Fluctuation of the background sky in the Hubble Extremely Deep Field (XDF) and its origin
Fluctuation of the background sky in the Hubble Extremely Deep Field (XDF) and its origin
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DOI：
10.1093/pasj/psz070
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发表时间：
2019-06
影响因子：
2.3
通讯作者：
T. Matsumoto;K. Tsumura
中科院分区：
文献类型：
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作者：
T. Matsumoto;K. Tsumura
我们对哈勃极深场（XDF）在四个光学波段进行了波动分析，发现了大的波动，其亮度明显高于普通星系的预期。在 ${0{^{\prime\prime}_{.}}2}$ 范围内发现与平坦光谱的良好互相关性，表明即使在 ${0{^{\prime\prime}_{.}}2}$ 尺度上也存在空间结构。检测到的自相关和互相关为 700-900 nm 处的绝对天空亮度提供了 24 nW m−2 sr−1 的下限，这与之前的观测结果一致。我们使用哈勃超深场（UDF）目录寻找候选天体来解释检测到的大波动，发现微弱致密天体（FCO）的表面数密度向微弱端快速增加。 FCO 的径向轮廓与点扩散函数 (PSF) 无法区分，并且基于德沃库勒定律的有效半径估计小于 ${0{^{\prime\prime}_{.}}02}$。 FCO 的光谱能量密度 (SED) 在光波长下遵循幂律，但在 $\lambda \gt 1\, \mu$m 处表现出更大的发射和结构。假设FCO是过度亮度和波动的原因，则F775W波段的微弱星等极限为34.9星等，表面数密度达到2.6 × 103 arcsec−2。最近的 γ 射线观测要求，如果 FCO 是多余光学和红外背景的来源，则 FCO 的红移必须小于 0.1。假设FCO由缺失的重子组成，单个FCO的质量和光度范围为102至103个太阳单位，且质光比显着低于1.0个太阳单位。 FCO 的最大有效半径为 4.7 pc。这些结果以及近红外和 X 射线背景之间的良好相关性表明 FCO 可以由与黑洞相关的引力能提供动力。
We performed a fluctuation analysis of the Hubble Extremely Deep Field (XDF) at four optical wavelength bands and found large fluctuations that are significantly brighter than those expected for ordinary galaxies. Good cross-correlations with flat spectra are found down to ${0{^{\prime\prime}_{.}}2}$, indicating the existence of a spatial structure even at the ${0{^{\prime\prime}_{.}}2}$ scale. The detected auto- and cross-correlations provide a lower limit of 24 nW m−2 sr−1 for the absolute sky brightness at 700–900 nm, which is consistent with previous observations. We searched for candidate objects to explain the detected large fluctuation using the catalog of the Hubble Ultra Deep Field (UDF), and found that the surface number density of faint compact objects (FCOs) rapidly increases toward the faint end. Radial profiles of FCOs are indistinguishable from the point spread function (PSF), and the effective radius based on de Vaucouleur’s law is estimated to be smaller than ${0{^{\prime\prime}_{.}}02}$. The spectral energy densities (SEDs) of FCOs follow a power law at optical wavelengths, but show greater emission and structure at $\lambda \gt 1\, \mu$m. Assuming that the FCOs are the cause of the excess brightness and fluctuations, the faint magnitude limit is 34.9 mag for the F775W band, and the surface number density reaches 2.6 × 103 arcsec−2. Recent γ-ray observations require that the redshift of FCOs must be less than 0.1, if FCOs are the origin of the excess optical and infrared background. Assuming that FCOs consist of missing baryons, the mass and luminosity of a single FCO range from 102 to 103 solar units, and the mass-to-luminosity ratio is significantly lower than 1.0 solar unit. The maximum effective radius of an FCO is 4.7 pc. These results and the good correlation between the near-infrared and X-ray background indicate that FCOs could be powered by the gravitational energy associated with black holes.