Investigation on Young radio AGNs based on SDSS spectroscopy

Abstract

The Gigahertz Peaked Spectrum (GPS) sources, Compact Steep Spectrum (CSS) radio sources, and High Frequency Peakers (HFP) radio sources are thought to be young radio AGNs, at the early stage of AGN evolution. We investigated the optical properties of the largest sample of 126 young radio AGNs based on the spectra in SDSS DR12. We find the black hole masses $M_{\rm BH}$ range from $10^{7.32}$ to $10^{9.84}$ $\rm M_{sun}$, and the Eddington ratios $R_{\rm edd}$ vary from $10^{-4.93}$ to $10^{0.37}$, suggesting that young radio AGNs have various accretion activities and not all are accreting at high accretion rate. Our young radio sources generally follow the evolutionary trend towards large-scale radio galaxies with increasing linear size and decreasing accretion rate in the radio power - linear size diagram. The radio properties of low luminosity young radio AGNs with low $R_{\rm edd}$ are discussed. The line width of [O III] $\lambda5007$ core ($\sigma_{\rm [O III]}$) is found to be a good surrogate of stellar velocity dispersion $\sigma_{\ast}$. The radio luminosity $L_{\rm 5GHz}$ correlates strongly with [O III] core luminosity $L_{\rm [O III]}$, suggesting that radio activity and accretion are closely related in young radio sources. We find one object that can be defined as narrow-line Seyfert 1 galaxies (NLS1s), representing a population of young AGNs both with young jet and early accretion activity. The optical variabilities of 15 quasars with multi-epoch spectroscopy were investigated. Our results show that the optical variability in young AGN quasars presents low variations ($\leqslant60\%$) similar to the normal radio-quiet quasars.