Daily Image

Click here or on the picture for a full size image.

Colloquium September 4, 2008 by A. Marecki (Torun CfA): "Post-active galaxies - more ubiquitous than we thought before"

Submitter: Antonis Polatidis
Description: Is activity a permanent feature of a given active galaxy? This fundamental question seems to be answered today - the activity is episodic, i.e. a normal galaxy can become active during its lifetime, e.g. as a result of a merger event, and vice versa: the active phase of a galaxy can come to its end. Observations of relic lobes created by previously radio-loud active galaxy are perfectly suited to trace that transition. This is because lobes that are no longer powered by the AGN can stay in the so-called coasting phase for a relatively long time and so they can be detected when the host galaxy already appears as a normal one. A galaxy of this kind can be labelled "post-active". Detection of relic lobes of a formerly active galaxy is not a trivial task but it has recently become possible by means of overlaying modern, comprehensive optical and radio catalogues. Searching for radio identifications of optical extragalactic objects this way has led us to a discovery of many post-active galaxies like e.g. J090805+060615. In optical domain - as seen in SDSS - J090805+060615 appears as a perfectly normal galaxy, particularly when one looks at its spectrum devoid of any AGN-related features. However, its radio identification in FIRST reveals very faint, relic lobes straddling the host galaxy. It turns out then that J090805+060615 must have been active and radio-loud in the past and so now it should be regarded as a post-active galaxy. At the current stage of this project, it is difficult to say how many normal galaxies are actually post-active but it's likely that this number is higher than we thought before.
Copyright: A. Marecki
  Follow us on Twitter
Please feel free to submit an image using the Submit page.