Introducing the Search for Intermediate-mass Black-hole In Nearby Galaxy (SIBLING) Survey

Abstract

Intermediate mass black holes (IMBHs) have masses between the $10^2-10^6$ M${}_{\odot }$ and are key to our understanding of the formation of massive black holes. The known population of IMBH remains small, with a few hundred candidates and only a handful of them confirmed as bona-fide IMBHs. Until now, the most widely used selection method is based on spectral analysis. Here we present a methodology to select IMBH candidates via optical variability analysis of the nuclear region of local galaxies ($z⩽0.35$). Active IMBH accreting at low rates show small amplitude variability with time scales of hours, as it is seen in one of the known IMBH NGC4395. We found a sample of $\sim 500$ galaxies evidencing fast and small amplitude variation in their weekly based light curves. We estimate an average occupancy fraction of 4\% and a surface density of $\sim 3$ deg${}^{-2}$, which represent an increase by a factor of $\sim 40$ compared to previous searches. A large fraction ($78\%$) of the candidates are in spiral galaxies. We preliminary confirm the AGN nature of 22 sources via BPT diagrams using SDSS legacy spectra. Further confirmation of these candidates will require multiwavelength observations, especially in X-ray and radio bands.

16 pages (including Appendix), 15 figures

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• Optical Variability of the Dwarf AGN NGC 4395 from the Transiting Exoplanet Survey Satellite
• Dwarf AGNs from Variability for the Origins of Seeds (DAVOS): Intermediate-mass black hole demographics from optical synoptic surveys
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• A consistency-test for determining whether ultra-compact dwarf galaxies could be the remnant nuclei of threshed galaxies
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• Intermediate Mass Ratio Inspirals in Milky Way Galaxies
• Variability as a new discovery channel for Intermediate-Mass Black Holes in the Time Domain Era
• Search of Intermediate Mass Black Holes at Low Redshift with Intra-night Variability