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G.A. Verdoes Kleijn (Leiden Observatory), S.A. Baum (STScI), P.T. de Zeeuw (Leiden Observatory)
I report on a study of the central regions in 21 nearby (v < 7000km/s) galaxies with large scale radio jets using HST photometry and spectroscopy. The main goal of this study is twofold. First, to better understand the physics of these radio-loud active galactic nuclei (AGN) acting on tens of parsec scales. Second, to constrain the triggering mechanism of the radio-loud activity by comparing the radio-loud nuclei with their radio-quiet counterparts. The HST/WFPC2 photometry indicates that the central stellar distributions resemble those of quiescent galaxies. Both galaxies with shallow and cuspy stellar cores appear capable of hosting a radio-loud active nucleus. Central reservoirs of dust and gas are detected in all sample galaxies. There is a dichotomy in apparent dust morphology and orientation. I discuss the relative intrinsic configuration of the radio jets, galaxies and reservoirs of interstellar matter and its connection to nuclear activity.
The radio and optical continuum/line fluxes from the AGN are strongly correlated. Both radio and optical emission are likely to be jet synchrotron emission and the amplitude of the correlation scatter puts constraints on its Doppler boosting. The active nuclei of nearby elliptical galaxies which do not harbor large scale radio jets seem to follow similar correlations. HST/STIS spectroscopy was used to map the kinematics and emission-line ratios of the central emission-line gas. I report on the results from dynamical modeling to measure black hole masses.
Thus, main conclusions of this study are: (i) there is no photometric indication that the activity in nearby elliptical galaxies is triggered by specific properties of the central stellar distributions, and (ii) there appears to be a continuous sequence in the properties of the radio-loud and quiet active nuclei in nearby elliptical galaxies.
Financial support for this work was provided by NASA/STScI and Leiden Observatory.
The author(s) of this abstract have provided an email address for comments about the abstract: verdoes@strw.leidenuniv.nl