The Murmur of the Sleeping Black Hole: Detection of Nuclear Ultraviolet Variability in LINER Galaxies
The Murmur of the Sleeping Black Hole: Detection of Nuclear Ultraviolet Variability in LINER Galaxies
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DOI：
10.1086/429795
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发表时间：
2005-02
期刊：
影响因子：
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通讯作者：
D. Maoz;N. Nagar;H. Falcke;A. Wilson
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文献类型：
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作者：
D. Maoz;N. Nagar;H. Falcke;A. Wilson
线性核存在于许多附近的星系核球中，可能是超大质量中心黑洞低速率或低辐射效率吸积的表现。然而，目前尚不清楚许多 LINER 中存在的紧凑型紫外核源是否是大质量恒星星团，而不是与吸积过程直接相关。我们使用哈勃太空望远镜监测了 17 个具有 LINER 核和紧凑型核紫外线源的星系样本的紫外线变化。 17个星系中的15个被多次观察到，每个星系有两到五个纪元，跨度长达一年。我们检测到大部分样本存在显着的变异性，峰峰值幅度从百分之几到 50% 不等。在大多数情况下，相关变化出现在两个独立的频段（F250W 和 F330W）中。与之前的紫外线测量结果相比，许多物体都存在数十年时间尺度的长期变化。在具有和不具有检测到的紧凑无线电核心的 LINER 中、在光谱中检测到具有宽 Hα 翼的 LINER 中（“LINER 1s”）以及没有检测到的 LINER 中（“LINER 2s”），都检测到了变异性。这种变化证明了所有类型的紫外线连续谱中都存在非恒星成分，并为该成分的光度设定了下限。有趣的是，所有检测到射电核心的 LINER 都具有可变的紫外线核，正如人们对真正的活跃星系核所期望的那样。我们注意到光谱类型的 UV 颜色 (F250W/F330W) 的趋势 - LINER 1 往往比 LINER 2 更蓝。这种趋势可能表明非恒星连续体的形状与宽线区域的存在或可见性之间存在联系。在一个目标——星暴后星系 NGC 4736 中，我们检测到先前提到的 UV 源的变化，该变化与核偏移 2.”5（投影中约为 60 pc）。这可能是双星活动核和导致黑洞合并过程的最接近的例子。
LINER nuclei, which are present in many nearby galactic bulges, may be the manifestation of low-rate or low-radiative-efficiency accretion onto supermassive central black holes. However, it has been unclear whether the compact UV nuclear sources present in many LINERs are clusters of massive stars, rather than being directly related to the accretion process. We have used the Hubble Space Telescope to monitor the UV variability of a sample of 17 galaxies with LINER nuclei and compact nuclear UV sources. Fifteen of the 17 galaxies were observed more than once, with two to five epochs per galaxy, spanning up to a year. We detect significant variability in most of the sample, with peak-to-peak amplitudes from a few percent to 50%. In most cases, correlated variations are seen in two independent bands (F250W and F330W). Comparison to previous UV measurements indicates, for many objects, long-term variations by factors of a few over decade timescales. Variability is detected in LINERs with and without detected compact radio cores, in LINERs that have broad Hα wings detected in their optical spectra ("LINER 1s"), and in those that do not ("LINER 2s"). This variability demonstrates the existence of a nonstellar component in the UV continuum of all types and sets a lower limit to the luminosity of this component. Interestingly, all the LINERs that have detected radio cores have variable UV nuclei, as one would expect from bona fide active galactic nuclei. We note a trend in the UV color (F250W/F330W) with spectral type—LINER 1s tend to be bluer than LINER 2s. This trend may indicate a link between the shape of the nonstellar continuum and the presence or the visibility of a broad-line region. In one target, the poststarburst galaxy NGC 4736, we detect variability in a previously noted UV source that is offset by 2.″5 (~60 pc in projection) from the nucleus. This may be the nearest example of a binary active nucleus and of the process leading to black hole merging.