在CANDELS/GOODS-S中首次发现早期宇宙中的直接坍缩黑洞
First Identification of Direct Collapse Black Hole Candidates in the Early Universe in CANDELS/GOODS-S
摘要：
第一个黑洞种子形成于宇宙年龄小于5亿年的时候，被认为对早期（z ~ 7）超大质量黑洞的生长起着重要作用。虽然在理解它们的形成和生长方面取得了进展，但它们的观测特征在很大程度上仍未得到探索。因此，迄今尚未证实发现此类放射源。在数值模拟的支持下，我们提出了一种新的光度方法来识别黑洞种子候选者在深多波长调查。我们预测，这些高度模糊的来源的特点是陡峭的红外光谱（1.6-4.5微米），即非常红的颜色。该方法选择了在CANDELS/GOODS-S巡天中发现的仅有的2个具有强大X射线探测的天体，其光度红移z > 6。仅用恒星成分来拟合它们的红外光谱将需要不切实际的恒星形成速率（每年超过2000个太阳质量）。迄今为止，选定的天体代表了最有希望的黑洞种子候选者，可能通过直接坍缩黑洞方案形成，预测质量>10^5太阳质量。虽然这一结果是基于迄今为止对高z源的最佳光度观测，但预计光谱和更深的X射线数据将取得更多进展。即将到来的天文台，如JWST，将大大扩大这项工作的范围。
英文摘要：
The first black hole seeds, formed when the Universe was younger than 500 Myr, are recognized to play an important role for the growth of early (z ~ 7) super-massive black holes. While progresses have been made in understanding their formation and growth, their observational signatures remain largely unexplored. As a result, no detection of such sources has been confirmed so far. Supported by numerical simulations, we present a novel photometric method to identify black hole seed candidates in deep multi-wavelength surveys. We predict that these highly-obscured sources are characterized by a steep spectrum in the infrared (1.6-4.5 micron), i.e. by very red colors. The method selects the only 2 objects with a robust X-ray detection found in the CANDELS/GOODS-S survey with a photometric redshift z > 6. Fitting their infrared spectra only with a stellar component would require unrealistic star formation rates (>2000 solar masses per year). To date, the selected objects represent the most promising black hole seed candidates, possibly formed via the direct collapse black hole scenario, with predicted mass >10^5 solar masses. While this result is based on the best photometric observations of high-z sources available to date, additional progress is expected from spectroscopic and deeper X-ray data. Upcoming observatories, like the JWST, will greatly expand the scope of this work.
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