Estimating black hole masses in young radio sources using CFHT spectroscopy

The correlation between black hole masses and stellar velocity dispersions provides an efficient method to determine the masses of black holes in active galaxies. We obtained optical spectra of a Compact-Steep-Spectrum (CSS) galaxy 4C +29.70, using the Canada-France-Hawaii Telescope (CFHT) equipped with OSIS, in August 6, 2003. Several stellar absorption features, such as Mg I (5175Å), Ca E band (5269Å) and Na D (5890Å), were detected in the spectra. The stellar velocity dispersion, $σ$, of the host galaxy, measured from absorption features is $\rm \approx 250 km s^{-1}$. If 4C +29.70 follows the $\rm M_{BH}-σ$ relation established for nearby galaxies, then its central black hole has a mass of $\rm \approx3.3\times10^{8}M_{\odot}$. In combination with the black hole masses of seven GPS galaxies in Snellen et al. (2003), we find that the average black hole mass of these eight young radio sources is smaller than that of the Bettoni et al. (2003) sample of extended radio galaxies. This may indicate that young radio sources are likely at the early evolutionary stage of radio galaxies, at which the central black holes may still undergo rapid growth. However, this needs further investigations.