Cake Talk: Kenneth Wong – University of Copenhagen

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Cake Talk: Kenneth Wong

Kenneth Wong (Academia Sinica Institute of Astronomy and Astrophysics)


The Inner Mass Distribution of the Gravitational Lens SDP.81 from ALMA Observations


The central image of a strongly lensed background source places constraints on the foreground lens galaxy's inner mass profile slope, core radius and mass of its nuclear supermassive black hole. Using high-resolution long-baseline ALMA observations and archival HST imaging, we model the gravitational lens SDP.81 and search for the demagnified central image. There is central continuum emission from the lens galaxy's AGN but no evidence of the central lensed image in any molecular line. We use the CO J=5-4 map to determine the flux limit of the central image excluding the AGN continuum. We predict the flux density of the central image and use the limits from the ALMA data to constrain the inner mass distribution of the lens. For the core radius of 0.15" measured from HST photometry of the lens galaxy assuming that the central flux is completely attributed to the AGN, we find that a black hole mass of log(M_BH/M_sun) > 8.5 is preferred. Deeper observations with a detection of the central image will significantly improve the constraints of the inner mass distribution of the lens galaxy.