它在$4\times10^{40}$ erg s $^{-1}$附近突然下降，这种断裂可能表明恒星黑洞群之间存在一个温和的边界，可能包括30个具有超爱丁顿辐射的$M_\odot$黑洞和中等质量黑洞。
英文摘要：
Based on the recently completed {\it Chandra}/ACIS survey of X-ray point sources in nearby galaxies, we study the X-ray luminosity functions (XLFs) for X-ray point sources in different types of galaxies and the statistical properties of ultraluminous X-ray sources (ULXs). Uniform procedures are developed to compute the detection threshold, to estimate the foreground/background contamination, and to calculate the XLFs for individual galaxies and groups of galaxies, resulting in an XLF library for 343 galaxies of different types. With the large number of surveyed galaxies, we have studied the XLFs and ULX properties across different host galaxy types, and confirm with good statistics that the XLF slope flattens from lenticular ($α\sim1.50\pm0.07$) to elliptical ($\sim1.21\pm0.02$), to spirals ($\sim0.80\pm0.02$), to peculiars ($\sim0.55\pm0.30$), and to irregulars ($\sim0.26\pm0.10$). The XLF break dividing the neutron star and black hole binaries is also confirmed, albeit at quite different break luminosities for different types of galaxies. A radial dependency is found for ellipticals, with a flatter XLF slope for sources located between $D_{25}$ and 2$D_{25}$, suggesting the XLF slopes in the outer region of early-type galaxies are dominated by low-mass X-ray binaries in globular clusters. This study shows that the ULX rate in early-type galaxies is $0.24\pm0.05$ ULXs per surveyed galaxy, on a $5σ$ confidence level. The XLF for ULXs in late-type galaxies extends smoothly until it drops abruptly around $4\times10^{40}$ erg s$^{-1}$, and this break may suggest a mild boundary between the stellar black hole population possibly including 30 $M_\odot$ black holes with super-Eddington radiation and intermediate mass black holes.
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