We detected a compact ionized gas associated physically with IRS13E3 , an Intermediate Mass Black Hole ( IMBH ) candidate in the Galactic Center , in the continuum emission at 232 GHz and H30 \alpha recombination line using ALMA Cy.5 observation ( 2017.1.00503.S , P.I .
M.Tsuboi ) .
The continuum emission image shows that IRS13E3 is surrounded by an oval-like structure .
The angular size is 0 \farcs 093 \pm 0 \farcs 006 \times 0 \farcs 061 \pm 0 \farcs 004 ( 1.14 \times 10 ^ { 16 } cm \times 0.74 \times 10 ^ { 16 } cm ) .
The structure is also identified in the H30 \alpha recombination line .
This is seen as an inclined linear feature in the position-velocity diagram , which is usually a defining characteristic of a rotating gas ring around a large mass .
The gas ring has a rotating velocity of V _ { \mathrm { rot } } \simeq 230 km s ^ { -1 } and an orbit radius of r \simeq 6 \times 10 ^ { 15 } cm .
From these orbit parameters , the enclosed mass is estimated to be M _ { \mathrm { IMBH } } \simeq 2.4 \times 10 ^ { 4 } M _ { \odot } .
The mass is within the astrometric upper limit mass of the object adjacent to Sgr A ^ { \ast } .
Considering IRS13E3 has an X-ray counterpart , the large enclosed mass would be supporting evidence that IRS13E3 is an IMBH .
Even if a dense cluster corresponds to IRS13E3 , the cluster would collapse into an IMBH within \tau < 10 ^ { 7 } years due to the very high mass density of \rho \gtrsim 8 \times 10 ^ { 11 } M _ { \odot } pc ^ { -3 } .
Because the orbital period is estimated to be as short as T = 2 \pi r / V _ { \mathrm { rot } } \sim 50 - 100 yr , the morphology of the observed ionized gas ring is expected to be changed in the next several decades .
The mean electron temperature and density of the ionized gas are \bar { T } _ { \mathrm { e } } = 6800 \pm 700 K and \bar { n } _ { \mathrm { e } } = 6 \times 10 ^ { 5 } cm ^ { -3 } , respectively .
Then the mass of the ionized gas is estimated to be M _ { \mathrm { gas } } = 4 \times 10 ^ { -4 } M _ { \odot } .