Estimating Black Hole Mass in the Lensing Galaxy of the Gravitational Lens SDP.81 using ALMA
Satoki Matsushita1*, Kenneth C. Wong2, Sherry H. Suyu3,1
1Institute of Astronomy and Astrophysics, Academia Sinica, Taipei, Taiwan
2National Astronomical Observatory of Japan, Mitaka, Japan
3Max Planck Institute for Astrophysics, Garching, Germany
* presenting author:Satoki Matsushita,
In a strong gravitational lens system, the central image of the background lensed galaxy is demagnified by the foreground lensing galaxy, and its brightness is very sensitive to the innermost mass distribution of the foreground galaxy, which contains the mass of the central supermassive black hole. Measuring the brightness of this demagnified central image will therefore provide us the black hole mass of the foreground galaxy. In optical images, this central image of the background galaxy is heavily contaminated by the foreground galaxy. In contrast, in the millimeter/submillimeter regime, the emission from the foreground galaxy is generally weak compared to the lensed background galaxy. Millimeter/submillimeter observations thus provide an opportunity to detect the faint central image. Using the Science Verification (SV) data from the ALMA Long Baseline Campaign 2014, we tried to identify the central image of the background lensed galaxy in the gravitational lens SDP.81. Since we did not detect the central image of the background lensed galaxy, we set a lower limit of the supermassive black hole in the foreground lensing galaxy as log(M_BH/M_solar) ≧ 8.5. Based on this result, we show that sensitive long baseline observations of strong gravitational lenses using ALMA hold great promise for measuring black hole mass directly at cosmological distances.

Keywords: Black Hole Mass, Gravitational Lensing, ALMA, Long Baseline