晚型星系核中的候选活动星系核
Candidate AGNs in Late-Type Galaxies
摘要：
我们已经组装了一个样本的64晚型旋涡星系（T型6.0-9.0，对应于哈勃类型Scd-Sm）与档案钱德拉数据。在信噪比（S/N）为3的阈值下，我们发现12个天体的X射线点源探测与核的光学或近红外位置非常接近（中位偏移δ= 1.6”），这表明可能存在低光度活动星系核（AGN）。包括3 > S/N > 1.5的测量，我们的检测增加到18。这些X射线源的亮度范围从L_X（2-10 keV）= 10^{37.1}到10^{39.6}尔格·秒^-1。考虑到低质量X射线双星（LMXB）的可能污染，我们估计，~5检测可能是LMXB而不是真正的活动星系核，基于观测LMXB的概率在核星团通常发现在这些晚型螺旋星系。考虑到核星团的典型年龄，高质量X射线双星的污染是不可能的。活动星系核的比例高于光学巡天观测到的比例，这表明活跃的原子核以及中心的黑洞比以前认为的更常见。活动星系核活动在这种晚型旋涡星系中的发生也表明，有核的大质量黑洞可以在星系中形成和生长，而很少或根本没有膨胀的证据。后续多波长观测将是必要的，以确认这些来源的真实性质。
英文摘要：
We have assembled a sample of 64 late-type spiral galaxies (T types 6.0-9.0, corresponding to Hubble types Scd-Sm) with archival Chandra data. At a signal-to-noise (S/N) threshold of 3, we find 12 objects with X-ray point-source detections in close proximity with the optical or near-infrared position of the nucleus (median offset δ= 1.6"), suggestive of possible low-luminosity active galactic nuclei (AGNs). Including measurements with 3 > S/N > 1.5, our detections increase to 18. These X-ray sources range in luminosity from L_X(2-10 keV) = 10^{37.1} to 10^{39.6} ergs s^-1. Considering possible contamination from low-mass X-ray binaries (LMXBs), we estimate that ~5 detections are possible LMXBs instead of true AGNs, based on the probability of observing a LMXB in a nuclear star cluster typically found in these late-type spiral galaxies. Given the typical ages of nuclear star clusters, contamination by high-mass X-ray binaries is unlikely. This AGN fraction is higher than that observed in optical surveys, indicating that active nuclei, and hence central black holes, are more common than previously suggested. The incidence of AGN activity in such late-type spiral galaxies also suggests that nuclear massive black holes can form and grow in galaxies with little or no evidence for bulges. Follow-up multiwavelength observations will be necessary to confirm the true nature of these sources.
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