Nuclei of early-type dwarf galaxies (dEs) are usually younger than the galaxy main body, and such discrepancy in age has been a puzzle. To explore the origin of young nuclei in dEs, we study a sample of dEs having compact star-forming blobs that are visually similar to dEs' nuclei but by far bluer. We find that (1) the compact star-forming blobs have a typical stellar mass of one percent of the host galaxy stellar mass; (2) some of the blobs are positioned slightly off from the center of the galaxies; (3) the H$α$ equivalent width measured from the publicly available Sloan Digital Sky Survey fiber spectroscopy shows their formation ages being an order of few Mega-year; and (4) their emission line metallicities, 12\,+\,log(O/H), are as high as the solar value, while the underlying galaxies have the typical stellar populations of dEs, i.e., log(Z/Z$_{\sun}$)\,$\sim$\,$-0.8$. Based on the results, we argue that the central star-forming blobs can provide a caught-in-the-act view of nuclei formation in dEs, and discussing possible formation mechanisms of young nuclei in old dEs. We particularly propose that these off-centered compact star-forming regions may act as seeds of nuclei as proposed in the `wet migration' scenario of \cite{Guillard16}.
Are "Changing-Look" Active Galactic Nuclei Special in the Coevolution of Supermassive Black Holes and their Hosts? II. The Case of Changing-Look Narrow-Line Seyfert 1 Galaxies
National Astronomical Observatories, Chinese Academy of Sciences（中国科学院国家天文台）；Guangxi Key Laboratory for Relativistic Astrophysics, School of Physical Science and Technology, Guangxi University（广西大学物理科学与技术学院相对论天体物理广西重点实验室）；School of Astronomy and Space Science, University of Chinese Academy of Sciences（中国科学院大学天文与空间科学学院）；Department of Astronomy, University of California, Berkeley（加州大学伯克利分校天文学系）；Max-Planck-Institut für Radioastronomie（马克斯·普朗克射电天文研究所）
The secular tidal disruption of stars by low-mass Super Massive Black Holes secondaries in galactic nuclei
恒星过于接近超大质量黑洞（SMBH）会产生潮汐破坏事件（TDE）。由于由此产生的恒星碎片可以产生电磁耀斑，因此TDE被认为可以探测星系核中单个SMBH的存在，否则它们会保持黑暗。在本文中，我们将展示恒星轨道IMBH二次扰动的SMBH主要。我们发现，恒星轨道的演变受到严重影响的主要SMBH由于长期的影响和恒星轨道相对于SMBH-IMBH轨道平面的高倾角结束其生命的TDE由于Kozai-Lidov振荡，从而照亮次级SMBH/IMBH。当SMBH的临界质量为$\approx 1.15 \times 10^8$ M $_{\odot}$以上时，老恒星星族中的典型恒星不会发生TDE，因为史瓦西半径超过了潮汐破裂半径。因此，由于这种大规模SMBH造成的任何TDE将保持黑暗。因此，在星系的膨胀质量大于$\approx 4.15\times 10^{10}$ M $_{\odot}$的星系中，不应该观测到TDE，除非还存在质量较低的次级SMBH或IMBH。因此，这里考虑的长期机制产生的TDE提供了一个有用的探测SMBH-SMBH/IMBH在最大质量的星系的二元性。我们进一步表明，TDE率可以是$\approx 10^{-4}-10^{-3}$ yr $^{-1}$，大多数TDE发生在$\approx 0.5$ Myr。最后，我们表明，恒星可能会喷出速度高达数千公里秒$^{-1}$，这可能有助于观察…
