The nature of compact radio-loud AGN: a systematic look at the LOFAR AGN population
arXiv:2402.19424
Abstract
We investigate the nature of low-luminosity radio-loud active galactic nuclei (RLAGN) selected from the LOFAR Two-metre Sky Survey (LoTSS) first data release (DR1). Using optical, mid-infrared, and radio data, we have conservatively selected 55 radiative AGN candidates from DR1 within the redshift range . We show using high-frequency {\it Karl G. Jansky} Very Large Array (VLA) observations that 10 out of 55 objects show radio emission on scales kpc, 42 are compact at the limiting resolution of 0.35 arcsec (taking an upper limit on the projected physical size, this corresponds to less than 1 kpc), and three are undetected. The extended objects display a wide range of radio morphologies: two-jet (5), one-jet (4), and double-lobed (1). We present the radio spectra of all detected radio sources which range from steep to flat/inverted and span the range seen for other compact radio sources such as compact symmetric objects (CSOs), compact steep spectrum (CSS) sources, and gigahertz peaked-spectrum (GPS) sources. Assuming synchrotron self-absorption (SSA) for flat/inverted radio spectrum sources, we predict small physical sizes for compact objects to range between pc. Alternatively, using free-free absorption (FFA) models, we have estimated the free electron column depth for all compact objects, assuming a homogeneous absorber. We find that these objects do not occupy a special position on the power/linear size () diagram but some share a region with radio-quiet quasars (RQQs) and so-called `FR0' sources in terms of radio luminosity and linear size.
Accepted for publication in the Monthly Notices of the Royal Astronomy Society (MNRAS) journal