Curvature of the spectral energy distribution, Compton dominance and synchrotron peak frequency in jetted AGNs

We collect a large sample with a reliable redshift detected by the Fermi satellite after 10 years of data (4FGL-DR2), including blazars, $γ$-ray Narrow-line Seyfert 1 galaxies ($γ$NLS1s), and radio galaxies. The spectral energy distributions (SEDs) of these Fermi sources are fitted by using a second-degree polynomial, and some important parameters including spectral curvature, synchrotron peak frequency, and peak luminosity are obtained. Based on those parameters, we discuss the Fermi blazar sequence and the particle acceleration mechanism. Our main results are as follows:(i) By studying the relationship between the synchrotron peak frequency and the synchrotron peak frequency luminosity, jet kinetic power, and $γ$-ray luminosity for jetted AGNs, we find an ``L'' shape in the Fermi blazar sequence. (ii) There is a significant anti-correlation between Compton dominance, black hole spin, and the synchrotron peak frequency for jetted AGNs, respectively. These results support that the $γ$NLS1s and radio galaxies belong to the Fermi blazar sequence. (iii) On the basis of previous work, statistical or stochastic acceleration mechanisms can be used to explain the relationship between synchrotron peak frequency and synchrotron curvature. For different subclasses, the correlation slopes are different, which implies that the Fermi sources of different subclasses have different acceleration mechanisms. (iv) The FSRQs and $γ$NLS1s have a higher median spin of a black hole than BL Lacs and radio galaxies.