NOVA | University of Groningen | 2015 Jun 01
[img3="This artist impression shows a galaxy with an ultraluminous nucleus and a double radio source straddling it -- a quasar. The radio-axis is more or less pointing towards the earth. Should one observe the object under a larger angle, the bright nucleus would be hidden behind a thick dust ring and hence be invisible. According to the unification model, the object would then be observed as a radio galaxy. (Credit: ESA, C. Carreau)"]http://www.astronomie.nl/media/medialib ... arreau.jpg[/img3][hr][/hr]Using the Herschel Space Observatory, an international group of astronomers led by Pece Podigachoski and Peter Barthel of the Kapteyn Institute at the University of Groningen (Netherlands) have found strong new evidence that quasars are in fact radio galaxies, observed under a favourable angle. Barthel proposed this unification model in 1989, on the basis of observations with optical and radio telescopes. The model found considerable support but also criticism. New observations in the far-infrared with Herschel provide strong evidence in its favour. The results of this research will appear shortly in The Astrophysical Journal Letters.
Quasars and radio galaxies are active phases in the life of a galaxy. Massive galaxies (ten to hundred times more massive than our galaxy, the Milky Way) harbour massive black holes in their nucleus. When such black holes become active by accreting matter, their immediate surroundings become very hot and the galaxy nucleus radiates an intense luminosity. Under certain conditions, a gigantic double radio source develops, straddling the galaxy. Barthel’s unification model states that the angle under which these radio-bright active galaxies are being observed is of crucial importance. An opaque dust ring surrounding the nucleus blocks its bright radiation in some directions but not in others. The Herschel observations in the far-infrared are in excellent agreement with the predictions of the model concerning the dust radiation in the active galaxies, both from their nuclear and larger scales.
The astronomers also report that combination of measurements in the infrared wavelength range indicate in a simple way if a galaxy has an active black hole or not. Moreover, the relative importance of the nuclear activity to the total energy output of the galaxy can in this way be assessed. This is an important diagnostic in future research concerning the growth of galaxies and their black holes in the early universe.
The Unification of Powerful Quasars and Radio Galaxies and Their Relation to Other Massive Galaxies - Pece Podigachoski et al
- Astrophysical Journal Letters 806(1) L11 (10 Jun 2015) DOI: 10.1088/2041-8205/806/1/L11
arXiv.org > astro-ph > arXiv:1505.03569 > 13 May 2015