Presentation #316.06 in the session AGN and Quasars V.
Systematic studies of quasars with young jets are essential for understanding the triggering, formation, and life cycles of jets and their connection to galaxy evolution. However, the faint (mJy-level) and high-redshift (z>1) populations of young radio jets have yet to be fully explored due to the limitations (e.g. sensitivity and/or resolution) of historical radio surveys. The comparison of sensitive widefield radio survey data taken over multiple epochs spanning years or longer provides a new opportunity to identify this unexplored population of young quasar jets on the basis of variability. Using this strategy, we compiled a sample of powerful quasars that appear to have recently “switched-on” based on a comparison between data from the Very Large Array Sky Survey (VLASS) and the Faint Images of the Radio Sky at Twenty-cm (FIRST) survey taken 1-2 decades apart. Multi-band VLA follow-up observations revealed compact (sub-kpc) morphologies and peaked radio spectral shapes consistent with young jets. However, additional multi-band follow-up is necessary to test whether alternative mechanisms, such as relativistic beaming, might contribute significantly to the radio variability. Here, we present new multi-band VLA data taken over a second observing epoch. We quantify the radio spectral variability on timescales of one year. Most sources exhibit steady or mildly varying radio spectral shapes that are consistent with young quasar jets. This study highlights the importance of multi-epoch, multi-band follow-up observations for monitoring the spectral variability of candidate young jets identified in the radio time domain.