First astrostatistics paper accepted by MNRAS - AGN dichotomy beyond radio loudness

AGN dichotomy beyond radio loudness: a Gaussian mixture model analysis

I am excited that my first astrostatistics paper, with my friends Pedro Paulo B. Beaklini, Marcio G. B. de Avellar, Maria Luiza Linhares Dantas, and André Cançado, has been accepted by Monthly Notices of the Royal Astronomical Society!

Beaklini, P. P. B., Quadros, A. V. C., de Avellar, M. G. B., Dantas, M. L. L., & Cançado, A. L. F. (2020). AGN dichotomy beyond radio loudness: a Gaussian mixture model analysis. Monthly Notices of the Royal Astronomical Society, 497(2), 1463-1474. https://doi.org/10.1093/mnras/staa2072

What the paper is about

Since their discovery, quasars have been traditionally split into radio-loud and radio-quiet sources, based on the ratio between their optical and radio emission. Whether this split reflects two real populations of active galactic nuclei (AGNs) or is an artifact of a single, very heterogeneous population has been an open question for decades.

Instead of looking at radio loudness alone, we used a soft clustering scheme based on Gaussian mixture models (GMM) to classify the objects using several parameters at the same time: black hole mass, colour, the R loudness index, and the usual radio and B-band luminosities. We applied the GMM to four independent catalogues combining optical and radio information.

The dichotomy persisted in all four data sets, although the discriminating power changed with the choice of parameters. Radio loudness alone does not seem to be enough to reveal the two populations, but the evidence for two groups of AGNs holds when other parameters are considered. Our results suggest that the dichotomy is real, not a misleading effect of the data.

Abstract

Since the discovery of quasi-stellar objects (QSOs), also known as quasars, they have been traditionally subdivided as radio-loud and radio-quiet sources. Whether such division is a misleading effect from a highly heterogeneous single population of objects, or real has yet to be answered. Such dichotomy has been evidenced by observations of the flux ratio between the optical and radio emissions (usually B band and 5 GHz). Evidence of two populations in quasars and samples of a wide diversity of active galactic nuclei (AGNs) has been accumulated over the years. Other quantities beyond radio loudness also seem to show the signature of the existence of two different populations of AGNs. To verify the existence of a dichotomy through different parameters, we employed a soft clustering scheme, based on the Gaussian mixture model (GMM), to classify these objects simultaneously using the following parameters: black hole mass, colour, and R loudness index, as well as the usual radio and B-band luminosity. To investigate whether different kinds of AGNs manifest any population dichotomy, we applied GMM to four independent catalogues composed of both optical and radio information. Our results indicate the persistence of a dichotomy in all data sets, although the discriminating power differs for different choices of parameters. Although the radio loudness parameter alone does not seem to be enough to display the dichotomy, the evidence of two populations of AGNs could persist even if we consider other parameters. Our research suggests that the dichotomy is not a misleading effect but real.

• Article: https://doi.org/10.1093/mnras/staa2072
• Full list of publications: /publications/