Computer Science
Scientific paper
Nov 2011
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011sacm.confe..48p&link_type=abstract
The Starburst-AGN Connection under the Multiwavelength Limelight, held 14-16 September 2011. Published online at http://www.scio
Computer Science
Scientific paper
The dusty nuclear regions of luminous infra-red galaxies (LIRGs) are heated by either an intense burst of massive star formation, an active galactic nucleus (AGN), or a combination of both. Disentangling the contribution of each of those putative dust-heating agents is a challenging task, and direct imaging of the innermost few pc can only be accomplished at radio wavelengths, using very high-angular resolution observations. We observed the nucleus A of the interacting starburst galaxy Arp 299, using very long baseline interferometry (VLBI) radio observations at 1.7 and 5.0 GHz. Our aim was to characterize the compact sources in the innermost few pc region of Arp299-A, as well as to detect recently exploded core-collapse supernovae. We used the European VLBI Network (EVN) to image the 1.7 and 5.0 GHz compact radio emission of the parsec-scale structure in the nucleus of Arp 299-A with milliarcsecond resolution. Our EVN observations show that one of the compact VLBI sources, A1, previously detected at 5.0 GHz, has a flat spectrum between 1.7 and 5.0 GHz and is the brightest source at both frequencies. Our 1.7 GHz EVN image shows also diffuse, low-surface brightness emission extending westwards from A1 and displays a prominent core-jet structure. The morphology, radio luminosity, spectral index and ratio of radio-to-X-ray emission of the A1-A5 region is consistent with a low-luminosity AGN (LLAGN), and rules out the possibility that it is a chain of young radio supernovae (RSNe) and supernova remnants (SNRs). We therefore conclude that A1-A5 is the long-sought AGN in Arp 299-A. This finding may suggest that both starburst and AGN are frequently associated phenomena in mergers. We also found that a recently (~8 yr-old) exploding core-collapse supernova is located at the mere distance (projected) of two parsecs from the putative AGN in Arp 299-A, which makes this supernova one of the closest to a central supermassive black hole ever detected. This result may also be relevant to accreting models in the central regions of galaxies, since it is not easy to explain the existence of very massive, supernova progenitor stars so close to an AGN. While seemingly contradictory, this could explain the low-luminosity of the AGN we see in Arp~299-A. In fact, since massive stars shed large amounts of mechanical energy into their surrounding medium, thereby significantly increasing its temperature, those massive stars would hinder the accretion of material to the central black hole, which could in turn result in a less powerful AGN than usual.
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