We present a multi-wavelength study of the active galactic nucleus in the nearby ( D = 14.1 Mpc ) low mass galaxy IC 750 , which has circumnuclear 22 GHz water maser emission .
The masers trace a nearly edge-on , warped disk \sim 0.2 pc in diameter , coincident with the compact nuclear X-ray source which lies at the base of the \sim kpc-scale extended X-ray emission .
The position-velocity structure of the maser emission indicates the central black hole ( BH ) has a mass less than 1.4 \times 10 ^ { 5 } ~ { } M _ { \odot } .
Keplerian rotation curves fitted to these data yield enclosed masses between 4.1 \times 10 ^ { 4 } ~ { } M _ { \odot } and 1.4 \times 10 ^ { 5 } ~ { } M _ { \odot } , with a mode of 7.2 \times 10 ^ { 4 } ~ { } M _ { \odot } .
Fitting the optical spectrum , we measure a nuclear stellar velocity dispersion \sigma _ { * } = 110.7 ^ { +12.1 } _ { -13.4 } km s ^ { -1 } . From near-infrared photometry , we fit a bulge mass of ( 7.3 \pm 2.7 ) \times 10 ^ { 8 } ~ { } M _ { \odot } and a stellar mass of 1.4 \times 10 ^ { 10 } ~ { } M _ { \odot } .
The mass upper limit of the intermediate mass black hole in IC 750 falls roughly two orders of magnitude below the M _ { BH } - \sigma _ { * } relation and roughly one order of magnitude below the M _ { BH } - M _ { Bulge } and M _ { BH } - M _ { * } relations – larger than the relations ’ intrinsic scatters of ( 0.58 \pm 0.09 ) dex , 0.69 dex , and ( 0.65 \pm 0.09 ) dex , respectively .
These offsets could be due to larger scatter at the low mass end of these relations .
Alternatively , black hole growth is intrinsically inefficient in galaxies with low bulge and/or stellar masses , which causes the black holes to be under-massive relative to their hosts , as predicted by some galaxy evolution simulations .