局域Lyman Break星系中黑洞生长的证据
Evidence for Black Hole Growth in Local Analogs to Lyman Break Galaxies
摘要：
我们已经使用XMM-牛顿观测到六个莱曼破裂类似物（LBA）：具有与遥远的莱曼破裂星系非常相似的性质的罕见的本地星系群体的成员。我们的六个目标被特别选择，因为它们具有介于星爆和2型（模糊）AGN之间的光学发射线特性。我们新的X射线数据提供了一个重要的诊断活动星系核的存在。我们发现X射线光度为10^{42} erg/s，X射线与远红外光度的比值比纯星暴星系的值高出约3至30倍。这强烈地暗示了至少在某些星系中存在活动星系核。硬X射线（2-10 keV）与[O III]λ5007发射线的光度比比1型活动星系核低一个数量级，但与2型活动星系核的宽范围一致。要么活动星系核的硬X射线被显著地遮蔽，要么[O III]辐射被星暴所支配。我们在~ 6.4 keV处寻找了铁发射线，这是活动星系核的一个关键特征，但只探测到了~ 2σ水平的发射。最后，我们发现这些LBA中的中红外（24μm）连续光谱与[O III]λ5007光度的比值比2型活动星系核的平均值高0.8dex。结合所有这些线索，我们得出结论，活动星系核很可能存在，但热光度主要是由强烈的星暴产生的。如果这些黑洞在爱丁顿极限辐射，它们的质量将在10^5到10^6 M_{sun}之间。这些天体可能为研究早期宇宙中黑洞的生长过程提供理想的本地实验室。
英文摘要：
We have used XMM-Newton to observe six Lyman Break Analogs (LBAs): members of the rare population of local galaxies that have properties that are very similar to distant Lyman Break Galaxies. Our six targets were specifically selected because they have optical emission-line properties that are intermediate between starbursts and Type 2 (obscured) AGN. Our new X-ray data provide an important diagnostic of the presence of an AGN. We find X-ray luminosities of order 10^{42} erg/s and ratios of X-ray to far-IR luminosities that are higher than values in pure starburst galaxies by factors ranging from ~ 3 to 30. This strongly suggests the presence of an AGN in at least some of the galaxies. The ratios of the luminosities of the hard (2-10 keV) X-ray to [O III]λ5007 emission-line are low by about an order-of-magnitude compared to Type 1 AGN, but are consistent with the broad range seen in Type 2 AGN. Either the AGN hard X-rays are significantly obscured or the [O III] emission is dominated by the starburst. We searched for an iron emission line at ~ 6.4 keV, which is a key feature of obscured AGN, but only detected emission at the ~ 2σlevel. Finally, we find that the ratios of the mid-infrared (24μm) continuum to [O III]λ5007 luminosities in these LBAs are higher than the values for Type 2 AGN by an average of 0.8 dex. Combining all these clues, we conclude that an AGN is likely to be present, but that the bolometric luminosity is produced primarily by an intense starburst. If these black holes are radiating at the Eddington limit, their masses would lie in the range of 10^5 to 10^6 M_{sun}. These objects may offer ideal local laboratories to investigate the processes by which black holes grew in the early universe.
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