Intermediate-Mass Black Holes in Green Pea Galaxies (IMBH-GP) I: a Candidate Sample from LAMOST and SDSS

Kavli Affiliate: Linhua Jiang

| First 5 Authors: Ruqiu Lin, Zhen-Ya Zheng, Fang-Ting Yuan, Jun-Xian Wang, Chunyan Jiang

| Summary:

The scaling relation of central massive black holes (MBHs) and their host
galaxies is well-studied for supermassive BHs (SMBHs, $M_{rm BH} ge 10^6,
M_{rm odot}$). However, this relation has large uncertainties in the mass
range of the intermediate-mass BHs (IMBHs, $M_{rm BH} sim10^3-10^{6},
M_{rm odot}$). Since Green Pea (GP) galaxies are luminous compact dwarf
galaxies, which may be likely to host less massive SMBHs or even IMBHs, we
systematically search for MBHs in a large sample of 2190 GP galaxies at $z <
0.4$, selected from LAMOST and SDSS spectroscopic surveys. Here, we report a
newly discovered sample of 59 MBH candidates with broad H$alpha$ lines. This
sample has a median stellar mass of $10^{8.83pm0.11}, M_{rm odot}$ and
hosts MBHs with single-epoch virial masses ranging from $M_{rm BH} sim
10^{4.7}$ to $10^{8.5}, M_{rm odot}$ (median $10^{5.85pm0.64}, M_{rm
odot}$). Among the 59 MBH candidates, 36 have black hole masses $M_{rm BH}
le 10^{6}, M_{rm odot}$ (IMBH candidates), one of which even has $M_{rm
BH} lesssim 10^{5}, M_{rm odot}$. We find that the $M_{rm BH}-M_{rm *}$
relation of our MBH sample is consistent with the $M_{rm BH}-M_{rm bulge}$
relation for SMBHs, while is above the $M_{rm BH}-M_{rm *}$ relation for MBHs
in dwarf galaxies in the same mass range. Furthermore, we show that 25 MBH
candidates, including 4 IMBH candidates, have additional evidence of black hole
activities, assessed through various methods such as the broad-line width, BPT
diagram, mid-infrared color, X-ray luminosity, and radio emission. Our studies
show that it is very promising to find IMBHs in GP galaxies, and the BH sample
so obtained enables us to probe the connection between the MBHs and compact
dwarf galaxies in the low-redshift Universe.

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