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arXiv 1802.01567astro-ph.GA
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在钱德拉COSMOS遗产巡天中矮星系中的中等质量黑洞达到红移$\sim$ 2.4

Intermediate-mass black holes in dwarf galaxies out to redshift $\sim$ 2.4 in the Chandra COSMOS Legacy Survey

M. Mezcua, F. Civano, S. Marchesi, H. Suh, G. Fabbiano, M. Volonteri

摘要:

我们提出了一个样本的40个活动星系在矮星系的红移$z \lesssim$ 2.4。这些星系是从\textit{Chandra} COSMOS-Legacy巡天中得出的,其恒星质量为$10^{7}\leq M_{*}\leq3 \times 10^{9}$ M $_{\odot}$。大多数矮星系都在形成恒星。除去恒星形成对X射线辐射的贡献后,这40个矮星系的活动星系核光度都在$L_\mathrm{0.5-10 keV} \sim10^{39} - 10^{44}$ erg s $^{-1}$范围内。在$z > 0.5$的12个源中,我们的样本构成了矮星系中活动星系核最高红移的发现。记录保持者是$z = 2.39$和$L_\mathrm{0.5-10 keV} \sim 10^{44}$ erg s $^{-1}$的1192。其中一个矮星系有$M_\mathrm{*} = 6.6 \times 10^{7}$ M $_{\odot}$,是迄今为止发现的最小质量的活动星系核。所有的活动星系核都属于2型,与中等质量黑洞(BH)的宿主一致,其质量为$\sim 10^{4} - 10^{5}$ M $_{\odot}$和典型的爱丁顿比$> 1\%$。我们还研究了演化,修正的完整性,AGN分数与恒星质量,X射线光度,和红移的矮星系$z$ = 0.7。我们发现$10^{9}< M_{*}\leq3 \times 10^{9}$ M $_{\odot}$和$L_\mathrm{X} \sim 10^{41}-10^{42}$ erg s $^{-1}$的活动星系核分数为$\sim$ 0 4%,$z \leq$ 0 3,它随X射线光度和恒星质量的减小而减小。与大质量星系不同的是,活动星系核的分数似乎随着红移而减少,这表明矮星系中活动星系核的演化与高质量星系不同。考虑到潜在的警告,结果似乎有利于早期宇宙中种子黑洞的直接坍缩形成机制。

英文摘要:

We present a sample of 40 AGN in dwarf galaxies at redshifts $z \lesssim$ 2.4. The galaxies are drawn from the \textit{Chandra} COSMOS-Legacy survey as having stellar masses $10^{7}\leq M_{*}\leq3 \times 10^{9}$ M$_{\odot}$. Most of the dwarf galaxies are star-forming. After removing the contribution from star formation to the X-ray emission, the AGN luminosities of the 40 dwarf galaxies are in the range $L_\mathrm{0.5-10 keV} \sim10^{39} - 10^{44}$ erg s$^{-1}$. With 12 sources at $z > 0.5$, our sample constitutes the highest-redshift discovery of AGN in dwarf galaxies. The record-holder is cid\_1192, at $z = 2.39$ and with $L_\mathrm{0.5-10 keV} \sim 10^{44}$ erg s$^{-1}$. One of the dwarf galaxies has $M_\mathrm{*} = 6.6 \times 10^{7}$ M$_{\odot}$ and is the least massive galaxy found so far to host an AGN. All the AGN are of type 2 and consistent with hosting intermediate-mass black holes (BHs) with masses $\sim 10^{4} - 10^{5}$ M$_{\odot}$ and typical Eddington ratios $> 1\%$. We also study the evolution, corrected for completeness, of AGN fraction with stellar mass, X-ray luminosity, and redshift in dwarf galaxies out to $z$ = 0.7. We find that the AGN fraction for $10^{9}< M_{*}\leq3 \times 10^{9}$ M$_{\odot}$ and $L_\mathrm{X} \sim 10^{41}-10^{42}$ erg s$^{-1}$ is $\sim$0.4\% for $z \leq$ 0.3 and that it decreases with X-ray luminosity and decreasing stellar mass. Unlike massive galaxies, the AGN fraction seems to decrease with redshift, suggesting that AGN in dwarf galaxies evolve differently than those in high-mass galaxies. Mindful of potential caveats, the results seem to favor a direct collapse formation mechanism for the seed BHs in the early Universe.

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