Speaker
Description
Peaked-spectrum sources, characterized by their distinctive peaked radio spectra, are likely progenitors of radio loud AGN and serves as an important tool to understand the formation and evolution of AGN. The new, high sensitivity Low Frequency Array (LOFAR) surveys make it possible to study these sources to a low frequency (< 100 MHz). In this work, for a sample of 1520 quasars, we use the LOFAR Low Band Array (LBA) 54 MHz, High Band Array (HBA) 144 MHz, and the Very Large Array (VLA) FIRST 1.4 GHz data to measure the spectral index: $\alpha^{144}_{54}$ and $\alpha^{1400}_{144}$. For all samples, there is no significant evolution of the spectral index with the redshift. Compared to compact sources, the extended sources have a steeper spectral index. We also use these parameters to find megahertz peaked sources. We find that the fraction of megahertz peaked spectrum sources is almost constant with the evolution of redshift, bolometric luminosity, and supermassive black hole (SMBH) mass, which points out that the fraction of MPS sources does not undergo significant changes in relation to the host galaxies' properties.
