The Radio Spectra of High Luminosity Compact Symmetric Objects (CSO-2s): Implications for Studies of Compact Jetted Active Galactic Nuclei

TL;DR

This study characterizes the radio spectra of high luminosity Compact Symmetric Objects (CSO-2s), revealing diverse spectral types and emphasizing the importance of complete, wide-frequency samples for understanding jetted active galactic nuclei.

Contribution

It provides the first comprehensive radio-spectrum analysis of high luminosity CSO-2s, highlighting spectral diversity and the need for inclusive, unbiased samples in AGN studies.

Findings

CSO-2s exhibit all spectral types, including flat, steep, and peaked spectra.

No clear correlation between spectral type and size, but a correlation between high-frequency spectral index and object type/size.

High-frequency spectral indices range from -1.3 to -0.3, affecting spectral-based discrimination of AGN types.

Abstract

This paper addresses, for the first time, a key aspect of the phenomenology of Compact Symmetric Objects (CSOs) -- the characteristics of their radio spectra. We present a radio-spectrum description of a complete sample of high luminosity CSOs (CSO-2s), which shows that they exhibit the \textit{complete} range of spectral types, including flat-spectrum sources ($\alpha \ge -0.5$), steep-spectrum sources ($\alpha < -0.5$), and peaked-spectrum sources. We show that there is no clear correlation between spectral type and size, but there is a correlation between the high-frequency spectral index and both object type and size. We also show that, to avoid biasing the data and to understand the various classes of jetted-AGN involved, the complete range of spectral types should be included in studying the general phenomenology of compact jetted-AGN, and that complete samples must be used, selected over a wide range of frequencies. We discuss examples that demonstrate these points. We find that the high-frequency spectral indices of CSO-2s span $-1.3 <\alpha_{\rm hi} < -0.3$, and hence that radio spectral signatures cannot be used to discriminate definitively between CSO-2s, binary galactic nuclei, and millilensed objects, unless they have $\alpha_{\rm hi} >-0.3$.