Institute of Astronomy

Using IFU data to disentangle the starburst-AGN connection

SpeakerTalk DateTalk Series
Rebecca Davies4 July 2014Institute of Astronomy Galaxies Discussion Group


The physical mechanisms driving the complex interplay between star-formation and AGN activity in galaxies are poorly understood. Spatially resolved spectroscopy presents the potential to probe the radial variations in star formation rate, stellar age and star-formation history, and analyse how these properties differ across the AGN host galaxy population. However, the
majority of integral field unit (IFU) surveys are focused at visible wavelengths, where spectroscopic star-formation rate indicators are strongly contaminated by AGN activity. In this talk, I will show that IFU data allow star-forming and AGN-dominated regions to be resolved both spatially and spectrally in local AGN host galaxies. The presence of curved "starburst-AGN
mixing sequences" on optical diagnostic diagrams allows AGN fractions to be calculated on a spaxel-by-spaxel basis. Both the star-formation and the AGN
contribute significantly to the global emission of [OIII], [OII] and Hbeta. We calculate theoretical starburst-AGN mixing curves and show that they are
able to reproduce our observed mixing sequences. We also present a new diagnostic for starburst-AGN mixing which requires only the [OII] 3727, 3729, [OIII] 5007 and Hbeta 4861 emission lines, and can therefore be used to
calculate AGN fractions up to redshifts as high as z \sim 0.85 (optical) and z \sim 3.5 (near infrared). We anticipate that this diagnostic will facilitate
studies of the relative optical contribution of star-formation and AGN activity over cosmic time.


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