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Discovery of five low luminosity active galactic nuclei at the centre of the Perseus cluster

Submitter: S. Park, J. Yang, R. Oonk, Z. Paragi
Description: For her summerstudent project Songyoun Park (Department of Astronomy, Yonsei, Korea) visited JIVE to work with ASTRON and JIVE astronomers Raymond Oonk, Jun Yang (now at the Onsala Space Observatory, Sweden) and Zsolt Paragi on a radio VLBI project to study the continuum emission from radio galaxies in the center of the Perseus galaxy cluster. In particular she focused on the red-and-dead, elliptical galaxy NGC 1277 and how it compares with its peers in the dense environment at the center of the Perseus Galaxy cluster. According to optical observations, an over-massive black hole resides within NGC 1277 (van den Bosch et al. 2012).

Westerbork Synthesis Radio Telescope (WSRT) observations show that NGC 1277 and other nearby ellipticals emit radio emission, but the observations lack the spatial resolution to pinpoint the origin of this emission. Songyouns summer project consisted of analyzing high resolution very long baseline interferometric observations, conducted with the EVN, of these sources. She selected five (incl. NGC 1277) in the central 10 arcminute region of the Perseus cluster, imaged them with a resolution of about eight milliarcseconds and detected all of them at 1.4 GHz. They show non-variable, compact structure and brightness temperatures above 10 million K, implying that the radio emission is non-thermal. Ongoing nuclear star formation is also ruled out.

Songyoun concludes that these VLBI-detected radio sources are parsec-scale jets associated with supermassive black holes in low luminosity active galactic nuclei (LLAGNs), although there are no clear signs of this nuclear activity observed in the optical and infrared bands. Using the fundamental plane relation in black holes, we find no significant evidence for or against an extremely massive black hole hiding in NGC 1277. The work by Songyoun shows that VLBI observations are an excellent tool to disentanle the nature of radio emission in nearby galaxies. The results have been accepted for publication in MNRAS and are also available here: http://adsabs.harvard.edu/abs/2016arXiv161105986P

The picture shows the combined image of the radio-optical emission with the compact radio sources detected from the EVN observation on milliarcsecond scale. The EVN maps of our five early-type galaxies and the phase-reference check source (J0320+412) are presented on the top and left-hand side. The contour levels on the VLBI images are powers of two times the 3 sigma noise level. The green contours represent the 1.4 GHz WSRT radio continuum (Sijbring 1993) which is overlaid on a SDSS g band image.
Copyright: S. Park
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