We report the discovery of three low-mass black hole candidates residing in the centers of low-mass galaxies at z < 0.3 in the Chandra Deep Field - South Survey .
These black holes are initially identified as candidate active galactic nuclei based on their X-ray emission in deep Chandra observations .
Multi-wavelength observations are used to strengthen our claim that such emission is powered by an accreting supermassive black hole .
While the X-ray luminosities are low at L _ { X } \sim 10 ^ { 40 } erg s ^ { -1 } ( and variable in one case ) , we argue that they are unlikely to be attributed to star formation based on H \alpha or UV-fluxes .
Optical spectroscopy with Keck/DEIMOS and VLT/FORS allows us to ( 1 ) measure accurate redshifts , ( 2 ) confirm their low stellar host mass , ( 3 ) investigate the source ( s ) of photo-ionization , and ( 4 ) estimate extinction .
With stellar masses of M _ { * } < 3 \times 10 ^ { 9 } M _ { \sun } determined from HST/ACS imaging , the host galaxies are among the lowest mass systems known to host actively accreting black holes .
We estimate BH masses M _ { BH } \sim 2 \times 10 ^ { 5 } M _ { \sun } based on scaling relations between BH mass and host properties for more luminous systems .
In one case , a broad component of the H \alpha emission-line profile is detected thus providing a virial mass estimate .
Black holes in such low-mass galaxies are of considerable interest as the low-redshift analogs to the seeds of the most massive BHs at high redshift which have remained largely elusive to date .
Our study highlights the power of deep X-ray surveys to uncover such low-mass systems .