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 $0.093pm0.006times 0.061pm0.004$ ( $1.14times10^{16}$ cm $times 0.74times10^{16}$ 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 $V_mathrm{rot}simeq230$ km s$^{-1}$ and an orbit radius of $rsimeq6times10^{15}$ cm. From these orbit parameters, the enclosed mass is estimated to be $M_{mathrm{IMBH}}simeq2.4times10^4$ $M_odot$. 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 $rho gtrsim8times10^{11} M_odot pc^{-3}$. Because the orbital period is estimated to be as short as $T=2pi r/V_mathrm{rot}sim 50-100$ 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 $bar{T}_{mathrm e}=6800pm700$ K and $bar{n}_{mathrm e}=6times10^5$ cm$^{-3}$, respectively. Then the mass of the ionized gas is estimated to be $M_{mathrm{gas}}=4times10^{-4} M_odot$.
تحميل البحث