A new sample of 204 low-mass black holes ( LMBHs ) in active galactic nuclei ( AGNs ) is presented with black hole masses in the range of ( 1 - 20 ) \times 10 ^ { 5 } M _ { \odot } .
The AGNs are selected from a systematic search among galaxies in the seventh Data Release ( DR 7 ) of the Sloan Digital Sky Survey ( SDSS ) , by careful analyses of their optical spectra and precise measurement of spectral parameters .
Combining them with our previous sample selected from the SDSS DR 4 makes it the largest LMBH sample so far , totaling over 500 objects .
Some of the statistical properties of the combined LMBH AGN sample are briefly discussed , in the context of exploring the low-mass end of the AGN population .
Their X-ray luminosities follow the extension of the previously known correlation with the [ O III ] luminosity .
The effective optical-to-X-ray spectral indices \alpha _ { OX } , albeit with a large scatter , are broadly consistent with the extension of the relation with the near-UV luminosity L _ { 2500 \text { \AA } } .
Interestingly , a correlation of \alpha _ { OX } with black hole mass is also found in the sense that \alpha _ { OX } is statistically flatter ( stronger X-ray relative to optical ) for lower black hole mass .
Only 26 objects , mostly radio loud , were detected in radio at 20 cm in the FIRST survey , giving a radio loud fraction of 4 % .
The host galaxies of LMBHs have stellar masses in the range of 10 ^ { 8.8 } -10 ^ { 12.4 } M _ { \odot } and optical colors typical of Sbc spirals .
They are dominated by young stellar populations which seem to have undergone a continuous star formation history .