# A Population of Bona Fide Intermediate Mass Black Holes Identified as Low Luminosity Active Galactic Nuclei

**Authors:** Igor V. Chilingarian, Ivan Yu. Katkov, Ivan Yu. Zolotukhin, Kirill A. Grishin, Yuri Beletsky, Konstantina Boutsia, David J. Osip  
**arXiv:** [1805.01467](https://arxiv.org/abs/1805.01467)  
**Date:** 2018-05-03  
**Summary page:** https://www.summarizepaper.com/en/paper/1805.01467v1/

## Key points

- The study focuses on identifying intermediate mass black holes (IMBHs) in galactic nuclei
- IMBHs are believed to be the missing link between smaller black holes and supermassive black holes
- Supermassive black holes exist in nearly every massive galaxy and correlate with properties of their host galaxies
- Two proposed channels for their formation include direct collapse of gas clouds or from smaller black holes formed by first stars
- Using data mining, this study identified a sample of 305 IMBH candidates with masses ranging from $3\times10^4$ to $2\times10^5 M_{\odot}$ that reside in galaxy centers and exhibit characteristic signatures of type-I active galactic nuclei (AGN)
- Ten sources were confirmed as AGNs, including five previously known objects that validated the method used
- All IMBH host galaxies possess small bulges and sit on the low-mass extension of the $M_{\mathrm{BH}}-M_{\mathrm{bulge}}$ scaling relation, suggesting that they have experienced very few major mergers over their lifetime
- This supports the stellar mass seed scenario for massive black hole formation from smaller black holes formed by first stars rather than direct collapse of gas clouds.
- Overall, this study provides important insights into the formation mechanisms for supermassive black holes and sheds light on an elusive population of intermediate mass black holes.

## Summary

This study focuses on the identification of intermediate mass black holes (IMBHs) in galactic nuclei, which are believed to be the missing link between smaller black holes and supermassive black holes. While the origin of supermassive black holes is still uncertain, they are known to exist in nearly every massive galaxy and correlate with properties of their host galaxies. The two proposed channels for their formation include direct collapse of gas clouds in the early universe or from smaller black holes formed by first stars. The latter channel would leave behind numerous IMBHs, but their existence has been debated due to a lack of definitive candidates. Using data mining in wide-field sky surveys and analyzing archival and follow-up optical spectra, this study identified a sample of 305 IMBH candidates with masses ranging from $3\times10^4$ to $2\times10^5 M_{\odot}$ that reside in galaxy centers and exhibit characteristic signatures of type-I active galactic nuclei (AGN). Ten sources were confirmed as AGNs, including five previously known objects that validated the method used. This confirms the existence of IMBHs in galactic nuclei and defines the first bona fide sample. All IMBH host galaxies possess small bulges and sit on the low-mass extension of the $M_{\mathrm{BH}}-M_{\mathrm{bulge}}$ scaling relation, suggesting that they have experienced very few major mergers over their lifetime. This supports the stellar mass seed scenario for massive black hole formation from smaller black holes formed by first stars rather than direct collapse of gas clouds. Overall, this study provides important insights into the formation mechanisms for supermassive black holes and sheds light on an elusive population of intermediate mass black holes.