Infrared SEDs of Seyfert Galaxies

  • Elitzur, Moshe (PI)

Grants and Contracts Details


As our understanding of the origin and evolution of normal galaxies grows. and as we learn more about the evolution of the extraordinary non-stellar activity that can appear in the nuclei of galaxies. we are changing our view of how these two phenomena are related. The evidence is pointing us to the idea that rather than nuclear activity being an aberrant event in the lifetimc of a fcw sclcct galaxics, it is likely to be an integral if relatively short-lived part of the evolution of all galaxies. Activc galactic nuclei. or AGNs. are powered by accretion onto a massivc black hole [1- 3]. Starbursts may be an inevitable consequence of the gas infall that is necessary to trigger the AGN [2. 4]. The observed relationship between black hole mass and bulge mass [5-8] suggests that nuclear activity is closely connected to star formation. Supporting this picture is the recent tlnding that the mean stellar age of narrow-linc AG'\Is is much younger than that of morphologically matched normal galaxies [9]. The evidence is therefore pointing us to the idea that nuclear activity is not an aberrant event in the lifetime of a few select galaxies; rather, an AGN may be an intcgral, albeit relatively short-lived. part of the evolution of all galaxies. Seyfert galaxies are the nearest and brightest class of AGN and are therefore arguably the best suited for studying the physics of the infall model and the resulting interplay between the AGN and the host galaxy. Recent detailed and statistical studies of Seyfert galaxies 110-12] are beginning to chart the evolutionary sequence that leads to the production of an AGN in disk galaxies and the dIect of that evolution on the host galaxy [13J. The picture that is emerging is one of a close tie between the galaxy environment and galaxy-galaxy interactions leading to a temporal sequence of circumnuclear starbursts and accretion onto the nuclear black hole [4, 14, 151. Recent studies have also found that star formation may be particularly enhanced in type 2 (narrow-line) Seyfcrts [] 6-18]. In addition, type 2 nuclei appear to show more pronounced and richcr dust-lane morphology in HST images [19], and they may also be intrinsically dustier than type 1 (broad-line) Seyferts 120]. as might be expected in a starburst environment. One way to interpret these results is that there may be an evolutionary connection between type I and type 2 Seyferts [13. 21]; perhaps a Seyfert galaxy begins as a nuclear starburst, the starburst disrupts the local ISM and triggers an apparcnt Seyfert 2 AGN [22], and eventually, as thc starburst recedes, a Seyfert 1 AGN is revealed. Ultimatcly the accretion disk depletes. leaving behind a low luminosity AGN [9J.
Effective start/end date7/15/047/31/07


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