How far actually is the Galactic Center IRS 13E3 from Sagittarius A

The Galactic Center IRS 13E cluster is a very intriguing infrared object located at similar to 0.13 pc from Sagittarius A* (Sgr A*) in projection distance. There are arguments both for and against the hypothesis that a dark mass like an intermediate mass black hole (IMBH) exists in the cluster. We recently detected the rotating ionized gas ring around IRS 13E3, which belongs to the cluster, in the H30 alpha recombination line using ALMA. The enclosed mass is derived to be M-encl similar or equal to 2 x 10(4) M-circle dot, which agrees with an IMBH and is barely less than the astrometric upper limit mass of an IMBH around Sgr A*. Because the limit mass depends on the true three-dimensional (3D) distance from Sgr A*, it is very important to determine it observationally. However, the 3D distance is indefinite because it is hard to determine the line-of-sight (LOS) distance by usual methods. We attempt here to estimate the LOS distance from spectroscopic information. The CH3OH molecule is easily destroyed by the cosmic rays around Sgr A*. However, we detected a highly excited CH3OH emission line in the ionized gas stream associated with IRS 13E3. This indicates that IRS 13E3 is located at r greater than or similar to 0.4 pc from Sgr A*.