AGN dichotomy beyond radio loudness: a Gaussian Mixture Model analysis. (arXiv:2007.07271v1 [astro-ph.GA])
<a href="http://arxiv.org/find/astro-ph/1/au:+Beaklini_P/0/1/0/all/0/1">Pedro P.B.Beaklini</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Quadros_A/0/1/0/all/0/1">Allan V.C.Quadros</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Avellar_M/0/1/0/all/0/1">Marcio G.B. de Avellar</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Dantas_M/0/1/0/all/0/1">Maria L.L. Dantas</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Cancado_A/0/1/0/all/0/1">André L.F. Cançado</a>
Since the discovery of radio emissions from 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 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 AGN. 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 datasets, 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.
Since the discovery of radio emissions from 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 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 AGN. 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 datasets, 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.
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